A combined X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) study have been carried out on copper films grown by atomic layer deposition at 400 degrees C. The copper films have been grown on single crystalline (001) oriented alpha-Al2O3 up to a thickness of 500 nm. The films were relaxed and the diffraction peak broadening in 20 was mainly dependent on the copper grain size. Broadening of the diffraction peaks in omega was found to be related to defects (mosaicity and intrinsic microstrain). The deposited films were epitaxial and grew with the (111) plane in parallel to the substrate surface. Extensive twinning in the copper grains in different Cu < 111 > directions occurred according to the TEM study, both in directions perpendicular to the substrate surface ([111] and [(1) over bar(1) over bar(1) over bar]) and along other < 111 > directions as well. As an effect of a ((1) over bar 11) twin, an extra Cu(511) orientation was present in the XRD data. (c) 2004 Elsevier B.V. All rights reserved.