A Cryo-transfer facility for the VG HB501 STEM

Abstract

A recently developed cryotransfer facility has been successfully used to transfer both hydrated and dehydrated sections from a cryo-microtome to the column of the HB501 STEM with no significant warming or ice formation during transfer. This new accessory enables X-ray and energy loss analytical work to be carried out on frozen biological sections at much higher spatial resolution than is possible with conventional TEM systems.The construction and operation of the cryotransfer stage are summarized schematically in Figs. 1 and 2. Fig. 1 shows the central region of the HB501 optical column containing the objective lens (1), the post-specimen dc ana ac scan coil assembly (2), the annular dark field detector (3), the diffraction screen (4) and the airlock (5) through which room temperature specimens are normally loaded into the top-entry stage. A special stage base (6) is used which incorporates a liquid nitrogen-cooled block into which specimens are loaded by means of a side-entry manipulator (10). This manipulator is mounted on a support bracket (7) and enters the column through an isolation valve (8). Movement is achieved by a mechanism (not shown) mounted on the outer end of the bracket (7) and vacuum sealed by a bellows (11). The manipulator is liquid nitrogen-cooled by cooling pipes passing axially through the bellows. Loading and unloading of specimens is via an entry lock (9) which can be vented to dry nitrogen. A liquid nitrogen cooled, shrouded transfer rod (not shown) is used to transport specimens from the cryo-microtome to the entry lock.