Preparation-dependent Co/Si(100) (2×1) interface growth: Spontaneous silicide formation versus interstitial-site mechanism

Extended x-ray-absorption fine-structure measurements, low-energy electron diffraction, and Auger-electron spectroscopy have been applied to study preparation-dependent room-temperature Co/Si(100) interface formation. Evaporation of Co onto chemically etched and annealed Si(100) (2×1) leads up to about 0.5 monolayer coverage for adsorption of Co in the fourfold-hollow sites of the locally unreconstructed Si(100) surface. At higher coverages Co atoms occupy interstitial (adamanthane) and substitutional sites of the Si lattice. Annealing at T=550–650 °C for 5 min induces the diffusion of Co into the Si lattice, where Co atoms reside in adamanthane sites only. After evaporation of Co onto sputter-annealed Si(100) (2×1), only the formation of a locally ordered ${\mathrm{CoSi}}_2$-like phase could be observed in the measured coverage regime between 0.8 and 14 monolayers.