Interactions between adsorbates and a stepped metallic surface studied with scanning tunneling microscopy and low energy electron diffraction.

摘要

The work presented in this thesis revolves around the use of a stepped metal surface, Ni(977), to further our understanding of the role of crystalline defects in surface processes such as metallic oxidation and interfacial ordering. A versatile UHV system designed specifically for STM experiments at elevated temperature was constructed. The proximity heater is a non-invasive modification to an existing commercial room-temperature microscope and is capable of radiatively heating samples up to 650 K in situ.;Time lapsed STM has been used to observe the oxygen induced reconstruction behavior of Ni(977). Sequential imaging recorded at temperature has elucidated mechanistic details for the merging of steps in the presence of small amounts of adsorbed oxygen. An optimal oxygen concentration of step edge saturation was found to enable the step merging to proceed most rapidly. Merging of steps is initiated by the bulging of one step in the downstairs direction toward its neighbor and coalescence into a doubled step subsequently proceeds via zippering. Excess oxygen was found to hinder the coalescence of neighboring steps by either forming overlayer structures on the terrace or, at sufficiently high temperatures, driving the surface back to single steps due to oxygen dissolution.;Phase behavior of oxygen on the vicinal Ni(977) surface was examined and compared with that for oxygen adsorbed on the flat Ni(111) surface. On Ni(977), the p(2x2) phase still disorders at 440 K, but a step-stabilized ordered phase that first appears just above room temperature survives until well above 500 K when the oxygen is finally incorporated into the bulk. Furthermore, the process of oxygen dissolution is qualitatively altered by the presence of regular steps.;Finally we show that it is possible to guide the formation of a novel non-close-packed xenon structure on a stepped nickel surface using an intentionally atomically-patterned substrate. Such templating effects, in which the corrugation and structure of the interface can be tuned by prior adsorption of an adsorbate, should be a general route to the formation of new self-organizing interfacial nanoscale structures.