Using a combination of stain-etching with subsequent annealing in hydrogen, porous germanium films with a high concentration of germanium nanocrystals (NCs) were prepared for the first time. Structural studies of the films were performed by X-ray reflectometry and high-resolution triple-crystal diffractometry and Raman light spectroscopy methods. From a thorough analysis of the experimental data obtained by both methods, it was revealed that the films consist of germanium NCs with average sizes approximately 8-10 nm in annealed films. Other basic information about thickness, porosity, roughness, and lateral coherence length of the films is also presented. (C) 2003 Elsevier Science B.V All rights reserved.