Association

68 4. Results I: Single-crystalline epitaxial EuO thin films on cubic oxides
Table 4.2.: Parameters set for creation of conductive YSZ by e-beam treatment.
substrate surface pre-annealing e − treatment post-annealing possible techniques
YSZ (9%) 2 h in vacuo at 600 ◦ C 3 h e-beam with U = 3 h in vacuo at RHEED, LEED, XPS,
+1× 10 −7 mbar O 2 1000 eV, I em = 10–20 mA T S = 700 ◦ C HAXPES, TEM, SEM,. . .
of a EuO thin film on cYSZ are observed. As zirconia substrates supply ionic oxygen through
lattice diffusion in the first five monolayers of EuO growth, 16 the time period of one monolayer
EuO is shorter in this initial phase. For cYSZ, however, every second oscillation in the
initial stage of EuO growth shows a reduced intensity which we ascribe to the significantly
reduced oxygen supply of the cYSZ underlayer. Moreover, if EuO is grown well below the stoichiometric
limit in the Eu distillation condition, the RHEED oscillations are equidistant and
homogeneously damped in time. If, however, the EuO growth is at the stoichiometric limit,
the time period for one monolayer EuO is 36% shorter and the intensity of some oscillations
is sensitive to manual re-adjustments of the Eu flux rate.
We conclude, that EuO can be synthesized on cYSZ (100) with comparable crystal quality as
for insulating YSZ (100). This renders EuO/cYSZ heterostructures accessible to investigations
using high-energy electrons, for example RHEED, TEM, or HAXPES.
4.1.3. Core-level spectra by hard X-ray photoemission spectroscopy of
single-crystalline EuO thin films on cYSZ
After a successful substrate treatment, synthesis of the magnetic oxide, and control of structural
properties, we now proceed with the investigation of the electronic structure of singlecrystalline
EuO thin films. The heterostructures under investigation are Si/EuO/cYSZ (100).
Different thicknesses of the single-crystalline EuO layer are investigated: bulk-like 20 nm
EuO, and 4 nm EuO as typical for a tunnel barrier, and also 1 nm EuO representing a quasi
two-dimensional layer. The magnetic oxide EuO is buried under Si capping, and requires a
probing technique with sufficiently large information depth. HAXPES reveals information
about the entire EuO slab, as depicted Fig. 4.10. In the following, we present a study of
selected core-level peaks of EuO, which are best-suited for analysis in this work.
100x10 3
80
inensity (counts)
60
40
20
Epitaxial stoichiometric EuO / conductive YSZ(001)
hv=5.9 keV, normal emission, dE=0.5 eV, T=63 K
Eu 3p
(doublet)
Eu 3d
(doublet)
O 1s
Zr 3s
Eu 4s
(exchange split)
Zr 3p (doublet)
Y 3p (doublet)
C 1s
Eu 4p (doublet)
Zr 3d (doublet)
Si 2s, Y 3d
Eu 4d (j multiplet)
Si 2p (doublet)
Eu 5s (exchange-split)
Eu 5p (doublet)
Eu 4f (multiplet)
(original intensity)
(intensity x2)
0
1700 1600 1500 1400 1300 1200 1100 500 400 300 200 100 0
binding energy (eV)
Figure 4.10.: Hard X-ray photoemission spectroscopy of EuO/cYSZ (100). All accessible core-levels of
EuO, Si, and YSZ are are showing in a survey spectrum.