Main content area

Ab Initio Thermodynamics and Kinetics for Coalescence of Two-Dimensional Nanoislands and Nanopits on Metal (100) Surfaces

Han, Yong, Stoldt, Conrad R., Thiel, Patricia A., Evans, James W.
The Journal of Physical Chemistry C 2016 v.120 no.38 pp. 21617-21630
Monte Carlo method, adsorption, algorithms, models, nanoparticles, silver, stochastic processes, thermodynamics
Postdeposition coalescence or sintering of pairs of low-strain two-dimensional nanoislands and nanopits on unreconstructed metal (100) surfaces is typically mediated by diffusion along step edges, and is highly sensitive to the associated kinetics. Thus, for selected systems, we provide an ab initio density functional theory (DFT) level description of both system thermodynamics and kinetics. Specifically, we assess lateral pair and trio interactions both conventionally with adatoms at 4-fold hollow adsorption sites, and unconventionally with one adatom at the bridge-site transition state for hopping. Rather than use standard cluster expansion algorithms, these interactions are determined subject to the constraint that key step-edge properties are recovered exactly. Together, both classes of interactions determine barriers for edge diffusion processes for any local step configuration, including diffusion along close-packed ⟨110⟩ edges, kink rounding, meandering processes at kinked ⟨100⟩ steps, and extraction processes at pit corners. Our formalism applies for homoepitaxial systems, and also for several lattice-matched heteroepitaxial systems. The barriers provide input for stochastic models of nanocluster evolution, which are analyzed by kinetic Monte Carlo simulation. Such modeling with DFT energetics from the PBEsol functional recovers extensive experimental observations of both the time scale and the island-size dependence for sintering of Ag islands on Ag(100). Description of pit sintering on Ag(100) is more delicate, being sensitive to specific unconventional trio interactions.