The Morphology of Thin Metal Coatings Formed by Rotary Shadowing Biological Species in High Vacuum

Rotary Shadowing has been used to increase the image contrast of biological species observed during edge-projection imaging in the transmission electron microscope. In this imaging mode, biological species are adsorbed from aqueous solutions onto a highly curved substrate and viewed, over its edge, in a direction parallel to its surface. Since the substrate is not placed between a biological adsorbate and the photographic emulsion that records its image, any material can be used as a support (including high-Z metals and semiconductors). Binding to these technologically interesting materials is observed with unusual clarity and contrast, even at 200kV. Individual adsorbates and multilayer structures are clearly delineated by a thin, metal shadow layer that surrounds them. As expected, gold and platinum form rough, discontinuous and coarse grained layers, while tungsten layers are smooth, continuous and fine grained on a subnanometer scale. Edge-projection imaging, in conjunction with rotary shadowing, is providing a unique view of shadow layer morphology, and the first images of protein molecules, virus particles, and multilayers formed by the immune reaction.