Kinetic Monte Carlo simulations of the diffusion and shape evolution of single-layer clusters on a hexagonal lattice with and without external force

Abstract

In this work we investigate the diusion of 2D surface islands and voids as a result of atomic diusion on terraces, by kinetic Monte Carlo simulations based on a hexagonal lattice. We show that the diusion coecient of small clusters strongly depends on their size and does not follow a monotonic law. In particular, the diusion coecient of small voids increases with the cluster size, reaches a plateau and then decreases. We also study the displacement velocity of clusters when a force biases the probability of the atomic jump direction. We show how the cluster velocity depends on the force and on the cluster size. According to the force direction and amplitude, the shapes of the clusters can be strongly modied.

Reflections on the effect of an external flux in surface physics

“…In our KMC model [27] the atoms jump from a position to a nearest neighbor empty position, in a 3D face centered cubic lattice (fcc). The island surface corresponds to a (111) plane of a fcc crystal.…”

Atomistic Description of Interdroplet Ice-Bridge Formation during Condensation Frosting

“…C ice eq is negligible with respect to C ice drop . The diffusion coefficient on the substrate is D = 1.5 exp nobreak0em.25em⁡ − E diff kT (see), with E diff = J when E S = 2 J (3 J – E S = J , see the section on the KMC model) in our simulations. Therefore, β should be about 10 –3 and 10 –5 for kT = 0.9 and 0.5 J , respectively, in agreement with the fitted values.…”

“…The concentration dependence on the temperature and on the droplet radius are due to the Gibbs–Thomson effect (ln­( c ) ∝ γ/( kT R ), where c is the concentration, γ the droplet surface energy, and R the droplet radius). The change of molecule concentration with the substrate wetting properties can be understood using the approach used in ref and is summarized in the Supporting Information. As regards the ice protrusions, within the range of parameters used in our simulations (strong binding energy), we have found that the molecule concentration around the ice phase is very low and is negligible with respect to that around the liquid phase.…”

Hole opening from growing interfacial voids: A possible mechanism of solid state dewetting

“…The increase in the average void size is more due to coalescence than to Ostwald-ripening coarsening. As shown in 23 , at low temperature the diffusion of mono-vacancies at interfaces is slower than the diffusion of 2D vacancy clusters. However, the diffusion coefficient of 2D vacancy clusters decreases for larger sizes, where universal scaling applies [24][25][26][27] .…”

“…We expect that the mobility of 3D vacancy clusters will behave in a similar way as a function of size. In addition, it is also known that the diffusion constants of atom clusters and vacancy clusters exhibit an oscillatory dependence on their size 23,26,28 . These combined effects are expected to lead to a complex dependence of the diffusion coefficient on size.…”