Preparation and evaluation of w03-bi2o3 composite thin films

Tungsten oxide/bismuth oxide composite thin films prepared by multi target radio frequency (RF) reactive sputtering were investigated. X-ray diffraction measurements of the crystallinity of thin films prepared at room temperature revealed amorphous structure. Although the compositional ratio of composite thin films prepared at 50 W and 75 W of the RF power of the Bi target was almost the same, those prepared at 50 W were transparent, and had a much smaller optical absorption coefficient at 3.0 eV than those prepared at 75 W. Bi 4f spectra of these thin films were measured by X-ray photoelectron spectroscopy, and were analyzed by full width at half maximum of Bi 4f7/2 peaks. As a result, the transparency is thought to be caused by the change of bonding state of Bi-O. Electrochromic properties of the composite thin films were also measured in 0.1 M H2SO4. Coloration of composite thin films prepared at 20 W of the RF power of the Bi target changed reversibly from transparent to black and brown.