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.