Title Page
Abstract
Contents
Chapter 1. Introduction 17
References 19
Chapter 2. Research Methods 21
2.1. X-ray Photoelectron Spectroscopy 21
2.1.1. Fundamental Principles of Photoemission Process 22
2.1.2. Instrumentation 26
2.2. Ambient Pressure X-ray Photoelectron Spectroscopy 30
2.2.1. Development of Ambient Pressure X-ray Photoelectron Spectroscopy 30
2.2.2. The operation principle of Ambient Pressure X-ray Photoelectron Spectroscopy 32
2.2.3. Commissioning of Ambient Pressure X-ray Photoelectron Spectroscopy Systems 36
2.3. References 45
Chapter 3. Crystallization and bandgap variation of non-stoichiometric amorphous Ga2O3-x thin films during post-annealing process[이미지참조] 49
3.1. Introduction 50
3.2. Experiments 52
3.3. Results and Discussion 54
3.4. Conclusion 67
3.5. References 68
Chapter 4. Nature of the surface space charge layer on undoped SrTiO₃(001) 74
4.1. Introduction 75
4.2. Experiments 78
4.3. Results and Discussion 82
4.4. Conclusion 98
4.5. Calculation of Debye length 100
4.6. References 102
Chapter 5. Correlation between structural phase transition and surface chemical properties of thin film SrRuO₃/SrTiO₃(001) 109
5.1. Introduction 110
5.2. Experiments 113
5.3. Results and Discussion 114
5.4. Conclusion 124
5.5. Estimation of atomic ratio (Sr/Ru) on SrRuO₃ thin film 125
5.6. References 127
Chapter 6. Summary and Conclusion 133
Appendix 135
Curriculum Vitae 143
Table 3.1. Fitting parameters for Ga 3d XP spectra. GL(30) indicates Gaussian-Lorentzian mixed form, where the ratios of Gaussian and Lorentzian function are 70% and 30%, respectively. FWHM stands for full... 59
Table 3.2. Fitting parameters for O 1s XP spectra. GL(30) indicates Gaussian-Lorentzian mixed form, in which the ratios of Gaussian and Lorentzian function are 70% and 30%, respectively. FWHM stands for full... 60
Table 4.1. Photon energy values used for depth profiling of each element considering the formula of TPP 2M. 79
Table 4.2. The band gap energies and conductivities of SrTiO₃ at each temperature under UHV (10-9 mbar) and O₂ (0.1 mbar) conditions calculated from the references.[이미지참조] 80
Table 4.3. C 1s binding energy of each pressure condition before the energy calibration. All C 1s binding energy was calibrated to 284.5 eV. 81
Table 4.4. Spectral fitting parameters for Sr 3d AP-XP spectra in Fig. 4.1(b) and (c). Binding energy positions of SrO1+x and SrTiO₃ components are referenced in Ref. Full width half maximum (FWHM) values and...[이미지참조] 85
Table 4.5. Characteristic binding energy positions of O 1s, Ti 2p3/2, and Sr 3d5/2 as a function of annealing temperature in Fig. 4.8(a). The △ values, the binding energy offset values between UHV and O₂ conditions, are...[이미지참조] 93
Table 4.6. Dielectric constant (εγ) and charge density (n) values of SrTiO₃ as a function of temperature. Charge density values are calculated by extrapolation from the references [42, 47], and Debye length... 101
Table 5.1. The calculated atomic fraction of Sr and Ru for each condition. 126
Figure 2.1. Schematics of a three-step photoemission process. 22
Figure 2.2. Schematics of the one-step model. In solid, an electron (Bloch wave) is excited into a wave with the attenuation, but propagates freely in a vacuum. (Reprinted from [3]) 23
Figure 2.3. The universal curve for the inelastic mean free paths of several materials as a function of electron kinetic energy. (Reprinted from [5]) 24
Figure 2.4. Superimposed XP spectrum on a schematic of the electronic structure to describe the electrons escaping from the specific orbital. (Reprinted from [6]) 25
Figure 2.5. Radiation by insertion devices: i) bending magnet, ii) undulator, and iii) wiggler. (Reproduced from[11]) 27
Figure 2.6. Schematic diagram of a hemispherical electron analyzer and transfer lens. (Reprinted from [6]) 29
