Effects of the oxygen partial pressure on pulsed-laser deposition of MgO buffer layers on silicon substrates were investigated. The overall growth process was monitored in situ by reflection high-energy electron diffraction (RHEED) method. It was found that the crystallinity and surface morphology of the MgO films were strongly affected by oxygen partial pressure in the deposition chamber. The oxygen-pressure dependence could be explained in terms of interactions of oxygen with species in the plume-like plasma. The MgO film obtained at an optimal oxygen-pressure range of 1 X 10(-2)-1 Pa exhibited an atomic-smooth and defect-free surface (the root-mean-square roughness being as low as 0.82 nm). For the metal-insulator-metal (MIM) structure of Au/MgO (150 nm)/TiN prepared at the optimal growth conditions achieved a very low leak current density of similar to10(-7) A cm(-2) at an electric field of 8 X 10(5) V cm(-1) and the permittivity (epsilon(r)) of about 10.6, virtually the same as that of the bulk MgO single crystals. (C) 2004 Elsevier B.V. All rights reserved.