Effect of gamma (γ-) irradiation on the structural, morphological, optical and electrical properties of spray pyrolysis-deposited h-MoO3 thin films

Abstract

In the present report, a simple and cost-effective spray pyrolysis technique (SPT) has been used to synthesize h-MoO3 thin films from ammonium heptamolybdate tetrahydrate as a precursor material. The deposited films are exposed, at room temperature, to different doses of 30, 60 and 90 kGy from highly-energetic Co-60 gamma (γ-) irradiation. Various measurement techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–vis spectrophotometer, and four-point probe method are employed to study the influence of γ-irradiation on the structural, morphological, optical and electrical properties. The XRD result reveals that films are nanocrystalline with the hexagonal phase and the crystallite size is found to decrease with the increase of γ-doses estimated from both Scherrer and Williamson-Hall methods. FESEM image of pure h-MoO3 displays well distributed grains with definite grains boundary. The average grain dimension reduces and aggregation of grains is observed after exposure of films to γ-radiation. The γ-irradiation leads to an increase of the optical bandgap from 3.00 to 3.20 eV as the γ-dose increases from 0 to 90 kGy, which is attributed to the deterioration in the crystallinity, accession in the crystal defects and the increase in disorder as well as lattice strain. The γ-irradiation has a significant impact on the electrical properties of the deposited h-MoO3 thin films. The conductivity increases with the γ-radiation dose and the temperature dependency of dc electrical conductivity (σ) exhibits a negative temperature coefficient, indicating the semiconducting characteristics of the films. Gamma irradiated h-MoO3 films address the suitability for the applications in different optoelectronic and photonic devices.