Structure of ultrathin Ag films on the Al(100) surface (original) (raw)
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Molecular-dynamics description of early film deposition of Au on Ag(110)
Physical Review B, 1995
We simulate the vapor deposition of the first three monolayers (ML) of Au on Ag(110) using surfaceembedded-atom potentials fit to both the bulk and surface properties of the low-index faces of the Au and Ag single crystals. The simulation is carried out with the molecular-dynamics code DAMsEL using the technique of computational annealing to mimic room-temperature deposition. We find that up to 1 ML most of the Au atoms interdiffuse to the substrate layer with little three-dimensional growth to that point. Subsequently the growth becomes more three-dimensional resembling a 3 X 1 missing-row reconstruction, with the top layers containing higher proportions of Au atoms. The simulations thus support the interdiffusion of a single layer of Au below the Ag surface and a Stranski-Krastanov (SK) growth mode consistent with recent scanning-tunneling-microscopy (STM) analyses. We examine the dynamic mechanisms of the deposition and find that atomic replacement and high Ag mobility largely account for the observed growth. Comparisons are carried out with previous analyses of medium-energy ionscattering and STM experiments with agreement on the interdiffusive SK growth mode interpretation.
Structure of Au on Ag(110) studied by scanning tunneling microscopy
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
The epitaxial growth of Au on Ag(110) has been studied by scanning tunneling microscopy up to 8 ML. In the submonolayer range the results show that gold atoms are intermixed with the silver atoms in the top two layers. Above 1 ML a two‐dimensional fingerlike growth gives rise to anisotropic three‐dimensional islands of gold, which appear to be thermal equilibrium structures. Above 5 ML, the gold overlayer forms a (1×3) reconstruction which is manifested as double rows of atoms growing along [11¯0]. The development of this reconstruction is followed as a function of coverage.
Physical Review B, 2003
In this work we present the results concerning the investigation of the temperature dependence of the first three interlayer spacings of Ag͑110͒ surface using low energy electron diffraction ͑LEED͒ analysis and density-functional theory and molecular dynamics over a wide temperature range. It was possible to observe significant changes in the thermal expansion of the first and second interlayer distances without detection of effects associated with an enhanced anharmonicity. The values of the Debye temperature of the first two layers were obtained by LEED and a comparison between these results and those from other techniques are presented and discussed.
Physical Review Letters, 1994
We simulate the vapor deposition of the first three monolayers of Au on Ag(110) with the molecular dynamics code DAMsEL using surface-embedded-atom potentials and utilizing simulated annealing. The simulations show interdiffusive Stranski-Krastanov growth, which is consistent with recent ion scattering and scanning tunneling microscopy studies. Most of the first deposited monolayer of Au burro~s to the substrate layer, with further deposition leading to 3D growth resembling a 3x l missing-row reconstruction. %'e discuss the dynamic mechanisms accounting for this growth.
Equilibrium morphology of the Ag(110) surface
Surface Science, 1996
This paper reports on He-atom scattering measurements performed in order to shed light on the equilibrium morphology of the bare Ag(ll0) surface. Measurements of the specular peak profile along (1"10) and slightly off the out-of-phase scattering condition show that the proposed "hill and valley" configuration is originated by thermally induced segregation of bulk impurities. Proper cleaning procedure is described to obtain the unfaceted surface which is proven to be the equilibrium morphology of Ag(110).
