Secondary electron coincidence detection and time of flight spectroscopy

Abstract

Secondary electrons (SE) have been detected in coincidence with different energy-selected, primary loss events in the HB501 STEM. Results are presented for a number of materials - amorphous carbon, diamond, silicon carbide and magnesium oxide. In most cases transmission geometry was employed so that surface excitations, bulk valence excitations and core excitations are all involved and produce SE with different degrees of efficiency. Aloof beam experiments carried out on diamond and on magnesium oxide smoke cubes involve only surface valence excitations, however, and these produce SE with relatively high efficiency. Time of flight data are readily available from the coincidence spectra. Using computations for SE trajectories in the objective lens field, this information can be used to derive SE energy spectra. The interpretation of these experiments is discussed. © 1993.