Momentum-resolved bremsstrahlung spectroscopy with a tunable photon detector

The first momentum-resolved bremsstrahlung (or inverse photoemission) experiments using a tunable light detector in the energy range from 10 to 40 eV are reported. The experimental setup comprises a Pierce-type electron gun, a Seya monochromator, and a position-sensitive channel plate detector. An energy resolution of 0.3 eV at 20 eV has been achieved and the momentum resolution is 0.1 Å-1 The apparatus has been used to determine the energy band dispersion of unoccupied minority spin 3d states in Co. A ferromagnetic exchange splitting of 0.93 ±0.1 eV between the unoccupied spin-down and occupied spin-up states (measured with photoemission) is derived. Another application is the measurement of unoccupied adsorbate levels of CO on Ni( 111). Detecting the polarization of the photons (using the polarization-dependent reflectivity of the monochromator) enables us to identify the symmetry character of the adsorbate orbitals. For a Si( 111)—(7 × 7) surface, empty surface states are found in the band gap. © 1983, American Vacuum Society. All rights reserved.