Epitaxial growth of Au on Ag(110) studied by scanning tunneling microscopy
1993
The epitaxial growth of Au on AgGlO) has been investigated by scanning tunneling microscopy up to 3 ML. A very consistent "intermixed Stranski-Krastanov" growth mode is demonstrated. Below 1 ML the open structure of the (110) surface allows the Au atoms to be incorporated mainly in the second layer. At higher coverages three-dimensional anisotropic islands of gold are observed. The anisotropic shape, the island density and the transition from ~~dimensional to three-dimensional growth are 0039-6028/93/$06.00 0 1993 -Elsevier Science Publishers B.V. All rights reserved
Langmuir, 2010
We report an extensive first-principles study of the structure and electronic properties of Ag n (n = 1-8) clusters isolated in gas phase and deposited on the R-Al 2 O 3 surface. We have used the plane wave based pseudopotential method within the framework of density functional theory. The electron ion interaction has been described using projector augmented wave (PAW), and the spin-polarized GGA scheme was used for the exchange correlation energy. The results reveal that, albeit interacting with support alumina, the Ag atoms prefers to remain bonded together suggesting an island growth motif is preferred over wetting the surface. When compared the equilibrium structures of Ag clusters between free and on alumina substrate, a significant difference was observed starting from n = 7 onward. While Ag 7 forms a three-dimensional (3D) pentagonal bipyramid in the isolated gas phase, on alumina support it forms a planar hexagonal structure parallel to the surface plane. Moreover, the spin moment of the Ag 7 cluster was found to be fully quenched. This has been attributed to higher delocalization of electron density as the size of the cluster increases. Furthermore, a comparison of chemical bonding analysis through electronic density of state (EDOS) shows that the EDOS of the deposited Ag n cluster is significantly broader, which has been ascribed to the enhanced spd hybridization. On the basis of the energetics, it is found that the adsorption energy of Ag clusters on the R-Al 2 O 3 surface decreases with cluster size.
Electrochimica Acta, 1999
Simulation studies are undertaken for the system Ag/Au(100) by means of grand canonical Monte Carlo applied to a large lattice system. The interactions are calculated using the embedded atom model. The formation of adsorbed Ag phases of low dimensionality on Ag(100) is investigated and the influence of surface defects on the shape of the adsorption isotherms is studied. The results of the simulations are discussed in the light of experimental information available from electrochemical measurements.
Ab initiostudy of edge smoothing, atom attraction, and downward funneling in Ag/Ag(100)
Physical Review B, 2011
The results of density-functional theory (DFT) calculations of the energy barriers for three low-barrier relaxation processes in Ag/Ag(100) growth-edge-zipping, atom attraction, and downward funneling-are presented and compared with embedded atom method (EAM) calculations. In general, we find good agreement between the DFT values for these processes and the values assumed in recent simulations of low-temperature Ag/Ag(100) growth [Shim and Amar, Phys. Rev. B 81, 045416 (2010)]. We also find reasonable agreement between our DFT results and the results of EAM calculations, although in a few specific cases there is a noticeable disagreement. In order to investigate the effects of long-range interactions, we have also carried out additional calculations for more complex configurations. While our EAM results indicate that long-range interactions such as "pinning" can significantly enhance the energy barriers for edge-zipping and atom attraction, these effects can be significantly weaker in our DFT calculations due to the redistribution of the electron density.
Physical Review B, 2010
Scanning tunneling microscopy analysis of the initial stages of film growth during deposition of Ag on NiAl͑110͒ reveals facile formation of bilayer Ag͑110͒ islands at temperatures of 130 K and above. Annealing subsequent to deposition at 130 K induces coarsening of the bilayer island distribution. The thermodynamic driving force for bilayer island formation reflects a lower relative surface energy for films of even layer thicknesses. This feature derives from quantum size effects due to electron confinement in the Ag film. The kinetics of island formation and relaxation is controlled by terrace and edge-diffusion barriers, detachment barriers, interlayer diffusion barriers, and layer-dependent adsorption and interaction energies. These key energies are determined from density-functional theory analysis and incorporated into an atomistic lattice-gas model for homogeneous island formation, where specification of the adatom hop rates is consistent with detailed balance. Model analysis via kinetic Monte Carlo simulation elucidates the role of strongly anisotropic interactions in development during deposition of elongated island growth shapes and also in facilitating upward mass transport needed for bilayer island formation. The model succeeds in recovering island densities at lower temperatures but experimental densities exceed model predictions at higher temperatures plausibly due to heterogeneous nucleation at surface defects. The same model successfully describes postdeposition coarsening of small islands grown at 130 K.