Dark-Field Electron Microscopy. I. Studies of Crystalline Substances in Dark-Field

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Abstract
Dark‐field images in the electron microscope were studied by means of an objective aperture system fixed to the object rather than to the objective lens. The resolution in images produced by the diffusely scattered component is in the range 100 to 200A, but the resolution in images produced by Bragg reflections approaches that obtainable in bright‐field operation. A resolution of about 50A was obtained with test objects consisting of evaporated films containing small crystallites, but it is estimated that crystallites having dimensions down to about 20A can be recorded with conditions prevailing in this work. Substances studied in dark‐field include evaporated films of metals and compounds and finely divided substances. It is concluded that the dark‐field method is of value for studying the size, location, and other characteristics of crystalline components in a specimen. Some of the theoretical factors influencing resolution in dark‐field are discussed.