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4 1. Introduction
EuO heterostructures by means of their crystalline structure and averaged magnetic properties,
and correlate these with the local intra-atomic exchange properties, as determined by
the MCD effect in hard X-ray photoemission spectroscopy.
In the second part of this thesis, we investigate ultrathin EuO films directly on silicon, with
the goal to establish spin-functional EuO tunnel barriers for application in spin filter contacts
to silicon. Establishing high-quality interfaces between the magnetic oxide EuO to Si is
by no means trivial, as we discuss in Chapter 5. Ferromagnetic tunnel junctions with additional
oxide barriers to avoid diffusion are known, 24–27 however, this approach increases the
thickness of the tunnel barrier significantly. Therefore, our objective is a seamless integration
of EuO directly with silicon, with focus on realizing a chemically clean and structurally
sharp functional interface. First, we synthesize EuO directly on HF-cleaned Si as a prototype
for an integration of EuO directly on Si. In order to engineer structurally sharp and
chemically clean EuO/Si interfaces, we conduct a comprehensive thermodynamic analysis
of possible reactions of the three-constituent system Eu–O 2 –Si at the functional interface,
and conduct three in situ passivation techniques for the Si (001) surface. Remarkably, these
chemical surface passivations allow for a heteroepitaxial integration of subsequent EuO layers.
We quantify the residual chemical interface reaction products of the passivated EuO/Si
interface by HAXPES. Finally, we correlate the optimized chemical interface properties with
the crystalline structure and magnetic properties of the ultrathin EuO layer.
We conclude our research on the fundamental properties of ultrathin EuO films and on the
integration of EuO tunnel contacts directly with Si (001) in Chapter 6.