本論文利用同步輻射X光吸收光譜（XAS）與X光放射光譜（XES）的量測來研究磁性元素摻雜對二氧化鈰(CeO2)納米粒子的電子結構，並針對其變化加以討論，藉此了解電子結構與磁性之間的關連性。利用Ce L3-edge和M4,5-edge的量測可以觀察出的Ce的價電子數的改變情況。觀察摻雜物(Fe與Cr)的價數變化，則可利用其K-edge和L2,3-edge的量測，也可以說明在摻雜時的其價電子數的改變情況。利用O K-edge吸收光譜，可以發現在其吸收前景所形成的特徵峰，是因為Ce 4f的電子與O 2p的電子混成所形成的，此混成軌域的吸收強度隨著磁性元素摻雜濃度的增加有很明顯的改變。
　　實驗結果說明，利用不同磁性元素的摻雜，在CeO2 NP的系統中所引起的磁性機制是不同的。在Fe摻雜系列的樣品，在Fe摻雜濃度較低時（低於5％），會形成具有鐵磁性的Fe3+-Vo-Ce3 +的電子組態(Vo表示為氧空缺)，因此在Fe低濃度摻雜時，其磁性會隨著摻雜量增加而提高。然而，隨著Fe摻雜濃度持續增加，除了原來具有磁性的Fe3+-Vo-Ce3 +的電子組態外，因為Fe摻雜濃度增加，也產生了反鐵磁的電子組態Fe3+-Vo-Fe3+，反而造成磁性的降低。而在Cr摻雜系列的樣品，隨著Cr3+摻雜濃度的增加，對系統形成了具有鐵磁性的Cr3+-Vo-Ce3+電子組態也隨之增加，因此造成了磁性的提升。

This study reports the electronic structure of magnetic element doped CeO2 nanoparticles (NPs). Systematic synchrotron radiation based X-ray spectroscopy analysis was utilized to investigate the electronic structures in CeO2 NPs, which is determined by coupled X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES). The result revealed that the magnetic properties are correlated to the electronic structures. Ce L3-edge and M4,5-edge spectra reveal the variations of the charge states of Ce. Transition metal (TM) K-edge and L2,3-edge spectra indicate the variations of their valence states upon TM doping. The pre-edge features of oxygen K-edge spectra due to the hybridization between cerium 4f and oxygen 2p states depend strongly on the concentration of magnetic element doping. Our results indicate that, for Fe-doped samples, ferromagnetic Fe3+-Vo-Ce3+ configuration is formed at low Fe concentrations (below 5%). While, at higher Fe concentrations, anti-ferromagnetic Fe3+-Vo-Fe3+ configuration is formed. For Cr-doped samples, the major effect of magnetic properties in Cr3+ doping system is formed the ferromagnetic Cr3+-Vo-Ce3+ configuration.

Table of Contents
Acknowledgment.............................................i
Abstract..................................................ii
Table of Contents.........................................iv
List of figures............................................v
1. Introduction
1.1 CeO2...................................................1
1.2 Diluted Magnetic Semiconductor.........................4
1.3 Sample Preparation.....................................6
2. Experiments Techniques
2.1 Introduce..............................................9
2.2 Synchrotron Radiation.................................11
2.3 Beamline utilities....................................15
2.4 X-ray Absorption Spectroscopy (XAS)...................17
2.5 X-ray Emission Spectroscopy (XES).....................24
2.5-1 Non-resonant X-ray emission Spectroscopy............25
2.5-2 Resonant X-ray Emission Spectroscopy................26
3. Results and Discussion
3.1 Fe doped CeO2 EXAFS, XAS and XES......................29
3.2 Cr doped CeO2 XAS and XES.............................62
4.Conclusion..............................................84
5.Bibliography............................................85


