Development of a ReaxFF potential for Ag/Zn/O and application to Ag deposition on ZnO

Abstract

A new empirical potential has been derived to model an Ag-Zn-O system. Additional parameters have been included into the reactive force field (ReaxFF) parameter set established for ZnO to describe the interaction between Ag and ZnO for use in molecular dynamics (MD) simulations. The reactive force field parameters have been fitted to density functional theory (DFT) calculations performed on both bulk crystal and surface structures. ReaxFF accurately reproduces the equations of state determined for silver, silver zinc alloy and silver oxide crystals via DFT. It also compares well to DFT binding energies and works of separation for Ag on a ZnO surface. The potential was then used to model single point Ag deposition on polar (0001) and non-polar (1010) orientations of a ZnO wurtzite substrate, at di↵erent energies. Simulation results then predict that maximum Ag adsorption on a ZnO surface requires deposition energies of  10 eV.

Growth of silver on zinc oxide via lattice and off-lattice adaptive kinetic Monte Carlo

“…This is a good approximation as single point deposition simulations 9 showed that no Ag atoms penetrate or damage the ZnO surface at low deposition energies and come to rest in stable lattice sites. Single atoms can diffuse around the surface, but concerted motion of clusters was not implemented, although some cluster motion was observed as a series of single atom moves.…”

“…First reactive force field potentials [7][8][9] have become accepted as a way to capture many of the effects missing from previous empirical potential descriptions and secondly adaptive KMC methods, introduced by Henkelman and Jónsson, 10 can be used to predict unexpected transitions which would be missed by KMC using predefined event tables. [11][12][13] Originally, a simplified model, using a combination of pair potentials for Ag-Zn and Ag-O interactions fitted to works of separation, 6 was first considered for the simulation of Ag growth on ZnO surfaces.…”

“…As a result, a more comprehensive many body potential function was developed for full thin film growth simulations. 9 In a previous publication 9 we reported on a new reactive force field (ReaxFF) potential, fit to a large set of ab initio data that captures many of the surface characteristics of Ag on ZnO-including works of separation. This newer model predicts that the interstitial Ag is metastable compared to an Ag adatom in agreement to ab initio results.…”

Reaction pathways in atomistic models of thin film growth

“…Figure 3 illustrates an intermediate situation when growing Ag on oxygen terminated ZnO(0001) using a reactive force field potential. 26 Ag growth on ZnO surfaces has been the subject of several investigations that indicate that Ag grows in islands rather than smooth layers. 24,25 In our simulations, atoms are deposited with an energy of 3 eV normal to the surface at 300 K and AKMC is compared with MD.…”

“…In this case, there are very few concerted motions during growth. 26,27 The most stable site is above a vacant site in the Zn layer but a metastable site is also over the Zn atom. Between impacts, diffusion occurs by a single atom translation mechanism with barriers of 0.52 eV from a stable to metastable site and 0.16 eV from a metastable to stable site.…”