Photoemission and RHEED study of the supported Pt and Au epitaxial alloy clusters

摘要

In this paper, we investigated formation and structure of gold, platinum and Pt-Au bimetallic clusters on tungsten oxide surface. Crystallographic structure and orientation were investigated by reflection high energy electron diffraction, chemical composition and cluster's electronic state by synchrotron radiation photoelectron spectroscopy. Small amount of Au and Pt was deposited on WO_3 (111) surface prepared by RF plasma oxidation and thermal annealing of (11 0) tungsten single crystal surface. Formation of 3D Pt or Au clusters with (111) epitaxial plane was observed. On the contrary to Au, strong metal substrate interaction between Pt and oxide was found, leading to the encapsulation of Pt clusters. Formation of Au-Pt bimetallic clusters was investigated at the temperature range of 160-870 K. It was found that cluster structure depends on the substrate temperature and order of materials deposition. At the temperatures around 570 K, metals formed bimetallic clusters with core-shell structure. Annealing to the temperatures over 770 K led to the decomposition of Pt-Au clusters and formation of Pt-W allov.