Surface structure and electronic states of epitaxialβ−FeSi2(100)/Si(001) thin films: Combined quantitative LEED,ab initioDFT, and STM study

Abstract

The surface structure of epitaxial $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{FeSi}}_{2}$(100) thin film grown on Si(001) was analyzed using the quantitative low-energy electron diffraction intensity-voltage (LEED I-V) method, ab initio density functional theory (DFT) calculations, and scanning tunneling microscopy (STM). LEED patterns measured on the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{FeSi}}_{2}$(100) surface reveal two domains of a $p(2\ifmmode\times\else\texttimes\fi{}2)$ reconstruction with $p2gg$ diffraction symmetry. The iron-silicide film truncation and atomic surface structure were determined by LEED I-V method: The smallest Pendry's reliability factor ${R}_{P}=0.22\ifmmode\pm\else\textpm\fi{}0.02$ was achieved for the bare $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{FeSi}}_{2}$ film truncated by an Si layer, whereas Si and Fe ad-atom structures were excluded. Significant atomic relaxations within the topmost surface layers were revealed by the LEED I-V method and confirmed by DFT. The simulated STM patterns from the best-fit model agree well with the measured STM images on the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{FeSi}}_{2}(100)/\mathrm{Si}(001)\text{\ensuremath{-}}p(2\ifmmode\times\else\texttimes\fi{}2)$ surface: Four Si atoms on a surface form one bright protrusion on STM patterns. Electronic band structure analysis of the bulk and epitaxial $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{FeSi}}_{2}$(100) was carried out. A bare truncated epitaxial film was found to be metallic. Surface electronic states were identified by a partial $k$-resolved atomic-orbital based local density-of-state analysis.