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Figure 8 Spectral hole-burning results in the range of the 1S e –1P e transition forphotoexcited CdSe, InP, and n-type ZnO nanocrystals at 10 K, demonstrating thenarrow homogeneous linewidths (
are two natural approaches to studying the broadening of intraband transitions.Figure 8 shows hole-burning spectra of CdSe, InP, and ZnO nanocrystalcolloids at 10 K [57]. These spectra also exhibit the LO phonon replica.Their strength is in good agreement with the bulk electron–LO phononcoupling, with values of the Huang-Rhys factor of 0.2 for the spectrum ofCdSe nanocrystals shown in Fig. 8. An interesting result is that for CdSenanocrystals, the homogeneous width remains narrower than f10 meV at 200K for a transition at f300 meV [57]. Compared to the overall inhomogeneouslinewidth of f100 meV, this value indicates that much progress is stillpossible in improving monodispersity of colloidal samples that should leadto a more precise control of intraband absorption features.V. CONCLUSIONSAs emphasized throughout the other chapters of this book, semiconductorcolloidal quantum dots hold an interesting place as chromophores. Thischapter focuses on the mid-IR properties that arise due to their intrabandtransitions. Whereas organic molecules can be made with great control andcomplexity, the strong electron–electron interactions and large electron–vibration coupling of the conjugated carbon backbone might preclude thepossibility of efficient organic chromophores in the mid-infrared. Comparedto organic materials, inorganic semiconductor quantum dots have weakerelectron–vibration coupling and weaker electron–electron interactions. Asbriefly reviewed in this chapter, the intraband transitions are spectrally welldefined in the mid-infared, strong, size-tunable, and controllable by electroninjection. The chemically synthesized quantum dots therefore have a uniqueappeal as mid-infrared ‘‘dyes’’ and have also a potential as nonlinear opticalelements [58,59]. The improvement in the quality of nanocrystal materials,however, is still required to improve the control over the intraband transitionenergies and electronic relaxation pathways. Ultimately, the intrabandresponse of the colloidal quantum dots may find widespread applications inmid-infrared technologies.REFERENCES1. West, L.C.; Eglash, S.J. Appl. Phys. Lett. 1985, 46, 1156.2. Levine, B.F.; Malik, R.J.; Walker, J.; Choi, K.K.; Bethea, C.G.; Kleinman, D.A.;Vandenberg, J.M. Appl. Phys. Lett. 1987, 50, 273.3. Rosencher, E.; Bois, P.; Nagle, J.; Costard, E.; Delaitre, S. Appl. Phys. LettCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
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Copyright 2004 by Marcel Dekker, In
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This book covers several topics of
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esult, some exciting topics were no
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3. Fine Structure and Polarization
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9. III-V Quantum Dots and Quantum D
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ContributorsUri BaninThe Hebrew Uni
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1‘‘Soft’’ Chemical Synthesi
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structure of energy states leads to
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growth can proceed by Ostwald ripen
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Figure 3 Transmission electron micr
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Figure 4 Temporal evolution of the
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No. 26, are f85% (Fig. 6) [21]. Alt
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tion spectra and broad PL spectra.
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ing surface-to-volume ratio with di
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Figure 8 Photoluminescence spectra
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lattice mismatch. Such a large latt
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match between InAs and ZnS of f11%.
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successfully repeated for up to thr
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Under a different growth regime, on
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Figure 14 Atomic model of the CdSe
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‘‘Teardrop-shaped’’ particl
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Figure 17 High-resolution TEMs of C
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allows isolation of tetrapods in f8
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ligand concentrations yield a reduc
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een determined and quantitatively c
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tion volumes were also shown to be
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synthesis temperatures of z400jC ar
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Figure 23 (a) Photoluminescence spe
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levels (fV1 Mn per NQD). Despite in
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Figure 25 X-ray diffraction pattern
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Figure 27 Transmission electron mic
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An additional factor that strongly
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Figure 30 (a,b) Schematics illustra
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Slow, controlled precipitation of h
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Figure 34 Schematic illustrating th
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achieving biological compatibility
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47. Yu H.; Gibbons P.C.; Kelton K.F
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2Electronic Structure inSemiconduct
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Figure 2 (a) Simple model of a nano
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electron and hole to be treated as
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independently, Eq. (13) is commonly
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a better description of the bulk ba
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investigated. For optical experimen
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Figure 4 (a) Absorption (solid line
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Figure 6 Normalized PLE scans for s
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Figure 8 A simplistic model for des
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Figure 10 Theoretically predicted p
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Figure 12 Schematics depicting the
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Figure 14 Calculated band-edge exci
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Figure 15 Absorption (solid line) a
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Figure 18 (a) Calculated band-edge
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IV.BEYOND CdSeA. Indium Arsenide Na
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the six-band Luttinger Hamiltonian.
