Abstract. In this investigation, tungsten oxide (WO 3 ) thin films have been deposited on unheated glass substrates by RF magnetron sputtering of tungsten target at constant oxygen partial pressure of 6x10 -2 Pa, sputtering power of 150 W and at different substrate bias voltages in the range from 0 to -150 V. The structural and optical properties of the films were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy and UV-Vis-NIR spectrophotometers. The films formed up to substrate bias voltage of -50 V were found to be amorphous in nature, while those films formed at -100 V showed a weak (200) reflection indicates the presence of monoclinic phase of WO 3 in amorphous matrix. The optical transmittance of the films was in the range 78 -95 % in the wavelength range of 500 -1200 nm. The absorption band edge was shifted towards higher wavelength side with increasing substrate bias voltage. The optical band gap of the films decrease from 2.81 to 2.69 eV with increase of substrate bias voltage from 0 to -150 V respectively. The refractive index of the films increased from 2.19 to 2.27 with increase of substrate bias voltage from 0 to -150 V respectively.
Introduction:In recent past, tungsten oxide (WO 3 ) has been extensively studied for its distinctive physical and chemical properties especially the electrochromic, photochromic, gas sensors properties. Electro chromism in amorphous tungsten oxide films has been extensively studied since it was discovered in 1961. The improvement of material properties requires a closer inspection of preparation conditions. Various techniques such as thermal evaporation The chemical composition, microstructure and physical behaviour of the deposited films relies more on the control of deposition parameters such as substrate temperature, gas pressures, sputtering power and substrate bias voltage. The primary purpose of biasing is to prevent the deposited film from becoming contaminated with gas atoms and other gas/metal reaction products. A negative potential applied to the substrate vary the ion energy, and further influence the nucleation and growth kinetics of the films. Subsequently, the microstructure and physical properties of the films are greatly modified. The present study is aimed to investigate the influence of substrate bias voltage on the growth characteristics of RF reactive magnetron sputtered WO 3 films.