CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

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133 5.3. Result and discussion: 5.3.1. TEM & XRD Studies The TEM pattern (figure 1) clearly shows crystallite size of about ~7nm. The CdSe core diameter is ~2nm as revealed by UV-Vis absorption studies. There is no clear discernable core and shell separation due to very small change in the lattice spacing between CdSe and ZnTe. The thickness of the shell as inferred from the TEM for CdSe-ZnTe sample is ~3.5nm. Figure 5.1: High-resolution TEM (HR-TEM) image of CdSe/ZnTe quantum dot core-shell (Panel A) and same picture in higher resolution Panel B). Insets: Selected electron diffraction patternof the corresponding particles. The XRD paterns given in figure 2 shows lattice spacing as observed in the above case is ~0.32nm which matched with the spacing for (111) plane. The clearly discerning feature is the broad peak at 25.4˚ can be assigned to (111) plane of CdSe. The peak
134 broadening in the present case is due to smaller crystallite size which is ~ 2nm according to optical absorption spectra. This value also matches with the domain size obtained from Debye Scherrer formula of ~2nm. (111) Intensity (a.u) (220) (311) 0 10 20 30 40 50 60 70 2 (Degrees) Figure 5.2: XRD Pattern for CdSe/ZnTe quantum dot core-shell 5.3.2. Steady state absorption and emission studies: In the present investigation to characterize the QD materials we have carried out steady state absorption and emission spectroscopy. Figure 3 indicates normalized steady state absorption spectrum of CdSe (Core) and CdSe/ZnTe core-shell material. In absorption spectrum it can be clearly seen that CdSe (shown in black solid line) has first exciton peak 1S(e)-1S 3/2 (h) around 455nm (Figure 3a) (referred hereafter as 1S). Assignment of this exciton is made by usual notation [5.14]. The exciton peak appears for CdSe QD appears at ~455nm which is considerably shifted compared to bulk band gap of ~1.9eV for CdSe
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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.
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47 Chapter 2
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49 chemical species. Since a partic
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51 fluorescence forms an important
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53 eliminated by use of standard wh
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55 sample. Raman spectroscopy is ba
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57 will appear bright and region wi
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59 volatile solvent is drop casted
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61 spots arise from diffraction fro
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63 The electrical signal is then ch
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65 delayed and inverted. The two si
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67 Pump-probe technique is one of t
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69 Amplifier Jade Stretcher fs Osci
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71 Figure 2.6. Optical layout of Ti
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73 Grating Convex Mirror Concave Mi
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75 changes the polarization from ho
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77 Grating Output Input Mirror Grat
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79 μJ has a very high peak power.
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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
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 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 151: 107 Chapter 4
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 173: 127 Chapter 5
Page 176 and 177: 129 been made in the synthesis of t
Page 178 and 179: 131 metallic synthesis by arrested
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
Page 188 and 189: 141 samples due to a very weak exci
Page 190 and 191: 143 dynamical spectrum is negligibl
Page 192 and 193: 145 Earlier authors [5.4] reported
Page 194 and 195: 147 Sample t r(ps) t 1(ps) t 2(ps)
Page 196 and 197: 149 In addition to the cooling dyna
Page 198 and 199: 151 pulse-width time scale followed
Page 200 and 201: 153 5.20. Sreejith Kaniyankandy, Sa
Page 203 and 204: 155 CHAPTER 6 Charge Separation in
Page 205 and 206: 157 Studies by Wang et. al. [6.15]
Page 207 and 208: 159 graphene in a 1M NaOH solution.
Page 209 and 210: 161 Intensity (a.u.) 5 4 3 2 1 CdTe
Page 211 and 212: 163 dynamics of graphene oxide and
Page 213 and 214: 165 GO as shown in the Figure 3 rev
Page 215 and 216: 167 electron acceptor for Graphene.
Page 217 and 218: 169 governs the recombination dynam
Page 219 and 220: 171 Sample τ 1 (ps) τ 2 (ps) τ 3
Page 221 and 222: 173 A (mO.D) 10.0 0.0 -10.0 -20.0 0
Page 223 and 224: 175 involved in the relaxation may
Page 225 and 226: 177 Electron quencher (benzoquinone
Page 227 and 228: 179 Scheme 6.1. Schematic of Electr
Page 229 and 230: 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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