The growth and epitaxy of Ag and Ag2O films on r-cut sapphire surfaces is reported for several different,growth conditions. Ag was deposited by electron beam evaporation in vacuum, in a molecular O-2 background, and in the presence of an electron cyclotron resonance (ECR) oxygen plasma. The presence of an oxygen background converts the random polycrystalline growth of Ag in vacuum to three dimensional epitaxial growth of Ag with a <110> surface normal. At sufficiently low deposition rates (0.1 nm/s), them presence of the ECR oxygen plasma leads to the growth of Ag2O films with a one dimensional epitaxy having the <111> direction normal to the surface but random orientation about this normal. The effects of thermal decomposition of Ag2O were examined by annealing the samples in vacuum above 625 K and characterizing the surfaces with X-ray photoelectron spectroscopy and atomic force microscopy to observe the segregation of silver into islands as the Ag2O decomposes. (C) 2004 Elsevier B.V. All rights reserved.