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VO<sub>x</sub> 박막의 구조적 특성과 전기적 특성에 대한 열처리 영향
이장우,정지원,Lee, Jang Woo,Chung, Chee Won 한국공업화학회 2006 공업화학 Vol.17 No.5
$VO_x$ thin films with the thickness of 450 nm were prepared on a $Pt/Ti/SiO_{2}/Si$ substrate at room temperature by a reactive radio frequency (rf) magnetron sputtering method. The deposition rates of $VO_x$ thin films were investigated as a function of $O_{2}$ concentration and rf power. As the $O_{2}$ concentration in a $O_{2}/Ar$ mixture increased, the deposition rate decreased. However, the deposition rate increased with increasing rf power. The deposited $VO_x$ thin films were annealed at $450^{\circ}C$ for 2, 4, and 6 h in $O_{2}$ and $N_{2}$ ambient. After annealing, the phase changes of $VO_x$ thin films were investigated using X-ray diffraction analysis. The plane and cross-sectional views of $VO_x$ thin films before and after annealing were observed by field emission scanning electron microscopy. The metal-insulator transition (MIT) properties of $VO_x$ thin films were measured using current-voltage measurement. The excellent MIT properties were observed in $VO_x$ thin films annealed in $O_{2}$ ambient. $VO_x$ 박막이 상온에서 $Pt/Ti/SiO_{2}/Si$ 기판위에 반응성 radio frequency (rf) 마그네트론 스퍼터링 방법에 의하여 450 nm 두께로 증착되었다. 증착 공정에서 산소의 농도와 타겟에 인가되는 rf power를 변수로 설정하여 증착 속도를 조사하였다. $VO_x$ 박막의 증착속도는 산소 농도가 증가함에 따라서 감소하고, rf power가 증가할수록 증가하는 것이 관찰되었다. 증착된 $VO_x$ 박막은 $O_{2}$와 $N_{2}$ 가스 분위기에서 $450^{\circ}C$의 온도로 2, 4, 그리고 6 h 동안 각각 열처리 되었고, 열처리 과정을 진행한 후 x-ray diffraction (XRD) 분석을 이용하여 열처리 전과 후의 결정성 변화를 관찰하였다. 그리고 열처리 전과 후의 $VO_x$ 박막의 표면과 단면을 field emission scanning electron microscopy (FESEM)를 이용하여 관찰하였으며 전류-전압 측정을 이용하여, 증착된 $VO_x$ 박막의 metal-insulator transition (MIT) 특성을 관찰하였다. $N_{2}$ 분위기에서 열처리된 $VO_x$ 박막보다 $O_{2}$ 분위기에서 열처리된 $VO_x$ 박막에서 더 우수한 MIT 특성을 관찰 할 수 있었다.
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Catalytic Combustion of Chlorobenzene over Supported Metal Oxide Catalysts
Moon, Sung Woo,Lee, Gun-Dae,Park, Seong Soo,Hong, Seong-Soo 한국공업화학회 2004 Journal of Industrial and Engineering Chemistry Vol.10 No.4
Catalytic combustion of chlorobenzene over supported metal oxides has been investigated. TiO₂was prepared by the sol-gel method from titanium isopropoxide. The supported metal oxide catalysts were prepared by the incipient wetness method and characterized by XRD, FT-Raman spectroscopy, and TPR. Among the supported metal oxides, VO_x supported on TiO₂had the highest activity for chlorobenzene oxidation; the activities decreased in the order VO_x > CrO_x > FeO_x > MnO_x. In addition, among the vanadium oxide catalysts supported on TiO₂, Al₂O₃ and SiO₂, the titania-supported catalyst (VO_x/TiO₂) had the highest catalytic activity. The VOx dispersed on the TiO₂surface acts as the active site of the VO_x/TiO₂catalysts during the oxidative decomposition of chlorobenzene. When the vanadium loading reached 3 wt%, the total conversion temperature was lowered to 310℃. In addition, VO_x supported on TiO₂calcined at 300~500℃ had a higher activity than that calcined at 600~700℃. This result suggests that the structure of the TiO₂support has an influence on the catalytic activity of chlorobenzene combustion. The catalytic activity decreases with an increase in the amount of water at a low reaction temperature, but it has a similar activity as that in the absence of water at a high reaction temperature.
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Temperature dependent structural, electrical and electronic investigation of VO2 (B) thin film
Kumar Manish,김영학,이현휘 한국물리학회 2021 Current Applied Physics Vol.30 No.-
Vanadium dioxide can exist in several polymorphs and among these the layered polymorph VO2 (B) with monoclinic symmetry has numerous applications. In this work, VO2 (B) phase thin film was prepared on quartz substrate via sputtering technique and its temperature dependent structural, electrical and electronic properties were investigated. We have witnessed a broader structural phase transition around 220 K; which encounter significant changes in the lattice constants yet the monoclinic symmetry is retained over a temperature range from 100 K to 380 K. Temperature dependent resistance measurement also exhibited a semi-metal to insulator like transition near 220 K displaying over 2 order of magnitude change in resistance across the transition. Small changes in the oxygen K-edge x-ray absorption spectrum were seen with change in temperature. At low temperature, an additional peak (d|| band) has emerged in the XAS spectra at energy higher than the σ* peak. The appearance of d|| band density of states is associated to the enhanced electron correlation effects driven by the localization of V–V pair’s interactions at low temperature.
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Directional Ostwald Ripening for Producing Aligned Arrays of Nanowires
Lee, Hye Jin,Yang, U Jeong,Kim, Kyeong Nam,Park, Soojin,Kil, Kye Hyoung,Kim, Jun Soo,Wodtke, Alec M.,Choi, Won Jun,Kim, Myung Hwa,Baik, Jeong Min American Chemical Society 2019 NANO LETTERS Vol.19 No.7
<P>The remarkable electronic and mechanical properties of nanowires have great potential for fascinating applications; however, the difficulties of assembling ordered arrays of aligned nanowires over large areas prevent their integration into many practical devices. In this paper, we show that aligned VO<SUB>2</SUB> nanowires form spontaneously after heating a thin V<SUB>2</SUB>O<SUB>5</SUB> film on a grooved SiO<SUB>2</SUB> surface. Nanowires grow after complete dewetting of the film, after which there is the formation of supercooled nanodroplets and subsequent Ostwald ripening and coalescence. We investigate the growth mechanism using molecular dynamics simulations of spherical Lennard-Jones particles, and the simulations help explain how the grooved surface produces aligned nanowires. Using this simple synthesis approach, we produce self-aligned, millimeter-long nanowire arrays with uniform metal-insulator transition properties; after their transfer to a polymer substrate, the nanowires act as a highly sensitive array of strain sensors with a very fast response time of several tens of milliseconds.</P> [FIG OMISSION]</BR>
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