Advances and New Developments in the Characterization of Nanoscale Processes Using Liquid-Phase TEM

The functional properties of bulk materials are frequently dependent on the collective individual properties of their nanomaterial precursors, and thus are the result of complex mechanistic pathways that govern nanoparticle morphological evolution and self-assembly. Developing a better understanding of the nanoscale mechanisms that control structure-function relationships is a crucial first step in developing new synthesis strategies to tune material performance but requires real-time characterization of dynamic processes. Characterization of nanomaterials is typically performed using transmission electron microscopy (TEM) as it can resolve sub-nanoscale structure and provide compositional mapping. However conventional TEM analysis of the dynamic processes which govern nucleation, growth and assembly is limited to static snapshots frozen in time and is often unable to capture transient or fragile intermediate states. These limitations have been mitigated by the development of in-situ TEM techniques that enable imaging of dynamic systems in non-vacuum environments, such as liquid-phase TEM (LP-TEM). Using LP-TEM, researchers have been able to observe the morphological evolution that occurs during nucleation and growth, etching processes, and particle assembly. These studies are achieved without compromising the high-vacuum environment of the TEM column by safely enclosing the reaction solution between two, ultrathin electron transparent membranes, creating a thin layer of liquid in which dynamic processes such as nanoparticle growth, assembly, and degradation can be observed in real-time.
Modern, commercial liquid-cell (LC) TEM systems are equipped with integrated microfluidics for flow and mixing, temperature control and can perform routine electrochemical experiments – all within the confines of the TEM. Here we will review recent LP-TEM studies and how they have been applied to study synthesis and particle-assembly mechanisms, new directions in in-situ and operando instrumentation, including a much wider temperature range from -50 to 300°C, and the role of machine-vision software in mitigating the pain-points inherent to in-situ and operando LP-TEM studies.