With the development of aberration corrected microscopy has come the necessity of more stable sample stages, one area that needs further refinement is cryogenic sample system, both for biological imaging and for sensitive materials samples that would benefit from cryo-stability.  The basic principles of the holder are given in Fig. 1. It shows the main components of the cooling holder, the main coldness losses and the measures taken to create a thermal equilibrium, such that the drift is minimized. This allows for drifts of less than 2 nm/min and sub 1 Å resolution. In the cross-section of the holder, schematically given in Fig. 1, the outside tube contains a heater close to thermal isolator near the tip, such that the temperature of the outside tube can be regulated to the temperature of the goniometer (or any other temperature). This is done to minimize the drift related to thermal expansion and to prevent any cooling (from the tip of the holder) of parts of the goniometer. 

The thermal expansion stability is important since the cooling of the goniometer parts can result in unpredictable (slow) changes in the specimen position, for instance in the electron beam direction resulting in a focus change. In case of the temperature difference between the holder and the goniometer, the heat transfer between the outside rod and the goniometer is uncertain because it depends on the mechanical contact (that can vary with tilt) and the effect of the thermal gradient on each of the relevant components in the goniometer.   Likewise the “coldness” influx depends on quite a number of parameters, like the size of the beard, how deep it is in the liquid nitrogen, whether the dewar has a “good” cover to isolate and to prevent turbulence. For that reason we have an option of a heater close to the cryo-beard. Fig. 2 shows the experimental setup of the JEOL ARM, the holder and the dewar.

Our initial tests with the prototype sample holder on a sample of small gold particles on a thin C film show a resolution stability in HRTEM showing sub 1Å information transfer (Fig. 3).  This stability is sufficient to operate the holder in STEM HAADF imaging conditions (Fig. 4) which was acquired at 2k resolution with 17.6 us pixel dwell time.  Further work needs to be done to increase the operational duty cycle, however the basic configuration of the holder seems to provide a workable solution for high-resolution cryo-imaging.

Figures:

Figure 1. Schematic representation of the basic components of the high resolution cooling holder (not to scale) and the details of the components of the cooling holder that determine the temperature and related to that the drift.

Figure 2. Image of the prototype cryogenic experimential configuration.

Figure 3. Fourier transform of the HREM image of Au particles on the thin C film.

Figure 4. STEM HAADF image of a sample of gold particles labelled nanoparticles in a biological matrix acquired at 2k resolution with 17.6 us pixel dwell time.

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EMC Abstracts - https://emc-proceedings.com/abstract/a-jeol-based-cooling-holder-with-a-low-specimen-drift-allowing-sub-1a-stem-imaging/