STRUCTURAL AND MORPHOLOGICAL PROPERTIES OF ANNEALED MoO3 FILMS ON DIFFERENT SUBSTRATES

Molybdenum oxide (MoO3) films were deposited on glass, Al, Mo and Si substrates at room temperature in Ar-O-2 plasma by RF magnetron sputtering system. The as-deposited films were annealed in air at 400 degrees C and 500 degrees C. X-ray diffraction (XRD) results revealed that films annealed at 400 degrees C on all the substrates exhibited diffraction peaks of orthorhombic (alpha) and monoclinic (beta) phases of MoO3. By increasing the annealing temperature to 500 degrees C, the alpha-MoO3 phase on glass became more significant when compared with the beta-MoO3 phase. In contrast, the beta-MoO3 phase was more prominent in the case of film grown on the Mo substrate. The Fourier transform infrared spectroscopy (FTIR) analysis indicated stretching vibrational modes of Mo=O and transverse optical modes of Mo-O-Mo on all the substrates. The surface morphology of MoO3 films on glass shows a flat surface at 400 degrees C that was changed into a layered-like structure at 500 degrees C. In the case of MoO3 films on Al and Si, arbitrary-shaped particles were transformed into needle and rod shapes, respectively, with increase of annealing temperature from 400 degrees C to 500 degrees C. The film annealed on Mo substrate at 400 degrees C revealed corrugated particles that were changed into coarse and elongated particles at 500 degrees C. The morphological changes in MoO3 film with increase of annealing temperature were associated with tensile strain developed inside MoO3 due to lattice and thermal mismatch between the film and the substrate.