Subsurface interstitials as promoters of three-dimensional growth of Ti on Si(111): An x-ray standing wave, x-ray photoelectron spectroscopy, and atomic force microscopy investigation

The adsorption and growth of Ti on Si(111)-7×7 surface at room temperature was studied with x-ray standing waves and high energy x-ray photoelectron spectroscopy. The surface morphology of the specimens was analyzed using atomic force microscopy. We observed that at the submonolayer (0.08–0.24 ML) coverage a significant fraction of the metal atoms are coherently located in the near-surface interstitial positions of the Si lattice. For a higher Ti coverage (1.8 ML), the coherently ordered fraction almost vanishes and the surface is covered with three-dimensional islands. The Ti-coverage results are interpreted in terms of an interfacial transition layer containing Ti interstitials below the Si surface at low coverage, and a disordered mixed Ti–Si phase at higher Ti concentration.