Communication: Diverse nanoscale cluster dynamics: Diffusion of 2D epitaxial clusters

The dynamics of nanoscale clusters can be distinct from macroscale behavior described by continuum formalisms. For diffusion of 2D clusters of N atoms in homoepitaxial systems mediated by edge atom hopping, macroscale theory predicts simple monotonic size scaling of the diffusion coefficient, D-N similar to N-beta, with beta = 3/2. However, modeling for nanoclusters on metal(100) surfaces reveals that slow nucleation-mediated diffusion displaying weak size scaling beta < 1 occurs for "perfect" sizes N-p = L-2 and L(L+1) for integer L = 3,4,... (with unique square or near-square ground state shapes), and also for N-p+3, N-p+4,.... In contrast, fast facile nucleation-free diffusion displaying strong size scaling beta approximate to 2.5 occurs for sizes N-p+1 and N-p+2. D-N versus N oscillates strongly between the slowest branch (for N-p+3) and the fastest branch (for N-p+1). All branches merge for N = O(10(2)), but macroscale behavior is only achieved for much larger N = O(10(3)). This analysis reveals the unprecedented diversity of behavior on the nanoscale. Published by AIP Publishing.