On a Nature of Cathodoluminescence Contrast of Fine-Dispersed Structures in the Scanning Electron Microscope

Fine-dispersed structures (FDS) consisting of a large number of microcrystalline or amorphous particles of different sizes and shapes were examined in cathodoluminescence (CL) mode scanning electron microscopy (SEM). Line dimension of each particle (about 10 - 100 μm) was larger than the electron beam diameter as well as electron scattering volume in material under investigation. An analysis of observed images showed the existence of some peculiarities in contrast which have not been observed in the CL-images for solid specimens. The FDS CL-image topographic contrast arises as a result of detection of CL-emission from an aggregate of FDS-elements surrounding an irradiated particle because of the bombardment of the elements by secondary electrons. A model was created for the quantitative description of the secondary electron scattering processes. The model takes into account random distribution of microcrystals in FDS-volume, secondary electron emission, elastic and inelastic electron scattering, elastic and inelastic CL-emission photon scattering, and CL-collector angle aperture. A computer model of the processes described above was made by the Monte-Carlo method to reveal a physical mechanism of FDS CL-image contrast formation. This allowed the calculation of a portion of topographic contrast of FDS CL-images and the dependence of that contrast on depth of a particle position in FDS-volume and on the incident angle of the electron beam on a particle surface. Comparison of the above results with real FDS CL-images shows a good agreement between the theoretical calculations and the experiments