Dynamic Restructuring during Processing: Approaches to Higher Temporal Resolution

Non-equilibrium dynamic structural fluctuations occur during many materials synthesis and processing conditions. Atoms can diffuse across a surface and spontaneously self-assemble to form quasi-stable non-equilibrium phases. The fundamental atomic scale processes taking place on the surface are not well understood and many intermediate structures may form with similar Gibbs free energies separated by low kinetic barriers Describing the structural evolution of the system in space and time is a major challenge which may be tackled with aberration corrected, in situ electron microscopy, allowing atomic columns to be located with picometer precision. Recently introduced direct electron detectors offer fast time resolutions and high detection quantum efficiencies. In practice, combining both high spatial and temporal resolution remains challenging, and careful consideration must be given to signal-to-noise and electron flux. High temporal resolution may compromise spatial precision due to degradation in signal-to-noise but may also reveal rapid structural fluctuations at the atomic level. Approaches to high temporal resolution are illustrated below for in situ imaging of metal and ceramic nanoparticles under vacuum and in the presence of reactive gas.