Figure 2.7. Schematic cross section drawing of the AP-XPS system, which consists of a pre-lens section and a hemispherical electron analyzer. The electrostatic lenses are integrated with separated pumping stages labeled... 32
Figure 2.8. Gas dynamic simulation along the z axis from the sample extending to the differential pumping stages for P0＝1 mbar. P0 is a gas pressure at the analysis chamber and z is the distance from the middle...[이미지참조] 33
Figure 2.9. The inside of the analysis chamber with X-ray Al window, sample manipulator, and analyzer front cone. 34
Figure 2.10. Schematic view of the laboratory-based AP-XPS installed at GIST. Detailed representation of the system is shown. The X-ray window in the analysis chamber transmits the X-ray while separating the gas and... 36
Figure 2.11. The inside view of the analysis chamber with manipulator, analyzer front cone, and Al polyimide X-ray window. The paths of X-ray and photoelectron are displayed. Au (100) sample was used for the... 37
Figure 2.12. The XPS survey scans for (a) 0.8 mm and (b) 0.3 mm cone aperture and Au 4f spectra for (c) 0.8 mm and (d) 0.3 mm cone aperture as a function of Ar gas pressure. (e) The intensity plot of Au 4f spectra,... 39
Figure 2.13. An example of one-dimensional chemical imaging mode is shown. (a) and (c) represent the integration of the detector image along the energy axis which shows that the spatial resolution is about 10 μm.... 42
Figure 2.14. (Left) Layout of the AP-XPS beamline and endstation in PAL. (Right) AP-XPS endstation with four chambers: a load-lock chamber for sample loading, a distribution chamber for sample storage, a... 44
Figure 3.1. Synchrotron XRD profiles of (a) as-grown and annealed Ga2O3-x films at (b) 300 ℃, (c) 400 ℃, (d) 500 ℃, and (e) 600 ℃. Colored lines in (a) show the fitting results of the amorphous peak in the Q＝1.5-...[이미지참조] 55
Figure 3.2. Off-specular XRD reflections of the sample annealed at 600 ℃. α-Ga2O3 (101̅4) scanned in (a) Qx direction, (c) Qz direction, and (e) azimuthal φ angle. ß-Ga₂O₃ (002) scanned in (b) Qx direction, (d) Qz...[이미지참조] 56
Figure 3.3. (a) EDX spectra of as-grown sample and sample annealed at 600 ℃. Yellow shaded area represents the increase in the amount of oxygen atoms in Ga2O3-x film after post-annealing. (b) Variation of chemical...[이미지참조] 57
Figure 3.4. (a) O 1s and (b) Ga 3d XPS spectra at each specific annealing temperature and oxygen gas pressure The AP-XPS experiments are performed through steps I-IV. In the O 1s spectra, the surface contamination... 61
Figure 3.5. X-ray diffraction profile of the sample annealed in the AP-XPS system. After AP-XPS measurement, the XRD profile of the sample annealed using a heater in the AP-XPS system was measured.... 63
Figure 3.6. (a) UV-Vis spectra of as-grown and annealed samples. In the visible light range, the average transmittance gradually increases from 74.2% for as-grown sample to 97.2% for sample annealed at 600 ℃.... 64
Figure 3.7. Comparison of UV-Vis spectroscopy results of samples annealed at 600 ℃ in air and vacuum. (a) Optical transmittance and (b) Tauc plot for estimating the optical bandgap. The effect of oxidation on the optical... 65
Figure 3.8. Summary of post-annealing effects on non-stoichiometric amorphous Ga2O3-x.[이미지참조] 67
Figure 4.1. AFM topography images of SrTiO₃ (001) film for (left) as-received and (right) after 2 treatment cycles of a deionized-water leaching and thermal annealing treatment, i.e., air annealing (1000℃, 1 hour) and... 78
Figure 4.2. AP-XP spectra of SrTiO₃ (001) films during thermal annealing under O₂ 0.1 mbar [red series, (a), (c), (e)] and UHV [blue series, (b), (d), (f)] conditions with the surface sensitive probing depth of 1.5 nm. Core... 82
