The effect of the surface structure of Pt on its electronic properties and the adsorption of CO, O2, and H2: A comparison of Pt(100) – (5×20) and Pt(100) – (1×1)

Abstract

We describe studies of the Pt(100) – (1×1) and Pt(100) – (5×20) surfaces with LEED, UPS, AES, and flash desorption spectroscopy. The clean Pt(100) – (1×1) surface is prepared by adsorbing CO, then reacting it off with oxygen ions in the form of CO2. The clean (1×1) surface formed is metastable, converting back to the (5×20) surface at 125 °C. This and other evidence leads us to the conclusion that the (5×20) surface is the clean equilibrium structure. The electronic structure of the (1×1) surface is characterized by a surface state or resonance 0.25 eV below the Fermi level, which is not observed on the (5×20) surface. Although O2 and H2 do not chemisorb at room temperature for exposures less than 102 equivalent monolayers on the (5×20) surface, the (1×1) surface readily chemisorbs O2 and H2. It is suggested that the structure sensitivity of the O2 and H2 chemisorption observed may be due to the corresponding change in surface electronic structure. CO adsorbs on both the (5×20) and (1×1) surfaces. At 0.5 saturation CO coverage on the (1×1) surface a previously unreported C(2×2) LEED pattern is observed. This same LEED pattern can be obtained from the (5×20) surface if a saturation coverage of CO is adsorbed and then partially desorbed at 140 °C.