Association

5.5. Interface engineering III: SiO x passivation of the EuO/Si interface 119
Figure 5.28.: Consistent peak fit analysis of the SiO x -passivated EuO/Si (001) interface using Si and
Eu core-levels of the HAXPES experiments.
itored by RHEED. Finally, the EuO/Si heterostructures are capped with 5 nm air-protective
Al. In order to investigate the electronic structure at the EuO/Si interface, we conducted
HAXPES studies of the EuO/Si hybrid structures at the undulator beamline P09 at PETRA III
(DESY, Hamburg), 97 and at the KMC-1 dipole beamline at BESSY II (Berlin) with the HIKE
endstation. 98 The Fermi edge of Au foil on the sample serves as calibration for the binding
energy. Tougaard-type backgrounds are used to account for inelastic photoelectron scattering.
Interface-sensitive HAXPES spectra of the EuO/Si heterostructures are depicted in Fig. 5.28a, b.
Stable silicon oxide is observed at chemical shifts of 3.2 and 4.1 eV in the Si 1s spectrum,
which identify Si 3+ (Si 2 O 3 ) and Si 4+ (SiO 2 ), in good agreement with recent PES studies of ultrathin
SiO 2 /Si (001). 139,208 Another component at the EuO/Si interface with a chemical shift
to lower BE is observed in the Si spectra as well as in the Eu3d, 4d, and 4f spectra, which is
identified as a metallic Eu silicide (EuSi y ). Due to the small chemical shift of EuSi y (−0.65 eV
for Si 2p), only the Si spectra and the narrow Eu 4f multiplet allow for a quantitative deconvolution
of the entire silicide fraction silicide components. In case of the complex Eu 3d and
4d multiplets, we can separate only the silicide component of one J final state at the lower
binding energy side. A quantitative thickness determination of the SiO x passivation at the
Si (001) interface and of the resulting silicide reaction layer is accomplished by consistent
least squares peak fitting after Levenberg-Marquard of the HAXPES spectra. The thickness
c of the interfacial passivation (SiO x ) and EuSi y reaction layers are determined from their
relative spectral weight, as derived in equations (3.16) and (3.19) (in Ch. 3.4.4 on p. 51). The
results are compiled in Fig. 5.29. Regarding the chemical reactivity of the EuO/Si interface
we found interfacial silicides to exceed 10 Å thickness for flashed Si (001), however by applying
an ultrathin SiO x interface passivation (d SiOx = 10–13 Å) silicide formation is suppressed