CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

More documents

Recommendations

Info

131 metallic synthesis by arrested precipitation at high temperature [5.3, 5.11]. We have chosen CdSe/ZnTe core-shell where lattice mismatch between core and shell is less than 1 % which ensures less defect (cleaner) surface and minimizes non radiative relaxation via interface defects or charged excitons. Core-shell materials have been characterized by steady state optical absorption and emission studies and also in high resolution TEM (HRTEM) technique. To unravel the charge transfer dynamics we have carried out transient absorption studies in ultrafast time scale detecting the transients in visible to near-IR region by exciting both CdSe core and CdSe/ZnTe core-shell material by exciting at 400 nm laser light. Detail mechanism of charge transfer and carrier cooling mechanism has been discussed. 5.2 Experimental 5.2.1. Materials: Cadmium chloride (≥99%), Te powder (≥98), 1-mercaptopropionic acid (≥99%), NaBH 4 and benzoquinone were purchased from Aldrich and used it as received without further purification. Isopropyl alcohol was used as received from s.d.fine chemicals. Pyridine (Fluka) was used after distillation. 5.2.2. Synthesis of CdSe QDs: Thiol capped CdSe QD was prepared by following previously reported method [5.12]. In brief, cadmium chloride (cadmium precursor) was dissolved in N 2 purged nanopure water followed by addition of 1-mercaptopropionic acid (MPA). The solution pH was adjusted to 9-10 using 1M NaOH. NaHSe (Selenium precursor) solution was prepared fresh
132 by reducing Se with NaBH 4 with Se: NaBH 4 =1:2 in water maintained at 273K for 1h. NaHSe was added to cadmium precursor solution with vigorous stirring. The ratio between Cd, MPA and Se was maintained at 1:2.5:0.5. The above solution was refluxed for six hours. Reaction mixture was allowed to cool naturally and was concentrated to 1/3rd of its original volume by using rotary evaporator. QDs were precipitated by adding Isopropyl alcohol as the nonsolvent. Supernatant was discarded and precipitate was re-dissolved in nanopure water and finally re-precipitated. The cleaning was complete by a 3 time dissolution and reprecipitation procedure to remove un-reacted precursors. These samples were dried in ambient for further use. 5.2.3. Shell Growth: For shell formation the concentration of the precursor for formation of 2.5nm shell was calculated according to reported methods. 10 -6 M MPA capped CdSe was dissolved in N 2 purged water. To this solution zinc nitrate hexahydrate and MPA solution in 1:2.5 molar ratio was added and pH was adjusted to 9-10. NaHTe (tellurium precursor) solution was prepared fresh by reducing Te with NaBH 4 with Te: NaBH 4 =1:2 in N 2 purged water maintained at 273K for 8h. This was added to the above prepared QD solution with Zn precursor with vigorous stirring. The Zn: MPA: Te molar ratio was maintained at 1:1.5:0.5. The solution was refluxed for 6h for the growth of shell. To obtain shells of different shell thickness the samples were eluted at different time (1/2h, 1h, 2h, and 6h). The cleaning procedure was the same as described above for the CdSe QDs. The four samples are named as CdSe/ZnTe1, CdSe/ZnTe2, CdSe/ZnTe3, and CdSe/ZnTe4 with increasing shell thickness order which were eluted at 1/h, 1h, 2h and 6h respectively.
Page 1:
Charge Transfer Dynamics in Quantum
Page 7:
DECLARATION I, hereby declare that
Page 11:
ACKNOWLEDGEMENTS It is my privilege
Page 14 and 15:
1.3.5. Defect Mediated Relaxation 2
Page 16 and 17:
2. 8. 4. White Light Generation- 45
Page 18 and 19:
6.2. Experimental 6.2.1.Synthesis o
Page 20 and 21:
devices based on QDs it has been sh
Page 22 and 23:
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 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 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 125:
83 Chapter 3
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 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 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
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.
Page 231:
183 6.26. Kaiser, A. B.; Navarro, C
Page 234 and 235:
185 assigned to injection into diff
Page 236 and 237:
187 transfer from CdSe core to ZnTe
Page 238 and 239:
189 However the position of bands i
show all

CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?