PLATINUM-INDUCED MORPHOLOGY AND REACTIVITY CHANGES ON W(111)

The structure and CO chemisorption properties of a model bimetallic system Pt on W(111) have been studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and thermal desorption spectroscopy (TDS). The results reveal that upon annealing, the Pt/W(111) system undergoes a variety of structural transformations, with the most striking being the reconstruction of the W(111) substrate to form pyramidal facets with {211} orientations. The presence or absence of facets, and size distribution of the facets, are sensitive functions of Pt coverage and annealing temperature. LEED results for faceted surfaces annealed to different temperatures correlate well with the STM data. CO has been used as a probe molecule to examine the chemisorption properties of the different structural phases. Increasing Pt coverage causes site blocking that results in reduced dissociative adsorption of CO.