Evolution of Pt Clusters on Graphene Induced by Electron Irradiation
CZ Dong and WP Zhu and SY Zhao and P Wang and HT Wang and W Yang, JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME, 80, 040904 (2013).
In situ low-voltage transmission electron microscopy (TEM) was performed to study the evolution of small Pt clusters on suspended graphene. Pt clusters, trapped by the edge of holes, generally take a stable shape of truncated octahedron for sizes ranging from sub-1 to similar to 5 nm. The interaction to the graphene dots takes in charge when they form composite nanostructures embedded in graphene. The Pt clusters are slowly flattened due to hole enlargement under electron irradiation. The planar structure is maintained by the peripheral Pt-C bonds and instantly collapses into a three-dimensional (3D) cluster if one side is detached from the edge. Based on the heat transfer model, the thermal effect can be excluded under the experimental condition. Atomistic evolution can be attributed to the electron irradiation. Molecular dynamics simulations revealed that the evolution kinetics was found to be dominated by the surface diffusion (characterized by the migration barrier Em), the temperature (the thermal activation energy similar to 5k(B)T), and the scattering from electrons (the maximum transferred energy E-max). The corresponding energies are comparable for the Pt cluster system, leading to similar evolution behaviors. A different scenario in graphene systems is due to the large difference in agitations, i.e., E-max >> E-m similar to 5k(B)T at 3000 K. This unique behavior comes from TEM observation, implying that electron beam irradiation can be utilized as a unique tool in shaping carbon nanostructures.
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