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A new embedded-atom method (EAM) potential has been constructed for Ag by fitting to experimental and first-principles data. The potential accurately reproduces the lattice parameter, cohesive energy, elastic constants, phonon frequencies, thermal expansion, lattice-defect energies, as well as energies of alternate structures of Ag. Combining this potential with an existing EAM potential for Cu, a binary potential set for the Cu-Ag system has been constructed by fitting the cross-interaction function to first-principles energies of imaginary Cu-Ag compounds. Although properties used in the fit refer to the 0 K temperature (except for thermal expansion factors of pure Cu and Ag) and do not include liquid configurations, the potentials demonstrate good transferability to high-temperature properties. In particular, the entire Cu-Ag phase diagram calculated with the new potentials in conjunction with Monte Carlo simulations is in satisfactory agreement with experiment. This agreement suggests that EAM potentials accurately fit to 0 K properties can be capable of correctly predicting simple phase diagrams. Possible applications of the new potential set are outlined.

Atomistic simulation is used to examine nanoindentation of a Au(111) crystal both near and far from a surface step. While the load needed to nucleate dislocations decreases significantly when indenting close to the step, the extent of the step's influence is not as great as seen experimentally. This behavior is explained by measuring the contact area from the simulation data. A new metric, the slip vector, shows material slip coinciding with the <112> directions of a lowest unstable stacking fault barrier. The slip vector is used to calculate an atomic critical resolved shear stress, which is shown to be a good dislocation nucleation criterion.

We present a combined study by scanning tunneling microscopy and atomistic simulations of the emission of dissociated dislocation loops by nanoindentation on a (001) fcc surface. The latter consist of two stacking-fault ribbons bounded by Shockley partials and a stair-rod dislocation. These dissociated loops, which intersect the surface, are shown to originate from loops of interstitial character emitted along the <110> directions and are usually located at hundreds of angstroms away from the indentation point. Simulations reproduce the nucleation and glide of these dislocation loops.

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We have used scanning tunneling microscopy to study the Ostwald ripening of 2D islands of Cu grown on Cu(001). By considering the time dependence of the sizes of individual islands we have characterized the mechanisms for the ripening. Our result is unexpected for a simple metal surface: The flow of atoms from one island to another is limited by attachment-detachment kinetics at the island edges. To explain this result, we propose that the transport of atoms between islands occurs by vacancy, rather than by adatom, diffusion. [S0031-9007(97)04112-4] PACS numbers: 68.35.Fx, 61.16.Ch, 82.65.Dp It is relatively easy to catalog the many atomic processes possibly involved in surface self-diffusion. It is much harder to quantify them experimentally or to determine which particular processes govern surface evolution on a large length scale. A basic process to consider is an adatom diffusing on a terrace towards a step edge, where the adatom is incorporated. On a simple metal surface there are no obvious additional barriers for this incorporation if the adatom approaches the step from below: The barrier for diffusion on the terrace will be the same or larger than the barriers associated with incorporation into the step edge. It is thus generally believed, and has been observed in 2D island decay on Ag(111) [1] and Cu(111) [2], that the flow of atoms to or from step edges is limited by the rate at which adatoms diffuse on the terraces. Since it is often assumed that surface morphology equilibrates by surface steps exchanging adatoms, this belief is central to models of surface self-diffusion which are detailed enough to take surface steps into account [3]. In this paper we will show, however, that mass transfer between islands on Cu(001) is not diffusion limited over a range of temperatures: Rather it is limited by the attachment and detachment processes at step edges. We propose that this occurs because surface self-diffusion on Cu(001) occurs by vacancy, rather than by adatom, diffusion.To probe the mechanisms of diffusion between step edges we have used scanning tunneling microscopy (STM) to measure the time dependence of the sizes of 2D Cu islands grown on Cu(001). The deposited islands are out of equilibrium: Large islands grow at the expense of small islands to reduce the total step length and thus the free energy of the system. By studying this ripening process it is possible to extract quantitative information on the kinetics of mass transport at the surface: 2D island ripening provides a geometry which can be readily analyzed because the driving force for adatom diffusion and step motion (step tension and curvature) can be determined from the island shapes and sizes.In the standard theory [4-6] of island ripening by adatom motion, the time rate of change of the area of an island is determined by two kinetic processes: the diffusion of adatoms on the surrounding terrace towards or away from the island, and the transfer of atoms onto, or off, the island edge. The diffusion rate on the terraces is determined by ...

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