A dynamical theory for the contrast of perfect and imperfect crystals in the scanning electron microscope using backscattered electrons

The defect evolution in shock loaded tantalum single crystals

“…It can be seen from Figure 3.1 that the BSE intensity is lower at the Bragg condition compared with w > 0, when neither of the Bloch waves is channelled. The width of the dislocation image is around 2 times the extinction distance, which is in good agreement with previous simulation results [48] [57] [58].…”

“…As shown in Figure 3.1, in the 0 rocking curve 0 of the electron intensity against incident angle, the intensity drops rapidly near the Bragg condition and gradually increases with deviation from the Bragg condition. In 1972, Spencer developed a full description of the dynamic theory on the channelling contrast image of a crystal containing defects, predicting the visibility of dislocations in the backscattered electron image [48]. However, at that time the resolution of SEM was not high enough to see those dislocations.…”

“…The background intensity is I B (0) without the term related to the sum of the Bloch waves, i.e. p 0 t 1+p 0 t [48]. The backscattering coe cients p 0 is a function of the Fourier coe cient C (i) g and hence is related to the deviation parameter w. From the electron-material interaction point of view, for an incident direction close to the Bragg condition, the electron wave (1) is close to the 0 channel 0 between the crystal planes and therefore it is backscattered less.…”

“…Electron channelling contrast imaging in SEM has been used as a characterisation method for dislocations for over twenty years. However, it received less attention than TEM since the resolution is not as high [42] [48]. The limited applications of ECCI have mostly been performed on relatively light materials like Ni, Al, Fe, semi-conductors, etc [49] [50] [51].…”

“…A method for calculating the Bloch wave function [64], backscattered electron intensity [48] in a crystal with dislocation and the column approximation [64] is introduced.…”