The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Shuit-tong Lee - One of the best experts on this subject based on the ideXlab platform.
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Ultraviolet Photoelectron Spectroscopy investigation of interface formation in an indium tin oxide fluorocarbon organic semiconductor contact
Applied Surface Science, 2006Co-Authors: S.w. Tong, K.m. Lau, H.y. Sun, Man-keung Fung, Chun-sing Lee, Yeshayahu Lifshitz, Shuit-tong LeeAbstract:Abstract It has been demonstrated that hole-injection in organic light-emitting devices (OLEDs) can be enhanced by inserting a UV-illuminated fluorocarbon (CFx) layer between indium–tin oxide (ITO) and organic hole-transporting layer (HTL). In this work, the process of interface formation and electronic properties of the ITO/CFx/HTL interface were investigated with Ultraviolet Photoelectron Spectroscopy. It was found that UV-illuminated fluorocarbon layer decreases the hole-injection barrier from ITO to α-napthylphenylbiphenyl diamine (NPB). Energy level diagrams deduced from the Ultraviolet Photoelectron Spectroscopy (UPS) spectra show that the hole-injection barrier in ITO/UV-treated CFx/NPB is the smallest (0.46 eV), compared to that in the ITO/untreated CFx/NPB (0.60 eV) and the standard ITO/NPB interface (0.68 eV). The improved current density–voltage (I–V) characteristics in the UV-treated CFx-coated ITO contact are consistent with its smallest barrier height.
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Ultraviolet Photoelectron Spectroscopy investigation of interface formation in an indium–tin oxide/fluorocarbon/organic semiconductor contact
Applied Surface Science, 2006Co-Authors: S.w. Tong, K.m. Lau, H.y. Sun, Man-keung Fung, Chun-sing Lee, Yeshayahu Lifshitz, Shuit-tong LeeAbstract:Abstract It has been demonstrated that hole-injection in organic light-emitting devices (OLEDs) can be enhanced by inserting a UV-illuminated fluorocarbon (CFx) layer between indium–tin oxide (ITO) and organic hole-transporting layer (HTL). In this work, the process of interface formation and electronic properties of the ITO/CFx/HTL interface were investigated with Ultraviolet Photoelectron Spectroscopy. It was found that UV-illuminated fluorocarbon layer decreases the hole-injection barrier from ITO to α-napthylphenylbiphenyl diamine (NPB). Energy level diagrams deduced from the Ultraviolet Photoelectron Spectroscopy (UPS) spectra show that the hole-injection barrier in ITO/UV-treated CFx/NPB is the smallest (0.46 eV), compared to that in the ITO/untreated CFx/NPB (0.60 eV) and the standard ITO/NPB interface (0.68 eV). The improved current density–voltage (I–V) characteristics in the UV-treated CFx-coated ITO contact are consistent with its smallest barrier height.
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Modification of the hole injection barrier in organic light-emitting devices studied by Ultraviolet Photoelectron Spectroscopy
Applied Physics Letters, 2000Co-Authors: X. M. Ding, Chun-sing Lee, Liang-sun Hung, L. F. Cheng, Z. B. Deng, Xiaoyuan Hou, Shuit-tong LeeAbstract:Ultraviolet Photoelectron Spectroscopy has been applied to the investigation of modified hole injection barriers in organic light-emitting devices (OLEDs). Different from those reported previously, the indium tin oxide (ITO) surface treated in situ by oxygen plasma possesses a work function of 5.2 eV, and the organic ITO interface thereafter formed shows a 0.5 eV smaller hole injection barrier compared to that on untreated ITO. Insertion of an ultrathin SiO2 layer between the organic and ITO results in a similar reduction of the barrier. This indicates that improved hole injection favors efficient operation of OLEDs, as manifested by enhanced efficiency by the SiO2 insertion.
Junfa Zhu - One of the best experts on this subject based on the ideXlab platform.