Figure 4.3. (a) Experimental scheme of depth-resolved AP-XPS measurement for identifying the surface redox chemistry of SrTiO₃ (001). (b & c) Sr 3d spectra, SrO1+x surface oxide (orange) and SrTiO₃ lattice oxide (cyan),...[이미지참조] 84
Figure 4.4. AP-XP spectra of Sr 3d obtained at 600℃ with probing depth of 1.5 nm during O₂ (red) and UHV (blue) conditions. To compare spectral shapes, Sr 3d spectra are superimposed to binding energy positions for... 87
Figure 4.5. Entire set of spectra in Fig. 4.2 are superimposed on the binding energy positions of SrTiO₃ lattice peaks. For Sr 3d spectra, the formation of SrO1+x surface oxide is clearly observed under both annealing...[이미지참조] 88
Figure 4.6. Valence band (VB) spectra of SrTiO₃ (001) film at probing depth of 1.5 nm under UHV condition during annealing from 200℃ up to 600℃. During annealing in UHV, TiO₂ layer in SrTiO₃ are gradually... 89
Figure 4.7. (a) LEED patterns of as-prepared, after O₂ annealed and UHV annealed SrTiO₃ (001) surface at 600℃. (b) Simulated LEED patterns for structural analysis. (c) The illustrations of lattice structures in real space. 90
Figure 4.8. (a) Characteristic binding energy positions of SrTiO₃ lattice component as a function of annealing temperature. [Each core level O 1s, Ti 2p3/2, Sr 3d5/2 is expressed as black, red, blue colors while the solid...[이미지참조] 92
Figure 4.9. (a) VB spectra of SrTiO₃ (001) film at probing depth of 1.5 nm and O₂ pressure of 0.1 mbar during annealing from 200℃ up to 600℃. The position of valence band maximum (VBM) is determined as the... 95
Figure 4.10. (a) The schematic illustration of the layer structure from top surface of as-prepared SrTiO₃ (001). (b) The proposed surface redox process in side and top views during the annealing under O₂ 0.1 mbar. [Sr, Ti,... 96
Figure 4.11. Formation of a space charge layer on the surface of SrTiO₃ (001) under functional material growth environments. 98
Figure 5.1. Schematic view of (a) T-SRO and (b) M-SRO thin film, respectively. An oxygen vacancy in the Sr-O plane of T-SRO is energetically favorable. 111
Figure 5.2. (a) XRD measurement of T-SRO (red) and M-SRO (black) along the surface normal direction. (b) Schematic view of T-SRO (left) and M-SRO (right). The lattice parameters of T-SRO and M-SRO along the c-... 114
Figure 5.3. (a) Core level XPS spectra of T-SRO (top) and M-SRO (bottom) under UHV conditions. (b) Valence band spectra of T-SRO (top) and M-SRO (bottom). Black (Red) lines indicate the results under UHV... 116
Figure 5.4. Comparison of core level XPS spectra of Sr 3d T-SRO and M-SRO under UHV environment. The enhancements of SrO1+x oxide near~133.5 eV can be clearly observed across the SPT temperature.[이미지참조] 118
Figure 5.5. Core level XPS spectra of T-SRO (top) and M-SRO (bottom) under (a) UHV and (b) oxygen partial pressure of 100 mTorr. Black lines and red lines indicate the spectra before and after SPT temperature,... 120
Figure 5.6. (a) Core level XPS spectra of T-SRO (top) and M-SRO (bottom) under oxygen partial pressure of 100 mTorr. (b) Valence band spectra of T-SRO (top) and M-SRO (bottom) under oxygen partial pressure of... 121
Figure 5.7. Comparison of core level XPS spectra of O 1s T-SRO (left) and M-SRO (right). The binding energy of the surface oxide peak under UHV (oxygen pressure environment) is 531.7 eV (531.0 eV) in T-SRO surface.... 122
Figure 5.8. XRD off-specular reflection elevated temperature under oxygen partial pressure of 100 mTorr. Each black, red, blue, and green lines indicate the off-specular direction along (103), (013), (103), (013),...[이미지참조] 123
Figure 5.9. The influence of surface migration of lattice oxygen process at the SrRuO₃-SrTiO₃ interface on the structural phase transition.[이미지참조] 124