Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Graphene has two kinds of edges which have different electronic properties. A singular electronic state emerges at zigzag edges, while it disappears at armchair edges. We study the edge-dependent transport properties in few-layer graphene by applying a side gate voltage to the edge with an ionic liquid. The devices indicating a conductance peak at the charge neutrality point have zigzag edges, confirmed by micro-Raman spectroscopy mapping. The hopping transport between zigzag edges increases the conductance.

DOI： 10.1021/nl3044844

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Publisher：AIP  

DOI： 10.1063/1.2937836

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

DOI： 10.1021/acs.inorgchem.4c03637

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

DOI： 10.1021/acsomega.4c01395

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

DOI： 10.1021/acs.chemmater.3c02832

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

DOI： 10.1021/acs.inorgchem.3c03737

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Publishing type：Research paper (scientific journal)  

The local structure of a two-dimensional layered material, Bi2Rh3Se2, in which superconducting (SC) and charge-density wave (CDW) states coexist, was investigated using Bi Lα and Lγ X-ray fluorescence holography (XFH). The crystal of Bi2Rh3Se2 adopts a monoclinic lattice with a space group of C2/m (No. 12) at room temperature; however, the structure below the CDW transition (∼240 K) is still unclear because of the difficulty in analyzing single-crystal X-ray diffraction. Therefore, information on the crystal structure below 240 K is significant to fully investigate the relationship between the SC and CDW states. Precisely, the value of β has not been definitely determined, i.e., β ∼ 90° or ∼134° is still unclear. Therefore, the crystal structure above 240 K is still under discussion. In this study, we attempted to determine the crystal structure at 300 and 200 K by comparing the atomic images reconstructed from Bi Lγ holograms with images simulated based on crystal structure models. A Bi Lα hologram was also exploited to determine suitable atomic locations by comparison with the simulated ones. The atomic image simulated with the crystal structure of Bi2Rh3S2 below the structural phase transition temperature reproduced well the experimental atomic image at 200 K. Specifically, the line profiles of the reconstructed images at 300 and 200 K, which exactly reflect the intensity of the atomic spots, clearly indicate the structural variation above and below the CDW transition temperature, i.e., the supercell structure is suggested as the atomic location for Bi2Rh3Se2 below the CDW transition temperature.

DOI： 10.1039/d4cp02694b

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

DOI： 10.1021/acs.inorgchem.3c02254

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

DOI： 10.1021/acs.jpcc.3c06294

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

DOI： 10.1021/acs.inorgchem.3c02405

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DOI： 10.1103/PhysRevB.108.035146

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

DOI： 10.1021/acs.chemmater.3c00391

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DOI： 10.1021/acs.inorgchem.3c00744

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

DOI： 10.1016/j.elspec.2023.147295

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

Abstract

Doping a typical topological insulator, Bi₂Se₃, with Ag impurity causes a semiconductor–metal (S-M) transition at 35 K. To deepen the understanding of this phenomenon, structural and transport properties of Ag-doped Bi₂Se₃ were studied. Single-crystal X-ray diffraction (SC-XRD) showed no structural transitions but slight shrinkage of the lattice, indicating no structural origin of the transition. To better understand electronic properties of Ag-doped Bi₂Se₃, extended analyses of Hall effect and electric-field effect were carried out. Hall effect measurements revealed that the reduction of resistance was accompanied by increases in not only carrier density but carrier mobility. The field-effect mobility is different for positive and negative gate voltages, indicating that the E_F is located at around the bottom of the bulk conduction band (BCB) and that the carrier mobility in the bulk is larger than that at the bottom surface at all temperatures. The pinning of the E_F at the BCB is found to be a key issue to induce the S-M transition, because the transition can be caused by depinning of the E_F or the crossover between the bulk and the top surface transport.

DOI： 10.1038/s41598-023-27701-5

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Other Link： https://www.nature.com/articles/s41598-023-27701-5

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

DOI： 10.1021/acs.inorgchem.2c03365

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

DOI： 10.1021/acs.jpcc.2c06505

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

DOI： 10.1021/acs.jpcc.2c04879

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

DOI： 10.1021/acs.jpcc.2c01972

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

The structural and superconducting properties of alkali-Bi-based compounds, KBi2 and RbBi2, were investigated over a wide pressure range for the first time. The samples of KBi2 and RbBi2 were prepared using a liquid ammonia (NH3) technique, and demonstrated superconductivity with superconducting transition temperatures, T-c, of 3.50 and 4.21 K at ambient pressure, respectively. The onset superconducting transition temperature, T-c(onset), of KBi2 decreased slightly; however, it suddenly jumped at 2 GPa and increased gradually with pressure, indicating the presence of two superconducting phases in the low-pressure range. The pressure-dependent X-ray diffraction patterns indicate that the KBi2 sample decomposed into KBi and Bi at pressures higher than 2.5 GPa. Moreover, a discontinuous change in T-c(onset) was observed for KBi2 at 9 GPa, which reflects the decomposition of KBi2 into KBi and Bi. By contrast, the value of T-c(onset) of RbBi2 was almost constant over a pressure range of 0-8 GPa. Thus, the superconducting properties and stability of alkali-Bi-based compounds against pressure were comprehensively explored in this study. In addition, the superconducting Cooper pair symmetry was investigated from the magnetic field dependence of T-c of KBi2 at 0.790 and 2.32 GPa, and of RbBi2 at 1.17 GPa, indicating the exact deviation from the simple s-wave paring model, which may be due to the complex electronic structure of Bi. The results elucidated the exotic superconducting properties of KBi2 and RbBi2 based on the pressure and magnetic field dependence of T-c and verified the chemical stability of KBi2 under pressure.

DOI： 10.1039/d2cp00679k

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

The magnitude of the field-effect mobility mu of organic thin-film and single-crystal field-effect transistors (FETs) has been over-estimated in certain recent studies. These reports set alarm bells ringing in the research field of organic electronics. Herein, we report a precise evaluation of the mu values using the effective field-effect mobility, mu(eff), a new indicator that is recently designed to prevent the FET performance of thin-film and single-crystal FETs based on various phenacene molecules from being overestimated. The transfer curves of a range of FETs based on phenacene are carefully categorized on the basis of a previous report. The exact evaluation of the value of mu(eff) depends on the exact classification of each transfer curve. The transfer curves of all our phenacene FETs could be successfully classified based on the method indicated in the aforementioned report, which made it possible to evaluate the exact value of mu(eff) for each FET. The FET performance based on the values of mu(eff) obtained in this study is discussed in detail. In particular, the mu(eff) values of single-crystal FETs are almost consistent with the mu values that were reported previously, but the mu(eff) values of thin-film FETs were much lower than those previously reported for mu, owing to a high absolute threshold voltage, vertical bar V-th vertical bar. The increase in the field-effect mobility as a function of the number of benzene rings, which was previously demonstrated based on the mu values of single-crystal FETs with phenacene molecules, is well reproduced from the mu(eff) values. The FET performance is discussed based on the newly evaluated mu(eff) values, and the future prospects of using phenacene molecules in FET devices are demonstrated.

DOI： 10.1021/acsomega.1c06932

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

3-Decyl-10-phenyl[5]phenacene (PhC10-PIC) molecule shows good FET characteristics in case of using ZrO₂ gate dielectric, owing to strong fastener effect and large π-overlap.

DOI： 10.1039/d2tc03383f

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

DOI： 10.1088/1361-648x/ac244b

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/ac244b/pdf

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

The pressure dependence of BaBi₃ superconductivity is investigated, demonstrating only the presence of the α phase, and <italic>p</italic>-wave superconductivity.

