Structure of Al/Si(111) interfaces: A photoemission extended x-ray-absorption fine-structure study.

Abstract

The atomic geometries of Al/Si(111) interfaces for 1.1 and 2.2 monolayer (ML) aluminum coverages at room temperature have been determined by photoemission extended x-ray-absorption fine structure (PEXAFS). The clean Si(111) surface was prepared by vacuum cleaving, which is known to have a (2\ifmmode\times\else\texttimes\fi{}1) reconstruction. For 1.1 and 2.2 ML Al/Si(111) interfaces, Si 2p and Al 2p PEXAFS data were acquired. The data were analyzed by Fourier analysis and curve-fitting procedures using the theoretical backscattering phase function of McKale et al. plus absorber phase function of Teo and Lee. For the clean Si(111)-(2\ifmmode\times\else\texttimes\fi{}1) surface, the first Si-Si bond length is determined as 2.40\ifmmode\pm\else\textpm\fi{}0.04 \AA{}, which is slightly larger than its bulk value (2.35 \AA{}). For Al/Si(111) interfaces, the average of Si-Si and Si-Al nearest-neighbor distances was determined as 2.47\ifmmode\pm\else\textpm\fi{}0.04 \AA{} from the Si 2p PEXAFS. For the 1.1 ML Al/Si(111) interface, the nearest-neighbor Al-Si bond length, derived from Al 2p PEXAFS, is 2.49\ifmmode\pm\else\textpm\fi{}0.04 \AA{}, which is in excellent agreement with the Al-Si bond length for the Al/Si(111)-(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 ) interface as reported in the literature. For the 2.2 ML Al/Si(111) interface, Al 2p PEXAFS yielded an Al-Al bond length of 2.94\ifmmode\pm\else\textpm\fi{}0.05 \AA{}, which is close to its value in Al metal.