Inelastic Energy Loss of Cluster ions in Solids

本研究致力于研究团簇离子与固体之间的相互作用。作为基本量，我们研究了电子能量损失率（阻止本领）。固体电子由传导电子和芯电子组成，其介电响应用波包模型描述。在分析中，我们考虑了以下几个因素：1）每个组成离子的电子分布; 2）在入射时团簇瞬间电离，电荷态达到速度相关平均值的假设; 3）用标准分子动力学方法估计的库仑爆炸过程; 4）团簇取向与入射方向的相关性。我们提出的结果表明，在电子能量损失的集群效应。被认为是一个碳原子团簇Cn（n = 1 - 8）与几个MeV/原子的情况下，入射到碳箔。为方便起见，我们定义了量R = Δ E（Cn）/（nDELTAE（C））和R ′ = Δ E（Cn）/n-DELTAE（C）。团簇效应是指R> 1或R '> 0。这里Δ E（Cn）是团簇Cn（n = 1 - 8）的能量损失。对250 * 厚碳的计算结果表明，R '值与n的关系与Baudin等人的实验数据吻合得很好，表明了团簇效应的存在。重要的结果是发现了阈值速度的存在，并且阈值速度与团簇尺寸n无关。接下来，作为与阻止本领相关的量，我们研究了由于团簇撞击下的动力学过程而产生的二次电子产额。在这里，在一个集群中的组成离子的大小被考虑到通过统计的方式和瞬时电离假设发生。在此条件下，可以发现簇效应对SE产率的影响。

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.