Temperature-dependent growth shapes of Ni nanoclusters on NiAl(110)

Abstract

Scanning tunneling microscopy studies reveal that two-dimensional nanoscale Ni islands formed by deposition of Ni on NiAl(110) between 200-400 K exhibit far-from-equilibrium growth shapes which change systematically with temperature. Island structure reflects the two types of adsorption sites available for Ni adatoms, and island shapes are controlled by the details of adatom diffusion along island edges accounting for numerous local configurations. The temperature dependence of the island shapes is captured and elucidated by kinetic Monte Carlo simulation of a realistic atomistic-level multisite lattice-gas model incorporating precise diffusion barriers. These barriers are obtained by utilizing density functional theory to probe energetics not just at adsorption sites but also at transition states for diffusion. This success demonstrates a capability for predictive atomistic-level modeling of nanocluster formation and shape selection in systems that have a high level of energetic and kinetic complexity. Scanning tunneling microscopy studies reveal that two-dimensional nanoscale Ni islands formed by deposition of Ni on NiAl(110) between 200-400 K exhibit far-from-equilibrium growth shapes which change systematically with temperature. Island structure reflects the two types of adsorption sites available for Ni adatoms, and island shapes are controlled by the details of adatom diffusion along island edges accounting for numerous local configurations. The temperature dependence of the island shapes is captured and elucidated by kinetic Monte Carlo simulation of a realistic atomisticlevel multisite lattice-gas model incorporating precise diffusion barriers. These barriers are obtained by utilizing density functional theory to probe energetics not just at adsorption sites but also at transition states for diffusion. This success demonstrates a capability for predictive atomistic-level modeling of nanocluster formation and shape selection in systems that have a high level of energetic and kinetic complexity.

Anisotropic coarsening: One-dimensional decay of Ag islands on Ag(110)

“…To this end, we adopt a recently developed multisite lattice-gas (msLG) model formulation. [27][28][29] In this class of models, we specify adsorption energies for adatoms at the energetically preferred adsorption sites in the troughs and at the two types of bridge sites corresponding to the transition states (TSs) for in-channel and cross-channel hopping. We also specify a set of "conventional" pairwise interactions between adatoms on nearby adsorption sites (E b and E ⊥ b in Fig.…”

Submonolayer Ag films on Fe(100): A first-principles analysis of energetics controlling adlayer thermodynamics and kinetics

“…All DFT total energy calculations reported in this paper were performed using the plane-wave VASP code [26][27][28][29]. The projector-augmented-wave (PAW) method [30,31] is used for the electron-core interactions, and the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) functional [32] is used for exchange and correlation, as is typically the case in analysis of metal-on-metal systems yielding considerable success [18][19][20][21][22]24]. The corresponding pseudopotentials were generated and released in 2013 by the VASP group.…”

“…As described in more detail in Sec. IV, activation barriers for diffusion can be determined with the aid of a distinct set of "unconventional" interactions ( 's) involving one Ag adatom at a bridge-site transition state (TS) for diffusive adatom hopping and the other adatoms are at 4fh sites [18][19][20][21]. Validation of this assignment of the TS will also be provided in Sec IV.…”

Analytic formulations for one-dimensional decay of rectangular homoepitaxial islands during coarsening on anisotropic fcc (110) surfaces

“…We assume nearest-neighbor pairwise attractions with a larger (smaller) magnitude E b < 0 (E ⊥ b < 0) for atoms separated by b (a) in the 1 10 ( 001 ) direction. For a realistic description of surface-diffusion kinetics, including edge diffusion and detachment, we adopt a multisite lattice-gas (msLG) model [14][15][16] in which we prescribe a second set of unconventional interactions between one adatom at a TS and others at nearby adsorption sites. Again, just short-range pairwise attractions are assumed [(E b < 0 and E ⊥ b < 0); see Fig.…”