CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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35 1. 7. 1. Electron Injection ET in dye-semiconductor system involves reactant state mostly localized on dye LUMO and product state consisting of electron in CB of the semiconductor. While reactant state in dye molecule are mostly consists of only one orbital while the product states are a continuum in a semiconductor. Therefore Franck-Condon overlap with weighted DOS should be considered for electron transfer rates. In the case of an adiabatic coupling, the problem is nontrivial due to involvement of several strongly interacting potential energy surfaces (PES). In nonadiabatic case, Marcus et al [1.45] showed ET rates as given below 2 0 2 4 1 2 ( G E) kET dE( E)(1 f( E, EF ) H( E) exp h 4kT (1.37) 4k B BT 0 In the above equation, free energy ( G ) is given as = ECB Eox ( E CB = energetic position of conduction band and E = oxidation potential of adsorbate LUMO; ( E) is the ox DOS at energy E. ( E) has contribution from CB and surface states. H( E) is the strength of electronic coupling between adsorbate LUMO and states in the semiconductor at the same energy E; and λ the total reorganization energy. The Fermi occupancy factor f( E E F ) is introduced to include only unoccupied states. It is generally neglected due to assumption that at room temperature electron population is negligible at room temperature in a wide band gap semiconductor. In real systems the electronic interaction between semiconductor and adsorbate is inhomogeneous leading to a distribution of electronic coupling, H , which in turns leads to a
36 distribution of injection rates. Therefore population of injected electron, Ne() t , can be written as, (1.38) ET ( ) () 0 1 ( ) K H t Ne t N g H e dH 0 In the above equation N 0 is the total number of excited molecules. Assuming injection is the only deexcitation mechanism and acceptor states on CB then DOS is given by (2 m*) ( EdE ) 2 2 3 3/2 EdE (1.39) In the above equation m * is the effective mass of electrons in the conduction band. S + -e CB S * -CB Potential Energy E S*/ S+ -E CB Nuclear Coordinates Fig. 1. 15. Schematic of ET from a reactant state to a continuum of product states.
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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
Page 24 and 25: shell). This clearly indicated that
Page 26 and 27: 12. V. I. Klimov, J. Phys. Chem. B,
Page 28 and 29: 1.13 Reactant and Product Potential
Page 30 and 31: light. Inset: Kinetic traces monito
Page 32 and 33: 6.5 Transient decay kinetics of gra
Page 34 and 35: 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 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 90 and 91: 49 chemical species. Since a partic
Page 92 and 93: 51 fluorescence forms an important
Page 94 and 95: 53 eliminated by use of standard wh
Page 96 and 97: 55 sample. Raman spectroscopy is ba
Page 98 and 99: 57 will appear bright and region wi
Page 100 and 101: 59 volatile solvent is drop casted
Page 102 and 103: 61 spots arise from diffraction fro
Page 104 and 105: 63 The electrical signal is then ch
Page 106 and 107: 65 delayed and inverted. The two si
Page 108 and 109: 67 Pump-probe technique is one of t
Page 110 and 111: 69 Amplifier Jade Stretcher fs Osci
Page 112 and 113: 71 Figure 2.6. Optical layout of Ti
Page 114 and 115: 73 Grating Convex Mirror Concave Mi
Page 116 and 117: 75 changes the polarization from ho
Page 118 and 119: 77 Grating Output Input Mirror Grat
Page 120 and 121: 79 μJ has a very high peak power.
Page 122 and 123: 81 2.6. Dynamical Theory of X-Ray D
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83 Chapter 3
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85 Therefore the study of interfaci
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87 3. 2. Experimental Section 3.2.1
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89 and intensity show absence of ot
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91 which is also neutral; therefore
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93 electron transfer times. This re
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95 r B a * 0 3.1 me / me Now the
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97 nonadiabatic case the electron t
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99 drastically reduced leading to a
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101 While the study of injection dy
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103 study. Based on the injection d
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105 17. L. E. Brus, J. Phys. Chem.
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107 Chapter 4
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109 of the QDs. As a result surface
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111 4.2.2. Synthesis: The CdTe QDs
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113 lower hole state. In CdSe the l
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115 4.2 inset. The kinetic traces a
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117 growth of the bleach kinetics (
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119 previous section we have discus
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121 lived charge transfer complex w
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123 100 times concentration of the
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125 4.5. References 4.1. Efros, Al.
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127 Chapter 5
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129 been made in the synthesis of t
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131 metallic synthesis by arrested
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133 5.3. Result and discussion: 5.3
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135 indicating a confinement induce
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137 absorption studies that on form
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139 1000 c b PL Intensity 100 10 a
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141 samples due to a very weak exci
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143 dynamical spectrum is negligibl
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145 Earlier authors [5.4] reported
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147 Sample t r(ps) t 1(ps) t 2(ps)
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149 In addition to the cooling dyna
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151 pulse-width time scale followed
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153 5.20. Sreejith Kaniyankandy, Sa
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155 CHAPTER 6 Charge Separation in
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157 Studies by Wang et. al. [6.15]
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159 graphene in a 1M NaOH solution.
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161 Intensity (a.u.) 5 4 3 2 1 CdTe
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163 dynamics of graphene oxide and
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165 GO as shown in the Figure 3 rev
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167 electron acceptor for Graphene.
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169 governs the recombination dynam
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171 Sample τ 1 (ps) τ 2 (ps) τ 3
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173 A (mO.D) 10.0 0.0 -10.0 -20.0 0
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175 involved in the relaxation may
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177 Electron quencher (benzoquinone
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179 Scheme 6.1. Schematic of Electr
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181 6.6. Reina, A.; Jia, X.; Ho, J.
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183 6.26. Kaiser, A. B.; Navarro, C
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185 assigned to injection into diff
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187 transfer from CdSe core to ZnTe
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189 However the position of bands i
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