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Figure 4 Temporal evolution of the full width at half-maximum (FWHM) of thePL band, the PL QY, and the PL peak position for identical reactions differing onlywith respect to their initial Cd : Se precursor ratios (see top graphs). (From Ref. 18,reprinted with permission.)emitting in the orange-red. However, high-QY NQDs representing a varietyof particle sizes are possible. By controlling precursor identity, total precursorconcentrations, the identity of the solvent system, the nucleation and growthtemperatures, and the growth time, NQDs emitting with >30% efficiencyfrom f510 to 650 nm can be prepared [18]. Finally, the important influence ofthe primary amine ligands may result from their ability to pack moreefficiently on the NQD surfaces. Compared to TOPO and TOP, primaryamines are less sterically hindered and may simply allow for a higher cappingdensity [19]. However, the amine–CdSe NQD linkage is not as stable as forother more strongly bound CdSe ligands [20]. Thus, growth solutionsprepared from this procedure are highly luminescent, but washing or processinginto a new liquid or solid matrix can dramatically impact the QY.Multidentate amines may provide both the desired high PL efficiencies andthe necessary chemical stabilities [18].High-quality NQDs are no longer limited to cadmium-based II–VIcompounds. Preparations for III–V semiconductor NQDs are well developedand are discussed in Chapter 9. Exclusively band-edge ultraviolet (UV) toblue-emitting ZnSe NQDs (j = 10%) exhibiting QYs from 20% to 50% havebeen prepared by pyrolysis of diethylzinc and TOPSe at high temperatures(nucleation: 310jC; growth: 270jC). Successful reactions employed hexadecylamine(HDA)–TOP as the solvent system (elemental analysis indicatingthat bound surface ligands comprised two-thirds HDA and one-third TOP),whereas the TOPO–TOP combination did not work for this material. Indeed,the nature of the reaction product was very sensitive to the TOPO/TOP ratio.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
Too much TOPO, which binds strongly to Zn, generated particles so smallthat they could not be precipitated from solution by the addition of a nonsolvent.Too much TOP, which binds very weakly to Zn, yielded particlesthat formed insoluble aggregates. As somewhat weaker bases compared tophosphine oxides, primary amines constitute as ligands of intermediatestrength and in addition may provide enhanced capping density (as discussedearlier) [19]. HDA, in contrast with shorter-chain primary amines (octylamineand dodecylamine), provided good solubility properties and permitted sufficientlyhigh growth temperatures for reasonably rapid growth of highly crystallineZnSe NQDs [19].High-quality NQDs absorbing and emitting in the infrared have alsobeen prepared by way of a surfactant-stabilized pyrolysis reaction. PbSecolloidal quantum dots can be synthesized from the precursors: lead oleate-{prepared in situ from lead(II) acetate trihydrate and oleic acid [21]} andTOPSe [10,21]. TOP and oleic acid are present as the coordinating solvents,whereas phenyl ether, a noncoordinating solvent, provides the balance of thereaction solution. Injection and growth temperatures were varied (injection:180–210jC; growth: 110–130jC) to control particle size from f3.5 to f9 nmin diameter [21]. The particles respond to ‘‘traditional’’ size-selection precipitationmethods, allowing the narrow as-prepared size dispersions (j V 10%)to be further refined (j = 5%) (Fig. 5) [10]. Oleic acid provides excellentcapping properties as PL quantum efficiencies, relative to infrared (IR) dyeFigure 5 (a) High-resolution TEM of PbSe NQDs, where the internal crystal latticeis evident for several of the particles. (b) Lower-magnification imaging revealsthe nearly uniform size and shape of the PbSe NQDs. (From Ref. 10, reprinted withpermission.)Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
Page 1: Copyright 2004 by Marcel Dekker, In
Page 4 and 5: Copyright 2004 by Marcel Dekker, In
Page 6 and 7: Copyright 2004 by Marcel Dekker, In
Page 8 and 9: This book covers several topics of
Page 10 and 11: esult, some exciting topics were no
Page 12 and 13: 3. Fine Structure and Polarization
Page 14 and 15: 9. III-V Quantum Dots and Quantum D
Page 16 and 17: ContributorsUri BaninThe Hebrew Uni
Page 18 and 19: 1‘‘Soft’’ Chemical Synthesi
Page 20 and 21: structure of energy states leads to
Page 22 and 23: growth can proceed by Ostwald ripen
Page 24 and 25: Figure 3 Transmission electron micr
Page 28 and 29: No. 26, are f85% (Fig. 6) [21]. Alt
Page 30 and 31: tion spectra and broad PL spectra.
Page 32 and 33: ing surface-to-volume ratio with di
Page 34 and 35: Figure 8 Photoluminescence spectra
Page 36 and 37: lattice mismatch. Such a large latt
Page 38 and 39: match between InAs and ZnS of f11%.
Page 40 and 41: successfully repeated for up to thr
Page 42 and 43: Under a different growth regime, on
Page 44 and 45: Figure 14 Atomic model of the CdSe
Page 46 and 47: ‘‘Teardrop-shaped’’ particl
Page 48 and 49: Figure 17 High-resolution TEMs of C
Page 50 and 51: allows isolation of tetrapods in f8
Page 52 and 53: ligand concentrations yield a reduc
Page 54 and 55: een determined and quantitatively c
Page 56 and 57: tion volumes were also shown to be
Page 58 and 59: synthesis temperatures of z400jC ar
Page 60 and 61: Figure 23 (a) Photoluminescence spe
Page 62 and 63: levels (fV1 Mn per NQD). Despite in
Page 64 and 65: Figure 25 X-ray diffraction pattern
Page 66 and 67: Figure 27 Transmission electron mic
Page 68 and 69: An additional factor that strongly
Page 70 and 71: Figure 30 (a,b) Schematics illustra
Page 72 and 73: Slow, controlled precipitation of h
Page 74 and 75: Figure 34 Schematic illustrating th
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Figure 36 Transmission electron mic
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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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Copyright 2004 by Marcel Dekker, In
Page 221 and 222:
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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Figure 7 Photoluminescence spectra
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Figure 8 Photoluminescence spectra
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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-
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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
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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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