Reptation : a mechanism for cluster migration on (111) face-centered-cubic metal surfaces

• Embedded-atom molecular-dynamics simulations were used to follow the diffusion dynamics of compact platinum clusters with up to 19 atoms on Pt(lll). The results reveal a cluster diffusion mechanism on (111) face-centered-cubic (fcc) surfaces involving successive shear translations of adjacent subcluster regions giving rise to reptation, a snake-like gliding motion. We show that for compact clusters with <7 atoms, this mechanism competes energetically with that of island diffusion through concerted motion. However, for cluster sizes of between 8 and similar or equal to 20 atoms, reptation becomes energetically favorable, especially for elongated clusters. Reptation is also shown to be an important migration mechanism for fractal (randomly ramified) and dendritic (symmetrically branched) islands. (C) 1999 Elsevier Science B.V. All rights reserved.

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atomistic dynamics; clusters; molecular dynamics; platinum; surface diffusion

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