Surface Reactions (oxidation, catalysis) and Electron Microscopy (in situ)

Dealing with oxidation is a major societal priority, yet oxidation also presents a fascinating challenge in thin film growth.  Classical theories of oxidation were based mostly on thermogravimetric analysis (TGA) that only measures weight change, not structural changes.  Hence, classical theories assume a uniform film growth, yet it is well known that oxides do not develop as uniform films.  Recent developments of in situ experimental tools permit visualization of the dynamic processes at the nanoscale.  Yang’s research group uses in situ ultra-high vacuum transmission electron microscopy (UHV-TEM) to improve the fundamental understanding of oxidation; figure 1 are bright field images of Cu and Cu-5%Ni thin films during oxidation at P(O2) 10-4 Torr in situ, where oxide islands are seen to nucleate and grow and their shapes depend sensitively on temperature.  Heteroepitaxial concepts, based on surface diffusion, strain and structural evolution, describe surprisingly well these initial oxidation stages.