Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.nanolett.3c00972

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Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsnano.3c01608

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/jsen.2023.3248021

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Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Dispersion stability of tin(IV) oxide nanoparticles dispersed in N-Methy-2-Pyrrolidone (NMP), dimethylformamide (DMF) and distilled water assisted by ultrasonication was investigated, aiming to identify a suitable liquid medium to effectively disperse tin(IV) oxide for many useful applications. The dispersions’ stability was characterized using field emission scanning electron microscopy, ultraviolet–visible spectroscopy and Zeta potential. The results show that distilled water has the highest stability with optimum sonication of 1 h. NMP shows better stability and consistency than DMF at different sonication timings. Good agreement between ultraviolet–visible absorbance and Zeta potentials shows that both distilled water and NMP are good mediums to produce highly stable tin(V) oxide dispersion.

DOI： 10.35848/1347-4065/acc0b5

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Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/acc0b5/pdf

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/eem2.12320

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/eem2.12320

Publishing type：Research paper (international conference proceedings)   Publisher：Optica Publishing Group  

A tin(IV) oxide based saturable absorber was demonstrated for the first time to mode-lock a ring erbium-doped fiber laser. The repetition rate achieved is ~1 MHz, with a pulse duration of ~160 ns.

DOI： 10.1364/assl.2022.jtu6b.2

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Two-dimensional (2D) hybrid perovskites have exhibited multiple features owing to their multiple quantum well structure. Here, we show the synthesis and characterization of 2D mixed-halide Cu-based perovskite crystals, R2Cu(Cl/Br)(4), with three different alkyl chains, where R is methyl, butyl, or hexyl ammonium cations. Exfoliated perovskite flakes exhibit reversible thermochromism with changes in color darkness with temperature variation. Differential scanning calorimetry and temperature-dependent X-ray diffraction measurements reveal that the thermochromic behavior mechanism of R2Cu(Cl/Br)(4) depends on the nature of the alkyl chain.

DOI： 10.1039/d2nj04693h

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsomega.2c00506

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry ({RSC})  

Formation of secondary phase polytypes through incorporation of copper into MAPbBr₃ perovskite yields bandgap reduction with generation of near-IR photocarriers.

DOI： 10.1039/D2QM00491G

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Light absorption enhancement was achieved through structure modulation of the Cs₃Bi₂Br₉ perovskite crystal via Cu-alloying. The Cs₃Bi₂Br₉ perovskite retains its matrix structure with homogeneously distributed Cs₂CuBr₄ large domains.

DOI： 10.1039/D2TC01762H

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Language：English   Publishing type：Research paper (scientific journal)  

Transition metal dichalcogenides (TMDCs), including MoS2 and WS2, are potential candidates for next-generation semiconducting materials owing to their atomically thin structure and strong optoelectrical responses, which allow for flexible optoelectronic applications. Monolayer TMDCs have been grown utilizing chemical vapor deposition (CVD) techniques. Enhancing the domain size with high crystallinity and forming heterostructures are important topics for practical applications. In this study, the size of monolayer WS2 increased via the vapor-liquid-solid growth-based CVD technique utilizing the confined space of the substrate-stacked microreactor. The use of spin-coated metal salts (Na2WO4 and Na2MoO4) and organosulfur vapor allowed us to precisely control the source supply and investigate the growth in a systematic manner. We obtained a relatively low activation energy for growth (1.02 eV), which is consistent with the surface diffusion-limited growth regime observed in the confined space. Through systematic photoluminescence (PL) analysis, we determined that a growth temperature of ∼820 °C is optimal for producing high-quality WS2 with a narrow PL peak width (∼35 meV). By controlling the source balance of W and S, we obtained large-sized fully monolayered WS2 (∼560 μm) and monolayer WS2 with bilayer spots (∼1100 μm). Combining two distinct sources of transition metals, WS2/MoS2 lateral heterostructures were successfully created. In electrical transport measurements, the monolayer WS2 grown under optimal conditions has a high on-current (∼70 μA/μm), on/off ratio (∼5 × 108), and a field-effect mobility of ∼7 cm2/(V s). The field-effect transistor displayed an intrinsic photoresponse with wavelength selectivity that originated from the photoexcited carriers.

DOI： 10.1021/acsnano.2c05076

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd  

Carbon nanotubes (CNTs) exhibit extremely high nanoscopic thermal/electrical transport and mechanical properties. However, the macroscopic properties of assembled CNTs are significantly lower than those of CNTs because of the boundary structure between the CNTs. Therefore, it is crucial to understand the relationship between the nanoscopic boundary structure in CNTs and the macroscopic properties of the assembled CNTs. Previous studies have shown that the nanoscopic phonon transport and macroscopic thermal transport in CNTs are improved by Joule annealing because of the improved boundary Van-der-Waals interactions between CNTs via the graphitization of amorphous carbon. In this study, we investigate the mechanical strength and thermal/electrical transport properties of CNT yarns with and without Joule annealing at various temperatures, analyzing the phenomena occurring at the boundaries of CNTs. The obtained experimental and theoretical results connect the nanoscopic boundary interaction of CNTs in CNT yarns and the macroscopic mechanical and transport properties of CNT yarns.

DOI： 10.1088/1361-6528/ac57d5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

To investigate photoinduced phenomena in various materials and molecules, ultrashort pulsed x-ray and electron sources with high brightness and high repetition rates are required. The x-ray and electron’s typical and de Broglie wavelengths are shorter than lattice constants of materials and molecules. Therefore, photoinduced structural dynamics on the femtosecond to picosecond timescales can be directly observed in a diffraction manner by using these pulses. This research created a tabletop ultrashort pulsed electron diffraction setup that used a femtosecond laser and electron pulse compression cavity that was directly synchronized to the microwave master oscillator (∼3 GHz). A compressed electron pulse with a 1 kHz repetition rate contained 228 000 electrons. The electron pulse duration was estimated to be less than 100 fs at the sample position by using photoinduced immediate lattice changes in an ultrathin silicon film (50 nm). The newly developed time-resolved electron diffraction setup has a pulse duration that is comparable to femtosecond laser pulse widths (35–100 fs). The pulse duration, in particular, fits within the timescale of photoinduced phenomena in quantum materials. Our developed ultrafast time-resolved electron diffraction setup with a sub-100 fs temporal resolution would be a powerful tool in material science with a combination of optical pump–probe, time-resolved photoemission spectroscopic, and pulsed x-ray measurements.

DOI： 10.1063/5.0086008

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Two-dimensional (2D) hybrid perovskites with novel functionalities and structural diversity are a perfect platform for emerging optoelectronic devices such as photodetectors, light-emitting diodes, and solar cells. Here, we demonstrate that excess concentration of Cesium bromide (CsBr) is key to the formation of easily exfoliated 2D Cs2Cu(Cl/Br)(4) perovskite crystal. Furthermore, by employing this trick to 2D perovskite MA(2)Cu(Cl/Br)(4) (MA=methylammonium), we achieve a phase-pure easily exfoliated 2D mixed-cation (MA/Cs)(2)Cu(Cl/Br)(4) perovskite crystal, which exhibits reduced bandgap (1.53 eV) with ferromagnetic behavior and photovoltaic property. The resultant mixed-cation structured device reveals enhanced efficiency compared to all MA and all Cs counterparts. These findings demonstrate the importance of cation-engineering in developing innovative materials with novel properties.

DOI： 10.1002/chem.202104316

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsanm.1c04236

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.carbon.2021.08.022

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<sec>
<title>Abstract</title>
Temperature-dependent studies of Ga₂O₃-based heterojunction devices are important in understanding its carrier transport mechanism, junction barrier potential, and stability at higher temperatures. In this study, we investigated the temperature-dependent device characteristics of the p-type γ-copper iodide (γ-CuI)/n-type β-gallium oxide (β‐Ga₂O₃) heterojunctions, thereby revealing their interface properties. The fabricated γ-CuI/β-Ga₂O₃ heterojunction showed excellent diode characteristics with a high rectification ratio and low reverse saturation current at 298 K in the presence of a large barrier height (0.632 eV). The temperature-dependent device characteristics were studied in the temperature range 273–473 K to investigate the heterojunction interface. With an increase in temperature, a gradual decrease in the ideality factor and an increase in the barrier height were observed, indicating barrier inhomogeneity at the heterojunction interface. Furthermore, the current–voltage measurement showed electrical hysteresis for the reverse saturation current, although it was not observed for the forward bias current. The presence of electrical hysteresis for the reverse saturation current and of the barrier inhomogeneity in the temperature-dependent characteristics indicates the presence of some level of interface states for the γ-CuI/β‐Ga₂O₃ heterojunction device. Thus, our study showed that the electrical hysteresis can be correlated with temperature-dependent electrical characteristics of the β‐Ga₂O₃-based heterojunction device, which signifies the presence of surface defects and interface states.


</sec><sec>
<title>Article Highlights</title>
<list list-type="bullet">
<list-item>
We revealed the interface properties of p-type γ-copper iodide (γ-CuI) and n-type β-gallium oxide (β-Ga₂O₃) heterojunction.


</list-item>
<list-item>
The developed heterostructure showed a large barrier height (0.632 eV) at the interface, which is stable at a temperature as high as 473 K.


</list-item>
<list-item>
We confirmed the current transport mechanism at the interface of the heterojunction by analyzing the temperature dependent current–voltage characterization.


</list-item>
</list>


</sec><sec>
<title>Graphic abstract</title>

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DOI： 10.1007/s42452-021-04774-3

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Other Link： https://link.springer.com/article/10.1007/s42452-021-04774-3/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.physrep.2021.10.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Understanding and controlling atomic motions in solid are essential in ionic materials, such as ion con-ductors, electrolyte and electrodes of batteries, and gas separators. Although photoinduced proton trans-port in solid materials has been demonstrated, photoinduced transport of heavier ions, such as the oxide ion, in solid materials remains entirely elusive. Herein, we apply ultrafast time-resolved electron diffrac-tion to observe the large displacement of oxide ions in a strongly correlated material, EuBaCo2O5.39, under near-ultraviolet photoexcitation at room temperature. The mechanism of the photoinduced transport of oxide ions is revealed via the combination of ultrafast optical spectroscopy and density functional theory calculations. Our findings show that photoexcitation induces ionic motions in a ceramic crystal at room temperature through the charge transfer that strongly couples with large ionic displacement under the nonequilibrium condition. (C) 2021 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.apmt.2021.101167

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acsaelm.1c00472

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

© 2021 Elsevier B.V. High room-temperature thermoelectric performance is important for low-grade waste heat power generation as there are plenty of heat thrown away uselessly in our daily life, most of which are below 100 °C. However, most of the thermoelectric materials are limited to high temperature application. In this work, room-temperature thermoelectric power factor of carbon nanotube (CNT) yarn is improved by controlled doping, which is achieved by making composite with poly 3-hexylthiophene −2, 5-diyl (P3HT) followed by doping with 2, 3, 5, 6-tetrafluo-7, 7, 8, 8-tetracyanoquinodimethane (F4TCNQ). The temperature-dependent Seebeck coefficient based on power–law model suggests that P3HT shifts the Fermi energy of CNT yarn towards the valence band edge, and reduces the ionic scattering and carrier relaxation time. As a result, the Seebeck coefficient is increased while the variation of Seebeck coefficient with temperature is reduced, and hence, the room-temperature thermoelectric power factor is improved. With controlled doping, the power factor of CNT yarn/P3HT composite reaches to 1640–2160 μW m−1K−2 at the temperature range of 25–100 °C, which is higher than that of CNT yarn alone.

DOI： 10.1016/j.orgel.2020.106056

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>Facile synthesis of single crystal of two-dimensional mixed-halide copper-based perovskites with tunable band gaps and their capability of exfoliation and reversible thermochromism.</p>

DOI： 10.1039/d0tc04307a

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

© 2020 Elsevier Ltd The high-strengthening mechanism of carbon nanotube (CNT) yarns subjected to Joule heating was investigated by nanostructural characterization. CNT yarns produced at two drawing speeds (40 and 120 mm/min) with a spindle rotation of 1000 min−1 were used. The mechanical properties of the CNT yarns were improved by Joule heating under a vacuum of 10−6 Pa. The mean tensile strength and Young's modulus of both yarns heated at 2273 K were approximately 1.1–1.4 GPa and 44–50 GPa, respectively; these values are approximately more than two times those of the as-spun samples. The high-strengthening of the Joule-heated CNT yarns is attributed to the synergistic effect of structural changes such as improvement in the crystallinity of the CNTs, formation of the bundle structure of individual CNTs possessing a polygonal structure, and entwining of these bundles. Meanwhile, the samples in which the high-strengthening mechanism by Joule heating did not initiate, were included in the CNT yarns produced at a drawing speed of 40 mm/min. Cross-sectional observation of the lower-strength CNT yarns revealed the presence of numerous voids in the outer portion of the yarn. The structural defects formed during the spinning of the CNT yarn strongly affected the tensile strength of the yarn.

DOI： 10.1016/j.carbon.2020.09.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0021338

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

© 2020 Elsevier Ltd Modern integrated devices and electrical circuits have often been designed with carbon nanostructures, such as carbon nanotubes (CNTs) and graphene due to their high thermal and electrical transport properties. These transport properties are strongly correlated to their acoustic phonon and carrier dynamics. Thus, understanding the phonon and carrier dynamics of carbon nanostructures in extremely small regions will lead to their further practical applications. Here, we demonstrate ultrafast time-resolved electron diffraction and ultrafast transient spectroscopy to characterize the phonon and carrier dynamics at the boundary of quasi-one-dimensional CNTs before and after Joule annealing. The results from ultrafast time-resolved electron diffraction show that the CNTs after Joule annealing reach the phonon equilibrium state extremely fast with a timescale of 10 ps, which indicates that thermal transport in CNTs improves following Joule annealing. The methodology described in this study connects conventional macroscopic thermo- and electrodynamics to those at the nanometer scale. Realistic timescale kinetic simulations were performed to further elaborate on the phenomena that occur in CNTs during Joule annealing. The insights obtained in this study are expected to pave the way to parameterize the unexplored thermal and electrical properties of carbon materials at the nanometer scale.

DOI： 10.1016/j.carbon.2020.08.026

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Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0012331

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

© 2020 The Author(s). Published by IOP Publishing Ltd. Carbon nanohorns (CNHs) are mixed with cellulose to make freestanding thin-film conductive sheets. CNHs, at different ratios (5, 10, 25, 50 wt%), form composites with cellulose (hydroxyethylcellulose). Freestanding cellulose-carbon nanohorn (CCN) sheets were fabricated using a 100 μm-thick metal bar coater. Surfactants or any other chemical treatments to tailor the surface properties of CNHs were avoided to obtain composite sheets from pristine CNHs and cellulose. Utilizing the hygroscopic property of hydroxyethylcellulose and the electrical conductivity of CNHs paved a path to perform this experiment. The synthesis technique is simple, and the fabrication and drying of the sheets were effortless. As the loading concentration of CNH increased, the resistance, flexibility, and strength of the CCN composite sheets decreased. The maximum loading concentration possible to obtain a freestanding CCN sheet is 50 wt%. The resistance of the maximum loading concentration of CNH was 53 kΩ. The response of the CCN sheets to water vapor was 4 s and recover time was 13 s, and it is feasible to obtain a response for different concentrations of water vapor. High-resolution transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, resistance measurement, tensile strength measurement, and thermogravimetric analysis were used to investigate the mechanical, morphological, electrical, and chemical properties of the CCN sheets.

DOI： 10.1088/2053-1591/ab89dc

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Flexible, light-weight and robust thermoelectric (TE) materials have attracted much attention to convert waste heat from low-grade heat sources, such as human body, to electricity. Carbon nanotube (CNT) yarn is one of the potential TE materials owing to its narrow band-gap energy, high charge carrier mobility, and excellent mechanical property, which is conducive for flexible and wearable devices. Herein, we propose a way to improve the power factor of CNT yarns fabricated from few-walled carbon nanotubes (FWCNTs) by two-step method; Joule-annealing in the vacuum followed by doping with p-type dopants, 2,3,5,6-tetrafluo-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Numerical calculations and experimental results explain that Joule-annealing and doping modulate the electronic states (Fermi energy level) of FWCNTs, resulting in extremely large thermoelectric power factor of 2250 µW m-1 K-2 at a measurement temperature of 423 K. Joule-annealing removes amorphous carbon on the surface of the CNT yarn, which facilitates doping in the subsequent step, and leads to higher Seebeck coefficient due to the transformation from (semi) metallic to semiconductor behavior. Doping also significantly increases the electrical conductivity due to the effective charge transfers between CNT yarn and F4TCNQ upon the removal of amorphous carbon after Joule-annealing.

DOI： 10.1038/s41598-020-64435-0

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Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

DOI： 10.3390/molecules25051144

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Carbon nanotube (CNT) yarns comprise few-walled CNTs (FWCNTs), mainly consisting of double- and triple-walled CNTs, and have several properties which are beneficial for practical bulk-scale carbon devices. These features include high tensile strength, electrical conductivity, thermal conductivity, chemical stability, and environmental tolerance. However, the synthesis window for fabricating CNT yarns with FWCNTs by the dry-spinning method is quite narrow and optimal conditions have yet to be determined. In this study, we fabricated CNT forests mainly comprised of FWCNTs at various synthesis conditions (temperature and time). The drawability of the CNT forests was characterized depending on the synthesis conditions. Our results show that optimum values exist for continuously drawable CNT forests in terms of both their height (>130 mu m) and bulk density (> 90 mg/cm(3)) for satisfying enough entanglement force between the CNT bundles. The diameter and number of walls of the CNTs are controlled by the temperature during the formation of catalyst particles because the sizes of catalyst particles are approximately equal to the outer diameter of CNTs. All temperature conditions in the range 350-500 degrees C, used to form catalyst particles, resulted in a drawable FWCNT forest. These insights will be useful for developing devices based on FWCNT yarns. (C) 2019 Published by Elsevier Ltd.

DOI： 10.1016/j.carbon.2019.11.038

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/1.5127993

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Authorship：Lead author,　Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

© 2020 The Society of Fiber Science and Technology, Japan. Carbon nanotube (CNT) yarn drawn from CNT arrays has recently attracted considerable interest for various applications in wiring harnesses, composites, smart textiles, and high strength structural materials. Although the excellent properties and functions of CNTs are expressed at nanometer scale, it is quite difficult to maintain these nanoscale properties while upscaling to bulk CNT spun yarn. This paper aims to provide an overview of the rapid synthesis of spinnable tall and dense CNT arrays, the processing and improvement of the physical properties of CNT spun yarn, and the application of CNT spun yarn in the fields of energy and mechanical devices.

DOI： 10.2115/fiberst.2020-0013

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：TRANS TECH PUBLICATIONS LTD  

A simple method to synthesize metal nanoparticles (Nps) has been proposed using high vacuum thermal deposition (HVTD) by reverse engineering of thin films to Nps. Metal Nps synthesized by this technique corresponds to the top-down approach of nanomaterial synthesis from bulk metals of silver and copper wires to metal Nps. A high-vacuum thermal deposition is a commonly used technique for thin-film deposition in many applications. Synthesis of metal Nps by HVTD is simple, efficient, and can provide particle of about few tens of nanometers is effortless. A precoated thin layer of polyethylene glycol (PEG) on a glass substrate (Petri dish), is allowed deposit with a metallic thin film by thermionically evaporating bulk metal wires in high vacuum. The deposited metal thin film is removed along with the PEG coating into a liquid medium and subjected to sonication, stirring, and deoxidation. Obtaining the particle size in tens of nanometer range in one step is one projecting factor by HVTD technique. Also, providing the feasibility of reusing large particles as precursors after synthesis is a unique vantage point. The Nps were analyzed by various characterizations tools to evaluate the underlying properties.

