Synthesis, structural, compositional, morphological and optoelectronic properties of tungsten oxide thin films

Abstract

Low cost sol–gel drop cast method has been successfully employed for preparation of nanocrystalline tungsten oxide (WO3) thin films. The effect of processing temperature on the structure, morphology, electrical conductivity, thermoelectric power and band gap was studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscope (FESEM), Transmission electron microscopy (TEM), Atomic force microscopy (AFM), two probe technique and UV-visible spectroscopy. XRD analysis showed that WO3 films are crystallized in the orthorhombic phase and present a random orientation. XPS confirms formation of WO3. FESEM analysis revealed that surface morphology of the tungsten oxide film consists nanocrystalline grains with uniform coverage of the substrate surface. TEM of WO3 film showed nanocrystals having diameter ranging from 60 to 80 nm. AFM analysis showed surface morphology of WO3 film is not smooth. The DC electrical conductivity showed the semiconducting nature with room temperature electrical conductivity increased from 7.264 × 10−8 to 1.606 × 10−7 (Ω cm)−1 as processing temperature increased from 400 to 700 °C. Thermo electric power measurement confirms n-type conduction. The band gap energy of WO3 film decreased from 3.264 to 2.531 eV as processing temperature increased from 400 to 700 °C.