CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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48 Chapter 2 Experimental 2.1. Introduction The present thesis work is aimed at understanding carrier dynamics in QD based nanostructures. Some of QD nanostructures presented are novel and require synthesis in our laboratory. Therefore characterization of these nanostructures is of paramount importance before carrying out carrier dynamics studies. We have used a variety of structural and optical characterization techniques to characterize these materials. Structural characterization techniques performed includes electron microscopy, electron diffraction, X-Ray diffraction, and Raman spectroscopy. Optical characterization was carried out by steady state UV-Vis absorption and photoluminescence (PL) studies. Carrier dynamics was mainly studied by time correlated single photon counting (TCSPC) and broadband ultrafast pump-probe transient absorption spectroscopy. The instrumental layouts of the instruments used and basic principles of these characterization techniques are described in this chapter. 2.2. UV-Visible Absorption Spectroscopy Atoms and molecules have discrete electronic levels and transition from ground to different excited states can be affected by light. Since electronic levels in a particular chemical species are unique, these can be used as fingerprint for identification of molecules. The absorption of light in ultraviolet-visible (UV-Vis) region can be used to characterize
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Charge Transfer Dynamics in Quantum
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DECLARATION I, hereby declare that
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ACKNOWLEDGEMENTS It is my privilege
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1.3.5. Defect Mediated Relaxation 2
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2. 8. 4. White Light Generation- 45
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6.2. Experimental 6.2.1.Synthesis o
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devices based on QDs it has been sh
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Furthermore generation of pump (~40
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shell). This clearly indicated that
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12. V. I. Klimov, J. Phys. Chem. B,
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1.13 Reactant and Product Potential
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light. Inset: Kinetic traces monito
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6.5 Transient decay kinetics of gra
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at 670 nm after exciting at 400 nm
Page 37 and 38: ABBREVIATIONS BET BQ CB CCD CdS CdT
Page 39: 1 Chapter 1
Page 42 and 43: 3 size dependent optical properties
Page 44 and 45: 5 1.2. Physics of Semiconductors 1.
Page 46 and 47: 7 As seen from the schematic, poten
Page 48 and 49: 9 Substituting this in Schrödinger
Page 50 and 51: 11 ( r, r ) ( r ) ( r ) (1.13) e
Page 52 and 53: 13 E E E 2 2 2 EX ne, le nh,
Page 54 and 55: 15 spherical symmetry of field. The
Page 56 and 57: 17 gE ( ) 2Em 2 3 3 (1.25) For a
Page 58 and 59: 19 1.3.2. Electron-Hole energy tran
Page 60 and 61: 21 Impact Ionization Figure 1.7. Sc
Page 62 and 63: 23 understanding on mechanistic asp
Page 64 and 65: 25 carriers are unable to sample th
Page 66 and 67: 27 CB VB QD Metal Figure. 1. 10. Sc
Page 68 and 69: 29 energy barrier. Therefore it is
Page 70 and 71: 31 1 f q 2 A qB (1.30) 2 In equa
Page 72 and 73: 33 Vibrational contribution can be
Page 74 and 75: 35 1. 7. 1. Electron Injection ET i
Page 76 and 77: 37 Under assumption of invariance o
Page 78 and 79: 39 distribution. To achieve good si
Page 80 and 81: 41 initially achieved monodispersit
Page 82 and 83: 43 and rate of charge transfer acro
Page 84 and 85: 45 1.32 P. V. Kamat, J. Phys. Chem.
Page 87: 47 Chapter 2
Page 91 and 92: 50 2.3. Fluorescence Spectroscopy F
Page 93 and 94: 52 of crystal planes appear at diff
Page 95 and 96: 54 different angles and intensities
Page 97 and 98: 56 2.6. Transmission Electron Micro
Page 99 and 100: 58 Electron Gun Condenser Lenses Sa
Page 101 and 102: 60 The kinetic energy variation ari
Page 103 and 104: 62 out in time domain. For example
Page 105 and 106: 64 Light Source Excitation Monochro
Page 107 and 108: 66 employed to retrieve lifetime va
Page 109 and 110: 68 ΔL Reference Pulse Δ t=2ΔL/c
Page 111 and 112: 70 photodiodes for each pulse. Mech
Page 113 and 114: 72 2. 8. 2. 2. Amplifier As mention
Page 115 and 116: 74 multimodal and circular. The sec
Page 117 and 118: 76 Figure 2.9. Optical layout of 2-
Page 119 and 120: 78 Here E is the electric field of
Page 121 and 122: 80 diagnostic. Additionally average
Page 123: 82 2.18. J. Manz, L. Wöste, Femtos
Page 127 and 128: 84 CHAPTER 3 Charge Carrier Dynamic
Page 129 and 130: 86 density of states. However, if o
Page 131 and 132: 88 3.3. Results & Discussion 3.3.1.
Page 133 and 134: 90 Absorbance (a.u) 1,0 d 2 1 c b a
Page 135 and 136: 92 The spectrum has been shown in t
Page 137 and 138: 94 injection dynamics where the con
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96 dye gave a pulse width limited i
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98 alizarin has extended -electron
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100 n=5 n=4 n=3 n=2 n=1 n=0 trappin
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102 energy change is the only facto
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104 2. Nazeeruddin, M. K.; Kay, A.;
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106 32. Duncan, W. R; Prezhdo, O. V
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108 CHAPTER 4 Effect of Size Quanti
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110 impossible in bulk systems. For
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112 4.3. Results & Discussion: 4.3.
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114 nm which exactly matched with t
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116 of 3.2ps (~90%) which can be at
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118 Figure 3: Panel A: Normalized k
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120 dynamics of hot electron. The p
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122 constants of τ 1 = 7ps (53%),
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124 4.4 Conclusion In conclusion we
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126 4.15. Ekimov, A. I.; Hache, F.;
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128 CHAPTER 5 Charge Carrier Dynami
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130 CdSe/ZnTe. Feldman and coworker
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132 by reducing Se with NaBH 4 with
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134 broadening in the present case
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136 vis absorption spectra of the t
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138 5.3.3. Time resolved emission s
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140 Sample t 1 (ns) t 2 (ns) t 3 (n
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142 can be attributed to absorption
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144 5.3.5. Transient absorption stu
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146 However, due to staggered band
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148 Scheme 5.1: Schematic represent
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150 are the reason for that contrib
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152 5.10. L. P. Balet, S. A. Ivanov
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154 Chapter 6
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156 Recently several methods like c
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158 6.2.2. Reduction of Graphene Ox
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160 isolated CdTe QD over graphene
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162 Figure 6.3: Time-resolved emiss
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164 carriers on laser excitation. I
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166 absorption in the present studi
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168 increases from 33.3% to 61.8% i
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170 as compared to that of GO. It i
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172 components could come from trap
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174 A (m O.D.) 0 -10 -20 -30 a b Cd
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176 The cooling dynamics does not s
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178 The study clearly shows that th
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180 From emission studies both stea
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182 6.18. C. X. Guo, H. Bin Yang, Z
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184 CHAPTER 7 Summary and Outlook 7
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186 bleach growth times from 500fs
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188 Study of interfacial electron t
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190 Chapter 8 List of Publications
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