Taming of Oxygen in the Electron Microscope : Effects of High Energy Electron Irradiation on O2 and Oxides

Abstract: Transmission electron microscopy (TEM) is an atomic resolution technique that allows for in depth analysis of the properties of different materials by passing high energy electrons through a thin sample and detecting how they are affected. However, due to the strong interaction between electrons and matter, the probability of the sample remaining unperturbed by the electron irradiation is small. This is an issue as there can be ambiguity about if the effects seen in TEM are inherent for the material or induced, fully or in part, by electron irradiation.One especially useful application of TEM is to observe dynamic processed by introducing external stimuli such the introduction of reactive gases into close proximity of the sample, referred to as Environmental TEM (ETEM). ETEM allows for the observation of morphological, elemental, atomic, and chemical changes in a solid in a solid–gas reaction, providing insight into the function of the solid during the reaction. However, during dynamic processes, due to the increased complexity of the interactions, it is even more difficult to deconvolve the inherent effects from the ones induced by electron irradiation. When a reactive gas is introduced into the TEM, it will be affected by the electron irradiation and may become even more reactive. The gas may also interact with defects in the sample caused by electron irradiation. Both these interactions generally lack equivalents in applications outside the ETEM, resulting in further ambiguity.Herein I discuss the ramifications of electron irradiation in TEM, both in vacuum and with reactive gases present, especially as they pertain to carbon black oxidation and the electron irradiation induced oxidation of cobalt nickel nanoparticles. In both of these cases there is a substantial effect from electron irradiation. For carbon black oxidation, the oxidation rate is highly dependent on the electron flux and in observations of cobalt nickel nanoparticles, electron irradiation induces surface oxidation of the particles. In this thesis I provide some suggestions for how the interpretative problems arising from electron irradiation can be compensated for, and how to best mitigate the effects in the first place.

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