CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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95 r B a * 0 3.1 me / me Now the effective mass of the electron, m * e of TiO 2 has been determined by several authors, who report values between 5 and 13 m e [3.18-3.20]. So the Bohr radius of the exciton as observed previously is in the range of 0.75 nm-1.9 nm. The previous studies [21- 22] on TiO 2 colloids revealed size quantization in the particles with diameter of < 3nm. In the present case we observe a clear shift in the absorption onset to blue side for particle sizes
96 dye gave a pulse width limited injection on TiO 2 . This could be due to the fact the studies were conducted on bulk TiO 2 . Furthermore, studies on size quantized ZnO with coumarin dyes by Murakoshi et al [3.28] revealed that the injection time based on their fluorescence study at femtosecond resolution was multiexponential, with lifetimes from fs-ns, while injection into TiO 2 occurred in a time of 150 fs. They attributed it to the solvent effect on the interfacial dynamics as they had used a methanol solution for ZnO and aqueous solution for TiO 2 . In the present case this could not be the reason as we have observed earlier [3.29] that the injection dynamics using a surface modified normal TiO 2 (synthesized by sol-gel procedure) in toluene and found a pulse width limited injected for the bulk TiO 2 -alizarin system. Therefore ruling out all the other causes that could give a multiexponential injection we conclude that in the present case it is due to discreteness in the conduction band. Furthermore, the injection times are large i.e 3 orders of magnitude larger than that of the bulk samples therefore this cannot be explained on the basis of change of solvent. The literature study on multiexponential injection as mentioned earlier have all been carried out on weak binding dyes. Like Ru-bipyridyl complex N3 and C-343. On the contrary the dye used in the present case is strong binding dye where injection is believed to proceed via adiabatic process [3.4]. Most electron injection event in literature studies could be explained on the basis of classical Marcus relation [3.30]. This equation is strictly valid only for nonadiabatic system, where the injection of the electron from the dye excited state proceeds into the CB via electron tunneling since the interaction between the dye and the semiconductor is weak, whereas in case of an adiabatic electron transfer process the electron transfer proceeds in the same Born-Oppenheimer surface as it moves from the dye to the CB of the semiconductor. The difference in the two majorly lies in the fact that since in
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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
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ABBREVIATIONS BET BQ CB CCD CdS CdT
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1 Chapter 1
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3 size dependent optical properties
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5 1.2. Physics of Semiconductors 1.
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7 As seen from the schematic, poten
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9 Substituting this in Schrödinger
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11 ( r, r ) ( r ) ( r ) (1.13) e
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13 E E E 2 2 2 EX ne, le nh,
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15 spherical symmetry of field. The
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17 gE ( ) 2Em 2 3 3 (1.25) For a
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19 1.3.2. Electron-Hole energy tran
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21 Impact Ionization Figure 1.7. Sc
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23 understanding on mechanistic asp
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25 carriers are unable to sample th
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27 CB VB QD Metal Figure. 1. 10. Sc
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29 energy barrier. Therefore it is
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31 1 f q 2 A qB (1.30) 2 In equa
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33 Vibrational contribution can be
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35 1. 7. 1. Electron Injection ET i
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37 Under assumption of invariance o
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39 distribution. To achieve good si
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41 initially achieved monodispersit
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43 and rate of charge transfer acro
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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
Page 128 and 129: 85 Therefore the study of interfaci
Page 130 and 131: 87 3. 2. Experimental Section 3.2.1
Page 132 and 133: 89 and intensity show absence of ot
Page 134 and 135: 91 which is also neutral; therefore
Page 136 and 137: 93 electron transfer times. This re
Page 140 and 141: 97 nonadiabatic case the electron t
Page 142 and 143: 99 drastically reduced leading to a
Page 144 and 145: 101 While the study of injection dy
Page 146 and 147: 103 study. Based on the injection d
Page 148 and 149: 105 17. L. E. Brus, J. Phys. Chem.
Page 154 and 155: 109 of the QDs. As a result surface
Page 156 and 157: 111 4.2.2. Synthesis: The CdTe QDs
Page 158 and 159: 113 lower hole state. In CdSe the l
Page 160 and 161: 115 4.2 inset. The kinetic traces a
Page 162 and 163: 117 growth of the bleach kinetics (
Page 164 and 165: 119 previous section we have discus
Page 166 and 167: 121 lived charge transfer complex w
Page 168 and 169: 123 100 times concentration of the
Page 170 and 171: 125 4.5. References 4.1. Efros, Al.
Page 176 and 177: 129 been made in the synthesis of t
Page 178 and 179: 131 metallic synthesis by arrested
Page 180 and 181: 133 5.3. Result and discussion: 5.3
Page 182 and 183: 135 indicating a confinement induce
Page 184 and 185: 137 absorption studies that on form
Page 186 and 187: 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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CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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