DOI： 10.4028/www.scientific.net/JNanoR.61.42

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Background: Conductive sheets of cellulose and carbon nanomaterials and its human skin applications are an interesting research aspect as they have potential for applications for skin compatibility. Hence it is needed to explore the effects and shed light on these applications. Method: To fabricate wearable, portable, flexible, lightweight, inexpensive, and biocompatible composite materials, carbon nanohorns (CNHs) and hydroxyethylcellulose (HEC) were used as precursors to prepare CNH-HEC (Cnh-cel) composite sheets. Cnh-cel sheets were prepared with different loading concentrations of CNHs (10, 20 50,100 mg) in 200 mg cellulose. To fabricate the bio-compatible sheets, a pristine composite of CNHs and HEC was prepared without any pretreatment of the materials. Results: The obtained sheets possess a conductivity of 1.83 × 10- 10 S/m and bio-compatible with human skin. Analysis for skin-compatibility was performed for Cnh-cel sheets by h-CLAT in vitro skin sensitization tests to evaluate the activation of THP-1 cells. It was found that THP-1 cells were not activated by Cnh-cel; hence Cnh-cel is a safe biomaterial for human skin. It was also found that the composite allowed only a maximum loading of 100 mg to retain the consistent geometry of free-standing sheets of < 100 μm thickness. Since CNHs have a unique arrangement of aggregates (dahlia structure), the composite is homogeneous, as verified by transmission electron microscopy (TEM) and, scanning electron microscopy (SEM), and other functional properties investigated by Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), conductivity measurement, tensile strength measurement, and skin sensitization. Conclusion: It can be concluded that cellulose and CNHs sheets are conductive and compatible to human skin applications.

DOI： 10.1186/s40824-020-00194-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Interfaces in nanocarbon materials are highly important, as they determine the properties of carbon-based devices. In terms of carrier and thermal transport properties, the interfacial features are often more important than the intrinsic characteristics. Herein, we describe how 1 min Joule annealing of carbon nanotube (CNT) yarns can convert the interfacial amorphous carbon into graphene fragments. After 1 min Joule annealing, we have obtained multiwalled CNT yams with extremely high Seebeck coefficients (+/- 100 mu V/K) and high thermoelectric power factor (400 and 1000 mu W/mK(2)) at room temperature, both with or without polyethylenimine doping. Theoretical simulations and experimental measurements helped to determine the optimal annealing conditions in terms of a rapid transformation of the interfacial amorphous carbon between the bundled CNTs in the yarn into graphene fragments at similar to 2000 K. The present approach represents significant progress in energy materials science, as it provides a guiding principle for the design of interfaces in nanocarbon materials with potential applications in energy-harvesting systems.

DOI： 10.1021/acsaem.9b01736

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of graphene used in practical applications. Different reduction processes produce different properties in graphene, affecting the performance of the final materials or devices. Therefore, an understanding of the mechanisms of GO reduction is important for controlling the properties of functional two-dimensional systems. Here, we determined the average structure of reduced GO prepared via heating and photoexcitation and clearly distinguished their reduction mechanisms using Graphene oxide ultrafast time-resolved electron diffraction, time-resolved infrared vibrational spectroscopy, and time-dependent density functional theory calculations. The oxygen atoms of epoxy groups are selectively removed from the basal plane of GO by photoexcitation (photon mode), in stark contrast to the behavior observed for the thermal reduction of hydroxyl and epoxy groups (thermal mode). The difference originates from the selective excitation of epoxy bonds via an electronic transition due to their antibonding character. This work will enable the preparation of the optimum GO for the intended applications and expands the application scope of two-dimensional systems.

DOI： 10.1021/acsnano.9b03060

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most commonly investigated conductive polymer due to its unique thermoelectric properties. Several post treatments using various acids have been reported to improve the thermoelectric properties of PEDOT:PSS. In most articles, however, only the role of acids on the structure and thermoelectric properties of PEDOT:PSS were reported. In this article, we report the major role of the pressure of nitrogen gas (N-2) on the structure and thermoelectric properties of PEDOT:PSS after treatment with various acids at optimized temperatures. After treatment with acids followed by N-2 gas-passing, electrical conductivity enhances significantly. Therefore, N-2 gas-passing after acid treatments results in higher thermoelectric properties than other traditional acid treatment methods. The enhancement in electrical conductivity is attributed to the removal of insulating PSS and the conformational change of the PEDOT chain. Furthermore, the pressure of N-2 is responsible for the additional conformation of PEDOT chain, favoring the linear orientation of the PEDOT structure and resulting in an improvement of the electrical conductivity.

DOI： 10.1007/s10854-019-01721-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We explore the temperature dependence of pressure-driven water permeation through membranes consisting of a vertically aligned double-walled carbon nanotube (VA DWCNT) array. The prepared membrane with CNT inner diameter of 3.9 nm exhibits no water permeation below the critical temperature of 26 degrees C, after which water permeability is first observed and increases with temperatures > 26 degrees C. Further, the critical temperature decreases to 18 degrees C when the CNT inner diameter increases to 6.0 nm. The water permeation in the CNT-confined space exhibits activation energy transitions around room temperature, thereby suggesting that the confined water molecules in CNTs exhibit plural ordered structures. (C) 2019 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2019.02.031

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Publishing type：Part of collection (book)   Publisher：Springer Singapore  

DOI： 10.1007/978-981-13-3417-7_8

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpca.8b08455

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We fabricated thermally driven metal-free soft-actuators consisting of poly(ethylene terephthalate) (PET) threads as the actuator and carbon nanotube (CNT) yarns as the heating source. The mechanical force, displacement, and response behavior of various structures of the coil-shaped soft-actuators were characterized. The actuation performance of the soft-actuators containing a homogeneous arrangement of PET threads and CNT yarns in their cross-sectional profile was the highest. The results of the calculations based on the heat diffusion equations indicated that inhomogeneous heat generation in the soft-actuator causes parts of the actuator to remain unheated and this interferes with the mechanical motions. Homogeneous thermal distribution in the soft-actuators, namely, the use of a multifilament structure, yields the highest performance in terms of the mechanical force and displacement. (C) 2018 Author(s).

DOI： 10.1063/1.5033487

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Annealing and functionalization of carbon nanotube yarns (CNYs) is a prospective way of increasing the electrical conductivity of this material. We show a novel way, the simultaneous annealing and instant coating of the CNY by its resistance-heating in atmospheres of hydrocarbons. This method is capable to preserve the lightweight properties of CNYs and increase the electrical conductivity. It could be raised by a factor of 2 through carbon deposition onto the yarns and the carbon nanotubes (CNTs) inside the yarn structure. By resistance-heating over a multistep process the conductivity could be even increased by a factor of 2.2. Comparison of annealing under atmosphere of different hydrocarbons and at different temperatures reveals the influence of resistance-heating on the structure of CNY. (C) 2018 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2018.03.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Physics Inc.  

Daytime radiative cooling potentially offers efficient passive cooling, but the performance is naturally limited by the environment, such as the ambient temperature and humidity. Here, we investigate the performance limit of daytime radiative cooling under warm and humid conditions in Okayama, Japan. A cooling device, consisting of alternating layers of SiO2 and poly(methyl methacrylate) on an Al mirror, is fabricated and characterized to demonstrate a high reflectance for sunlight and a selective thermal radiation in the mid-infrared region. In the temperature measurement under the sunlight irradiation, the device shows 3.4 °C cooler than a bare Al mirror, but 2.8 °C warmer than the ambient of 35 °C. The corresponding numerical analyses reveal that the atmospheric window in λ = 16 ∼ 25 μm is closed due to a high humidity, thereby limiting the net emission power of the device. Our study on the humidity influence on the cooling performance provides a general guide line of how one can achieve practical passive cooling in a warm humid environment.

DOI： 10.1063/1.5030156

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We studied the dynamics of the expansion of a Shockley-type stacking fault (SSF) with 30 degrees Si(g) partial dislocations (PDs) using a scanning electron microscope. We observed SSFs as dark lines (DLs), which formed the contrast at the intersection between the surface and the SSF on the (0001) face inclined by 8 degrees from the surface. We performed experiments at different electron-beam scanning speeds, observing magnifications, and irradiation areas. The results indicated that the elongation of a DL during one-frame scanning depended on the time for which the electron beam irradiated the PD segment in the frame of view. From these results, we derived a formula to express the velocity of the PD using the elongation rate of the corresponding DL during one-frame scanning. We also obtained the result that the elongation velocity of the DL was not influenced by changing the direction in which the electron beam irradiates the PD. From this result, we deduced that the geometrical kink motion of the PD was enhanced by diffusing carriers that were generated by the electron-beam irradiation. Published by AIP Publishing.

DOI： 10.1063/1.5010861

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

We have developed a vacuum-compatible chamber for in-situ X-ray diffraction (XRD) studies and have used it to characterize the changing crystal structure of an inorganic-organic hybrid perovskite material, CH3NH3PbI3 (MAPbI3), during interactions with water vapor at room temperature. In the XRD spectra, we have observed the degradation of MAPbI3 and the creation of MAPbI3 hydrates, which follow simple rate equations. The time constant for the degradation of MAPbI3 during accelerated aging suggests that multiple collisions of water molecules with the MAPbI3 crystal trigger the degradation of the crystal.

DOI： 10.7567/JJAP.57.028001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOURNAL OF VISUALIZED EXPERIMENTS  

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

DOI： 10.3791/57612

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DOI： 10.5772/intechopen.70702

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

As a thermoelectric (TE) material suited to applications for recycling waste-heat into electricity through the Seebeck effect, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) is of great interest. Our research demonstrates a comprehensive study of different post-treatment methods with nitric acid (HNO3) to enhance the thermoelectric properties of PEDOT:PSS. The optimum conditions are obtained when PEDOT:PSS is treated with HNO3 for 10 min at room temperature followed by passing nitrogen gas (N-2) with a pressure of 0.2 MPa. Upon this treatment, PEDOT:PSS changes from semiconductor-like behaviour to metal-like behaviour, with a simultaneous enhancement in the electrical conductivity and Seebeck coefficient at elevated temperature, resulting in an increase in the thermoelectric power factor from 0.0818 to 94.3 W m(-1) K-2 at 150 degrees C. The improvement in the TE properties is ascribed to the combined effects of phase segregation and conformational change of the PEDOT due to the weakened coulombic attraction between PEDOT and PSS chains by nitric acid as well as the pressure of the N-2 gas as a mechanical means.

DOI： 10.1039/c8ra06094k

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Aromaticity of photoexcited molecules is an important concept in organic chemistry. Its theory, Baird's rule for triplet aromaticity since 1972 gives the rationale of photoinduced conformational changes and photochemical reactivities of cyclic pi-conjugated systems. However, it is still challenging to monitor the dynamic structural change induced by the excited-state aromaticity, particularly in condensed materials. Here we report direct structural observation of a molecular motion and a subsequent packing deformation accompanied by the excited-state aromaticity. Photoactive liquid crystal (LC) molecules featuring a pi-expanded cyclooctatetraene core unit are orientationally ordered but loosely packed in a columnar LC phase, and therefore a photoinduced conformational planarization by the excited-state aromaticity has been successfully observed by time-resolved electron diffractometry and vibrational spectroscopy. The structural change took place in the vicinity of excited molecules, producing a twisted stacking structure. A nanoscale torque driven by the excited-state aromaticity can be used as the working mechanism of new photoresponsive materials.

DOI： 10.1021/jacs.7b08021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

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A common challenge for pump-probe studies of structural dynamics at X-ray free-electron lasers (XFELs) is the determination of time zero (T-0)-the time an optical pulse (e.g., an optical laser) arrives coincidently with the probe pulse (e.g., a XFEL pulse) at the sample position. In some cases, T-0 might be extracted from the structural dynamics of the sample's observed response itself, but generally, an independent robust method is required or would be superior to the inferred determination of T-0. In this paper, we present how the structural dynamics in ultrafast melting of bismuth can be exploited for a quickly performed, reliable and accurate determination of T-0 with a precision below 20 fs and an overall experimental accuracy of 50 fs to 150 fs (estimated). Our approach is potentially useful and applicable for fixed-target XFEL experiments, such as serial femtosecond crystallography, utilizing an optical pump pulse in the ultraviolet to near infrared spectral range and a pixelated 2D photon detector for recording crystallographic diffraction patterns in transmission geometry. In comparison to many other suitable approaches, our method is fairly independent of the pumping wavelength (UV-IR) as well as of the X-ray energy and offers a favorable signal contrast. The technique is exploitable not only for the determination of temporal characteristics of the experiment at the interaction point but also for investigating important conditions affecting experimental control such as spatial overlap and beam spot sizes. (C) 2017 Author(s).

DOI： 10.1063/1.4999701

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Nanofluidics in CNTs is argumentative though it is theoretically calculated by various reports. It is because only a few of experimental reports are available, and the measured permeability is not so large as that suggested from the theoretical calculations. Also, water motion suppression in the confined space has not been exhibited by flux measurement. The present work explores these yet-unsolved discrepancies using the measurable size membrane of vertically aligned double-walled carbon nanotube array, which is borne with durability and flexibility, and a conventional measurement method is applied to the membranes. Water motion suppression occurs in the CNT confined space significantly, depending on temperature. Additionally, it is confirmed that the obtained permeability correlates to the reported experimental results with regard to the relationship between CNT length and permeability, and the correlation does not agree with permeability calculated from the Hagen-Poiseuille law. These results pose an insight into the inherent water transport characteristics in the CNT confined space. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2017.05.034

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Plasmonic metamaterials have overcome fundamental limitations in conventional optics by their capability to engineer material resonances and dispersions at will, holding great promise for sensing applications. Recent demonstrations of metamaterial sensors, however, have mainly relied on their resonant nature for strong optical interactions with molecules, but few examples fully exploit their functionality to manipulate the polarization of light. Here, we present cross-polarized surface-enhanced infrared absorption (SEIRA) by the Fano-resonant asymmetric metamaterial allowing for strong background suppression as well as significant field enhancement. The metamaterial is designed to exhibit the controlled Fano resonance with the cross-polarization conversion property at 1730 cm(-1), which spectrally overlaps with the C=O vibrational mode. In the cross-polarized SEIRA measurement, the C=O mode of poly(methyl methacrylate) molecules is clearly observed as a distinct dip within a Fano-resonant transmission peak of the metamaterial. The vibrational signal contrast is then improved based on the cross-polarized detection scheme where only the light interacting with the metamaterial-molecular coupled system is detected by totally eliminating the unwanted background light. Our metamaterial approach achieves the zeptomole sensitivity with a large signal-to-noise ratio in the far-field measurement, paving the way toward the realization of ultrasensitive IR inspection technologies.

DOI： 10.1038/s41598-017-03545-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Owing to its unique properties, graphene has attracted tremendous attention in many research fields. There is a great space to develop graphene synthesis techniques by an efficient and environmentally friendly approach. In this paper, we report a facile method to synthesize well-dispersed multilayer graphene (MLG) without using any chemical reagents or organic solvents. This was achieved by the ozone-assisted sonication of the natural graphite in a water medium. The frequency or number of ozone treatments plays an important role for the dispersion in the process. The possible mechanism of graphene exfoliation and the introduction of functional groups have been postulated. The experimental setup is unique for ozone treatment and enables the elimination of ozone off-gas. The heat generated by the dissipation of ultrasonic waves was used as it is, and no additional heat was supplied. The graphene dispersion was stable, and no evidence of aggregation was observed-even after several months. The characterization results show that well-dispersed MLG was successfully synthesized without any significant damage to the overall structure. The graphene obtained by this method has potential applications in composite materials, conductive coatings, energy storage, and electronic devices.

DOI： 10.3390/nano7060125

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

ZnO decked few layered graphene (FLG; 1.0, 2.0 and 3.0 wt%) nanocomposites were synthesized by simple and cost effective way using ultrasonic-assisted synthesis method. The morphological, optical and structural properties of as-synthesized nanocomposites were analyzed by field emission scanning electron microscopy and high-resolution transmission electron microscopy, UV-Visible spectroscopy with diffuse reflectance, fourier transform infrared spectroscopy, X-ray diffractometry and ramam spectroscopy. The synthesized FLG (1.0, 2.0 and 3.0 wt%)/ZnO nanocomposite were used as photoanode materials and deposited as thin films on fluorine-doped tin oxide substrate by doctor blade method for dye-sensitized solar cell (DSSC) fabrication. By varying the FLG weight percentage (1.0, 2.0 and 3.0 wt%) in ZnO nanocomposites the power conversion efficiency (PCE) in DSSC was optimized. Using N719 dye the current density-voltage (J-V) was measured under AM 1.5G, 100 m W/m(2) of the solar simulator. Results obtained after optimization showed PCE of 4.61% at the suitable FLG (1.0 wt%)/ZnO, compared to ZnO and other photoanodes.

DOI： 10.1007/s10854-016-6301-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Hybrid films of multilayer graphene (MG) containing amorphous carbon (a-C) were synthesized on Al substrates by microwave surface-wave plasma chemical vapor deposition. Raman scattering and surface transmission electron microscopy showed that the carbon films contained a large quantity of MG when a radio frequency (RF) substrate bias was not applied. Amorphization of graphene in the carbon film was promoted by applying an RF bias, which generated Ar+ in the plasma. The bandgaps of the films were found to increase as the Raman intensity ratios between the 2D-band (at 2700cm(-1)) and D-band (at 1350cm(-1)) decreased, indicating the formation of a-C. The MG/a-C all-sp(2) phase of carbon hybrid films exhibited an increase in current density under 5mW/cm(2) of AM1.5G solar simulated irradiation as the RF bias increased because of Ar+-induced amorphization of the graphene. Copyright (c) 2016 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.6133

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

In this paper, we describe the effects of helium plasma and ozone treatments on the dispersibility of carbon nanohorns (CNHs) in water. The experimental setups have been designed to efficiently generate helium plasma and ozone by dielectric barrier discharge at atmospheric pressure. After being treated with ozone, the oxygen-containing functional groups were introduced to the surface of CNHs, and are responsible for better dispersion. Helium plasma treatment was performed separately and it resulted in hydroxyl functional groups on the surface of CNHs. It was also found that the sizes of CNHs in water were smaller after ozone treatment. However, plasma-treated CNHs were bigger than ozone treated CNHs. The dispersed CNHs modified by ozone treatment were stable for more than three months without precipitation. In contrast, though helium plasma treatment introduced hydroxyl groups to the surface of CNHs, the dispersibility decreased and the flocculation of CNHs was observed in a few minutes. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.56.01AB08

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We demonstrate automatic design of infrared (IR) metamaterials using a genetic algorithm (GA) and experimentally characterize their IR properties. To implement the automated design scheme of the metamaterial structures, we adopt a digital metamaterial consisting of 7 x 7 Au nano-pixels with an area of 200 nm x 200 nm, and their placements are coded as binary genes in the GA optimization process. The GA combined with three-dimensional (3D) finite element method (FEM) simulation is developed and applied to automatically construct a digital metamaterial to exhibit pronounced plasmonic resonances at the target IR frequencies. Based on the numerical results, the metamaterials are fabricated on a Si substrate over an area of 1 mm x 1 mm by using an EB lithography, Cr/Au (2/20 nm) depositions, and liftoff process. In the FT-IR measurement, pronounced plasmonic responses of each metamaterial are clearly observed near the targeted frequencies, although the synthesized pixel arrangements of the metamaterials are seemingly random. The corresponding numerical simulations reveal the important resonant behavior of each pixel and their hybridized systems. Our approach is fully computer-aided without artificial manipulation, thus paving the way toward the novel device design for next-generation plasmonic device applications.

