At room temperature deposited Ge films (thickness < 3 nm) homogeneously wet CaF2/Si(1 1 1). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200 degrees C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600 degrees C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF2 film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeFx complexes which desorb at these temperatures. (C) 2007 Published by Elsevier B.V.