Epitaxial copper layers, 6.6 nm to 1.2 mu m thick, were grown on MgO(001) by ultra-high vacuum magnetron sputter deposition at 100 degrees C. The surface morphology, as determined by in-situ scanning tunneling microscopy, exhibits a regular mound structure. The mounds grow in width w and height h as a function of layer thickness t from h=3 nm and w=20 nm for t=20 nm to h=5 nm and w=200 nm for t=1.2 mu m. The resistivity increases with decreasing layer thickness from 1.70 mu Omega-cm for t=1.2 mu m to 8.35 mu Omega-cm for t=6.6 nm. The resistivity increase is consistent with the Fuchs-Sondheimer model for completely diffuse surface scattering. The diffuse scattering is attributed to a high density of surface steps, which are separated by less than 1 nm. (C) 2007 Elsevier B.V. All rights reserved.