AVS 56th International Symposium & Exhibition
    In Situ Microscopy and Spectroscopy: Interfacial and Nanoscale Science Topical Conference Friday Sessions
       Session IS+AS-FrM

Paper IS+AS-FrM2
The Surface Kinetics of the Initial Oxidation Stages of Cu Alloys

Friday, November 13, 2009, 8:40 am, Room C4

Session: In-Situ Microscopy and Spectroscopy: Dynamic Nanoscale Processes
Presenter: J.C. Yang, University of Pittsburgh
Authors: Z. Li, University of Pittsburgh
J.C. Yang, University of Pittsburgh
Correspondent: Click to Email
We are studying the dynamics of the initial and transient oxidation stages of a metal and alloys with in situ ultra-high vacuum (UHV) transmission electron microscopy (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 and temperatures. The addition of a secondary non-oxidizing element, Au, revealed a self-limiting growth due to the depletion of Cu near the oxide island that significantly slows down the oxide growth as well as lead to an unusual dendritic shape, limiting its ability to form a uniform protective oxide. The Cu-Ni alloys show more complex behavior, where the two components are 100% solid-soluble down to ~300°C but Cu2O and NiO show limited miscibility. Nickel oxide, which has the cubic NaCl crystal structure, has a more negative standard free energy of formation than Cu2O, which is simple cubic, and is expected to form more readily. In this case, depending on the environmental pO2, either one or both components of the alloy will oxidize, thus enabling a systematic determination of the effects of compositional and phase development during oxidation. We noted remarkable differences between Cu-Ni oxidation and our past observations of Cu and Cu-Au oxidation: 1) a second rapid nucleation of compact and dense oxide islands occurred and 2) polycrystalline oxides formed, where only cube-to-cube epitaxial Cu2O islands nucleated on Cu (001) and CuAu (001) for all temperatures and pressures studied. The surface segregation of Cu and Ni towards or away, respectively, from the alloy surface during oxidation could disrupt and cause polycrystalline oxide formation. In addition to being excellent model systems for understanding environmental stability of metal alloys, knowledge of the oxidation behavior of Cu-based alloys is also of practical interest in diverse areas, such as electronics, functional oxides and catalysis.