Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

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D. Dark-Exciton Lifetime in a Magnetic FieldStrong evidence for the dark-exciton state is provided by fluorescence linenarrowing(FLN) experiments as well as by studies of the luminescence decayin external magnetic fields. In Fig. 8a, we show the magnetic field dependenceof the FLN spectra between 0 and 10 T for 12-A˚ -radius dots. Each spectrum isnormalized to the zero-field, one-phonon line for clarity. In isolation, the F2Figure 8 (a) The FLN spectra for 12-A˚ -radius dots as a function of an externalmagnetic field. The spectra are normalized to their one-phonon line (1PL). A smallfraction of the excitation laser, which is included for reference, appears as the sharpfeature at 2.467 eV to the blue of the ZPL; (b) luminescence decays for 12-Å-radiusdots for magnetic fields between 0 and 10 T measured at the peak of the ‘‘full’’luminescence (2.436 eV) and a pump energy of 2.736 eV. All experiments were done inthe Faraday configuration (H || k); (c) observed luminescence decays for 12-A˚ -radiusdots at 0 and 10 T; (d) calculated decays based on the three-level model described inthe text. Three weighted three-level systems were used to simulate the decay at zerofield with different values of c 2 (0.033, 0.0033, 0.00056 ns 1 ) and weighting factors (1,3.8, 15.3). c 1 (0.1 ns 1 ) and g th (0.026 ps 1 ) were held fixed in all three systems.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
state would have an infinite lifetime within the electric-dipole approximation,because the emitted photon cannot carry an angular momentum of 2. However,the dark exciton can recombine via LO-phonon-assisted, momentumconservingtransitions [39]. Spherical LO phonons with orbital angularmomenta of 1 or 2 are expected to participate in these transitions; the selectionrules are determined by the coupling mechanism [12,22]. Consequently, forzero field, the LO phonon replicas are strongly enhanced relative to the ZPL.With increasing magnetic field, however, the F2 level gains an optically activeF1 character [Eq. (42)], diminishing the need for the LO-phonon-assistedrecombination in dots for which the hexagonal axis is not parallel to themagnetic field. This explains the dramatic increase in the ZPL intensityrelative to LO phonon replicas with increasing magnetic field.The magnetic-field-induced admixture of the optically active F1 statesalso shortens the exciton radiative lifetime. Luminescence decays for 12-A˚ -radius NCs between 0 and 10 T at 1.7 K are shown in Fig. 8b. The sample wasexcited far to the blue of the first absorption maximum to avoid orientationalselection in the excitation process. Excitons rapidly thermalize to the groundstate through acoustic and optical phonon emission. The long microsecondluminescence at zero field is consistent with LO-phonon-assisted recombinationfrom this ground state. Although the light emission occurs primarilyfrom the F2 state, the long radiative lifetime of this state allows the thermallypopulated F1 L state to contribute to the luminescence also.With increasing magnetic field, the luminescence lifetime decreases;because the quantum yield remains essentially constant, we intepret this resultas due to an enhancement of the relative rate. The magnetic field dependenceof the luminescence decays can be reproduced using three-level kinetics withF1 L and F2 emitting states [2]. The respective radiative rates from thesestates, G 1 (h H , H ) and G 2 (h H , H ), in a particular NC, depend on the angle h Hbetween the magnetic field and the crystal hexagonal axis. The thermalizationrate, G th of the F1 L state to the F2 level is determined independently frompicosecond time-resolved measurements. The population of the F1 L level isdetermined by microscopic reversibility. We assume that the magnetic fieldopens an additional channel for ground-state recombination via admixture inthe F2 state of the F1 states: G 2 (h H , H ) = G 2 (0, 0) + 1/s 2 (h H , H ). This alsocauses a slight decrease in the recombination rate of the F1 L state.The decay at zero field is multiexponential, presumably due to sampleinhomogeneities (e.g., in shape and symmetry-breaking impurity contaminations).We describe the decay using three three-level systems, each having adifferent value of G 2 (0, 0) and each representing a class of dots within theinhomogeneous distribution. These three-level systems are then weighted toreproduce the zero field decay (Fig. 8c). We obtain average values of 1/G 2 (0, 0)= 1.42 ls and 1/G 1 (0, 0) = 10.0 ns. The latter value is in a good agreementCopyright 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
Page 95 and 96: investigated. For optical experimen
Page 97 and 98: Figure 4 (a) Absorption (solid line
Page 99 and 100: Figure 6 Normalized PLE scans for s
Page 101 and 102: Figure 8 A simplistic model for des
Page 103 and 104: Figure 10 Theoretically predicted p
Page 105 and 106: Figure 12 Schematics depicting the
Page 107 and 108: Figure 14 Calculated band-edge exci
Page 109 and 110: Figure 15 Absorption (solid line) a
Page 111 and 112: Figure 18 (a) Calculated band-edge
Page 113 and 114: IV.BEYOND CdSeA. Indium Arsenide Na
Page 115 and 116: the six-band Luttinger Hamiltonian.
