Deposition and characterization of highly oriented Mg3(VO4)2 thin film catalysts. 2. Controlled variation of oxygen content

Thin films of magnesium vanadates oriented to expose a single crystalline face, could potentially serve as ideal models for high surface area magnesium vanadate catalysts for oxidative dehydrogenation. The growth of oriented films of one particular magnesium vanadate phase, the orthovanadate (Mg3(VO4)2), has been achieved by rf sputter deposition of the orthovanadate onto Au(111) surfaces. X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy have been used to investigate the structure and composition of the films. The orthorhombic orthovanadate grows epitaxially with the (021) plane oriented parallel to the surface. By varying oxygen flow rates during deposition the stoichiometry of the films can be varied from fully oxidized to highly oxygen deficient. At very low oxygen flow rates or in the complete absence of oxygen, a reduced Mg3V2O6 phase is formed. This reduced phase has a cubic structure and grows with the (100) plane parallel to the surface.