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11. Norris, D.J.; Efros, Al.L.; Ros
Page 119 and 120: 69. Gaponenko, S.V.; Woggon, U.; Sa
Page 121 and 122: formation of a long-lived dark exci
Page 123 and 124: where the constant A is determined
Page 125 and 126: In crystals for which the function
Page 127 and 128: The respective wave functions areC
Page 129 and 130: passive, as was shown in Ref. 12. T
Page 131 and 132: square of the matrix element of the
Page 133 and 134: where e F = e F ieV and e F F = e x
Page 135 and 136: see that for all nanocrystal shapes
Page 137 and 138: optical recombination of the excito
Page 139 and 140: B. Recombination of the Dark Excito
Page 141 and 142: where x = cos h and f = l B g e H/3
Page 143 and 144: The theory of the polarization memo
Page 145 and 146: Figure 7 The size dependence of the
Page 147 and 148: state would have an infinite lifeti
Page 149 and 150: crystal axis [see Eq. (40)]. As a r
Page 151 and 152: time of the exciton momentum relaxa
Page 153 and 154: One must also account for the influ
Page 155 and 156: observed in one of the first studie
Page 157 and 158: REFERENCES1. Bawendi, M.G.; Wilson,
Page 159 and 160: 4Intraband Spectroscopyand Dynamics
Page 161 and 162: The solid line in Fig. 1 shows the
Page 163 and 164: Figure 2 FTIR spectra of n-type CdS
Page 165 and 166: of the center frequency. The experi
Page 167 and 168: limit given by radiative relaxation
Page 169: from a long lifetime due to the pho
Page 173 and 174: 32. Inoshita, T.; Sakaki, H. Physic
Page 175 and 176: continuous spectral tunability over
Page 177 and 178: function and envelope function mome
Page 179 and 180: ottleneck’’ [14,28]. Further re
Page 181 and 182: in NQDs is dominated by nonphonon e
Page 183 and 184: Figure 4 Dynamics of the IR postpum
Page 185 and 186: Figure 5 (a) Time-resolved PL spect
Page 187 and 188: Figure 6 (a) The time delay of the
Page 189 and 190: and due to Auger-type e-h interacti
Page 191 and 192: Figure 9 Dynamics of the 1S bleachi
Page 193 and 194: significantly greater than the fast
Page 195 and 196: Figure 11 (a) Pump-intensity-depend
Page 197 and 198: NQD size. For small NQD sizes (R =
Page 199 and 200: Figure 14 Nonlinear absorption/gain
Page 201 and 202: sorption change associated with a s
Page 203 and 204: where n h em is the hole ‘‘emit
Page 205 and 206: ultrafast (subpicosecond to picosec
Page 207 and 208: Figure 18 Schematic of transitions
Page 209 and 210: Figure 19 Dynamics of pump-induced
Page 211 and 212: where n i (i=1, 2 . . . , N ) is th
Page 213 and 214: Figure 21 (a) Two-e-h-pair (biexcit
Page 215 and 216: the volume fraction (filling factor
Page 217 and 218: intensity dependence of this peak (
Page 219 and 220: Copyright 2004 by Marcel Dekker, In
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can contribute to the saturation of
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coupling between ‘‘volume’’
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numerous discussions on the photoph
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53. Kang, K.; Kepner, A.; Gaponenko
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the ‘‘on-off ’’ emission in
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parallel form of data acquisition i
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Figure 3 (a) Spectral time trace of
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transition energies. In fact, these
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distribution (dark line) does not d
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exposure to only room light. In our
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statistics for the off times are in
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230Shimizu and BawendiCopyright 200
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Figure 10 (a) Time trace of a CdSe(
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and excited QD core states to fluct
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arrows indicate the on-time truncat
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W. K. Woo and V. C. Sundar for assi
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size allows the electron affinity a
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II.THEORY OF ELECTRON TRANSFER BETW
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For the specific case of charge tra
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dominates, the mobility is often fi
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where the constant A and the temper
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components of modulation which are
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nanocrystals [41], understanding ph
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and ionization potential through tw
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quantum dots. Furthermore, because
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For many applications, a host mater
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form blends with morphologies that
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Figure 11 Photoluminescence efficie
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Figure 12 (a) Room-temperature PIA
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discussed briefly in Section IV. Ch
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dithiolates to thiol-terminated DNA
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Films of passivated CdSe nanocrysta
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Figure 16 Photocurrent action spect
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decay with stretched exponential ki
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siderably larger than might be esti
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dispersing CdSe nanocrystal chromop
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memory and charge storage effects [
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all) of the optically excited elect
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composites of nanocrystals and conj
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55. Asbury, J.B.; Hao, E.C.; Wang,
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108. Morgan, N.Y.; Leatherdale, C.A
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The approaches to fabrication of se
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Figure 1 Experimental realization o
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Due to this voltage division, the m
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Figure 3 Simulated tunneling spectr
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electron charging. In both positive
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Figure 5 shows the typical features
