Multiscale atomistic simulation of metal-oxygen surface interactions: methodological development, theoretical investigation, and correlation with experiment. Final report
- Univ. of Florida, Gainesville, FL (United States). Materials Science and Engineering
Our long-term vision is for a comprehensive and fundamental understanding of a critical gas-surface reaction, nano-oxidation from the adsorption of oxygen atoms on the metal surface to the coalescence of the bulk oxide via coordinated multi-scale theoretical and in situ experimental efforts. Reaching this goal necessitates close collaborations between theorists and experimentalists, and the development and utilization of unique and substantial theoretical and experimental tools. Achievement of this goal will be a major breakthrough in dynamic surface/interface reactions that will dramatically impact several scientific fields. Many of these are of interest to DOE, such as thin films and nanostructures that use oxidation for processing, heteroepitaxy, oxidation and corrosion, environmental stability of nano-devices, catalysis, fuel cells and sensors. The purpose of this specific DOE program was the support for the theoretical effort. Our focus for the first round of funding has been the development of a Kinetic Monte Carlo (KMC) code to simulate the complexities of oxygen interactions with a metal surface. Our primary deliverable is a user-friendly, general and quite versatile KMC program, called Thin Film Oxidation (TFOx). TFOx-2D presently simulates the general behavior of irreversible 2-dimensional nucleation and growth of epitaxial islands on a square or rectangular lattice. The TFOx model explicitly considers a very large range of elementary steps, including deposition, adsorption, dissociation of gas molecules (such as O2), surface diffusion, aggregation, desorption and substrate-mediated indirect interactions between static adatoms. This capability allows for the description of the numerous physical processes involved in nucleation and growth. The large number of possible input parameters used in this program provides a rich environment for the simulation of epitaxial growth or oxidation of thin films. As a first demonstration of the power of TFOx-2D, the input parameters were systematically altered to observe how various physical processes impact morphologies. It was noted that potential gradients, developed to simulate medium-range substrate mediated interactions such as strain, and the probability of an adatom attaching to an island, have the largest effect on island morphologies. Nanorods, and round, square and dendritic shapes have all been observed which correlate well with experimental observations of the wide range of oxide morphologies produced during in situ oxidation of Cu thin films. To allow TFOx to be accessible to the rest of the scientific community, a web-site describing TFOx has been developed: www.tfox.org. Brief highlights of our progress to date are summarized as: Development of TFOx-2D, a versatile kinetic Monte Carlo code that can simulate atomistic transport, nucleation and growth, and includes potential gradients to simulate medium-range substrate mediated effects (e.g., strain); Systematic study of TFOx-2D input parameters to reveal a variety of nano-structures that resemble those seen experimentally; Parallelization of the Streitz-Mintmire potential and Rappe-Goddard approach for determining dynamic charge transfer at a metal-oxide interface, which is the critical step required for molecular dynamic simulations of oxygen-metal interactions; Benchmark calculations of Cu and Cu2O physical properties to determine the most accurate electronic structure approach; and, Demonstration of the greater universality of the Tersoff-Tromp elastic strain relief model of nano-rod formation to a gas-surface reaction. Hence, we have established the ground work for a truly comprehensive and multi-scale theoretical tool that can simulate any gas-surface reaction, including oxidation, from the atomic level to the mesoscale, from first principles. The direct comparison between these simulations and in situ experiments of metal nano-oxidation will lead to new knowledge of this important surface reaction.
- Research Organization:
- Univ. of Pittsburgh, PA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- FG02-01ER45919
- OSTI ID:
- 1067349
- Report Number(s):
- DOE/ER/45919-3
- Country of Publication:
- United States
- Language:
- English
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