Extra Spots in Electron Diffraction Patterns

Abstract

MANY photographs have recently been published showing extra spots in X-ray diffraction patterns from single crystals. These extra diffractions are ascribed to thermal vibrations of the atoms or molecules in the crystal ; they are close to the normal Laue-spot positions and comparable in size with the Laue spots. The close parallelism between the electron and X-ray diffraction phenomena leads us to expect that diffractions of this kind should also occur in electron-diffraction patterns, but although we observed1 much more diffuse maxima two years before the work of Preston2 directed attention to the X-ray extra spots, no extra spots of the X-ray type have hitherto been observed in electron diffraction, nor has the diffuse electron type been observed in X-ray patterns. It therefore appeared desirable to discover whether this distinction was of fundamental importance, or simply due to the difference in experimental conditions so far adopted. The absence of the diffuse electron type of maxima in X-ray patterns is apparently due to the experimental conditions3, but we were unable to explain the lack of such extra spots in electron diffraction.