Journal Highlights


Techniques


Introducing and Controlling Water Vapor in Closed-Cell In Situ Electron Microscopy Gas Reactions by KA Unocic, FS Walden, NL Marthe, AK Datye, WC Bigelow, and LF Allard, Microsc Microanal | doi:10.1017/S1431927620000185 In situ TEM reactions using an environmental TEM with


dry gases are well reported. However, reactions with water vapor using a closed-cell gas-reaction in situ holder are poorly understood. Here, we establish protocols for introducing and controlling water vapor concentrations in experimental gases, from 2% at a full atmosphere to 100% at ∼17 Torr. Gas composition was measured using a residual gas analyzer (RGA) on the return side of the gas-reactor holder, and changes in the mass spectra with and without water vapor (Figure) were used to correlate dynamic changes in cube-shaped MgO crystals. We showed that interaction of MgO with water vapor results in the formation of surface morphological and chemical changes of MgO, creating a thin, nonuniform, spiky-like surface Mg(OH)2


film. Tese results


provide validation that integrating an RGA with an in situ (S)TEM closed-cell gas-reaction system is an invaluable tool to measure gas composition and water vapor content such that correlations between gas composition and dynamic surface reactions can be determined at high spatial resolution.


Mass spectra generated by RGA system on the exit side of the gas cell without water vapor and with flowing water vapor at 16.2 Torr at room temperature and E-chip heated to 250°C, confirming the presence of water vapor.


2020 May • www.microscopy-today.com


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