Coverage dependence and surface atomic structure ofMn/Si(111)−3×3studied by scanning tunneling microscopy and spectroscopy

Abstract

Thin manganese silicide films of different thicknesses on Si(111) have been studied in detail by low-energy electron diffraction (LEED), scanning tunneling microscopy, and scanning tunneling spectroscopy (STM/STS). Up to a Mn coverage of 3--4 monolayers (ML), island formation is favored. For higher Mn coverages up to 12 ML uniform film growth is found. The silicide film morphology at low coverages supports a layered Mn-Si film structure. The silicide surfaces displayed a $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ LEED pattern. STM images recorded from the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ surfaces mostly show a hexagonal pattern but a honeycomb pattern has also been observed. A surface atomic structure based on chained Mn triangles is proposed. Our STM results are in good agreement with a recent theoretical model. The high-quality STS spectra recorded from the different surfaces show a clear metallic character at 1.5 ML and higher coverages. The filled-state features in the STS spectra at surfaces with 3--4 ML Mn coverages are similar to earlier published angle-resolved photoelectron spectroscopy data.