Thesis High-Resolution Photoemission Study of Kondo Insulators ...

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24 Chapter 2. Photoemission Spectroscopy hemispherical analyzer (Fig. 2.4), where voltage is supplied to inner and outer conducting hemispheres to pass electrons with a selected energy, is adopted. We have used a VSW CLASS-150 analyzer, a Scienta SES-200 analyzer, and an Omicron EA 125 HR analyzer. These light sources and electron analyzers are commercially available now. Details are described elsewhere [2.2, 3]. We show a typical arrangement of the measurement system in Fig. 2.5. The specific measurement conditions, including temperature, pressure, surface preparation, energy calibration, and energy resolution, are described in each Chapter. Exit slit R1 R2 Fringe Field Plate Entrance slit Channeltron (VSW, Omicron) MCP + CCD camera (Scienta) Electrostatic input lens photoelectron Outer hemisphere Vp Inner hemisphere R(retardation) Figure 2.4: Schematic illustration of a hemispherical analyzer. Here we make some comments on a pumping system for low-temperature photoemission spectrometers with the He lamp. We focus on the newly developed system with the VG He lamp and the Omicron EA 125 HR analyzer, which we have constructed and have improved. For photoemission spectroscopy measurements with a He lamp, a specially designed pumping system is needed. Photoelectrons excited by photons of 21.2 eV (He I α) and 40.8 eV (He II), which are emitted from the He discharge lamp, have a short escape depth of 5-20 ˚A[2.2] and thus an ultrahigh vacuum is required to exclude extrinsic signals owing to contaminations. However, direct connection is required between the discharge gas atmosphere of 0.1 - 10 Torr and the high-vacuum measurement chamber because no material is transparent for photons of such high energies.
2.2. Experimental 25 Figure 2.5: Illustration of the layout of the measurement chamber [2.9], which was used in the studies of Chaps 3, 4, and 7. The He gas that is introduced slowly into the VG lamp is differentially pumped by a rough (first) and fine (second) stage pumping and is only slightly leaked to the measurement chamber. The first and second differential stages are pumped by a rotary and a turbo pump, respectively. We have installed two turbo pumps in series as well as an ion pump to the chamber while standard ultrahigh vacuum chambers are usually closed systems with an ion pump only. 6 Typical pressures at the pumping stages and the chamber are [2.10]: Mode First Stage Second Stage Chamber He I 5 × 10−2 Torr 3 × 10−6 Torr 1.5 × 10−8 Torr He II 5 × 10−3 Torr 1.5 × 10−7 Torr 5 × 10−9 Torr The VG lamp is designed to operate efficiently for the He I (21.2 eV) line with a relatively low intensity for the He II (40.8 eV) line. If the pressure is reduced the intensity of He II is increased and becomes comparable to the intensity of He I. Some adsorption is critically increased at low temperatures (< 50 K) even if no 6 Without the turbo pump the base pressure continues to increase. He gas itself is not reactive but accumulating He gas might weaken the pumping power for other reactive gases.
Page 1: Thesis High-Resolution Photoemissio
Page 4 and 5: ii CONTENTS 5.2 Experimental . . .
Page 6 and 7: 2 Chapter 1. Introduction Figure 1.
Page 8 and 9: 4 Chapter 1. Introduction Figure 1.
Page 10 and 11: 6 Chapter 1. Introduction peaks, wh
Page 12 and 13: 8 Chapter 1. Introduction only the
Page 14 and 15: 10 Chapter 1. Introduction directio
Page 16 and 17: 12 Chapter 1. Introduction activati
Page 18 and 19: 14 References [1.14] F. Iga, M. Kas
Page 21 and 22: Chapter 2 Photoemission Spectroscop
Page 23 and 24: 2.1. General Principles 19 Photoele
Page 25 and 26: 2.1. General Principles 21 where R(
Page 27: 2.2. Experimental 23 DOS Intensity
Page 31 and 32: 2.2. Experimental 27 baking out the
Page 33: References [2.1] O. Gunnarsson and
Page 36 and 37: 32 Chapter 3. Photoemission Study o
Page 48 and 49: 44 References the Kondo peak positi
Page 50 and 51: 46 Chapter 4. Evolution of Electron
Page 63 and 64: References [4.1] G. Aeppli and Z. F
Page 65: References 61 [4.25] P. Weibel,M. G
Page 68 and 69: 64 Chapter 5. Temperature Dependenc
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74 References [5.10] N. Shimizu, F.
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Chapter 6 Substitution and Temperat
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6.1. Introduction 79 Figure 6.2: Ma
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6.3. Results and Discussion 81 6.3
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6.3. Results and Discussion 83 DOS
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6.3. Results and Discussion 85 dist
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6.3. Results and Discussion 87 Apar
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6.3. Results and Discussion 89 of E
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6.3. Results and Discussion 91 the
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6.4. Summary 93 and consistent anal
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96 References [6.11] M. J. Rozenber
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98 Chapter 7. Temperature and Co-Su
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100 Chapter 7. Temperature and Co-S
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References [7.1] G. Aeppli and Z. F
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Chapter 8 Temperature and Al-Substi
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8.2. Experimental 113 and Fisk [8.2
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8.3. Results and Discussion 115 8.3
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8.3. Results and Discussion 117 Int
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8.3. Results and Discussion 119 dep
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8.3. Results and Discussion 121 σ
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8.4. Summary 123 temperature magnet
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126 References [8.14] T. Tonogai, A
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128 Chapter 9. Conclusion has shown
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130 Chapter 9. Conclusion (a) FeSi
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132 Chapter 9. Conclusion developed
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