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5.3. Interface engineering I: Hydrogen passivation of the EuO/Si interface 109 110 100 90 80 70 60 50 102 101 100 99 98 97 T S = 350 °C, Si T S = 450 °C, Si 20 T S = 350 °C pure Si 0.65 nm silicide T S = 450 °C pure Si 0.30 nm silicide 50 9.7% EuSi y T S = 350 °C, H-Si T S = 450 °C, H-Si 10 0 50 25 T S = 350 °C H-Si 0.56 nm silicide 4.4% EuSi y T S = 450 °C H-Si 0.14 nm silicide 25 0 60 30 0 0 96.5 102.5 100.5 98.5 100.5 98.5 96.5 102.5 Figure 5.19.: The EuO/H-Si interface analyzed by least-squares peak fitting of the Si 2p core-levels. the epitaxial growth mode of thin EuO films on Si, while at higher T S heteroepitaxy of EuO directly on Si (001) is generally possible. A chemical insight into the buried EuO/Si (001) heterointerface is obtained by a HAXPES analysis of the Si orbitals from the interface. We select an interface-sensitive geometry by tuning the excitation energy to a minimum of 2.3 keV together with off-normal emission. The recorded Si 2p peaks are shown in Fig. 5.19c–d for the different interface treatments. With a chemical shift of −0.6 eV, the silicide component can be clearly identified on the low binding energy side of the bulk Si doublet peak. The silicide fraction shows a clear development: an increase of substrate temperature as well as the hydrogen passivation of Si reduce the silicide thickness. In order to quantify the silicide reaction at the EuO/Si interface for every set of passivation parameters, we conduct a peak fitting analysis based on the least squares method. The resulting thicknesses of the buried interfacial silicide layer are summarized in Fig. 5.20. Comparing the diminishments of the interfacial silicide, the impact of synthesis temperature from 350 ◦ C to an optimum of 450 ◦ C on the EuO/Si interface reaction is larger (−38% silicide) than the application of hydrogen termination (−14% silicide) to the clean Si surface. The advantage of a higher synthesis temperature can be understood from a thermodynamic analysis of EuSi 2 (Ch. 5.2): this silicide favors a disappearance reaction during EuO distillation growth (Fig. 5.10) yielding EuO and Eu. Any excess Eu, however, is readily re-evaporated at higher T S , thus minimizing the available constituents for silicide formation. The advantage of a hydrogen passivation, although smaller than for the temperature variation, is explained by its larger thermodynamic stability compared to the silicide (Fig. 5.8). In conclusion, the parameters for a minimized interfacial silicide formation (d min (EuSi 2 ) = 0.14 nm) are the ap-
110 5. Results II: EuO integration directly on silicon Figure 5.20.: Quantitative results of the EuO/H-Si silicide analysis by HAXPES. plication of a higher synthesis temperature (450 ◦ C) and a complete hydrogen passivation of Si (001). The thin film magnetic properties were investigated by SQUID magnetometry. Three magnetization curves are depicted in Fig. 5.21a, which originate from polycrystalline bulk-like EuO on Si (001) with a native oxide SiO 2 layer at the interface, and two ultrathin EuO layers (∼2 nm) on in situ hydrogen-passivated Si (001), which exhibited epitaxial growth. Coinciding with the HAXPES results, the dominating effect of the temperature of synthesis on the silicide formation is observed in the ferromagnetic properties of the EuO/Si heterostruc- Figure 5.21.: Magnetic properties of EuO on Si, dependent on synthesis temperature and H- passivation.
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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
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Contents 1. Introduction 1 2. Theor
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List of Figures 2.1. Phase diagram
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List of Figures xi 5.12. Resulting
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1. Introduction Smart and powerful
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3 In the thesis at ha
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2. Theoretical background . . . The
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2.1. The challenge of stabilizing s
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2.2. Electronic structure of EuO 9
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2.3. Magnetic properties of EuO 11
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2.4. Hard X-ray photoemission spect
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2.5. Magnetic circular dichroism in
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3. Experimental details Die Pläne
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3.1. Molecular beam epitaxy for oxi
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3.2. In situ characterization techn
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3.2. In situ characterization techn
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3.3. Experimental developments at t
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3.4. Ex situ characterization techn
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4. Results I: Single-crystalline ep
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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
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Page 104 and 105: 5.1. Chemical stabilization of bulk
Page 114 and 115: 5.2. Thermodynamic analysis of the
Page 122 and 123: 5.3. Interface engineering I: Hydro
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Page 128 and 129: 5.4. Interface engineering II: Eu p
Page 134 and 135: 5.5. Interface engineering III: SiO
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Page 140 and 141: 6. Conclusion and Outlook In the th
Page 142 and 143: 125 Outlook and perspectives In the
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Page 146 and 147: A.1. EuO-related phases and cubic o
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Page 150 and 151: Bibliography 133 [13] S. S. P. Park
Page 152 and 153: Bibliography 135 [36] R. E. Dickers
Page 154 and 155: Bibliography 137 [65] R. Sutarto, S
Page 156 and 157: Bibliography 139 [91] P. Braun, M.
Page 158 and 159: Bibliography 141 [116] S. Hüfner.
Page 160 and 161: Bibliography 143 [144] R. Feder and
Page 162 and 163: Bibliography 145 [171] H. Miyazaki,
Page 164 and 165: Bibliography 147 [197] J. Qi, T. Ma
Page 166 and 167: Software and Internet Resources [21
Page 168 and 169: List of own publications 151 [10] R
Page 170 and 171: List of conference contributions 15
Page 172 and 173: Schriften des Forschungszentrums J
Page 175: Schlüsseltechnologien / Key Techno
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