CO adsorption on Cu (100) has been found to be completely reversible over the temperature range 77-300 o K and Pco = 10-1L 10-4 torr using LEED and work function measurements. The isosteric heat has been determined as a function of coverage, and strong correlations have been found with surface structural changes. An in-registry-tout-of-registry transition was observed at 0.5 monolayer suggesting once again that localization on high coordination substrate sites may not be so important as commonly believed.

Articles you may be interested inRealistic adsorption geometries and binding affinities of metal nanoparticles onto the surface of carbon nanotubes Appl. Phys. Lett. 94, 073105 (2009); 10.1063/1.3083548Size dependence of core and valence binding energies in Pd nanoparticles: Interplay of quantum confinement and coordination reduction J. Appl. Phys.The structural arrangement and binding energy of CO adsorbed on a (100) surface of palladium have been determined and related to each other over the submonolayer coverage range. There are four distinct equilibrium structural arrangements of CO: (1) At low coverages «0.4 monolayers) a random lattice gas configuration is observed in which each CO molecule is localized on a specific adsorption site. (2) Just below 0.5 monolayers a liquidlike short-range order arrangement is found. (3) At exactly 0.5 monolayers a c(4X2)-45° overlayer structure forms which is in complete registry with the substrate. (4) For coverages greater than 0.5 monolayers, the c(4X2)-45° structure is uniaxially compressed to form an overlayer which is out of registry with the palladium substrate. The observed linear decrease in binding energy with coverage up to 0.5 monolayers suggests that the only important CO-CO interaction occurs between nearest neighbors. Near 0.5 monolayers an almost discontinuous decrease in the binding energy of 0.35 eV is attributed to loss of registry between the overlayer and substrate. As the coverage increased above 0.6 monolayers the binding energy again decreased sharply as a consequence of neighboring CO orbital overlap.

The adsorption of CO on Ni(100) has been studied using LEED, Auger, and work function measurements and was found to be completely reversible. The isosteric heat of adsorption was approximately 1.30 eV/molecule independent of coverage up to 0.61 monolayers. Three surface structures were observed: (1) a disordered phase at high temperature and/or low coverage, (2) a c(2× 2) phase at coverages up to and including 0.5 monolayers at sufficiently low temperature, and (3) a compressible hexagonal phase between 0.61 and 0.69 monolayers. Evidence is presented which supports an attractive CO–CO interaction at coverages of less than 0.5 monolayers. A number of two-dimensional phase transitions were observed and suggest an interesting T—θ phase diagram with a eutecticlike triple point. The importance of scrupulous cleaning procedures in allowing all possible adsorbed phases to be observed has again been demonstrated.

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An Auger electron spectrometer for studies of solid surfaces which is considerably more sensitive than currently used instruments has been developed. The greatly improved signal-to-noise ratio of the spectrometer made it possible to display the 0–1000 eV Auger spectrum on an oscilloscope at a scanning rate of 20 000 V/sec. Alternatively, the scanning rate may be reduced to that typical of present instruments (∼2 V/sec) and the primary beam current reduced from 5 × 10−5 to 10−8 A.