PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Experimental Techniques 48 the number of Auger electrons emitted is equal to the number of core holes which are created in the first 20 Å from the surface. The Auger electron yield method is a measurement of only 20 Å of material, hence the Auger electron yield is rather surface sensitive. In fluorescence yield XAS mode, the fluorescence decay of the core hole is measured instead of Auger decay electrons. The intensity of the fluorescence yield is small compared to Auger electron yield mode for the elements of atomic number Z ≤ 50. The main advantage of fluorescence yield is that the created photon has a mean free path of the same order of magnitude as the x-ray (∼ 1000 Å) and hence it probes the bulk. In ion yield mode, only the surface ions created by Auger decay are measured. So it is highly surface sensitive and is used for special surface study. The most applied detection technique for soft XAS is the total electron yield. In total electron yield mode, all escaping electrons are counted regardless of their energy. The count rate is very large in this case. This thesis contains the XAS spectra measured in total electron yield and fluorescence yield mode. In TEY mode, the electrons are detected by the hemispherical analyser, which is discussed in the last section. In the FY mode the radiative photons are detected by the Si-photodiode. Si - photodiode Silicon photodiode detectors are widely used over a broad wavelength range extending from the x-ray to the visible regions. The detector used for the XAS measurement involved in this thesis are AXUV and SXUV photodiodes [50, 51]. The photodiodes are fabricated by an ULSI (Ultra large Scale Integrated circuit) compatible process. Fig. 2.16 shows the cross section structure of the AXUV and SXUV photodiodes. The AXUV photodiode has a thin nitrided SiO 2 surface layer (approximately 7 nm thick) and 100 % internal quantum efficiency. The SiO 2 layer is known to have a fixed positive charge which repels minority carrier holes generated at the surface by strongly absorbing extreme ultra-violet (EUV) radiation. The SXUV photodiode has metal silicide surface layer which replaces the oxide layer on the AXUV photodiode and improves the radiation hardness. However, the absence of the oxide layer causes significant surface recombination in the SXUV photo diodes and reduces the internal quantum efficiency below 100 % value, that is characteristics of AXUV photodiodes. When the silicon photodiode is exposed to photons with energy greater than 1.12 eV (wavelength less than 1100 nm), electron-hole pairs (carriers) are created. These photogenerated carriers are separated by the p-n junction electric field and a current
Experimental Techniques 49 Figure 2.16: Schematic of the Si-photodiode. proportional to the number of electron hole pairs created flows through an external circuit. Several unique properties of the AXUV photodiodes have resulted in previously unattained stability and 100 % carrier collection efficiencies giving rise to near theoretical quantum efficiencies. The first property is the absence of a surface dead region i.e no photogenerated carrier recombination occurs in the doped n-type region and at the silicon-silicon dioxide interface. As the absorption depths for the majority of UV/EUV photons are less than 1 micrometer in silicon, the absence of a dead region yields complete collection of photogenerated carriers by an external circuit resulting into 100 % collection efficiency. The second unique property of the AXUV diodes is their extremely thin (4 to 8 nm), radiation-hard silicon dioxide junction passivating, protective entrance window. Owing to their 100 % collection efficiency and the thin entrance window, the quantum efficiency of the AXUV diodes can be approximately predicted in most of the XUV region by the theoretical expression E ph /3.65, where E ph is the photon energy in electron volts. 2.5 Synchrotron Radiation The unique properties of synchrotron radiation are its continuous spectrum, high flux and brightness, and high coherence, which make it an indispensable tool in the
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SPECTROSCOPIC INVESTIGATIONS OF THE
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iii To My Parents
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Maharana, P. Khare, D. K. Basa, K.
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List of Publications/Preprints [1]
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Synopsis The perovskite type mangan
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to the t 2g and e g spin-up states
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Bibliography [1] R. von Helmolt, J.
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Contents CERTIFICATE Acknowledgemen
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List of Figures 1.1 Temperature dep
Page 19 and 20: 2.2 Schematic view of the energetic
Page 21 and 22: 3.4 O K edge x-ray absorption spect
Page 23 and 24: Chapter 1 Introduction 1
Page 25 and 26: Introduction 3 The temperature and
Page 27 and 28: Introduction 5 Figure 1.2: Schemati
Page 29 and 30: Introduction 7 Figure 1.4: A schema
Page 31 and 32: Introduction 9 Figure 1.6: Schemati
Page 33 and 34: Introduction 11 Figure 1.8: Differe
Page 35 and 36: Introduction 13 Figure 1.10: A sche
Page 37 and 38: Introduction 15 Figure 1.12: Schema
Page 39 and 40: Introduction 17 Figure 1.13: Phase
Page 41 and 42: Bibliography [1] R. von Helmolt, J.
Page 43 and 44: Introduction 21 [31] Damien Saurel,
Page 45 and 46: Chapter 2 Experimental Techniques 2
Page 47 and 48: Experimental Techniques 25 Figure 2
Page 49 and 50: Experimental Techniques 27 Let us n
Page 51 and 52: Experimental Techniques 29 and G(k,
Page 55 and 56: Experimental Techniques 33 point wi
Page 57 and 58: Experimental Techniques 35 negative
Page 59 and 60: Experimental Techniques 37 ∆E = E
Page 63 and 64: Experimental Techniques 41 ( ) dσ
Page 65 and 66: Experimental Techniques 43 The expe
Page 67 and 68: Experimental Techniques 45 are weld
Page 69: Experimental Techniques 47 Figure 2
Page 77 and 78: Bibliography [1] H. Hertz, Ann. Phy
Page 79 and 80: Experimental Techniques 57 [35] K.
Page 81 and 82: Chapter 3 Electronic Structure of P
Page 83 and 84: Electronic Structure of Pr 0.67 Ca
Page 95 and 96: Bibliography [1] I. G. Deac, J. F.
Page 99 and 100: Chapter 4 Electronic Structure of P
Page 101 and 102: Electronic Structure of Pr 1−x Ca
Page 119 and 120: Electronic Structure of Ca 0.86 Pr
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Electronic Structure of Ca 0.86 Pr
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Bibliography [1] C. Zener, Phys. Re
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Summary and Conclusions 109 In this
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PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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