Several SiGe alloys of various compositions were bombarded with ultra-low-energy primary ions, and the energy spectra of the resulting secondary ions were studied. We report here on the effects of alloy composition and primary ion beam energy on the spectra. It was found that the shape of the Si+ and Ge+ energy spectra are strongly dependent on the Ge fraction. The high energy tail on the spectra increases with Ge alloy percentage, whilst the peak position remains the same regardless of sample composition, primary beam energy or the mass of the secondary ion. It was also found that for low primary beam energies there is a narrowing of the atomic energy spectra so that atomic and molecular characteristics are indistinguishable. (C) 2002 Elsevier Science B.V. All rights reserved.