Preparation of Geological and Biological TEM Specimens by Embedding in Sulfur

Abstract

Abstract The technique of embedding TEM specimens in polymer resins for subsequent ultra-thin sectioning is well established. For geological materials, this protocol prevents specimen damage introduced by ion beam thinning, and is often used for preparing friable or porous materials. However, traditional polymer-based embedding resins may introduce organic carbon contaminants, producing artifacts in carbon analyses. Thus, a carbon-free substitute for traditional embedding media is required to ensure accurate carbon analyses of embedded and ultramicrotomed TEM specimens. A suitable technique that was first reported by Bradley is to embed specimens in pure sultur. In this technique, the specimen is immersed in liquid sulfur, the liquid is solidified, and the resulting block is ultramicrotomed as with traditional resins. Since sulfur has a high vapor pressure at room temperature, the ultra-thin sections are then placed in a separate vacuum chamber to sublimate the sulfur, yielding TEM specimens free of any embedding medium.