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3.2. In situ characterization techniques 41 diffuse background, due to scattering from statistically distributed centers. Since the area on a sample surface in which constructive diffraction occurs is smaller than the coherence width of the electron beam, which amounts to ∼100 Å, a LEED probe is point-like. 79 Thus, LEED probes a microscopic area, while with RHEED one can “scan” the entire surface of the sample. In this work, LEED investigations are used to monitor the surface crystal structure by a qualitative comparison with simulated patterns of the LEEDpat software. 224 In practice, we use a three mesh VG Microtech RVL 640 Rear View LEED system. 3.2.3. Auger electron spectroscopy (AES) Whenever functional heterostructures with the highest chemical quality of interfaces and surfaces are designed, an in situ analysis of the chemical composition and a quantification of surface oxidation or possible carbon contamination is essential. Among the non-destructive and element-selective chemical probing techniques, the Auger electron spectroscopy (AES) is well-established for analyzing the kinetic energy of secondary electrons. For light elements (Z 30), the Auger-Meitner cascade is the dominant emission process, when surface atoms are excited by X-rays or electrons. The external excitation leaves an electron core-hole (A), which is filled by an upper shell electron (B). This recombination energy is characteristic for the particular elemental atom and is used to emit an outer shell electron (C) carrying the characteristic kinetic energy E kin = E A − E B − E C − E vac . The specific Auger processes are named by the participating shells, e. g. KLM for transitions between the s and p orbitals and an emission from the d shell. Figure 3.6.: Cylindrical mirror analyzer for Auger electron spectroscopy. The pass energy E 0 and voltage U p between the two cylinders are related by E 0 = eU p /0.77ln(b/a), with a and b denoting the radii of the inner and the outer cylinders. 79 A cylindrical mirror analyzer (CMA) is used for Auger electron spectroscopy. The Auger electrons are focused from an entrance point into a certain cone by two concentric cylindrical
42 3. Experimental details electrodes onto an image point, where a Channeltron detector is positioned. The electric field determining the pass energy is a radial field between the two concentric electrodes, as schematically shown in Fig. 3.6. For AES, a non-retarding mode is used in which the electrons pass through the analyzer with their initial kinetic energy, and the energy range being swept by varying the potential on the outer cylinder. With this geometry, an energy resolution of 0.6% of the electron kinetic energy can be reached, which is limited by the angular deviation of the incoming electron trajectories (see Lüth (2010)). 79 In this work, AES is employed to routinely check the surface quality by means of chemical cleanliness, and to quantify the thickness of the in situ oxidation of silicon. A VARIAN cylindrical mirror analyzer is used with electrons of E exc = 3 keV from a VARIAN 981 e-gun source. In practice, the energy resolution is ∼1 eV due to the sweep generator. 3.3. Experimental developments at the Oxide-MBE setup Figure 3.7.: Details of the Oxide-MBE setup at PGI-6. (a): Atomic gas supply with robust tungsten filament in a high pressure cracking bulb. (b): Oxygen nozzles which are located 10 mm in front of the sample surface and the mass spectrometer filament. (c): Flashing stage for Si wafer pieces. Right: Oxide-MBE setup at PGI-6 equipped a drive-through fast load lock system (I), a preparation chamber (II), the main deposition chamber (III), and an analysis chamber (IV). The Oxide-MBE setup utilized in the frame of this thesis allows for the deposition of magnetic oxide heterostructures in conjunction with oxides or silicon substrates. Historically, mainly metallic three-layer structures have been fabricated in this system since the 1980s in order to explore novel electronic effects. In particular, in 1988 Fe/Cr/Fe structures showed an “en-
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Member of the Helmholtz Association
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Forschungszentrum Jülich GmbH Pete
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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
Page 56 and 57: 3.2. In situ characterization techn
Page 60 and 61: 3.3. Experimental developments at t
Page 62 and 63: 3.4. Ex situ characterization techn
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
Page 104 and 105: 5.1. Chemical stabilization of bulk
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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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