CORE-LEVEL SPECTROSCOPIC STUDY OF THE EVOLUTION OF THE SULFUR-PASSIVATED INP(001) SURFACE DURING ANNEALING

Core-level photoemission spectroscopy and theoretical predictions of s tructure and spectra are used to study the fully S-covered InP(001) su rface 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 (2x2)-reconstructed structure, where the surface h as two types of S atoms. On annealing, a fascinating sequence of struc tures unfolds from the fully S-covered ground state as the other stabl e structures become energetically accessible. The surface S atoms exch ange with bulk P atoms on annealing, forming new strong S-P bonds whil e 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 ato m in the structure. The measured excitation energies and spectra agree with theoretical predictions of the core-level spectra for the (2x2) reconstruction and its evolution to partial S coverages. We conclude t hat the annealed surface around 700 K is most likely to be a (2x2) rec onstructed surface with the surface cell containing two S-P bonds, wit h just one type of S atom.