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 energy spectra of Auger electrons from clean Au, Ag, Cu, Pd, and Ni surfaces have been determined. Uniform deposition of a second metal onto clean metal surfaces has made it possible to assess the depth of the surface region which contributes to the Auger peaks in the secondary electron energy distribution characteristic. These results indicate that the mean escape depth for Auger electrons in Ag (without significant loss of energy) varies between 4 and 8 Å for energies of 72 and 362 eV, respectively. It has been shown (using Auger electron spectroscopy for detection of surface imuprities and low-energy electron diffraction for determining surface structure) that a clean Au (100) surface is reconstructed into a (1×5) structure, while clean Ag (100), Cu (100), and Pd (100) surfaces are characterized by bulk atomic arrangement. The combination of these two techniques has also been effectively applied to the interpretation of the structure and composition of CuAu surface alloys.

It has been shown, through analysis of simple overlayer structures consisting of a monolayer of Au or Ag on Cu(100) and Pd(100) surfaces, that Au atoms have an abnormal tendency to contract when positioned in a surface environment. This strong tendency for reduced interatomic spacing of Au surface layers is related to the atomically rearranged Au(100) surface, which consists of a hexagonal layer of Au atoms superimposed on a square array of substrate atoms. The driving force for rearrangement is interpreted in terms of the extreme sensitivity of the effective valency of Au to its atomistic environment. It is concluded that this interpretation of surface rearrangement is consistent with other unique properties of gold reported for binding energies of molecules in the vapor, and features of the band structure. In addition to providing information regarding the Au(100) surface structure, examination of metal overlayer structures has shown that pseudomorphism occurs during early growth stages of Ag and Au on the Pd(100) surface. Surface alloying of Au and Cu on the Cu(100) and on the Au (100) surfaces are also discussed.

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