Atomic Scale Understanding of Cu and Cu Alloy Oxidation Using In Situ Environmental TEM

Although high-temperature corrosion is a relatively well-established field of study, it is still based on classical models such as Wagner’s model, which lacks microstructural information. Therefore, these models are less accurate in explaining earlier stages of oxidation and cannot predict how factors such as surface orientations, defects, and boundaries affect the oxidation process. This is because experimental tools capable of observing these early-stage oxidation stages have not been unavailable. Recent developments involving in situ environmental TEM (ETEM) have demonstrated the great promise of this capability for examining early stages of oxidation. In this presentation, we use in situ ETEM experiments, with advanced data analysis and correlated theoretical simulations, to investigate the initial stages of Cu thin film oxidation. The originally clean metal surface was first observed to reconstruct, forming a Missing Row Reconstruction (MRR). Oxide nucleation is then observed on the reconstructed surface followed by growth into Cu₂O islands, which demonstrate a layer-by-layer island growth mechanism. To better understand the mechanisms behind these experimental observations, a multiscale simulation framework generalizes density functional theory results via force fields, applying these results to molecular dynamics and kinetic Monte Carlo simulations at larger size and time scales. Correlation between dynamic in situ experiments and theoretical computations lead into deeper fundamental insights into the atomic mechanisms and the role of surfaces and its defects on oxidation. The authors acknowledge funding from National Science Foundation (NSF) grants DMR-1410055, DMR-1508417, DMR-1410335, and CMMI-1905647, as well as support from Hitachi-High-Tech and technical assistance from the Nanoscale Fabrication and Characterization Facility (NFCF) in the Petersen Institute of Nano Science and Engineering (PINSE) at the University of Pittsburgh. This research used the Electron Microscopy facility of the Center for Functional Nanomaterials (CFN), which is a U.S. Department of Energy Office of Science User Facility, at Brookhaven National Laboratory under Contract No. DESC0012704.