担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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出版者・発行元：AIP  

DOI： 10.1063/1.2937836

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.3c03737

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.3c02254

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcc.3c06294

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.inorgchem.3c02405

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.108.035146

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.chemmater.3c00391

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.inorgchem.3c00744

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier {BV}  

DOI： 10.1016/j.elspec.2023.147295

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： https://www.nature.com/articles/s41598-023-27701-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.inorgchem.2c03365

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.2c06505

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcc.2c04879

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcc.2c01972

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-648x/ac244b

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/ac244b/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/d1cp00042j

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.jpcc.1c06207

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.inorgchem.0c02836

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/d1ra00511a

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-648x/abd99c

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/abd99c/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/physrevb.102.155118

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.102.155118/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/d0cp04771f

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-648x/abaad2

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/abaad2/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/d0ra04541a

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-648x/ab9911

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-648X/ab9911/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2053-1591/ab7c85

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その他リンク： https://iopscience.iop.org/article/10.1088/2053-1591/ab7c85/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1367-2630/ab5034

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.7567/1347-4065/ab4ef5

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その他リンク： http://iopscience.iop.org/article/10.7567/1347-4065/ab4ef5/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-648X/ab4605

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.100.094525

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c8tc05824e

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-019-41906-7

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その他リンク： http://www.nature.com/articles/s41598-019-41906-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-019-39899-4

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PubMed

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記述言語：英語  

DOI： 10.1088/2053-1591/aae9d2

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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 < 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 > 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：Pan Stanford Publishing Pte. Ltd.  

DOI： 10.1201/b19365

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-BLACKWELL  

DOI： 10.1002/aelm.201500085

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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 <= 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Royal Society of Chemistry  

DOI： 10.1039/c5tc90044a

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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, <mu >, 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 <|V-th|> of similar to 11 V, was implemented, together with the above high <mu > 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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, <mu >, 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 <mu > and average values of absolute threshold voltage, <vertical bar V-th vertical bar >, 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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記述言語：英語   出版者・発行元：ROYAL SOC CHEMISTRY  

DOI： 10.1039/c5tc90044a

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記述言語：英語   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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 (<mu >) 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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4795626

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1088/1742-6596/232/1/012015

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.physc.2010.05.142

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1088/1742-6596/232/1/012002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.physc.2010.05.146

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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出版者・発行元：North-Holland  

DOI： 10.1016/j.physc.2007.11.050

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出版者・発行元：Elsevier  

DOI： 10.1016/j.physe.2007.09.149

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DOI： 10.1088/1742-6596/109/1/012031

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：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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記述言語：日本語  

DOI： 10.7209/tanso.2017.188

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>(NH_3_)_y_M_x_FeSe (M: Li, Cs)では高圧での高温超伝導相の存在が確認されている。この高圧超伝導相は圧力印加に伴い常圧超伝導相が一度消失した後に、再び超伝導相が現れるという興味深い性質を示している。したがって、他の金属原子を挿入したFeSe結晶での高圧超伝導特性を調べることは、この物質の超伝導機構の解明につながることになる。さらに、本研究の主題としているNaを挿入したFeSeは2つの常圧超伝導相を有するため、それぞれの超伝導相の高圧での特性を調べることは興味深い。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_2174

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>電子供与性をもつ自己組織化単分子膜上に2層グラフェンデバイスを作製し、その上から電子受容性をもつ分子を吸着させることで、2種類の分子がつくる電界を用いて2層グラフェンにバンドギャップを開けることを試みた。しかし、伝導率の温度依存性はバンドギャップが開くというよりも、微小なpn接合が散乱体として働いていることを示した。この原因について、上下層の分子がつくる微視的な電場から考察する。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_1691

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

<p>二次元層状物質のMoS2において電界誘起超伝導が観測されて以来、遷移金属ダイカルコゲナイド系の化合物への電界効果キャリア注入が注目されている。本研究では、SeとTeの濃度を変えた薄い単結晶を用いた電界効果トランジスタを作製し、カルコゲンの種類とその濃度が電界効果トランジスタ動作に与える影響について考察する。また、イオン液体による電気二重層を用いて電界効果キャリアドーピングを行い、新規な超伝導相の可能性を探る。</p>

