AVS 60th International Symposium and Exhibition
    In Situ Spectroscopy and Microscopy Focus Topic Friday Sessions
       Session IS+AS+SP-FrM

Invited Paper IS+AS+SP-FrM1
In Situ Atomic-Scale Observations of the Oxidation of Metals

Friday, November 1, 2013, 8:20 am, Room 203 B

Session: Evolving In Situ Microscopic and Spectroscopic Techniques and Applications
Presenter: G. Zhou, State University of New York, Binghamton University
Authors: G. Zhou, State University of New York, Binghamton University
L. Luo, State University of New York, Binghamton University
L. Li, State University of New York, Binghamton University
J. Ciston, Lawrence Berkeley National Laboratory
E. Stach, Brookhaven National Laboratory
J. Yang, University of Pittsburgh
Correspondent: Click to Email
Transmission electron microscopy (TEM) has evolved dramatically in recent years and allows for temperature-, time-, and pressure-resolved imaging of gas-surface reactions at the atomic scale. This is accomplished by differentially pumped environmental TEM (max pressures of several Torr) and the incorporation of aberration correction techniques. Here we describe how dynamic, atomic-scale TEM observations of terraces and steps during oxidation of Cu surfaces demands revisions in the current held oxidation mechanism. The canonical description of oxide formation in metals involves a solid-solid transformation proceeding with initial oxygen chemisorption induced reconstructions followed by oxygen subsurface incorporation. Such a mechanism has been inferred from idealized experiments that are primarily restricted to planar surfaces under ultrahigh vacuum conditions. In practice, however, metallic surfaces are seldom perfect. Rather, they contain a high density of low-coordinated surface sites. Thus, in order to gain a detailed understanding of the mechanism of oxide formation under realistic conditions, the role of surface defects during surface oxidation must be elucidated under practical environments. By observing the coordinated step retraction and oxide propagation on surface terraces in real time with in-situ TEM, we demonstrate that the oxide grows via an adatom process, in which Cu atoms detach from step edges and diffuse in along the surface terrace. This process involves neither reconstructive oxygen adsorption nor oxygen subsurface incorporation and is rather different from the mechanism of solid-solid transformation of bulk oxidation that is most commonly postulated. These results demonstrate that the presence of surface steps can promote the development of a flat metal-oxide interface by kinetically suppressing subsurface oxide formation at the metal-oxide interface.