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126 results on '"Sakanoue, Tomo"'

2. Photodetection in p-n junctions formed by electrolyte-gated transistors of two-dimensional crystals

Author

Kozawa, Daichi, Pu, Jiang, Shimizu, Ryo, Kimura, Shota, Chiu, Ming-Hui, Matsuki, Keiichiro, Wada, Yoshifumi, Sakanoue, Tomo, Iwasa, Yoshihiro, Li, Lain-Jong, and Takenobu, Taishi

Subjects
Condensed Matter - Materials Science
Abstract

Transition metal dichalcogenide (TMDC) monolayers have attracted much attention due to their strong light absorption and excellent electronic properties. These advantages make this type of two-dimensional crystal a promising one for optoelectronic device applications. In the case of photoelectric conversion devices such as photodetectors and photovoltaic cells, p-n junctions are one of the most important devices. Here, we demonstrate photodetection with WSe2 monolayer films. We prepare the electrolyte-gated ambipolar transistors and electrostatic p-n junctions are formed by the electrolyte-gating technique at 270 K. These p-n junctions are cooled down to fix the ion motion (and p-n junctions) and we observed the reasonable photocurrent spectra without the external bias, indicating the formation of p-n junctions. Very interestingly, two-terminal devices exhibit higher photoresponsivity than that of three-terminal ones, suggesting the formation of highly balanced anion and cation layers. The maximum photoresponsivity reaches 5 mA/W in resonance with the first excitonic peak. Our technique provides important evidence for optoelectronics in atomically thin crystals., Comment: Accepted in Applied Physics Letters (2016)

Published
2016
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7. Ultrafast photoinduced electron transfer in face-to-face charge-transfer π-complexes of planar porphyrins and hexaazatriphenylene derivatives† †Electronic supplementary information (ESI) available: 1H, 13C NMR and MALDI-TOF mass spectra, cyclic voltammograms, fluorescence spectra, fluorescence titration spectra, 1H NMR titration, femtosecond laser-induced transient absorption spectral measurement data, and DFT data. See DOI: 10.1039/c4sc02787f Click here for additional data file

Author

Aoki, Toru, Sakai, Hayato, Ohkubo, Kei, Sakanoue, Tomo, Takenobu, Taishi, Fukuzumi, Shunichi, and Hasobe, Taku

Subjects
Physics::Biological Physics, Chemistry
Abstract

We have successfully observed ultrafast photoinduced electron transfer in face-to-face charge-transfer π-complexes of planar porphyrins and hexaazatriphenylene derivatives., Charge-transfer (CT) π-complexes are formed between planar porphyrins and 1,4,5,8,9,12-hexaazatriphenylene (HAT) derivatives with large formation constants (e.g., 104 M–1), exhibiting broad CT absorption bands. The unusually large formation constants result from close face-to-face contact between two planar π-planes of porphyrins and HAT derivatives. The redox potentials of porphyrins and HAT derivatives measured by cyclic voltammetry indicate that porphyrins and HAT derivatives act as electron donors and acceptors, respectively. The formation of 1 : 1 CT complexes between porphyrins and HAT derivatives was examined by UV-vis, fluorescence and 1H NMR measurements in nonpolar solvents. The occurrence of unprecedented ultrafast photoinduced electron transfer from the porphyrin unit to the HAT unit in the CT π-complex was observed by femtosecond laser flash photolysis measurements. A highly linear aggregate composed of a planar porphyrin and an HAT derivative was observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM).

Published
2014

13. Charge separation and transport behavior of a two-dimensional charge sheet at organic donor-acceptor heterointerfaces.

Author

Sakanoue, Tomo, Irie, Toru, and Adachi, Chihaya

Subjects
*INTERFACES (Physical sciences), *ELECTRON donor-acceptor complexes, *EXCITON theory, *MOLECULAR orbitals, *LIGHT emitting diodes
Abstract

Charge separation and transport behavior were investigated at an organic heterolayered interface consisting of a 4,4′,4″-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) organic donor and a hexadecafluoro-copper-phthalocyanine (F16CuPc) organic acceptor. A two-dimensional charge sheet of electron-hole pairs was induced due to the formation of charge-transfer complexes at the heterointerface. The induced charges could be separated by application of an electric field perpendicular to the heterointerface. The charge-separation behavior was independent of the work function of the contact electrodes but was strongly dependent on the energy-level alignment between the highest occupied molecular orbital of the donor molecules and the lowest unoccupied molecular orbital of the acceptor molecules. This enabled the preparation of an organic light-emitting diode without injecting holes from the anode. The charge-transport behavior along the heterointerface was also investigated by fabricating laterally arranged contact electrodes. The F16CuPc/m-MTDATA heterointerface exhibited high conductivity of 0.001 S/cm, which is seven orders of magnitude higher than that of a single-layer F16CuPc or m-MTDATA film. In situ electrical measurements during formation of the heterointerface enabled the effective thickness of the charge sheet to be determined as being accumulated within 2–3 nm, which corresponds to the bilayer of both F16CuPc and m-MTDATA. [ABSTRACT FROM AUTHOR]

Published
2009
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14. Electrical characteristics of single-component ambipolar organic field-effect transistors and effects of air exposure on them.

Author

Sakanoue, Tomo, Yahiro, Masayuki, Adachi, Chihaya, Takimiya, Kazuo, and Toshimitsu, Akio

Subjects
*PARTICLES (Nuclear physics), *ELECTRON mobility, *FREE electron theory of metals, *FIELD-effect transistors, *ELECTRON distribution
Abstract

We investigated the electrical characteristics of single-component ambipolar organic field-effect transistors (OFETs) by controlling the device structure and preparation and the measurement conditions. Six organic semiconductor materials (copper-phthalocyanine, tris-(8-hydroxyquinoline)aluminum (Alq3), alpha-sexithiophene, 4-4′-bis-styrylphenyl, 2,7-diphenyl[1]benzothieno[3,2-b]benzothiophene, or a photopolymerized polydiacethylene derivative (PDA) were used as the active layer, and all were found to transport both holes and electrons. The PDA-based FETs had the highest hole and electron mobilities (0.12 and 0.025 cm2/V s, respectively). We also investigated the effect of air exposure on the OFETs. The hole mobility was barely affected by the exposure while the electron mobility was significantly affected. The threshold voltage for p-channel operation was shifted by the exposure while that for n-channel operation was not, indicating that the hole density in the active layer is increased by air exposure whereas the electron density is independent of air exposure. Furthermore, we prepared an Alq3-based p-channel OFET and investigated the effect of air exposure on it. While its operation was stable in vacuum, air exposure degraded its characteristics. These behaviors indicate that irreversible chemical reactions occur between cationic Alq3 species and oxygen or water molecules. [ABSTRACT FROM AUTHOR]

Published
2008
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38. Hall-Effect Measurements Probing the Degree of Charge-Carrier Delocalization in Solution-Processed Crystalline Molecular Semiconductors

Author

Chang, Jui-Fen, primary, Sakanoue, Tomo, additional, Olivier, Yoann, additional, Uemura, Takafumi, additional, Dufourg-Madec, Marie-Beatrice, additional, Yeates, Stephen G., additional, Cornil, Jérôme, additional, Takeya, Jun, additional, Troisi, Alessandro, additional, and Sirringhaus, Henning, additional

Published
2011
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