| Research Abstract |
This research is devoted to the study of interaction between a cluster-ion and a solid. As a basic quantity, we investigated the electronic energy-loss rate (stopping power). The solid electrons consist of conduction electrons and core electrons, whose dielectric response are described by the wave-packet model. In this analysis, we took into account the followings : 1)the electron distribution of each constituent ions, 2)the assumption that on entrance the cluster is instantly ionized and the charge state attains to the velocity-dependent average value, 3)the coulomb explosion process estimated by a standard molecular dynamics method, and if so, 4)the correlation between the cluster orientation and the direction of the incidence. We present the results that show the cluster effect in the electronic energy loss. The case is considered where a carbon cluster Cn(n=1-8) with a few MeV/atom is incident on a carbon foil. For convenience, we defined the quantities R=DELTAE(Cn)/(nDELTAE(C)) and R'=DELTAE(Cn)/n-DELTAE(C). The cluster effect means R>1 or R'>0.Here DELTAE(Cn) is the energy loss of a cluster Cn(n=1-8). The calculated R' values vs n for a carbon of 250* thickness shows good agreement with the experimental data, showing the cluster effect, obtained by Baudin et al. The important results are that the existence of the threshold velocity was clearly found, and that the threshold velocity is independent of cluster size n. Next, as a quantity related to the stopping power, we investigated the secondary electron yield due to the kinetic process under cluster impact. Here the size of constituent ions in a cluster is taken into account by a statistical manner and the instantaneous ionization is assumed to take place. Under these conditions, the cluster effect on the SE yield could be found.
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