Structural transformation of CoSi2 islands on a Si(111)-(5×2)/Au surface：step effect

• Main Authors: Shang-wei Kuo, 郭上瑋
• Other Authors: Fu-Kwo Men
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/62127533244018338543

碩士 === 國立中正大學 === 物理所 === 98 === We have studied the growth of cobalt silicide islands by heating Co-deposited Si(111)-(5×2)/Au surface by scanning tunneling microscopy. By using a silicon wafer with a 0.3° miscut angle as substrate, we are able to observe both steps and terraces on the surface at the same time. After depositing Co on the surface, two types of islands form: terrace islands (islands grow on terraces) and step islands (islands grow on steps). At the early stage of island formation, i.e., before the start of coarsening process, we have observed a structural transformation on islands’ top layer: a (2×2) reconstruction to a featureless structure. Both of the two type islands have the same properties:(1) island height depends on annealing temperature, and (2) island structure decides island height. The reason why islands undergo the structural transformation is due to a lattice constant difference between CoSi2 and the substrate. In the early growth stage where islands are relatively small, the substrate has a large effect on islands’ structure. When islands reached some critical height, the substrate effect becomes weaker and islands revert into their bulk structure. Where islands are strain-relieved, we have found that the structural transformation for step islands happens at a height lower than that of terrace islands. We attribute this height difference in the structural transformation to a vertical lattice mismatch induced by the steps buried in step islands. This vertical lattice mismatch allows a faster strain relaxation in a step island, which in turn lowers the island’s free energy.