PHYS07200604007 Manas Kumar Dala - Homi Bhabha National ...

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Experimental Techniques 38 passed through a vacuum feedthrough and then directly into the preamplifier. And then the signal is passed onto a pulse counter for processing and production of an electron energy spectrum. 2.3 Inverse Photoemission Spectroscopy 2.3.1 Historical background The inverse photoemission spectroscopy (IPES) [17, 18, 19] is a powerful technique to study the unoccupied electronic states of solids. The IPES experiment can be carried out in two different photon energy regimes. One is at higher energy range (detected photons are in x-ray range) called Bremsstrahlung isochromat spectroscopy (BIS) and the other one is at low energy region (detected photons are in the ultraviolet range) which is called UV-IPES or simply IPES. The history of IPES technique was developed in 1915 by Duane and Hunt [20] when an inverse relationship is observed between the short wave-length cutoff of emitted x-rays and incident electron energy when a solid is bombarded with electrons. Then pursued by Ohlin [21] and Nijboer [22] in 1940s and was resumed in the 1950s by Ulmer and Vernickel [23]. The IPES work in the ultra-violet region is of relatively recent origin. The experimental work was started by Dose [24] and the theoretical work by Pendry [25, 26]. The experimental advances since then have been rapid. 2.3.2 Basic principle When a beam of electrons is incident on a solid surface, after entering the system, the electrons decay either radiatively or non-radiatively to states at lower energy. If the decay is radiative the emitted photon can be detected, and gives the information about the unoccupied states of the system. So this is complementary to direct photoemission spectroscopy (PES) [17, 18, 19, 27]. A schematic of the inverse photoemission spectroscopy is shown in the Fig. 2.10 The energy of the photons (hν) emitted when a beam of electrons having kinetic energy E k is incident on a solid surface and then relax to a lower energy unoccupied state (E f ), is given by the conservation of energy as, E k = hν + E f − φ, (2.26)
Experimental Techniques 39 Figure 2.10: Schematic diagram of inverse photoemission spectroscopy (IPES). where φ is the work function of the material. There are two modes [18, 19, 27] used for this measurement . One is isochromat mode and the other one is spectrograph mode. In isochromat mode, the incident electron energy is ramped and the emitted photons are detected at a fixed energy. In the spectrograph mode, the energy of the incident electron remains fixed and the emitted photons are detected over a range of photon energies. 2.3.3 Basic interpretation of inverse photoemission The Inverse photoemission process can be described [28] by a comparison with photoemission. Both photoemission and inverse photoemission involve the interaction between photons and electrons. Now the interaction Hamiltonian associated with the electromagnetic field can be written as,
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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]
Page 9 and 10: Synopsis The perovskite type mangan
Page 11 and 12: to the t 2g and e g spin-up states
Page 13 and 14: 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,
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Page 57 and 58: Experimental Techniques 35 negative
Page 59: 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 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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