Cryogenic TEM Sample Holder and MEMS-Chips Development for In Situ Cooling, Heating and Biasing Applications

Recent developments in the cryogenic scanning transmission electron microscopy (cryo-STEM) have sparked significant interest from the quantum materials community [1]. Cryo-STEM is becoming an indispensable tool to visualize phase transitions at the atomic scale with improved stability [2-4]. The reduced sample drift comes from the advancements in the cryo-STEM sample holders [5] and the usage of the microelectromechanical systems (MEMS)-based chips [6] which opens up the possibility to locally and continuously change the temperature of the sample in a wide temperature range and, at the same time to measure its electrical response. The ability to understand the structure, electronic and transport properties of materials under an applied thermal and/or electrical stimulus at low temperatures enable applications in the field of quantum materials like superconductors and topological insulators, chare ordering, metal to insulator transitions, magnetic materials, ferroelectrics and many more.<br/><br/>To majority of the in situ cryogenic experiments have been performed employing cooling holders compatible with Thermo Fischer Scientific microscopes. Till now there are only a few reports showing stable cryogentic imaging in JEOL TEMs. In this talk, we will share our new development with respect of a combined in situ cooling and biasing system for JEOL microscopes. The system includes a double-tilt multi contact cryogenic JEOL sample holder that is MEMS-chips based. The holder has no integrated dewar and uses liquid nitrogen for cooling. The specially developed MEMS-chips possess eight electrical contacts, where four contacts are used for accurate resistive heating control using four-point-probe method and the other four electrodes are used for supplying electrical stimuli to the sample. The chips enable simultaneous in situ heating and biasing experiments up to 900^oC in the absence of the cooling agent. In a cooled state, the sample can reach temperatures of ~ - 170^oC and the microheater of the chip will allow to continuously vary the temperature. By exploiting the high stability of this system and its double tilt capability, we will demonstrate atomic resolution imaging at various intermediate temperatures in a wide temperature range. We will present a number of application examples of cooling, biasing and heating experiments with Focused Ion beam (FIB) lamellas of variety of samples.<br/><br/>[1] JL Hart et al., Nano Lett 21, 5449 (2021)<br/>[2] E. Bianco, et al., Microscopy and Microanalysis 26, 1090-1092 (2020).<br/>[3] B. H. Goodge, et al., Microscopy and Microanalysis 27, 346-347 (2021).<br/>[4] N. Schnitzer, et al., Microscopy and Microanalysis 26, 2034-2035 (2020).<br/>[5] H. Perez Garza,<i> <i>et al., 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS)</i>, </i>2155-2158 (2017).<br/>[6] Y. Pivak, et al., Microscopy and Microanalysis 29, 1695 (2023).