Self-diffusion on Au(100): a density functional theory study.
ABSTRACT We used density functional theory to detail new self-diffusion mechanisms on perfect and imperfect Au(100) surfaces. Herein, we report binding energies of stable intermediates and transition states lying on the potential energy surface for these systems. We report migration pathways in the presence of a variety of surface defects and along different step edges, explaining their energetics in terms of chemical bonding. Furthermore, diffusion rate constants are deduced, which are useful for both experimental verification and for implementation into large-scale kinetic Monte Carlo simulations.
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ABSTRACT: We describe a multiscale modeling hierarchy for the particular case of Au-island ripening on Au(100). Starting at the microscopic scale, density functional theory was used to investigate a limited number of self-diffusion processes on perfect and imperfect Au(100) surfaces. The obtained structural and energetic information served as basis for optimizing a reactive forcefield (here ReaxFF), which afterwards was used to address the mesoscopic scale. Reactive force field simulations were performed to investigate more diffusion possibilities at a lower computational cost but with similar accuracy. Finally, we reached the macroscale by means of kinetic Monte Carlo (kMC) simulations. The reaction rates for the reaction process database used in the kMC simulations were generated using the reactive force field. Using this strategy, we simulated nucleation, aggregation, and fluctuation processes for monoatomic high islands on Au(100) and modeled their equilibrium shape structures. Finally, by calculating the step line tension at different temperatures, we were able to make a direct comparison with available experimental data.Advances in Physical Chemistry 01/2011;
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ABSTRACT: Motivated by experimental studies of two-dimensional Ostwald ripening on Au(100) electrodes in chlorine-containing electrolytes, we have studied diffusion processes using density functional theory. We find that chlorine has a propensity to temporary form AuCl complexes, which diffuse significantly faster than gold adatoms. With and without chlorine, the lowest activation energy is found for the exchange mechanism. Chlorine furthermore reduces the activation energy for the detachment from kink sites. Kinetic Monte Carlo simulations were performed on the basis of extensive density functional theory calculations. The island-decay rate obtained from these Monte Carlo simulations, as well as the decay rate obtained from the theoretical activation energies and frequency factors when inserted into analytical solutions for Ostwald ripening, are in agreement with experimental island-decay rates in chlorine-containing electrolytes.ChemPhysChem 10/2012; · 3.36 Impact Factor
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ABSTRACT: Ostwald ripening of metal islands has been investigated by kinetic Monte Carlo simulations using the results of quantum-chemical calculations and of the embedded atom method as input data. On Au(100) Ostwald ripening was found to be kinetically hindered at ambient temperatures. In contrast, small islands on Ag(100) decayed readily at uncharged and at positively charged surfaces. The rate of ripening increases both with temperature and with the surface charge. The latter effect is caused by the interaction of local dipole moments with the double-layer field. This work confirms and extends recent investigations of the effect of the field on the surface mobility of metal electrodes.Electrochimica Acta 07/2010; 55(19):5411-5413. · 4.09 Impact Factor