Core-level spectroscopic study of the evolution of the sulfur-passivated InP(001) surfaceduring annealing

Abstract

Core-level photoemission spectroscopy and theoretical predictions of structure and spectra are used to study the fully S-covered InP(001) surface and its evolution during annealing. The theory predicts a number of stable structures besides the lowest-energy ground state which is the fully S-covered (2\ifmmode\times\else\texttimes\fi{}2)-reconstructed structure, where the surface has two types of S atoms. On annealing, a fascinating sequence of structures unfolds from the fully S-covered ground state as the other stable structures become energetically accessible. The surface S atoms exchange with bulk P atoms on annealing, forming new strong S--P bonds while dissociating preexisting S--S dimers. The S--P bonds are tilted with the P atoms just above the surface and there is only one type of S atom in the structure. The measured excitation energies and spectra agree with theoretical predictions of the core-level spectra for the (2\ifmmode\times\else\texttimes\fi{}2) reconstruction and its evolution to partial S coverages. We conclude that the annealed surface around 700 K is most likely to be a (2\ifmmode\times\else\texttimes\fi{}2) reconstructed surface with the surface cell containing two S--P bonds, with just one type of S atom.