Scanning tunneling microscopy studies of the structures and dynamics of molecular monolayers on the rhodium(111) and platinum(111) single crystal surfaces

The structures and dynamics of the chemisorbed overlayers of oxygen, nitric oxide, propylene and four cyclic aromatic hydrocarbon compounds on the Rh(111) and/or Pt(111) at room temperature were investigated by scanning tunneling microscopy (STM). The topography of the Rh(111) surface during the propylene thermal decomposition process was inspected. The STM tip catalyzed oxidation and hydrogenation of carbonaceous clusters were successfully performed on Rh(111).; Oxygen and nitric oxide both form (2 x 2) type overlayers on Rh(111) in ultrahigh vacuum. The (2 x 2) oxygen structure remains in the presence of up to 10 torr of O₂. However, at higher pressure, large disordered features were found on the surface, suggesting the concurrent nucleation of atomic oxygen localized around carbon impurities. The (2 x 2) nitric oxide overlayer has 1/3 of molecules on atop site and the remaining on hollow sites.; On Pt(111) propylene forms a stable (2 x 2) propylidyne overlayer, but upon exposed to CO it decomposes to disordered small fragments. On Rh(111), however, propylene briefly forms a unstable (2 x 2) propylidyne structure, which further decomposes into disordered mixture of ethylidyne and C-H species.; The adsorption behaviors of benzene, naphthalene, phenanthrene and anthrancene on Rh(111) and Pt(111) were systematically investigated. The characteristic shapes of all four molecules were differentiated. All molecules lie flat on the substrate. Benzene alone forms (3 x 3) and c(2√3 x 4) overlayers, and when co-adsorbed with NO, it arranges to a (3 x 3) overlayer. Naphthalene forms (3 x 3) and (3√3 x 3√3)R30° overlayers on Rh(111). On both Rh(111) and Pt(111), phenanthrene and anthracene have no long-range ordering, regardless of whether it is alone or co-adsorbed with other molecules. However, the C₂ axis of phenanthrene is always along one of the close-packed directions of the Rh(111) substrate, while anthracene is randomly oriented.; Topography images were taken after the propylene adsorbed Rh(111) surface was heated at 155°C, 265°C, 400°C and 600°C, where C _xH fragment, carbonaceous clusters, polymers, and graphite form, respectively.; Platinum STM tip-catalyzed hydrogenation and oxidation of carbonaceous species on the Rh(111) surface were observed for the first time. The reactions only took place when a Pt (not W or Au) tip was used in the presence of O ₂ or H₂. The reaction rate rises with the increase of background pressure increase and/or the decrease of tunneling gap. (Abstract shortened by UMI.)...