Mean and Anomalous Absorption Coefficients of Electrons for Magnesium Oxide Single Crystal

Intensity profiles of electron microscopic images formed by elastically scattered electrons were analyzed for three different diffraction conditions: (1) The incident beam is parallel to the (100)-plane, (2) No Bragg reflection is excited and (3) (200) Bragg reflection is at the exact Bragg condition. Accelerating voltages were 50, 75 and 100 kV. Inelastically scattered electrons were eliminated by Ichinokawa's magnetic velocity analyzer. The absorption coefficients were determined by comparison of the observed intensity profiles with those calculated by the formulae of h00-six-beam approximation. The result showed that the mean absorption coefficient is µ0=1.5×103Å-1, and the anomalous absorption coefficient is µ200=0.24×10-3Å-1 at 100 kV. Both of µ0 -1 and µ200 -1 were approximately proportional to the square of the electron velocity. Intensity profiles of ordinary images are explained by basis on the results for elastically scattered electrons.