Liquid Helium TEM Sample Holder—Swift Cool-Down and Long Holding Time

Quantum materials display a variety of unique electronic and magnetic properties—including superconductivity, charge ordering, and topological states—which are predominantly observed at cryogenic temperatures [1, 2]. Swift progress in cryogenic scanning transmission electron microscopy (S)TEM methodologies has been achieved at liquid nitrogen (LN₂) temperatures. While LN₂-cooled side-entry sample holders and cartridge-integrated microscopes are tailored to suit the demands of the life sciences, the study of phase transitions within materials science typically necessitates adjustable temperatures with a base in the liquid helium (LHe) range [3].<br/><br/>Historically, LHe solutions for electron microscopes were constructed in a cryo-stage setup [4-7], achieving temperatures as low as 1.5 K utilising superfluid helium alongside LN₂-cooled shields, and thus enabling high-resolution imaging over a continuous five-hour span [8]. Despite these achievements, the preference for technically versatile side-entry holders has hindered further advancements in cryo-stage development. Presently, LHe side-entry holders are limited by considerable mechanical and thermal instability, and their base temperature holding times are short due to LHe's low latent heat and the limited cryogen storage capacity of the dewar attached to the holder. Efforts to extend cryogenic holding periods have led to integrating a commercial LHe continuous flow cryostat into a modified 60 mm pole piece gap following the removal of the objective lens [9]. This modification has facilitated temperature control within a range of 6.5 K to 400 K, maintainable over several days. However, the substantial alterations to the microscope structure and the requirement to vent the column for specimen loading present practical challenges for routine operation.<br/><br/>Here, we present recent innovations of a lightweight, ultra-low-temperature LHe TEM sample holder. Starting from room temperature, a base temperature of 5.2 K—measured adjacent to the specimen by a Cernox sensor—can be attained within one minute and sustained for days with a temperature stability of +/- 2.5 mK. Initially designed for X-ray diffraction studies of quantum matter in pulsed magnetic fields, condenZero, a spin-off company from the University of Zurich, has adapted their miniaturisable cryostat design for cryo-TEM usage. Collaborative efforts with the ER-C at the Research Centre Juelich have led to additional enhancements and optimisations. Here, we demonstrate the capabilities of our latest LHe cryo-TEM setup.<br/><br/>References:<br/>[1] Y. Zhu, Acc. Chem. Res. <b>54</b>, 3518-3528 (2021).<br/>[2] A. M. Minor, P. Denes, D. A. Muller, MRS Bulletin, <b>44</b>, 961-966 (2019)<br/>[3] R. E. A. Williams, D. W. McComb, S. Subramaniam, MRS Bulletin, <b>44</b>, 929-934 (2019)<br/>[4] J. A. Venables, Rev. Sci. Intrum., <b>34</b>, 582-583 (1963)<br/>[5] H. G. Heide, K. Urban, J. Phys. <b>E 5</b>, 803 (1972).<br/>[6] G. R. Piercy, R. W. Gilbert, L. M. Howe, J. Sci. Instrum., <b>40,</b> 487 (1963)<br/>[7] U. Valdrè, M. J. Goringe, J. Sci. Instrum., <b>42</b>, 268 (1965)<br/>[8] Y. Fujiyoshi et al. Ultramicroscopy, <b>38</b>, 241 (1991).<br/>[9] F. Börrnert et al. Ultramicroscopy, <b>203</b>, 12 (2019).