Page 117 and 118: 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: Figure 7 The size dependence of the
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 and 170: from a long lifetime due to the pho
Page 171 and 172: are two natural approaches to study
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
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where n h em is the hole ‘‘emit
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ultrafast (subpicosecond to picosec
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Figure 18 Schematic of transitions
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Figure 19 Dynamics of pump-induced
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where n i (i=1, 2 . . . , N ) is th
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Figure 21 (a) Two-e-h-pair (biexcit
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the volume fraction (filling factor
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intensity dependence of this peak (
Page 219 and 220:
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can contribute to the saturation of
Page 223 and 224:
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coupling between ‘‘volume’’
Page 227 and 228:
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
Page 263 and 264:
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
Page 307 and 308:
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/
Page 333 and 334:
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
Page 345 and 346:
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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Page 359 and 360:
Page 361 and 362:
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
Page 379 and 380:
Page 381 and 382:
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
Page 387 and 388:
Figure 23 Change of the PL intensit
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(viz. the absorbed light intensity)
Page 391 and 392:
Figure 25Impact ionization in QDs.m
Page 393 and 394:
prevent electron-hole recombination
Page 395 and 396:
36. Miller, R.D.J.; McLendon, G.; N
Page 397 and 398:
91. Vurgaftman, I.; Singh, J. Appl.
Page 399 and 400:
139. Mićić, O.I.; Ahrenkiel, S.P.
Page 401 and 402:
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
Page 409 and 410:
on the other hand, provide an ensem
Page 411 and 412:
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
Page 429 and 430:
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
Page 435 and 436:
with the effect of the particle com
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Figure 1a shows the surface plasmon
Page 439 and 440:
Figure 2 (a) Ultraviolet-visible ab
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agents [34]. The short-wavelength b
Page 443 and 444:
Figure 4 (a) Plot of the plasmon ab
Page 445 and 446:
the framework of traditional Mie’
Page 447 and 448:
show that effects due to the surrou
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is located at the position of the g
Page 451 and 452:
Page 453 and 454:
Figure 8 Ultraviolet-visible absorp
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laser pulses while being mixed in t
Page 457 and 458:
Figure 10 shows HR-TEM images of go
Page 459 and 460:
Page 461 and 462:
final irradiation product. At the s
Page 463 and 464:
following the laser excitation appe
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36. Papavassiliou, G.C. Prog. Solid
Page 467 and 468:
particles to expand. Because the he
Page 469 and 470:
was frequency doubled in a 1-mm B-
Page 471 and 472:
Figure 2 Frequency of the acoustic
Page 473 and 474:
Figure 3 Change in radius (DR/R) ve
Page 475 and 476:
In this model, the electrons couple
Page 477 and 478:
Figure 5 Transient bleach data for
Page 479 and 480:
Figure 7 (a) Transient bleach data
Page 481 and 482:
that the particles with >80% Au hav
Page 483 and 484:
3. Del Fatti, N.; Valle´e, F.; Fly
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