Methodologies for the preparation of soft materials using cryoFIB SEM

Abstract

The recent advent of focused ion beam (FIB) technology in combination with the more familiar scanning electron microscope (SEM) is bringing new insights to the characterization of a range of bulk materials. Furthermore, the FIB SEM can be augmented by a cryo-preparation/transfer system, enabling both frozen and frozen-hydrated soft materials to be FIB-milled at low temperature. This provides an opportunity to perform in situ site-specific crosssectioning, and hence study the interior of a bulk material in two and three dimensions, and serves as an alternative to the freeze-fracturing techniques associated with conventional cryo-SEM. For soft materials in particular, the quality of FIB SEM results is dependent on correct preparation of the specimen's top surface, which is rather challenging for specimens at low temperature. We therefore demonstrate methods for 'cold deposition' of a protective, planarising surface layer on a cryo-prepared sample, enabling high-quality cross-sectioning and investigation of structures at the nano-scale.