In overlayers on Si(111)7×7: Growth and evolution of the electronic structure

The formation of thin overlayers of In on Si(111)7×7 substrate surfaces has been studied in the temperature range from room temperature to ∼500 °C by Auger-electron spectroscopy, low-energy electron diffraction, direct and inverse photoemission spectroscopy (UPS and IPES), and electron-energy-loss spectroscopy (EELS). Up to In coverages ${\mathit{FTHETA}}_{\mathrm{In}}$ of about 1–2 monolayers (ML), uniform layer growth prevails irrespective of the substrate temperature, but ordered surface structures can only be observed at elevated temperatures. Beyond ${\mathit{FTHETA}}_{\mathrm{In}}$≊1–2 ML, three-dimensional island clustering according to the Stranski-Krastanov mechanism appears, but the growth rate appears to be greatly reduced for substrate temperatures >300 °C. This may be attributed either to a low sticking probability of In on the ordered (1×1)R30° In-Si phase, which develops at T>300 °C for ${\mathit{FTHETA}}_{\mathrm{In}}$≊1–2 ML, or to drastically different In island shapes at elevated temperatures. The ordered In-Si reconstructions (√3 × √3 )R30°, (4×1), and (1×1)R30° have been characterized by UPS, IPES, and EELS, and distinctly different interface state characteristics have been obtained for the various surfaces; these differences are particularly striking in the IPES spectra. It is suggested that the different interface state behavior reflects different local bonding geometries of In atoms at the various interfaces, and the data are discussed in terms of plausible models for interface geometries.