Electronic Properties of Two-Dimensional Nicrocluster Arrays

Au、C、Sb、Bi和Te的微团簇通过准分子激光烧蚀或在真空和氦气中普通热汽化的方法在高度定向热解石墨的c平面上沉积，沉积的表面用扫描隧道显微镜(纳米II)在空气中操作。微团簇以各种大小和形状被吸附。对于由少于100个原子组成的小星团，可以观察到星团的原子图像。对于激光烧蚀沉积碳，一些小团簇以单层的形式吸附在衬底上。在大约50托的氦气下，它们主要以三维方式堆积在衬底上，即使是那些只有几个原子的衬底。虽然大多数团簇随机分布在衬底表面，但它们倾向于吸附在晶体缺陷周围，如沿台阶或在晶面上。这些团簇具有相似的大小和形状，并以几乎相等的间隔排列，从而形成大小选定的团簇的规则排列。通过激光烧蚀碳团簇以及通过热汽化对Au、C、Sb和Te团簇观察到这样的阵列。

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.