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Page 6 of 23 Zhou et al. Microstructures 2023;3:2023043 https://dx.doi.org/10.20517/microstructures.2023.38

Figure 3. Auxiliaries for enabling cryogenic APT specimen transfer. (A) Glovebox with a dewar (blue arrow) and a loadlock (green
arrow) with a cooling stage and turbo pump. The inset shows a specimen-transfer suitcase (by Ferrovac) equipped with a cooling finger
connecting to a dewar (blue arrow). Red circles show the docking port connecting the loadlock and the suitcase. (B) Cryo-puck with a
thermo-insulating washer (red arrow). (C) Cryo-carousel compatible with commercial APT system (LEAP by CAMECA) with a slot
dedicated to cryo-specimen (red arrow), which is distinct from a normal metallic slot (blue arrow). (D) Commercial APT instrument
(LEAP 4000 XS) with a suitcase attached.

the glovebox (indicated by the green arrow in Figure 3A). The loadlock is indirectly cooled with a cold
finger, which needs to be pre-evacuated to sufficiently low pressure typically between 10 and 10 Pa, which
-5
-6
is similar to the level of the loadlock of a commercial APT instrument. The puck, containing the cryo-
specimens, is then evacuated within the loadlock before being transferred to the pre-cooled vacuum suitcase
[Figure 3A inset] using the transfer arm. Next, the entire suitcase, along with the cryo-specimen, is
transported to the APT instrument. A docking port is essential for accepting the specimen transferred from
the suitcase (Arrow #1 in Figure 3D). Once the suitcase is connected to the APT loadlock, the cryo-
specimen is moved into the pre-cooled PEEK slot within the cryo-carousel [Figure 3C]. The cryo-carousel is
then shifted into the buffer chamber (Arrow #2 in Figure 3D) before loading the cryo-puck/specimen into
the cryo-stage in the analysis chamber for APT measurement (Arrow #3 in Figure 3D). To measure the
specimen temperature, a method utilizing the temperature response of the cryo-stage after cryo-specimen
[34]
loading was demonstrated in .
Cryo-specimen fabrication
The process of cryo-APT specimen fabrication is complex due to its stringent geometric requirements. The
specimen must have a tip diameter of less than 100 nanometers while maintaining a low-temperature
working condition. Electropolished metallic specimens with good mechanical strengths (see [37,38] for
electropolishing) can undergo direct plunge-freezing in coolants after treatments such as deuteration [33,34]