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Jacob Jokisaari1 Arijita Mukherjee1 Xuan Hu1 Robert Klie1

1, University of Illinois at Chicago, Chicago, Illinois, United States

Understanding the details of chemical reactions, particularly in biologically significant materials systems, has driven considerable effort in developing liquid cell stages to utilize the spatial resolution of the transmission electron microscope (TEM). However, containment of the liquid in the vacuum environment and scattering of electrons within the liquid cell and encapsulation window limit the achievable resolution. Recently, considerable effort has been invested in using 2D materials for liquid cell windows, with some success, particularly using graphene. In this case, the window is composed of pockets of water between a few sheets of graphene, creating a thin blister of liquid environment, minimizing scattering from the window and the liquid volume, known as a graphene liquid cell (GLC). Furthermore, recent work on the interaction of the electron beam and water provides a mechanism to use the electron beam to drive pH sensitive reactions. We apply this knowledge to drive pH dependent reactions in graphene liquid cells on hydroxyapatite (HAP), a biomaterial for which dissolution and precipitation processes are important. Using the electron beam to change local pH, we can examine the electron-beam induced change in pH, and the resulting dissolution/reprecipitation of HAP in GLCs. The reactions are captured in real time and processed using computer vision techniques to track the change in individual particles. These results demonstrate the world of new capabilities allowed by 2D window thin liquid cells and quantification of electron-beam/liquid interactions, which can be applied to many questions involving chemical reactions in liquid environments at the nano scale.

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