CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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93 electron transfer times. This reveals that the dynamics observed at the dye cation maxima and the conduction band electron monitors the same events. The individual contributions to the electron injection time and BET times are given in the Table 3.1. 0,004 A 0,003 0,002 0,001 0,000 A 0,004 0,003 0,002 0,001 0,000 -2 0 2 4 6 8 10 Delay Time (ps) 0 100 200 300 400 500 Delay Time (ps) Figure 3.5: Kinetic Decay Traces of B- TiO 2 -Alizarin in toluene after 400nm excitation at λ pr =550nm. In the present investigation we have observed multi-exponential electron injection in alizarin/TiO 2 system. There could be several reasons to why this can happen. Some of the known possibilities are multilayer formation or aggregation of the dyes on TiO 2 surface. However, in the present investigation we have kept the concentration of alizarin below 10 -4 M, where possibility of aggregation is very remote. Assuming that the dye molecules are evenly distributed on the surface of TiO 2 we can argue that the concentration is not enough to form aggregate on the dye surface. We have carried out the ultrafast dynamics study on surface modified TiO 2 bulk particle (capped with DBS) and did not observe any multiple
94 injection dynamics where the conditions (concentration of the dye, laser intensity etc) are very similar as compared to the present investigation. The dynamics revealed that the electron injection event in the case of bulk surface modified particle is monophasic and the injection event is pulse width limited which we have already reported in our previous study [3.3]. This proves that the injection dynamics observed in the case is not from a dye aggregate or multilayers of the dye. Wavelength (nm) Electron Injection Times BET Times inj1 ,ps (A 1 ) inj2 ,ps (A 2 ) inj3 ,ps (A 3 ) BET1 ,ps (A 2 ) BET2 ,ps (A 3 ) 550 0.11 (60%) 17 (27%) 50 (13%) 0.2 (44.7 %) > 1ns (55.3%) 900 0.08 (85%) 18 (8.5%) 50 (6.5%) 0.2 (80%) > 1ns (20%) Table 3.1. Parameters for the multi-exponential Fits to the electron injection and back electron transfer (BET) kinetics of alizarin sensitized B-TiO 2 after monitoring both alizarin cation at 550 nm and electron in the conduction band at 900 nm. The other possibility in the presence case is finite size effect, which could lead to discreteness in the conduction band levels leading to different injection times to different levels within the conduction band. The average size of the particles in the present case is r= ~1.7nm. In case of TiO 2 , the size of Bohr exciton radius is a range of values. This is due to the fact that the electron and hole effective mass is not known accurately due to unavailability of high quality single crystals. According to Brus [3.17] the radius r B of an exciton can be calculated in terms of
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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 138 and 139: 95 r B a * 0 3.1 me / me Now the
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
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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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