PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Experimental Techniques 44 The photon detector Gas filled band-pass Geiger-Muller (GM) type counters are used for photon detection in IPES because of their high efficiency, low cost and simple design [31, 32, 33, 34, 35, 36, 37, 38]. In our IPES experiment the acetone/CaF 2 detector [39] was used. The design of the photon detector is based on the following operating principle : the high energy cut-off of the acetone/CaF 2 detector is due to the CaF 2 window that does not transmit photons with energy > 10.2, while the threshold for the photoionization of acetone at 9.7 eV sets the low energy cut-off [40]. This determines the band pass function and results [33] in a mean photon detection energy of 9.9 eV with a FWHM of 0.4 eV. Thus, 9.9±0.2 eV photons can enter the detector to photoionize acetone. Figure 2.13: Schematic cross section of the photon detector showing the window (1), O-ring (2), cylindrical cap (3), detector tube (4), teflon spacer (5), anode (6), double sided DN40 CF flanges (7, 10), gas inlet and outlet (8, 9), barrel connector (11), teflon sleeve (12), DN40 CF flange (13) and SHV connector (14). The detector assembly [41] (2.13) has a modular design consisting of a 250 mm long stainless steel cylindrical tube with inner diameter 17.8 mm and outer diameter 21.2 mm (Fig), welded to a double-sided DN40 CF flange (7) with a through hole equal to the inner diameter of the tube (4). Another double-sided DN40 CF flange (10) with a similar through hole has two additional 6 mm diameter through holes drilled in the radial direction. Two 6 mm diameter of stainless steel tubes of length 25 mm
Experimental Techniques 45 are welded to these radial holes, and on the other end, DN16 CF flanges (8, 9) are welded to these tubes. These are used as gas inlet (8) and outlet (9). The anode (6) is attached to a SHV feedthrough (14) mounted on another DB40 CF flange (13) by a barrel connector (11). The three DN40 CF flanges (7, 10, 13) are mounted together on a linear translator. The anode is a 1.6 mm diameter electropolished stainless steel wire and is held by two perforated teflon spacers (5) in the detector tube. High voltage is applied to the anode. A 25 mm diameter, 2 mm thick CaF 2 window (1) sits on a viton O-ring (2) and is tightly pressed by a stainless steel cap (3) at the entrance of the detector. This isolates the detector from the UHV chamber. Use of viton O-ring ensures easy exchange of windows at the testing stage of the detector. The count rate increases with higher solid angle of detection. So the detector is brought as close as possible to the sample using the linear translator. 2.4 X-ray Absorption Spectroscopy X-ray absorption spectroscopy (XAS) is another technique to study the unoccupied electronic states as well as the geometrical arrangements of any materials around an atom [42, 43]. But in this thesis XAS technique is used only to study the electronic structure of the materials. 2.4.1 Basic principle When a beam of monochromatic x-ray enters a solid, either it will be scattered by the electrons or absorbed and excite the core electrons. In the absorption process the core electron is excited to an empty state [21, 45]. The schematic of XAS is shown in Fig. 2.14. If the energy of the x-ray is much larger than the binding energy of the core state the excited electron behaves like a free electron in the solid. If however the x-ray energy is just enough to excite a core electron, it will occupy a lowest available empty state. When a monochromatic x-ray beam of intensity I 0 goes through a material of thickness d, its intensity I will get reduced as, I = I 0 e −ρµd (2.39)
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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.
Page 15 and 16: 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: Experimental Techniques 43 The expe
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 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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