DOI： 10.1117/12.2273607

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

Engineered metallodielectric nanostructures offer a new platform for controlling thermal emission in a desired manner, thus promise potential applications in passive cooling devices. Here, we present optimization design of metallodielectric multilayer structures for high-efficiency daytime radiative cooling and experimentally characterize their cooling performance. The device structure consists of alternating layers of SiO2 and PMMA on an Ag mirror, which works as a selective thermal emitter at 8-13 μm with a high reflectance for sunlight. Automated design scheme based on simulated annealing method combined with photonic-thermal analysis is developed and applied to search the optimized number and thickness of the layers. The evaluation function in the optimization process is predefined such that a net emission power would be maximized at the ambient temperature of 27 °C (300 K) under the sunlight irradiation of AM1.5G. The numerical results prove efficient radiative cooling to 3.0 °C lower than the ambient temperature, corresponding to 6.6 °C below the bare Ag mirror temperature. Based on the optimized design, the device is fabricated on an Al mirror by using reactive evaporation and spin-coating process over an area of 25 × 25 mm2. The reflectance and absorption properties of the fabricated device are characterized to demonstrate the selective thermal radiation through an atmospheric window. The equilibrium temperature of the device is also investigated to demonstrate the cooling performance under the direct sunlight irradiation.

DOI： 10.1117/12.2273640

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper presents a growth and characterization of vertically aligned PdxCo1-x alloy encapsulated inside Multi-Walled Carbon Nanotube (MWCNT) arrays on Pd/Co thin layers coated on Si substrate by a dc bias-enhanced plasma chemical vapor deposition (CVD) method. The Metal Alloy Encapsulated within MWCNTs (MAE-MWCNTs) were characterized by a scanning electron microscope (SEM) and a transmission electron microscopy (TEM). The SEM images show the teardrop-shape particles encapsulated within the tube top of MWCNTs. A vibrating sample magnetometer was used to study the magnetism of a large number of MAE-MWCNTs on Si substrate at room temperature. The hysteresis loop of the ME-MWCNTs shows clear ferromagnetic behavior and the easy axis of magnetization is parallel to the MEA-MWCNT tube axis, as can be elucidated from the large coercive fields and remanence values. Moreover, TEM off-axis electron holograms were used to study the magnetism of the individual MAE-MWCNT or the two pair of MAE-MWCNTs. Based on electron holography, we have successfully obtained the saturation magnetization of 0.7 T and 1.12 T for the individual MAE-MWCNT with diameters of 41 nm and 83 nm, respectively.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

This report deals with a simple and efficient method to develop hybrid carbon nanoparticles (Nps) employing Multi-walled carbon nanotubes (MWCNTs) and Fullerene nps. Fullerene nps were self-assembled via Ultrasonicated Liquid-Liquid Precipitation. Surface treated MWCNTs were entangled with fullerene nps during the process of assembling of the fullerene nps. Fullerene nps are formed by reaction between two solutions, one is the saturated solution which contains dissolved fullerene and other solution is a rough alcohol. This reaction increases the concentration of carbon in the solution and leads to super saturate hence self-assembling into nanoparticles. The obtained hybrid nanoparticles sizes were in the range of 100 nm to 300 nm with entangled mwcnts and were confirmed by characterization using SEM, Raman, UV-Vis, XRD, and DLS.

DOI： 10.4028/www.scientific.net/MSF.900.46

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BACKGROUND: The use of carbon nanotubes has increased lately. However, the cardiovascular effect of exposure to carbon nanotubes remains elusive. The present study investigated the effects of pulmonary exposure to single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) on atherosclerogenesis using normal human aortic endothelial cells (HAECs) and apolipoprotein E-deficient (ApoE-/-) mice, a model of human atherosclerosis. METHODS: HAECs were cultured and exposed to SWCNTs or DWCNTs for 16 h. ApoE-/- mice were exposed to SWCNTs or DWCNTs (10 or 40 μg/mouse) once every other week for 10 weeks by pharyngeal aspiration. RESULTS: Exposure to CNTs increased the expression level of adhesion molecule (ICAM-1) and enhanced THP-1 monocyte adhesion to HAECs. ApoE-/- mice exposed to CNTs showed increased plaque area in the aorta by oil red O staining and up-regulation of ICAM-1 expression in the aorta, compared with vehicle-treated ApoE-/- mice. Endothelial progenitor cells (EPCs) are mobilized from the bone marrow into the circulation and subsequently migrate to the site of endothelial damage and repair. Exposure of ApoE-/- mice to high-dose SWCNTs or DWCNTs reduced the colony-forming units of EPCs in the bone marrow and diminished their migration function. CONCLUSION: The results suggested that SWCNTs and DWCNTs enhanced atherosclerogenesis by promoting monocyte adhesion to endothelial cells and inducing EPC dysfunction.

DOI： 10.1186/s12989-016-0166-0

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Language：English   Publisher：The Materials Research Society of Japan  

<p>We synthesized carbon nanowalls on a Si substrate by microwave surface-wave plasma chemical vapor deposition. The Raman scattering I_D/I_G ratio was changed by altering the DC bias applied to the growth substrate and the decrease in I_D/I_G with increasing DC bias appears to arise from the growing length of the carbon nanowalls. The ultrasonically separated carbon nanowalls in ethanol exhibited strong 2D-peak intensity and significant graphitization. A graphite layer of approximately 10 nm grew parallel to the substrate initially, and the carbon nanowalls grew on top of that. When the nanowalls were dispersed in ethanol and spin-coated onto PET, they exhibited a transmittance of 81% and a sheet resistance of 52 kΩ/□ without reduction treatment used in the graphene oxide.</p>

DOI： 10.14723/tmrsj.41.229

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

We demonstrated time-resolved electron diffraction and vibrational spectroscopy to characterize the structure and dynamics of molecules in liquid crystal state. Our findings present the ultrafast local deformation triggering helical twisting motion in molecules.

DOI： 10.1364/UP.2016.UTh2B.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

We successfully synthesized graphene by microwave surface-wave plasma chemical vapor deposition (CVD) and investigated the effect of UV light and ion collision from the plasma exposure during graphene synthesis. The graphene obtained here was multilayer graphene consisting of approximately 5 layers according to crosssectional transmission electron microscopy results. The quality of the graphene was compared between the.case where UV light was irradiated from the plasma and the case where the UV light was blocked by a grid inserted CVD configuration. Quality was evaluated by Raman scattering spectroscopy. There were more defects in the graphene prepared with irradiation of UV light than with blocking of UV light. Furthermore, we investigated the effects of ion collisions that occurred in the plasma, but they had no effect on graphene quality. These results suggest that during graphene synthesis, UV light from the plasma affects its crystallinity. The electrical conductivity, optical transmittance and mobility of the transferred graphene films were measured to clarify the effects of UV light irradiation. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2016.04.012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

the widespread interest in the chemistry, physics and materials science of such molecules and their potential applications. In particular, extended phenacene molecules, consisting of coplanar fused benzene rings in a repeating W-shaped pattern have attracted much attention because field-effect transistors (FETs) using phenacene molecules show promisingly high performance. Until now, the most extended phenacene molecule available for transistors was [8] phenacene, with eight benzene rings, which showed very high FET performance. Here, we report the synthesis of a more extended phenacene molecule, [9] phenacene, with nine benzene rings. Our synthesis produced enough [9] phenacene to allow the characterization of its crystal and electronic structures, as well as the fabrication of FETs using thin-film and single-crystal [9] phenacene. The latter showed a field-effect mobility as high as 18 cm(2) V-1 s(-1), which is the highest mobility realized so far in organic single-crystal FETs.

DOI： 10.1038/srep21008

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

A high-sensitive polarized surface-enhanced infrared absorption (polarized SEIRA) is proposed and demonstrated by utilizing the resonant coupling of Fano-resonant mode of the asymmetric metamaterials and IR vibrational mode of a polymer nano-film. The asymmetric metamaterials consisting of an Au nano-rod pair with a coupling nano-antenna were fabricated and characterized to demonstrate the controlled Fano resonances at 1730 cm(-1), which spectrally overlapped with the C=O stretching vibrational mode. In the co-polarized SEIRA measurement, the C=O mode of the PMMA nano-film was clearly observed as a conventional anti-resonant peak within the Fano line-shape of the metamaterial. For the cross-polarized case, on the other hand, a distinctive dip appeared within a cross-polarized transmission peak of the metamaterial. Since the unwanted background is strongly suppressed in the cross-polarized detection scheme, the signal contrast was dramatically improved, allowing for the attomole detection of the C=O bond in the far-field measurement. Our metamaterial approach achieves the significant improvement of signal-to-background ratio in the far-field measurement, thus paving the way toward the high-sensitive analysis of functional group in direct IR spectroscopy.

DOI： 10.1117/12.2237559

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In this article, we report C60 Fullerene Nano Cylindrical Tubes (FNCT). The FNCTs were synthesized by a liquid-liquid interface precipitation (LLIP) method using m-Xylene as a saturating solvent and TBA (Tetra butyl alcoholic) as precipitation agent leading to the formation of FNCTs with uniquely structured and well oriented size and shape. The experiment was conducted in a closed atmosphere maintaining a low temperature. The main advantage of these structures is that they are stable up to 5 months in normal room temperature. Characterizations were done to the FNCTs and concluded to have applications in the field of electronics. Enhanced semiconducting properties have been observed in the nanostructures which can be used in the application of solar cells, FET transistors, etc.

DOI： 10.1109/NANO.2016.7751386

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

This paper describes the effect of ozone treatment on water dispersibility of micrometer order long multi-walled carbon nanotubes by using simple ozone generation set up. Inverter type neon transformer was used to supply required energy. The dispersed nanotubes suspension was stable for a few months after treatment. Laser Raman Spectroscopy, Fourier Transform Infrared Spectroscopy, and Transmission Electron Miscroscope were used to characterize the resulted nanotubes. Analyzed data revealed that the multi-walled carbon nanotubes were functionalized by oxygen and hydrogen containing groups.

DOI： 10.1541/ieejfms.136.180

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Here in, we report carbon nanostructures (nanorods) synthesized via liquid-liquid interface precipitation method (LLIP) with its application in field effect transistor as gate terminal. The carbon nanorods were synthesized by supersaturating and shape shifting Bucky ball fullerene into nanorods. The nanoparticles synthesis process is fast, efficient and the reaction is carried out in 24hrs. The obtained nanorods were found to have semiconducting property which was confirmed by analyzing TEM, SEM and RAMAN, FET analysis by IV measurements. Hence the nanorods where fabricated as gate terminal in field effect transistor.

DOI： 10.1109/NEMS.2016.7758292

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Carbon nanotube (CNT) yarns are fabricated by drawing (combined with spinning) from CNT forests and grown on a substrate. Three types of phenomena occur in these CNT yarns with increasing amounts of current: yarn rotation, catalyst evaporation, and breakage of the yarn. These phenomena result from the resistive heating occurring during the current flow, and have been observed in situ under vacuum by transmission electron microscopy. If these CNT yarns are applied to electronic circuits, the rotation and breakage may lead to circuit failure. However, catalyst evaporation is a useful method for purifying CNT yarns without additional treatments prior to yarn fabrication. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.micron.2015.04.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI  

Zinc oxide (ZnO) nanoparticles are widely used in various products, and the safety evaluation of this manufactured material is important. The present study investigated the inflammatory and fibrotic effects of pulmonary exposure to ZnO nanoparticles in a mouse model of pulmonary fibrosis. Pulmonary fibrosis was induced by constant subcutaneous infusion of bleomycin (BLM). Female C57BL/6Jcl mice were divided into BLM-treated and non-treated groups. In each treatment group, 0, 10, 20 or 30 mu g of ZnO nanoparticles were delivered into the lungs through pharyngeal aspiration. Bronchoalveolar lavage fluid (BALF) and the lungs were sampled at Day 10 or 14 after administration. Pulmonary exposure by a single bolus of ZnO nanoparticles resulted in severe, but transient inflammatory infiltration and thickening of the alveolar septa in the lungs, along with the increase of total and differential cell counts in BLAF. The BALF level of interleukin (IL)-1 beta and transforming growth factor (TGF)-beta was increased at Day 10 and 14, respectively. At Day 10, the synergistic effect of BLM and ZnO exposure was detected on IL-1 beta and monocyte chemotactic protein (MCP)-1 in BALF. The present study demonstrated the synergistic effect of pulmonary exposure to ZnO nanoparticles and subcutaneous infusion of BLM on the secretion of pro-fibrotic cytokines in the lungs.

DOI： 10.3390/ijms16010660

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Notable progress has been made recently on the properties and applications of Carbon nanotube ( CNT). However, CNT has not achieved any remarkable practical applications from the industrial point of view. In this article, we report our recent progress on the bulk fiber structure of CNT yarn spun from the CNT forest. The unique fiber-like structure of CNT yarns gives them exceptional mechanical toughness, electrical conductivity, resilience to bending stress, and blend with polymer materials for a composite structure. CNT yarn, which is produced by spinning of high dense and relatively long CNT forest, has emerged as a new high-performance CNT-based bulk and composite material. We have made improvements in properties of CNT yarn by applying high voltage ( HV) to the CNT yarn in a vacuum chamber. The tensile strengths of as-spun and HV-treated CNT yarns were 624 MPa and 955 MPa, respectively. The crystallization behavior of the amorphous carbon on CNTs was confirmed by a Transmission Electron Microscope ( TEM). The CNT yarns provide them mechanical properties different from those of original high-performance fiber.

DOI： 10.1109/3M-NANO.2015.7425488

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Field-effect transistors (FETs) with single crystals of a new phenacene-type molecule, [8]phenacene, were fabricated and characterized. This new molecule consists of a phenacene core of eight benzene rings, with an extended p-conjugated system, which was recently synthesized for use in an FET by our group. The FET characteristics of an [8]phenacene single-crystal FET with SiO2 gate dielectrics show typical p-channel properties with an average field-effect mobility, &lt;mu &gt;, as high as 3(2) cm(2) V-1 s(-1) in two-terminal measurement mode, which is a relatively high value for a p-channel single-crystal FET. The hmi was determined to be 6(2) cm(2) V-1 s(-1) in four-terminal measurement mode. Low-voltage operation was achieved with PbZr0.52Ti0.48O3 (PZT) as the gate dielectric, and an electric-double-layer (EDL) capacitor. The &lt;mu &gt; and average values of absolute threshold voltage, &lt;vertical bar V-th vertical bar &gt;, were 1.6(4) cm(2) V-1 s(-1) and 5(1) V, respectively, for PZT, and 4(2) x 10(-1) cm(2) V-1 s(-1) and 2.38(4) V, respectively, for the EDL capacitor; these values were evaluated in two-terminal measurement mode. The inverter circuit was fabricated using [8]phenacene and N, N'-1H, 1H-perfluorobutyldicyanoperylene-carboxydi-imide single-crystal FETs. This is the first logic gate circuit using phenacene molecules. Furthermore, the relationship between mu and the number of benzene rings was clarified based on this study and the previous studies on phenacene single-crystal FETs.

DOI： 10.1039/c5tc00960j

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_2683

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Language：Japanese   Publisher：The Surface Science Society of Japan  

DOI： 10.14886/sssj2008.35.0_272

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High surface area and accessibility to the surface are very important for designing advanced electrodes for energy storage, battery, and capacitor systems because electrons are delivered at the surfaces of carbon based electrodes after diffusion into pore spaces. In this study, phenol resin carbonized porous films with controllable mesostructures and highly accessible surfaces were fabricated using the common EOnPOmEOn-type triblock copolymer. Unique mesostructural transformation of cage-type and tubular mesopores by anisotropic shrinkage was demonstrated from analytical data of the films carbonized at different temperatures. The development of the soft-templating method to obtain surfactant assisted carbon films showing high surface areas is quite significant because further design of mesostructure (anisotropic shrinkage), composition (nitrogen doping, combination with other well-designed carbon based materials) and morphology (coating, spraying, etc.) would be possible for making high-performance electrodes for fuel cells, solar cells, batteries, and energy storage systems, as well as catalytic supports and adsorbents for functional chemical synthesis, purification, and separation. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3ta13026f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We demonstrate a unique strategy to fabricate highly transparent and flexible field electron emitters (FEEs) based on combined carbon nanostructures, i.e., conical nanocarbon structures (CNCSs) and single-walled carbon nanotubes (SWNTs). The combined structure was prepared by spray coating of 1,2-dichloroethane (DCE) dispersed SWNTs onto neon ion (Ne+) irradiation induced CNCSs on nafion substrate. The field emission (FE) property of SWCNTs on both flat nafion and CNCSs surfaces increased with increasing the SWCNTs amount. The best FE result was attained for the highest amount of SWCNTs on the CNCSs substrate. This kind of collective structures is found to be effective emitters on transparent and flexible ion-irradiated nafion substrate. Moreover, the combined carbon nanostructures showed improved transparency and emission performance compared to the individual nanostructures. The FE properties of 0.5 ml SWCNTs solution on CNCSs surfaces were equal to those of 1.5 ml SWCNTs solution on flat nafion surface. The hybrid structure based emitters (CNCSs and SWCNTs) produced by this method are lower-cost cathode materials than hybrid structures of SWCNTs and flat nafion. Thus the combined nanostructures of SWCNTs/CNCSs might have huge prospects for the fabrication of efficient transparent and flexible FEEs and their broad application in next-generation portable display devices. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI： 10.1002/pssr.201308169

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

This paper demonstrates all-carbon photovoltaic devices made of amorphous carbon (a-C) and C-60 thin films. C-60 film is deposited by the sublimation in vacuum and a-C film is synthesized by exposing N-2 radicals to C-60 during the deposition. C-60 is converted into a-C when the rf power is larger than 150 Wand the optical band gap decreases with increasing the power. Photovoltaic properties of device with the structure of Al/C-60/a-C/indium tin oxide/glass are presented. It is shown that the present cell has a strong spectral response in the wavelength range shorter than 550 nm and a small response at around 620 nm. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2013.02.050

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In the present study, we investigated the direct intercalation of three kinds of ionic liquids (ILs) of different salts (imidazolium and ammonium) and cation sizes into montmorillonite (M) clay, and successfully fabricated the IL intercalated montmorillonite (M-IL) compounds. The peak shifts of the M-IL intercalated compounds in comparison with dried montmorillonite powder as observed by XRD results showed that crystal swelling was significantly influenced by the cation sizes of the ILs. The intercalation behaviors of the M-IL compounds were also compared by TEM and the results are in good agreement with the XRD. The TEM-EDS results further confirmed the intercalation of three types of ILs into the montmorillonite. Based on the cation exchange capacity as measured by ICP and mathematical calculations, the extent of the intercalation and arrangement of cations in the interlayers of the montmorillonite are proposed. The TG-DTA results showed an improved thermal stability of all three kinds of M-IL intercalated compounds, and the XRD indicated that the remaining IL initiates a carbonization process with the montmorillonite at 1000 degrees C. Furthermore, the AC impedance results of the M-IL compounds showed an ionic conductivity. These results suggest the possible application of the M-IL intercalated compounds in electrical conductive films, solar cells, fuel cells, etc. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ssi.2013.03.032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The properties of soluble zinc phthalocyanines with trifluoroethoxy substituents (TFEO-ZnPcs) were studied to evaluate their possible use in organic thin-film solar cells. We prepared five TFEO-ZnPcs with different numbers and positions of the TFEO substituents. The solubilities, UV-visible absorption spectra, and cyclic voltammograms of these ZnPcs varied with their substituents. TFEO-ZnPc thin-films fabricated by spin-casting exhibited photocurrent generation at wavelengths between 600 and 850 nm. Flat heterojunction solar cells consisting of a poly(3-hexylthiophene) (P3HT) layer as a donor and a TFEO-ZnPc layer as an acceptor exhibited photocurrent generation over a wide range of wavelengths corresponding to both the P3HT and TFEO-ZnPc absorption spectra. The best solar cell performance was obtained with (beta-TFEO)(4)ZnPc film. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.05DA07

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE Computer Society  

In situ environmental transmission electron microscopy (ETEM) observation was used to reveal Sn inside Sn-filled carbon nanofibers (CNFs) during heating. Before and during heating, the Sn was covered completely by CNFs. The volume of Sn present in the Sn-filled CNFs gradually decreased during heating, with new Sn particles appearing at the top of the Sn-filled CNFs. It is thought that Sn diffused out of the Sn-filled CNFs and into the carbon wall of the metal-filled CNFs (MFCNFs). The specific surface area at the top of Sn-filled CNFs is higher specific surface than that at other parts and the temperature at the top of the MFCNF is lower than that at other parts
therefore, diffused Sn particles were formed at only the top of the Sn-filled CNF. Fabrication of Sn metal particles was tried by heating the Sn-filled CNFs, and it was clear that the metal particle size could be controlled by controlling the heating time. © 2013 IEEE.

