Tungsten cluster migration on nanoparticles: minimum energy pathway and migration mechanism |
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Authors: | D Chen W Hu F Gao H Deng L Sun |
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Institution: | 1.Department of Applied Physics,Hunan University,Changsha,P.R. China;2.Pacific Northwest National Laboratory,Richland,USA;3.Materials and Thermochemistry Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,Dalian,P.R. China |
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Abstract: | Saddle point searches have been employed to investigate the migration
mechanisms of W clusters on W nanoparticles, and to determine the
corresponding migration energies for the possible migration paths of these
clusters. The tungsten clusters containing up to four adatoms are found to
prefer 2D-compact structures with relatively low binding energies. The
effect of interface and vertex regions on the migration behavior of the
clusters is significantly strong, as compared to that of nanoparticle size.
The migration mechanisms are quite different when the clusters are located
at the center of the nanoparticle and near the interface or vertex areas.
Near the interfaces and vertex areas, the substrate atoms tend to
participate in the migration processes of the clusters, and can join the
adatoms to form a larger cluster or lead to the dissociation of a cluster
via the exchange mechanism, which results in the adatom crossing the facets.
The lowest energy paths are used to be determined the energy barriers for W
cluster migrations (from 1- to 4-atoms) on the facets, edges and vertex
regions. The calculated energy barriers for the trimers suggest that the
concerted migration is more probable than the successive jumping of a single
adatom in the clusters. In addition, it of interest to note that the dimer
shearing is a dominant migration mechanism for the tetramer, but needs to
overcome a relatively higher migration energy than other clusters. |
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