NiO layers have been epitaxially grown in an ultrahigh vacuum (UHV) sputtering chamber on MgO substrates at high temperature. We studied the influence of the substrate orientation on the surface morphology of the deposited layers. The epitaxial growth and surface structures were investigated by reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), X-ray diffraction and transmission electron microscopy (TEM). These experiments give evidence for a flat NiO surface on MgO(0 0 1), whereas layers on MgO(1 1 0) and MgO(1 1 1) are rough. On the NiO(1 1 0) surface, we observed wires consisting of (1 0 0) and (0 1 0) elongated facets and tetrahedrons with (1 0 0) type facets on the NiO/MgO(1 1 1) surface, These particular surface configurations are due to a minimization of the surface energy during the growth process. (C) 2002 Elsevier Science B.V. All rights reserved.