DOI： 10.1109/NMDC.2013.6707468

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We demonstrate synthesis of large area graphene on a metal (Ni and Cu) foil by the thermal chemical vapor deposition (CVD) process using the solid camphor (C10H16O) as a carbon source. The graphene growth process on a polycrystalline metal foil significantly influence by the gas composition and quantity of solid precursor. Synthesis of high quality continuous graphene film is achieved in the developed technique. Fully flexible transparent conductor is fabricated by transferring the graphene film on a plastic substrate. © 2013 IEEE.

DOI： 10.1109/INEC.2013.6466023

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The domain structure of graphene films deposited by the chemical vapor deposition (CVD) process has a great influence on the electrical and physical properties. Here, we tackled the synthesis of increased domain size of single layer and bi-layer graphene along with few-layer graphene on Ni foil using solid camphor as a carbon source. To achieve this, effect of the composition of carrier gas for the evaporated camphor was investigated. Raman mapping and peak width (FWHM) analyses gave the insight of the quality and number of graphene layers. Optical and scanning electron microcopy studies show significance difference in domain structure of the synthesized graphene in different gas atmosphere. As confirmed by optical and scanning electron microscopes, the graphene domain grown with the carrier gas of Ar/H2 mixture was more than 10 times larger than those grown with pure Ar carrier gas. © 2012 Elsevier B.V.

DOI： 10.1016/j.matlet.2012.11.090

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We demonstrate synthesis of large area graphene on a metal (Ni and Cu) foil by the thermal chemical vapor deposition (CVD) process using the solid camphor (C10H16O) as a carbon source. The graphene growth process on a polycrystalline metal foil significantly influence by the gas composition and quantity of solid precursor. Synthesis of high quality continuous graphene film is achieved in the developed technique. Fully flexible transparent conductor is fabricated by transferring the graphene film on a plastic substrate.

DOI： 10.1109/INEC.2013.6466023

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We demonstrate the formation of a photoinduced charge transfer composite with graphene oxide (GO) and ferrocene (Fc) molecules. Derived insulating GO was partially reduced to improve the conductivity and modified with the Fc molecules. Transmission electron microscopy (TEM), elemental mapping, X-ray photoelectron and UV-visible spectroscopy studies confirm that the Fc molecules were well grafted to the surface of a GO sheet. Photoresponsivity of the prepared GO-Fc composite was investigated by fabricating a metal/GO-Fc/metal device. The fabricated device shows enhanced current density under light illumination, suggesting a photo-induced charge transfer process in the developed GO-Fc composite.

DOI： 10.1039/c2cp43427j

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We demonstrate synthesis of graphene using the solid precursor camphor in a microwave excited surface wave plasma chemical vapor deposition technique. Highly sublimely camphor was introduced into the plasma chamber in the vapor phase along with Ar and uniform plasma formation was obtained. Rapid deposition of a graphene film on Cu foil was achieved at a relatively low temperature (&lt;600 degrees C). Raman spectroscopy and transmission electron microscopy clearly showed that the deposited film on Cu foil consist of few-layer graphene. Fully flexible transparent electrode was fabricated by transferring the graphene film with excellent properties for device application. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssa.201228554

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

Poor electrical conductivity of carbon nanotube (CNT) yarn and sheets has been one of the main hurdles in their practical application. Here, we demonstrate that the ozone irradiation can be an effective approach to reduce the resistivity of spun CNTs bundle with oxidization and induced defects. The CNT yarn and sheet are fabricated from a spinnable vertically aligned CNT forest synthesized by a thermal chemical vapor deposition. The electrical resistance of a CNT yarn and sheet reduces with a certain period of ozone irradiation; however for a long duration of ozone irradiation resistance increases with structural deformation of the CNTs. A comparative study on the effect of shapes between the CNT yarn and sheet with morphological change in the CNTs due to the ozone irradiation is performed. It was observed that the desorption energy of ozone molecules was slightly large for the CNT yarn due to the difference of adsorption sites. The fraction of defects induced by the ozone irradiated on the CNT yarn was estimated from the ultimate resistance change with temperature and Raman spectroscopy.

DOI： 10.1166/mex.2012.1092

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Mixed matrix hollow fibers composed of multi-walled carbon nanotubes (MWCNTs) and polyetherimide (PEI) were fabricated. Pre-treatment of MWCNTs was carried out prior to the incorporation into the polymer matrix using a simple and feasible two stages approach that involved dry air oxidation and surfactant dispersion. The characterizations of the surface treated MWCNTs using TEM and Raman spectroscopy have evidenced the effectiveness of dry air oxidation in eliminating undesired amorphous carbon and metal catalyst while surfactant dispersion using Triton X100 has suppressed the agglomeration of MWCNTs. The resultant mixed matrix hollow fibers were applied for O-2/N-2 pure gas separation. Interestingly, it was found that removal of disordered amorphous carbons and metal particles has allowed the hollow structures to be more accessible for the fast and smooth transport of gas molecules, hence resulted in noticeable improvement in the gas separation properties. The composite hollow fibers embedded with the surface modified MWCNTs showed increase in permeability as much as 60% while maintaining the selectivity of the O-2/N-2 gas pair. This study highlights the necessity to establish an appropriate pre-treatment approach for MWCNTs in order to fully utilize the beneficial transport properties of this material in mixed matrix polymer nanocomposite for gas separation. (c) 2012 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jcis.2012.07.033

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

In situ transmission electron microscopy (TEM) of single Fe-Included carbon nanofibers (CNFs) revealed that the fine polycrystalline structure in the shank region of CNFs transformed to graphitic, hollow structures during a field emission (FE) process. The iron metal platelets agglomerated during the FE process and perceptibly were emitted from the shank, which featured bamboo-like carbon nanotube (CNT) structures. The structural evolution also improved the electrical properties, and the FE current was remarkably increased, that is, 1000 times higher than the initial value (from 10(-9) to 10(-6) A). The structural transformations were effectuated by Joule heating that generated simultaneously during the FE process The in situ TEM study of room-temperature-synthesized CNFs could provide essential information regarding CNFs structural.. transformation for their possible application in future electron emitter sources.

DOI： 10.1021/nn302889e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Multi-segmented one-dimensional metal nanowires were encapsulated within carbon nanotubes (CNTs) through in-situ filling technique during plasma-enhanced chemical vapor deposition process. Transmission electron microscopy (TEM) and environmental TEM were employed to characterize the as-prepared sample at room temperature and high temperature. The selected area electron diffractions revealed that the Pd4Si nanowire and face-centered-cubic Co nanowire on top of the Pd nanowire were encapsulated within the bottom and tip parts of the multiwall CNT, respectively. Although the strain-induced deformation of graphite walls was observed, the solid-state phases of Pd4Si and Co-Pd remain even at above their expected melting temperatures and up to 1,550 +/- 50A degrees C. Finally, the encapsulated metals were melted and flowed out from the tip of the CNT after 2 h at the same temperature due to the increase of internal pressure of the CNT.

DOI： 10.1186/1556-276X-7-448

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A fully transparent and flexible field emission device (FED) has been demonstrated. Single-walled carbon nanotubes (SWCNTs) coated on arylite substrate were used as electron emitters for the FED and a novel metavanadate phosphor coated on the SWCNTs/arylite film was used as transparent and flexible screen. The SWCNTs/arylite based emitters and the SWCNTs/arylite/metal-vanadate-based phosphor showed a transmittance value of 92.6% and 54%, respectively. The assembled device also showed satisfactory transparency and flexibility as well as producing significant current. Metavanadate phosphor is considered to be an excellent candidate due to its superior luminescence properties and easy fabrication onto transparent and flexible conductive substrate at room temperature while retaining reasonable transparency of the substrate. Thus, its transparency and flexibility will open the door to next-generation FEDs. ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI： 10.1002/pssr.201206251

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The present work investigates the relation between ferromagnetism and intrinsic defects of C-doped ZnO thin films. The room-temperature ferromagnetism (RTFM) in C-doped ZnO is due to the charge transfer between Zn 4s and C 2p orbitals. The long-range magnetic interaction in C-doped ZnO is due to carboncarbon interaction mediated by oxygen. The oxygen- and zinc-related defects in C-doped ZnO affect the mediation of ferromagnetic interaction and the existence of hybridization between Zn and C, respectively.

DOI： 10.1002/pssb.201147609

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We investigated the potential of trifluoroethoxy-coated phthalocyanine [(4TFEO)(4)-ZnPc] as an organic thin-film solar cell material. (4TFEO)(4)-ZnPc dissolves well in several organic solvents, thus a fluorinated phthalocyanine (Pc) thin film can be fabricated by a wet process. Additionally, (4TFEO)(4)-ZnPc has lowest unoccupied molecular orbital (LUMO) energy level close to that of a fullerene derivative owing to the electron-withdrawing effect of fluorine substituents. We fabricated two types of fluorinated Pc solar cells by spin casting "(4TFEO)(4)-ZnPc single-layer solar cells" and "two-layer heterojunction solar cells" consisting of a (4TFEO)(4)-ZnPc layer and a poly(3-hexylthiophene) (P3HT) layer. P3HT is a common donor solar cell material. On the other hand, we used (4TFEO)(4)-ZnPc as an acceptor material. For the single-layer solar cells, the (4TFEO)(4)-ZnPc film acts as the photoactive layer of the solar cells, and P3HT/(4TFEO)(4)-ZnPc solar cell properties were improved as compared with that of P3HT or (4TFEO)(4)-ZnPc single-layer solar cells. Additionally, the photovoltaic properties of these solar cells were significantly improved by annealing treatment. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.04DK09

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Single carbon nanotube (CNT) has exceptional electrical and mechanical properties. And CNT fiber is an interesting application because it can become the wire which is more excellent than exiting one. Some groups reported the fabrication of CNT fiber spun from vertically aligned CNTs forest (VACNF), but mechanism of spinning has not clear yet. In this paper, we present the optimum parameters for spinnable VACNF via the difference between spinnable and unspinnable VACNF. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2012.01.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The direct fabrication of fully transparent conical nanocarbon structures (CNCSs) of controlled nanoscopic dimension on a flexible nafion substrate was achieved, using field electron source, by a novel room temperature ion irradiation technique. By controlling the sizes (below the wavelength of visible light) of the CNCSs, the transparency of the substrate can be tailored satisfactorily. The transparency of the CNCSs was observed to be around 90% in the visible regime depending on the ion irradiation time. Our results suggest that the direct fabrication of well controlled fully transparent CNCSs on any transparent and flexible substrate at room temperature could open a novel route for potential applications in future highly transparent, flexible (bendable), low weight and portable field emission displays (FEDs). (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

DOI： 10.1002/pssr.201206037

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WO3 nanorods targeted for applications in electric devices were grown from a tungsten wire heated in an oxygen atmosphere inside an environmental transmission electron microscope, which allowed the growth process to be observed to reveal the growth mechanism of the WO3 nanorods. The initial growth of the nanorods did not consist of tungsten oxide but rather crystal tungsten. The formed crystal tungsten nanorods were then oxidized, resulting in the formation of the tungsten oxide nanorods. Furthermore, it is expected that the nanorods grew through cracks in the natural surface oxide layer on the tungsten wire.

DOI： 10.1186/1556-276X-7-85

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Germanium (Ge) surfaces were irradiated by argon (Ar) ions at 600 eV with a simultaneous Ge, Al, or Au supply at room temperature. The surfaces thus ion-irradiated were characterized by densely distributed nanowalls, nanobelts (narrower than the nanowalls in width), and cones tipped with nanoribbons (narrower than the nanobelts in width), depending on the supplied particle species and the supply rate. The higher the melting points of the supplied materials, the narrower the width of the top of the nanostructures. Thus the melting point and the supply rate of the supplied material are the key parameters for controlling the shape and size in the fabrication of ion-induced Ge nanostructures. It was also demonstrated that for nanowalls and nanobelts, a higher particle supply rate yielded wider nanostructures. For many nanoribbon-tipped cones, the width of the nanoribbon increased with distance from the cone top, and hence resulted in a bottleneck structure. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.01AB05

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

ZnO nanoparticles have been incorporated inside the pore system of mesoporous carbon (MC) which has been synthesized by polymerization of resorcinol and formaldehyde via soft templating approach. 5-20% of ZnO, with an interval of 5, have been incorporated almost exclusively within the mesopores by simple wet impregnation, drying and calcination procedures. The pristine MC shows high surface area (600 m(2)/g) with large pore diameter around 7 nm. After impregnation of ZnO in mesopores, the pore diameter has been decreased from 7 to 6.24 nm which may relate to shrinkage of the framework or deposition of ZnO particles on the inner wall of the pores. With the increase in the ZnO percentage, the specific surface area and pore volume decreased linearly confirming the incorporation of nanoparticles inside the mesopores. TGA confirms ZnO confined in the pores of MC which also prevents the collapsing of mesoporous carbon framework upto 325 degrees C. Interestingly, the graphitic nature of MC remains same even after impregnation of ZnO nanoparticles inside the pores. However, we strongly believe that this novel composite of ZnO and MC may play significant role in the application like oxygen reduction reactions. photocatalysis, photovoltaics, optoelectronics, catalysis and many more. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cej.2011.10.087

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Indium tin oxide (ITO) and related oxide based materials have been widely used as transparent electrode in optoelectronic devices and organic solar cells. Here, we demonstrate application of chemical vapor deposited (CVD) graphene films as transparent electrode for organic solar cells. Large area graphene films are deposited by control pyrolysis of botanical derivative camphor (C10H16O) and transparent electrode were fabricated by direct synthesis or transfer process. Raman spectroscopy and transmission electron microcopy studies are used to characterize the synthesized graphene based materials. Direct synthesized and transferred graphene films on glass or plastic substrates show very good optical transparency, electrical conductivity and mechanical stability. P3HT:PCBM bulk heterojunction solar cells are fabricated successfully on graphene based transparent electrode and compared with ITO based device. The dark light characteristic shows very good rectification with minimum leakage current. Under illumination of light the device shows very good open circuit voltage, short circuit current density and conversion efficiency.

DOI： 10.1109/PVSC.2012.6318244

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We demonstrate a solid phase reaction approach to synthesise transfer-free graphene on an insulating substrate by controlling the C diffusion process. Metal assisted crystallization by annealing of a C thin film was carried out to synthesise transfer-free graphene, in the presence of a top metal oxide and metal layer. Without the metal oxide layer, a large amount of C atoms diffused to the top of the metal surface and hence the formation of only small graphene domains was observed on the underneath of the metal layer. Introducing the metal oxide layer at the top surface, C diffusion was reduced and consequently the thin C film was crystallized to form large area graphene at the metal-insulating substrate interface. The metal oxide or metal catalyst layer was removed after graphene formation and transfer-free graphene was obtained directly on the base substrate. This finding shows that the thin metal oxide layer is critical to synthesise graphene with better quality and continuous domain structures.

DOI： 10.1039/c2nr31723k

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Mixed matrix membranes (MMM) combine useful molecular sieving properties of inorganic fillers with the desirable mechanical and processing properties of polymers. The current trend in polymeric membranes is the incorporation of filler-like nanoparticles to improve the separation performance. Most MMM have shown higher gas permeabilities and improved gas selectivities compared to the corresponding pure polymer membranes. Carbon nanotubes based mixed matrix membrane was prepared by the solution casting method in which the functionalized multiwalled carbon nanotubes (f-MWNTs) were embedded into the polyimide membrane and the resulting membranes were characterized. The effect of nominal MWNTs content between 0.5 and 1.0 wt% on the gas separation properties were looked into. The as-prepared membranes were characterized for their morphology using field emission scanning electron microscopy (FESEM) and Transmission Electron Microscopy (TEM). The morphologies of the MMM also indicated that at 0.7 % loading of f-MWNTs, the structures of the MMM showed uniform finger-like structures which have facilitated the fast gas transport through the polymer matrix. It may also be concluded that addition of open ended and shortened MWNTs to the polymer matrix can improve its permeability by increasing diffusivity through the MWNTs smooth cavity.

DOI： 10.4028/www.scientific.net/AMR.364.272

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This paper presents direct growth of horizontally-aligned carbon nanotubes (CNTs) between two predefined various inter-spacing up to tens of microns of electrodes (pads) and its use as CNT field-effect transistors (CNT-FETs). Using the conventional photolithography technique followed by thin film evaporation and lift off, the catalytic electrodes (pads) were prepared, consisting of Pt, Al and Fe triple layers on SiO2/Si substrate. The grown CNTs were horizontally-aligned across the catalytic electrodes on the modified gold image furnace hot stage (thermal CVD) at 800 degrees C by using an alcohol vapor as the carbon source. Scanning and transmission electron microcopies (SEM/TEM) were used to observe the structure, growth direction and density of CNTs, while Raman spectrum analysis was used to indicate the degree of amorphous impurity and diameter of CNTs. Both single- and multi-wall CNTs with diameters of 1.1-2.2 nm were obtained and the CNT density was controlled by thickness of Fe catalytic layer. Following horizontally-aligned growth of CNTs, the electrical properties of back-gate CNT-FETs were measured and showd p-type conduction behaviors of FET.

DOI： 10.1166/jnn.2011.3964

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The composite thin film of poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate)/single-wall carbon nanotubes (PEDOT:PSS/SWCNTs) for a hole transport layer in polymer solar cells have been explored. PEDOT:PSS/SWCNT composite film exhibited higher electrical conductivity than the control PEDOT:PSS film, suggesting the increase in carrier transport passes through SWCNTs in the hole transport layer. We also demonstrated the improvement of a fill factor and short circuit current density in the polymer solar cells with the hole transport layer of PEDOT:PSS/SWCNT as compared with PEDOT:PSS.

DOI： 10.1142/S1793292011002901

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Graphite surfaces were irradiated by argon (Ar+) ions at 1 key with a simultaneous cobalt (Co) supply at room temperature. Various kinds of carbon nanocomposites, such as nanocones with and without single nanofibers on their tops, nanorods and fish-scale-like nanoprotrusions, were formed depending on Co supply rates. It has been observed that with increasing the Co supply rate the formation of nanoprotrusions without nanofibers became prominent. Both nanofibers and nanoprotrusions were surely composed of carbon and Co, as confirmed by energy-dispersive X-ray analysis. The cobalt carbon nanocomposite fibers (CCNFs), similar to 1.5 mu m in average length, were grown on the top of the nanocones at the Co supply rate of 1.0 nm/min. The field electron emission characteristics of CCNFs thus grown indicated that there is an optimum parameter for the CCNF growth to achieve the better emission performance than that of pristine Ar+-induced carbon nanofibers.

DOI： 10.1166/jnn.2011.4021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINESE CENTER DISEASE CONTROL & PREVENTION  

Objective To investigate in vitro cytotoxicity and oxidative stress response induced by multiwalled carbon nanotubes (MWCNTs).
Methods Cultured macrophages (murine RAW264.7 cells) and alveolar epithelium cells type II (human A549 lung cells) were exposed to the blank control, DNA salt control, and the MWCNTs suspensions at 2.5, 10, 25, and 100 mu g/mL for 24 h. Each treatment was evaluated by cell viability, cytotoxicity and oxidative stress.
Results Overall, both cell lines had similar patterns in response to the cytotoxicity and oxidative stress of MWCNTs. DNA salt treatment showed no change compared to the blank control. In both cell lines, significant changes at the doses of 25 and 100 mu g/mL treatments were found in cell viabilities, cytotoxicity, and oxidative stress indexes. The reactive oxygen species (ROS) generation was also found to be significantly higher at the dose of 10 mu g/mL treatment, whereas no change was seen in most of the indexes. The ROS generation in both cell lines went up in minutes, reached the climax within an hour and faded down after several hours.
Conclusion Exposure to MWCNTs resulted in a dose-dependent cytotoxicity in cultured RAW264.7 cells and A549 cells, that was closely correlated to the increased oxidative stress.

