The PEEM can not only be used to display magnified images of the sample
surface. When the projection lenses are set to display the focal plane of the
objective lens, the angular distribution of the emitted electrons is obtained.
In connection with the imaging energy filter this can be used to display
two-dimensional photoelectron angular distribution patterns on the screen of
the PEEM. In this way spatial, angular, and energy resolution can be obtained
simultaneously within the same instrument.
The figures show such angular distribution patterns of photoelectrons from the
Fermi energy of a Cu(001) single crystal surface. Different photon energies
(Fig. (a): 95 eV, (b): 122 eV) yield different cuts through the three
dimensional Fermi surface of Cu (pink = high, red = low intensity). The
complete three-dimensional Fermi surface can be obtained rather quickly by
acquiring a series of such images for different photon energies. A slice
through a data-set of 59 images is shown in Fig. (c). The well-known
"dog-bone" shape of the Cu Fermi surface is clearly seen. |
