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Atomistic Study of Creation of Bimetallic Clusters by Coalescence

Published online by Cambridge University Press:  01 February 2011

S. Mizuno  and
K. Shintani
S. Mizuno
Affiliation:
mizuno@nmst.mce.uec.ac.jp, University of Electro-Communications, Department of Mechanical Engineering and Intelligent Systems, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan
K. Shintani
Affiliation:
shintani@mce.uec.ac.jp, University of Electro-Communications, Department of Mechanical Engineering and Intelligent Systems, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan, 81-42-443-5393, 81-42-484-3327
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Abstract

Metallic clusters show excellent performance as catalysts because of their high surface-to-volume ratio. An inert-gas aggregation source is an experimental method by which clusters are produced. In such a method, cluster coalescence is one of growth modes of clusters. Bimetallic clusters also attract much attention of researchers because of their novel physical and chemical properties. At coalescence of two metallic clusters of different species, alloying or core-shell structuring tends to occur spontaneously. Resulting alloyed clusters or core-shell clusters will behave as unique catalysts. In this paper, morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics simulation. All pair combinations of the elements Au, Ag, Pt, and Pd are considered. The interactions between such metallic atoms are calculated by using generic embedded-atom method (GEAM) potential. Two clusters of icosahedral structure are equilibrated at specified temperature beforehand. The two clusters are put close to each other, where the nearest two atoms belonging to the two clusters, respectively, start to interact with each other. After coalescence the original surfaces of the two clusters decrease, and the surface energy is transformed into the kinetic energy. Consequently, the temperature of the united cluster rises. If this temperature is higher than the melting temperature, melting and local alloying at the interface occur. If alloying spreads into the united cluster, an alloyed bimetallic cluster is synthesized. If melting occurs only in one of the two clusters, and the atoms in liquid phase gradually cover the surface of the other cluster, a core-shell cluster appears. The morphological evolutions in the two modes of coalescence are followed, and under what conditions each mode of coalescence occurs is discussed.

The results show that the surface energy and atom size of two clusters determine which mode is selected at coalescence.

Keywords

cluster assemblynanostructuremetal
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1087: Symposium V – Crystal-Shape Control and Shape-Dependent Properties – Methods, Mechanism, Theory, and Simulation , 2008 , 1087-V08-01
Copyright
Copyright © Materials Research Society 2008

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