About this Research Topic
Many important and interesting chemistries happen in nanoparticles. Synthetic nanoparticles such as amphiphile assemblies, polymers, perovskites, quantum dots, and metal organic frameworks, are central in the development of advanced technology, while processes in atmospheric nanoparticles play a critical role in climate change. Physical and chemical characterization of these nanoparticles is indispensable in understanding their formation and properties.
Transmission electron microscopy (TEM) is a powerful and versatile characterization tool with sub-nanometric resolution. Besides providing structural information, precision chemical analysis can be carried out by energy-dispersive X-ray spectroscopy (EDS) or electron energy loss spectroscopy (EELS) in scanning (S)TEM. With tomography, three-dimensional structural and chemical maps of the sample can be obtained. Bonding states, as well as information on the electric field, magnetic field, and strain can also be probed with holography and four-dimensional STEM (4D STEM). Computational techniques such as ptychography have significantly improved the achievable resolution. In addition, field ion beam (FIB) milling allows the studies of thick samples.
Nevertheless, nanoparticles present special challenges in TEM, with many of them prone to being damaged by the electron beam. They very often contain light elements (e.g. Li) or volatile components such as organic molecules or S, which sublime under the electron beam. Moreover, many nanoparticles exist or function in a liquid environment (e.g. drug carriers or electrolytes) incompatible with conventional electron microscopy, due to the vacuum in the TEM column necessary to prevent stray electron scattering.
Recent developments in hardware, data collection strategy, and data analysis have improved our ability to image and to perform spectroscopies on these challenging nanoparticles. The development of direct electron detectors, including hybrid pixel detectors, has drastically reduced the dose necessary to obtain meaningful data. Cryo-electron microscopy further reduces beam damage while vitrification allows the study of liquid samples and the possibility to trap metastable intermediate in reactions. Together with the fast detectors, the advancement of liquid cells has allowed us to follow dynamical events in real time. While electron dose has been reduced with these technological advances, radiation damage remains a concern. Electron beam-liquid interactions in confined volumes, for instance, need to be better understood for liquid state electron microscopy. Criteria needs to be established to assure that results are free from the influence of the electron beam and represent the pristine state of the sample.
In this Research Topic, we welcome authors to describe the role of modern electron microscopy in characterizing and tuning the chemistry of beam-sensitive nanoparticles. Articles will reflect the challenges and opportunities in understanding chemical processes in radiation-sensitive nanoparticles. Potential themes may include:
• Processes on surfaces and solid-liquid interfaces elucidated by electron microscopy, including time-resolved cryo-electron microscopy and liquid cell electron microscopy
• Sample preparation protocols for electron microscopy studies that preserve the pristine states of radiation-sensitive nanoparticles
• Methodologies or technical advancements that reduce electron dose while pushing the resolution limit in imaging and diffraction of materials with weak bonds
• Theoretical and experimental studies to understand radiation damage in electron microscopy, including the direct effect on the nanoparticles and the indirect effect from the interaction of electrons with solvent molecules
• Beam-induced chemical transformation of nanoparticles in the electron microscope
Keywords: Nanoparticles, Electron Microscopy, Characterization, Solid-Liquid Interfaces, Radiation Sensitive
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