THE SURFACE DYNAMICS OF THE Initial OXIDATION STAGES OF CU AND CU ALLOYS

Judith C Yang

 Mechanical Engineering and Materials Science

University of Pittsburgh, Pittsburgh, PA, USA

Surface oxidation processes play critical roles in environmental stability, high temperature corrosion, electrochemistry, catalytic reactions, gate oxides and thin film growth as well as fuel reactions. Much is known about oxygen interaction with metal surfaces and about the macroscopic growth of thermodynamically stable oxides. At present, the 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. Furthermore, since environmental stability is an essential property of most engineered materials, many theories exist to explain its mechanisms. However, nearly all classical theories assume a uniform growing film, where structural changes are not considered because of the previous lack of experimental methods to visualize this non-uniform growth under conditions that allowed for highly controlled surfaces and impurities. One can now see structural changes under controlled surface conditions, by in situ ultra-high vacuum transmission electron microscopy (UHV-TEM), and thereby challenge the commonly used assumption of a uniform oxide formation. Here, we present a systematic study of the dynamics of the initial and transient oxidation stages of a metal and alloys with in situ UHV-TEM. We have previously demonstrated that the formation of epitaxial Cu₂O islands during the transient oxidation of Cu(100), (110) and (111) films bear 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. We are presently investigating the early stages of oxidation of Cu-Au and Cu-Ni as a function of oxygen partial pressures, temperatures and composition. 

Biographical Sketch:  Professor Judith Yang received her PhD in physics, with a minor in materials science and engineering, in 1993 from Cornell University.  She was then a National Science Foundation post-doctoral fellow at the Max-Planck-Institute für Metallforschung in Stuttgart, Germany.  In 1995, she returned to the US as a post-doc and visiting lecturer at the University of Illinois at Urbana-Champaign.  In 1999, she joined the faculty at the University of Pittsburgh as an Assistant Professor and promoted to Associate Professor in 2004, where she is presently the B.P. America faculty fellow with secondary appointments in Chemical Engineering and Physics departments.  Her research interests include surface science, oxidation, catalysis, nanomaterials, advanced TEM methods, including in situ, with nearly 60 publications in these topics.