A chamber attached to the SEM for fracturing and coating frozen biological samples

Abstract

SUMMARY A chamber for introducing, fracturing and coating frozen biological samples has been developed as an attachment to the specimen chamber of a scanning electron microscope. Together with a eucentric‐tilt cold‐stage, this chamber constitutes a complete system for viewing fractured biological surfaces of the type normally only seen by replica techniques. An air‐lock on the chamber accepts a transfer module to allow insertion of the frozen sample without frost build‐up. Fracturing is carried out with a precisely adjustable cooled knife under a 10–100 × binocular microscope. The sample can tilt and rotate while being coated with carbon or metals evaporated from rechargeable sources introduced through the air‐lock. Cooling in the chamber is provided by a cylindrical copper tank filled with liquid nitrogen. The chamber has its own LN 2 trapped high vacuum system. After preparation the sample can be placed directly into the SEM through an isolation valve. The cold‐stage utilizes a Joule‐Thomson refrigerator. The sample can be kept below 103 K at all times though there are provisions for heating it in the fracturing and cold‐stage positions. A system of controls, sensors and interlocks simplifies the operation of the system.