DOI： 10.3967/0895-3988.2011.06.002

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A single amorphous carbon nanofiber (CNF) was grown on a commercial Si cantilever by the argon ion (Ar+) bombardment of carbon coated silicon cantilever. The CNF probe was mounted on a piezo controlled arm opposing a soft cantilever to measure the axial force acting on the CNF in a scanning electron microscope (SEM). The buckling force was measured while observing the buckling behavior. The CNF probes have an elliptical cross section with short and long axis of 20-29 and 25-59 nm, respectively, and a length of 350-760 nm. The Young's modulus was determined from Euler's formula using the measured buckling force and had a value of 38-48 GPa, almost independent of the CNF size. The Young's modulus was lower than that of high quality carbon nanotubes (CNTs) and higher than that of defective CNTs. It was also demonstrated that the CNF probes were elastic, similar to the CNT probes. Thus CNF probes produced by Ar+ ion bombardment are quite promising as practical nanocarbon probes. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2011.05.051

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The Ge surfaces irradiated by Ar(+) ions at 600 eV with simultaneous Ni supply at room temperature were characterized by various kind of densely distributed nanostructures, such as tiny cones, nanorods with a bottlenecked and nanoneedles, depending on the Ni supply rate during Ar(+) ion irradiation. As the Ni supply rate decreased, the width of nanostructure formed on the cone tip became thin, and finally slender Ge nanoneedles of 60-80 nm in diameter and 100-300 nm in length were realized. Because the simultaneously supplied Ni fulfills the prerequisite for the so-called "seed" which enhances the surface texturing, size of clustered Ni atoms during of Ar(+) ion irradiation might affect the size of nanostructures formed after the prolonged sputtering. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.surfcoat.2011.04.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Carbon nanotube (CNT) fibers have interesting applications because of their good electrical and mechanical properties. CNT fiber is fabricated in a simple way, that it is spun from a vertically aligned CNT forest (VACNF). Spinning occurs by joining of CNT when the CNT at the edge of a VACNF is drawn horizontally. However, the mechanism of spinning is still not clear. To investigate it, we fabricated a spinnable VACNF by thermal chemical vapor deposition (CVD) and compared it with unspinnable VACNF by scanning electron microscope (SEM) observation and polarized Raman spectroscopy. It was found that there were a few big differences between spinnable and unspinnable VACNFs. In the case of spinnable VACNF, most of the CNTs are straight and well aligned. Spinnable VACNF also contains CNT bundles consisting of 8-10 CNTs that are not vertically aligned. This CNT bundle was shared by a few adjacent thicker CNT bundles. These points are very important for continuous fiber spinning. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssa.201084170

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To understand the motion of DNA and DNA complexes, the real-time visualization of living DNA in liquids is quite important. Here, we report the high-resolution imaging of plasmid DNA in water using a rapid-scan atomic force microscopy (AFM) system equipped with a carbon nanofiber (CNF) probe. To achieve a rapid high-resolution scan, small SiN cantilevers with dimensions of 2 (width) × 0.1 (thickness) × 9μm (length) and a bent end (tip view structure) were employed as base cantilevers onto which single CNFs were grown. The resonant frequencies of the cantilever were 1.5 MHz in air and 500 kHz in water, and the spring constant was calculated to be 0.1 N/m. Single CNFs, typically 88 nm in length, were formed on an array of the cantilevers in a batch process by the ion-irradiation method. An AFM image of a plasmid DNA taken in water at 0.2fps (5s/image) using a batch-fabricated CNF-tipped cantilever clearly showed the helix turns of the double strand DNA. The average helical pitch measured 3.4 nm (σ: 0.5 nm), which was in good agreement with that determined by the X-ray diffraction method, 3.4 nm. Thus, it is presumed that the combined use of the rapid-scan AFM system with the ion-induced CNF probe is promising for the dynamic analysis of biomolecules. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.08LB14

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To understand the motion of DNA and DNA complexes, the real-time visualization of living DNA in liquids is quite important. Here, we report the high-resolution imaging of plasmid DNA in water using a rapid-scan atomic force microscopy (AFM) system equipped with a carbon nanofiber (CNF) probe. To achieve a rapid high-resolution scan, small SiN cantilevers with dimensions of 2 (width) x 0.1 (thickness) x 9 mu m (length) and a bent end (tip view structure) were employed as base cantilevers onto which single CNFs were grown. The resonant frequencies of the cantilever were 1.5 MHz in air and 500 kHz in water, and the spring constant was calculated to be 0.1 N/m. Single CNFs, typically 88 nm in length, were formed on an array of the cantilevers in a batch process by the ion-irradiation method. An AFM image of a plasmid DNA taken in water at 0.2 fps (5 s/image) using a batch-fabricated CNF-tipped cantilever clearly showed the helix turns of the double strand DNA. The average helical pitch measured 3.4nm (sigma:0.5 nm), which was in good agreement with that determined by the X-ray diffraction method, 3.4 nm. Thus, it is presumed that the combined use of the rapid-scan AFM system with the ion-induced CNF probe is promising for the dynamic analysis of biomolecules. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.08LB14

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This paper presents the growth evolutions in terms of the structure, growth direction and density of rapid grown carbon nanotube (CNT) forests observed by scanning and transmission electron microcopies (SEM/TEM). A thermal CVD system at around 700 degrees C was used with a catalyst of Fe films deposited on thin alumina (Al2O3) supporting layers, a very fast raising time to the growth temperature below 25 degrees C/s, and a carbon source gas of acetylene diluted with hydrogen and nitrogen without water vapor. Activity of Fe catalyst nanoparticles was maintained for 5 min during CVD process, and it results in CNT forests with heights up to 0.6 mm. SEM images suggest that the disorder in CNT alignment at the initial stage of CM&apos;s plays a critical role in the formation of continuous CNT growth. Also, the prolonged heating process leads to increased disorder in CNT alignment that may be due to the oxidation process occurring at the Fe nanoparticles. TEM images revealed that both double- and few-walled CNTs with diameters of 5-7 nm were obtained and the CNT density was controlled by thickness of Fe catalytic layer. The number of experiments at the same conditions showed a very good repeatability and reproducibility of rapid grown CNT forests. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2011.02.003

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A graphite foil was irradiated with argon (Ar+) ions to fabricate conical structures with a carbon nanofiber (CNF) on top of the structure. The field emission (FE) properties of one-dimensional individual CNF-tipped cones that had been fabricated were carefully measured by in situ transmission electron microscopy (TEM) facilities. The highest FE current, 550 nA, was observed in the current-voltage (I-V) measurement of a single CNF. Almost no degradation in I-V properties were detected during the reliability test after 30 min. TEM images indicated that the CNF was amorphous in nature initially, and that the electron current flow in the FE process induced the dramatic change in the crystalline structure of both the CNF and of the tip region of the basal cone part. After performing the FE process, the crystalline structures of the amorphous CNFs were transformed into ring-shaped graphene layers, whereas nanodiamond like nanoparticles formed in the outer layer of the tip region of the basal cone. The structural changes induced can be attributed to Joule heating under the high electric field. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3591420]

DOI： 10.1116/1.3591420

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The synergistic combinations of organic polymers for separation applications with inorganic substances such as multi-walled carbon nanotubes (MWNTs), have resulted in a new class of membrane material called mixed matrix membrane (MMM) for the separation of CO2/CH4 gases. Mixed matrix membrane incorporated functionalized MWNTs (f-MWNTs) were fabricated by the solution casting method, in which the f-MWNTs were embedded into the polyimide membrane and the resulting membranes were characterized. The effect of nominal MWNTs content between 0.5 and 1.0 wt% on the gas separation properties was investigated. The mixed matrix membranes showed 100% enhancement for the selectivity of CO2/CH4 compared to the corresponding neat polymer membrane. This new class of mixed matrix membrane has the ability to separate gases at the molecular level and has the potential to ultimately reduce the energy consumed in present-day separation operations. This study has shown that addition of CNTs to polymeric membranes has improved separation properties of the membranes to a certain extent. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.seppur.2011.02.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

In this article, we performed dehydration polycondensation of bromosuccinic acid and methylsuccinic acid with 1,4- butanediol at 80 1C to synthesize aliphatic polyesters containing pendent bromo groups without dehydrobromination using scandium trifluoromethanesulfonate (Sc(OTf) 3) as the catalyst. Azidation of the resultant polyesters was carried out readily in N, Ndimethylformamide at room temperature using sodium azide (M-n = 8.3 x 10(3) (M-w/M-n=2.17)). H-1 nuclear magnetic resonance analysis of the product revealed that 65% contained azide functionality, and dehydrobromination occurred in 35% during the azidation process. On the other hand, azidation of poly(butylene bromoadipate-co-butylene methylsuccinate) (poly(BBA-co-BMS)) proceeded successfully under the same conditions to generate poly(butylene azidoadipate-co-butylene methylsuccinate) (poly(BAA-co-BMS)) without dehydrobromination (M-n=10.4 x 10(3) (M-w/M-n=2.71)). We successfully photo-crosslinked the resultant azidopolyester by ultraviolet irradiation and examined it using scanning electron microscope. We also described azidation of polyesters having pendent hydroxyl groups by using the 'DPPA (diphenylphosphoryl azide)-DBU (1,8diazabicyclo[5.4.0] undec-7-ene) substitution strategy' to produce water-soluble polyesters containing pendent azido groups (M-n=7.5 +/- 103 (M-w/M-n=2.25)). These azidopolyesters might be extremely useful not only for their derivatization by simple chemical modification but also for their effective utilization as photolithography material. Polymer Journal (2011) 43, 272-278; doi: 10.1038/pj.2010.135; published online 12 January 2011

DOI： 10.1038/pj.2010.135

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Carbon nanofibers (CNFs) with a diameter of 17 nm, and carbon nanoneedles (CNNs) with sharp tips have been synthesized on graphite substrates by ion irradiation of argon ions with the Co supplies rate of 1 and 3.4 nm/min, respectively. Energy dispersive X-ray spectrometry, combined with selected area electron diffraction patterns has been used to identify the chemical composition and crystallinity of these carbon nanostructures. The CNFs were found to be amorphous in nature, while the structures of the CNNs consisted of cubic CoC(x), orthorhombic Co(2)C and Co(3)C depending on the cobalt content in the CNNs. The diameter of the carbide crystals was almost as large as the diameter of the CNN. Compared to the ion-induced nickel carbides and iron carbides, the formation of single-crystalline cobalt carbides might be due to the high temperature produced by the irradiation. (C) 2010 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.apsusc.2010.10.134

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There has been a considerable amount of research on MFCNTs and MFCNFs; however, research on the behavior of the internal metal used in MFCNF under heating has been limited. Therefore, in this study, an MFCNF was heated and the behavior of the internal metal was investigated using in-situ TEM observations. The internal metal used in the MFCNF did not melt. It was supposed that the non-melting was because of the high pressure of the internal metal resulting from a difference in the coefficients of linear thermal expansion of the graphite wall of the MFCNF and the internal metal. The pressure of the internal metal was calculated; it was approximately 12 GPa when the MFCNF was heated at 1500 degrees C. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2010.12.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

Graphite surfaces were bombarded with oblique Ar+ ions at 1 keV to induce the carbon nanofiber (CNF) growth at room temperature and at high temperature (300 degrees C), and their dependence of length, diameter and number density on ion-incidence angle and sputtering rate was investigated in detail. The sputtered surface ion-irradiated at normal incidence produced huge cones and rod-like structures. It was found that some of the cones possessed the non-aligned thick carbon fibers on the top. By contrast, obliquely ion-irradiation induced the formation of densely distributed CNF-tipped cones. The higher ion-incidence angle produced CNF of smaller diameter and high fabrication temperature favors the formation of longer fiber with higher numerical density. In addition, the number density of the CNF-tipped cones strongly depended upon the ion-incidence angle rather than the sputtering rate. Thus, the diameter, length and number density of CNFs were strongly dependent upon the ion-irradiation parameters. It is believed that myriad of applications is possible with ion-induced CNFs by selecting the suitable ion-irradiation parameters. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.01AF10

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The WO3 nanorods were fabricated in environmental transmission electron microscopy (ETEM) by simply heating it in oxygen atmosphere. Altough, WO3 nanorod showed high crystalline, but the stacking fault existed in nanorod. Furthermore, the nanorod was grown on tungsten wire through slit of oxide layer on it. © 2011 IEEE.

DOI： 10.1109/INEC.2011.5991617

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Single-walled carbon nanotubes (SWNTs) have been used successfully to fabricate highly transparent and flexible field emission displays (FEDs). Field emission measurements indicated that SWNTs films have great potential to work as building blocks for next generation transparent and flexible FEDs.

DOI： 10.1039/c0cc05677d

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Direct growth of aligned metal composite carbon nanofibers (MCNFs) was achieved by a highly reproducible room temperature growth process on cost effective electrically conductive copper (Cu) substrate without any catalyst. The direct fabrication of MCNFs on electrically conductive substrate might offer new perspectives in the field of field emission displays (FEDs).

DOI： 10.1039/c1cc10655d

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Carbon nanotube (CNT) fibers are having interesting applications because of its good electrical and mechanical properties. CNT fiber is fabricated by simple way that it is spun from vertically aligned CNT forest (VACNF). Spinning is occurred by joining of CNT when the CNT at edge of VACNF is drawn horizontally. © 2011 IEEE.

DOI： 10.1109/INEC.2011.5991734

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The organic-organic self-assembly method with Resorcinol (R)/Formaldehyde (F) and Pluronic F127 has been employed to synthesize mesoporous carbon (MC). The pore diameter of the MC has been tuned from 7 to 12.5 nm by changing the molar ratio of carbon sources to surfactant and polymerization time.

DOI： 10.1039/c1cc13471j

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We report the polymer solar cells using newly synthesized fullerene derivatives with fluorocarbon substituent (F-PCBM). F-PCBMs were synthesized to improve a solar cell property byadding them to P3HT/PCBM mixture. According to the UV-vis absorption spectra and the cyclic voltammograms for F-PCBMs, the energy levels of the F-PCBMs couldn't be influenced by fluorocarbon substituent. We fabricated the polymer solar cells consist of P3HT/PCBM with each F-PCBM, and investigated their solar cell property. Some solar cells with F-PCBM showed increase of the short circuit current density (J(sc)). F-PCBM with short fluorocarbon chain (PCB2F) significantly increased J(sc), and it showed higher solar cell efficiency (E-ff = 2.31 %) than the solar cell with only PCBM (E-ff = 2.04 %). We also fabricated solar cells with PCB2F on the three condition of drying time before thermal annealing. As a result, the condition of "30 min" showed the highest solar cell efficiency than other tried one. (C) 2010 Published by Elsevier B.V.

DOI： 10.1016/j.phpro.2011.05.039

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The Zn nanowires covered with ZnO were grown by oxygen plasma-assisted molecular beam irradiation method and characterized, was reported. To grow these nanowires, oxygen plasma was irradiated to Zn thin film evaporated on Si(100) substrate. Scanning electron microscopy and transmission electron microscopy observation results of nanowires revealed that the nanowire has diameter of 80 nm, and nanowires was constructed with crystalline ZnO. Moreover NWs surface was covered by crystalline ZnO. Further Zn and ZnO orientation was coincident and resulted the ZnO appeared by oxidation of Zn nanowires. © 2011 IEEE.

DOI： 10.1109/INEC.2011.5991618

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We report the synthesis of poly[(3-hexylthiophene)-block-(3-(4,4,5,5,6,6,7,7,7-nonafluoroheptyl)thiophene)], P(3HT-b-3SFT), carried out by the Grignard Metathesis Method (GRIM). The copolymers composition was determined by H-1 and F-19 NMR spectroscopies, and gel permeation chromatography (GPC). The thin films of P(3HT-b-3SFT) were investigated by ultraviolet-visible absorption spectroscopy and atomic force microscopy (AFM). We also fabricated bulk-hetero junction (BHJ) solar cells based on blends of P(3HT-b-3SFT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). Although the composition ratio of P3SFT in P(3HT-b-3SFT) was low, the influence of P3SFT on the morphology and properties of solar cells was significant. The annealing process for the BHJ solar cells induced the formation of large domains and led to poor solar cell performance. The BHJ solar cells, based on PCBM and P(3HT-b-3SFT), prepared by the non-annealing process, had a maximum power conversion efficiency of 0.84% under 100 mW/cm(2) (AM 1.5 solar illumination) in air.

DOI： 10.3390/ijms11125027

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The Fe-incorporated carbon nanofibers (Fe-CNFs) grew on the graphite plate surface irradiated by Ar⁺ ions with a simultaneous Fe supply. The average diameter and length of the Fe-CNFs were in the range of 10-50 nm and 0.5-3 μm, respectively. As confirmed by TEM observation, the Fe-CNFs thus grown were characterized by amorphous-like or very fine crystalline nature. Compared with bulk Fe, they possessed higher coercivities for both parallel and perpendicular directions to the substrate at room temperature. In addition, magnetic properties of the Fe-CNFs strongly depended on the Fe content: The higher the Fe content, the stronger the saturation magnetization, whereas perpendicular coercivity was obtained for lower Fe supply rates.

DOI： 10.14723/tmrsj.35.755

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An efficient method for the fabrication of zinc (Zn) nanostructures (nanoneedles and nanofibers) of controllable density and morphology without any catalyst, hazardous chemicals or external heat supply has been investigated. By varying the ion irradiation time and the ion current density, morphological control and the density of Zn nanostructures were successfully achieved using a fast and viable ion irradiation technique. Scanning (SEM) and transmission electron microscopy (TEM) results revealed that the sputtered surface was almost entirely covered with densely distributed conical and needle-like protrusions with linear shaped (sometimes curved) nanostructures (such as nanoneedles and nanofibers) with diameters and lengths of about 20-50 nm and several hundred nanometers, respectively. Detailed analysis of selected area electron diffraction (SAED) patterns with TEM analysis indicates that the Zn nanofibers were polycrystalline in nature. A possible mechanism of the formation of Zn nanostructures is briefly discussed. These aligned arrays of Zn nanoneedles/nanofibers could be a promising material for the fabrication of zinc oxide nanostructures by subsequent oxidation of Zn nanostructures and their future application in nanodevices. Thus, it is believed that this ion irradiation technique could open up a new approach for the fabrication of many kinds of nanomaterials of controllable density.

DOI： 10.1166/jnn.2010.2508

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Polyaniline (PANI) nanobrushes were synthesized by template-free electrochemical galvanostatic methods. When the same method was applied to the carbon nanohorn (CNH) solution containing aniline monomers, a hybrid nanostructure containing PANI and CNHs was enabled after electropolymerization. This is the first report on the template-free method to make PANI nanobrushes and homogeneous hybrid soft matter (PANI) with carbon nanoparticles. Raman spectroscopy was used to analyze the interaction between CNH and PANI. Electrochemical nanofabrication offers simplicity and good control when used to make electronic devices. Both of these materials were applied in supercapacitors and an improvement capacitive current by using the hybrid material was observed.