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Figure 7 Map of levels for InAs nan
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Figure 8 Scanning electron microsco
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D CB = 0.31 eV is thus obtained. On
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Figure 11 Correlation of optical an
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atomistic approach based on pseudop
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charging indicated that the tunneli
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capacitance values were also kept t
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could not be detected in the QD/DT/
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Figure 18 Tunneling conductanceF sp
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data in the inset of Fig. 19 repres
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corresponding to the s-like wave fu
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7. Grabert, H.; Devoret, M.H., Eds.
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66. Su, B.; Goldman, V.J.; Cunningh
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dimensional confinement are created
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Figure 1 Transmission electron micr
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The room-temperature absorption and
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narrower in samples with larger mea
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GaInP 2 QDs from a plot of the squa
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crystal, indicating lattice-matched
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Figure 5 Evolution of Stranski-Kras
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C. Efficient Anti-Stokes Photolumin
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Because HF treatment has been shown
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intensity of the PL when it is on a
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eV stems from recombining carriers
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Figure 16 Model to explain two-colo
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although this term is not rigorousl
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10 ps (about an order of magnitude
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electron relaxation is inhibited an
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QDs, the nature of the QD capping s
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QD solution. For an interdot distan
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emission spectra of the two individ
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Figure 23 Change of the PL intensit
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(viz. the absorbed light intensity)
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Figure 25Impact ionization in QDs.m
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prevent electron-hole recombination
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36. Miller, R.D.J.; McLendon, G.; N
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91. Vurgaftman, I.; Singh, J. Appl.
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139. Mićić, O.I.; Ahrenkiel, S.P.
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10Synthesis and Fabrication of Meta
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Figure 2 (A-C) Progression of HR-TE
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Figure 3 Schematic for gold nanocry
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Nanocrystal growth can occur by two
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on the other hand, provide an ensem
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Figure 6 (a) SAXS patterns for disp
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Figure 8 The gold nanocrystal film
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of the stabilizing ligand, and the
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successfully modeled the 2D island
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2. Steric Stabilization and a Soft
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are fully extended. Moving away fro
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Figure 11 High-resolution SEM image
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Figure 13 (A) Transmission electron
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function of the density of localize
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Figure 15 High-resolution SEM image
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thiol-capped nanocrystals [2]. The
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41. Ackerson, B.J. Nature 1993, 365
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with the effect of the particle com
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Figure 1a shows the surface plasmon
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Figure 2 (a) Ultraviolet-visible ab
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agents [34]. The short-wavelength b
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Figure 4 (a) Plot of the plasmon ab
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the framework of traditional Mie’
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show that effects due to the surrou
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is located at the position of the g
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Figure 8 Ultraviolet-visible absorp
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laser pulses while being mixed in t
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Figure 10 shows HR-TEM images of go
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final irradiation product. At the s
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following the laser excitation appe
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36. Papavassiliou, G.C. Prog. Solid
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particles to expand. Because the he
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was frequency doubled in a 1-mm B-
Page 471 and 472:
Figure 2 Frequency of the acoustic
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Figure 3 Change in radius (DR/R) ve
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In this model, the electrons couple
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Figure 5 Transient bleach data for
Page 479 and 480:
Figure 7 (a) Transient bleach data
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that the particles with >80% Au hav
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3. Del Fatti, N.; Valle´e, F.; Fly
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