Phase contrast electron microscopy of amorphous specimens supported on thin crystals

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Abstract
Significant enhancement can be obtained for electron microscope image contrast of amorphous specimens if the specimens are supported on thin crystals and viewed in the vicinity of bend contours in the crystal support. The enhanced contrast is due to the ability of the crystal support to attenuate the unscattered electron waves and to shift the phase either of the unscattered electron waves or of the electron waves scattered from the specimen. The crystal support contrast effects are significant if the specimen scatters electron waves appreciably through angles in excess of (gξg)−1, which is 1 mradian for 110 bend contours in graphite crystals. Experimental results are presented for amorphous carbon disks about 500 Å in diameter supported on graphite crystals 400 and 1200 Å thick. Both dark-field type contrast and shadow contrast are observed. With shadow contrast, strong highlights or shadows are observed at the edges of the amorphous carbon disks.