DOI： 10.1088/0957-4484/21/43/435702

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Cu-doped ZnO and AlN films both exhibiting room-temperature (RT) ferromagnetism (FM) were deposited by helicon magnetron sputtering. Magnetic anisotropy was observed for all the films; saturated magnetization was larger under the applied field perpendicular to the sample surface than the [0 0 0 2] direction. Electron spin resonance (ESR) analysis showed that spins tended to align in a perpendicular direction to the surface, which might account for the observed magnetic anisotropy. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2010.06.036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Association of the Scientific Medical Societies in Germany  

A new technical approach to breast-tumor detection is proposed. The technique is based on fluorescence x-ray analysis, and can identify a miniature malignant tumor within the breast. The primary beam intensity needed in fluorescence x-ray analysis is on a lower order of magnitude than that used in mammography. Thus, the newly-proposed technique would enable detection of a still tiny breast cancer while dramatically lowering the radiation dose. Field-emission x-ray sources might be a key for translating this concept into a medical technique. © 2010 Hayashi et al.

DOI： 10.3205/000107

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The irradiation of graphite surfaces with a simultaneous Fe supply have resulted into the development of various types of carbon nanocomposites. Their morphologies - diameter, density, length and apex angle strongly depend on the ratios of Fe deposition rate (D(Fe)) to ion sputtering rate (S(ion)). By optimizing the ratio of D(Fe)/S(ion) (2.40%), the denser and well-aligned Fe-carbon nanocomposite fibers (Fe-CNFs) could be obtained, whose average length and diameter were 0.95 mu m and 17 nm, respectively. As confirmed by energy-dispersive X-ray analysis, the Fe-CNFs with amorphous-like or fine-polycrystalline phase were surely composed of carbon and Fe. Two types of growth models have been employed to explain the formation of metal-carbon nanocomposites. (C) 2010 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.apsusc.2010.04.019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

The functionalization of multiwalled carbon nanotubes (MWNTs) with beta cyclodextrin (beta-CD) is described. The functionalization using beta-CD treatment is an environmentally friendly and nondestructive method to modify carbon nanotubes. It was observed that the degree of functionalization increases with increasing ratios of beta-CD as seen from the Raman analysis. The Raman spectra also indicated that the nanotubes walls were not damaged. The presence of functional groups associated with beta-CD on the functionalized MWNTs indicated that the cyclodextrin groups were found to be adsorbed at the surface of the nanotubes walls. Mixed matrix membrane (MMM) was prepared by a phase inversion process. Enhanced selectivity and permeability for CO(2) over CH(4) was observed for MMM prepared using functionalized MWNTs.

DOI： 10.1142/S1793292010002104

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

The effect of ion species and fabrication temperature on the size of ion-induced carbon nanofibers (CNFs) grown on tips of scanning probe microscope cantilevers was investigated in detail. Similarly to that using Ar(+) ions, the fabrication of CNF probes using Ne(+) and Xe(+) ions was possible. Xe(+) sputtering yielded the shortest CNF probes owing to its large sputtering effect; however, a significant difference in the size of the CNF probes between Ne(+) and Ar(+) ion irradiation was not observed. The CNFs increased in length with fabrication temperature owing to the enhanced diffusion of C atoms at elevated temperatures; however, the CNF diameter remained almost constant independent of fabrication temperature. Therefore, the fabrication at elevated temperatures was effective for the rapid fabrication of practical CNF probes. Thus, the CNF probe size was controllable by adjusting the fabrication temperature and ion species. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.08LB15

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Aligned Fe-carbon composite nonofibers (Fe-CNFs) grew on graphite substrates bombarded by Ar+ ions at an oblique incident angle with a simultaneous Fe supply at room temperature. Morphology alteration and crystallinity variation of Fe-CNFs were achieved by adjusting the supply rate of Fe atoms. The effects of different Fe concentrations on the morphological and crystalline structures of Fe-CNFs were discussed in detail. The higher the Fe supply rates, the higher the Fe concentration in Fe-CNFs. Higher Fe concentration in Fe-CNFs favors the graphitization of carbon materials, but destroys the directivity of Fe-CNFs pointing to ion beam incident direction. The magnetic properties of Fe-CNFs with different Fe contents were also analyzed in detail. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2010.03.023

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In this work, we have studied the combination of ferrocene (Fc), the donor material and fullerene derivatives such as [6,6]-phenyl C(61)-butyric acid methyl ester (PCBM) and the acceptor material, for fabricating organic photovoltaic devices. The effect of temperature on open circuit voltage (V(oc)), short-circuit current density (J(sc)), fill factor (FF) and the photoconversion efficiency (PCE), eta has been investigated. By varying the annealing temperature, the V(oc) FF and PCE, eta, were increased up to 140 degrees C and further increasing of temperature it remains constant. However, the short-circuit current density was not varied concomitantly with other parameters. The maximum PCE was observed to be 0.053% at 140 degrees C, which is the best annealing temperature in the present study. There have been many attempts to synthesize Fc and fullerene dyads but as an application wise very few report are available. Therefore here we have tried to use Fc and PCBM for photovoltaic device applications. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.synthmet.2010.01.020

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The fabrication of conical nanocarbon structures (CNCSs) on a transparent and flexible nafion substrate at room temperature using an ion irradiation technique and their application toward field emission displays (FEDs) have been demonstrated. The main advantage of this technique is that CNCSs can be fabricated directly on the transparent substrate while retaining the transparency of the substrate. A scanning electron microscopy (SEM) image revealed that the sputtered surface was entirely covered with CNCSs with a calculated numerical density of 6 x 10(6)/mm(2). Such nafion based CNCSs have proved to be an effective electron emitter with turn-on and threshold fields of 6.1 and 9.5 V/mu m, respectively. The field enhancement factor was estimated to be 1020 from the Fowler-Nordheim (F-N) plot. Thus the room temperature fabricated CNCSs based on transparent and flexible nafion substrate would be very promising for future flexible (roll-up) and transparent FEDs.

DOI： 10.1021/ja909346e

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A direct growth of carbon nanofibers (CNFs) on the metal meshes by an ion irradiation method has been demonstrated. The average diameter and length of CNFs were found to be 50 nm and 2.0 mu m for Cu meshes, and 20 nm and 1.0 mu m for Mo meshes, respectively. Scanning electron microcopy images revealed that sputtering time and metal species of meshes influenced the morphology of the obtained nanofibers. High resolution transmission electron microscopy images indicated that the nanofibers were metal-composite CNFs in which the very fine metal crystallites dispersed in the amorphous carbon matrix. It was also demonstrated that the amorphous based structure changed to nanowires covered with graphene layers after the current flow in the composite CNFs.

DOI： 10.1116/1.3318694

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Ge surfaces were irradiated by Ar+ ions at 600 eV with and without a simultaneous supply of Ge, Au or Al at room temperature. The surfaces ion-irradiated without any simultaneous metal supply were characterized by densely distributed conical protrusions. By contrast, various kinds of nanostructures were formed on the Ge surfaces ion-irradiated with a simultaneous metal supply. They featured cones and nanobelts with a flattened top for Ge supply cases, whereas they were characterized by nanorods for Au supply cases and by nanorods, nanobelts and nanowalls for Al supply cases. Very interestingly, the nanorods formed with Au or Al supply possessed a bottleneck structure. Thus, the ion-induced Ge nanostructures were controllable in morphology by species and amount of simultaneously supplied metals.

DOI： 10.1109/INEC.2010.5424518

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1-dimensional (1-D) nanocarbon materials such as carbon nanotubes [1] (CNTs) and carbon nanofibers (CNFs) are quite promising as electron emission sources[2] in the near future. These 1-D nanocarbon materials possess very high aspect ratio, thus readily allowing to emit electrons under relatively low applied electric fields even at low vacuum pressures. During the field emission (FE) process, degradation in current and structural damages of the nanocarbon emitters often occurs. Regarding these phenomena, for the practical use it is essential to fully understand the fundamental physics underlying the FE process particularly for individual nanocarbon emitters. In this paper, we are challenging to study the structural change of individual ion-induced CNF by electron current flow during FE process, using in situ transmission electron microscopy (TEM) facilities. © 2010 IEEE.

DOI： 10.1109/IVESC.2010.5644429

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Publishing type：Research paper (scientific journal)   Publisher：Thin-Film Solar Cells  

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The metal oxide nanorods are widely studied, as the electronic characteristics of the metal oxide nanorods are different from the electronic characteristics of bulk metal oxide. [1-3] Tungsten oxide nanorods are one of the metal oxide semiconductors can be easily made. Therefore considering its semiconducting properties it is applied for electrical devices. But the growth mechanism of the tungsten oxide nanorods is not clarified yet, and growth control of tungsten oxide nanorods is not succeeded. Then, the tungsten oxide nanorods growth process was observed by Environmental transmission electron microscope (ETEM) observation, and the growth mechanism was examined. © 2010 IEEE.

DOI： 10.1109/IVESC.2010.5644241

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Graphite surfaces were irradiated by Ar+ ions at 1 keV with a simultaneous Co supply at room temperature. Various kinds of carbon nanocomposites, such as nanocones with and without nanofibers (NFs) on top, nanorods and bean-like nanoprotrusions, formed depending on Co supply rates. The NFs, -1.5 mu m in average length, grew on the top of the nanocones at Co supply rate of 1.0 nm/min, and with increasing the Co supply rate the formation of nanoprotrusions without NFs became prominent. As confirmed by energy-dispersive X-ray analysis, NFs and nanoprotrusions were surely composed of C and Co.

DOI： 10.1109/INEC.2010.5424534

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Highly oriented and densely packed one dimensional (ID) polycrystalline Zn nanorods were fabricated on zinc plate without any catalyst at room temperature by bombardment with obliquely incident Ar(+) ion via ion irradiation method. The sputtered surfaces were fully covered with Zn nanostructures with diameter and the length around 60 nm and 1.3 mu m, respectively, confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The numerical density of Zn nanostructures (nanoneedle or nanorods) was found to be 2.1 x 10(6) to 9 x 10(6)/mm(2) depends upon the crystal orientation and the atomic density on different crystallographic faces. The outstanding feature of this growth technique is that it provides a new direction for the controllable growth of desired nanostructures of variable density at room temperature without any catalyst. These well-aligned arrays of Zn nanorods/nanoneedle might be a promising material for the future application in nanodevices.

DOI： 10.1109/INEC.2010.5424501

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper presents direct growth of horizontally aligned carbon nanotubes (CNTs) between two predefined various inter-spacing up to tens of microns of electrodes (pads) and its use as CNT field-effect transistors (CNT-FETs). The catalytic metals were prepared, consisting of iron (Fe), aluminum (Al) and platinum (Pt) triple layers, on the thermal silicon oxide substrate (Pt/Al/Fe/SiO2). Scanning electron microscopy measurements of CNT-FETs from the as-grown samples showed that over 80% of the nanotubes are grown across the catalytic electrodes. Moreover, the number of CNTs across the catalytic electrodes is roughly controllable by adjusting the growth condition. The Al, as the upper layer on Fe electrode, not only plays a role as a barrier to prevent vertical growth but also serves as a porous medium that helps in forming smaller nano-sized Fe particles which would be necessary for lateral growth of CNTs. Back-gate field effect transistors were demonstrated with the laterally aligned CNTs. The on/off ratios in all the measured devices are lower than 100 due to the drain leakage current.

DOI： 10.1109/INEC.2010.5424640

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Rapid grown vertically aligned carbon nanotubes forests (VACNFs) have received enormous attention for nanotube spinning. VACNFs are composed of not only straight CNTs, those are parallel to each other, but also curly CNTs. The bundle formation and alignment in VACNFs are crucial for spinnability of CNT fibers. In the present study, we present the effect of morphology control of VACNFs on fibers spinning. © 2010 IEEE.

DOI： 10.1109/IVESC.2010.5644118

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Highly oriented and densely packed one-dimensional (1D) polycrystalline Zn nanorods were fabricated on zinc plate without any catalyst at room temperature by bombardment with obliquely incident Ar(+) ion via ion irradiation method. The sputtered surfaces were fully covered with Zn nanostructures with diameter and the length around 60 nm and 1.3 mu m, respectively, confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal orientation of the Zn plate was investigated by electron back scattering pattern method (EBSP). The numerical density and morphology of Zn nanostructures (nanoneedle or nanorods) were found to be 2.1 x 10(6) to 9 x 10(6)/mm(2) depending upon the crystal orientation and the atomic density on different crystallographic faces. (2 (1) over bar(1) over bar0) faces of Zn polycrystal tended to form more dense nanostructures compared to (000 (1) over bar ) faces. This is because of lower atomic density on (2 (1) over bar(1) over bar0) faces in comparison with (000 (1) over bar )faces. This indicates that lower atomic density on any crystallographic faces is favorable to form nanostructure of higher density. The outstanding feature of this growth technique is that it provides a new direction for the controllable growth of desired nanostructures of variable density at room temperature without any catalyst. These well-aligned arrays of Zn nanorods/nanoneedle might be a promising material for the future application in nanodevices. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apsusc.2009.09.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Ge surfaces were irradiated by Ar+ ions at 600eV with and without simultaneous supply of Ge or At at room temperature. The surfaces ion-irradiated without any simultaneous metal supply were characterized by densely distributed conical protrusions. By contrast, various kinds of nanostructures were formed on the Ge surfaces ion-irradiated with a simultaneous metal supply. They featured cones and nanobelts with a flattened top for Ge supply cases, whereas they were characterized by the nanorods, nanobelts and nanowalls for Al supply cases. Very interestingly, most of the nanorods and nanobelts formed with an Al supply possessed a bottleneck structure. Thus, the Ge nanostructures were controllable in morphology by species and amount of simultaneously supplied metals.

DOI： 10.1587/transele.E92.C.1417

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Carbon nanofibers (CNFs) were fabricated on graphite plates using "Ar+ ion sputtering method" in large amount at room temperature. The morphology of CNFs was controlled by a simultaneous carbon supply during ion sputtering. CNF-tipped cones were formed on graphite plate surfaces without carbon supply whereas those with a simultaneous carbon supply featured mainly needle-like protrusions of large size. The field electron emission (FE) properties, measured using parallel plate configurations in 10(-4) Pa range, showed the threshold fields of 4.4 and 5.2 V/mu m with a current density of 1 mu A/cm(2) for CNF-tipped cones and needle-like protrusion, respectively. Reliability test results indicated that CNF-tipped cones were more stable than needle-like protrusion. The morphological change after reliability test showed a so-called "self-regenerative" process and structure damage for CNF-tipped cones and needle-like protrusions, respectively.

DOI： 10.1587/transele.E92.C.1449

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：VERLAG Z NATURFORSCH  

Wurtzite structure ZnO films (3 x 3 mm(2)) with a partial-area Cu doping were successfully prepared using a micro-area Ar(+)-ion beam (similar to 380 mu m in diameter) and a simultaneous Cu supply at room temperature. A Cu(2)O phase was formed in the ZnO films by Cu doping. The partially Cu-doped ZnO films exhibited room-temperature ferromagnetism (RTFM) with a saturation magnetization of 1.6 x 10(-5) emu and a coercive field of 40 Oe. Since Zn, Cu, and their compounds are not ferromagnetic, the observed RTFM is attributed to the intrinsic property of Cu-doped ZnO films. As confirmed by the low temperature photoluminescence (PL) spectra, no serious optical damage was recongnized in the region without Ar(+)-ion irradiation. Thus, it was believed that the micro-area Ar(+)-ion irradiation. Thus, it was believed that the micro-area Ar(+)-ion irradiation with a simultaneous Cu supply was promising to integrate the magnetic and optical properties of ZnO-based materials.

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Influence of liquid nitrogen on the structural, electrical and optical properties of indium tin oxide (ITO) coated glass substrates, has been studied. These studies indicate that treatment of the ITO coated glass substrates with liquid nitrogen is found to reduce the surface roughness, concomitant with the increase in contact angle up to a critical value, followed by its decrease upon prolonged treatment. Optical transmittance study of the ITO glass substrate shows the increase in transmittance of &gt;90% and X-ray diffraction studies show the negligible change in structural properties while FWHM of the peak at 2 theta = 30.48 degrees for (222) has been reduced with increase in treatment time. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2009.09.039

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

AlN films doped with 3.2-8.2 at. % Cu were deposited by helicon magnetron sputtering. The films exhibited ferromagnetism with a Curie temperature above 360 K. The observed magnetic anisotropy and exclusion of ferromagnetic contamination indicated that the ferromagnetism was the intrinsic property of Cu-doped AlN films. Room-temperature (RT) saturation magnetization (M(s)) tended to decrease with increasing Cu concentration and the maximum RT Ms obtained was about 8.5 emu/cm(3) (0.6 mu(B)/Cu). Vacuum annealing increased the RT M(s) values and meanwhile reduced ratio of N/(Al+Cu), which suggested that Al interstitial and N vacancy might contribute to the observed ferromagnetic behavior. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3232238]

DOI： 10.1063/1.3232238

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Wurtzite structure ZnO films doped with similar to 2 at% Cu were deposited at substrate temperatures (T-s) from 350 to 600 degrees C by helicon magnetton sputtering. All the films exhibited room-temperature (RT) ferromagnetism (FM) and the maximum saturation magnetization (M-s) was 1.2 emu/cm(3) (similar to 0.15 mu(B)/Cu). Cu ions were mainly in a divalent state as identified by X-ray photoelectron spectroscopy. FM tended to increase with decreasing T-s, and vacuum annealing enhanced the M-s. These results suggested that oxygen vacancies and/or zinc interstitials might contribute to the ferromagnetic performance. Thus, the observed FM was explained in terms of the defect related mechanism. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2009.07.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We synthesize ferromagnetic Co nanowire, and Co/Pd multisegment nanowires encapsulated inside multi-walled carbon nanotubes CNTs (MWCNTs) by plasma-enhanced chemical vapor deposition (PECVD). High-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED) patterns and energy dispersive X-ray spectroscopy (EDS) were used to characterize the microstructures and elemental analyses of the nanowires. Quantitative magnetization measurements of Co nanowires encapsulated inside MWCNTs were experimentally established by TEM off-axis electron holography at room temperature. The MWCNTs grew up to 100-110 nm in diameter and 1.5-1.7 mu m in length. The typical bright-field TEM images revealed both Co nanowire and Co/Pd multisegment nanowires encapsulated inside vertically aligned MWCNTs on the same substrate. The composition of metal encapsulated inside MWCNTs were characterized by EDS. Experimental results revealed that the Co nanowire encapsulated inside MWCNT was always presented as the face-centered-cubic (fcc) Co structure. The component of magnetic induction was then measured to be 1.2 +/- 0.1 T based on TEM off-axis electron holography results, which is lower than the expected saturation magnetization of fcc Co bulk of 1.7 T. The partial oxidation of the ferromagnetic metal during the process and the magnetization direction may play an important role in the determination of the quality of the remanent states. The ferromagnetic metal nanowires encapsulated inside CNTs demonstrate very high potential in providing the required magnetic properties, low dimensionality, and small volume for future nanoscale devices.

