Self-Assemly Of Palladium Deposited Clusters On Si(111)-7×7 Reconstruction Surface

Pd-Si system has excellent electrical performance and the heterogeneous contact in nanometer scale is potential candidate for the basic unit of the next generation of electronic device. Besides, Palladium as active catalyst gets higher efficiency with a configuration of clusters in the range of several atoms. As a result, the research on Pd nanostructure on Si surface and their properties is of great importance for the catalyst mechanism and catalyst on-chips.In this thesis, the molecular beam epitaxial (MBE) growth of Palladium (at room temperature and quite low deposition rate) on Si(111)-7×7 reconstruction surface in ultra-high vacuum system were studied. Unisized Palladium atomistic clusters preferential deposition near the step edges of vicinal Si(111)-7×7 surfaces was observed with scanning tunneling microscope.Using the silicon substrate with sharp step edge as template, Palladium atoms tend to distribute along the step edge. The deposited Pd atoms have a preference at step edge area and cluster-covered part with growth frontier parallel to the straight step edge formed which extend on the terrace from the step edge area. The clusters in the covered part of terrace have almost uniform size (about 0.8nm in diameter) and were intensively arranged with high density. The step edge has great control on the mode of Pd epitaxial growth.Using the substrate with the step edge not straight as template, Palladium atoms tend to distribute along the step edge to from triangle covered part. In the Pd covered area, the clusters have almost uniform size (about 0.8nm in diameter) and were intensively arranged with high density which is similar with that of the straight step edge area. Besides, in the middle of the terraces far away from the step edge triangle Pd covered areas were observed and these areas were connected by the wire-like areas covered with the unisized clusters.Besides, by controlling annealing temperatures, the dynamic diffusion as well as structure and configuration evolution of clusters was studied for different coverages. It was found that in the annealing process the defects immerse, clusters size increases. With coverage and annealing temperature, the self-assembled Pd nanostructures and their morphology were better controlled.