Sub-Kelvin thermometry for evaluating the local temperature stability within in situ TEM gas cells.

In situ TEM utilizing windowed gas cells is a promising technique for studying catalytic processes, wherein temperature is one of the most important parameters to be controlled. Current gas cells are only capable of temperature measurement on a global (mm) scale, although the local temperature at the spot of observation (µm to nm scale) may significantly differ. Thus, local temperature fluctuations caused by gas flow and heat dissipation dynamics remain undetected when solely relying on the global device feedback. In this study, we overcome this limitation by measuring the specimen temperature in situ utilizing parallel-beam electron diffraction at gold nanoparticles. By combining this technique with an advanced data processing algorithm, we achieve sub-Kelvin precision in both, vacuum as well as gaseous environments. Mitigating charging effects is furthermore shown to minimize systematic errors. By utilizing this method, we characterize the local thermal stability of a state-of-the-art gas cell equipped with heating capability in vacuum and under various gas-flow conditions. Our findings provide crucial reference for in situ investigations into catalysis.