Abstract
PhotoEmission Electron Microscopy (PEEM) enables imaging a surface via its work function. If a CO covered Pt(100) surface is exposed to oxygen patches are formed which appear dark in the PEEM image due to their high work function. As the surface is heated to temperatures above 650 K we observe the conversion of these dark islands into very bright ones with work functions much lower than even that of the clean surface. These findings are attributed to a change in the dipole moment of the adsorbed oxygen induced by their migration beneath the surface. A total work-function decrease of up to 1.2 eV has been evaluated independently using a Scanning Photoemission Microscope (SPM). The properties of this new kind of oxygen were also further investigated with thermal desorption spectroscopy and with Auger-electron spectroscopy.
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