DOI： 10.1039/d1cp00042j

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

DOI： 10.1021/acs.jpcc.1c06207

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

DOI： 10.1021/acs.inorgchem.0c02836

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

<p>A ring oscillator consisting of p-channel and n-channel organic FETs.</p>

DOI： 10.1039/d1ra00511a

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

DOI： 10.1088/1361-648x/abd99c

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/abd99c/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.102.155118

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.102.155118/fulltext

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

<p>A possible Dirac semimetal, BaTi₂Bi₂O, indicates a sign of topologically nontrivial nature in superconductivity at high pressure.</p>

DOI： 10.1039/d0cp04771f

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

DOI： 10.1088/1361-648x/abaad2

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/abaad2/pdf

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

<p>A superconducting KBi₂ sample was successfully prepared using a liquid ammonia (NH₃) technique.</p>

DOI： 10.1039/d0ra04541a

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

DOI： 10.1088/1361-648x/ab9911

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/ab9911/pdf

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

DOI： 10.1088/2053-1591/ab7c85

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Other Link： https://iopscience.iop.org/article/10.1088/2053-1591/ab7c85/pdf

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© 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft. We prepared two superconducting phases of (NH3) y Li x FeSe0.5Te0.5, which show superconducting transition temperatures (T c's) as high as 20.2 and 29.5 K at ambient pressure, here called the 'low-T c phase' and 'high-T c phase'. The temperature dependence of electrical resistance (R) was measured for the low-T c phase of (NH3) y Li x FeSe0.5Te0.5 over a pressure (p) range of 0-14 GPa, and for the high-T c phase of (NH3) y Li x FeSe0.5Te0.5 over 0-19 GPa, yielding double-dome superconducting T c-p phase diagrams, i.e. two superconducting phases (SC-I and SC-II) were found for both the low-T c and high-T c phases under pressure. For the low-T c phase, the maximum T c was 20.2 K at 0 GPa for SC-I, and 19.9 K at 8.98 GPa for SC-II. For the high-T c phase, the maximum T c was 33.0 K at 1.00 GPa for SC-I, and 24.0 K at 11.5-13.2 GPa for SC-II. These results imply that the maximum T c value of the high pressure phase (SC-II) does not exceed the maximum value of the SC-I, unlike what was shown in the T c-p phase diagrams of (NH3) y Li x FeSe and (NH3) y Cs x FeSe investigated previously. Nevertheless, the double-dome T c-p phase diagram was found in metal-doped FeSe0.5Te0.5, indicating that this feature is universal in metal-doped FeSe1-zTe z . Moreover, no structural phase transitions were observed for either the low-T c or high-T c phases of (NH3) y Li x FeSe0.5Te0.5 over the wide pressure range of 0-15.3 GPa, and the T c-lattice constant (c) plots for both phases were recorded to determine the critical point separating SC-I and SC-II.

DOI： 10.1088/1367-2630/ab5034

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

DOI： 10.7567/1347-4065/ab4ef5

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Other Link： http://iopscience.iop.org/article/10.7567/1347-4065/ab4ef5/pdf

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© 2019 IOP Publishing Ltd. Herein, we investigated the pressure dependence of electric transport in a new type of superconducting metal iridate compound, SrIr2, that exhibits a superconducting transition temperature, T c, as high as 6.6 K at ambient pressure, in order to complete the T c-pressure (p ) phase diagram. Very recently, this sample's superconductivity was discovered by our group, but the superconducting behavior has not yet been clarified under pressure. In this study, we fully investigated this sample's superconductivity in a wide pressure range. The T c value decreased with an increase in pressure, but the onset superconducting transition temperature, (R-T plot), increased above a pressure of 8 GPa, indicating an unconventional superconductivity different from a BCS-type superconductor. The magnetic field dependence of electric resistance (R) against temperature (R-T plot) recorded at 7.94 and 11.3 GPa suggested an unconventional superconductivity, followed by a p -wave polar model, supporting the deviation from a simple s-wave pairing. Moreover, we fully investigated the pressure dependence of crystal structure in SrIr2 and discussed the correlation between superconductivity and crystal structure. This is the first systematic study on superconducting behavior of a new type of metal iridate compound, MIr2 (M: alkali-earth metal atom), under pressure.

DOI： 10.1088/1361-648X/ab4605

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© 2019 American Physical Society. We systematically investigated the pressure dependence of electrical transport and the crystal structure of topological insulator, Bi2-xSbxTe3-ySey, which showed no superconductivity down to 2.0 K at ambient pressure. The Bi2-xSbxTe3-ySey crystal showed two structural phase transitions under pressure, from rhombohedral structure (space group No. 166, R3m, termed phase I) to monoclinic structure (space group No. 12, C2/m, termed phase II), and from phase II to another monoclinic structure (space group No. 12, C2/m, termed phase III). Superconductivity appeared when applying pressure; actually the superconductivity of all Bi2-xSbxTe3-ySey samples emerged in phase I. The superconducting transition temperature, Tc, increased against pressure in a pressure range of 0-15 GPa for all Bi2-xSbxTe3-ySey samples, and the maximum Tc was 5.45 K, recorded at 13.5 GPa in Bi2-xSbxTe3-ySey at x=0 and y=1.0. The magnetic field (H) dependence of the R-T plot for Bi2-xSbxTe3-ySey was measured to characterize the superconducting pairing mechanism of pressure-induced superconducting phase.

DOI： 10.1103/PhysRevB.100.094525

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© 2019 The Royal Society of Chemistry. The transport properties of 3,10-ditetradecylpicene ((C14H29)2-picene) and [6]phenacene thin-film field-effect transistors (FETs) on Si and plastic substrates are reported, in which SiO2 and parylene are used as gate dielectrics, respectively. These devices show p-channel normally-off FET characteristics. A μ value of 1.34 cm2 V-1 s-1 is obtained in the (C14H29)2-picene thin-film FET, where 500 μm thick polyethylene terephthalate (PET) and 1 μm thick parylene are used as the substrate and gate dielectric, respectively. Moreover, excellent FET performance is obtained in the (C14H29)2-picene thin-film FET using a high-k gate dielectric, ZrO2, which is formed on a 350 μm thick PET substrate, showing p-channel normally-off FET properties and low voltage operation. The μ value reaches 6.31 cm2 V-1 s-1 in the FET device. The FET properties of N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDIC8) thin-film FETs formed on PET are also reported, showing n-channel normally-off FET characteristics. We report a bias stress effect on flexible [6]phenacene thin film FETs that are fabricated on a PEN substrate. Two types of experiments are performed for investigating the bias stress effect on FETs, and the bias stress effect under light irradiation is very different from that under no irradiation. This difference is well explained based on the hole-filling of trap states by electron excitation. We show the characteristics of a complementary MOS inverter (CMOS), constituting a [6]phenecene thin-film FET (p-channel) and a PTCDIC8 thin-film FET (n-channel) formed on the PET and PEN substrates, i.e., a flexible CMOS inverter. The maximum gain reaches 300. Furthermore, we report low-voltage operation for the flexible CMOS inverter, where ZrO2 is used as the gate dielectric. Through this study, we have achieved the fabrication of flexible thin-film FETs with a high μ and low voltage operation, and flexible CMOS inverters with a high gain as well as low operation voltage. This study could provide a basis for future practical/human-compatible electronic devices.

DOI： 10.1039/c8tc05824e

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

DOI： 10.1038/s41598-019-41906-7

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Other Link： http://www.nature.com/articles/s41598-019-41906-7

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© 2019, The Author(s). The [10]phenacene and [11]phenacene molecules have been synthesized using a simple repetition of Wittig reactions followed by photocyclization. Sufficient amounts of [10]phenacene and [11]phenacene were obtained, and thin-film FETs using these molecules have been fabricated with SiO 2 and ionic liquid gate dielectrics. These FETs operated in p-channel. The averaged measurements of field-effect mobility, <μ>, were 3.1(7) × 10 −2 and 1.11(4) × 10 −1 cm 2 V −1 s −1 , respectively, for [10]phenacene and [11]phenacene thin-film FETs with SiO 2 gate dielectrics. Furthermore, [10]phenacene and [11]phenacene thin-film electric-double-layer (EDL) FETs with ionic liquid showed low-voltage p-channel FET properties, with <μ> values of 3(1) and 1(1) cm 2 V −1 s −1 , respectively. This study also discusses the future utility of the extremely extended π-network molecules [10]phenacene and [11]phenacene as the active layer of FET devices, based on the experimental results obtained.

