Development of a Method to Understand Morphological Changes in Materials at Ultrahigh Pressures Using Electron Microscopy

High-pressure chemical reactions are critical to a wide range of industrial processes, such as mining operations, catalysis, manufacturing, power generation, carbon sequestration and energy storage. Understanding the high-pressure nano-scale dynamics of material interfaces (gas/liquid, liquid/solid) at the nanoscale will permit the optimization of these reactions based on their fundamental physics. This knowledge can also lead to the discovery of cleaner and more sustainable processes. The technological challenges to obtaining the necessary information to pursue these optimizations are significant because the relevant features are extremely small (tens of nanometers or smaller), and the reaction kinetics under investigation only activate at extremely high pressures (10-100 bars). Precise concentrations of multiple reagents or precursors and reaction temperatures are required to recreate the exact conditions found in nature and industry. Atmospheric transmission electron microscopy (TEM) has been important for understanding some of the processes mentioned above, but these experiments are confined to one or at most two atmospheres of pressure. Here we will describe our development of a new experimental apparatus that allows us to achieve ultrahigh pressure materials characterization using the transmission electron microscope. The experiments we will describe rely upon changes to the existing methods that allow a closed-cell TEM holder to withstand higher pressures without breaking the confining membranes and exploit the extra pumping of an environmental transmission electron microscope (ETEM) to protect the electron source. We will describe how we have determined spatial resolution using both scanning transmission electron microscopy and energy-filtered high-resolution transmission electron microscopy as a function of gas pressure and composition, how we have explored the limits to structure determination via electron diffraction, and the difficulties associated with spectroscopy using this approach.