DOI： 10.1109/TMAG.2009.2018668

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Wurtzite structure ZnO films doped with 0.5 and 1.7 at% Cu were deposited by helicon magnetron sputtering. The prepared films exhibited room-temperature (RT) ferromagnetism (FM). Maximum RT saturation magnetization of 2 emu/cm (similar to 0.3(mu B)/Cu) was observed for ZnO films with 1.7 at% Cu. Cu ions were in a bivalent state as identified by X-ray photoelectron spectroscopy (XPS). In photoluminescence spectra, the green emission peak increased and redshifted due to the incorporation of Cu or defects induced by Cu incorporation Since. Cu and Cu related oxides are not RT ferromagnetic and no trace of ferromagnetic-contamination was detected in XPs results, the observed FM is considered to be an intrinsic property of Cu-doped ZnO films. The FM was thought to originate from defect-related mechanisms. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.200945091

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Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine-fullerene dyad 2 has been described. While nonfluorinated phthalocyanine-fullerene dyad 1 showed an efficient property of intramolecular photoinduced electron transfer, dyad 2, regardless of its covalently linked dyad system, appears not to show any electronic communication between fullerene and phthalocyanine. This observation is presumably due to the strong electron withdrawing nature of 12 trifluoroethoxy groups; fluorine leads phthalocyanine to become an acceptor whose electronic accepting property is equivalent to that of fullerene. This is a unique example that fluorine can terminate electronic communication in the covalently fullerene-phthalocyanine dyad system. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jfluchem.2008.11.005

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Small-scale batch fabrication of Co-included carbon nanofibers (Co-CNFs) onto commercially available Si cantilevers for scanning probe microscope by an Ar+-ion-irradiation method with a simultaneous Co supply was demonstrated (eight chips/batch). As confirmed by scanning and transmission electron microscopes equipped with energy dispersive x-ray spectroscopy, Co-CNFs were fibrous and contained Co and C. With increasing the Co supply rate, Co-CNFs decreased in length from similar to 600 to similar to 400 nm, whereas their diameter was almost independent of the Co supply rate, 20-30 nm. As proven by magnetic force microscope (MFM) measurements using the Co-CNF probes, they were applicable as MFM probes. Since various metals including alloys can be incorporated into CNFs, this ion-irradiation method with a simultaneous metal supply was believed to be quite promising for the functionalization of CNF probes for a variety of applications. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3010730]

DOI： 10.1116/1.3010730

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A number of diarylmethanofullerene derivatives were synthesized. The cyclopropane ring of the derivatives has two aryl groups substituted with electron-withdrawing and -donating groups, the latter with long alkyl chains to improve solubility in organic solvents, an important property in processing cells. First reduction potentials of most derivatives were less negative than that of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which is possibly ascribed to their electron-withdrawing nature. Organic thin-film photovoltaic cells fabricated with poly(3-hexylthiophene) (P3HT) as the electron-donor and diarylmethanofullerene derivatives as the electron-acceptor material were examined. The {(methoxycarbonyl) phenyl[bis(octyloxy)phenyl] methano} fullerene showed power conversion efficiency as high as PCBM, but had higher solubility in a variety of organic solvents than PCBM. The V(oc) value was higher than that of PCBM, which is derived from the electron-donating (octyloxy) phenyl group, possibly raising the LUMO level. Photovoltaic effects of the devices fabricated with the derivatives having some electron-withdrawing groups were also examined.

DOI： 10.3762/bjoc.5.7

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We have successfully demonstrated the multiwall carbon nanotube (MWCNT) based field emission cathode fabricated on highly porous, flexible and conductive carbon fiber (CF) sheet without damage of CF sheet by chemical vapor deposition. CF sheet was composed of thin fibers with diameter of about 3 pm prepared by electrospray deposition. Well aligned MWCNTs grown on, or well anchored to. the flexible CF sheet was confirmed by transmission electron microscope. The field enhancement factor for MWCNT emitter fabricated on CF sheet was about 14,000 and 1.6 times higher than that of MWCNT emitter fabricated on Si substrate. Scanning electron microscopy image indicates that the electron emission occurred from the MWCNT field emitter arrays grown on carbon fibers not only at surface but also under layers in CF sheet. Field emission measurements revealed that this flexible MWCNT field emitter array has a great potential for the flexible field emission displays. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2008.09.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We demonstrate the improvement in the surface properties of an indium tin oxide (ITO) anode contact to an organic bulk-heterojunction device via cooling down the ITO glass substrate by liquid nitrogen treatment. This treatment effectively improves the smoothness of ITO glass, the transmittance and the contact angle measurement, which thereby results in fairly good contact with organic material. The enhancement of short circuit current, efficiency and fill factor of the photovoltaic devices was also achieved. The surface properties of both the untreated and the treated ITO substrates were studied by atomic force microscopy and the electrical properties of the substrates were studied by the Hall effect measurement.

DOI： 10.1088/0022-3727/42/4/042002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INDERSCIENCE ENTERPRISES LTD  

Graphite plates were Ar(+) ion-irradiated with and without a simultaneous Fe supply at room temperature. The surfaces ion-irradiated without an Fe supply were covered with densely distributed conical projections with a carbon nanofibre (CNF) on file top. The CNFs thus grown were 20-50 nm in diameter and 0.3-2 mu m in length. By contrast, the graphite surfaces ion-bombarded with a simultaneous Fe supply were characterised by various kinds of carbon composites, such as conical protrusions with and without a single carbon nanocomposite fibre (CNCF) on the top, depending oil the Fe supply rates. As confirmed by transmission electron microscope (TEM), the CNCFs thus grown were amorphous-like and possessed no hollow structure. Energy dispersive X-ray analysis disclosed that CNCFs consisted of carbon and iron, and quite fine Fe crystallites were dispersed over the CNCF. Since various metals can be incorporated into the room-temperature grown carbon nanofibres, this ion-irradiation method is believed to be promising as a new approach to synthesise one-dimensional (1-D) nanomaterials at low temperatures.

DOI： 10.1504/IJNT.2009.025313

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Phthalocyanine-C-60 dyad 1 via a flexible saturated carbon linker was synthesized. The UV/Vis and fluorescence spectra studies of I revealed that intramolecular, not intermolecular, photoinduced electronic communication was observed in the solution state. We also examined UV-Vis and fluorescence spectra of a mixture of C-60 and conventional tetra tert-Bu phthalocyanine 2 for comparison

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DOI： 10.1109/IVNC.2009.5271843

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN ASSOC CRYSTAL GROWTH, INC  

Polymer/fullerene bulk heterojunction solar cells with poly[2-methoxy-5-(20-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV), zinc-phthalocyanine (ZnPc) and 6,6-phenyl C61-butyric acid methyl ester (PCBM), were produced and characterized. A device based on MEH-PPV and PCBM provided better efficiency, fill factor and short-circuit current compared to those of a device on MEH-PPV(ZnPc) and PCBM. The solar cells with a MEH-PPV and PCBM structure showed a higher photoresponse in the range of 300 to 60 nm. The energy levels of the molecules were calculated and are discussed.

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Single-crystal GaN thin films were successfully grown on porous Si (Psi) substrates using metalorganic chemical vapor deposition. The full-width at half-maximum (FWHM) of the asymmetric rocking curve for a GaN film on a Psi substrate was narrower than that for a GaN film on a normal flat-Si substrate (Flat-Si), whereas the FWHM of the symmetric one is broader. Compared with a GaN film on Flat-Si, the extent of wafer bending was reduced and the band-edge emission from GaN was enhanced. Moreover, the tensile stress in the film was significantly reduced. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2008.08.030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

In this paper, we report on the synthesis and applications of semiconducting nanostructures. Nanostructures of interest were zinc oxide (ZnO) nanowires and tungsten disulfide (WS2) nanotubes where transistors/phototransistors and photovoltaic (PV) energy conversion cells have been fabricated. ZnO nanowires were grown with both high- and low-temperature approaches, depending on the application. Individual ZnO nanowire side-gated transistors revealed excellent performance with a field-effect mobility of 928 cm(2)/V . s. ZnO networks were proposed for large-area macroelectronic devices as a less lithographically intense alternative to individual nanowire transistors where mobility values in excess of 20 cm(2)/V . s have been achieved. Flexible PV devices utilizing ZnO nanowires as electron acceptors and for photoinduced charge separation and transport have been presented. Phototransistors were fabricated using individual WS2 nanotubes, where clear sensitivity to visible light has been observed. The results presented here simply reveal the potential use of inorganic nanowires/tubes for various optoelectronic devices.

DOI： 10.1109/TED.2008.2005166

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Flexible carbon fabrics (CFs) prepared by electrospray deposition were used for the substrate of carbon nanotube (CNT) field emitter arrays. CNTs were grown on the CFs by chemical vapor deposition. The CNT field emitter arrays on CFs produced a higher current density at a lower turn-on voltage compared to ones on a Si substrate.

DOI： 10.1063/1.2967868

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We have successfully synthesized the Co/Pd magnetic and nonmagnetic multisegment nanowires encapsulated inside multiwalled carbon nanotubes (MWCNTs) by using Co and Pd thin-layers deposited on Si substrate by microwave plasma enhanced chemical vapor deposition. Energy dispersive X-ray spectroscopy revealed that MWCNTs were encapsulated with Co and Pd nanowires, separately, at the tube top and the bottom of Co nanowire, respectively. The face-centered-cubic (fcc) structure of Co nanowires was confirmed by a selected area diffraction pattern. We proposed a fruitful description for the encapsulating mechanisms of both Co and Pd multisegment nanowires. The component of magnetic induction from Co region, not Pd region, was then estimated to be 1.2 +/- 0.1 T, based on results of off-axis electron holography, which is lower than the expected saturation magnetization of fcc bulk Co of 1.7 T. We proposed a fruitful description for the mechanisms of reduced magnetic induction from Co nanowires. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2008.03.012

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Polymer/fullerene bulk heterojunction solar cells with poly[3-hexylthiophene] (P3HT), poly [2-methoxy-5-(20-ethylhexoxy)-1,4-phenylenevinylene] (MEH-PPV), and 6,6-phenyl C61-butyric acid methyl ester (PCBM) were produced and characterized. A device based on P3HT and PCBM provided better efficiency, fill factor, and short-circuit current compared to those of a device based on MEH-PPV and PCBM. The solar cell with P3HT and PCBM structure showed a higher photoresponse in the range of 400-650 nm. Energy levels of the molecules were calculated and discussed. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2007.10.117

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Graphite surfaces were bombarded with Ne+, Ar+ and Xe+ ions at 450 eV-1 keV to induce the carbon nanofiber (CNF) growth at room temperature, and the dependence of size and numerical density of ion-induced CNFs on the ion species and ion energy was investigated in detail. The ion-sputtered surfaces were covered with densely distributed conical protrusions and aligned CNFs grew on the tips, except for the low-energy Xe+-sputtered surfaces. Longer CNFs grew by lighter-mass-ion irradiation, and finer CNFs formed by heavier-mass-ion bombardment. In addition, the higher the ion energy, the longer the length of the ion-induced CNFs. Because the size and numerical density were controllable by the ion-irradiation parameters, ion-induced CNFs were believed to be quite promising for myriad of applications such as high-resolution scanning probe microscope cantilevers, bio-cell manipulators and field emission source operating at low voltage. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2008.01.043

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The graphite surfaces were irradiated by Ar+ ions with and without a simultaneous Co supply at room temperature. The sputtered surface without Co supply was characterized by densely distributed conical protrusions with aligned carbon nanofibers (CNFs) on the tops, whereas Ar+-bombarded surfaces with a simultaneous Co supply were covered with asparagus-like (micrometer order in base diameter) or nanofibrous (10-50 nm in diameter) structures depending on the supply rate of Co atoms. No CNF-tipped cones were observed to form. For the nanofibers containing carbon and cobalt, the hysteresis behavior observed in the magnetization property by applying magnetic fields in directions perpendicular and parallel (in-plain) to the substrate was almost identical, whereas a continuous 1 mu m thick-Co film showed the strong in-plane anisotropy. Other materials could be readily incorporated into CNFs by choosing the suitable metal sources. Thus, the ion-irradiation method is expected to open up a new approach to fabricate ferromagnetic 1-D nanomaterials at room temperature. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2008.01.092

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We report a study of the effect of the poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) on the organic solar cell based on poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction structure (BHJ). The most obvious effect of incorporating MEH-PPV in the P3HT:PCBM BJT solar cells was the increase in the open-circuit voltage (V-oc) from 0.38 to 0.50 V. This result is interpreted in terms of the band structure of BHJ where the energy level difference between the highest occupied molecular orbital (HOMO) of the polymer (P3HT + MEH-PPV) and the lowest occupied molecular orbital (LUMO) of PCBM is increased. The highest power conversion efficiency of 1.12% under air mass 1.5 simulated solar illumination (100 mW/cm(2)) was achieved from the optimized amount of MEH-PPV. The spectral response of the P3HT:PCBM BHJ solar cells is influenced by the change of molecular packing structure (interchain spacing) of P3HT by incorporating MEH-PPV. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfa.2007.04.162

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

We present STM and STS results obtained for double-walled carbon nanotubes. In the case displayed here, the STS results exhibit the Van Hove singularities corresponding to semi conducting tubes for both the outer and the inner shell and a finite density of states at the Fermi level (E-F) is observed for a DWNT. We associate this behavior to the presence of an intershell interaction.

DOI： 10.1002/adma.200700399

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Graphite surfaces were bombarded by Ar(+) ions with and without a simultaneous Ni supply at room temperature. The sputtered surfaces without Ni supply were characterized by densely distributed conical protrusions with aligned single carbon nanofibers (CNFs) on the tops. By contrast, an excess Ni supply during Ar(+) bombardment suppressed the CNF formation, while under the proper Ni supply conditions, single Ni-doped CNFs grew on slender needle-like structures or conical protrusions depending on the supply rate of Ni atoms. Non-doped CNFs were characterized by the amorphous-like or very fine-crystallites nature, whereas the Ni-doped CNFs were featured by polycrystalline structure. Thus, the crystalline structure was controllable by Ni doping. Because any kinds of materials can be doped into ion-induced CNFs, it is believed that the ion-irradiation method will open up a new approach to fabricate 1-dimensional composite nanomaterials at room temperature.

DOI： 10.1088/1742-6596/100/1/012029

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We synthesize Co nanorod filled inside multi-walled CNTs (MWCNTs) by microwave plasma enhanced chemical vapor deposition (MPECVD) and utilize off-axis electron holography to observe the remanent states of the filled metal nanorod inside MWCNTs at room. The MWCNTs grew up to 100-110 nm in diameter and 1.5-1.7 pm In length. The typical bright-field transmission electron microscope (TEM) Images revealed both Co/Pd multisegment nanorod and Co nanorod filled inside MWCNTs on the same substrate. We have also performed energy-dispersive X-ray spectrometer (EDS) measurements to characterize the composition of metal filled inside MWCNTs. Based on high-resolution TEM measurements, we observed the face-centered-cubic (fcc) Co filled Inside MWCNT. The component of magnetic Induction was then measured to be 1.2 +/- 0.1 T, which Is lower than the expected saturation magnetization of fcc Co of 1.7 T. The partial oxidation of the ferromagnetic metal during the process and the magnetization direction may play an important role in the determination of the quality of the remanent states.

DOI： 10.1109/INEC.2008.4585664

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Graphite plates were Ar+ ion-sputtered with a simultaneous Fe supply at room temperature. The sputtered surfaces were characterized by various kinds of carbon compostites, such as conical protrusions with and without single carbon nanocomposite fibers (CNCFs) on the top, depending on the Fe supply rates. The CNCFs thus grown were confirmed to be amorphous-like fibers without a hollow structure and possess no distinct boundary between the cone and the CNCF by transmission electron microscope. As revealed by their compositional analysis, CNCFs surely composed of carbon and iron. Since the various kind of metals can be doped Into the room-temperature grown carbon nanofibers, this Ion-irradiation method Is believed to be promising as a new approach to synthesize one-dimensional nanomaterials at low temperatures.

DOI： 10.1109/INEC.2008.4585458

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In this work, we present the evolution of optical constants as a function of [6,6]-phenyl C-61-butyric acid methyl ester (PCBM) concentration for conjugated poly(3-hexylthiophene)/[6,6]-phenylC(61)-butyric acid methyl ester composites. The PCBM concentration of the utilized samples varies from 1 to 50 wt %. The dielectric functions for all these composites reveal electronic structural changes as a result of the addition of PCBM. We have deconvoluted the contribution of the substrate using a two-layer Fabry-Perot structural model. The extracted optical properties contain crucial absorption peaks of singlet exciton states and vibronic sidebands for poly(3-hexylthiophene) (P3HT) conjugated polymer as well as two PCBM-related states at higher energies. With the addition of PCBM, we have observed a limit of 20 wt % PCBM beyond which two discrete energy levels (3.64 and 4.67 eV) appear in the spectrum. For the highest concentration composite, the results suggest that the interchain interactions provide a small excitonic contribution in the absorption spectrum at energies where the conjugated polymer absorbs (1.85-2.7 eV) and a strong rise of PCBM states (3.64 and 4.67 eV) which are responsible for the subsequent exciton dissociation. In addition, the energy gap between the higher occupied molecular orbitals and the lower unoccupied molecular orbitals of the highest concentration composite (50 wt %) is 1.85 eV. The tuning of the optical properties of P3HT with the addition of PCBM shows that ellipsometry can be used to monitor layer concentration toward optimization of plastic solar cells. (C) 2007 American Institute of Physics.

DOI： 10.1063/1.2799049

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Well-aligned zinc oxide (ZnO) nanorods were densely grown on Si substrate using ZnO thin-film seed layer without any catalysts and/ or additives by a simple solid-vapour phase thermal sublimation technique. The growth mechanism can be interpreted as self-catalyst of zinc particles based on vapour-solid (VS) mechanism. High-resolution transmission electron microscopy (HRTEM) image and selected area electron diffraction (SAED) pattern confirmed that the single-crystalline growth of the nanorods were preferentially along c-axis of hexagonal crystal system. High-crystal quality ZnO nanorods with strong near band edge emission centred at 380 nm can be achieved on Si substrate by the introduction of sufficient oxygen during the nanorod growth processing. (c) 2007 NIMS and Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.stam.2007.02.012

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The authors have studied ultrafast carrier dynamics on poly(3-hexylthiophene)/[6,6]-phenylC(61)-butyric acid methyl ester (PCBM) composites up to 50% PCBM concentration. They have resolved the exciton intraband relaxation of composites as well as the subsequent electron/polaron relaxation of dissociated excitons. The observed fast time constant of intraband relaxation is found to be 0.5-1.5 ps, whereas the second long-live relaxation (0.5-1 ns) is strongly fullerene related. A wavelength dependent ultrafast study is performed giving fundamental information on the nonradiative exciton relaxation, exciton dissociation, and electron relaxation of PCBM-related states.

DOI： 10.1063/1.2785120

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Single crystalline Ge nanowires have been fabricated by filtration of rod-shaped Ge precipitates from aged Al-Ge alloy using HCl solution. The diameter of the Ge nanowires ranged from 30 to 100 nm when the aging conditions of the Al-Ge alloy was altered. The Ge nanowires grow preferentially in the [110] direction, which is the same as observed earlier for rod-shaped Ge precipitates in the aged Al-Ge alloy. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2007.03.054

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Three-dimensional (3-D) ZnO random-wall nanostructures and one-dimensional (I-D) ZnO nanorods were prepared on silicon substrates by a simple solid-vapour phase thermal sublimation technique. Optical pumped random lasing has been observed in the ZnO random-wall arrays with a threshold intensity of 0.38 MW/cm(2) in the emission wavelength from 380 to 395 nm. The optical gain was attributed to the closed-loop scattering and light amplification of the ZnO random-wall. The experimental result suggests that the morphology of nanostructure is the key factor to effect random lasing. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.susc.2006.12.011

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We report the synthesis of multiwalled carbon nanotubes (MWCNTs) encapsulated with Co/Pd magnetic and nonmagnetic multi-metal nanowires using Co and Pd thin-layers deposited on Si substrate by microwave plasma enhanced chemical vapor deposition using a bias-enhanced growth method. Detailed structural and compositional investigations of these metal nanowires inside MWCNTs were carried out by scanning electron microscopy and transmission electron microscopy to elucidate the growth mechanisms. Energy dispersive X-ray spectroscopy revealed that MWCNTs were encapsulated with Co and Pd nanowires, separately, at the tube top and the bottom of Co nanowire, respectively. The face-centered-cubic (fcc) structure of Co nanowires was confirmed by a selected area diffraction pattern. We proposed a fruitful description for the encapsulating mechanisms of both Co and Pd multi-metal nanowires. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2006.11.039

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Vertically aligned carbon nanotubes (VA-CNTs) filled with Pd-Co nanocomposites on an Si substrate have been synthesized by microwave plasma-enhanced chemical vapor deposition. It was confirmed that adjacent Pd-Co nanocomposites in the VA-CNTs were compositionally separated. Most CNTs contained Co pillars on top; however, Pd pillars were rarely present. The strong magnetic induction from an individual Co pillar was revealed by electron holography. The simultaneous phenomenon of the demixing by plasma hydrogen irradiation and the preferential encapsulation into CNTs realized the unique Pd-Co nanocomposites. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2718268

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MATERIALS RESEARCH SOCIETY JAPAN-MRS-J  

Transparent zinc oxide (ZnO) films have been prepared by sol-gel method using spin coating method on quartz glass from 0.5M zinc acetate 2-methoxyethonal solution, and using monoethanolamine(MEA) as stabilizer. The as-prepared samples were heat-treated at 550 degrees C for 90min in air, oxygen and vacuum ambient, respectively. XRD patterns show that the prepared samples exhibit wurtzite structure, the sample annealed in O-2 has best crystalline quality and biggest degree of preferential orientation of (0O2) plane, and the sample annealed in vacuum nearly has,no preferential orientation. It can be found from AFM images that surface roughness of the three films are: Vacuum &gt; air &gt; O-2. The sample annealed in O-2 has rod-like and uniform particles, the sample annealed in air with ball-like particles and sample heat treated under vacuum ambient with ball-like uniform particles. PL analysis tells that vacuum atmosphere leads to more oxygen vacancy (VO) and zinc excess, however annealed in O-2 can decrease the oxygen vacancy (VO) and zinc excess obviously. The band gap of prepared ZnO films is about 3.3eV from PL spectra. Through analyze the UV-Vis result, it can be found that the surface morphology does influence the absorptance. Generally speaking, the annealed ambient influences the intrinsic defect and extrinsic defect, and then influence the properties of prepared ZnO films.