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band alignment of zno cdse quantum dots heterojunction determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation
Applied Surface Science, 2013Co-Authors: Chunfeng Cai, Wenhua Zhang, Junfa ZhuAbstract:Abstract Band alignments of ZnO/CdSe nanocrystal quantum-dots (NQDs) heterojunctions are determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation source. To obtain ideal heterojunction interface, 1,2-ethanedithiol was used for CdSe NQDs as a ligand substitute. A type II band alignment of the ZnO/CdSe NQDs heterojunctions with changeable band offsets by varying the sizes of CdSe NQDs is concluded. The tunable band alignment of ZnO/CdSe NQDs heterojunctions is beneficial to the improvement of the design and fabrication of quantum-dot-sensitized solar cells.
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Band alignment of ZnO/CdSe quantum dots heterojunction determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation
Applied Surface Science, 2013Co-Authors: Chunfeng Cai, Wenhua Zhang, Junfa ZhuAbstract:Abstract Band alignments of ZnO/CdSe nanocrystal quantum-dots (NQDs) heterojunctions are determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation source. To obtain ideal heterojunction interface, 1,2-ethanedithiol was used for CdSe NQDs as a ligand substitute. A type II band alignment of the ZnO/CdSe NQDs heterojunctions with changeable band offsets by varying the sizes of CdSe NQDs is concluded. The tunable band alignment of ZnO/CdSe NQDs heterojunctions is beneficial to the improvement of the design and fabrication of quantum-dot-sensitized solar cells.
Satoshi Kera - One of the best experts on this subject based on the ideXlab platform.
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Anisotropic valence band dispersion of single crystal pentacene as measured by angle-resolved Ultraviolet Photoelectron Spectroscopy
Journal of Materials Research, 2018Co-Authors: Yasuo Nakayama, Masataka Hikasa, Naoki Moriya, Matthias Meissner, Takuma Yamaguchi, Koki Yoshida, Mimi Murata, Kazuhiko Mase, Takahiro Ueba, Satoshi KeraAbstract:Electronic structures of single crystal pentacene are of great interest for the elucidation of charge carrier transport in organic semiconductor materials. Experimental observation of valence band dispersion was recently achieved on single crystal samples of pentacene; however, its intrinsic properties are still unresolved because past experiments were performed on specimens with surface oxides formed by exposure to the ambient atmosphere. In this work, X-ray Photoelectron Spectroscopy (XPS) and angle-resolved Ultraviolet Photoelectron Spectroscopy (ARUPS) were conducted on single-crystal pentacene samples prepared without ambient exposure. The XPS results confirmed the reduction of the abundance of oxide impurities on the present samples. The ARUPS measurements clearly resolved the valence band structures of the single-crystal pentacene in four symmetry directions of the surface Brillouin zone, indicating anisotropy of at least a factor of 2.4 for the intermolecular transfer integral and hole effective mass at the valence band maximum.
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Ultraviolet Photoelectron Spectroscopy (UPS) II: Electron–Phonon Coupling and Hopping Mobility
Electronic Processes in Organic Electronics, 2014Co-Authors: Satoshi Kera, Hiroyuki Yamane, Nobuo UenoAbstract:The study of charge mobility in organic semiconductor systems has been one of the most important subjects that has remained a puzzle for many years. It is essential to quantitatively understand conduction charge-molecular vibration coupling as well as the intermolecular interaction to discuss mobility. This chapter describes recent successes with direct measurements of valence hole-vibration coupling in ultrathin films of organic semiconductors by using Ultraviolet Photoelectron Spectroscopy (UPS), which can be used to experimentally study charge mobility based on energy and momentum conservation rules. The method may thus be categorized as a first-principles study of charge mobility. The detection of hole-vibration coupling of the highest occupied molecular orbital (HOMO) state in a thin film by UPS is essential to comprehend hole-hopping transport and polaron-related transport in organic semiconductors. Only careful measurements can attain the high-resolution spectra and provide these key parameters in hole-transport dynamics. A key method in achieving such high-resolution UPS measurements is also described.
