Very well-resolved 2p core-level spectra were obtained from clean (001) surfaces. It was found that the spectra from cold c(4 x 2), and room-temperature (2 x 1), surfaces were very similar. This suggested that the local structure of the 2 reconstructions was the same. Shifted components, which originated from both the 'up' and 'down' atoms of asymmetrical dimers (as well as second-layer atoms), were identified. A split of about 0.55eV, between the 2 dimer-atom components, indicated the possible occurrence of substantial charge transfer within the dimers. No support was found for the recently proposed occurrence of crystal-field splitting of the surface components.

E.Landemark, C.J.Karlsson, Y.C.Chao, R.I.G.Uhrberg: Physical Review Letters, 1992, 69[10], 1588-91