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

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Melting into spheres having a comparable volume to the originalnanorods or partial melting (shorter and wider rods for femtosecond pulsesand ‘‘f-shaped’’ particles for nanosecond pulses) are, however, not the onlyproducts observed. When higher energy pulses are used, a fragmentation ofthe nanorods into small spheres can be observed [26,27]. Figures 11c and 11dcompare the different particle shapes obtained after fragmentation of the goldnanorods using femtosecond (Fig. 11c) and nanosecond (Fig. 11d) laserpulses. In the case of irradiation with femtosecond pulses, mostly irregularshaped nanoparticles are formed (Fig. 11c), whereas the particles are nearlyspherical after fragmentation caused by nanosecond pulses (Fig. 11d).Fragmentation with femtosecond pulses can be explained by a rapid explosionof the nanorods caused by their multiphoton ionization. The repulsion ofthe accumulated positive charges on the particles after multiphoton ionizationleads to fragmentation [27,58]. Because the initial excitation energy isreleased directly into the solvent by means of photoejected electrons, thelattice of the nanorods never becomes hot, which explains the irregularparticle shapes seen in Fig. 11c. In the case of fragmentation with nanosecondpulses (Fig. 11d), more regular spherical shapes of the fragments are observed.This was attributed to the absorption of additional photons by the hot latticewithin the nanosecond pulse duration [26,27]. Fragmentation would thereforenot necessarily lead to the total cooling of the fragmented parts, but atomicrearrangement into a more spherical shape is possible. Basically, hot particlesfragment in the case of nanosecond laser pulses.Fragmentation is not only observed for gold nanorods but also forspherical metal nanoparticles [58–63]. Irradiation of gold particles with 532nm nanosecond laser pulses was found to cause fragmentation, as reported byKoda et al. [59,60]. This was explained in terms of the slow heat release of thedeposited laser energy into the surrounding solvent, which, in turn, leads tomelting and vaporization of the nanoparticles, as estimated from the depositedlaser energy and the absorption cross section. As the nanoparticles cannotcool off as fast as they are heated, they fragment into smaller nanodots. On theother hand, in a study of silver nanoparticles that were irradiated with 355-nmpicosecond laser pulses, Kamat et al. [58] proposed that strong laser excitationcauses the ejection of photoelectrons. As the particles become positivelycharged, the repulsion between the charges then leads to fragmentation.Mafune et al. [61–63] combined the creation of gold nanoparticles by laserablation in aqueous solution with subsequent fragmentation in order toproduce size-selected gold nanoparticles. The ablation was carried out with1064-nm laser light, whereas the fragmentation was induced by 532-nm light,which was in resonance with the gold nanoparticle absorption. These examplestogether with the above-presented results demonstrate that the laser pulsewidth is an important factor that strongly influences the size and shape of theCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
final irradiation product. At the same time, these studies show the possibilitiesfor ‘‘machining’’ nanostructured materials using pulsed laser light.An interesting question is how long it takes to melt a gold nanorod. Toaddress this question, time-resolved pump-probe spectroscopy was used tomonitor the disappearance of the longitudinal surface plasmon absorption[30]. As the longitudinal surface plasmon absorption is characteristic of therodlike shape, the rise time for the permanent bleaching of this bandcorresponds to the melting time of nanorods. This experiment was carriedout in a flow cell with a large sample volume in order to assure that the overallpercentage of nanorods destroyed by laser irradiation remained small enoughthat a new probe volume contained mainly unexposed nanorods [30] (theseprecautions allowed a continuous averaging of the transient absorption). Theresults of these measurements are shown in Fig. 12 for a rod sample with anFigure 12 Transient absorption dynamics of the rod-to-sphere shape transformationrecorded at 790 nm for the excitation at 400 nm. The rise time for the permanentbleaching of the longitudinal surface plasmon band (see inset) corresponds tothe ‘‘melting’’ (transformation) time. The gold nanorods in this example had an aspectratio of 2.9.Copyright 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
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69. Gaponenko, S.V.; Woggon, U.; Sa
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formation of a long-lived dark exci
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where the constant A is determined
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In crystals for which the function
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The respective wave functions areC
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passive, as was shown in Ref. 12. T
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square of the matrix element of the
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where e F = e F ieV and e F F = e x
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see that for all nanocrystal shapes
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optical recombination of the excito
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B. Recombination of the Dark Excito
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where x = cos h and f = l B g e H/3
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The theory of the polarization memo
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Figure 7 The size dependence of the
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state would have an infinite lifeti
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crystal axis [see Eq. (40)]. As a r
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time of the exciton momentum relaxa
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One must also account for the influ
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observed in one of the first studie
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REFERENCES1. Bawendi, M.G.; Wilson,
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4Intraband Spectroscopyand Dynamics
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The solid line in Fig. 1 shows the
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Figure 2 FTIR spectra of n-type CdS
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of the center frequency. The experi
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limit given by radiative relaxation
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from a long lifetime due to the pho
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are two natural approaches to study
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32. Inoshita, T.; Sakaki, H. Physic
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continuous spectral tunability over
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function and envelope function mome
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ottleneck’’ [14,28]. Further re
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in NQDs is dominated by nonphonon e
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Figure 4 Dynamics of the IR postpum
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Figure 5 (a) Time-resolved PL spect
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Figure 6 (a) The time delay of the
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and due to Auger-type e-h interacti
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Figure 9 Dynamics of the 1S bleachi
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significantly greater than the fast
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Figure 11 (a) Pump-intensity-depend
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NQD size. For small NQD sizes (R =
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Figure 14 Nonlinear absorption/gain
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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 (
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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
Page 409 and 410: on the other hand, provide an ensem
Page 411 and 412: Figure 6 (a) SAXS patterns for disp
Page 413 and 414: Figure 8 The gold nanocrystal film
Page 415 and 416: of the stabilizing ligand, and the
Page 417 and 418: successfully modeled the 2D island
Page 419 and 420: 2. Steric Stabilization and a Soft
Page 421 and 422: are fully extended. Moving away fro
Page 423 and 424: Figure 11 High-resolution SEM image
Page 425 and 426: Figure 13 (A) Transmission electron
Page 427 and 428: function of the density of localize
Page 429 and 430: Figure 15 High-resolution SEM image
Page 431 and 432: thiol-capped nanocrystals [2]. The
Page 433 and 434: 41. Ackerson, B.J. Nature 1993, 365
Page 435 and 436: with the effect of the particle com
Page 437 and 438: Figure 1a shows the surface plasmon
Page 439 and 440: Figure 2 (a) Ultraviolet-visible ab
Page 441 and 442: 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
Page 449 and 450: is located at the position of the g
Page 451 and 452: Copyright 2004 by Marcel Dekker, In
Page 453 and 454: Figure 8 Ultraviolet-visible absorp
Page 455 and 456: laser pulses while being mixed in t
Page 457 and 458: Figure 10 shows HR-TEM images of go
Page 459: Figure 11 Transmission electron mic
Page 463 and 464: following the laser excitation appe
Page 465 and 466: 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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