INSITU SCANNING TUNNELING MICROSCOPY AS A PROBE OF ADSORBATE-INDUCED RECONSTRUCTION AT ORDERED MONOCRYSTALLINE ELECTRODES - CO ON PT(100)

The atomic-level structure of ordered Pt(100) electrodes prepared by air-hydrogen flame annealing followed by iodine dosing and solution-phase replacement by CO has been examined by in situ scanning tunneling microscopy. While large (1 x 1) substrate terraces are discernible in the presence of iodine adlayers, subsequent CO adsorption in 0.1 M HClO4 yields dense arrays of smaller, 20-40 angstrom, (1 x 1) islands. These domains coalesce upon positive alterations in the electrode potential. Parallel in situ infrared spectroscopic measurements shows that these structural changes are accompanied by an attenuation of bridge-bound CO in the close-packed adlayer structure. The bridging CO is speculated to be present at the edges of the (1 x 1) domains, contained within which are predominantly atop-coordinated CO.