Structure of the initial stages of oxidation of A1{111} surfaces from low-energy-electron diffraction and Auger electron spectroscopy

Abstract

The structure of the initial stages of oxidation of A1{111} surfaces has been determined by low-energy-electron diffraction (LEED) and Auger-electron-spectroscopy (AES) measurements. The oxidation process can be described by a four-stage mechanism depending on the oxygen exposure: 0-30 L; 30-100 L; 100-200 L; and 200 onwards. At the end of the first stage, the transition density of states (TDOS) obtained by self-deconvolution of the A1{111} \char22{}25-L RT ${\mathrm{O}}_{2}$-exposure ${L}_{2,3}\mathrm{VV}$ AES spectra and comparison with theoretical calculations of the DOS for this coverage show that the oxygen atoms occupy the fcc threefold hollows in an underlayer configuration, with an interplanar distance ${d}_{12}=0.0\ensuremath{-}0.5$ \AA{}. At 100-L RT ${\mathrm{O}}_{2}$ exposure, AES and LEED indicate the formation of a complete A1{111} 1 \ifmmode\times\else\texttimes\fi{} 1-O overlayer structure with the oxygen atoms occupying the fcc threefold hollows at ${d}_{12}=0.73\ifmmode\pm\else\textpm\fi{}0.05$ \AA{}. At 150 L, ${d}_{12}=0.80\ifmmode\pm\else\textpm\fi{}0.03$ \AA{} for the same A1{111} 1 \ifmmode\times\else\texttimes\fi{} 1-O structure. These LEED values solve the discrepancy with the surface-extended x-ray-absorption fine-structure measurements, and suggest the need for a revision of interplanar distances previously determined by LEED for oxygen-metal structures.