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Ultrafast studies using liquid cells
Advances in microscopy techniques aim to make it possible to study materials under more realistic conditions, such as in liquid cells, or to use fast probes to capture dynamics. Fu et al. combined liquid cell transmission electron microscopy with ultrafast pump-probe spectroscopy to perform time-resolved studies of nanoscale objects (see the Perspective by Baum). They successfully captured the change in rotational dynamics of coupled gold nanoparticles and also observed the dynamics as two particles fused together in a liquid environment.
In real time and space, four-dimensional electron microscopy (4D EM) has enabled observation of transient structures and morphologies of inorganic and organic materials. We have extended 4D EM to include liquid cells without the time resolution being limited by the response of the detector. Our approach permits the imaging of the motion and morphological dynamics of a single, same particle on nanometer and ultrashort time scales. As a first application, we studied the rotational dynamics of gold nanoparticles in aqueous solution. A full transition from the conventional diffusive rotation to superdiffusive rotation and further to a ballistic rotation was observed with increasing asymmetry of the nanoparticle morphology. We explored the underlying physics both experimentally and theoretically according to the morphological asymmetry of the nanoparticles.