石墨上纳米尺度金岛的形成

SCANNING TUNNELING MICROSCOPY INVESTIGATION OF GOLD ISLANDS FORMED ON HOPG SURFACE BY VACUUM DEPOSITION

用扫描隧道显微镜研究了真空蒸镀在高定向热解石墨上金岛的形成和形状．随着蒸镀量的增加及时间的推移，金原子在表面通过扩散而逐渐合并成越来越大的原子团，以至岛，甚至岛群．虽然几个纳米大小的原子团仍十分可动，但在蒸镀量大于２０单层时的岛或岛群已十分稳定．研究发现，同一蒸镀量下，各个金岛具有非常接近的宽度和高度，用薄膜成核的圆柱状模型计算岛的宽度与高度之比表明，金岛非常接近热力学平衡状态．

Formation and shape of the gold islands formed by vacuum deposition on the highly oriented pyrolytic graphite (HOPG) surface has been studied by means of scanning tunneling microscopy (STM). In the early stage of formation, gold atoms tend to aggregate into large clusters, which may be disturbed easily by the STM tip in the course of imaging. With the increasing coverage, the gold clusters can move and coalesce into large oblong islands, and the islands can further aggregate into clusters with variable shapes. When the coverage reaches about 20 monolayers, the islands or island clusters can be imaged without being disturbed by the tip, provided that the tunneling resistance is high enough. It has been noticed that the islands have a very similar ratio of width to height. The value of this ratio indicates that the islands essentially have a thermodynamically equilibrium shape. Such islands formed by self assembly may have potential in investigations of mesoscopic physics as well as applications.