Adsorbates on Gd(0001): A combined scanning tunneling microscopy and photoemission study

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1999

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We report on the electronic structure of hydrogen, oxygen, and carbon monoxide on (Formula presented) and the development of adsorption processes studied by means of photoelectron spectroscopy in combination with scanning tunneling microscopy and spectroscopy, respectively. Due to its high spatial resolution, the visualization of the adsorption process is obtained. For hydrogen, it was found that the adsorption occurs in two steps. It starts at crystallographic surface imperfections. From these nucleation centers, a domainlike spreading is present which is strongly hindered at surface steps. Oxygen on the Gd monolayer possesses an ordered structure which could be determined to be (Formula presented) Carbon monoxide adsorbs molecularly at low temperatures and dissociatively at room temperature. The adsorption process of a hydrogen-covered Gd film being exposed to carbon monoxide consists of five steps. At the beginning the whole amount of adsorbed hydrogen atoms is removed from the surface. In the intermediate regime, carbon and oxygen is adsorbed at or near the surface. The last step demonstrates the oxidation to (Formula presented) acting as a catalyst for the transformation of CO to (Formula presented) which creates stable carbonate species at the surface. This formation also occurs for the adsorption of oxygen and carbon monoxide. © 1999 The American Physical Society.

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Forschungsinformationssystem der UHH

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