The interface structures of Ag films on (001) GaAs substrates with and without an Fe buffer, grown by molecular-beam epitaxy technique, were investigated with transmission electron microscopy. Although both epitaxial films are (001) orientated, cross-sectional observation reveals different in-plane orientation relationships. The buffer-free Ag film holds an orientation relationship of (001) Ag//(001) GaAs, [100] Ag//[100] GaAs, whereas the relation for the Fe-buffered Ag film is (001) Ag//(001) Fe//(001) GaAs, [100] Ag//[110] Fe//[1101 GaAs. Lattice images do not reveal any significant reaction layer between the films and GaAs substrates. The rough GaAs surface does not affect the nucleation and growth of Fe and Ag films significantly, but can induce misfit dislocations in Ag films. The observed orientation relationships of films are discussed with respect to the effects of pre-cleaning, lattice mismatch, and possible surface structure and reconstruction of the GaAs surface. (c) 2006 Elsevier B.V All rights reserved.