Developments in the measurement of spectral momentum densities with (e,2e) spectrometers

The introduction of multiparameter high energy electron momentum spectroscopy (EMS) spectrometers, with high energy and momentum resolution and coincidence count rates, has made it possible to obtain detailed information on the electronic structure of condensed matter and surfaces. In particular it gives direct information on the spectral-momentum density of the material under study, which may be a single crystal, polycrystalline, or amorphous. The first such spectrometer, the Flinders University spectrometer, uses asymmetric kinematics in the measurement of the energies and momenta of the two outgoing electrons in the (e,2e) collision. The new ANU spectrometer uses symmetric kinematics and much higher energies. It is therefore less affected by deleterious multiple-scattering events. On the other hand the Flinders spectrometer is surface sensitive, whereas the ANU spectrometer is more bulk sensitive. Some aspects of EMS measurements of condensed-matter specimens and the performance of the two spectrometers are discussed.