DOI： 10.11316/jpsgaiyo.71.2.0_2198

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2377

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2150

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_1929

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_2151

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.71.1.0_1851

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2066

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_1894

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2751

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_1246

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.1.0_2236

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DOI： 10.11316/jpsgaiyo.70.2.0_1719

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1994

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1718

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

DOI： 10.11316/jpsgaiyo.70.2.0_1995

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

有機薄膜電界効果トランジスタ(FET)の駆動に要する電圧である「しきい値電圧」(V_<th>)が非常に高いため,実用化に向けて大きな問題となっている.本研究は,イオン液体を用いたFETである電気二重層トランジスタ(Electric Double-Layer Transistor:EDLT)を使って,この問題を解決することを目指している.活性層としてピセン薄膜を用いてEDLTを作製し,その特性を詳細に評価した.固体酸化物である400nm厚みのSiO_2をゲート絶縁膜として用いたピセン薄膜FETでは,V_<th>の絶対値(|V_<th>|)が70V程度であるのに対し,ゲル状のイオン液体を用いたEDLTでは,1.7Vで駆動させることができた.また,イオン液体をシート状にしたものを用いたEDLTでは,0.87Vで駆動させることに成功した.これらピセンEDLTの|V_<th>|は,実用化を視野に入れた研究開発を行うため,集積化などへの取り組みを開始できるものと期待される.

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

[6]フェナセンは,6個のベンゼン環がジグザグに結合した分子である.この薄膜を活性層とする有機薄膜電界効果トランジスタ(FET)は,非常に良好なpチャネル型のFET特性を示す.しかし,一般に有機薄膜FETには「しきい値電圧」の絶対値(|V_<th>|)が大きいという問題がある.[6]フェナセンFETにおいても,この特徴が存在するので,これを解決し[6]フェナセンFETを実用デバイスに向けて発展させることが重要である.本研究は,これまであまり注目されなかった有機分子薄膜(活性層)とSiO_2ゲート誘電絶縁膜の界面制御によって,V_<th>を変化させる可能性を探る.このため,系統的に電子受容体もしくは供与体分子を界面に挿入することでV_<th>の変化を観測した.また,絶縁膜表面をパリレンからヘキサメチルジシラザン(HMDS)に変えることで,移動度を5.0cm^2V^<-1>s^<-1>まで向上させることに成功した.

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.1.3.0_561_4

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.68.2.3.0_587_2

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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J-GLOBAL

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

DOI： 10.1016/j.physc.2010.05.146

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

DOI： 10.1016/j.physc.2010.05.146

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人 日本真空学会  

&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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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：物性研究刊行会  

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その他リンク： http://hdl.handle.net/2433/142726

記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyog.48.3.0_234_2

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyod.47.3.0_367_2

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyod.46.3.0_298_1

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記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Warsaw, Poland  

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記述言語：英語   会議種別：口頭発表（一般）  

開催地：Sapienza University of Rome, Italy  

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記述言語：英語   会議種別：ポスター発表  

開催地：Okayama University, Okayama, Japan  

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記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：Ischia, Naples, Italy  

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記述言語：英語   会議種別：口頭発表（一般）  

開催地：Okayama University, Okayama, Japan  

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記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：San Sebastian, Spain  

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記述言語：英語   会議種別：口頭発表（一般）  

開催地：Okayama University, Okayama, Japan  

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記述言語：英語   会議種別：ポスター発表  

開催地：Miramare-Trieste, Italy  

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記述言語：英語   会議種別：ポスター発表  

開催地：Tokyo Institute of Technology, Tokyo, Japan  

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記述言語：英語   会議種別：ポスター発表  

開催地：Sendai, Japan  

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記述言語：英語   会議種別：口頭発表（一般）  

開催地：Ha Long City, Vietnam  

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記述言語：英語   会議種別：口頭発表（一般）  

開催地：Ischia, Naples, Italy  

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記述言語：英語   会議種別：ポスター発表  

開催地：Okayama University, Japan  

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記述言語：英語   会議種別：口頭発表（招待・特別）  

開催地：National University of Singapore, Singapore  

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