Computer Simulation of Culster Implantation

为了研究团簇离子注入固体的基本过程，我们开发了时间演化蒙特卡罗模拟程序DYACAT和分子动力学程序MDACOCT，计算了团簇离子注入固体的深度分布及其投影范围，以阐明团簇对注入过程的影响。我们分别使用DYACAT和MDACOCT计算了E> 100 eV和E <100 eV的原子团簇和单原子离子碰撞的深度分布。由于开路效应，团簇碰撞射程与单原子离子射程之比大于1。对于非常高的能量（> 5keV/atom），由于团簇增强的随机化，比率变得小于1。在E <30 eV的情况下，由于多体效应的影响，DYACAT比MDACOCT小。目前的模拟表明，有三个重要的集群效应，即，多体效应 关于我们 利用分子动力学模拟程序MDACOCT，结合嵌入原子势和屏蔽库仑势发展了混合原子间势，研究了团簇离子束沉积薄膜的生长机理。为了阐明团簇能量转化为表面迁移能的机理，我们模拟了Cu_（111）和Pt（111）上团簇碰撞现象，团簇能量为5eV/atom。<201>对于后一种情况，一半的团簇原子以相对高的能量迁移到衬底表面上，而对于前一种情况，大部分团簇原子嵌入到衬底中。在转换机制中，最重要的一点是当团簇中的高密度区形成在团簇的中心部分时，即，当团簇在表面上受到轰击时，在团簇中总是产生高密度区。用MDACOCT方法研究了Cu_（111）和Pt_（111）碰撞过程中，团簇能量在5~50 keV范围内变化时，高密度对穿透原子角分布的影响.结果表明，高密度的形成强烈地依赖于团簇能量和团簇原子与靶原子的质量比，对于低能团簇碰撞，由于高密度的形成，团簇原子在横向附近的角分布增强.<201><201>少

In order to investigate the basic processes of the cluster implantation interaction of an ionized cluster beam with solids, we have developed the time-evolution Monte Carlo simulation codes DYACAT and the molecular dynamics code MDACOCT.In order to clarify the cluster effect on the cluster implantation, we calculated the depth profiles and its projected range in the wide energy range. We used the DYACAT and MDACOCT for E> 100 eV and for E<lO0eV, respectively, in order to calculated the depth profiles due to cluster and monatomic ion impact. The ratios of cluster-impact range to the monatomic ion range are larger than unity due to the clear-the-way effect. For the very high-energy (>5 kev/atom) the ratio become less than unity due to the cluster-enhanced-randomization. In the case of E < 30 eV the ratios by the DYACAT is less than those by the MDACOCT because of the many body effect. The present simulation says that there are important three cluster effects, i.e., many-body effect, clea … More r-the-way effect and cluster-enhanced-randomization, for the cluster implantation.The mechanism of thin-film growth by ionized cluster beam deposition has been investigated, using molecular dynamics simulation code MDACOCT with the hybrid interatomic potentials which have been developed by combining embedded-atom potentials with the screened Coulomb potential. In order to clarify the conversion mechanism of cluster energy into surface migration energy, we have simulated the cluster-impact-phenomena for Cu_<201> on Cu(111) and Pt(111) with the cluster energy 5eV/atom. For the latter case, a half of cluster atoms migrated on the substrate surface with the relatively high energy and for the former case most of the cluster atoms are embedded into the substrate. In the conversion mechanism the most important point is when the high-density zone in the cluster is formed in the central part of the cluster, i.e., above or below the surface.When the cluster is bombarded on the surface, the high-density zone is always produced in the cluster. This high-density effect on the angular distribution of penetrating cluster atoms has been studied by the MDACOCT for Cu_<201> impact on Pt(111) and Pt_<201> impact on Cu(111), where the cluster energies are changed from 5eV to 50 keV.It is found the high-density formation is strongly dependent on the cluster energy and the mass ratio between cluster atom and target atom and that the angular distributions of cluster atoms are enhanced near the lateral direction for low-energy cluster impact due to the high-density formation. Less