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. These issues can only be understood through detailed study of the relevant microscopic processes at the nanoscale in situ. We are studying the dynamics of the initial and transient oxidation stages of a metal and alloys with in situ methods, including ultra-high vacuum (UHV) transmission electron microscopy (TEM). We have previously demonstrated that the formation of epitaxial cuprous oxide 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. For Cu-Au oxidation, the oxidation mechanisms change where the cuprous oxide reveals a dendritic growth. For Cu-Ni oxidation, the addition of Ni causes the formation cuprous oxide and/or NiO where the oxide type(s) and the relative orientation with the film depend on the Ni concentration, oxygen partial pressure and temperature.
Professor Judith Yang , Dept. of Chemical and Petroleum Engineering, Dept. of Physics, University of Pittsburgh.