SECONDARY-ELECTRON COINCIDENCE DETECTION AND TIME-OF-FLIGHT SPECTROSCOPY

Secondary electrons (SE) have been detected in coincidence with differ ent energy-selected, primary loss events in the HB501 STEM, Results ar e presented for a number of materials - amorphous carbon, diamond, sil icon 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 degre es 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 o f flight data are readily available from the coincidence spectra. Usin g computations for SE trajectories in the objective lens field, this i nformation can be used to derive SE energy spectra. The interpretation of these experiments is discussed.