Ultrathin films of MgO (similar to 6 nm) were deposited on Si(100) using dual ion beam sputtering in different partial pressures of oxygen. These thin films were characterized by X-ray photoelectron spectroscopy (XPS) for chemical state analysis and conducting atomic force microscopy for topography and local conductivity map. No trace of metal Mg was evidenced in these MgO films. The XPS analysis clearly brought out the formation of oxygen interstitials and Mg(OH)(2) primarily due to the presence of residual water vapors in the chamber. An optimum value of oxygen partial pressure of similar to 4.4x10(-2) Pa is identified with regard to homogeneity of film and stoichiometry across the film thickness (O:Mg::0.93-0.97). The local conductivity mapping investigations also established the film homogeneity in respect of electrical resistivity. Non-linear local current-voltage curves revealed typical tunneling characteristics with barrier width of similar to 5.6 nm and barrier height of similar to 0.92 eV. (C) 2012 Elsevier B. V. All rights reserved.