Computer Studies on Cluster Impact Phenomena

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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