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

The introduction of multiparameter high energy electron momentum spectrosco py (EMS) spectrometers, with high energy and momentum resolution and coinci dence count rates, has made it possible to obtain detailed information on t he electronic structure of condensed matter and surfaces. In particular it gives direct information on the spectral-momentum density of the material u nder study, which may be a single crystal, polycrystalline, or amorphous. T he first such spectrometer, the Flinders University spectrometer, uses asym metric 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 affecte d by deleterious multiple-scattering events. On the other hand the Flinders spectrometer is surface sensitive, whereas the ANU spectrometer is more bu lk sensitive. Some aspects of EMS measurements of condensed-matter specimen s and the performance of the two spectrometers are discussed. (C) 2000 Else vier Science B.V. All rights reserved.