Scaling behavior of the penetration depth of energetic silver clusters in graphite

Abstract

Molecular dynamics simulations have been carried out to determine the penetration depth for implantation of Ag clusters incident normally on graphite in the energy range 0.5-5 keV. The mean penetration depth for Ag 7 clusters is found to be linearly dependent on the impact velocity but there is a transition to a more linear scaling of depth with energy as the cluster size increases. An explanation for this behavior is given in terms of the different natures of the collision cascades over picosecond time scales. The results are in good agreement with corresponding experimental measurements of the penetration depth.

Scaling Relations for Implantation of Size-Selected Au, Ag, and Si Clusters into Graphite

“…3(a) and 3(b) indicates that, in both cases, there is a linear relationship between the implantation depth and the velocity, not the kinetic energy, of the clusters (though the slopes are different). These results confirm the velocity scaling reported in the preliminary measurements of Ag 7 ÿ implantation [13,14] and show that the same type of velocity scaling also applies to the Au 7 clusters (but not, at first sight, Si 7 ).…”

“…Our MD simulations show that the covalent attraction between the C and Si atoms (the Si-C bond energy is 4.6 eV in SiC [30], while the Ag adsorption energy on graphite lies in the range 0.23 to 0.54 eV [31]) has a negligible effect on the implantation depths. If the mass of the Si atom is artificially increased to that of Ag, but with the covalent Si-C interaction unchanged, almost exactly the same results are found as for Ag itself [14]. The mass effect is illustrated by the fact that the maximum energy transfer in a binary collision between a Ag atom of incident energy E 0 and a C atom at rest is 0:36E 0 , whereas for an incident Si atom it is 0:84E 0 .…”

“…Further, MD simulations for the size range n 20-200 indicate an implantation depth, D, which scales linearly with the kinetic energy, E, and inversely with the cross-sectional area of the cluster; D / E=N 2=3 [12]. However, first experimental measurements for (smaller) Ag 7 ÿ clusters [13] indicate that the implantation depth scales with velocity, not energy, a difference which is also reflected in MD results [14]. In order to shed further light on the intriguing dynamics of the cluster-surface impact, we report in this Letter a systematic experimental study of the implantation depth of three different kinds of clusters, including both metal clusters, Au 7 and Ag 7 , and semiconductor clusters, Si 7 , into the graphite surface.…”

“…To explore further the behavior of the Si 7 clusters, we have conducted MD simulations [14] of their implantation into graphite. The Brenner potential [25] was employed for graphite, together with interlayer terms [26], while Si and SiC were treated by the Tersoff potential [27,28].…”

“…In the case of the Ag N =graphite system, significant progress has recently been reported [11][12][13][14]. For cluster sizes in the range n 50-200, the threshold energy for ''pinning'' of the incident cluster to the point of impact scales linearly with the cluster size.…”