CHEM01200604009 Sreejith Kaniyankandy - Homi Bhabha ...

More documents

Recommendations

Info

156 Recently several methods like chemical vapor deposition (CVD) [6.6], decomposition of SiC at higher temperature [6.7], and chemical methods like oxidation promoted exfoliation [6.8] have been proposed as possible route to synthesis of graphene. Decomposition of SiC to form hexagonal graphene lattice have shown promising behavior similar to the ones prepared by micromechanical cleavage used by Geim et al [6.4]. However this method suffers from the formation of multilayers along the surface, leading to inhomogeneity along the films of graphene. Furthermore strong interaction with the SiC substrate lead to breakdown of A-B sub-lattice symmetry leading to band gap opening at the K-point [6.9]. Klaus Mullen et al have used bottom up approach to synthesize graphene sheets which are in principle defect free however these methods are economically nonviable [6.10].On the other hand oxidation induced exfoliation has captured the attention of several groups due to their ability to produce these layer of GO in a large scale [6.11]. Furthermore, these samples can be processed by chemical reduction to obtain monolayer graphene [6.8]. In the present study our focus is on charge separation behavior in graphene QD nanocomposite. The graphene used is chemical reduced graphene oxide. Several previous have demonstrated previously that for an efficient photovoltaics employing QD one needs to separate charge carriers before trapping or recombination. This problem is particularly acute in case of QD due to larger surface to volume ratio [6.12]. Studies by Alivisatos et al [6.13] have demonstrated use to conducting polymers for charge separation which helps in improving photovoltaic effcicincy. Kamat and coworkers [6.14] employing carbon nanotubes for charge separation for TiO 2 based photovoltaics have demonstrated an increase in efficiency.
157 Studies by Wang et. al. [6.15] and Cao et. al. [6.16] have demonstrated growth of quantum dots of CdS and CdSe on graphene and good steady state optical properties. Apart from this potential of graphene in improvement of photovoltaics effcicincy also has been demonstrated. quantum dots-graphene assembly also has shown potential application in photovoltaic measurements [6.17, 6.18]. Cao et al [6.16] have shown effcicint electron transfer from CdS QD to graphene from time-resolved emission spectroscopy. To address this issue we have synthesized CdTe QD decorated on graphene and performed femtosecond transient absorption studies. 6.2. Experimental 6.2.1. Synthesis of Graphene Oxide GO was synthesized from graphite by the modified Hummers method [6.19]. To 250 mL flask filled with graphite (2 g), 50ml H 2 SO 4 was added at room temperature. Above solution was cooled to 0 ○ C followed by addition of 7g of KMnO 4 slowly while maintaining the temperature below 10 ○ C. After complete addition of KMnO 4 , the temperature was increased to 10 ○ C. The mixture was stirred for 2 h. Excess water was added into the mixture at 0 ○ C (ice bath) and then H 2 O 2 (30 wt% in water) was added until the effervescence ceases. The GO powder was washed with copious amount of water and dried in the ambient.
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 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
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: 155 CHAPTER 6 Charge Separation in
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?