Scanning Electron Microscopy


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.

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