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106 5. Results II: EuO integration directly on silicon (a) Si (001) flashed ► (b) Si (001) in situ hydrogenannealed ► E=9.8 keV, θ=3° E=9.8 keV, θ=3° E=60 eV E=62 eV (2x1) surface (1x1) bulk 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.
5.3. Interface engineering I: Hydrogen passivation of the EuO/Si interface 107 (a) (b) (c) focussed ion beam cut HR-TEM RHEED, E=10 keV micrograph RHEED, E=10 keV Si (001) (1x1) + (2x1) surface flashed Si (001) EuO/Si (001) 2 min EuO/Si (001) 4 min EuO/Si (001) 6 min EuO/Si (001) 8 min EuO/Si (001) 10 min poly poly EuO EuO layer layer Si Si (001) (001) ↑ EuO/Si (001) 12 min cryst. cryst. EuO EuO (fcc) (fcc) EuO EuO defect defect EuO-Si EuO-Si diffusion diffusion bulge bulge strained EuO (001) / Si (001) EuO/Si (001) 14 min Si (001) (1x1) bulk-like surface strained EuO (001) / Si (001) EuO/Si (001) 16 min evolution of the EuO/Si surface structure Al capping cryst. cryst. EuO EuO (fcc), (fcc), t = 7 nm nm poly poly EuO EuO layer, layer, t ≈ 3 nm nm Si (001) EuO/Si (001) 20 min H-passivated Si (001) EuO/H-Si (001) 2 min EuO/H-Si (001) 4 min EuO/H-Si (001) 6 min EuO/H-Si (001) 8 min (no LEED) LEED EuO/H-Si (001) 10 min EuO/H-Si (001) 12 min EuO/H-Si (001) 14 min EuO/H-Si (001) 18 min EuO/H-Si (001) 20 min EuO/H-Si, 60 eV Al (d) Al capping evolution of the EuO/H-Si surface structure Al FFT: EuO crystalline EuO (fcc) focussed ion beam cut polycrystalline EuO layer HR-TEM micrograph Si (001) ↑ Si 5 nm Figure 5.18.: Surface and interface structure development of EuO on Si (001) and on H-passivated Si (001). RHEED photographs elucidate the EuO surface structure when grown on clean Si (001) (a), the cross-section is depicted by HR-TEM in (b). EuO growth on hydrogen-passivated Si (001) is documented by RHEED and LEED in (c), and the cross-section in real space and selected images of the reciprocal space are depicted in (d).
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Magnetic Oxide Heterostructures: Eu
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Abstract In the thesis at hand, we
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viii Contents 4. Results I: Single-
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x List of Figures 3.18. Photoelectr
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List of Tables 2.1. Photoemission f
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2 1. Introduction Ferromagnetic oxi
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4 1. Introduction EuO heterostructu
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6 2. Theoretical background stoichi
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8 2. Theoretical background mole of
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10 2. Theoretical background 2.2.2.
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12 2. Theoretical background such a
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14 2. Theoretical background Hybrid
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16 2. Theoretical background well.
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18 2. Theoretical background (a) 4
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20 2. Theoretical background the si
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22 2. Theoretical background E F =
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24 2. Theoretical background or eve
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26 2. Theoretical background I. Pho
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28 2. Theoretical background III. T
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30 2. Theoretical background must d
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32 2. Theoretical background (a) re
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34 2. Theoretical background LS-cou
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36 3. Experimental details γ F fil
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38 3. Experimental details pressure
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40 3. Experimental details a very g
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42 3. Experimental details electrod
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44 3. Experimental details Figure 3
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46 3. Experimental details is moved
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48 3. Experimental details coordina
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50 3. Experimental details electron
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52 3. Experimental details hard x-r
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54 3. Experimental details Fig. 3.1
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Page 140 and 141: A. Appendix A.1. Properties of EuO-
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Page 146 and 147: Bibliography [1] G. Binasch, P. Gr
Page 148 and 149: 134 Bibliography [25] A. Schmehl, V
Page 150 and 151: 136 Bibliography [49] M. Arnold and
Page 152 and 153: 138 Bibliography [77] H. Hertz. Üb
Page 154 and 155: 140 Bibliography [103] L. Plucinski
Page 156 and 157: 142 Bibliography [130] W. Braun. Ap
Page 158 and 159: 144 Bibliography [158] K. Kobayashi
Page 160 and 161: 146 Bibliography [184] B. Sinković
Page 162 and 163: 148 Bibliography [211] D. Wandner,
Page 164 and 165: List of own publications [1] Casper
Page 166 and 167: List of conference contributions [1
Page 168 and 169: Acknowledgement . . . These days, i
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Erklärung Hiermit erkläre ich, da
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