Liquid phase (or liquid cell) transmission electron microscopy (TEM) has become a powerful platform for in situ investigation of various chemical processes at the nanometer or atomic level [1]. Throughout the development of liquid phase TEM, accelerated accomplishments in improving the spatial resolution have been achieved, from the initial low magnification (the 1940s) [2] to a few nanometers (∼5 nm) in 2003 [3], sub-nanometer in 2009 [4, 5], atomic resolution in 2012 [6-9], and beyond [10] (Fig. 1a). The advanced liquid cell design and fabrication have contributed critically to these achievements. The thin liquid cells [4, 10, 11] have also enabled chemical analysis using in situ energy-dispersive x-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS), which is significant for characterizing many chemical reactions (Fig. 1b) [1].
Interactions of the electron beam with a liquid solution often result in the formation of many reactive species, which may change the chemical potential and introduce perturbation to the original chemical processes of study. Thus, understanding the radiolysis reactions in liquids is essential for the design of meaningful liquid cell experiments, connecting the liquid cell experiments with the real-world chemical processes. We have directly measured the reaction products from the interaction of the electron beam with an aqueous carbonate solution, by collecting time-resolved EELS spectra (Fig. 2). Radiolysis of the carbonate solutions yields a number of molecular products (CO2, CO, O2, H2O2, and H2), all with characteristic features in the low-loss region of the EELS spectrum. Our results show that CO2 is formed as a result of radiolytic decomposition of aqueous carbonate solution. With the low-dose STEM and temperature-dependent EELS experiments, we have been able to develop a detailed understanding of the different stages of the radiolytic degradation of liquids during in situ liquid cell experiments. These insights are crucial to limiting the impact of radiolysis on the results of liquid cell experiments by developing efficient protection strategies [13].
![Development of liquid phase TEM for investigating chemical processes [1]. (a) The resolution road map of liquid phase TEM with selected milestones (blue), which is overlaid on the original road map of TEM created by Pennycook et al. [12]. (b) A schematic showing the effort to connect the liquid phase TEM studies with the real-world chemical processes. ✽: The first closed liquid cell [2]; ⋆: ∼5 nm in 2003 [3]; ▴: 1 nm—sub-nanometer in 2009 [4, 5]; △#: atomic resolution in 2012 [6-9]; ▽: atomic resolution or beyond [10].](https://oup.silverchair-cdn.com/oup/backfile/Content_public/Journal/mam/30/Supplement_1/10.1093_mam_ozae044.804/2/m_ozae044.804f1.jpeg?Expires=1750739643&Signature=FwDeKRqk2jjMBZhTAf4w49NWuD8ws-8gS~Iuh9Iy9JhIlHDoC2K0mDeFCG7KwWWvW8J2J1RD0LCl4mqGqn3rCJ3Qp6xoHF1njtNJwXWdWQJsuhmAw3sK2~BNdOxuWkbr4kpylUnme4HAly0g-PlfGNu1Na4ecFWAjfzK4sju2Qg5FXCtcGgPcg8Xwl1wRgFCCCzAvevkeWa5~3UBHTfc4Fu21EjucI3vqBVviOFCCy4fm7zhSKDK6qf6ujjpC7AhMgdTURop5HonrgxQHPop7j6kxySkB4EcdZsG~8AqxAO268FF8FvSbYjNdlBVNbIEjA0opRRuqn64yleUTj71aw__&Key-Pair-Id=APKAIE5G5CRDK6RD3PGA)
Development of liquid phase TEM for investigating chemical processes [1]. (a) The resolution road map of liquid phase TEM with selected milestones (blue), which is overlaid on the original road map of TEM created by Pennycook et al. [12]. (b) A schematic showing the effort to connect the liquid phase TEM studies with the real-world chemical processes. ✽: The first closed liquid cell [2]; ⋆: ∼5 nm in 2003 [3]; ▴: 1 nm—sub-nanometer in 2009 [4, 5]; △#: atomic resolution in 2012 [6-9]; ▽: atomic resolution or beyond [10].
Direct measurements of the reaction products from the interaction of the electron beam with an aqueous carbonate solution using in situ EELS. (a) A schematic of liquid cell TEM setup. (b) Schematic illustration of the reaction pathways from the electron beam interaction with an aqueous carbonate solution.
