Spontaneous alloying on HOPG by successive deposition of Sb clusters and Au atoms

Abstract

Alloying of gold atoms into nanometer-sized antimony clusters deposited on highly oriented pyrolitic graphite (HOPG) has been studied by transmission electron microscopy (TEM) for morphological and structural characterisations and by energy dispersive X-ray spectroscopy (EDX) for analysis of composition. First, large antimony clusters (≈5.4 nm) generated by the gas aggregation technique in a thermal source were deposited on HOPG. These antimony clusters diffused on graphite and formed, by collision and irreversible sticking, ramified islands the density of which can be predicted, prior to deposition, with suitable cluster flux and substrate temperature. Then, the gold atoms were evaporated at various mean thicknesses on the same Sb N –HOPG substrate. For this post-deposition of gold, the morphology of the deposit was quite different, depending on the evaporation method (Knudsen cell heated by electron bombardment or spiral tungsten filament heated by the Joule effect): ramified islands of Sb–Au alloys plus gold supported particles when using the first method and only ramified Sb–Au islands for the second one. In this paper, we give an explanation of these two different morphologies and we study the alloy formation versus the gold content.