Temperature distributions in MEMS microheaters during gas phase experiments in an environmental TEM

• Temperature gradients on MEMS heating-biasing chips in flowing gases in the ETEM are modelled by CFD • Comparing H 2 , O 2 and vacuum, the temperature distribution is least homogeneous in H 2 • Approx. 60 °C difference between heater and sample position at a set temperature of 900 °C in 3 mbar H 2 • The temperature difference between heater and sample position increase linearly with set temperature Reliable sample temperature measurements are essential in environmental transmission electron microscope (ETEM) experiments. In this study, the effect of flowing gases on the temperature distribution at a MEMS microheater in gas phase is investigated. A computational fluid dynamics model is developed and compared with experimental data. The modeling results agree well with experimental measurements based on the melting temperature of Zn nanoparticles, confirming the model's reliability. The results show that the temperature profile across the heating chip in the case with H 2 environment is less uniform compared to the case of vacuum and O 2 . For example, at a set temperature of 900 °C in 3 mbar H 2 , a temperature difference of 60 °C is observed between the central sample position compared to the surrounding arc-shaped heater which also is the temperature sensor, while the difference in the vacuum case is only 13°C. Temperature is one of the key parameters in in-situ TEM experiments and, therefore, these findings are important in the design of ETEM experiments, especially when using MEMS microheaters with relatively large distances between TEM sample and microheater/sensor.