Optimum conditions for generating channelling patterns in the scanning electron microscope

The optimum conditions are discussed for generating channelling patterns (i.e. orientation dependent lines and bands of contrast) in the scanning electron microscope. From considerations of the electron optics it is shown that patterns of highest angular resolution may be obtained by establishing a compromise between a small divergence in a collimated beam and a high beam current at the specimen surface. It is also shown that surface detail finer than 50 μm may be resolved and superimposed on channelling patterns with only small loss in pattern resolution. Finally, a technique is presented for obtaining selected area channelling patterns from areas smaller than 100 μm across.