Theory of Auger line shapes in chemisorption of Cl on Si(111)

$L_1{L}_{2,3}V$ and $L_{2,3}\mathrm{VV}$ Auger line shapes have been calculated for Cl and Si in the adsorption system Si(111)-Cl(1 × 1), based on an empirical tight-binding surface band-structure calculation. The fact that Cl and Si orbitals do not mix strongly means that the local densities of states (LDOS) at the Cl and Si atoms are very different; this difference is reflected in the predicted Cl and Si Auger spectra, and its experimental observation would be of considerable interest, as a demonstration that Auger spectra can provide local electronic structure information. The Si $L_1{L}_{2,3}V$ spectra from clean and Cl-covered Si(111) will probably not be different enough, because of the breadth of the Si $2s$ level, to permit one to obtain useful information from their difference. However, if one uses a grazing incidence beam to enhance the contributions of the outermost Si layers, the differences between the Si $L_{2,3}\mathrm{VV}$ spectra for the clean and covered surfaces should be quite prominent, and will reflect the changes in the Si electron energy distribution induced by the formation of strong $\sigma$- and weak $\pi$-bonds with the Cl. The calculated Cl spectra decompose readily into contributions from the $s$- and $p$-like components of the Cl LDOS and from convolutions of them, a fact which will permit the experimental determination of Auger matrix-element angular-momentum dependence.