Electron Microscope Study on the Extinction and Absorption of 100 kV Electrons in Magnesium Oxide Single Crystals

Abstract

The intensity profile of equal thickness fringes due to 200 reflection was studied by the photographic method. The orientation of the specimen crystal was systematically changed by use of a tilting stage in the electron microscope. The real part of 200-Fourier coefficient and the imaginary part of the mean inner potential were determined to be V₂₀₀ ^r =7.43±0.11 volt and V₀ ⁱ =0.58±0.04 volt, respectively, provided no simultaneous reflection took place. When the deviation from the exact Bragg position, viz. the Bethe's parameter W, was varied, the behavior of intensity profile was found to be entirely different from that predicted by the two-beam approximation of the dynamical theory assuming the phenomenological complex potential. It was shown that the so-called anomalous transmission in the case of electrons can not be ascribed to the decrease of effective absorption coefficient at the Bragg position.