• Title/Summary/Keyword: $WO_3$ films

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Gas Sensing Characteristics of WO3:In2O3 Prepared by Ball-mill Time (볼밀시간에 의한 WO3:In2O3 가스센서의 감응특성)

  • Shin, Deuck-Jin;Yu, Yun-Sik;Park, Sung-Hyun;Yu, Il
    • Korean Journal of Materials Research
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    • v.21 no.6
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    • pp.299-302
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    • 2011
  • [ $WO_3$ ]powders were ball-milled with an alumina ball for 0-72 hours. $In_2O_3$ doped $WO_3$ was prepared by soaking ball-milled $WO_3$ in an $InCl_3$ solution. The mixed powder was annealed at $700^{\circ}C$ for 30 min in an air atmosphere. A paste for screen-printing the thick film was prepared by mixing the $WO_3$:In2O3 powders with ${\alpha}$-terpinol and glycerol. $In_2O_3$ doped $WO_3$ thick films were fabricated into a gas sensor by a screen-printing method on alumina substrates. The structural properties of the $WO_3$:$InO_3$ thick films were a monoclinic phase with a (002) dominant orientation. The particle size of the $WO_3$:$InO_3$ decreased with the ball-milling time. The sensing characteristics of the $In_2O_3$ doped $WO_3$ were investigated by measuring the electrical resistance of each sensor in the test-box. The highest sensitivity to 5 ppm $CH_4$ gas and 5 ppm $CH_3CH_2CH_3$ gas was observed in the ball-milled $WO_3$:$InO_3$ gas sensors at 48 hours. The response time of $WO_3$:$In_2O_3$ gas sensors was 7 seconds and recovery time was 9 seconds for the methane gas.

The influence of substrate temperature on the chemical stability of WO3Films prepared by electron beam deposition (기판온도가 전자비임으로 제작된 텅스텐 산화물박막의 화학적 안정성에 미치는 영향)

    • Journal of the Korean Vacuum Society
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    • v.5 no.4
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    • pp.365-370
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    • 1996
  • Electrochromic $WO_3$ films were prepared by using an electron-beam deposition method. The dependence of the chemical stability of film on the substrate temperature was studied. From the experimental results, The optical property and chemical stability of as-deposited films strongly depended on the substrate temperature. The $WO_3$ film prepared at a substrate temperature of $80^{\circ}C$ was found to be the most stable when subjected to repeated coloring and bleaching cycles in an organic 0.6M $LiClO_4$ solution.

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The Vacuum Pressure Effects on Electrochromic Properties of Tungsten Oxide Thin Films by Electron Beam Evaporation (전자비임에 의해 제작된 WO$_3$ 박막의 전기적착색 특성에 대한 진공도의 효과)

  • 이길동
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
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    • 1995.05a
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    • pp.41-44
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    • 1995
  • The electrochromic WO$_3$ thin films were prepared by using an electron - beam evaporation technique. The influence of the electron - beam evaporation conditions. especially the vacuum pressure, and resistance of ITO substrate on the structural and electrochromic properties of the investigated film was presented. This films showed electrochromic behavior in an aqueous electrolyte of 1 M H$_2$SO$_4$. Among these WO$_3$ thin films, films prepared at a vacuum pressure of 10$^{-4}$ mbar were found to be most stable in terms of cycling durability. The chemical stability of film against dissolution in the aqueous solution was also shown to depend on the quantity of water in the film.

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Transmission and Durability of Electrochromic WO3 Thin Films (전기적착색 $WO_3$ 박막의 투과율과 내구성)

  • Lee, Kil-Dong
    • Solar Energy
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    • v.19 no.1
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    • pp.1-8
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    • 1999
  • Electrochromic $WO_3$ thin films were prepared by electron beam deposition. The transmission and durability of films were investigated. Coloring and bleaching experiments were repeated in an electrolyte of propylene carbonate with 0.6M of $LiClO_4$ by cyclic voltammetry. Spectrophotometer was used to measure the transmission in the degraded films. The 5000 ${\AA}$ thick film was found to be the stable after repeated cycles. The durability of the annealed film also showed improvements over unannealed samples. Tungsten oxide films with titanium content of about $10{\sim}15$ mol% was found to be most stable, undergoing the least degradation during the repeated cycles.

