Three Methods For the Preparation of High-Resolution Freeze-Dried Specimens in a Freeze-Etch Module

The first satisfactory freeze-dry procedure for electron microscopy was described by Williams. An improvement permitted the shadowing of specimens in the same system where freeze-drying was accomplished. Our freeze- etch module is ideal also for the preparation of freeze-dry specimens and high-resolution specimens have been prepared by the 3 different procedures.Procedure #1: A particulate suspension in distilled water or a volatile buffer is sprayed onto a thin mica sheet held down with high vacuum grease to a flat-topped specimen cap clamped onto the specimen stage (all pre-cooled to −150°C). Freeze-drying is accomplished with a vacuum of 2 × 10−6 Torr and specimen temperature of −98 to −75° (approximately 15 min).