Molecular Dynamics Simulations of Cluster Ion Impact on Diamond Surface
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Molecular Dynamics Simulations of Cluster Ion Impact on Diamond Surface Takaaki Aoki1, 2, Jiro Matsuo1, Gikan Takaoka1 and Isao Yamada1, * Ion Beam Engineering Experimental Laboratory, Kyoto University, Sakyo, Kyoto 606-8501, JAPAN 2 Osaka Science and Technology Center, Utsubo-honmachi, Nishi-ku, Osaka 550-0004, JAPAN * Present address: Laboratory of Advanced Science and Technology for Industry, Himeji Institute of Technology, CAST, Ako, Hyogo, 678-1205, Japan 1
ABSTRACT Molecular dynamics (MD) simulations of various cluster ions impacting on solid targets were performed in order to examine the implant and damage formation processes. Ne and Ar rare gas cluster with various cluster sizes, and fullerene (C60) were impacted on diamond (001) surface. It was shown that the impact process of cluster ion depends on the cluster size. When the cluster size is small and incident energy-per-atom is high, such as Ar15 with 800eV/atom, all incident Ar atoms penetrate the surface and reside in the substrate. As the cluster size increases and the incident energy-per-atom decreases, the implant depth decreases and the profile of the displacement becomes shallower. A large cluster, such as Ar60 with 200eV/atom, shows a shallower implant depth and a higher sputtering yield than Ar15. However, Ar240 with 50eV/atom shows a shallower implant depth, but less sputtering yield than Ar60.These results suggest that there is proper cluster size and incident energy where the maximum sputtering yield is achieved. INTRODUCTION Cluster is an aggregated material comprising of ten to several thousand atoms or molecules. Cluster ion irradiation on materials shows different phenomena compared with conventional monomer ion irradiation. Many advantages in surface modification process, such as high-yield sputtering, surface smoothing and hardness improvement, have been observed experimentally [1-4]. It has been suggested that these advantages are due to the fact that each cluster atom impacts in narrow region on the surface with high-density. The impact process of cluster ions has not been studied completely. In order to clarify the difference and similarity between cluster and monomer ions in the impact process, it is necessary to examine the dynamics of each cluster and substrate atom through the collisional process. Molecular dynamics (MD) simulation is one of the useful methods to examine the interaction between energetic particle and solid surface with a high time and space resolution. The impact process of large cluster has been discussed in detail in previous work, including the boundary energy where a cluster ion shows different properties from a monomer. For example, when a large Ar cluster (cluster size > 100) impacts on a solid surface, the incident Ar atoms impinge deeper than an Ar monomer with same energy-per-atom. Large number of collisions occur and crater-like damage is formed, and some substrate atoms on the edge of crater leave the substrate, which is termed as `lateral sputtering’ [5]. In order to understand the impact process of a
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