Silicon (2p) surface core-level line shape of Si(111)–B

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Abstract
Several recent structural studies of the Si(111)–B ((3)1/2×(3)1/2) surface have established that the boron atoms occupy substitutional sites in the second full Si layer and have Si adatoms directly above them. High-resolution (∼80–100 meV) Si(2p) core-level photoemission was used to determine the B-induced perturbation of the surface Si atoms. The samples were prepared by surface segregation from Si(111) wafers (∼1.5 at. % B) after thermally removing the thin protective oxide layer on the surface. Photoemission spectra for photon energies from 110 to 140 eV show three peaks, indicative of at least two well-separated spin-orbit doublet components. Attempts to fit the data with only two components were unsatisfactory unless a Doniach–Šunjić line shape was used for the B-induced component. This suggests that the surface region influenced by the B impurities is metallic, i.e., the Fermi level lies within the B-modified valence band. The intensity of the bulk component goes through a minimum at a photon energy of 130 eV corresponding to a kinetic energy of 26 eV and is 0.19 of the total intensity. This leads to an escape depth of ∼3 Å if the B-influenced region includes three layers below the adatom layer. Improved fits were obtained by using three distinct surface components. These are identified with the Si adatoms, the three B-influenced surface layers, and the Si in the third layer which directly bonded to B.

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