Observations of restricted beam-induced specimen motion with small-spot illumination.

When lattice images of monolamellar paraffin crystals are recorded with a beam of diameter on the order of 1000 A, image contrast in part of the image is found to be at least three times higher than contrast in images obtained with conventional, flood illumination. Variations in contrast within these images, observed in previous experiments, are now found to be the result of radiation damage caused by the beam, which causes the crystal lattice to expand. This residual mode of beam-induced specimen motion, as well as distortions which propagate to adjacent, unirradiated areas of the specimen, are detected in a number of different ways. It thus appears that beam-induced specimen motion can be virtually eliminated over at least part of the illuminated area. Deleterious effects of the remaining mode of motion can be minimized by appropriate choice of exposure, beam-spot diameter, and spacing between exposed spots.