DOI： 10.1038/s41598-019-39899-4

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Language：English   Publishing type：Part of collection (book)   Publisher：World Scientific Publishing Co.  

In this chapter, the principles behind the mechanism of operation of organic transistors are described, as they are both important in their own right and also a representative example of organic electronics. Accordingly, the recent progress in organic transistors will be explored in depth. The term “organic transistor” generally refers to the field-effect transistor (FET), which uses thin films of organic materials. The study of these “organic FETs” began in the 1980s.1 Initially, the available fieldeffect mobility (µ), which is one determinant of the performance of an FET, was ca. 10-5 cm2 V-1 s-1, a value that is insufficient for practical applications. In the late 1990s, it was found that pentacene, in which five benzene rings are connected in a linear structure (Fig. 8.1.1), and C60, in which 60 carbon atoms form a spherical structure, were good candidates for the active layer of an FET device. The µ value became ~1 cm2 V-1 s-1 in FETs using these molecules.2, 3 This µ value raised the expectation that organic FETs might in the future become practical devices. On the other hand, since the year 2000, some work on FETs has demonstrated that the physical properties of materials can be controlled by carrier accumulation, such as the field-induced carrier doping of C60 for inducing superconductivity. These studies were not the case, but the interest in field-induced carrier doping to control the physical properties of materials has attracted much attention from researchers in solid-state physics. Consequently, some control of the physical properties of inorganic materials has been achieved by field-induced carrier accumulation using a device with the structure of an FET.4, 5 Research on organic FETs has been brought to a new stage by the participation of many researchers from other fields, where FET performance was pursued not only to find practical applications, but also to investigate fundamental physics. In 2003, a device with excellent FET properties that used a single crystal was fabricated using rubrene (Fig. 8.1.1).6 This showed that transistor operation in an organic FET could be achieved using not only thin films but also single crystals. An FET using a single crystal is superior to a thin-film FET for studying the intrinsic nature of organic materials because many interfering factors such as structural defects, grain boundaries, and impurities can be removed from the active layer. Generally, FET performance is also higher in a single-crystal FET than in a thin-film FET. Clearly, these studies have led to remarkable advances in the research on organic FETs. Furthermore, Hall-effect measurements were achieved in single crystals of organic molecules, 7, 8 and angle-resolved photoemission spectroscopy (ARPES) was performed on some organic single crystals.9, 10 Based on these results, it was suggested that electron transport in organic singlecrystal FETs occurs by band transport rather than hopping transport. Since then, the idea that electron transport in an organic thin-film FET is explained by simple hopping transport has been modified due to analyses based on the multiple shallow trap-and-release (MTR) model for the temperature-dependence of transport properties in organic thinfilm FETs exhibiting a high µ value.11-13 The MTR model assumes that the carriers in a band are captured by trap states and thermally excited up to the conduction (or valence) band, i.e. this concept is substantially based on band transport. Furthermore, the reduction of µ value caused by thermal scattering of phonons was determined from the temperature-dependence of µ in organic single-crystal FETs.14, 15 This constituted the direct observation of band transport in organic single-crystal FETs. These studies have enabled the full discussion of the mechanism of organic FET operation. An FET using pentacene (Fig. 8.1.1) as the active layer shows typical pchannel operation with Au source/drain electrodes, but shows n-channel operation with Ca source/drain electrodes.16 So an organic FET can operate both as p-channel and n-channel depending on the electrode metal, a flexibility termed “ambipolar”. Thus, an organic FET can operate in an ambipolar way by changing the metal of the source/drain electrodes (or changing the work function of the electrodes), unlike the operation of Si MOSFETs, which can operate in either p-channel or n-channel through the formation of an inversion layer in which minority carriers in the bulk become the majority in the channel region. Also, neither organic thin films nor crystals are doped with any impurities, unlike the Si crystal used in Si MOSFETs, which can be doped with an acceptor (p-type Si) or with a donor (n-type Si) material. In Section 8.1.1, we will fully examine organic FETs based on the background described above.

DOI： 10.1142/9789813273672_0010

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DOI： 10.1088/2053-1591/aae9d2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

We prepared two superconducting phases, which are called "low-Tc phase" and "high-Tc phase" of (NH3)yNaxFeSe showing Tc's of 35 and 44 K, respectively, at ambient pressure, and studied the superconducting behavior and structure of each phase under pressure. The Tc of the 35 K at ambient pressure rapidly decreases with increasing pressure up to 10 GPa, and it remains unchanged up to 22 GPa. Finally, superconductivity was not observed down to 1.4 K at 29 GPa, i.e., Tc&lt
1.4K. The Tc of the 44 K phase also shows a monotonic decrease up to 15 GPa and it weakly decreases up to 25 GPa. These behaviors suggest no pressure-driven high-Tc phase (called "SC-II") between 0 and 25 GPa for the low-Tc and high-Tc phases of (NH3)yNaxFeSe, differing from the behavior of (NH3)yCsxFeSe, which has a pressure-driven high-Tc phase (SC-II) in addition to the superconducting phase (SC-I) observed at ambient and low pressures. The Tc-c phase diagram for both low-Tc and high-Tc phases shows that the Tc can be linearly scaled with c (or FeSe plane spacing), where c is a lattice constant. The reason why a pressure-driven high-Tc phase (SC-II) was found for neither low-Tc nor high-Tc phases of (NH3)yNaxFeSe is fully discussed, suggesting a critical c value as the key to forming the pressure-driven high-Tc phase (SC-II). Finally, the precise Tc-c phase diagram is depicted using the data obtained thus far from FeSe codoped with a metal and NH3 or amine, indicating two distinct Tc-c lines below c=17.5Å.

DOI： 10.1103/PhysRevB.97.094505

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We investigated the pressure dependence of electric transport and crystal structure of Ag-doped Bi2Se3. In the sample prepared by Ag doping of Bi2Se3, the Bi atom was partially replaced by Ag, i.e., Ag0.05Bi1.95Se3. X-ray diffraction patterns of Ag0.05Bi1.95Se3 measured at 0-30 GPa showed three different structural phases, with rhombohedral, monoclinic, and tetragonal structures forming in turn as pressure increased, and structural phase transitions at 8.8 and 24 GPa. Ag0.05Bi1.95Se3 showed no superconductivity down to 2.0 K at 0 GPa, but under pressure, superconductivity suddenly appeared at 11 GPa. The magnetic field (H) dependence of the superconducting transition temperature Tc was measured at 11 and 20.5 GPa, in order to investigate whether the pressure-induced superconducting phase is explained by either p-wave polar model or s-wave model.

DOI： 10.1103/PhysRevB.97.104503

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

We have produced a superconducting binary-elements intercalated graphite, CaxSr1-xCy, with the intercalation of Sr and Ca in highly-oriented pyrolytic graphite; the superconducting transition temperature, T(c1)was similar to 3 K. The superconducting CaxSr1-xCy sample was fabricated with the nominal x value of 0.8, i.e., Ca0.8Sr0.2Cy. Energy dispersive X-ray (EDX) spectroscopy provided the stoichiometry of Ca0.5(2)Sr0.5(2)C-y for this sample, and the X-ray powder diffraction (XRD) pattern showed that Ca0.5(2)Sr0.5(2)Cy took the SrC6-type hexagonal-structure rather than CaC6-type rhombohedral-structure. Consequently, the chemical formula of CaxSr1-xCy sample could be expressed as 'Ca0.5(2)Sr0.5(2)C6'. The XRD pattern of Ca0.5(2)Sr0.5(2)C6 was measured at 0-31 GPa, showing that the lattice shrank monotonically with increasing pressure up to 8.6 GPa, with the structural phase transition occurring above 8.6 GPa. The pressure dependence of Tc was determined from the DC magnetic susceptibility and resistance up to 15 GPa, which exhibited a positive pressure dependence of T-c up to 8.3 GPa, as in YbC6, SrC6, KC8, CaC6 and Ca0.6K0.4C8. The further application of pressure caused the rapid decrease of Tc. In this study, the fabrication and superconducting properties of new binary-elements intercalated graphite, CaxSr1-xCy, are fully investigated, and suitable combinations of elements are suggested for binaryelements intercalated graphite.

