ANALYTICAL FILTERING OF LOW-ANGLE INELASTIC-SCATTERING CONTRIBUTIONS TO CBED CONTRAST

A theory which includes the multiple low-angle inelastic scattering contributions to convergent beam electron diffraction contrast is presented. It is based on a slice model where many-beam Bragg scattering may take place in the upper part, z, of the crystal. The inelastic electron scattering takes place in a slice dz at crystal thickness z, and these electrons are then Bragg scattered in the lower part, (t - z), of the crystal. The total intensity is obtained through an integration over thickness and an addition of the separate contributions due to multiple inelastic scattering. Theoretical profiles for the individual plasmon scattering contributions to the intensity have been calculated across the (220) CBED disk in Si for the systematic (220) case. The theoretical calculations are compared to the corresponding experimental intensities obtained by an energy filtering system. The experimental results are semi-quantitatively in good agreement with the calculations. The main features after elastic as well as after one to four times plasmon scattering are well reproduced by the theory.