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Indium films up to 6 ML thick on the Ge(001) surface in ultrahigh vacuum have been both deposited at and investigated at room temperature. The investigation techniques used were scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and low energy electron diffraction. Correlated AES and STM observations strongly suggest In–Ge intermixing, while XPS rules out compound formation. For a film 5 ML thick, nanoparticles approximately 15 nm high and 60 nm across with a pronounced faceted shape were observed in STM using a Pt–Ir tip scanning as far from the surface as possible. For smaller tip-sample distances, a dynamic tip-sample interaction was observed which resulted in sawtooth topographic data inconsistent with the topography observed at larger tip-sample separations. The evidence is that the epitaxial film is in the liquid phase at room temperature, in spite of the In bulk melting point at atmospheric pressure being 430 K. The liquid phase hypothesis is supported by a thermodynamic calculation which considers the impact of heteroepitaxial stress on the melting point. © 1999 American Vacuum Society.