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

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 characterisation s and by energy dispersive X-ray spectroscopy (EDX) for analysis of composi tion. First, large antimony clusters (approximate to 5.4 nm) generated by t he gas aggregation technique in a thermal source were deposited on HOPG. Th ese antimony clusters diffused on graphite and formed, by collision and irr eversible 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 sa me Sb-N-HOPG substrate. For this post-deposition of gold, the morphology of the deposit was quite different, depending on the evaporation method (Knud sen 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 t he second one. In this paper, we give an explanation of these two different morphologies and we study the alloy formation versus the gold content. (C) 1999 Elsevier Science S.A. All rights reserved.