A detailed study of the formation of β-FeSi 2 films by ion-beam mixing of Fe/Si bilayers with noble gas ions is presented. Fe films of 35-50 nm deposited on Si (100) were irradiated with 80-700 keV Ar, Kr, or Xe ions in a wide temperature interval, from room temperature to 600 °C. The structures were analyzed by Rutherford backscattering spectroscopy, x-ray diffraction, conversion electron Mössbauer spectroscopy, elastic recoil detection analysis, cross-section high resolution transmission electron microscopy, and energy dispersive x-ray spectroscopy. Already after Xe irradiation at 300 °C the whole Fe layer is transformed to a mixture of Fe 3 Si, ε-FeSi, and β-FeSi 2 phases. At 400-450 °C, a unique, layer by layer growth of β-FeSi 2 starting from the surface was found. A full transformation of 35 nm Fe on Si to a 105 nm β-FeSi 2 layer was achieved by irradiation with 205 keV Xe to 2×10 16 ions/cm 2 , at a temperature of 600 °C. The fully ion-beam grown layers exhibit a pronounced surface roughness, but a sharp interface to Si. This structure is assigned to a growth of β-FeSi 2 grains in a local surrounding of interdiffused silicon. Rapid diffusion of silicon to the surface was observed during all ion irradiations. Single-phase β-FeSi 2 layers were also synthesized by vacuum annealing for 2 h at 600 °C of 35 nm Fe/Si bilayers premixed with Xe at 450 °C. In this case, the layers form with a smoother surface topography. It is concluded that ion-beam mixing can be used successfully for growth of β-FeSi 2 layers at moderate temperatures, either directly or combined with postirradiation annealing. © 2001 American Institute of Physics.