Spectroscopic signatures of a symmetry-breaking surface phase transition: Ag/Si (111)?3 × ?3 -> 3 × 1

High resolution synchrotron radiation Si 2p core level spectra from the clean Si(111) 7 × 7 surface and the silver-induced 3 × 1 reconstruction (1/3 monolayer coverage) present a striking similarity in overall lineshapes and decompositions. This questions the existing structural models of the 3 × 1-Ag surface and indicates that both 7 × 7 and 3 × 1 substrate selvedges should share a common atomic geometry. We suggest that this could be sixfold Si rings arranged in a faulted-unfaulted sequence.