Transmission electron microscopy has proven to be a powerful tool to measure composition, chemistry and internal structure at the nanoscale and below. The two transformative developments in electron microscopy in the last two decades are (1) the emergence of aberration-corrected lenses that allow for unprecedented spatial and spectral resolution and (2) the rapid advances in in situ capabilities for observations of dynamic phenomena.
Recent and rapid developments of in situ transmission electron microscopy (TEM) has demonstrated it to be a transformative tool to gain unique dynamic processing/structure/property relationships of nanomaterials. Of particular interest are the structural changes occurring under “real” environmental conditions observable by environmental TEM (ETEM). The ETEM allows for dynamic studies for fundamental, atomic-level understanding of surface chemical reactions, such as oxidation and heterogeneous catalysis. The first part of my talk will focus on the dynamics of the initial and transient oxidation stages of metals. Using a ultra-high vacuum ETEM, we have demonstrated that the transient oxidation stage of Cu and its alloys bear a striking resemblance to heteroepitaxy, where the initial stages of growth are dominated by oxygen surface diffusion. The second part of my talk will focus on heterogeneous catalysis, which depends sensitively on the nano-sized 3-dimensional structural habits of nanoparticles (NPs) and their physicochemical structural sensitivity to the environment. My focus is on the development of integrated characterization and modeling tools and their applications appropriate for carrying out detailed studies on metallic nanoparticles (NPs) comprised of a few to as many as 100 metal atoms. The structures of small metal NPs do not behave like atoms or bulk material. For example, we have shown that Pt NPs may be both ordered and disordered, depending on its size, support and adsorbates. A statistical description of nanoparticles is more appropriate in understanding structure/property of nanoparticles and their surface reactions.