SI 2P CORE-LEVEL SHIFTS AT THE AS SI(001) AND SB/SI(001) SURFACES/

We calculate the Si 2p core-level shifts at the As/Si(001)-(2x1) and S b/Si(001)-(2x1) surfaces using final-state pseudopotential theory. We find a large difference in the surface core-level shifts originating f rom the first-layer Si atoms between the two systems, in good agreemen t with photoemission experiments. We also find the surface components of Si 2p core levels for second- and third-layer Si atoms. Our results for the As/Si(001) system provide an interpretation of several surfac e components observed in a recent high-resolution core-level spectra.