DOI： 10.1038/s41598-017-07763-y

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

We have studied new superconductors prepared by metal doping of two-dimensional (2D) layered materials, FeSe and FeSe0.5Te0.5, using ethylenediamine (EDA). The superconducting transition temperatures (T(c)s) of metal-doped FeSe and metal-doped FeSe0.5Te0.5, i.e., (EDA)(y)MxFeSe and (EDA)(y)MxFeSe0.5Te0.5 (M: Li, Na, and K), were 31-45 K and 19-25 K, respectively. The stoichiometry of each sample was clarified by energy dispersive x-ray (EDX) spectroscopy, and the x-ray powder diffraction pattern indicated a large expansion of lattice constant c, indicating the cointercalation of metal atoms and EDA. The pressure dependence of superconductivity in (EDA)(y)NaxFeSe0.5Te0.5 has been investigated at a pressure of 0-0.8GPa, showing negative pressure dependence in the same manner as (NH3)(y)NaxFeSe0.5Te0.5. The T-c-c phase diagrams of MxFeSe and MxFeSe0.5Te0.5 were drawn afresh from the T-c and c of (EDA)(y)MxFeSe and (EDA)(y)MxFeSe0.5Te0.5, showing that the T-c increases with increasing c but that extreme expansion of c reverses the T-c trend.

DOI： 10.1103/PhysRevB.96.014502

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

Field-effect transistors (FETs) were fabricated using exfoliated single crystals of Mo(Se1-x Te-x)(2) with an x range of 0 to 1, and the transistor properties fully investigated at 295 K in four-terminal measurement mode. The chemical composition and crystal structure of exfoliated single crystals were identified by energy-dispersive x-ray spectroscopy (EDX), single-crystal x-ray diffraction, and Raman scattering, suggesting the 2H - structure in all Mo(Se1-x Te-x)(2). The lattice constants of a and c increase monotonically with increasing x, indicating the substitution of Se by Te. When x &lt; 0.4 in a FET with a thin single crystal of Mo(Se1-x Te-x)(2), n-channel FET properties were observed, changing to p-channelor ambipolar operation for x &gt; 0.4. In contrast, the polarity of a thick single-crystal Mo(Se1-x Te-x)(2) FET did not change despite an increase in x. The change of polarity in a thin single-crystal FET was well explained by the variation of electronic structure. The absence of such change in the thick single-crystal FET can be reasonably interpreted based on the large bulk conduction due to naturally accumulated electrons. The mu value in the thin single-crystal FET showed a parabolic variation, with a minimum mu at around x = 0.4, which probably originates from the disorder of the single crystal caused by the partial replacement of Se by Te, i.e., a disorder that may be due to ionic size difference of Se and Te.

DOI： 10.1103/PhysRevB.95.245310

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

Electrostatic carrier-doping is attracting serious attention as a meaningful technique for producing interesting electronic states in two-dimensional (2D) layered materials. Ionic-liquid gating can provide the critical carrier density required to induce the metal-insulator transition and superconductivity. However, the physical properties of only a few materials have been controlled by the electrostatic carrier-doping during the past decade. Here, we report an observation of superconductivity in a 2D layered material, LaOBiS2, achieved by the electrostatic electron-doping. The electron doping of LaOBiS2 induced metallic conductivity in the normally insulating LaOBiS2, ultimately led to superconductivity. The superconducting transition temperature, T-c, was 3.6 K, higher than the 2.7K seen in LaO1-xFxBiS2 with an electron-doped BiS2 layer. A rapid drop in resistance (R) was observed at low temperature, which disappeared with the application of high magnetic fields, implying a superconducting state. This study reveals that electron-doping is an important technique for inducing superconductivity in 2D layered BiS2 materials. Published by AIP Publishing.

DOI： 10.1063/1.4972400

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

From the C 1s and K 2p photoelectron holograms, we directly reconstructed atomic images of the cleaved surface of a bimetal-intercalated graphite superconductor, (Ca, K) C-8, which differed substantially from the expected bulk crystal structure based on x-ray diffraction (XRD) measurements. Graphene atomic images were collected in the in-plane cross sections of the layers 3.3 angstrom and 5.7 angstrom above the photoelectron emitter C atom and the stacking structures were determined as AB-and AA-type, respectively. The intercalant metal atom layer was found between two AA-stacked graphenes. The K atomic image revealing 2 x 2 periodicity, occupying every second centre site of C hexagonal columns, was reconstructed, and the Ca 2p peak intensity in the photoelectron spectra of (Ca, K) C-8 from the cleaved surface was less than a few hundredths of the K 2p peak intensity. These observations indicated that cleavage preferentially occurs at the KC8 layers containing no Ca atoms.

DOI： 10.1038/srep36258

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

Na-intercalated FeSe0.5Te0.5 was prepared using the liquid NH3 technique, and a superconducting phase exhibiting a superconducting transition temperature (T-c) as high as 27 K was discovered. This can be called the high-T-c phase since a 21 K superconducting phase was previously obtained in (NH3)(y)NaxFeSe0.5Te0.5. The chemical composition of the high-T-c phase was determined to be (NH3)(0.61(4))Na-0.63(5) Fe0.85Se0.55(3) Te-0.44(2). The x-ray diffraction patterns of both phases show that a larger lattice constant c (i.e., FeSe0.5Te0.5 plane spacing) produces a higher T-c. This behavior is the same as that of metal-doped FeSe, suggesting that improved Fermi-surface nesting produces the higher T-c. The high-T-c phase converted to the low-T-c phase within several days, indicating that it is a metastable phase. The temperature dependence of resistance for both phases was recorded at different magnetic fields, and the critical fields were determined for both phases. Finally, the T-c versus c phase diagram was prepared for the metal-doped FeSe0.5Te0.5, which is similar to that of metal-doped FeSe, although the T-c is lower.

DOI： 10.1103/PhysRevB.94.174505

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

Potassium-doped picene (K(3.0)picene) with a superconducting transition temperature (TC) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The TC showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

DOI： 10.1088/0953-8984/28/44/444001

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

This article reviews new superconducting phases of carbon-based materials. During the past decade, new carbon-based superconductors have been extensively developed through the use of intercalation chemistry, electrostatic carrier doping, and surface-proving techniques. The superconducting transition temperature T-c of these materials has been rapidly elevated, and the variety of superconductors has been increased. This review fully introduces graphite, graphene, and hydrocarbon superconductors and future perspectives of high-T-c superconductors based on these materials, including present problems. Carbon-based superconductors show various types of interesting behavior, such as a positive pressure dependence of T-c. At present, experimental information on superconductors is still insufficient, and theoretical treatment is also incomplete. In particular, experimental results are still lacking for graphene and hydrocarbon superconductors. Therefore, it is very important to review experimental results in detail and introduce theoretical approaches, for the sake of advances in condensed matter physics. Furthermore, the recent experimental results on hydrocarbon superconductors obtained by our group are also included in this article. Consequently, this review article may provide a hint to designing new carbon-based superconductors exhibiting higher T-c and interesting physical features.

DOI： 10.1088/0953-8984/28/33/334001

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

We report syntheses of new superconducting metal-doped MoSe2 materials (MxMoSe2). The superconducting MxMoSe2 samples were prepared using a liquid NH3 technique, and can be represented as '(NH3)(y)MxMoSe2'. The T(c)s of these materials were approximately 5.0 K, independent of x and the specific metal atom. X-ray diffraction patterns of (NH3)(y)NaxMoSe2 were recorded using polycrystalline powders. An increase in lattice constant c showed that the Na atom was intercalated between MoSe2 layers. The x-independence of c was observed in (NH3)(y)NaxMoSe2, indicating the formation of a stoichiometric compound in the entire x range, which is consistent with the x-independence of T-c. A metallic edge of the Fermi level was observed in the photoemission spectrum at 30 K, demonstrating its metallic character in the normal state. Doping of MoSe2 with Li and K also yielded superconductivity. Thus, MoSe2 is a promising material for designing new superconductors, as are other transition metal dichalcogenides.

