Imaging rotational dynamics of nanoparticles in liquid by 4D electron microscopy
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.
Additional Information© 2017 American Association for the Advancement of Science. 14 June 2016; resubmitted 19 September 2016. Accepted 15 December 2016. This work was supported by the Air Force Office of Scientific Research, grant FA9550-11-1-0055S, for research conducted at The Gordon and Betty Moore Center for Physical Biology at the California Institute of Technology. We thank J. S. Baskin for very helpful discussion and for his help setting up the new femtosecond laser system. We appreciate J. K. Barton, R. A. Marcus, and J. F. Brady for helpful discussion and suggestions. We also thank J. Hu and H. Li for fruitful discussion.
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