Stem microanalysis by transmission electron energy loss spectroscopy in crystals

The interpretation of microdiffraction patterns from crystals formed with a coherent electron probe which is "smaller" than the crystal unit cell is discussed, with particular reference to the problem of extracting atomic number information. Some characteristic features of the elastic microdiffraction pattern are demonstrated which allow heavy and light atom sites in the crystal to be distinguished. The formation of a STEM lattice image is also discussed. The theory of energy-filtered microdifraction patterns from localized core-loss excitations in crystal is outlined and the characteristic features of these discussed. The form of energy-filtered characteristic loss STEM lattice images is discussed, and the effects of partial localization on these images described. Experimental microdiffraction patterns and energy loss spectra collected at symmetry points within a single unit cell of a barium alumina specimen are used, together with the results of dynamical calculations, to discuss the interpretation and usefulness of filtered microdiffraction patterns and lattice images.