ATOMIC STRUCTURE AND INTERACTIONS AT SINGLE CRYSTAL METAL SURFACES

The aim of the research contained in this thesis was to broaden the range of available surface diffusion data, specifically extending the established techniques to include lighter metals of metallurgical and theoretical interest, and to investigate the capabilities and limitations of the FIM for determining the atomic structure of metal surfaces that are known to display clean surface reconstruction. Accordingly, the diffusional characteristics of nickel and aluminum surfaces have been examined using an extension of routine FIM procedures, and the atomic structure of W, Mo and Nb(001) surfaces have been studied using a new procedure which provides results that clearly demonstrate the power of the FIM technique for the study of surface reconstruction. Results of single atom self diffusion on Ni(311), (331), (110), (111) and (100) planes, and on Al(311), (331) and (110) planes are presented. One dimensional motion of adatoms is observed on the (311) and (331) planes of Ni and Al, with motion of adatoms being two-dimensional on the rest of the planes. Two types of adsorption site and surface site geometry exist for single nickel atoms on the Ni(111) surface. Entirely different diffusion characteristics are found on Ni(110) depending on whether the surface is prepared by thermal annealing or prepared by hydrogen etch. The presence of absorbed hydrogen on the Ni(110), (311), and (331) surfaces is shown to lower the onset temperature for self-diffusion on these planes dramatically. The atomic structures of clean W and Mo(001) surfaces have been examined by FIM in the temperature range 15-580 K. Field evaporation, especially at elevated temperatures, preferentially removes alternate surface atoms resulting in c(2 x 2), (SQRT.(2xSQRT.(2) - R45(DEGREES) structures.(\u27 ) Temperature cycling, followed by low-temperature field evaporation has resulted in occasional observation of intensity variations over a W(001) plane. The reconstruction model suggested by these results for the W and Mo(001) surfaces consists of a vertically rippled surface with no, or at least very small, lateral displacements