A simple device for obtaining complementary fracture planes at liquid helium temperature in the freeze‐etching technique

Abstract

SUMMARY This paper describes a simple technique for obtaining complementary replicas of specimens fractured under liquid helium. Ordinary hollow brass rivets are used as specimen holders and are frozen in an end‐to‐end position. The pairs of rivets are placed in a device consisting basically of two concentric steel tubes which can be twisted and moved relative to each other guided by a peg‐in‐slot mechanism. The rivets are inserted while the device is under liquid nitrogen, and the device is then transferred to liquid helium and the tubes are moved so that the upper rivet is knocked away and falls into a collector. The device is then transferred back to liquid nitrogen, the fracture faces being protected from contamination throughout the process. Replicas are then obtained by any of the standard methods for specimens fractured under liquid nitrogen. The device has been tested using yeast cells as a model system, and some typical results are presented and discussed.

The direct measurement of temperature changes within freeze‐fracture specimens during rapid quenching in liquid coolants

“…2a). These results, together with those of Umrath (1975), appear especially relevant for the freezefracture specimen holder developed by Sleytr & Umrath (1974).…”

Understanding the artefact problem in freeze‐fracture replication: a review

“…The present state of the art makes it possible to evaluate specimens that have been freeze-cleaved at 4 K, either under liquid helium (Sleytr, 1974;Sleytr & Umrath, 1974) or under vacuum (Escaig & Nicholas, 1976;Kirchanski et al, 1979). For many model systems, and some biological membranes, it has been shown that deformation can be reduced by lowering the cleavage temperature (for review, see Sleytr & Robards, 1977a;Kirchanski et al, 1979).…”

“…The other approach uses sophisticated UHV technology with an airlock system for specimen transfer and a chamber in which every part must be baked to 500-700 K to desorb trapped molecules (Escaig & Nicholas, 1976;Gross et al, 1978a). Techniques are also available which allow the contamination-free transfer of specimens fractured under liquid nitrogen (Bullivant & Ames, 1966;Sleytr et al, 1981) or liquid helium (Sleytr & Umrath, 1974;Sleytr, 1974) into a vacuum unit for etching and/or replication. It seems important at this point to recall that: (i) if the correct methods are used, specimens freeze-cleaved under liquid nitrogen or liquid helium show the same structural details on fracture faces as specimens cleaved at the same temperatures under improved high vacuum conditions involving either cold shrouds of UHV technology; (ii) only the local vacuum conditions around the specimen (partial pressure of condensable gases) are important; it is not necessary to seek an improvement in the vacuum of the whole system as achieved by using complicated UHV technology; (iii) the formation of a 'disturbing' or resolution-limiting (non-etchable) adsorption layer (Moor, 1973a) is not detectable even when specimens have been freeze-cleaved under liquid helium and transferred under liquid nitrogen into an evaporation unit for replication (Sleytr et al, 1981).…”

A method for adapting the Leybold device for obtaining complementary replicas to the Balzers unit

“…The technical problem of obtaining replicas of complementary fracture planes has been solved in different ways in a number of laboratories. The various methods in use can be divided into two groups: freeze-cleaving is done either under vacuum conditions (Steere & Moseley, 1970;Wehrli, Miihlethaler & Moor, 1970;Sleytr & Umrath, 1974a;Tonosaki & Yamamoto, 1974) or under the surface of a liquid gas such as nitrogen (Chalcroft & Bullivant;Sleytr, 1970a, b) or liquid helium (Sleytr, 1974;Sleytr & Umrath, 1974b).…”