Downing K H
Donner Laboratory, Lawrence Berkeley Laboratory, Berkeley, California 94720.
Ultramicroscopy. 1988;24(4):387-97. doi: 10.1016/0304-3991(88)90129-5.
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.
当用直径约为1000埃的光束记录单层石蜡晶体的晶格图像时，发现图像部分区域的图像对比度比用传统泛光照明获得的图像对比度至少高三倍。在先前的实验中观察到的这些图像内对比度的变化，现在发现是由光束引起的辐射损伤所致，这种损伤会导致晶格膨胀。光束引起的样品运动的这种残留模式，以及传播到样品相邻未辐照区域的畸变，可以通过多种不同方式检测到。因此，似乎至少在照明区域的一部分上，光束引起的样品运动几乎可以消除。通过适当选择曝光量、束斑直径和曝光点之间的间距，可以将剩余运动模式的有害影响降至最低。
