Influence of surface orientation and defects on early-stage oxidation and ultrathin oxide growth on pure copper

Abstract

We investigate oxidation and oxide growth on single-crystal copper surfaces using reactive molecular dynamics simulation. The kinetics of surface oxide growth are strongly correlated with the microstructure of the metal substrates. Simulating oxide layer growth along the (100), (110), and (111) orientations of crystalline copper, oxidation characteristics are investigated at temperatures of 300 K and 600 K. The oxidation kinetics are found to strongly depend on the surface orientation, ambient temperature, and surface defects. The effect of surface morphology on oxidation characteristics is analyzed by comparing oxygen adsorption on various sites and the structure factor. The surface oxide formed on (100) retains the initial crystal structure in the 300–600 K range. The (100) surface shows the highest oxidation rate at both temperature conditions but saturates, facilitating oxygen adsorption on hollow sites. The oxidation kinetics of the (100) orientation are found to be not significantly affected by surface defects. (110) shows modest oxidation at 300 K but the highest oxidation is observed at 600 K. By surface disorder and reconstruction, the oxide layer is produced continuously. The (111) surface is sensitive to ambient temperature and surface defects, showing that surface reconstruction is a key element for further oxidation. The charge distribution of oxidized Cu atoms indicates multiple groups of stoichiometric oxides, while the fraction of CuO-like characteristics increases significantly on the (110) and (111) orientations at higher temperature (600 K). The energetics and mechanisms of oxidation on Cu metal substrates at the nanoscale are discussed in detail, and comparisons with available experimental and other theoretical studies are presented wherever possible.

Keywords:

• ReaxFF
• copper
• oxidation
• molecular dynamics

Acknowledgments

This work has been supported by the Office of Naval Research, contract No. N00014-10-1-0346. The computational facilities have been provided by the Center for Nanoscale Materials (CNM) at Argonne National Laboratory and the Center for Nanoscale Systems (CNS) – National Nanotechnology Infrastructure Network (NNIN) at Harvard University. Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.