Surface energy bands and atomic position of Cl chemisorbed on cleaved Si(111)

Angle-resolved photoemission measurements using synchrotron radiation have been performed on a cleaved Si(111) surface covered to saturation with Cl. Two main Cl-induced peaks, identified as the $\sigma$ and $\pi$ bonding levels, are observed, and the angular dependence of their intensities supports the onefold site for the Cl adatoms. The two-dimensional energy bands for the $\sigma$, $\pi$, and two previously unobserved levels, designated $b$ and $s$, are mapped directly from the angular dependence of peak positions. As far as dispersion and rough energy location are concerned, these Cl-induced surface energy bands are in remarkably good agreement with self-consistent pseudopotential calculations. There are some minor differences in detail, concerning precise energy locations and band splittings. The $b$ level is identified, on the basis of the pseudopotential charge densities, as a state involving the Si back-bonding orbitals. The $s$ level is attributed to bonding between $\mathrm{Cl} p_z$ and $\mathrm{Si} s$ orbitals, in contrast to the $\sigma$ level which involves bonding between $\mathrm{Cl} p_z$ and $\mathrm{Si} p_z$ orbitals.