Structural, optical and morphological studies on laser ablated nanostructured WO3 thin films

Thin films of tungsten trioxide (WO3) are prepared by reactive pulsed laser deposition (PLD) technique on glass substrates at three different substrate temperatures (Ts). The structural, morphological and optical properties of the deposited films are systematically studied using X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD), micro-Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-VIS spectrophotometry techniques. X-ray diffraction analysis reveals that crystalline WO3 films can grow effectively even at 300 K at an oxygen pressure of 0.12 mbar. All the films deposited at various Ts exhibit mixed oxide phase consisting of orthorhombic and triclinic phase of tungsten oxide with a preferred orientation along (0 0 1) lattice plane reflection. Micro-Raman results are consistent with X-ray diffraction findings. The SEM analysis shows that deposited films are porous and crystalline grains are of nano-metric dimension. The effect of Ts on mean surface roughness studied by AFM analysis reveals that mean surface roughness decreases with increase in Ts. The optical response of WO3 layers measured using UV-VIS spectrophotometry is used to extract the optical constants such as refractive index (n), extinction coefficient (k) and optical band gap (Eg), following the method of Swanepoel.