  In-situ environmental transmission electron microscopy (E-TEM) provides
sub-Angstrom spatiotemporal information on nanoscale chemical transformations.
However, the high-energy electron probe can significantly affect the
surrounding medium's chemistry and induce side reactions within the area of
interest. Radiolysis, or the dissociation of molecules under electron beam
irradiation, has become an increasingly important consideration in in-situ
nanomaterials characterization. While numerous studies have explored this
phenomenon in liquid-cell TEM, there are no reported extensions to gas phase
TEM thus far. Herein, we present a generalized computational model to elucidate
radiation chemistry in both gas and liquid E-TEM. Our model reveals that gas
phase E-TEM produces radiolytic species with lower reactivity than in the
liquid phase. However, these radiolysis species can accumulate to levels that
interfere with desired reactions, especially at higher pressures. We verify our
model by studying the radiation-promoted oxidation of aluminum nanocubes and
the disproportionation of carbon monoxide, where we find increasing the
electron beam dose rate increases the rate of AlOx production and deposited
carbon, respectively. Additionally, we propose guidelines to control the
production of radiolysis species within these closed-cell in-situ nanoreactors.
Taken together, these findings should pave the way for nanoscale control of
chemical reactions in E-TEM.
