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유학기 한국센서학회 2020 센서학회지 Vol.29 No.6
A hydrogen sensor was fabricated by utilizing a bundle of metal oxide nanostructures whose growth positions were selectively controlled by utilizing graphene, which is a carbon of atomic-unit thickness. To verify the reducing ability of graphene, it was confirmed that the multi-composition metal oxide V2O5 was converted into VO2 on the graphene surface. Because of the role of graphene as a reducing catalyst, it was confirmed that ZnO and MoO3 nanostructures were grown at high density only on the graphene surface. The fabricated gas sensor showed excellent sensitivity.
Low Resistance and Themarlly Stable Ohmic Contact on p-type GaN Using a RuO2 Diffusion Barrier
손준호,유학기,송양희,이종람 대한금속·재료학회 2008 ELECTRONIC MATERIALS LETTERS Vol.4 No.4
A low resistance, thermally stable reflective ohmic contact on p-type GaN was developed using Ru/Ag overlayers on an oxidized Ni/Au contact. A specific contact resistivity of < 8.4 × 10-5 Ωcm2 was maintained during annealing from 300°C to 600°C in O2 ambient. In addition, the Ni/Au/Ru/Ag contact showed excellent thermal stability after annealing at 500°C for 24 hrs. The RuO2 layer oxidized during oxidation annealing acted as a diffusion barrier for intermixing of the Ag reflector with the oxidized Ni/Au contact, resulting in enhancement of the thermal stability of the contact.
이예정,예병욱,이동규,백정민,유학기,김명화 한국물리학회 2019 Current Applied Physics Vol.19 No.4
We report the synthesis of single crystalline alkali metal vanadate nanowires, Li-vanadate (Li4V10O27), Na-vanadate (NaV6O15), and K-vanadate (KV4O10) and their electrical properties in a single nanowire configuration. Alkali metal vanadate nanowires were obtained by a simple thermal annealing process with vanadium hydroxides( V(OH)3) nanoparticles containing Li+, Na+, and K+ ions and further the analysis of the migration of charged particles (Li+, Na+, and K+) in vanadate by measuring the conductivity of them. We found that their ionic conductivities can be empirically explained by the Rasch-Hinrichsen resistivity and interpreted on the basis of transition state theory. Our results thus indicate that the Li ion shows the lowest potential barrier of ionic conduction due to its small ionic size. Additionally, Na-vanadate has the lowest ion number per unit V2O5, resulting in increased distance to move without collision, and ultimately in low resistivity at room temperature.
Photochemical Tuning of Ultrathin TiO2/p-Si p-n Junction Properties via UV-Induced H Doping
이상연,김진서,안병민,조인선,유학기,서형탁 대한금속·재료학회 2017 ELECTRONIC MATERIALS LETTERS Vol.13 No.2
We report a modified TiO2/p-Si electronic structure that uses ultravioletexposure for the incorporation of H. This structure was characterized usingvarious photoelectron spectroscopic techniques. The ultraviolet (UV) exposureof the TiO2 surface allowed the Fermi energy level to be tuned by the insertionof H radicals, which induced changes in the heterojunction TiO2/p-Si diodeproperties. The UV exposure of the TiO2 surface was performed in air. On UVexposure,a photochemical reaction involving the incorporation of UV-inducedH radicals led to the creation of a surface Ti-O-OH group and caused interstitialH doping (Ti-H-O) in the bulk, which modified the electronic structures indifferent ways, depending on the location of the H. On the basis of the bandalignment determined using a combined spectroscopic analysis, it is suggestedthat the UV-induced H incorporation into the TiO2 could be utilized for thesystematic tuning of the heterojunction property for solar cells, photocatalyticapplications, and capacitors.
Effects of cobalt oxide catalyst on pyrolysis of polyester fiber
박찬영,이나현,조인선,안병민,유학기,이제찬 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.12
Polyester fiber is a high-molecular-weight compound made from fossil fuels and is used in various syntheticfiber manufacturing processes. In this study, we performed non-catalytic and catalytic pyrolysis experimentsusing cobalt oxide as a catalyst to recover energy from polyester fiber. The experiment was carried out between 500-900 oC in the presence of N2. Amount of oil formation was the highest at 600 oC in non-catalytic pyrolysis and oil formationof catalytic pyrolysis was the highest at 500 oC. In both non-catalytic pyrolysis and catalytic pyrolysis, gas contentwas increased and char was decreased with increasing temperature. A marked difference was observed when thecatalyst was used; the formation of char was suppressed and oil and gas yields increased. In the catalytic pyrolysis oil,benzoic acid compounds accounted for the largest proportion (16.15 wt%) at 900 oC, but polycyclic aromatic hydrocarbonsand phenols were not observed. Benzoic acid is an important precursor material used to synthesize other organicsubstances, such as phenol and caprolactam. The non-condensable gas content increased from 11.55 wt% to 22.39 wt%,with increasing temperature. In particular, H2 gas yield was 4.44 wt% at 900 oC. Therefore, by using catalytic pyrolysis,high value-added chemicals such as benzoic acid compounds and H2 gas can be recovered at high yield at 900 oC fromthe polyester fiber. Consequently, unlike the existing treatment methods, the environmental impact of plastics can bereduced by catalytic pyrolysis.