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Pd/Co-based metal-filled carbon nanotubes (MF-CNTs) were synthesized by a microwave plasma-enhanced chemical vapor deposition method using a bias-enhanced growth technique. Pd/Co-based MF-CNTs were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) electron energy loss spectroscopy (EELS), and Raman spectroscopy. MF-CNTs were well-aligned and uniform in size on a Si substrate. Both multiwall nanotube carbon nanotubes (CNTs) and herringbone (or stacked cups structure) structures were observed. High-resolution TEM revealed that MF-CNTs were composed of highly ordered graphite layers, and the elemental maps of EELS indicate that both Co and Pd metals are present inside the nanotubes. TEM results clearly showed that both Pd and Co metals were successfully encapsulated into the CNTs. We observed a low value for the Raman intensity ratio between D (1355 cm(-1)) and G (1590 cm(-1)) bands with no shift of the G-peak position and no broadening of the G-peak, indicative of high-quality Pd/Co-based MF-CNTs. Based on TEM characterization, we propose a description for the encapsulating mechanisms.

DOI： 10.1109/TNANO.2006.880456

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Demixing in a solid-soluted Co-40 at. % Pd alloy has been induced by microwave plasma hydrogen irradiation on mixture of Pd-Co island grains on Si substrate. The microstructure observation and X-ray microanalysis by a transmission electron microscope before and after the microwave plasma hydrogen irradiation provide a clear evidence of demixing in metallic Co-Pd alloys, that may indicate a possibility of the decomposition into Pd hydride and Co under a hydrogen irradiation at high temperatures.

DOI： 10.1143/JJAP.45.L860

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N-doped and In-N-codoped ZnO films were fabricated on quartz glass substrate by sol-gel spin coating. Their p-type conductivities were characterized by the Hall measurements, revealing low resistivities of the order of 10(-1) Omega cm. Thin-film junctions comprising an undoped ZnO layer and a N-doped ZnO layer displayed the typical rectifying characteristics, suggesting formation of p-n homojunctions at the interfaces. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2215618

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Fully encapsulated face-centered-cubic (fcc) Co nanorods in multiwalled carbon nanotubes were produced by microwave plasma enhanced chemical vapor deposition. Quantitative magnetization measurements of the Co nanorods were carried out by off-axis electron holography using a theoretical cylindrical model. The component of magnetic induction was then measured to be 1.2 +/- 0.1 T, which is lower than the expected saturation magnetization of fcc Co of 1.7 T. The reason for the reduced magnetic component was discussed.

DOI： 10.1063/1.2213202

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We report the synthesis of multiwalled carbon nanotubes (MWCNTs) and the characterization of ternperature-dependent electrical transport properties of MWCNT networks by using a two-point configuration without the lithographical technique. MWCNTs were grown by microwave plasma chemical vapor deposition with the bias enhanced growth technique. The Raman intensity ratio between the D- (similar to 1360 cm(-1)) and G- (similar to 1590 cm(-1)) peaks (I(D)/I(G)) as well as the full width at half maximum of the G-peak decreased from 1.03 to 0.03 and 18 to 13 cm(-1), respectively, with the increase in the oxidative purification time. This indicates that the crystallinity of graphite sheets is improved by the oxidative purification process and burn-off of the defects in MWCNT networks. The metal electrodes were attached on both the top and the bottom of the insulating thin films, and the as-grown and oxidative-purified MWCNT networks were connected between the electrodes for I-V measurements at various temperatures. At room temperature, the conductance for the MWNT networks at around zero bias was 0.65 G(0) (G(0): fundamental conductance unit), which was less than the value of 1 G(0) for metallic MWCNTs. Further, the conductance increased linearly with the bias voltage until it attained its peak. In the 190-390 K range, the temperature characteristic of the I-V shows that the electron transport of the as-grown MWCNT networks was activated by a lower activation energy than that in oxidative-purified MWCNT networks. (c) 2006 Elsevier B.V All rights reserved.

DOI： 10.1016/j.diamond.2006.01.006

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We describe the characterization of nitrogen-incorporated amorphous carbon (a-C:N) films by using a double beam method. The carrier transport of a-C:N films deposited at various substrate temperatures was investigated using a bottom-gated thin-film transistor (TFT). At substrate temperatures below 300 degrees C, the optical band gap (E-opt) and the Raman intensity ratio between the D (similar to 1360cm(-1)) and G (similar to 1590cm(-1)) peaks (I-D/I-G) of an a-C:N film deposited at room temperature were observed to vary only marginally from 1.9eV and 0.88, respectively. The electrical conductivity of the a-C:N film increased by more than four orders of magnitude with an increase in the substrate temperature from 150 to 300 degrees C due to an improvement in the activation of the nitrogen-incorporated a-C film caused by the thermal annealing effect. Based on the E-opt and I-D/I-G values, we concluded that this behavior is not responsible for the change in the hybridization of carbon atoms. The a-C:N based TFT exhibited an ambipolar transport with the strong p-type operation. The field effect hole mobility (mu(h)) attained a value as high as 1.7 x 10(-4) cm(2)/Vs. In this study, one of the important results is that mu(h) increased with the substrate temperature due to the increase in film conductivity. We found that the highest success yield of transistor operation of 38% was obtained from the a-C:N TFTs deposited at a substrate temperature of 290 degrees C. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2006.01.009

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Indium-doped ZnO (IZO) films with low In content (&lt; 6at.%) were fabricated by rf helicon inagnetron sputtering. The uniformity of the composites was confirmed by elemental analysis. The formation of an In-Zn-O solid Solution was verified using X-ray diffraction (XRD) patterns. A wide, high-transmittance re ion (400-2000 nm) and &gt; 80% transmittance in the window of fiber optics telecommunication (1.30-1.55 mu m) were observed. The incorporation of indium enhances the optical transmission in the designated visible and infrared wavelengths. The optical band gap shows a slight blue-shift with increasing In doping which call be explained by the Burstein-Moss effect. The Urbach tail parameter E-0 increases with increasing indium content, which coincides with the increase in the full width half maximum (FWHM) of (0002) planes in XRD patterns. A decline in crystal quality with In incorporation in IZO films is also confirmed from photoluminescence (PL) spectra.

DOI： 10.1143/JJAP.45.1623

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Pd/Co-based metal-filled carbon nanotubes (MF-CNTs) were synthesized by a microwave plasma-enhanced chemical vapour deposition method using a bias-enhanced growth technique. Pd/Co-based MF-CNTs were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) electron energy loss spectroscopy (EELS), and Raman spectroscopy. MF-CNTs were well-aligned and uniform in size on a Si substrate. Both multiwall nanotube carbon nanotubes (CNTs) and herringbone (or stacked cups structure) structures were observed. High-resolution TEM revealed that MF-CNTs were composed of highly ordered graphite layers, and the elemental maps of. EELS indicate that both Co and Pd metals are present inside the nanotubes. TEM results clearly showed that both Pd and Co metals were successfully encapsulated into the CNTs.. We observed a low value for the Raman intensity ratio between D (1355 cm(-1)) and G (1590 cm(-1)) bands with no shift of the G-peak position and no broadening of the G-peak, indicative of high quality Pd/Co-based MF-CNTs. Based on TEM characterization, we propose a description for the encapsulating mechanisms.

DOI： 10.1109/TNANO.2006.880456

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Polymer photovoltaic cells (PVCs) consisting of a blend of p-type poly(3-hexylthiophene) (P3HT) and n-type [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were fabricated and Investigated the role of the PCBM concentration. The photocurrent and the power conversion efficiency gradually increased with increase in PCBM concentration up to 50% and decreased with further increase In PCBM concentration. Both the root mean square and average roughnesses measured by atomic force microscopy decrease as the PCBM concentration increases from 0 to approximately 70%. The surface morphology of P3HT/PCBM blended and improved donor-acceptor proximity, leading to electron conductivity, contribute to the increase in power conversion efficiency.

DOI： 10.1109/WCPEC.2006.279443

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Pd/Co-based metal-filled carbon nanotubes (MF-CNTs) were synthesized by a microwave plasma-enhanced chemical vapour deposition method using a bias-enhanced growth technique. Pd/Co-based MF-CNTs were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) electron energy loss spectroscopy (EELS), and Raman spectroscopy. MF-CNTs were well-aligned and uniform in size on a Si substrate. Both multiwall nanotube carbon nanotubes (CNTs) and herringbone (or stacked cups structure) structures were observed. High-resolution TEM revealed that MF-CNTs were composed of highly ordered graphite layers, and the elemental maps of. EELS indicate that both Co and Pd metals are present inside the nanotubes. TEM results clearly showed that both Pd and Co metals were successfully encapsulated into the CNTs.. We observed a low value for the Raman intensity ratio between D (1355 cm(-1)) and G (1590 cm(-1)) bands with no shift of the G-peak position and no broadening of the G-peak, indicative of high quality Pd/Co-based MF-CNTs. Based on TEM characterization, we propose a description for the encapsulating mechanisms.

DOI： 10.1109/NANOEL.2006.1609696

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Publishing type：Research paper (scientific journal)   Publisher：Advanced Materials Research  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

ZnO nanobamboos and nanowires with diameters of 10-30 nm and lengths of 2-4 mu m have been prepared by laser ablation in vacuum with precisely controlled pressure, growth and post-annealing temperature. XRD results show the annealed sample is hexagonal ZnO. Low-magnified TEM observation reveals the annealed sample includes ZnO nanobamboos and nanowires. High resolution TEM image and electron diffraction pattern confirm that the structure of ZnO nanobamboo is regular stacking of Zn and 0 layers with high crystal quality. The growth direction is determined as along [001] direction (c axis). TEM observations confirm that the formation of bamboo-shape ZnO is due to the stacking fault and cleavage. The bundle of those stacking faults seems to be the origin of the black contrast at the nodes. The uniformity of chemical composition for the nanobamboos is identified by EDS profiles. A strong-narrow UV band centred at 390 nm and a weak-broad green band centred at 515 nm are observed at room temperature in the PL spectrum recorded from the annealed ZnO nanobamboos and nanowires.

DOI： 10.1142/S0217979205031730

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Unusual morphologies of carbon nanofibers (CNFs) fabricated by the microwave plasma-enhanced chemical vapor deposition method were confirmed by transmission electron microscopy. In particular, the presence and distribution of wedge-shaped carbon films, consisting of amorphous carbon and CNFs, were observed by three-dimensional electron tomography (3D-ET), and their growth mechanisms were modeled. High-resolution transmission electron microscopy (HRTEM) revealed the presence of amorphous carbon on carbon nanofibers. Wedge-shaped carbon films are most likely caused by the bridging of individual CNFs by amorphous carbon from plasmarized carbon. The combination of 3D-ET and HRTEM clearly provides a successful strategy for determining 3D morphologies with characteristic sizes on the nanometer scale. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2005.03.007

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The optical and electrical properties of boron doped amorphous carbon thin films using methane and trimethylboron by plasma enhanced chemical vapor deposition are studied with varying the rf power. The optical bandgap is decreased from 2.4 to 1.4 eV with increasing the rf power due to the increase of sp(2) carbon. The boron doped amorphous carbon deposited at 300 W shows large photoconductivity (the ratio of conductivity under illumination to under dark) with high spin density. The open circuit voltage of boron doped amorphous carbon/n-Si structure photovoltaic cell is increased with the increase of rf power and then saturates over 100 W. On the other hand, the short circuit current is increased gradually with increasing the rf power up to 300 W. (c) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2004.11.123

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A new type of palladium-based metal-filled carbon nanotubes (MF-CNTs) was fabricated and their characteristics were investigated. The MF-CNTs were grown on Pd/SiO2/Si substrates and Pd/Mo mesh by a microwave plasma-enhanced chemical vapor deposition method using CH4 and H-2 gasses with the technique of bias-enhanced growth method. The structure and composition of Pd-based MF-CNTs were thoroughly investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. TEM and EDS analyses showed that MF-CNTs were composed of thick cylindrical graphite walls, and filled with Pd metal inside their roots. Based on TEM characterizations, we proposed a fruitful description for the encapsulating mechanisms. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2004.12.008

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Conductivity of amorphous carbon (a-C) was successfully controlled by incorporation of nitrogen atoms using a double beam method (DBM), where both rf nitrogen radical and if methane plasma sources were controlled separately to optimize the nitrogen incorporation. The as-grown a-C is p-type with a conductivity of 10(-11) Omega cm and activation energy (E-a) of 333 meV The addition of nitrogen atoms under varying nitrogen flow rate from 0 to 2.0 seem caused the conductivity to reach 10(-4) Omega cm as maximum and E-a of 41 meV at 1.5 seem. The optical band gap is shown to vary only marginally from standard of the as-grown of a-C film (1.39 eV) to 1.45 eV by nitrogen incorporation. The depth profile of a secondary ion mass spectroscopy (STMS) shows that the uniform concentration of C and N in the films and the sharp interface between nitrogen doped and undoped regions from the doped/undoped sandwich-like a-C structure. Furthermore, the changes in the chemical structure and relative bond fractions as a function of nitrogen flow rate are reported based on the results of an X-ray photoelectron spectroscopy and a Raman spectroscopy. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.diamond.2005.01.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We have fabricated both blended and bilayered organic photovoltaic cells (OPVCs) using C-60 and poly [2-methoxy-5-(2&apos;-ethyihexoxy)-1,4-phenylenevinylene] (MEH-PPV). Improvements in photovoltaic performance are seen in blended OPVCs when the C-60 concentration is increased. It is believed that the optimized surface morphology of MEH-PPV/C-60 Composite and improved donor-acceptor proximity, leading to electron conductivity, contribute to the increase in power conversion efficiency E-ff. Two broad peaks were observed in the spectral response of the blended OPVCs, with maximum peaks at similar to 490 nm (= I-BL1) and similar to 350 nm (= I-BL2). The intensity ratio of I-BL1 to I-BL2 (I-BL1/I-BL2) decreases with an increase in the C-60 concentration. Also, I-BL1 is blue-shifted by 25-30 nm with an increase in the C-60 concentration. The significant improvement in the performance was observed in the bilayered OPVCs on the thermally induced interdiffusion Of C-60 into the MEH-PPV network, leading to the existence of C-60 molecules within the exciton diffusion radius of the MEH-PPV, network. The spectral response of bilayered OPVCs reveals two peaks at 535 nm and 345 nm. The former peak is red-shifted by 45 nm compared to that in blended OPVCs. We also investigate the effect of top electrode materials on the photovoltaic performances. To the best of our knowledge, we have obtained the best performances of blended and bilayered OPVCs fabricated with the Al and Mg electrodes, respectively. In both OPVC structures, the nanoscale composition control of the two materials, the choice of metal electrode, and the device processing techniques all play an important role in determining or enhancing the solar cell performance.

DOI： 10.1143/JJAP.44.1296

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We have demonstrated the solution-processed p- and n-type transports including ambipolar transport organic thin-film transistors (OTFTs), required for complementary thin-film integrated circuit technology, by. a facile method of blending the n-type C-60 and the p-type [poly2-methoxy-5-[2'-ethyl-hexyloxy]-1,4-phenylene vinylene] (MEH-PPV). The carrier transport of PPV-based thin-film field-effect transistors with various C60 compositions are investigated by using the field-effect gated structure. One of the important findings is that tunable electronic properties of OTFTs are achieved by controlling C60 composition using a simple and an inexpensive spin-cast technology. The mobility increases with increase in the C60 composition in both n- and p-type OTFTs. Temperature measurements on n-type OTFTs revealed that transport follows a thermally activated hopping transport model with small activation energy. (C) 2005 American Institute of Physics.

DOI： 10.1063/1.1861115

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Solar cells with high efficiency and low price have long been desired, however, the commercially available solar cells are still expensive and the efficiencies of them are not high enough yet. A tandem solar cell was fabricated to develop a high-efficiency solar cell, and amorphous carbon solar cells were fabricated to develop a low-price solar cell.
An AlGaAs/Si tandem solar cell was successfully fabricated by heteroepitaxial growth of AlGaAs on Si substrate. At first, a p-n junction was formed in Si substrate by the impurity diffusion method. Then, an AlGaAs p-n junction was grown by MOCVD. Since the AlGaAs p-n junction has a graded band gap emitter, the photo-excited minority carriers can be collected efficiently. The energy conversion efficiency of AlGaAs/Si tandem solar cell was 21.4% (AM0) in spite of large lattice mismatch and difference in thermal expansion coefficients between AlGaAs and Si.
Solar cells were fabricated by using amorphous carbon films deposited by Ion Beam Sputtering and Pulse Laser Deposition (PLD). The highest efficiency of 1.82% (AM0) was attained with a-C(IBS)/p-C(pyrolysis)/p-Si structure. Solar cells using a-C:H were also fabricated by PLD and Plasma CVD, and the efficiencies of them were 2.1% (AM1.5) and 0.04% (AM0), respectively.
Other research activities on solar cells in Nagoya Institute of Technology are briefly mentioned. (c) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.stam.2004.07.002

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Language：Japanese   Publisher：公益社団法人 化学工学会  

DOI： 10.11491/scej.2005.0.606.0

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Nanostructure diamond (NSD) films on Si substrate are prepared by microwave plasma enhanced chemical vapor deposition (MPECVD) using methane and hydrogen as the reactants with two-step negative substrate bias (SB). The dependencies of the NSD film morphology, grains, surface roughness, crystal and bonding structures and hardness on the negative SB at the bias-enhanced growth (BEG) step and substrate temperature during growth have been investigated by conducting atomic force microscopy (CAFM), X-ray diffraction (XRD), Raman spectroscopy and nanoindentation. The hardness of the NSD film is found to be as high as 80 GPa with CAFM average and root mean square roughness of 7 and 9 nm, respectively, under optimal negative SB at the BEG step. From the studies of substrate temperature effect, the hardness of the NSD film is as high as 70 GPa, with average and root mean square CAFM roughness of 9 and 11 nm, respectively, which were obtained at a substrate temperature of 500 degreesC. In both cases, the film hardness was found to be affected by the size of clusters, which are composed of many small NSD particles, the amount of NSD in an amorphous matrix as well as surface roughness. We also synthesized transparent NSD films by MPECVD under optimized single-step growth conditions on quartz substrates, which are scratched with several micrometers diamond powder. A hardness as high as 60 GPa and a maximum transmittance of 60% in the visible light region are achieved for an NSD coating of 1.0 mum thickness with small surface roughness. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.triboint.2004.07.014

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