Advances and Opportunities in Closed Gas-Cell Transmission Electron Microscopy

Direct in situ characterizations of the solid-fluid interface on the nanoscale can provide profound implications for addressing bulk-scale enigmas. The advent of closed-cell environmental transmission electron microscopy (E-TEM) enables the implementation of a confined nanoscopic reactor within the high-vacuum microscope. With the encapsulations of reactant fluids and solid species under various stimuli, the whole reaction process can be observed with atomic precision and high temporal resolution. This experimental technique has been adopted widely throughout the field of nanoscience, with applications extending to the synthesis of low-dimensional materials, gas-phase catalysis, and modifications of nanomaterials, where Professor C. N. R. Rao has made substantial contributions over six decades. Here, we delve into the recent representative applications and enhancement strategies of the close gas-cell E-TEM methodology from the early development stages to the latest up-to-date ultrathin (UT) SiN_x technique. Remarkable advancements in the capabilities of multimodal data acquisition, including the quantitative electron diffraction, on-site spatiotemporal mapping of the gas molecules, and atomic-resolution real-space imaging in the gas cell E-TEM, are demonstrated. Furthermore, the integration of machine learning (ML)-assisted data acquisition and analysis is anticipated to represent the next major breakthrough, significantly expanding the applicability of gas-cell E-TEM across a wide range of research fields.