Publication Date

12-15-2017

Department

Ames Laboratory; Physics and Astronomy; Mathematics

Campus Units

Mathematics, Physics and Astronomy, Ames Laboratory

OSTI ID+

1411960

Report Number

IS-J 9487

DOI

10.1103/PhysRevB.96.235406

Journal Title

Physical Review B

Volume Number

96

Issue Number

23

First Page

235406

Abstract

For diffusion of two-dimensional homoepitaxial clusters of N atoms on metal (100) surfaces mediated by edge atom hopping, macroscale continuum theory suggests that the diffusion coefficient scales like DN∼N−β with β=3/2. However, we find quite different and diverse behavior in multiple size regimes. These include: (i) facile diffusion for small sizes N<9; (ii) slow nucleation-mediated diffusion with small β<1 for “perfect” sizes N=Np=L2 or L(L+1), for L=3,4, ... having unique ground-state shapes, for moderate sizes 9≤N≤O(102); the same also applies for N=Np+3, Np+4, ...(iii) facile diffusion but with large β>2 for N=Np+1 and Np+2 also for moderate sizes 9≤N≤O(102); (iv) merging of the above distinct branches and subsequent anomalous scaling with 1≲β<3/2, reflecting the quasifacetted structure of clusters, for larger N=O(102) to N=O(103); (v) classic scaling with β=3/2 for very large N=O(103) and above. The specified size ranges apply for typical model parameters. We focus on the moderate size regime where we show that diffusivity cycles quasiperiodically from the slowest branch for Np+3 (not Np) to the fastest branch for Np+1. Behavior is quantified by kinetic Monte Carlo simulation of an appropriate stochastic lattice-gas model. However, precise analysis must account for a strong enhancement of diffusivity for short time increments due to back correlation in the cluster motion. Further understanding of this enhancement, of anomalous size scaling behavior, and of the merging of various branches, is facilitated by combinatorial analysis of the number of the ground-state and low-lying excited state cluster configurations, and also of kink populations.

Language

en

Department of Energy Subject Categories

36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY

Publisher

Iowa State University Digital Repository, Ames IA (United States)

Share

COinS