A Simple Process for Synthesis of Transparent Thin Films of Molybdenum Trioxide in the Orthorhombic Phase (α-MoO3)

Transparent orthorhombic molybdenum trioxide (α-MoO3) thin films were prepared on glass substrates by sol–gel dip coating technique of a quality comparable to those prepared by more sophisticated techniques regarded as very costly and difficult to carry out. The prepared films were annealed in air at different temperatures in the range of 150–350°C. X-ray diffraction analysis of the films prepared at 250°C and 350°C confirmed the formation of a single-phase of MoO3 in an orthorhombic crystal system (α-MoO3). Scanning electron microscopy of the films annealed at 350°C indicated a stack of nano-layers with thickness of approximately 30 nm–40 nm. Fourier transform infrared transmittance analysis revealed the Mo=O stretching vibration, which is an indicator of the layered orthorhombic MoO3 phase. Energy dispersive x-ray analysis confirmed the existence of Mo and O in the deposited films. A maximum optical transmittance of 82% in the visible range was obtained from the films annealed at 350°C. The band gap value of the films was evaluated and it was in the range of 3.28 eV–3.40 eV. The obtained results showed that the α-MoO3 thin films prepared at 350°C exhibit good structural, chemical, and optical properties, which might be of interest to the photovoltaic and optoelectronic devices.