Properties of Low-Resistivity Undoped indium-Oxide Films Grown by Reactive Ion Plating and Electrochromic Tungsten-Oxide
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plating (AIIP) technique. Films with resistivity of less than 1.5 x 10-4 Q cm and high visible transmission (over 90%) have been readily obtained without any post-deposition annealing. These properties are comparable or superior to the ITO films previously reported, and excellent reproducibility has been achieved. There are certain materials which are able to change their colors reversibly according to the external stimulus. Electrochromism is one of these chromic phenomena, and is defined to be reversible change in color or transmission according to the applied voltage or current. The electrochromic (EC) films have attracted attention owing to their many practical applications for display devices, building exteriors and interiors, automobile rear-view mirrors, and so on. W0 3 films has been known to have the EC properties [13, 14]. Their color can be changed reversibly between transparency and blue according to the apllied
current. This film was prepared by electron-beam evaporation, and the properties such as transmittance, optical density and coloring efficiency were investigated along with characterization by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and scanning electron microscopy (SEM). EXPERIMENTAL Reactive AIIP was used to prepare In20 3 films on microslide glasses (Coming No. 2947). In grains as pure as 99.99% were evaporated using an ordinary thermal source (usually a W boat). The 02 gas was admitted through a mass flow controller. The details of the experimental system can be found in Ref. 15. The substrate was grounded during the deposition. The distance between the evaporation source and the substrate was 30 cm. The other deposition parameters used in this experiment were as follows ; deposition rate of 300 1500 A/min, substrate temperature of 25 - 300°C, 02 partial pressure of (1 - 10) x 10' Torr, film thickness of 500 - 6000 A, ionization voltage of 20 - 80 V, ionization current of 1 - 6 A, and filament current of 40 - 60 A. The film thickness was monitored by a quartz crystal sensor calibrated by a stylus profiler. W0 3 films were deposited by electron-beam evaporation of WO 3 granules as pure as 99.99%, and a self-made EC cell (Fig. 1) was employed to carry out the coloring and bleaching experiment on the prepared EC films. 1-mole solution of H2S0 4 was used as the electrolyte, and Pt or C as the counterelectrode in the EC cell. The deposition parameters employed in the preparation were as follows ; electron-beam power of 6 kV and 20 mA, deposition rate of 2000 A/min, substrate temperature of 25 - 300°C, 02 partial pressure of (0.05 - 3) x 10 -4Torr, film thickness of 4000 - 10000 A. The atomic concentrations of In20 3 films were measured by AES (Auger electron spectroscopy) and XPS using standard In and In 20 3 grains, and calculated by the method of Lin et al. [16]. The WO 3 films were measured by XPS using standard W0 3 powder. Resistivity was measured by the four-point probe method. Carrier concentration and Hall mobility were calculated from the 428
Hall effect measu
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