Role of step roughening in the formation of Ce silicide on Si(1Â 1Â 1)

We investigated the formation and diffusion process of the Ce silicide formed by the adsorption of Ce atoms (⩽1.5 ML) on Si(1 1 1) at room temperature followed by annealing at 500 °C using scanning tunneling microscopy and X-ray photoelectron spectroscopy. We found that Ce atoms first form a cluster with Si atoms on the terrace, and then diffuse toward the step edges whilst forming a more stable Ce silicide. The step roughening at the step edge of the Si(1 1 1) surface, which manifests as a submonolayer (0.3 ML), occurs due to the presence of Si atoms remote from this step edge, and this is regarded as the onset of the silicide formation process. At higher coverage (1.5 ML), the width of this Ce silicide step increases with annealing time at the same temperature.