Association

106 5. Results II: EuO integration directly on silicon
Figure 5.17.: Hydrogen termination of the clean Si (001) surface as observed by RHEED (blue), LEED
(green), and simulated by LeedPat 224 and SSD 226 . The flashed Si (001) surface (a) shows diffraction
pattern of the bulk and the (2x1) surface reconstruction dimers as indicated orange.
These cleaned Si substrates show a (2 × 1) reconstruction dimers aligned along the [100] as
well as [010] axes of the Si (001) single-crystal, as observed in Fig. 5.17a. After applying the
in situ hydrogen passivation procedure, the surface reconstruction completely vanishes and
only the (1 × 1) bulk structure of Si is observed by electron diffraction (Fig. 5.17b). Remarkably,
the RHEED and LEED spots of the passivated H-Si (001) surface are equally sharp as for
the freshly flashed Si surface, and no polycrystalline fraction is emergent. The latter would
be indicated by diffuse circular intensities in LEED. A chemical characterization by Auger
electron spectroscopy of the H-Si surface in comparison with other surface treatments can be
found in the appendix (Ch. A.2).
Structural optimization of EuO and the EuO/Si interface
With a chemically clean and structurally crystalline H-passivated Si (001) surface at hand,
we proceed to the synthesis of EuO on top of H-Si and as a reference on clean Si (001).
We recorded electron diffraction pattern during EuO deposition (RHEED) and after EuO
growth has finished (LEED), as compiled in Fig. 5.18. For bare Si (001), the clean and singlecrystalline
surface allows for an initial heteroepitaxial growth of EuO, as indicated by streaks
in the RHEED pattern (Fig. 5.18a). The EuO diffraction pattern, however, develops vertically
aligned spots and a diffuse background from non-crystalline scattering already after
2 nm growth. Finally, after 7 nm EuO synthesis, the crystalline pattern are largely replaced
by circular intensities as expected for a polycrystalline film. No LEED is observed after
EuO growth. High-resolution transmission electron microscopy (HR-TEM) provides a crosssectional
view of the EuO/Si heterostructure in the nanometer regime. In Fig. 5.18b, the
Si substrate shows a perfect diamond structure, but in the 10 nm-thick EuO slab, a polycrystalline
EuO layer of 3 nm thickness is identified in contact with the Si surface. Above
this intermediate layer, crystalline EuO is observed. However, bulges of lateral dimension
However, we remark that such a clean hydrogen passivation needs weeks of bake out of the H 2 supply lines
and a cryo trap system for residual vapors such as oxygen or organics. The H 2 cracker itself must be properly
cleaned and degased, too.