Effect of Equivalent Sites on the Dynamics of Bimetallic Nanoparticles
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Effect of Equivalent Sites on the Dynamics of Bimetallic Nanoparticles C. Fernández-Navarro1, A. J. Gutiérrez-Esparza2, J.M. Montejano-Carrizales3 and S.J. MejíaRosales1 1 Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, San Nicolás de los Garza, Nuevo León, México 66450 2 División de Ciencias e Ingenierías, Universidad de Guanajuato, León, Gto. México 37150 3 Instituto de Física, Universidad Autónoma de San Luis Potosí, San Luis Potosí, S.L.P., México 78000 ABSTRACT Using a Sutton and Chen interatomic potential, we study the molecular dynamics of AuPd nanoparticles with an initial icosahedral structure at different temperatures and concentrations, where each relative concentration of the 561-atom particles was made by placing atoms of the same species at equivalent sites, in order to identify under which conditions the melting transition temperature appears for each particle. In addition, we compute global order parameters in order to correlate the obtained results with the caloric curves of each particle. As a result, we observe that the melting transition temperature depends on the relative atomic positions of gold and palladium. The melting transition temperature of the Au-Pd alloy particles appears at higher temperature than that of the pure-gold particle. From the analysis of the structure of the particles, we found that the melting temperature increases with the proportion of gold atoms, and for those particles with a higher concentration of palladium on the surface, we observe an early migration of gold atoms before the melting transition temperature appears. Keywords: Nanoparticles, gold, palladium, molecular dynamics. INTRODUCTION The uses of nanoparticles have grown in a large measure both in number and scope over the last decade. Besides their use as catalysts, metallic nanoparticles are very promising agents in the development of electronic devices. Nowadays the application of nanostructured materials as protein detectors [1] contrast enhancers in imaging techniques [1], catalysts [2], drug delivery [3], and antibacterial agents [4], has become of great importance, mainly due to their stability and selectivity features. As applications of nanoparticles grow in different and sometimes unexpected directions, the need of a better understanding of the influence of structure on the properties of the particles becomes more accentuated, specially when the choice of a method of synthesis is determined by how the final structure and size of the nanoparticle depend on the chosen technique [5-7]. Synthesis is possible with chemical based methods to obtain colloidal dispersions of nanoparticles [8] and physical methods of deposition, where the nanoparticles are formed by high-pressure sputtering in a controlled gas flow atmosphere, can be used to generate particles with narrow size distributions and, more important, with well defined chemical composition [9,10]. Along with the variety in the methods of synthesis, characterization techniques have been improving constantly. One of the most
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