Abstract
Transmission electron microscopy (TEM) has long been an essential tool for understanding the structure of materials. Over the past couple of decades, this venerable technique has undergone a number of revolutions, such as the development of aberration correction for atomic level imaging, the realization of cryogenic TEM for imaging biological specimens, and new instrumentation permitting the observation of dynamic systems in situ. Research in the latter has rapidly accelerated in recent years, based on a silicon-chip architecture that permits a versatile array of experiments to be performed under the high vacuum of the TEM. Of particular interest is using these silicon chips to enclose fluids safely inside the TEM, allowing us to observe liquid dynamics at the nanoscale. In situ imaging of liquid phase reactions under TEM can greatly enhance our understanding of fundamental processes in fields from electrochemistry to cell biology. Here, we review how in situ TEM experiments of liquids can be performed, with a particular focus on microchip-encapsulated liquid cell TEM. We will cover the basics of the technique, and its strengths and weaknesses with respect to related in situ TEM methods for characterizing liquid systems. We will show how this technique has provided unique insights into nanomaterial synthesis and manipulation, battery science and biological cells. A discussion on the main challenges of the technique, and potential means to mitigate and overcome them, will also be presented.
Highlights
Visualizing liquid phase processes at the nanoscale can yield essential information for understanding fundamental processes in physics, chemistry and biology
This review is primarily focused on the transmission electron microscopy (TEM) study of liquid samples that are encapsulated inside microchip liquid cells
Other in situ liquid cell TEM works on more complex systems include nanocage formation using galvanic replacement [86], metal–organic framework’s (MOF) nucleation and growth rate with respect to different metal-to-ligand ratio [92], iron Keggin ion’s building/conversion process to magnetite and ferrihydrite [105], the growth of various metal–Fe–oxide nanoparticles using various combinations of different precursor metal solutions [106] etc
Summary
Visualizing liquid phase processes at the nanoscale can yield essential information for understanding fundamental processes in physics, chemistry and biology. Liquid cell TEM allows the observation of processes that cannot be imaged with conventional TEM or 2 other techniques. Liquid cell TEM preserves the liquid state of the specimens inside the TEM vacuum, and allows the in situ observation of biological process [9]. Compared with other in situ techniques like atomic force microscopy (AFM), scanning tunnelling microscopy (STM) and various X-ray methods, TEM has the advantage of having both high temporal and spatial resolution, it provides direct visualization of any changes in structural, morphological [22] or elemental distribution [23,24] at the nanoscale. The development of enclosed liquid cells has allowed the in situ TEM imaging of liquid phase reactions, opening up fields from electrochemistry to cell biology for study. We will cover the basics of the technique, its strengths and weaknesses with respect to related in situ TEM methods for characterizing liquid systems, and its application in biological, chemical and materials science fields
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