Structural, Optical and Electrochromic Investigations on Nano Crystalline MoO3 Thin Films

Abstract

Thin films of MoO3 were deposited on quartz glass, Silicon (100) and Indium Tin Oxide (ITO) substrates by dc magnetron sputtering at two substrate temperatures of 300 K and 600 K and at sputtering pressures of 5 Pa and 10 Pa and at a fixed sputtering power of 50 W. The deposited films were characterized by Grazing Incidence X-ray Diffraction (GIXRD), Raman and Optical Transmittance Spectra and Cyclic Voltametry (CV) studies. The GIXRD reveales that the crystallanity of films starts at low temperature (300 K) and crystallizes in orthorhombic phase. The crystallanity increases with increase of substrate temperature. The Raman spectral studies reveals strong shift in the emission peak position for films deposited at 5 Pa and 300 K, and there is no significant peaks in case of films deposited at 10 Pa and 600 K. The optical transmittance of the films is 78 % for films deposited at 5 Pa and 300 K and is maximum (95 %) when deposited at 600 K. The transmittance is decreasing to 90 % with increase in sputtering pressure. The absorption edge is shifting towards lower wavelength with increase in substrate temperature due to increase in the reactivity of the ionic species (molybdenum ions and oxygen ions) and shifting towards higher wavelengths with sputtering pressures due to the scattering of atomic species which decreases the reactivity between ionic species. The average diffusion coefficient (D) of the films deposited at 5 Pa and 300 K is 7x10-14 cm2/sec and decreasing with increase in substrate temperature of the deposited films. With further increase in the sputtering pressure to 10 Pa and at low temperatures a large increment in the D value was observed (8.2x10-12 cm2/sec) due to the enhancement in the mobility of the Li+ ions through the internal and intra grain boundaries due to low grain size of MoO3 (8 nm) of the film. The measured thickness of the films by Taly stip profilometer is 3000 Å.