Thickness dependent structural, morphological and optical properties of molybdenum oxide thin films

Abstract

Molybdenum oxide ( $${\text {MoO}}_3$$ ) is a chromogenic and a wide band gap n-type semiconductor. Thickness of thin films is usually observed to have significant influence on various properties of chromogenic materials. $${\text {MoO}}_3$$ thin films of different thicknesses (100 nm, 200 nm and 400 nm) were deposited on glass substrates by thermal evaporation technique. The effect of thickness of deposited thin films on the structural, morphological and optical properties was investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM) and UV–visible spectroscopy. XRD analysis revealed the amorphous nature of deposited thin films of different thicknesses. FTIR spectrum showed the characteristic vibrations of intermolecular bonds in molybdenum oxide. The surface morphology of $${\text {MoO}}_3$$ films showed nanoflakes like structures which became densely stacked with increase in film thickness and transformed to large grains with uniform coverage of the substrate surface with randomly oriented morphology. The transmission spectra revealed the slight increase in average transmittance in the visible-NIR region with increase in thickness of thin films. The optical band gap of the deposited thin films of different thicknesses was found to be increasing with increase in thickness of the films which may be attributed to decreased defect centres. The decrease in the values of Urbach energy with increase in thickness may be due to the increased homogeneity and decrease in scattering centres.