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Ultraviolet Photoelectron Spectroscopy (UPS) I: Band Dispersion Measurements of “Insulating” Organic Single Crystals
Electronic Processes in Organic Electronics, 2014Co-Authors: Yasuo Nakayama, Steffen Duhm, Qian Xin, Satoshi Kera, Hisao Ishii, Nobuo UenoAbstract:Operation mechanisms and efficiencies of organic electronic devices are principally dominated by the electronic structures of organic semiconductor solids via charge carrier behaviors inside the active materials of the devices; that is the band dispersion for high-mobility crystalline materials being desirable to e.g. organic field effect transistor application. Angle-resolved Ultraviolet Photoelectron Spectroscopy (ARUPS) is one of the most direct and sophisticated techniques to access the valence band of the matters. Several essential physical properties, the effective mass of transport hole and intermolecular transfer integral, in direct relevance to the charge carrier mobility are accessible through accurate analyses of the ARUPS results. In this chapter, we describe technical essences of this methodology and introduce several examples of successful demonstrations of the valence band structures of crystalline organic semiconducting materials.
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Charge reorganization energy and small polaron binding energy of rubrene thin films by Ultraviolet Photoelectron Spectroscopy.
Advanced materials (Deerfield Beach Fla.), 2012Co-Authors: Steffen Duhm, Qian Xin, Shunsuke Hosoumi, Hirohiko Fukagawa, Kazushi Sato, Nobuo Ueno, Satoshi KeraAbstract:The hole–phonon coupling of a rubrene monolayer on graphite is measured by means of angle resolved Ultraviolet Photoelectron Spectroscopy. Thus, the charge reorganization energy λ and the small polaron binding energy is determined, which allows insight into the nature of charge transport in condensed rubrene.
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highest occupied molecular orbital band dispersion of rubrene single crystals as observed by angle resolved Ultraviolet Photoelectron Spectroscopy
Physical Review Letters, 2010Co-Authors: Shin Ichi Machida, Steffen Duhm, Qian Xin, Nobuo Ueno, Satoshi Kera, Yasuo Nakayama, Akihiro Funakoshi, Naoki Ogawa, Hisao IshiiAbstract:The electronic structure of rubrene single crystals was studied by angle-resolved Ultraviolet Photoelectron Spectroscopy. A clear energy dispersion of the highest occupied molecular orbital-derived band was observed, and the dispersion width was found to be 0.4 eV along the well-stacked direction. The effective mass of the holes was estimated to be $0.65(\ifmmode\pm\else\textpm\fi{}0.1){m}_{0}$. The present results suggest that the carrier conduction mechanism in rubrene single crystals can be described within the framework of band transport.
Nobuo Ueno - One of the best experts on this subject based on the ideXlab platform.
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Ultraviolet Photoelectron Spectroscopy (UPS) II: Electron–Phonon Coupling and Hopping Mobility
Electronic Processes in Organic Electronics, 2014Co-Authors: Satoshi Kera, Hiroyuki Yamane, Nobuo UenoAbstract:The study of charge mobility in organic semiconductor systems has been one of the most important subjects that has remained a puzzle for many years. It is essential to quantitatively understand conduction charge-molecular vibration coupling as well as the intermolecular interaction to discuss mobility. This chapter describes recent successes with direct measurements of valence hole-vibration coupling in ultrathin films of organic semiconductors by using Ultraviolet Photoelectron Spectroscopy (UPS), which can be used to experimentally study charge mobility based on energy and momentum conservation rules. The method may thus be categorized as a first-principles study of charge mobility. The detection of hole-vibration coupling of the highest occupied molecular orbital (HOMO) state in a thin film by UPS is essential to comprehend hole-hopping transport and polaron-related transport in organic semiconductors. Only careful measurements can attain the high-resolution spectra and provide these key parameters in hole-transport dynamics. A key method in achieving such high-resolution UPS measurements is also described.
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Ultraviolet Photoelectron Spectroscopy (UPS) I: Band Dispersion Measurements of “Insulating” Organic Single Crystals
Electronic Processes in Organic Electronics, 2014Co-Authors: Yasuo Nakayama, Steffen Duhm, Qian Xin, Satoshi Kera, Hisao Ishii, Nobuo UenoAbstract:Operation mechanisms and efficiencies of organic electronic devices are principally dominated by the electronic structures of organic semiconductor solids via charge carrier behaviors inside the active materials of the devices; that is the band dispersion for high-mobility crystalline materials being desirable to e.g. organic field effect transistor application. Angle-resolved Ultraviolet Photoelectron Spectroscopy (ARUPS) is one of the most direct and sophisticated techniques to access the valence band of the matters. Several essential physical properties, the effective mass of transport hole and intermolecular transfer integral, in direct relevance to the charge carrier mobility are accessible through accurate analyses of the ARUPS results. In this chapter, we describe technical essences of this methodology and introduce several examples of successful demonstrations of the valence band structures of crystalline organic semiconducting materials.