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Characterization of $V_2O_5$ thin films as a counter electrode for complementary electrochromic devices (상보형 전기변색소자용 $V_2O_5$박막의 대향전극 특성)

  • 조봉희;김영호
    • Electrical & Electronic Materials
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    • v.9 no.7
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    • pp.690-695
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    • 1996
  • We have systematically investigated the characterization of V$_{2}$O$_{5}$ thin films as a counter electrode for lithium based complementary electrochromic devices. The V$_{2}$O$_{5}$ thin films were prepared by thermal vacuum evaporation with varing the substrate temperature and film thickness. In electrochromic devices for smart windows, the WO$_{3}$ thin films with 400-800 nm thickness require to be capable of reversibly injection 10-15 mC/cm$^{2}$ of lithium, which is readily accomplished charge-balanced switching in a V$_{2}$O$_{5}$ thin films with 100-150nm thick. The V$_{2}$O$_{5}$ thin films produces considerably small changes in optical modulation properties in the visible and near infrared region(500-1100 nm) compared to the amorphous WO$_{3}$ thin films on 10-15 mC/cm$^{2}$ of lithium injection and the V$_{2}$O$_{5}$ thin films can therefore act as a counter electrode to WO$_{3}$ in a lithium based complementary clectrochromic devices. After 10$^{5}$ coloration/bleaching switching time, the degradation does not occurs and the devices exhibit a stable optical modulation in V$_{2}$O$_{5}$ thin films. It has shown that the injected lithium ion amounts in crystalline V$_{2}$O$_{5}$ thin films with the same thickness is large by 3-5 mC/cm$^{2}$ of lithium compared to the amorphous thin films in the same driving conditions. Therefore, to optimize the device performance, it is necessary to choose an appropriate film thickness and crystallinity of V$_{2}$O$_{5}$ for amorphous WO$_{3}$ film thickness as a working electrode.

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$NO_{2}$ Sensing Properties of Oxide Semiconductor Thick Films (산화물 반도체형 후막 가스 센서의 이산화질소 감지 특성)

  • Kim, Seung-Ryeol;Yun, Dong Hyun;Hong, Hyung-Ki;Kwon, Chul-Han;Lee, Kyu-Chung
    • Journal of Sensor Science and Technology
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    • v.6 no.6
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    • pp.451-457
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    • 1997
  • The thick films of oxide semiconductors such as $WO_{3}$, $SnO_{2}$ and ZnO for the $NO_{2}$ detection of sub-ppm range have been prepared and their characteristics were investigated. It is showed that the optimum operating temperatures of the sensors are $300^{\circ}C$ and $220{\sim}260^{\circ}C$ for $WO_{3}$-based and $SnO_{2}$-based thick films, and ZnO-based thick films, respectively. Since the resistance of ZnO-based thick films are extremely high($>10^{6}{\Omega}$), the signal to noise ratio was comparatively low. In order to determine the selectivity, the films are exposed to the interfering gases such as ozone, ammonia, methane and the mixture of carbon monoxide and propane. $WO_{3}$-ZnO(3 wt.%) and $SnO_{2}-WO_{3}$(3 wt.%) thick film sensors show high sensitivity, good selectivity, excellent reproducibility and the linearity of $NO_{2}$ concentration versus sensor resistance. The preliminary results clearly demonstrated that the sensor can be successfully applied for the detection of $NO_{2}$ in sub-ppm range.

