Adatom-step interactions: Atomistic simulations and elastic models

Abstract

We derive an analytical expression for the interaction energy between an adatom and a step within the framework of linear elasticity. There are two unknowns in this theory: the strength of the elastic fields associated with the adatoms and the strength of the fields associated with the steps. In order to determine these parameters independently, we perform a series of atomistic simulations of a square lattice of Ni adatoms and a regular array of steps on the nominal (001) Ni surface using embedded-atom method potentials. The results are shown to yield good agreement with elastic theory. Fitting these simulations to the theory allows us to determine the adatom and step strengths. These results are then used to predict the step-adatom interaction energy. Atomistic simulations of a surface with a periodic array of steps interacting with an adatom are performed and compared with the predictions of the elastic theory with no adjustable parameters. A comparison of simulation and theory shows that the step-adatom interactions are dominated by dipole-dipole interactions, but that higher-order terms can also be significant. However, the absolute magnitude of the step-adatom interaction energy show significant errors. We believe that these errors are associated with the neglect of anisotropic effects in the elastic analysis used to extract that adatom dipole strength.