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Charge reorganization energy and small polaron binding energy of rubrene thin films by Ultraviolet Photoelectron Spectroscopy.
Advanced materials (Deerfield Beach Fla.), 2012Co-Authors: Steffen Duhm, Qian Xin, Shunsuke Hosoumi, Hirohiko Fukagawa, Kazushi Sato, Nobuo Ueno, Satoshi KeraAbstract:The hole–phonon coupling of a rubrene monolayer on graphite is measured by means of angle resolved Ultraviolet Photoelectron Spectroscopy. Thus, the charge reorganization energy λ and the small polaron binding energy is determined, which allows insight into the nature of charge transport in condensed rubrene.
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highest occupied molecular orbital band dispersion of rubrene single crystals as observed by angle resolved Ultraviolet Photoelectron Spectroscopy
Physical Review Letters, 2010Co-Authors: Shin Ichi Machida, Steffen Duhm, Qian Xin, Nobuo Ueno, Satoshi Kera, Yasuo Nakayama, Akihiro Funakoshi, Naoki Ogawa, Hisao IshiiAbstract:The electronic structure of rubrene single crystals was studied by angle-resolved Ultraviolet Photoelectron Spectroscopy. A clear energy dispersion of the highest occupied molecular orbital-derived band was observed, and the dispersion width was found to be 0.4 eV along the well-stacked direction. The effective mass of the holes was estimated to be $0.65(\ifmmode\pm\else\textpm\fi{}0.1){m}_{0}$. The present results suggest that the carrier conduction mechanism in rubrene single crystals can be described within the framework of band transport.
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Low-density band-gap states in pentacene thin films probed with ultrahigh-sensitivity Ultraviolet Photoelectron Spectroscopy
Applied Physics Letters, 2009Co-Authors: Tomoki Sueyoshi, Hirohiko Fukagawa, Satoshi Kera, Masaki Ono, Nobuo UenoAbstract:We detected a very low density of electronic states in the band gap of a nondoped pentacene thin film by using Ultraviolet Photoelectron Spectroscopy with ultrahigh sensitivity and ultralow background. The gap states, which may originate from the highest occupied molecular orbital (HOMO) state in imperfect molecular packing regions, are distributed exponentially up to the Fermi level and control the Fermi level relative to the HOMO band.
Chunfeng Cai - One of the best experts on this subject based on the ideXlab platform.
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band alignment of zno cdse quantum dots heterojunction determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation
Applied Surface Science, 2013Co-Authors: Chunfeng Cai, Wenhua Zhang, Junfa ZhuAbstract:Abstract Band alignments of ZnO/CdSe nanocrystal quantum-dots (NQDs) heterojunctions are determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation source. To obtain ideal heterojunction interface, 1,2-ethanedithiol was used for CdSe NQDs as a ligand substitute. A type II band alignment of the ZnO/CdSe NQDs heterojunctions with changeable band offsets by varying the sizes of CdSe NQDs is concluded. The tunable band alignment of ZnO/CdSe NQDs heterojunctions is beneficial to the improvement of the design and fabrication of quantum-dot-sensitized solar cells.
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Band alignment of ZnO/CdSe quantum dots heterojunction determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation
Applied Surface Science, 2013Co-Authors: Chunfeng Cai, Wenhua Zhang, Junfa ZhuAbstract:Abstract Band alignments of ZnO/CdSe nanocrystal quantum-dots (NQDs) heterojunctions are determined by Ultraviolet Photoelectron Spectroscopy using synchrotron radiation source. To obtain ideal heterojunction interface, 1,2-ethanedithiol was used for CdSe NQDs as a ligand substitute. A type II band alignment of the ZnO/CdSe NQDs heterojunctions with changeable band offsets by varying the sizes of CdSe NQDs is concluded. The tunable band alignment of ZnO/CdSe NQDs heterojunctions is beneficial to the improvement of the design and fabrication of quantum-dot-sensitized solar cells.
