Approaching the low-temperature limit in nucleation and two-dimensional growth of fcc (100) metal films Ag/Ag(100)

Abstract

We analyze the formation of two-dimensional Ag islands following deposition of about 0.1 ML of Ag on Ag(100) over a temperature regime ranging from classical nucleation and growth behavior to almost immobile adatoms, from 300 to 125 K. Particular emphasis is placed on the post-deposition dynamics at the lower end of the temperature range, where the saturation island density is not reached at the end of the deposition, and nucleation and aggregation processes continue with adatoms from the remaining adatom gas. Our analysis combines VT scanning tunneling microscopy experiments with kinetic Monte Carlo simulation of appropriate atomistic models. The only adjustable parameters in the model are the terrace diffusion barrier and prefactor, which can be determined from island density behavior near room temperature. Other processes such as rapid edge diffusion, and "easy" nucleation and aggregation of diagonally adjacent adatoms, are treated as instantaneous. The model excellently reproduces all aspects of behavior at low temperatures, demonstrating that nucleation and growth processes can be described in one consistent scheme, down to the regime of almost immobile adatoms. We analyze the formation of two-dimensional Ag islands following deposition of about 0.1 ML of Ag on Ag͑100͒ over a temperature regime ranging from classical nucleation and growth behavior to almost immobile adatoms, from 300 to 125 K. Particular emphasis is placed on the post-deposition dynamics at the lower end of the temperature range, where the saturation island density is not reached at the end of the deposition, and nucleation and aggregation processes continue with adatoms from the remaining adatom gas. Our analysis combines VT scanning tunneling microscopy experiments with kinetic Monte Carlo simulation of appropriate atomistic models. The only adjustable parameters in the model are the terrace diffusion barrier and prefactor, which can be determined from island density behavior near room temperature. Other processes such as rapid edge diffusion, and ''easy'' nucleation and aggregation of diagonally adjacent adatoms, are treated as instantaneous. The model excellently reproduces all aspects of behavior at low temperatures, demonstrating that nucleation and growth processes can be described in one consistent scheme, down to the regime of almost immobile adatoms.

Energetic Parameters for Atomic-Scale Processes on Ag(100)

“…In other words, it is plausible that our data could be reinterpreted to include some contribution from dimer diffusion at 300 K. This correction could affect the values of E d1 derived from temperaturedependent data by increasing the diffusion barrier slightly (not more than about 0.05 eV). The change would be small, because the data for N isl vs T span a range from about 180 to 300 K, 12,26 and over almost all of this range dimer diffusion would be negligible. This correction would, in turn, increase the predicted flux-scaling exponent, but the increase might be so slight that it would still be compatible with the data.…”

“…26 The diffraction data versus T could be fit with a LG model using E d1 ≈ 0.40 eV and ν 1 ) 3 × 10 13 / s. 26 More recently, STM studies yielded E d1 ) 0.40 eV, also from eq 1. 12 Actual values of N isl versus T could be fit with a LG model using E d1 ≈ 0.40 eV and ν 1 ) 5 × 10 12 /s. 12 The scatter in the STM data was significantly lower than in the HRLEED data, so we regard the STM-based values as more reliable.…”

“…12 Actual values of N isl versus T could be fit with a LG model using E d1 ≈ 0.40 eV and ν 1 ) 5 × 10 12 /s. 12 The scatter in the STM data was significantly lower than in the HRLEED data, so we regard the STM-based values as more reliable.…”

“…[5][6][7] For some time, we have engaged in measurements and simulations of nonequilibrium nanostructuressboth their formation and relaxationsin clean Ag thin films on Ag(100) in ultrahigh vacuum. 8 The main result has been the ability to develop tailored atomistic models for various aspects of silver surface dynamics that are sufficiently robust and comprehensive as to have predictiVe capability between 300 and 120 K. [9][10][11][12] We believe that such models could be used, for instance, to guide fabrication of films for SERS that have a particular desired morphology, or to predict the lifetimes of Ag nanostructures, in this range of temperature. Not only the models themselves, but also the parameters in these models, are significant.…”

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

“…Moreover, BCS values are also compared to experimental results [16,54,69,[71][72][73][74][75][76][77][78], as well as barriers obtained from our nudged-elasticband (NEB) calculations using an embedded atom method interatomic potential [79]. Activation barriers for selected processes are listed in Table I.…”