Growth and characterization of molybdenum oxide nanorods by RF magnetron sputtering and subsequent annealing

High-densely packed and uniformly distributed molybdenum oxide nanorods have been grown onto glass substrates by RF magnetron sputtering and subsequent annealing in an oxygen atmosphere. A two-step growth mechanism (sputtering redeposition and enhanced rearrangement during annealing) for the formation of MoO3 nanorods has been proposed. The morphological, structural, optical and electrical properties of the nanorods have been investigated systematically using atomic force microscopy, scanning electron microscopy, x-ray diffraction, micro-Raman, UV-visible, photoluminescence (PL) spectroscopy and dc resistivity studies. The nanorods in the as-sputtered film and the film annealed at 473 K are amorphous in nature. However, the nanorods in the films annealed at 573 and 673 K exhibit the presence of monoclinic Mo8O23 and orthorhombic MoO3, respectively. Vibrational analysis of the molybdenum and oxygen atoms in the nanorods is carried out by micro-Raman spectra. The nanorods show room temperature PL in the UV-visible region. The PL emission is found to be strongly enhanced by post-deposition annealing. The low temperature resistivity measurement is done on the as-deposited film; the activation energy and polaron hopping energy for electrical conduction are calculated. The MoO3 nanorods are expected to exhibit enhanced functionality, particularly in nanoscale, photochromic and gas sensing applications.