Electrical and optical properties of mixed phase tungsten trioxide films grown by laser pyrolysis

Abstract

Laser pyrolysis is a synthesis method used to produce thin films and nanomaterials of high quality and purity, by intersecting a laser beam with a chemical precursor. We have chosen laser pyrolysis to synthesize tungsten trioxide starting with tungsten ethoxide precursor. The film had a thickness that varied from 205 nm to 1 μm. Xray diffraction and Raman spectroscopy confirmed the presence of a mixture of hexagonal and tetragonal phase WO3 in the synthesized film, and it was clear that annealing greatly influenced the phases and types of structures formed. I-V curves of the films showed n-type semiconducting behaviour, but the mixed phase appeared to cause a similar behaviour of dopants in a semiconductor. The refractive index decreased with increasing wavelength and gave values of up to 21 at low wavelengths. The average optical band gap was found to 3.6 eV from UV/Vis spectroscopy. Scanning Electron Microscopy (SEM) showed a mixture of nano- and microstructures and shapes formed after annealing. One of the grown nanostructures was nanorods, this isolated using FIB for possible applications such as an active sensing medium in gas sensors.