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MICROSCOPY, SCANNING TUNNELING
Electron microscopy in which a very sharp conducting needle is swept just a little angstroms above the surface of a sample. The tiny tunneling current that flows between the sample and the needletip is measured and from this are produced three-dimensional topographs, with a lateralresolution often as good as 1-2 angstroms and a verticalresolution of smaller than 1 angstrom. Due to their composition, biological samples are generally coated with a conductive layer, e.g., by depositing a thinmetal or carbon movie on top of the sample, to enhance their conductivity.