Electron channelling: a method in real-space crystallography and a comparison with the atomic location by channelling-enhanced microanalysis

A method is described to show how electron channelling can successfully be applied to the determination of substitutional and interstitial lattice sites of atoms in crystals. The experiments are performed in a conventional transmission electron microscope equipped with an X-ray detector. The method includes the detailed measurement of channelling profiles as well as calculations of these profiles. A fitting procedure allows us to determine the location of specific atoms within the elementary cell. It is found that a good fit is obtained only if the interference of Bloch waves, the X-ray production by inelastically scattered electrons, the delocalization of the inner-shell ionization event, and the crystal thickness and shape are considered in the calculation. The applicability of the method is demonstrated by applying it to known crystal structures (Mo and GaAs). Its relation to atomic location by channelling-enhanced microanalysis (ALCHEMI) and the problems of ALCHEMI are discussed. A comparison with channelling with positively charged particles is given. (author)