DOI： 10.1038/srep29292

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

Metal intercalation to graphite produces various types of superconductors. The highest superconducting transition temperature T-c (onset temperature, T-c(onset), of 11.5 K) was found in Ca intercalated graphite, denoted CaC6.T-c(onset) increased up to 15.1 K at 7.5 GPa, implying a positive pressure dependence. However, no new metal-intercalated graphite superconductors with T-c(onset) higher than 11.5 K at ambient pressure have so far been reported. To search for new graphite superconductors, we successfully synthesized binary-element-intercalated graphite, CaxK1-xCy. Their structure resembles that of KC8. T-c increased continuously with increasing x. Furthermore, the pressure dependence of T-c in Ca0.6K0.4C8 was investigated over a wide pressure range from 0-43 GPa. T-c (= 9.6 K at 0 GPa) increased to 11.6 K at 3.3 GPa, and decreased to 2.0 K at 41 GPa. This behavior is similar to that of CaC6, albeit with a lower maximum T-c. Xray diffraction patterns were measured under high pressures of 0-24 GPa, and suggest a structural transition at 15 GPa. Evidence is given for superconducting graphite involving binary metal intercalation. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2016.01.071

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

The superconducting transition temperature T-c of ammoniated metal-doped FeSe (NH3)(y)MxFeSe (M: metal atom) has been scaled with the FeSe plane spacing, and it has been suggested that the FeSe plane spacing depends on the location of metal atoms in (NH3)(y)MxFeSe crystals. Although the crystal structure of (NH3)(y)LixFeSe exhibiting a high T-c (similar to 44 K) was determined from neutron diffraction, the structure of (NH3)(y)MxFeSe exhibiting a low T-c (similar to 32 K) has not been determined thus far. Here, we determined the crystal structure of (NH3)(y)Cs0.4FeSe (T-c = 33 K) through the Rietveld refinement of the x-ray diffraction (XRD) pattern measured with synchrotron radiation at 30 K. The XRD pattern was analyzed based on two different models, on-center and off-center, under a space group of 14/mmm. In the on-center structure, the Cs occupies the 2a site and the N of NH3 may occupy either the 4c or 2b site, or both. In the off-center structure, the Cs may occupy either the 4c or 2b site, or both, while the N occupies the 2a site. Only an on-center structure model in which the Cs occupies the 2a and the N of NH3 occupies the 4c site provided reasonable results in the Rietveld analysis. Consequently, we concluded that (NH3)(y)Cs0.4FeSe can be assigned to the on-center structure, which produces a smaller FeSe plane spacing leading to the lower T-c.

DOI： 10.1103/PhysRevB.93.104508

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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：Part of collection (book)   Publisher：Pan Stanford Publishing Pte. Ltd.  

DOI： 10.1201/b19365

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

DOI： 10.1002/aelm.201500085

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

We previously discovered multiple superconducting phases in the ammoniated Na-doped FeSe material, (NH3)(y)NaxFeSe. To clarify the origin of the multiple superconducting phases, the variation of T-c was fully investigated as a function of x in (NH3)(y)NaxFeSe. The 32 K superconducting phase is mainly produced in the low-x region below 0.4, while only a single phase is observed at x = 1.1, with T-c = 45 K, showing that the T-c depends significantly on x, but it changes discontinuously with x. The crystal structure of (NH3)(y)NaxFeSe does not change as x increases up to 1.1, i.e., the space group of I4/mmm. The lattice constants, a and c, of the low-T-c phase (T-c = 32.5 K) are 3.9120(9) and 14.145(8) angstrom, respectively, while a = 3.8266(7) angstrom and c = 17.565(9) angstrom for the high-T-c phase (similar to 46 K). The c increases in the high T-c phase, implying that the T-c is directly related to c. In (NH3)(y)LixFeSe material, the T-c varies continuously within the range of 39 to 44 K with changing x. Thus, the behavior of T-c is different from that of (NH3)(y)NaxFeSe. The difference may be due to the difference in the sites that the Na and Li occupy.

DOI： 10.1038/srep12774

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

'Aromatic hydrocarbon' implies an organic molecule that satisfies the (4n + 2) pi-electron rule and consists of benzene rings. Doping solid aromatic hydrocarbons with metals provides the superconductivity. The first discovery of such superconductivity was made for K-doped picene (K(x)picene, five benzene rings). Its superconducting transition temperatures (T-c's) were 7 and 18 K. Recently, we found a new superconducting K(x)picene phase with a T-c as high as 14 K, so we now know that K(x)picene possesses multiple superconducting phases. Besides K(x)picene, we discovered new superconductors such as Rb(x)picene and Caxpicene. A most serious problem is that the shielding fraction is &lt;= 615% for K(x)picene and Rb(x)picene, and it is often similar to 1% for other superconductors. Such low shielding fractions have made it difficult to determine the crystal structures of superconducting phases. Nevertheless, many research groups have expended a great deal of effort to make high quality hydrocarbon superconductors in the five years since the discovery of hydrocarbon superconductivity. At the present stage, superconductivity is observed in certain metaldoped aromatic hydrocarbons (picene, phenanthrene and dibenzopentacene), but the shielding fraction remains stubbornly low. The highest priority research area is to prepare aromatic superconductors with a high superconducting volume-fraction. Despite these difficulties, aromatic superconductivity is still a core research target and presents interesting and potentially breakthrough challenges, such as the positive pressure dependence of T-c that is clearly observed in some phases of aromatic hydrocarbon superconductors, suggesting behavior not explained by the standard BCS picture of superconductivity. In this article, we describe the present status of this research field, and discuss its future prospects. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2015.02.015

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

The pressure dependence of the superconducting transition temperature (T-c) and unit cell metrics of tetragonal (NH3)(y)Cs0.4FeSe were investigated in high pressures up to 41 GPa. The T-c decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The T-c vs. c plot is compared with those of various (NH3)(y)MxFeSe (M: metal atoms) materials exhibiting different T-c and c, showing that the T-c is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the T-c. No superconductivity was observed down to 4.3 K in (NH3)(y)Cs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the T-c reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, T-c slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

DOI： 10.1038/srep09477

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

DOI： 10.1039/c5tc90044a

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

Field-effect transistors (FETs) have been fabricated with thin films of a series of 2,9-dialkylated phenanthro [1,2-b:8,7-b'] dithiophene derivatives (C-n-PDTs). The FET characteristics of C-n-PDT thin-film FETs with an SiO2 gate dielectric as well as high-k gate dielectrics were recorded, and the dependence of the field-effect mobility, mu, on the number (n) of carbon atoms in the alkyl chains was investigated, showing that the 2,9-didodecylphenanthro[1,2-b:8,7-b'] dithiophene (C-12-PDT) thin-film FET displays superior properties, with mu s as high as 1.8 cm(2) V-1 s(-1) for the SiO2 gate dielectric and 2.2 cm(2) V-1 s(-1) for the HfO2 gate dielectric. The average mu values, &lt;mu &gt;, reach 1.1(5) and 1.8(6) cm(2) V-1 s(-1), respectively, for the SiO2 and ZrO2 gate dielectrics. Low-voltage operation, showing an absolute average threshold voltage &lt;|V-th|&gt; of similar to 11 V, was implemented, together with the above high &lt;mu &gt; of similar to 2 cm(2) V-1 s(-1). Also, a flexible FET was fabricated with a parylene gate dielectric. The results of this study show the potential of the C-12-PDT molecule for application in a high-performance transistor.

