Atomically Stable Cryogenic In Situ TEM Biasing Holder with Accurate Temperature Control

Cryo scanning transmission electron microscopy (STEM) becomes an indispensable tool to study phase transitions in various quantum materials [1-3] at the atomic scale. Detailed characterization of the structural and electronic properties of these samples across phase transitions necessitates the need of the double tilt capability of the sample holder, atomic image stability and a continuous temperature control of the specimen. The latter is achieved through using microelectromechanical systems (MEMS)-based heating and biasing chips [4] in combination with a cryo TEM sample holder.<br/>To accurately control the temperature during in situ cooling and heating experiments, the chips need to be calibrated to correlate the resistance of the microheater with the temperature of the sample. Since not all heater materials possess a linear resistance-temperature response and the high temperature coefficient of temperature resistance might not be valid for negative temperatures, a dedicated calibration of chips on cooling is required. While the calibration above the room temperature is nowadays done routinely by different methods [5, 6], it’s not so common in cryogenic conditions. In this talk we will present a novel method of subzero chip calibration based on Raman spectroscopy. The temperature calibration performed in a wide temperature range reveals the need for a correction factor for the R-T correlation at cryo conditions. The resulting calibration factor was used to continuously control the temperature of Au-Pd nanoparticles -175^oC to +800^oC while keeping the holder cooled. It was found that the atomically stable imaging at -175^oC is maintained till the highest temperature of +800^oC though the stabilization time increases as the difference between the holder and the sample temperature rises. Similar in situ cooling experiments with continuously varied temperature but in a smaller temperature range have been performed using ferroelectric FIB lamellas. With the help of electron diffraction and TEM imaging, we were able to follow all, known and unknown phase transitions, in these samples.<br/> <br/>[1] E. Bianco, et al., Microscopy and Microanalysis 26, 1090-1092 (2020).<br/>[2] B. H. Goodge, et al., Microscopy and Microanalysis 27, 346-347 (2021).<br/>[3] N. Schnitzer, et al., Microscopy and Microanalysis 26, 2034-2035 (2020).<br/>[4] H. Perez Garza,<i> <i>et al., 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS)</i>, </i>2155-2158 (2017).<br/>[5] J. Tijn van Omme, et al., Ultramicroscopy 192, 14-20 (2018).<br/>[6] I. K. van Ravenhorst, et al., ChemCatChem 11, 5505-5512 (2019).