Computer Studies on Cluster Impact Phenomena

为了研究电离簇束与固体的相互作用，我们开发了时间演化蒙特卡罗模拟代码DYACOCT(1)和DYACAT(2)。DYACAT程序可用于研究非晶固体中的团簇撞击现象，DYACOST程序可用于研究结晶固体中的团簇撞击现象。在这些基于二元碰撞近似的程序中，离子和反冲原子的轨迹被动态跟踪。为了克服低能弹丸二元碰撞近似的困难，采用分子动力学方法对弹丸与其碰撞直径内的多个原子同时碰撞的多体碰撞进行了数值求解。这些代码可以成功地应用于辐射损伤(3)、星团撞击现象（4-11）和星团撞击引起的溅射（11）。文献4、5和10研究了团簇原子的能量特性（加速效应），文献8和9研究了团簇原子的深度分布（扫清效应）。发现团簇原子（M_1）和靶原子（M_2）的质量比对加速效应和清道效应有很大的影响。在M_<21>M_1 >1的情况下，由于团簇碰撞引起的团簇原子能量分布的高能尾部（n>100）可以用Maxwell-Boltzmann函数很好地描述，其温度与团簇能量和团簇大小成线性关系。即大集群撞击在一定时间后产生准平衡状态，这取决于集群-目标组合。经过一定时间后状态的加速度取决于簇-目标组合。团簇原子的加速度由费米穿梭过程粗略估计。在M_<21 bb_0 M_1 < 1的情况下，可以清楚地观察到清道效应。反冲原子为后来的簇原子扫清了道路，有效地降低了簇原子的阻挡力，因此簇原子的投射范围比单原子离子轰击大几倍，簇原子的能谱呈梯形。在高能光原子团撞击的情况下，不存在清道效应，由于增强了表面能量的去除，其投射范围小于单原子离子。少

In order to investigate the interaction of an ionized cluster beam with solids, we have developed the time-evolution Monte Carlo simulation codes DYACOCT(1) and DYACAT(2). The DYACAT code can be applied to the investigation of the cluster-impact phenomenon in an amorphous solid, and the DYACOST code to that in a crystalline solid. In these programs which are based on the binary collision approximation, trajectories of ions and recoil atoms are followed dynamically. In order to overcome the difficulties of the binary collision approximation of a low-energy projectile, many body encounter are numerically solved by the molecular dynamics method, where a projectile collides at the same time with many atoms within its collision diameter. These codes can be successfully applied to the radiation damage(3), the cluster-impact phenomenal(4-11), and sputtering due to cluster impacts(11). The energy property of cluster atoms (acceleration effect) was studied in Refs.4, 5 and 10, and the depth pro … More files of cluster atoms(clear-the-way effect) in Refs. 8 and 9.It is found that the acceleration effect as well as the clear-the-way effect strongly depend on the mass ratio of the cluster atoms (M_1) and the target atom (M_2). In the case of M_<21>M_1 >1 the high-energy tail of the energy distribution of cluster atoms due to big cluster impacts (n>100) can be well described in terms of the Maxwell-Boltzmann function, and its temperature is linearly proportional to the cluster energy and the cluster size. Namely, the big cluster impact produces a quasi-equilibrium state after a certain time which depends on the cluster-target combination. The acceleration of the state after a certain time which depends on the cluster-target combination. The acceleration of the cluster atom is roughly estimated by the Fermi-shuttle process.In the case of M_<21>M_1 < 1 the clear-the-way effect is cleary observable. The recoil atoms clear the way for aftercoming cluster atoms, and the stopping power of the cluster atom is effectively reduced, and so the projected range of the cluster atoms is several times larger than of the monoatomic ion bombardment, and the energy spectrum of the cluster atom is trapezoidal. In the case of the high-energy light atom cluster impact, there is no clear-the-way effect, and its projected range is less than that of monoatomic ion due to the enhanced energy removal from the surface. Less