DOI： 10.1039/c4tc02413c

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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：English   Publisher：ROYAL SOC CHEMISTRY  

DOI： 10.1039/c5tc90044a

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

The characteristics of field-effect transistors (FETs) fabricated from thin films and single crystals of phenacene molecules are fully reported in this review together with the electronic and crystal structures of phenacenes. Phenacene molecules possess a low HOMO level and a wide band gap. The highest mobility observed in the phenacene thin-film FETs is 7.4 cm(2)V(-1)s(-1) for [6]phenacene, and in single-crystal FETs the highest value is 6.3 cm(2)V(-1)s(-1) for [7]phenacene. The phenacene thin-film FETs show O-2-sensing properties unlike their single-crystal FETs. The bias-stress effect is fully investigated for phenacene single-crystal FETs. Furthermore, the low-voltage operation of phenacene single-crystal FETs with electric-double-layer (EDL) capacitors is reported. The temperature dependence of phenacene single-crystal FETs is reported to clarify the transport mechanism, which is suggestive of band-like transport.

DOI： 10.1002/ejic.201402168

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

A new phenacene-type molecule, [8] phenacene, which is an extended zigzag chain of coplanar fused benzene rings, has been synthesised for use in an organic field-effect transistor (FET). The molecule consists of a phenacene core of eight benzene rings, which has a lengthy pi-conjugated system. The structure was verified by elemental analysis, solid-state NMR, X-ray diffraction (XRD) pattern, absorption spectrum and photoelectron yield spectroscopy (PYS). This type of molecule is quite interesting, not only as pure chemistry but also for its potential electronics applications. Here we report the physical properties of [8] phenacene and its FET application. An [8] phenacene thin-film FET fabricated with an SiO2 gate dielectric showed clear p-channel characteristics. The highest m achieved in an [8] phenacene thin-film FET with an SiO2 gate dielectric is 1.74 cm(2) V-1 s(-1), demonstrating excellent FET characteristics; the average mu was evaluated as 1.2(3) cm(2) V-1 s(-1). The mu value in the [8] phenacene electric-double-layer FET reached 16.4 cm(2) V-1 s(-1), which is the highest reported in EDL FETs based on phenacene-type molecules; the average m was evaluated as 8(5) cm(2) V-1 s(-1). The mu values recorded in this study show that [8] phenacene is a promising molecule for transistor applications.

DOI： 10.1038/srep05330

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

Field-effect transistors (FETs) were fabricated with a thin film of 3,10-ditetradecylpicene, picene-(C14H29)(2), formed using either a thermal deposition or a deposition from solution (solution process). All FETs showed p-channel normally-off characteristics. The field-effect mobility, m, in a picene-(C14H29)(2) thin-film FET with PbZr0.52Ti0.48O3 (PZT) gate dielectric reached similar to 21 cm(2) V-1 s(-1), which is the highest mu value recorded for organic thin-film FETs; the averagem mu value (&lt;mu &gt;) evaluated from twelve FET devices was 14(4) cm(2)V(-1) s(-1). The, m. values for picene-(C14H29)(2) thin- film FETs with other gate dielectrics such as SiO2, Ta2O5, ZrO2 and HfO2 were greater than 5 cm(2) V-1 s(-1), and the lowest absolute threshold voltage, vertical bar V-th vertical bar, (5.2 V) was recorded with a PZT gate dielectric; the average jVthj for PZT gate dielectric is 7(1) V. The solution-processed picene-(C14H29)(2) FET was also fabricated with an SiO2 gate dielectric, yielding mu = 3.4 x 10(-2) cm(2) V-1 s(-1). These results verify the effectiveness of picene-(C14H29)(2) for electronics applications.

DOI： 10.1038/srep05048

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

Superconducting phases of (NH3)(y)MxFeSe1-z Te-z have been synthesized by the intercalation of metal atoms (M: Li, Na, Ca) into FeSe and FeSe0.5Te0.5 using a low-temperature liquid NH3 technique. The superconducting transition temperature (T-c) is 31.5 K for Na-doped FeSe, and for Li-, Na-, and Ca-doped FeSe0.5Te0.5 it is 26, 22, and 17 K, respectively. The 31.5 K superconducting is the superconducting phase in ammoniated Na-doped FeSe. The T-c is lower than that (onset T-c = 46 K) of the superconducting phase reported previously. The reason why the T-c of this phase is lower is discussed based on the structure. The pressure dependences of T-c in the (NH3)(y)Na0.5FeSe and (NH3)(y)Na0.4FeSe0.5Te0.5 samples have been measured and a negative pressure dependence is observed; i.e., a decrease in lattice constant c leads to a decrease in Tc, consistent with the behavior of (NH3)(y)Cs0.4FeSe reported previously by our group. Furthermore, the magnetic behavior of (NH3)(y)Na0.4FeSe0.5Te0.5 has been fully investigated at different applied magnetic fields (H) to determine the critical magnetic This is a successful metal intercalation into FeSe1-z Te-z (z not equal 0) and an observation of superconductivity.

DOI： 10.1103/PhysRevB.89.144509

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DOI： 10.1103/PhysRevB.89.144509

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

The interface between the single crystal and the Au source/drain electrodes in [7]phenacene single-crystal field-effect transistors (FETs) was modified using 14 electron acceptors with different redox potentials. The effective hole-injection barrier heights (phi(eff)(h)s) for [7]phenacene single-crystal FETs have been plotted as a function of the redox potential (E-redox) of the inserted electron acceptors, showing that the phi(eff)(h) decreases with increasing E-redox. The highest phi(eff)(h) occurs without inserted material (electron acceptors), and this deviates from the otherwise linear relationship between phi(eff)(h) and E-redox. We have investigated the temperature dependence of phi(eff)(h) in an attempt to determine why the phi(eff)(h) value without inserted material is so high, which suggests that no additional barrier, such as a tunneling barrier, is formed in the device. We conclude that the pure Schottky barrier in this FET is lowered very significantly by the insertion of an electron acceptor. The gate-voltage dependence of phi(eff)(h) suggests a slight reduction of Schottky barrier height owing to hole accumulation. Furthermore, the clear correlation between threshold voltage and redox potential suggests a relationship between threshold voltage and phi(eff)(h). Controlling the interface between the single crystal and the source/drain electrodes in this FET produced a very high mu (similar to 6.9 cm(2) V-1 s(-1)) and low absolute threshold voltage, i.e., excellent FET characteristics. The topological characterization of inserted materials on [7]phenacene single crystals are achieved using atomic force microscope (AFM) and X-ray diffraction (XRD). The results show that the single crystals are not completely covered with the inserted materials and the inhomogeneous modification of inserted materials for single crystals effectively leads to the drastic change of hole-injection barrier between source/drain electrodes and single-crystal active layer.

DOI： 10.1021/jp4107469

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

Alkali-metal-intercalated FeSe materials, (NH3) yM0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)yCs 0.4FeSe shows a superconducting transition temperature (T c) as high as 31.2 K, which is higher by 3.8 K than the Tc of nonammoniated Cs0.4FeSe. The Tcs of (NH 3)yK0.4FeSe and (NH3) yRb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The Tc of (NH 3)yCs0.4FeSe shows a negative pressure dependence. A clear correlation between Tc and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.094521

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

Single crystal field-effect transistors (FETs) using [6] phenacene and [7] phenacene show p-channel FET characteristics. Field-effect mobilities, mu s, as high as 5.6 x 10 (1) cm(2) V (1) s (1) in a [6] phenacene single crystal FET with an SiO2 gate dielectric and 2.3 cm(2) V (1) s (1) in a [7] phenacene single crystal FET were recorded. In these FETs, 7,7,8,8-tetracyanoquinodimethane (TCNQ) was inserted between the Au source/drain electrodes and the single crystal to reduce hole-injection barrier heights. The mu reached 3.2 cm(2) V (1) s (1) in the [7] phenacene single crystal FET with a Ta2O5 gate dielectric, and a low absolute threshold voltage vertical bar V-TH vertical bar (6.3 V) was observed. Insertion of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ) in the interface produced very a high mu value (4.7-6.7 cm(2) V (1) s (1)) in the [7] phenacene single crystal FET, indicating that F(4)TCNQ was better for interface modification than TCNQ. A single crystal electric double-layer FET provided mu as high as 3.8 x 10 (1) cm(2) V (1) s (1) and vertical bar V-TH vertical bar as low as 2.3 V. These results indicate that [6] phenacene and [7] phenacene are promising materials for future practical FET devices, and in addition we suggest that such devices might also provide a research tool to investigate a material's potential as a superconductor and a possible new way to produce the superconducting state. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2013.03.035

