HOLOGRAPHY OF CLEAN AND SULPHUR-COVERED NI/(111) USING MULTIPLE WAVE NUMBER PHOTOELECTRON DIFFRACTION PATTERNS

摘要

Angular distributions of Ni 3p(3/2) photoelectrons for clean Ni(111) and of S 2p(3/2) photoelectrons for the p(2 X 2)S and (5 root 3 X 2)S structures on Ni(111) were measured at seven different kinetic energies ranging from 239 to 417 eV for Ni 3p(3/2) and from 130 to 322.5 eV for S 2p(3/2). From the photoelectron diffraction patterns, holographic reconstructions were performed using (1) the single wave number reconstruction method and (2) the multiple wave number phased sum method. For the clean surface, neighboring atoms in the plane of the emitter and some atoms in the second and third plane above the emitter can be identified; the holographic reconstruction in the first plane above the emitter is however dominated by intense artifacts. For Ni(111)-p(2 X 2)S, the three-fold hollow fee adsorption site of sulphur can be unequivocally identified with a distance to the first Ni layer of about 1.6 Angstrom. Holographic reconstructions for Ni(111)-(5 root 3 x 2)S allow to exclude the three-fold hollow position of sulphur and disagree with a proposed mixing of different non-symmetric adsorption sites. The distance of the sulphur atoms from the top Ni layer is determined to 1.1-1.2 A. The reconstructions are consistent with a quasi-(100) reconstruction of the Ni(111) crystal surface. For all systems the potential of using only an azimuthal sector instead of the full hemispherical holograms for the reconstruction is discussed. References: 55