Epitaxial growth and properties of MoOx(2<x<2.75) films -: art. no. 083539

We report the growth of epitaxial molybdenum oxide (MoOx,2 < x < 2.75) films on c plane of sapphire substrate using pulsed laser deposition in oxygen environment. The structure was characterized using x-ray diffraction, high resolution transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). Electrical resistivity and optical properties were investigated using four-point-probe resistivity measurements and spectroscopy techniques, respectively. It was found that the film had a monoclinic structure based on MoO2 phase and showed an unusual combination of high conductivity and high transmittance in the visible region after annealing. The unusual combination of these properties was realized by systematically controlling the relative fraction of different oxidation states of molybdenum, namely Mo4+, Mo5+, and Mo6+ in the monoclinic phase. For a film 60 nm thick and annealed at 250 degrees C for 1 h, the ratio of Mo6+/(Mo4++Mo5+) was determined to be similar to 2.9/1 using XPS, and a typical value of transmittance was similar to 65% and resistivity close to 1x10(-3) Omega cm. These results demonstrate growth of epitaxial MoOx films with tunable electrical and optical properties. Further optimization of these properties is expected to result in applications related to display panels, solar cells, chromogenic (photochromic, electrochromic, gasochromic) devices, and transparent conducting oxides. Our ability to grow epitaxial MoOx films can further aid their integration with optoelectronic and photonic devices. (C) 2005 American Institute of Physics.