Trapping and desorption of energetic Cu atoms on Cu(111) and (001) surfaces at grazing incidence

Abstract

Molecular-dynamics (MD) simulations of Cu atoms impacting both Cu(111) and (001) surfaces at grazing incidence have been performed to study trapping (or surface skipping), desorption, and energy dissipation. An energetic Cu atom $(10\mathrm{}<~E<~100\mathrm{eV})$ can become trapped by the mean attractive potential above the surface, oscillating normal to the surface. While in this trapped state, it can traverse hundreds of $\AA$ as it dissipates energy to the surface. Until the atom either desorbs or comes to rest, it experiences an energy loss, that is piecewise linear in time, typically comprised of two or more linear regions. In each region, the energy loss rate, $dE/dt,$ is approximately constant. The process can be characterized by two parameters: the desorption probability at each oscillation and an average energy loss rate (per oscillation) that is independent of energy. These parameter values are the same for both the (111) and (001) surfaces. A phenomenological model based on these parameters is presented, and the predictions of sticking probability, average energy transfer to the surface, and total distance traveled, agree with full MD simulations. The dependence of the desorption probability on the surface temperature was also studied.