High Band Gap Nanocrystalline Tungsten Carbide (nc-WC) Thin Films Grown by Hot Wire Chemical Vapor Deposition (HW-CVD) Method

Abstract

In present study nanocrystalline tungsten carbide (nc-WC) thin films were deposited by HW-CVD using heated W filament and CF4 gas. Influence of CF4 flow rate on structural, optical and electrical properties has been investigated. Formation of WC thin films was confirmed by low angle XRD, Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) analysis. Low angle XRD analysis revealed that WC crystallites have preferred orientation in (101) direction and with increase in CF4 flow rate the volume fraction of WC crystallites and its average grain size increases. Formation of nano-sized WC was also confirmed by transmission electron microscopy (TEM) analysis. UV-Visible spectroscopy analysis revealed increase in optical transmission with increase in CF4 flow rate. The WC film deposited for 40 sccm of CF4 flow rate show high transparency (- 80-85 %) ranging from visible to infrared wavelengths region. The band gap shows increasing trend with increase in CF4 flow rate (3.48-4.18 eV). The electrical conductivity measured using Hall Effect was found in the range - 103-141 S/cm over the entire range of CF4 flow rate studied. The obtained results suggest that these wide band gap and conducting nc-WC films can be used as low cost counter electrodes in DSSCs and co-catalyst in electrochemical water splitting for hydrogen production.