Cryogenic transmission electron microscopy has revolutionized structural biology and materials science. To image below liquid nitrogen temperatures, various liquid helium stages have been constructed but have proven to be complex and unstable, making high-resolution imaging challenging. This problem is even more pronounced in side-entry specimen holders common on modern transmission electron microscopes. Here, we introduce an ultracold liquid helium transmission electron microscope side-entry specimen holder, featuring continuous cryogen flow and vibration decoupling. This instrument is compatible with modern aberration-corrected microscopes and achieves sub-25 K base temperature, [Formula: see text]2 mK thermal stability over many hours, and atomic resolution-setting the stage for a new era of cryogenic electron microscopy.
Keywords: cryo-EM; cryo-TEM; electron microscopy; liquid helium.