Diploma - Max Planck Institute for Solid State Research

4.1 Overview – properties and classification 33
Figure 4.7: (a) Atomic cross section of Eu 4f, Rh 4d, Si 3s and Si 3p. A discussion on the
validity of the their usage has been given in ch. 3.1; (b) Wide range overview for Eu 4d-4f
resonance measured at hν = 142 eV with vertical polarization. The pure divalent character of
Eu in EuRh 2 Si 2 is in accordance with Mössbauer experiments in [48] (SLS-SIS, T ≈ 15 K)
4.1.4 Surface and bulk band structure
In general, the PE spectrum of EuRh 2 Si 2 can be regarded in a first approximation as a
superposition of a valence band PE spectrum (states with significant dispersion) and a
spectrum of atomic transitions. The latter can be identified as lines because they do not
reveal an angular / k dependency because the overlap of their atomic-like wavefunctions
from different sites is negligible. Furthermore, we have to deal with the short mean
free inelastic scattering path of the photo electrons (see ch. 3.1), thus it is necessary to
distinguish between electronic states localized at the surface of the compound and states
belonging to the bulk since both have a comparable share in the spectra. Therefore in
the following part the major contribution of specific spectral structures will be discussed
with respect to the studied [001]-surface. To identify surface and bulk states one can
perform theoretical calculations (see bulk, projected bulk and surface configuration in
ch. 4.1.1) to compare the band structure to the PE spectrum. The calculations for
the itinerant states were performed mainly with FPLO whereat the atomic transitions
for the localized 4f states were taken from configuration interaction based calculations
in [49]. Experimentally it would be possible to verify the origin of a state by surface
deposition of a noble metal, e.g. Ag (a surface state changes in binding energy whereat
a bulk state does not vary severely), or by adjusting the energy of the photons probing
different layers k x × k y since the incident photon energy determines k z . This is just
an indication because also bulk states can have a small or negligible k z -dispersion.
Both have not been performed, because the atomic cross section in the range of the
available photon energies already varies strongly. Hence PE on EuRh 2 Si 2 is sensitive
to valence states (mainly Rh 4d) for hν = [40 − 55] eV whereas for hν = [120 − 140] eV