The Surface Kinetics of the Initial Oxidation Stages of Cu and Cu Alloys Judith C. Yang,* Yihong Kang,* Langli Luo,** Chris Fleck,* Minyoung Lee,*** Jeffrey A. Eastman,**** Alan McGaughey*** and Guangwen Zhou** * Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261 ** Department of Mechanical Engineering, State University of New York, Binghamton, NY13902 *** Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213 **** Materials Science Division, Argonne National Laboratory, Argonne, IL, 60439 Environmental stability is one of the most important properties for materials exposed to air. As the dimensions of engineered systems approach the nanoscale, fundamental understanding of reactions with oxygen at this length scale becomes critical for environmental stability as well as for processing oxide nanostructures, where surface reactions are commonly used. Because environmental stability is an essential property of most engineered materials, many theories exist to explain oxidation and corrosion mechanisms. However, nearly all classical oxidation theories assume a uniform growing film, where structural changes are not considered because of the previous lack of experimental procedures to visualize non-uniform growth conditions. These macroscopic depictions do not address how initial surface conditions and early stages of oxidation lead to the final oxide scale morphology, though it is well known that surface conditions and secondary elements dramatically impact the oxide structure. These transient stages of oxidation — from the nucleation of the metal oxide to the formation of the thermodynamically stable oxide — represent a scientifically challenging and technologically important terra incognito. These issues can only be understood through detailed structural study of the relevant microscopic processes at the nanoscale in situ, combined with comparison to theoretical models. Hence, we are studying the dynamics of the initial and transient oxidation stages of a metal and its alloys with in situ methods, including ultra-high vacuum transmission electron microscopy (UHV-TEM) and synchrotron X-ray diffraction. We examined the dynamic responses of Cu and Cu alloy thin films to variations in thermodynamic variables such as temperature, oxygen partial pressure (pO 2 ), strain, and crystallographic orientation. Our past work demonstrated that the formation of epitaxial Cu 2 O islands during the transient oxidation of Cu(100), (110) and (111) films bears a striking resemblance to heteroepitaxy, where the initial stages of growth are dominated by oxygen surface diffusion and strain impacts the evolution of the oxide morphologies [1-4]. We are currently developing multi- scale simulations to directly compare to the Cu oxidation data and provide insight into the mechanisms controlling the initial stages of oxidation [5]. For example, a kinetic Monte Carlo code has been developed to describe three-dimensional island nucleation and growth (www.tfox.org ) [6]. The kinetics of early stage oxidation of Cu, Cu-Au and Cu-Ni alloys were visualized using in situ ultra-high vacuum transmission electron microscopy (UHV-TEM), where the initial oxidation stages can be observed in real-time under well-controlled surface conditions. These experiments were carried out in a modified JEOL 200CX TEM. This microscope is equipped with an ultra-high vacuum (UHV) chamber with base pressure ~ 10 -8 Torr. The microscope was operated at 100KeV to minimize the possibility of radiation-induced effects. A controlled leak valve attached to the column permits the introduction of oxygen gas directly into the microscope at a pO 2 between 5×10 -5 and 1406 doi:10.1017/S143192761005453X Microsc. Microanal. 16 (Suppl 2), 2010 © Microscopy Society of America 2010 https://doi.org/10.1017/S143192761005453X Published online by Cambridge University Press