Thickness Fringes of Complicated Profiles in Electron Micrographs of Magnesium Oxide Wedge Crystals

Thickness fringes from single crystals of magnesium oxide were taken at 100 kV, 350 kV and 500 kV. By the use of a tilting stage, the direction of the incident beam was adjusted nearly parallel to the [01̄1] direction where many diffracted beams were excited and the complicated thickness fringes were produced. Their profiles and spacings were studied systematically. It was proved that the profiles become more complicated at higher voltages and that spacings are roughly in agreement with those calculated by using Bethe's second approximation.