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The oxidation of CO on Ir(111) surfaces was investigated under UHV conditions in the temperature range 360 K to 700 K by CO[sub 2] rate measurements utilizing mass spectroscopy. Steady-state CO[sub 2] rates were measured at constant total CO+O[sub 2] gas flux and variable gas composition (Y[sub CO]=Y, Y[sub O[sub 2]]=1-Y) using mass flow controllers which allowed changes in the CO/O[sub 2] gas composition down to 0.1%. Between 360 K and 450 K the CO[sub 2] rates initially increase proportional to Y (T<400 K) or to Y[sup 1.5] (420 K

Benzene and (1,4)-dimethyl-cyclohexane monolayers were physisorbed on graphite covered Pt(111) surfaces. Exposure of benzene monolayers at 125 K to D atoms (1700 K) initially hydrogenates sp2 hybridized C atoms with a cross section of ca. 8 Å2 producing C6H6D intermediates. Additional D atom reactions either transform this intermediate via a second hydrogenation reaction to cyclohexadiene-d2, C6H6D2, or restore benzene, C6H5D, via H abstraction. Once the aromaticity is broken, successive hydrogenation of the diene occurs rapidly generating the saturated cyclohexane-d6, C6H6D6. The C6H5D reaction product can undergo further H/D exchange reactions and, at any level of deuteration, the benzene species might get hydrogenated. Monolayers of the saturated hydrocarbon (1,4)-dimethyl-cyclohexane (DMCH) that are exposed to D atoms produce deuterated DMCH via successive abstraction/hydrogenation reactions. Thermal desorption mass spectra revealed that H atoms at the ring were exchanged with an apparent cross section of 1.7 Å2. Methyl groups H atoms were exchanged much more slowly than ring H atoms. It was also observed that D exposed molecules/radicals exhibit a tendency to desorb from the surface, which is ascribed to the exothermicity of the reactions which lead to these species. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Hydrogen containing carbon (C:H) films have been prepared by ion beam deposition of 160 eV ethane ions on a carrier consisting of a Pt(111) single crystal surface covered with a monolayer of graphite. Several monolayers thick films deposited at 350 K contain hydrogen bound to sp, sp2, and sp3 hybridized carbon. Vibrational spectroscopy reveals that thermal D(H) atoms directed to the C:H film surface hydrogenate unsaturated CH groups at the surface and transform sp and sp2 hybridized carbon to sp3. The observed reaction mechanism explains the microscopic processes in chemical erosion of graphite by hydrogen atoms which is a crucial reaction step in the low pressure synthesis of diamondlike carbon. [ABSTRACT FROM AUTHOR]

Ultraviolet photoelectron spectroscopy (UPS) and electron spectroscopy by deexcitation of metastable noble gas atoms (MDS) were used to follow the continuous oxidation of Cs films. While UPS has a finite information depth, MDS probes only the properties of the outermost atomic layer. Small doses of O2 cause the formation of a ‘‘monolayer’’ of Cs11O3 in which the O2- ions are incorporated below the surface, while the surface itself consists merely of metallic Cs atoms. Further uptake of oxygen leads to a continuous transformation of the subsurface layer into Cs2O2, while a small concentration of adsorbed O atoms builds up on the surface which act as nucleation centers for subsurface oxidation. Finally, the surface layer is completely oxidized into CsO2 which then retards further oxygen penetration into the bulk. The chemical state of the surface can be directly correlated with the associated change of the work function. A monolayer of Cs adsorbed on a Cu(110) surface exhibits quite different properties. [ABSTRACT FROM AUTHOR]

Presents a study which investigated mono layers thick hydrogenated carbon films doped with boron (C⁄B:H) in an ultrahigh-vacuum environment by high-resolution electron energy loss, Auger electron, electron energy loss and thermal desorption and decomposition spectroscopies. Materials and methods used; Characteristics of the C⁄B:H films; Overview of thermal decomposition of the C⁄B:H films.4

Presents information on a study which investigated the growth and thermal decomposition of ultrathin ion-beam deposited hydrogenated carbon films. Characteristics of film deposition; Experimental details; Results and discussion; Conclusions.