Electronic Properties of Two-Dimensional Nicrocluster Arrays

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Microclusters of Au, C, Sb, Bi, and Te are deposited under a monolayer coverage on the c-plane of highly oriented pyrolytic graphite by excimer laser ablation or by ordinary thermal vaporization of constituent elements in vacuum and in He gas.Deposited surfaces are examined by a scanning tunneling microscope (Nanoscope II) operated in air. Microclusters are adsorbed in a variety of sizes and shapes. Atomic images of clusters are observed for small clusters consisting of less than a hundred atoms. For depositing carbon by laser ablation, some of small clusters are adsorbed on the substrate in single layers. Under He gas of around 50 torr, they are dominantly stacked in three-dimension on the substrate, even for those consisting of only several atoms. Although most of clusters are distributed randomly over the surface of substrate, they tend to be adsorbed around crystal defects such as along a step or on a terrace.These clusters are of similar sizes as well as shapes and are aligned in nearly an equal separation so that they form a regular arrangement of size selected clusters. Such arrays are observed for carbon clusters by laser ablation, and for Au, C, Sb, and Te clusters by thermal vaporization.