Origin of nonlinear sputtering during nanocluster bombardment of metals

Abstract

Recent experiments ͓S. Bouneau et al., Phys. Rev. B 65, 144106 ͑2002͔͒ show that the sputtering of atoms from surfaces by cluster impacts behaves differently from what is expected in the classical stopping theory. The most significant unresolved questions are that the sputtering yield divided by cluster nuclearity squared ͑Y / N 2 ͒ is independent of N in the size range N =2-13 and that the energy maximum is not at the position expected from the nuclear stopping power. We use classical molecular dynamics simulations to examine the energy deposition from 0.1-18.5 MeV Au 5 and Au 13 clusters to the Au͑111͒ surface to investigate this question. The simulations show that only a portion of the energy deposited from the cluster atoms to the crystal contributes to the formation of the displacement cascade because either the cluster channels through the surface layers as one entity or, if strong collisions occur, the energy deposited in these collisions is mostly carried away from the collision region by fast knock-on atoms. Based on the observations in the simulations, we develop an analytical model that explains the N 2 effect and an energy maximum that differs from the nuclear stopping.

Influence of electronic stopping on sputtering induced by cluster impact on metallic targets

“…9. The data by Samela et al 35 are presumably the best data available; they assume LS electronic stopping ͑␤ =1͒ above a cut-off energy E c = 5 eV, and ␥ = 0 otherwise. The simulation lasted 100 ps; the dynamics of the sputtered material was continued beyond 2 s, in order to take fragmentation and back deposition of sputtered clusters on the surface into account.…”

Atomistic modeling of the sputtering of silicon by electrosprayed nanodroplets

“…Although sputtering by light particles is well understood on the basis of Sigmund's collision cascade linear model, 1 this theory underestimates the sputtering by larger projectiles like heavy atoms, molecular ions, and gas cluster ions. 2, 3 Instead, other mechanisms such as thermal spikes caused by high density collision cascades and thermal evaporation are known to control the sputtering by these larger projectiles. 4,5 The former is a prototypical nonequilibrium process, while the latter is formulated within the confines of partial thermodynamic equilibrium.…”

Depth profiling by cluster projectiles as seen by computer simulations

“…Recently, large noble gas clusters are being promoted into this field 15–17. In the past several years there have been numerous computational studies that investigated the dynamics of sputtering by these projectiles 4, 18–34. However, almost all these studies were performed on a flat surface.…”