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DOI： 10.1103/PhysRevB.87.060505

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

We report the observation of zero resistivity (rho) in a hydrocarbon superconductor, and describe the temperature dependence of rho in metal-doped hydrocarbons. The resistivity of K-doped picene (K(x)picene) has been recorded from pellet samples in a four-terminal measurement mode. A drop in rho is observed below 7 K for K(3.1)picene and below 11 K for K(3.5)picene, which clearly displays zero resistivity. The resistivity drop at 7 K is consistent with the superconducting critical temperature (T-c) obtained from the magnetic susceptibility of the 7 K phase of K(3)picene, while the drop at 11 K is inconsistent with the T-c's of both the 7 and 18 K phases of K(3)picene reported previously. The temperature dependence of rho for both samples exhibits granular-metal-like behavior in the normal state. DOI: 10.1103/PhysRevB.87.060505

DOI： 10.1103/PhysRevB.87.060505

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

Field-effect transistors (FETs) based on [6]phenacene thin films were fabricated with SiO2 and parylene gate dielectrics. These FET devices exhibit field-effect mobility in the saturation regime as high as 7.4 cm(2) V-1 s(-1), which is one of the highest reported values for organic thin-film FETs. The two- and four-probe mobilities in the linear regime display nearly similar values, suggesting negligible contact resistance at 300 K. FET characteristics were investigated using two-probe and four-probe measurement modes at 50-300 K. The two-probe mobility of the saturation regime can be explained by the multiple shallow trap and release model, while the intrinsic mobility obtained by the four-probe measurement in the linear regime is better explained by the phenomenon of transport with charge carrier scattering at low temperatures. The FET device fabricated with a parylene gate dielectric on polyethylene terephthalate possesses both transparency and flexibility, implying feasibility of practical application of [6] phenacene FETs in flexible/transparent electronics. N-channel FET characteristics were also achieved in the [6] phenacene thin-film FETs using metals that possess a small work function for use as source/drain electrodes.

DOI： 10.1039/c3cp53598c

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

DOI： 10.1063/1.4795626

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

A new picene-type molecule, phenanthro[1,2-b : 8,7-b'] dithiophene, has been synthesized for use in organic field-effect transistors (OFETs). The molecule consists of a phenanthrene core with two thiophene rings fused on the ends. This molecule can be recognized as a picene analogue. The electronic structure of the molecule was determined by its optical absorption spectrum together with a theoretical calculation based on density functional theory (DFT). The topological and electronic structures of thin films produced by direct thermal evaporation of the compounds and by deposition from a solution were characterized by optical imaging, X-ray diffraction, and atomic force microscopy. FET devices were fabricated with these thin films, and showed field-effect mobility as high as 10(-1) cm(2) V-1 s(-1).

DOI： 10.1039/c3ra44050h

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

We report electronic-structure and physical properties of metal-doped picene as well as selective synthesis of the phase that exhibits 18-K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules, where a softening of Raman scattering peaks enables us to determine the number of transferred electrons. From this, we have identified that three electrons are transferred to each picene molecule in the superconducting doped picene solids. Second, we report pressure dependence of T-c in 7- and 18-K phases of K(3)picene. The 7-K phase shows a negative pressure dependence, while the 18-K phase exhibits a positive pressure dependence which can not be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a synthesis method for superconducting K(3)picene by a solution process with monomethylamine CH3NH2. This method enables us to prepare selectively the K(3)picene sample exhibiting 18-K superconducting transition. The method for preparing K(3)picene with T-c = 18 K found here may facilitate clarification of the mechanism of superconductivity.

DOI： 10.1103/PhysRevB.86.214507

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

Transistor characteristics are studied for field-effect transistors (FETs) with thin films of [6]phenacene, which has six benzene rings and W-shape structure. The molecular alignment preferable for FET transport is found to be formed in [6]phenacene thin films. The transistor shows clear p-channel FET characteristics with field-effect mobility mu as high as 3.7 cm(2) V-1 s(-1). The similar O-2 sensing properties to picene FET are observed in [6]phenacene thin film FET. The bias stress properties are observed in [6]phenacene thin film FET. The pulse-voltage application suppresses the bias-stress effect and it enables a continuous O-2 sensing in [6]phenacene FET. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4747201]

DOI： 10.1063/1.4747201

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

Transistor characteristics and O-2 gas sensing properties are investigated for picene thin film field-effect transistors (FETs) with ZrO2, Ta2O5, HfO2 and BaxSr1-xTiO3 (x = 0.4). The low-voltage operation is achieved using the above oxides with high gate dielectric constant, contrary to SiO2 gate dielectric. The O-2 gas sensing is achieved at 11 s intervals without any bias stress by an application of pulse drain and gate voltages (V-D and V-G), in contrast to previous result in which the O-2 gas sensing was performed at least at 1 h step because of bias stress effect. The actual O-2 sensing-speed in the picene thin film FET was similar to 10 s for 3.8 Torr O-2, and the O-2 sensing limit was concluded to be 0.15-0.38 Torr. Furthermore, it has been found that the O-2 sensing properties are observed only under irradiation of light with wavelength below 400 nm. From the result, we have presented two scenarios for O-2 sensing mechanism in picene thin film FET. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.snb.2012.05.030

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

Picene is a phenacene-type aromatic hydrocarbon molecule with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liquid gate dielectrics. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielectric and TCNQ:coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm(2) V-1 s(-1) in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liquid gate dielectric, [1-butyl-3-methylimidazolium][hexafluorophosphate], showing the field-effect mobility of 1.8 X 10(-1) cm(2) V-1 s(-1) and low absolute value, 1.9 V, of threshold voltage.

DOI： 10.1021/jp300052p

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

Thin film transistors (TFTs) with ionic liquid gate dielectrics, [1-ethyl-3-methylimidazolium][bis(trifluoromethanesulfonyl) imide] (emim[TFSI]) and [1-butyl-3-methylimidazolium][hexafluorophosphate] (bmim[PF6]), are fabricated with thin films of one dimensional (1D) hydrocarbon, [7]phenacene. P-channel characteristics are observed for [7] phenacene TFTs with both ionic liquids by use of platinum electrode. The field-effect mobility mu for [7]phenacene TFT with bmim[PF6] was recorded to be 0.28 cm(2) V-1 s(-1). The value of absolute threshold voltage, vertical bar V-TH vertical bar, was less than 2.5 V, showing low-voltage operation. The accumulation of hole in the [7]phenacene TFTs with ionic liquids was confirmed from the voltage or time dependence of capacitance in metal-insulator-semiconductor structure, which shows that these TFTs operate electrochemically and the carriers are accumulated in the whole of [7]phenacene thin films. (C) 2011 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.orgel.2011.08.016

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

A method for inducing nonuniform strain in graphene films is developed. Pillars made of a dielectric material (electron beam resist) are placed between graphene and the substrate, and graphene sections between pillars are attached to the substrate. The strength and spatial pattern of the strain can be controlled by the size and separation of the pillars. Application of strain is confirmed by Raman spectroscopy as well as from scanning electron microscopy (SEM) images. From SEM images, the maximum stretch of the graphene film reaches about 20%. This technique can be applied to the formation of band gaps in graphene. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/APEX.4.075102

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

While ideal graphene has high mobility due to the relativistic nature of carriers, it is known that the carrier transport in actual graphene samples is dominated by the influence of scattering from charged impurities, which almost conceals the intrinsic splendid properties of this novel material. The common techniques to improve the graphene mobility include the annealing in hydrogen atmosphere and the local annealing by imposing a large biasing current. Although annealing is quite important technique for the experimental study of graphene, detailed evaluation of the annealing effect is lacking at present. In this paper, we study the effect of the current annealing in multilayer graphene devices quantitatively by investigating the change in the mobility and the carrier density at the charge neutrality point. We find that the current annealing sometimes causes degradation of the transport properties.

