Self-learning kinetic Monte Carlo simulations of self-diffusion of small Ag islands on the Ag(111) surface

Shah, Syed Islamuddin; Nandipati, Giridhar; Karim, Altaf; Rahman, Talat S.

doi:10.1088/0953-8984/28/2/025001

Cited by 7 publications

(4 citation statements)

References 48 publications

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“…It is natural to consider extension of this analysis to treat sintering of islands and pits on fcc (111) metal surfaces. ,, However, high-level treatment of kinetics in these systems is expected to be more challenging than for fcc (100) metal surfaces. It is recognized at least for island diffusion on these surfaces that concerted motion and possible formation of stacking-fault defects can play a role. − From the perspective of providing precise ab initio treatment of kinetics, our preliminary analysis indicates an additional challenge in that there is not a single TS geometry that applies for PD at different types of step edges. Thus, some refinement of the formulation developed in this Article, for example, to incorporate multiple TS, is required.…”

Section: Discussionmentioning

confidence: 98%

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

et al. 2016

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Postdeposition coalescence or sintering of pairs of lowstrain 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.

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Section: Discussionmentioning

confidence: 98%

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

et al. 2016

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“…To illustrate our theoretical formulation we present computational simulations of monolayer growth using the Kinetic Monte Carlo (KMC) method. ,,,,− We use a typical lattice-gas model and the rejection-free, time-dependent implementation. ,,, Although the algorithmic details are provided in the Supporting Information, here we stress the fact that the time increment is calculated as Δt = −log( e )/ R e , where e ∈ (0, 1] is a uniform random number and R e is the total event rate (see eqs –). With some exceptions, self-learning KMC studies usually indicate that only a few key barriers are important in order to describe surface diffusion, even if the KMC simulations automatically generate many dozens of barriers. , Thus, in this study the activation energies are chosen in order to generate realistic morphologies for both triangular and square lattices while keeping the resulting models (i) simple enough (to enable a foundational analysis of the apparent activation energy of the tracer diffusivity) and (ii) disengaged from any specific material (to maintain a general discussion for both OSS and CVD). Although the particular activation energies are listed in Table 1S of the Supporting Information, we indicate here that (i) they fulfill detailed balance , and (ii) a few barriers for the triangular lattice are so large that they can be regarded as ∞ for the discussions below.…”

Section: Computational Methodsmentioning

confidence: 99%

“…With some exceptions, 37 self-learning KMC studies usually indicate that only a few key barriers are important in order to describe surface diffusion, even if the KMC simulations automatically generate many dozens of barriers. 38,39 Thus, in this study the activation energies are chosen in order to generate realistic morphologies for both triangular and square lattices while keeping the resulting models (i) simple enough (to enable a foundational analysis of the apparent activation energy of the tracer diffusivity) and (ii) disengaged from any specific material (to maintain a general discussion for both OSS and CVD). Although the particular activation energies are listed in Table 1S of the Supporting Information, we indicate here that (i) they fulfill detailed balance 27,33 and (ii) a few barriers for the triangular lattice are so large that they can be regarded as ∞ for the discussions below.…”

Section: ■ Theorymentioning

confidence: 99%

Microscopic Origin of the Apparent Activation Energy in Diffusion-Mediated Monolayer Growth of Two-Dimensional Materials

Gosálvez

Alberdi-Rodríguez

2017

J. Phys. Chem. C

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Current trends indicate that mass production of high-quality, two-dimensional materials will likely be based on the use of on-surface synthesis (OSS) and/or chemical vapor deposition (CVD) on selected substrates. However, the success of these techniques heavily relies on a deeper understanding of terrace and perimeter diffusion of the adspecies across and around many self-generated, mobile clusters, and/or motionless islands with a variety of shapes (dendritic, compact, irregular, polygonal, ...). We show that, for typical monolayer growth conditions at constant deposition rate, the total square distance traveled by all adsorbed particles departs from the total number of diffusion hops due to the onset of correlations between subsequent hops along the perimeters of a growing density of obstacles. As a result, we propose a new expression to determine the tracer diffusivity of the adparticles, directly providing a simple understanding of the temperature and coverage dependence of this observable. Most importantly, we describe the microscopic origin of the apparent diffusion barrier extracted from a typical Arrhenius plot at any given coverage.

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“…NNN interactions are often intentionally neglected; but their effect could be crucial or at least among the most effective mechanisms for step dynamics; consequently, on the meandering instability, as we will see for the case of copper. Kinetic Monte Carlo (kMC) is well suited for this kind of study [22]. Before presenting our kMC results, we summarize the main results concerning the meandering instability.…”

Section: Iii-theoretical Predictions Vs Experimental Results For Coppermentioning

confidence: 99%

Competing growth processes induced by next-nearest-neighbor interactions: Effects on meandering wavelength and stiffness

et al. 2017

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Abstract:In this paper we explore the meandering instability of vicinal steps with a kinetic Monte Carlo simulations (kMC) model including the attractive next-nearest neighbor (NNN) interactions. kMC simulations show that increase of the NNN interaction strength leads to considerable reduction of the meandering wavelength and to weaker dependence of the wavelength on the deposition rate F. The dependences of the meandering wavelength on the temperature and the deposition rate obtained with simulations are in good quantitative agreement with the experimental result on the meandering instability of Cu (0 2 24 (2001)]. The effective step stiffness is found to depend not only on the strength of NNN interactions and the Ehrlich-Schwoebel barrier, but also on F. We argue that attractive NNN interactions intensify the incorporation of adatoms at step-edges and enhance step roughening. Competition between NNN and NN interactions results in a 'new form' of meandering instability which we call "roughening-limited" growth, rather than attachment-detachment limited growth that governs the Bales-Zangwill (BZ) instability. The computed effective wavelength and the effective stiffness behave as:

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Self-learning kinetic Monte Carlo simulations of self-diffusion of small Ag islands on the Ag(111) surface

Cited by 7 publications

References 48 publications

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

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

Microscopic Origin of the Apparent Activation Energy in Diffusion-Mediated Monolayer Growth of Two-Dimensional Materials

Competing growth processes induced by next-nearest-neighbor interactions: Effects on meandering wavelength and stiffness

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