PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Experimental Techniques 46 Figure 2.14: Schematic diagram of x-ray absorption spectroscopy where µ is the absorption coefficient of the material, which depends on the types of atoms and density ρ of the material. The absorption coefficient decreases smoothly with higher energy, except for certain photon energies where the absorption increases drastically, and gives rise to an absorption edge. Each such edge occurs when the energy of the incident photons is just sufficient to excite a core electron to an unoccupied state or into the continuum state (leave the atom). After each absorption edge the absorption coefficient continues to decrease with increasing photon energy (Fig. 2.15). There are two distinguishable parts in x-ray absorption process : The low energy, near edge x-ray absorption fine structure (NEXAFS) [46, 47] or x-ray absorption near edge structure (XANES) region and the extended x-ray absorption fine structure (EXAFS) [48, 49], where the ejected electrons have high kinetic energy with single scattering. In this thesis work, only the XANES (or NEXAFS) region has been taken to study the unoccupied states.
Experimental Techniques 47 Figure 2.15: The x-ray loses its intensity via interactions with material. The absorption coefficient decreases smoothly with higher energy, except for special photon energies. When the photon energy reaches a critical value for a core electron transition, the absorption coefficient increases abruptly. 2.4.2 Detection techniques The normal way to measure the x-ray absorption is in the transmission mode [21]. The intensity of the x-ray is measured before and after the sample and the percentage of transmitted x-rays is determined. Such transmission mode of experiment is standard for hard x-rays. But for soft x-rays they are difficult to perform because of the strong interaction of soft x-rays with matter and requires a very thin sample of 0.1 µm to obtain a detectable signal. An alternative to the tansmission mode experiment is the ”Yield mode”, where the decay product of the core hole (created in x-ray absorption) will be measured. The decay of the core hole gives rise to an avalanche of electrons, photons and ions escaping from the sample surface. There are four types of detection methods [21] in yield mode XAS measurement such as Auger electron yield (or partial yield), fluorescence yield, ion yield and total electron yield. In Auger electron yield method, the electrons of a certain energy range (i.e electrons of a specific Auger decay channel of the core hole) are detected. It is found that the mean free path of a 500 eV Auger electron is of the order of 20 Å. Hence
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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
Page 17 and 18: 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: Experimental Techniques 45 are weld
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
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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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