Скачать или смотреть 2014 Microscopy & Microanalysis - Radiolysis during Liquid Cell Electron Microscopy

Radiolysis during Liquid Cell Electron Microscopy

Nicholas M. Schneider1, Michael M. Norton1, Brian J. Mendel1, Joseph M. Grogan1, Frances M. Ross2, and Haim H. Bau1

1. Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104, USA.
2. IBM T. J. Watson Research Center, Yorktown Heights, NY 10598, USA.


Liquid cell electron microscopy is an exciting technique that enables direct in situ imaging of nanoscale processes and objects in liquids. However, the irradiating electrons affect the underlying chemistry of the medium and may impact the imaged phenomena. The beam-sample interactions produce molecular and radical products such as hydrogen, oxygen, and hydrated electrons that lead to beam-mediated phenomena. A good understanding of the interactions between the electrons and the irradiated medium is necessary to correctly interpret experiments, minimize artifacts, and take advantage of the irradiation. Here we employ a detailed kinetic model, adapted for conditions relevant to transmission electron microscopy, to compute the concentrations of water radiolysis products as functions of solution composition, dose rate, time, and spatial position with respect to the beam. We use our model’s predictions to explain experimental observations made during liquid cell microscopy. We find, among other things, that by controlling the dose rate, one can switch between etching and growth of metal nanoparticles and that radiolysis can significantly reduce the pH of the solution, inducing aggregation in colloidal systems and altering reaction kinetics. Our predictive model is useful for designing experiments that minimize unwanted beam effects; extending liquid cell microscopy to new applications; taking advantage of beam effects for nanomanufacturing such as the patterning of nanostructures; and correctly interpreting experimental observations.

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