The surface structures of the Ba-induced 3 x 1, 5 x 1, and 2 x 8 reconstructions on the Si(111) surface were investigated by means of Si2p and Ba4d core-level photoemission and the coverage was estimated by X-ray photo-emission. In the Si2p core-level spectrum of every reconstructed surface, three prominent surface components that were shifted to lower and higher binding energies from the bulk peak were observed. In the case of the 3 x 1 surface, these surface components were well explained by the so-called honeycomb-chain-channel model which was considered to be the most plausible structure for alkali-metal-induced 3 x 1 surfaces. The similarity of the core-level spectra between the 2 x 8 surface and the Ca - or Yb -induced 2 x 1 surface suggested that both the 2 x 8 and 2 x 1 surfaces have similar short range Si structures. The observed double component in the Ba4d core-level spectra of the 5 x 1 and 2 x 8 surfaces implied the existence of more than one Ba adsorption configuration on these surfaces. The estimated metal coverages by X-ray photo-electron spectroscopy for the 5 x 1 and 2 x 8 surfaces were ∼0.2 and ∼0.3 monolayers which were different from those of previous studies for the Ca∕Si(111) system. On the basis of these results, possible surface structural models were proposed for the 5 x 1 and 2 x 8-Ba surfaces; based upon a combination of the honeycomb-chain-channel and Seiwatz chain structures.

Structural Analysis of Ba-Induced Surface Reconstruction on Si(111) by Means of Core-Level Photoemission. T.Okuda, K.S.An, A.Harasawa, T.Kinoshita: Physical Review B, 2005, 71[8], 085317 (9pp)