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Abstract Accurate control and measurement of real-time sample temperature are critical for the understanding and interpretation of the experimental results from in situ heating experiments inside environmental transmission electron microscope (ETEM). However, quantifying the real-time sample temperature remains a challenging task for commercial in situ TEM heating devices, especially under gas conditions. In this work, we developed a home-made micro-electrical-mechanical-system (MEMS) heater with unprecedented small temperature gradient and thermal drift, which not only enables the temperature evolution caused by gas injection to be measured in real-time but also makes the key heat dissipation path easier to model to theoretically understand and predict the temperature decrease. A new parameter termed as “gas cooling ability ( H )”, determined purely by the physical properties of the gas, can be used to compare and predict the gas-induced temperature decrease by different gases. Our findings can act as a reference for predicting the real temperature for in situ heating experiments without closed-loop temperature sensing capabilities in the gas environment, as well as all gas-related heating systems. 

Redox‐induced interconversions of metal oxidation states typically result in multiple phase boundaries that separate chemically and structurally distinct oxides and suboxides. Directly probing such multi‐interfacial reactions is challenging because of the difficulty in simultaneously resolving the multiple reaction fronts at the atomic scale. Using the example of CuO reduction in H₂gas, a reaction pathway of CuO → monoclinic m‐Cu₄O₃→ Cu₂O is demonstrated and identifies interfacial reaction fronts at the atomic scale, where the Cu₂O/m‐Cu₄O₃interface shows a diffuse‐type interfacial transformation; while the lateral flow of interfacial ledges appears to control the m‐Cu₄O₃/CuO transformation. Together with atomistic modeling, it is shown that such a multi‐interface transformation results from the surface‐reaction‐induced formation of oxygen vacancies that diffuse into deeper atomic layers, thereby resulting in the formation of the lower oxides of Cu₂O and m‐Cu₄O₃, and activate the interfacial transformations. These results demonstrate the lively dynamics at the reaction fronts of the multiple interfaces and have substantial implications for controlling the microstructure and interphase boundaries by coupling the interplay between the surface reaction dynamics and the resulting mass transport and phase evolution in the subsurface and bulk.

 

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics. However, current epitaxial oxide growth methods are based on macroscopic empirical knowledge, lacking fundamental guidance at the nanoscale. Using correlated in situ environmental transmission electron microscopy, statistically-validated quantitative analysis, and density functional theory calculations, we show epitaxial Cu₂O nano-island growth on Cu is layer-by-layer along Cu₂O(110) planes, regardless of substrate orientation, contradicting classical models that predict multi-layer growth parallel to substrate surfaces. Growth kinetics show cubic relationships with time, indicating individual oxide monolayers follow Frank-van der Merwe growth whereas oxide islands follow Stranski-Krastanov growth. Cu sources for island growth transition from step edges to bulk substrates during oxidation, contrasting with classical corrosion theories which assume subsurface sources predominate. Our results resolve alternative epitaxial island growth mechanisms, improving the understanding of oxidation dynamics critical for advanced manufacturing at the nanoscale.