Tomoaki Masuzawa
Shizuoka University
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Publication
Featured researches published by Tomoaki Masuzawa.
Journal of Physics D | 2016
Takatoshi Yamada; Tomoaki Masuzawa; Hidenori Mimura; Ken Okano
Hydrogen (H)-terminated surfaces of diamond have attracted significant attention due to their negative electron affinity (NEA), suggesting high-efficiency electron emitters. Combined with n-type doping technique using phosphorus (P) as donors, the unique NEA surface makes diamond a promising candidate for vacuum cold-cathode applications. However, high-electric fields are needed for the electron emission from the n-type doped diamond with NEA. Here we have clarified the electron emission mechanism of field emission from P-doped diamond having NEA utilizing combined ultraviolet photoelectron spectroscopy/field emission spectroscopy (UPS/FES). An UP spectrum has confirmed the NEA of H-terminated (1 1 1) surface of P-doped diamond. Despite the NEA, electron emission occurs only when electric field at the surface exceeds 4.2 × 106 V cm−1. Further analysis by UPS/FES has revealed that the emitted energy level is shifted, indicating that the electron emission mechanism of n-type diamond having NEA surface does not follow a standard field emission theory, but is dominated by potential barrier formed within the diamond due to upward band bending. The reduction of internal barrier is the key to achieve high-efficiency electron emitters using P-doped diamond with NEA, of which application ranges from high-resolution electron spectroscopy to novel vacuum nanoelectronics devices.
international vacuum nanoelectronics conference | 2016
Yasuhito Gotoh; Hiroshi Tsuji; Tamotsu Okamoto; Masayoshi Nagao; Masafumi Akiyoshi; Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Nobuhiro Sato; Ikuji Takagi
Radiation tolerance of a field emitter array and a cadmium telluride-based photoconductor was investigated. The variation of the performance of these devices were investigated during the γ-ray irradiation by every 100-200 kGy. Total dose of irradiation reached 1.2 MGy, but no significant deterioration of the properties has been observed. A test tube exhibited successful photo-signal detection even after the irradiation of 1 MGy. As a result, it was found that the field emitter array and the photoconductor have sufficient radiation tolerance against γ-ray irradiation.
international vacuum nanoelectronics conference | 2014
Takatoshi Yamada; Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Taishi Ebisudani; Ken Okano; Takashi Taniguchi
Graphene/hexagonal boron nitride (h-BN) was characterized. Field emission from graphene/h-BN/Si structure showed low threshold voltage and enhanced emission current. Fowler-Nordheim (F-N) plots were applied to discuss the obtained field emission properties. We also examined work function using ultraviolet photoelectron spectroscopy (UPS). The obtained data suggested that graphene modified work function and possibility of graphene field emitters.
international vacuum nanoelectronics conference | 2017
Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Akinori Ohata; Jun Ochiai; Joshua D. John; Ichitaro Saito; Ken Okano; Takatoshi Yamada
In this study, amorphous selenium based photoconductor with different film thicknesses were fabricated and applied to prototype photodetectors. The use of thick photoconductor resulted in higher sensitivity due to carrier multiplication. Advantages and disadvantages of the thick photoconductor were investigated.
international vacuum nanoelectronics conference | 2017
Takatoshi Yamada; Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Shuichi Ogawa; Yuji Takakuwa; Ken Okano
Energies of emitted electrons from n-type diamond NEA surface and graphene/n-type diamond junction were measured by combined field emission spectroscopy/ultraviolet photoelectrons spectroscopy (FES/UPS) system. For n-type diamond NEA surface, the energies of emitted electrons indicated that the electrons emitted from conduction band of the diamond. For graphene/diamond junction, electron emission from both valance bands of diamond and graphene are confirmed.
