Nonlinear Phenomena in Cluster Ion impact on Solid Surfaces

研究了簇离子与固体表面的相互作用，即所谓“非线性现象”。分子动力学计算表明，簇离子撞击过程与二元碰撞理论所描述的单体离子撞击过程相去甚远。在飞秒时间尺度内，许多原子撞击在很小的表面上。因此，期望团簇组成原子与表面原子的每次碰撞产生新的相互作用。利用战斗时间（TOF）技术，本研究中使用的平均聚类大小约为3000。由于重离子的二次电子发射效率小于1，需要考虑多通道板的检测效率。为了精确地测量簇离子的大小分布，我们对效率进行了仔细的校准。在TOF光谱中不仅发现了单荷电簇离子，还发现了多荷电簇离子。据报道，有簇离子撞击形成的陨石坑。我们发现形成陨石坑的最小尺寸是10。这一结果也得到了MD计算的证实。为了实现簇离子模拟，研究了二次离子发射。用掺Sb硅测量了以Ar簇离子为主离子的SIMS光谱。二次离子发射产率与溅射产率成正比。这表明簇离子在实现高深度分辨率SIMS方面具有很大的优势。簇离子在固体表面独特的轰击效应使得溅射表面平滑率高、注入深度浅、二次离子发射率高。

Interaction between cluster ions and solid surfaces, which is the so-called "nonlinear phenomena", has been studied. Molecular dynamics calculation shows that cluster ion impact process is far from monomer ion impact process, which is well described with binary collision theory. Many atoms impact on small surface area within femto-second time scale. Therefore, a new interaction of each collision of the cluster constituent atoms with the surface atoms is expected.Average cluster size used in this study was about 3000 by using Time of fight (TOF) technique. Detection efficiency of multi channel plate (MCP) should be considered because secondary electron emission efficiency of heavy ion was less than 1. We have calibrated the efficiency carefully in order to measure the size distribution of cluster ion precisely. Not only singly charged cluster ions but also multiple-charged cluster ions were found in the TOF spectra. Crater formation with cluster ion impact has been reported. We have found that the minimum size for crater formation is 10. This result was also confirmed by MD calculation. Secondary ion emission was studied in order to realize cluster ion SIMS. Sb doped silicon was used to measure the SIMS spectra with Ar cluster ions as primary ions. Secondary ion emission yield is proportional to the sputtering yield. This indicates that cluster ion has a great advantage to realize high-depth resolution SIMS. These unique bombardment effects of cluster ions on solid surfaces cause high yield of sputtering surface smoothing, shallow implantation and high yield of secondary ion emission.