Fundamental In Situ Nano-Oxidation Mechanisms of Metals and Metallic Alloys

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

TECHNICAL: 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. At present, however, the nanoscale 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. The objective is to fundamentally understand nanoscale oxidation processes by coordinated experimental (in situ UHV-TEM) and theoretical efforts, where the impact is potentially a new paradigm for oxidation. To meet this objective, directly correlated experimental and theoretical investigations of the initial stages of Cu and Cu alloy (Cu-Au and Cu-Ni) oxidation will be performed. The in-situ experiments of the initial stages of Cu have been performed by PI in the past. The extension to Cu alloy oxidation will be conducted in an in situ UHV-TEM at various temperatures, pressures and oxidizing atmospheres in Yang's laboratory where a unique in--situ UHV TEM exists. To bridge the temporal gap between simulations and experiments, a newly developed dynamic TEM (DTEM) with nanoseconds time resolution, will be used as well at Lawrence Livermore National Lab (LLNL). Determination of the Cu/Cu2O interface structure formed by in-situ oxidation by cross-sectional TEM and scanning TEM (STEM) methods, including high-resolution electron microscopy (HREM), Z-contrast imaging, tomography and electron energy loss spectroscopy (EELS) and the comparison with theoretical simulations will provide critical insights into the oxidation transformation mechanisms. The sample preparation and TEM/STEM studies will be conducted in the new Peterson Institute of NanoScience and Engineering (PINSE) at Univ. of Pittsburgh (UPitt). The in-situ and ex-situ experimental TEM results will be directly correlated to theoretical models, where a first-principles kinetic Monte Carlo, called Thin Film Oxidation (TFOx) is being developed. TFOx is a C++ code that presently simulates 2D nucleation and growth, and will be developed to simulate 3D island formation where computer clusters at CMU and UF and the supercomputer facility at UPitt will be utilized for significantly enhanced simulation speed. The direct comparison between these simulations and in-situ experiments will lead to new knowledge. NON-TECHNICAL: The combined experimental with theoretical partnership between UPitt, LLNL,UF and CMU will significantly enrich and broaden the education of all of the graduate and undergraduate students involved in this program. Yang has a strong track record in advising women students. Dissemination of results will include a web-site: www.tfox.org. Yang will integrate her research program in thin films, gas surface reactions and electron microscopy into several of the Mechanical Engineering and Materials Science department (MEMS) undergraduate and graduate-level courses, such as undergraduate crystallography/diffraction laboratory and graduate nano-courses, such as thin films, nanocharacterization and electron microscopy as well as nanomaterials, at UPitt.