Association

3.4. Ex situ characterization techniques 49
highly brilliant synchrotron light sources are available (e. g. PETRA III), the reduced photoemission
cross-sections can be compensated by high-intensity hard X-ray radiation: photoemission
spectra with a wide range of electron kinetic energies are thus available (example
in Fig. 3.13). This, in turn, fulfills the key prerequisite for depth profiling of the electronic
properties in multilayer structures including buried layers and interfaces, by analyzing photoelectrons
of largely different kinetic energies.
The HAXPES experiment at KMC1 beamline in the BESSY II storage ring
Figure 3.14.: The HIKE endstation (a) is located at the KMC1 dipole magnet beamline (b) at the
BESSY II storage ring in Berlin.
Since 1994, the third generation synchrotron light source of the Helmholtz-Zentrum Berlin
(Germany) provides access to a variety of experiments employing highly brillant X-ray light.
Electrons are accelerated up to an energy of 1.7 GeV and are injected into the storage ring
BESSY II. A variety of X-ray sources (undulator, wiggler and dipole magnet sources) with
high energy resolution are in operation.
The KMC-1 beamline disperses light from a dipole light source, and is coupled to the HIKE
endstation with a SCIENTA R4000 electron spectrometer. Spectroscopy experiments can be
conducted with a high energy resolution and an excitation energy up to 12 keV. A two-crystal
Si monochromator provides mono-energetic light, achieving an overall energy resolution of
200 meV. Very high resolution is achieved around 2, 6 and 8 keV photon excitation energy
due to an optimal Bragg reflection of the monochromator crystals. The instrumental resolution
of the spectrometer can be better than 40 meV at 6 keV (Gorgoi et al. (2009)). 98 As
depicted in Fig. 3.14a, the R4000 analyzer is positioned at an angle of 90 ◦ with respect to
the incoming X-ray light. Thus, the excitation is at grazing incidence which lets the photo-