List of figures
Fig. 1-1 Structure of CeO2 is cubic fluorite structure, where the red circle is oxygen and yellow circle is cerium.....................................................3
Fig. 1-2 Schematic diagram of solid oxide electrochemical cells (SOCs)...............................................3
Fig. 1-3 (a) XRD results for pure CeO2 NPs and Cr doped with various concentrations from 1% to 20%, and (b) Fe doped concentrations from 1% to 11%..............................8
Fig. 2-1 The electromagnetic spectrum spans the range from radio waves at long wavelengths to gamma rays at short wavelengths...............................................11
Fig. 2-2 (a) Advanced Light Source (ALS), Lawrence Berkeley National Lab (LBNL), CA. (b) National synchrotron radiation center (NSRRC), Taiwan....................................14
Fig. 2-3 Schematic diagram of produce of synchrotron light source....................................................14
Fig. 2-4 The experimental device of beamline 7.0.1 including the x-ray emission spectrometer...........................16
Fig. 2-5 Schematic diagram of the electron beam disturbed by the undulator magnet to alternative magnetic field emitted radiation into the beamline...............................16
Fig. 2-6 Schematic illustration of x-ray absorption spectroscopy process......................................19
Fig. 2-7 Energy levels, absorption edges and different fluorescence emission linesz..............................19
Fig. 2-8 X-ray absorption spectrum of Fe K-edge, as an example with corresponds to excitation of a Fe 1s electron into empty p state. The spectrum is divided into XANES and EXAFS.....................................................21
Fig. 2-9 (a) EXAFS, pictorial pictorial view of photoelectron scattering process in the single scattering regime, and (b) in the multiple scattering regimes........22
Fig. 2-10 Schematic view of x-ray absorption spectrometer.23
Fig. 2-11 The decay mechanism of XAS total electron yield and the total fluorescence modes..........................23
Fig. 2-12 Schematic process of O K-edge XAS and XES.......25
Fig. 2-13 RXES of CeO2 and corresponding transitions between energy levels diagram...................................................28
Fig. 2-14 The end-station experimental arrangement for XES experime..................................................28
Fig. 3.1-1 Ce L3-edge EXAFS of CeO2 bulk, NP and NPs with different Fe concentrations (1% to 11%)...................30
Fig. 3.1-2 Fe K-edge EXAFS of CeO2 bulk, NP and NPs with different Fe concentrations (1% to 11%)...................31
Fig. 3.1-3 Ce L3-edge XAS of CeCl3, CeO2 bulk, NP and NPs with different Fe concentrations (1% to 11%) and fitting result....................................................34
Fig. 3.1-4 The variation of IC/Itotal in the XAS spectra of CeO2 NPs as a function of concentration of Fe doping......35
Fig. 3.1-5 Ce M4, 5-egde XAS of CeO2 NPs with various Fe contents (1% to 11%) and of reference samples that contains trivalent and tetravalent Ce..............................36
Fig. 3.1-6 (a) Enlargement of experimental (black line) M5-edge and that fitted (red line) by linear combination of CeO2 and CeAl2 spectra. (b) Enlargement of 4f0 satellite feature. (c) Comparison of intensities of satellite features and Ce3+/ (Ce3++Ce4+) ratios..............................38
Fig. 3.1-7 (a) Fe L3-edge XAS of Fe doped CeO2 samples and the reference oxides......................................40
Fig. 3.1-7 (b) Fe K-edge derivative spectra (symbolic lines) of 3% Fe doped CeO2 and the reference oxides..............41
Fig. 3.1-8 Fe L2, 3-edge of XAS of CeO2 NPs with different concentrations of Fe; inset shows those of FeO, Fe2O3 and Fe3O4.....................................................44
Fig. 3.1-9 (a) Fe charge state against L3/L2 ratio. (b) Correlation among Fe L3/L2 ratio, A5/B5 intensity ratio and Ce3+/ (Ce3++Ce4+) ratio...................................45
Fig. 3.1-10 O K-edge XAS of CeO2 bulk, NP and NPs with different Fe concentrations (1% to 11%)...................48
Fig. 3.1-11 (a) Enlargement of pre-edge region. The red area at the bottom is fitted a Gaussian function, from which is determined the amount of Ce 4f-O 2p hybridized states. (b) Variation of intensity of peak A3.........................49
Fig. 3.1-12 O K-edge X-ray absorption-emission spectrums..53
Fig. 3.1-13 (a) First-order derivative of XAS and XES spectra for bandgap determination. (b) Bandgap versus Fe concentration.............................................54
Fig. 3.1-14 O Kα RXES (O 1s → 2p → 1s) spectra of pure CeO2......................................................56
Fig. 3.1-15 The RXES spectra of Fe doped CeO2 NPs with the 3% and 7% content of Fe doping that recorded the excitation energy at (a) 530eV and (b) 532.4 eV, respectively........57
Fig. 3.1-16 RXES spectra of pure CeO2 NPs recorded at different excitation energies near the Ce 3d5/2 thresholds................................................59
Fig. 3.1-17 The Ce 3d5/2 thresholds REXS spectra of Fe doped CeO2 NPs recorded the excitation energy at (a) 881.1 eV and (b) 882.1 eV..............................................60
Fig. 3.1-18 The Ce 3d5/2 thresholds REXS spectra of Fe doped CeO2 NPs recorded the excitation energy at 883.6 eV.......60
Fig. 3.2-1 Ce L3-edge XAS of CeO2 NP and NPs with different Cr concentrations (3% to 11%) and fitting result..........64
Fig. 3.2-2 The variation of IC/Itotal in the XAS spectra of CeO2 NPs as a function of concentration of Cr doping......65
Fig. 3.2-3 Ce M4, 5-edge XAS spectum results for CeAl2, pure CeO2 NPs and Cr doped samples.............................68
Fig. 3.2-4 (a) Schematic diagram of is fitted result (red dots) by linear combination of CeO2 (Ce4+) and CeAl2 (Ce3+) spectra. (b) Enlargement of experimental data (black line) M5-edge and that fitted data (red dots) with Cr doped CeO2 samples. (c) Comparison of intensities of satellite features and Ce3+/ (Ce3++Ce4+) ratios..............................69
Fig. 3.2-5 Cr L3-edge XAS of Cr doped CeO2 samples and the reference oxides..........................................72
Fig. 3.2-6 Cr L2, 3-edge XAS of different concentrations Cr doped CeO2 NPs and Cr2O3..................................73
Fig. 3.2-7 O K-edge XAS spectrum results for pure CeO2 NPs and Cr doped samples......................................75
Fig. 3.2-8 O K-edge X-ray absorption-emission spectrums...77
Fig. 3.2-9 (a) First-order derivative of XAS and XES spectra for bandgap determination. (b) Bandgap versus with Cr concentration.............................................78
Fig. 3.2-10 The RXES spectra of Cr doped CeO2 NPs with the lowest and highest content of Cr doping that recorded the excitation energy at (a) 530eV and (b) 532.4 eV, respectively..............................................81
Fig. 3.2-11 The Ce 3d5/2 thresholds REXS spectra of Cr doped CeO2 NPs with the lowest and highest content of Cr doping that recorded the excitation energy at (a) 881.1 eV and (b) 882.1 eV, respectively....................................82
Fig. 3.2-12 The Ce 3d5/2 thresholds REXS spectra of Cr doped CeO2 NPs with the lowest and highest content of Cr doping that recorded the excitation energy at 883.6 eV...........83

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