We have been focusing on fabricating a photodetector that consists of a diamond cold cathode and an amorphous selenium (a-Se) photoconductor, which is one of the practical applications of a cold cathode. We have previously succeeded in achieving a proto-type photodetector of which a heavily nitrogen (N)-doped diamond was used as the cold cathode, and the results indeed showed a low operation voltage. This heavily N-doped diamond was fabricated using urea as a dopant and the saturated solution of urea and methanol was diluted with acetone and used as a reactant gas. Although this diamond cathode exhibited low extraction voltage, the reproducibility of obtaining low threshold cathode was not as high as expected and the improvement should be considered for wider extensive application. In order to solve this problem, dimethylurea was introduced due to its structure more similar to diamond and soluble in acetone, where urea is insoluble without the use of methanol. Dimethylurea-saturated solutions of acetone diluted at a ratio of 1:100, 1:1000, and 1:10000 with acetone is vaporized and used as the reactant gas and diamond is grown on a silicon substrate by hot filament CVD method. The N/C ratio in the CVD apparatus is 1000 ppm, 100 ppm and 10 ppm respectively. The electron emission characteristics of N-doped diamond doped with dimethylurea are then measured. The experiment was performed under a base pressure of 4 x 10 -6 Pa. Anode-cathode distance is fixed to 50mum and the current versus voltage (I-V) characteristics are measured.
Aiming at a practical use of superconducting fault current limiter, a newly designed device which consists of YBCO thin films and normal conducting films has been developed. The configuration allows increase of the resistance of the YBCO film without excess heating and partial overvoltage. To verify the current limiting performance and the reliability of the device, an analogue simulator test with a condition equivalent to a typical distribution system has been conducted. The developed device can limit a fault current to a target level within a half cycle and the increasing speed of the resistance is fast enough to mitigate the current overshoot after the fault. The series and parallel connection of the unit devices are feasible to attain large capacity. These test results prove that the proposed device has sufficient performance for applying to an actual power system.
In order to utilize negative electron affinities (NEA) on diamond surfaces, field emission from n-type diamond with NEA was investigated. It was confirmed, by ultraviolet photoelectron spectroscopy (UPS), that hydrogen-plasma treated n-type diamond surface has NEA. Field electron emission properties as a function of anode-diamond distances were measured and a potential drop in vacuum was evaluated. It was found that electric fields of over few 10V/µm were required to emit electrons from n-type diamond NEA surface. It was considered that such higher electric fields were necessary to reduce an internal barrier at NEA surface. From the field emission results, the internal barrier height was estimated to be about 3.3 eV.
To investigate the effects of ultraviolet (UV) irradiation on perfluoropolyether (PFPE) lubricants with identical main chains but different end groups, three types of PFPEs (UV sensitive AM3001, less UV sensitive but functional Zdo12000, and less UV sensitive and nonfunctional Z03) coated on magnetic disk surfaces at nanometer thickness were irradiated by 172 nm UV rays, and bonded lubricant thickness, surface energy, and lubricant spreading measurements were subsequently conducted. Over the irradiation time range investigated, Zdo12000 showed a linear increase in bonded thickness, whereas AM3001 and Z03 showed a saturating increase and the saturating bonded thickness matched the gyration diameter (2.8 nm) of bulk AM3001 and the cross-sectional diameter (0.7 nm) of Z03 molecules, respectively. For surface energy, except for Z03, the polar component decreased significantly with UV irradiation compared to the dispersive component, suggesting the preferential effects of UV irradiation on the functional end groups rather than the main chains. Spreading of AM3001 to bare disk surface was drastically decelerated by UV irradiation; for Zdo12000 and Z03, however, it was worth noting that the thickness profiles after UV irradiation changed to a layered structure featuring a forward-spreading shoulder. A peak/valley structure caused by molecular flow from the non-irradiated toward the irradiated areas was observed for functional AM3001 and Zdo12000, but was not observed for nonfunctional Z03.
Single crystals of CuAlS 2 doped with Tb were prepared by the iodine vapor transport technique. These crystals showed bright yellow photoluminescence at room temperature when excited by the 365 nm line of a Hg lamp. The photoluminescence spectrum consists of a yellow broad band at 2.0 eV and sharp emission lines at 2.278 eV and 2.532 eV which are tentatively assigned to Tb 3+ ion.
Utilization of carbon dioxide (CO 2 ) as a feedstock of valuable chemicals is necessary to achieve carbon neutrality. CO 2 electrolysis producing valuable organic molecules such as carbon monoxide (CO) is one of the most promising methods. To implement this technology in society, a large-sized electrolyzer that can convert a huge amount of CO 2 are required. Toshiba is developing a low-temperature zero-gap type CO 2 electrolysis cell/stacks with 400 cm 2 electrodes to produce CO [1,2] , which can be converted into chemicals and fuels by catalytic reactions with hydrogen. With properly designed gas flow plates and optimal operation conditions, CO faradaic efficiency of the 400cm2 single cell were comparable to that of a smaller cell with 4 cm 2 electrode [3] . Another problem to be solved is low durability of the electrolyzer. During continuous operation of the electrolyzer, several failure modes such as cathode flooding, salt precipitation, diaphragm degradation, corrosion of flow plates, and catalyst dissolution often occur. By resolving each of these failure modes, stable performance over 500 h was achieved. Additionally, in this presentation, we report the results of electrolysis tests using CO 2 gas containing impurities that are expected to be contaminated in an actual environment, and the results of electrolysis tests to confirm effects of a ripple current generated from AC/DC converter on the efficiency of CO 2 electrolyzer. Part of this work is commissioned by Ministry of the Environment, Government of Japan. [1] Y. Kofuji, A. Ono, Y. Sugano, A. Motoshige, Y. Kudo, M. Yamagiwa, J. Tamura, S. Mikoshiba, and R. Kitagawa, Chem. Lett. , 50, 482-484 (2021). [2] Y. Kiyota, Y. Kofuji, A. Ono, S. Mikoshiba, and R. Kitagawa, 2 42nd ECS Meeting , I05, 1942, (2022). [3] Naoya Fujiwara, Yusuke Kofuji, Satoshi Mikoshiba, Ryota Kitagawa, Atsushi Matsunaga, Isamu Kikuchi, Soichiro Shimotori, 244th ECS Meeting , I05, 2328, (2023).
