Formation of an Au-Si eutectic on a clean silicon surface

We investigated the formation of an AuSi eutectic from a silicon (100) surface cleaned under ultrahigh vacuum conditions and an evaporated 3-nm-thick gold layer using a suite of surface-sensitive x-ray techniques and Auger spectroscopy. The signature of the presence of the eutectic liquid came from its recently discovered surface-ordered state, whose diffraction pattern is confirmed. As expected, the eutectic started to form at its melting temperature (380 degrees C), but a small change in the film thickness was detected beforehand. The surface-ordered state was found to disappear at T=473 degrees C without the appearance of a second phase, but also to persist after resolidification of the liquid. Subsequent electron and x-ray microscopy after the sample was removed from vacuum showed the presence of phase-separated gold in the form of micronsized crystals on the surface.