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3.2. In situ characterization techniques 39 reciprocal rods RHEED screen l pattern part of the Ewald sphere incident e − beam sample beam Figure 3.3.: RHEED working principle. parameter (k =2π/d, for cubic lattices), the intersection between both is not very sharp and the diffraction condition k − k 0 = G ‖ (hkl) (3.4) is fulfilled over a range of vertical angles θ. This leads to streaks instead of points on the fluorescence screen. Based on the Bragg equation nλ =2d sinφ, the in-plane cubic lattice parameter d can easily be extracted from the distance l between two reciprocal streaks, 129 d =2λ· L l L: distance sample–screen l: distance between neighboring rods, with λ = λ e− deBroglie = hc √ Ekin (2E0 e− + E kin) E kin =10 keV = 0.12 Å. If the sample surface is flat on an atomic scale, the diffraction pattern consists of well-defined parallel lines. If the surface structure is three-dimensional due to island growth, these parallel lines shorten to elongated dots, and many orders of these dots are observable. If, however, an extremely flat and ideal surface is probed (e. g. flashed Si under best UHV condition) and Figure 3.4.: Illustration of layer-by-layer growth observed by high-energy electron diffraction (RHEED). A maximum reflection of the specular RHEED spot occurs for an atomically flat surface (i), whereas the intensity is damped when deposition has reached half a monolayer (ii). Once the deposition of a monolayer is completed (iii), the maximum reflection is observed again. 223
40 3. Experimental details a very good electron focusing is achieved, one can observe very sharp diffraction spots of only one order rather than elongated rods. Some inelastically scattered electrons penetrate the bulk crystal and can be detected besides the surface diffraction pattern. If they fulfill Bragg diffraction conditions in the bulk, they are observed as diagonal Kikuchi pattern connecting the intense surface diffraction points. 130 If there is no pattern at all or if it consists of concentric circles, the surface is not well ordered or even polycrystalline. Recording RHEED intensity oscillations of the specular reflex with time allows one to quantify the number of monolayers grown in MBE, if the Van-der-Merve growth mode is predominant, as illustrated in Fig. 3.4. The Oxide-MBE system at PGI-6 is equipped with a self-constructed RHEED system having a VARIAN 981 e-gun source in the main deposition chamber. 3.2.2. Low-energy electron diffraction (LEED) camera LEED window screen incident beam Ewald sphere sample reciprocal rods electron gun spots 4-grid LEED optics Figure 3.5.: LEED working principle. Low-energy electrons with energies from about 20 to 500 eV are ideal probes for surface studies, because they are mainly elastically scattered by atoms. According to the de Broglie relation, λ = √ 150.4/E0 e− ([λ] = Å, [E] = eV), typical LEED wavelengths are of the same magnitude as interatomic distances in crystals and comparable with that used in X-ray diffraction (see Sec. 3.4.2). The Ewald sphere intersects only the lattice rods at particular points that fulfill the Laue diffraction condition eq. (3.4), and the resulting LEED pattern consists of an ordered arrangement of spots. All surface diffraction patterns show a symmetry reflecting that of the crystal class and are centrally symmetric. The scale of the diffraction pattern depends on the electron energy and the size of the surface unit cell as √ 2π 2mE d ∝ 2 −|G ‖ | 2 , (3.5) where d is the real space lattice parameter, and G ‖ a reciprocal lattice vector in the surface plane. 79,131 In the experimental work, a LEED image shall exhibit a sharp pattern and low background intensity. Defects and crystallographic imperfections will broaden spots and increase the
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Member of the Helmholtz Association
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Forschungszentrum Jülich GmbH Pete
Page 6: Zusammenfassung In dieser Doktorarb
Page 10 and 11: Contents 1. Introduction 1 2. Theor
Page 12 and 13: List of Figures 2.1. Phase diagram
Page 14: List of Figures xi 5.12. Resulting
Page 18 and 19: 1. Introduction Smart and powerful
Page 20 and 21: 3 In the thesis at ha
Page 22 and 23: 2. Theoretical background . . . The
Page 24 and 25: 2.1. The challenge of stabilizing s
Page 26 and 27: 2.2. Electronic structure of EuO 9
Page 28 and 29: 2.3. Magnetic properties of EuO 11
Page 36 and 37: 2.4. Hard X-ray photoemission spect
Page 46 and 47: 2.5. Magnetic circular dichroism in
Page 52 and 53: 3. Experimental details Die Pläne
Page 54 and 55: 3.1. Molecular beam epitaxy for oxi
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Page 60 and 61: 3.3. Experimental developments at t
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Page 74 and 75: 4. Results I: Single-crystalline ep
Page 76 and 77: 59 Table 4.1.: Parameters for stoic
Page 78 and 79: 4.1. Coherent growth: EuO on YSZ (1
Page 92 and 93: 4.2. Lateral tensile strain: EuO on
Page 94 and 95: 4.2. Lateral tensile strain: EuO on
Page 96 and 97: 4.3. Lateral compressive strain: Eu
Page 102 and 103: 5. Results II: The integration of t
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5.1. Chemical stabilization of bulk
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5.2. Thermodynamic analysis of the
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5.3. Interface engineering I: Hydro
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5.4. Interface engineering II: Eu p
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5.5. Interface engineering III: SiO
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5.5. Interface engineering III: SiO
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5.6. Summary 121
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6. Conclusion and Outlook In the th
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125 Outlook and perspectives In the
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A.1. EuO-related phases and cubic o
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A.1. EuO-related phases and cubic o
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A.2. In situ analysis of the Si (00
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Bibliography 133 [13] S. S. P. Park
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Bibliography 135 [36] R. E. Dickers
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Bibliography 137 [65] R. Sutarto, S
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Bibliography 139 [91] P. Braun, M.
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Bibliography 141 [116] S. Hüfner.
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Bibliography 143 [144] R. Feder and
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Bibliography 145 [171] H. Miyazaki,
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Bibliography 147 [197] J. Qi, T. Ma
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Software and Internet Resources [21
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List of own publications 151 [10] R
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List of conference contributions 15
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Schriften des Forschungszentrums J
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Schlüsseltechnologien / Key Techno
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