Geometry-DependentSi(2p)Surface Core-Level Excitations for Si(111) and Si(100) Surfaces

Structure-dependent $\mathrm{Si}\mathrm{}\left(2p\right)\mathrm{}$ surface core-level shifts and $2p$ photothreshold spectra which yield new surface geometry information are reported. For Si(100)-(2×1), ∼0.5 monolayer of surface atoms are found shifted to smaller binding energy (-0.5 eV) relative to the bulk; this rules out symmetric pairing models. Si(111)-(7×7) and Si(111)-(2×1) show different surface $2p$ core-level spectra (e.g., $\frac{1}{6}$ layer shifted -0.7 eV versus ½ layer shifted - 0.4 eV), suggesting different geometries. Si(111)-(1×1)H exhibits first-layer (+ 0.26 eV) and second-layer (+ 0.15 eV) shifts.