Archive | 2017
Hisaya Nakagawa; Tsuyoshi Terao; Tomoaki Masuzawa; Tetsu Ito; Hisashi Morii; Akifumi Koike; Volodymyr Gnatyuk; Toru Aoki
CdTe radiation detectors have been used for γ-ray and X-ray detection because CdTe have good physical properties. A current issue of CdTe detectors is instability in long-term operation. This instability is called polarization, however, the details of this phenomenon are still being discussed with suggested some mechanism by many researchers. In this study, we measured pulse height and carrier transit time under the polarization condition with aim of estimating mechanism of polarization from carrier transport properties. For evaluation of carrier transport properties, we have developed a new measurement system, which enables real time monitoring of both pulse height and carrier transit time of signal pulse. First, the carrier transit time is later after biasing. However, the carrier transit time is earlier due to reducing depletion layer. As a result, we estimated a mechanism of polarization and the distribution of electric field including carrier transport properties.
international vacuum nanoelectronics conference | 2016
Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Takatoshi Yamada
Permeation of low-energy electrons through graphene was investigated. A multi-layered graphene was transferred on a Cu mesh, and electron beam was scanned over the mesh and the graphene. Up to 1% of the incident electron beam permeated through the graphene at landing energy of 20 eV. The result suggested a possibility of graphene to be used as a window material for scanning electron microscopy and cathode luminescence using low-energy electrons.
international vacuum nanoelectronics conference | 2016
Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Yasuhito Gotoh; Tamotsu Okamoto; Masafumi Akiyoshi; Masayoshi Nagao; Nobuhiro Sato; Ikuji Takagi
A CdTe-based photoconductive target was designed for a radiation tolerant compact image sensor using field emitter array. Gamma-ray irradiation using 60Co showed that this target maintained its photoconductivity even after 1 MGy of gamma-ray irradiation.
Proceedings of SPIE | 2016
Tomoaki Masuzawa; Taishi Ebisudani; Jun Ochiai; Ichitaro Saito; Takatoshi Yamada; Daniel H. C. Chua; Hidenori Mimura; Ken Okano
Although present imaging devices are mostly silicon-based devices such as CMOS and CCD, these devices are reaching their sensitivity limit due to the band gap of silicon. Amorphous selenium (a-Se) is a promising candidate for high- sensitivity photo imaging devices, because of its low thermal noise, high spatial resolution, as well as adaptability to wide-area deposition. In addition, internal signal amplification is reported on a-Se based photodetectors, which enables a photodetector having effective quantum efficiency over 100 % against visible light. Since a-Se has sensitivity to UV and soft X-rays, the reported internal signal amplification should be applicable to UV and X-ray detection. However, application of the internal signal amplification required high voltage, which caused unexpected breakdown at the contact or thin-film transistor-based signal read-out. For this reason, vacuum devices having electron-beam read-out is proposed. The advantages of vacuum-type devices are vacuum insulation and its extremely low dark current. In this study, we present recent progresses in developing a-Se based photoconductive films and photodetector using nitrogen-doped diamond electron beam source as signal read-out. A novel electrochemical method is used to dope impurities into a-Se, turning the material from weak p-type to n-type. A p-n junction is formed within a-Se photoconductive film, which has increased the sensitivity of a-Se based photodetector. Our result suggests a possibility of high sensitivity photodetector that can potentially break the limit of silicon-based devices.
Proceedings of SPIE | 2016
Tomoaki Masuzawa; Yoichiro Neo; Hidenori Mimura; Tamotsu Okamoto; Masayoshi Nagao; Masafumi Akiyoshi; Nobuhiro Sato; Ikuji Takagi; Hiroshi Tsuji; Yasuhito Gotoh
A growing demand on incident detection is recognized since the Great East Japan Earthquake and successive accidents in Fukushima nuclear power plant in 2011. Radiation tolerant image sensors are powerful tools to collect crucial information at initial stages of such incidents. However, semiconductor based image sensors such as CMOS and CCD have limited tolerance to radiation exposure. Image sensors used in nuclear facilities are conventional vacuum tubes using thermal cathodes, which have large size and high power consumption. In this study, we propose a compact image sensor composed of a CdTe-based photodiode and a matrix-driven Spindt-type electron beam source called field emitter array (FEA). A basic principle of FEA-based image sensors is similar to conventional Vidicon type camera tubes, but its electron source is replaced from a thermal cathode to FEA. The use of a field emitter as an electron source should enable significant size reduction while maintaining high radiation tolerance. Current researches on radiation tolerant FEAs and development of CdTe based photoconductive films will be presented.
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National Institute of Advanced Industrial Science and Technology
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