Freeze‐fracturing for conventional and field emission low‐temperature scanning electron microscopy: the scanning cryo unit SCU 020

Abstract

SUMMARYA dedicated cryopreparation system, the SCU 020 (Balzers), is introduced and described in detail for use in low‐temperature scanning electron microscopy (LTSEM). The basic unit consists of two parts: (i) a high‐vacuum preparation chamber equipped with a cold‐stage, motor‐driven fracturing microtome, planar magnetron (PM) sputter source, quartz‐crystal thin‐film monitor, Meissner cold trap, and turbo molecular pump stand; and (ii) a second part (separated from the first by a sliding, high‐vacuum valve) residing in the SEM chamber. This is equipped with an anti‐contamination cold trap, a fully movable goniometer cold stage (having motor drives for x, y, and rotation) and replaces the SEM's original stage (Raith). The SCU 020 is entirely self contained allowing independence from, and synchroneity with, the SEM of choice.LTSEM micrographs of specimen (that are fully frozen hydrated or partially freeze‐dried) surfaces or fracture faces, without or with various metal coatings, can be examined over a broad temperature range (‐150 to +50°C). This is made possible by the combined application of the two, independently controlled, cold stages and the on‐line, high‐vacuum, specimen cryo transfer between them. In‐situ etching is simple and straightforward. Intramembranous particles and membrane fracture steps, typically imaged in transmission electron microscopy (TEM), are resolved by PM sputtering with platinum at low specimen temperature and high‐resolution LTSEM in a field emission microscope.