DOI： 10.1088/1742-6596/232/1/012015

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

We report experimental observation of the proximity-induced supercurrent in superconductor-multilayer graphene-superconductor junctions. We find that the supercurrent is a linearly decreasing function of the junction length (separation of the superconducting electrodes), which is quite different from the usual behavior of exponential dependence. We suggest that this behavior originates from the intrinsic large contact resistance between the multilayer and the superconducting electrodes. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2010.05.142

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We report the gate-voltage dependence of the spin transport in multilayer graphene (MLG) studied experimentally by the local measurement. The sample consists of a Ni/MLG/Ni junction, where the thickness of the MLG is 9 nm and the spacing of two Ni electrodes is 300 nm. At zero gate voltage, we observed the normal spin valve effect, in which the resistance for the antiparallel alignment of magnetization in ferromagnetic electrodes is larger than that for the parallel alignment. By applying a large gate voltage, on the other hand, the spill valve effect is reversed: the resistance for the antiparallel alignment becomes smaller than that for the parallel alignment. The result is qualitatively interpreted as a quantum interference effect, indicating that the mean free path and the spin relaxation length of the MLG are longer than the electrode spacing (300 nm).

DOI： 10.1088/1742-6596/232/1/012002

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

Graphene is a single layer of graphite. Graphene is expected to exhibit the relativistic Josephson effects, when ballistic transport is realized in it. Here, we report a method to fabricate ultrashort graphene Josephson junctions with length as short as several tens of nm, which is much shorter than the estimated mean free path of the graphene film after the junction fabrication processes. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2010.05.146

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

Electric conduction in thin graphite film was tuned by two gate electrodes to clarify how the gate electric field induces electric carriers in thin graphite. The graphite was sandwiched between two gate electrodes arranged in a top and bottom gate configuration. A scan of the top gate voltage generates a resistance peak in ambiploar response. The ambipolar peak is shifted by the bottom gate voltage, where the shift rate depends on the graphite thickness. The thickness-dependent peak shift was clarified in terms of the inter-layer screening length to the electric field in the double-gated graphite film. The screening length of 1.2 nm was experimentally obtained. (C) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.034007

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

We report Coulomb blockade oscillations in an atomically thin graphite ribbon fabricated by the micromechanical cleavage technique. Aperiodic current oscillations as a function of the gate voltage indicate the formation of multiple Coulomb islands inside the thin graphite ribbon. We conclude that the Coulomb islands originate from puddles of electrons and holes caused by the inhomogeneous interface between the ribbon and the substrate. (C) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.024001

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DOI： 10.1016/j.physc.2007.11.050

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DOI： 10.1016/j.physe.2007.09.149

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DOI： 10.1088/1742-6596/109/1/012031

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

We have studied vortex expulsion processes in a superconducting disk with a multi-terminal Hall sensor. Various combinations of these terminals enabled us to obtain an angular dependence of magnetization in the disk. The resolution of π/4 allowed us to identify three vortices. With a decrease in magnetic fields, vortices were expelled one by one from the different edges. After each expulsion the residual vortices were reconfigured in a complicated way. Their equilibrium positions changed with lowering temperatures. These results are interpreted in terms of repulsively interacting particles in the confinement and the pinning potential. The latter potential is found to be important at low temperatures. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2007.06.021

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Magnetic response of a superconductor/normal-metal (S/N) concentric disk is studied by use of a ballistic Hall magnetometer, which enables us to investigate the mutual proximity effects in a single and a micrometer-sized sample. The core of the sample is a type-I superconductor whose diameter is comparable to the coherence length and the magnetic penetration depth. The core and the surround are prepared by an improved double-angle evaporation method to realize their metallic contacts. At T = 1.3 K, the pair breaking effect on the S has been predominant. We have observed the smaller diamagnetic susceptibility, the larger critical field, and the less stable vortex states in the S/N sample than in only S sample. These results are attributed to the suppression of the surface superconductivity, which effectively decreases the diameter of the superconductor.

DOI： 10.1063/1.2354923

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DOI： 10.7209/tanso.2017.188

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DOI： 10.11316/jpsgaiyo.71.2.0_2174

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DOI： 10.11316/jpsgaiyo.71.1.0_1851

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DOI： 10.11316/jpsgaiyo.70.2.0_1995

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

Electric-double-layer (EDL) field-effect transistors are fabricated with thin films of picene, in order to reduce the operation voltage. We used two types of ionic liquids for the picene-thin-film EDL FET (EDLT). One is ionic liquid gel, which provides the absolute threshold voltage (|V_<th>|) as low as 1.87V, while the other is ionic liquid polymer sheet which provides the |V_<th>| as low as 0.87V. The small |V_<th>| values in these EDLTs are available for practical electronic devices, which may lead to the new development for integration of organic transistors

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Language：Japanese   Publisher：The Institute of Electronics, Information and Communication Engineers  

The [6]phenacene molecule consists of six benzene rings and takes a W-shaped structure. It is well known that [6]phenacene field-effect transistor (FET) shows an excellent p-channel FET characteristics. However, the organic FET device has a serious problem that the absolute threshold voltage (|V_<th>|) is too high. Actually, the [6]phenacene thin film FET has such a serious problem. Here we tried to insert either electron acceptor or donor in the interface between [6]phenacene thin film and SiO_2 gate dielectric in order to decrease the |V_<th>|. In this study, we used diverse electron acceptors and donors, and the variation of |V_<th>| was systematically investigated, showing the V_<th>-shift of 30V in some electron acceptors. Furthermore, the drastic change of mobility (μ) in [6]phenacene FET was observed depending on the hydrophobic treatment of surface of SiO_2 gate dielectric, showing the μ value increased up to 5.0cm^2V^<-1>s^<-1> by the hydrophobic treatment with hexamethyldisilazane (HMDS).

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DOI： 10.11316/jpsgaiyo.69.1.3.0_561_4

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DOI： 10.11316/jpsgaiyo.68.2.3.0_587_2

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

DOI： 10.1016/j.physc.2010.05.146

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

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

DOI： 10.1016/j.physc.2010.05.146

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

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Language：Japanese   Publisher：The Vacuum Society of Japan  

&nbsp;&nbsp;Present understanding of electric transport in graphene, a crystalline layer of carbon, is reviewed. In the first part, emphasis is placed on the gap between the ideal and reality of electron transport, which is mostly caused by disorder (charged impurities) in the experimental samples. Disorder which affects the graphene transport originates mainly from charged impurities in the substrate, comtaminants on the graphene surface due to, e.g., resists and sticky tapes, and absorbed gas molecules. The amount of charged impurities and the methods to remove them are discussed. In the second part, the characteristic phenomena in multilayer graphene are explained for spins and Cooper-pair transport, which are relevant to the nonuniform distribution of the carrier density under nonzero gate voltages.<br>

DOI： 10.3131/jvsj2.53.85

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

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

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

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

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Language：Japanese   Publisher：Bussei Kenkyu  

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Other Link： http://hdl.handle.net/2433/142726

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyog.48.3.0_234_2

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyod.47.3.0_367_2

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyod.46.3.0_298_1

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Warsaw, Poland  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Sapienza University of Rome, Italy  

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Language：English   Presentation type：Poster presentation  

Venue：Okayama University, Okayama, Japan  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Ischia, Naples, Italy  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Okayama University, Okayama, Japan  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：San Sebastian, Spain  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Okayama University, Okayama, Japan  

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Language：English   Presentation type：Poster presentation  

Venue：Miramare-Trieste, Italy  

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Language：English   Presentation type：Poster presentation  

Venue：Tokyo Institute of Technology, Tokyo, Japan  

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Language：English   Presentation type：Poster presentation  

Venue：Sendai, Japan  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Ha Long City, Vietnam  

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Language：English   Presentation type：Oral presentation (general)  

Venue：Ischia, Naples, Italy  

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Language：English   Presentation type：Poster presentation  

Venue：Okayama University, Japan  

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Language：English   Presentation type：Oral presentation (invited, special)  

Venue：National University of Singapore, Singapore  

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