CONDENSED MATTER ELECTRON MOMENTUM SPECTROMETER WITH PARALLEL DETECTION IN ENERGY AND MOMENTUM

An electron momentum spectrometer has been constructed which measures electron binding energies and momenta by fully determining the kinemat ics of the incident, scattered, and ejected electrons resulting from ( e,2e) ionizing collisions in a thin solid foil. The spectrometer opera tes with incident beam energies of 20-30 keV in an asymmetric, non-cop lanar scattering geometry. Bethe ridge kinematics are used which for 2 0 keV incident energy has scattered electron energies of 18.8 keV at a polar angle of theta(s) = 14-degrees and azimuthal angles phi(s) in t he range from -18-degrees to +18-degrees and ejected electrons of 1.2 keV and theta(e) = 76-degrees with phi(e) = pi +/- 6-degrees. The tech nique uses transmission through the target foil, but it is most sensit ive to the surface from which the 1.2 keV electrons emerge, to a depth of about 2 nm. Scattered and ejected electron energies and azimuthal angles are detected in parallel using position sensitive detection, yi elding true coincidence count rates of 6 Hz from a 5.5 nm thick evapor ated carbon target and an incident beam current of around 100 nA. The energy resolution is approximately 1.3 eV and momentum resolution appr oximately 0. 15 a0(-1). The energy resolution could readily be improve d by monochromating the incident electron beam.