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Preparation of WO3 by using sol-gel method for photoelectrode and its application for PEC cell (물분해로부터 수소 제조를 위한 광촉매용 텅스텐 산화물 박막 제조)

  • Hong, Eun-Mi;Im, Dong-Chan
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2015.05a
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    • pp.101-101
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    • 2015
  • Photoelectrochemical water splitting is considered as a promising method of transforming solar energy into chemical energy stored in the type of hydrogen. An n-type $WO_3$ semiconductor is one of the most promising photoanodes for hydrogen production from water splitting. Films annealed at lower temperatures consisted of amorphous, whereas films annealed above $500^{\circ}C$ comprised solely of monoclinic $WO_3$. In this study, we observed photoactivity of $WO_3$ as increasing thickness of $WO_3$. And it shows good photoacivity as thickness increases. Also we tried to improve photoactivity through surface modification and bulk modification by using hydrogen treatment and conducting polymer. The photocurrent was measured in potentiostatic method with the three electrode system. A Pt wire and Ag / AgCl electrode were used as the counter electrode and the reference electrode, respectively. photocurrent-time (I-T) curve was measured at a bias potential of 0.79 V.

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Preparation of $WO_3$ Films by CVD and their Application in Electrochromic Devices (화학기상 증착법을 이용하여 제조된 텅스텐 산화막의 전기변색 소자 응용 연구)

  • Jung, Hun;SunWoo, Changshin;Kim, Do-Heyoung
    • Korean Chemical Engineering Research
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    • v.49 no.4
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    • pp.405-410
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    • 2011
  • A study on chemical vapor deposition(CVD) of $WO_3$ and the electrochromic properties of the CVD $WO_3$ films have been carried out. The crystalinity, purity, and growth rate of the films depending on substrate temperatures are investigated. The highest growth rate is $8{\mu}m/min$ at the substrate temperatures above $300^{\circ}C$ and the estimated activation energy for overall film growth is about 45.9 kJ/mol at the temperatures of $225{\sim}275^{\circ}C$, where the CVD process is controlled by a surface reaction kinetics. The films grown below $275^{\circ}C$ are amorphous, while those deposited above $300^{\circ}C$ are crystalline. The effects of thickness and deposition temperature of the $WO_3$ films on electrochromic activity are also investigated. The coloration efficiency of the films increases with increase in film thickness and decrease in deposition temperature.

Gas Sensing Characteristics of WO3-Doped SnO2 Thin Films Prepared by Solution Deposition Method (용액적하법으로 제조된 WO3 첨가 SnO2 박막의 가스감응 특성)

  • Choi, Joong-Ki;Cho, Pyeong-Seok;Lee, Jong-Heun
    • Korean Journal of Materials Research
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    • v.18 no.4
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    • pp.193-198
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    • 2008
  • $WO_3$-doped $SnO_2$ thin films were prepared in a solution-deposition method and their gas-sensing characteristics were investigated. The doping of $WO_3$ to $SnO_2$ increased the response ($R_a/R_g,\;R_a$: resistance in air, $R_g$: resistance in gas) to $H_2$ substantially. Moreover, the $R_a/R_g$ value of 10 ppm CO increased to 5.65, whereas that of $NO_2$ did not change by a significant amount. The enhanced response to $H_2$ and the selective detection of CO in the presence of $NO_2$ were explained in relation to the change in the surface reaction by the addition of $WO_3$. The $WO_3$-doped $SnO_2$ sensor can be used with the application of a $H_2$ sensor for vehicles that utilize fuel cells and as an air quality sensor to detect CO-containing exhaust gases emitted from gasoline engines.

Properties of Sol-gel $WO_3$ thin films (졸겔 $WO_3$박막의 특성)

  • 이길동
    • Journal of the Korean Vacuum Society
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    • v.10 no.1
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    • pp.61-66
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    • 2001
  • $WO_3$ films were multicoated on the microscope slide glass and ITO-coated glass using a tungsten alkoxide type solution by the sol-gel deposition process. The effect of dipping and processing parameters on the structure, optical and electrochemical properties of the film were also investigated. Coating using alkoxide solution was very uniformed for low dipping speed of 0.005 m/s, but thickness variations across the sample became apparent for dipping speeds greater than 0.007 m/s. Electrochemical coloration experiments showed that films fired at lower temperatures color more easily than film fired to > $200^{\circ}C$. Rutherford backscattering spectroscopy studies revealed that $K^+$ ions were uniformly distributed throughout the $WO_3$layer in the colored sample.

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