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ferent samples while keeping the same overall experimental time. We calculateaverage on times of 312, 283, and 256 ms for the same CdSe/ZnS sample under10 K and 175 W/cm 2 , 10 K and 700 W/cm 2 and RT and 175 W/cm 2 excitationintensity, respectively. The effective truncation times (1.5, 4.6, and 71 s, respectively)can be extrapolated by determining the end point within thepower-law distribution that corresponds to the measured average on time.In Figs. 9c and 9d, the vertical lines correspond to this calculated averagetruncation point, indicating the crossover in the time domain from oneblinking mechanism to the other.Furthermore, we can understand the consequence of this secondarymechanism in terms of single-QD quantum efficiency. For ensemble systems,quantum efficiency is defined as the rate of photons emitted versus the photonsabsorbed. Figure 10a shows the changes to the single-QD time tracewith increasing excitation intensity: The intensity values at peak heightsincrease linearly with excitation power, but the frequency of the on–offtransitions also increases. Moreover, the measured time-averaged single-QD emission photon flux at different excitation intensities, marked by emptytriangles in Fig. 10b, clearly shows a saturation effect. This saturationbehavior is due to the secondary blinking-off process shown in Fig. 9. Thefilled triangles in Fig. 10b plot the expected time-averaged emitted photonflux at different excitation intensities calculated from a power-law blinkingdistribution and truncation values similar to those in Fig. 9. The similarity ofthe two saturation plots (triangles) in Fig. 10b demonstrates the significanceof the secondary mechanism to the overall fluorescence of the QD system.The filled circles represent the peak intensity of the single QD at each of theexcitation intensities.Modification of the surface morphology or excitation intensity showedno difference in the statistical nature of the off times or blinking-on process.The statistical data are consistent with previous work [12,22]; however, theseparation of the power-law statistics from truncation effects clearly demon-Figure 9 (a) Three single-QD on-time probability distributions at 10 K, 700 W/cm 2 . The arrows indicate the truncation point for the probability distribution foreach QD. (b) Four single-QD on-time probability distributions for CdSe(ZnS) QDsat RT, 100 W/cm 2 . (c) Average on-time probability distribution for 25-Å-radiusCdSe(ZnS) QD at 300 K and 175 W/cm 2 (E), 10 K and 700 W/cm 2 (5), and 10 Kand 175 W/cm 2 (n). The straight line is a best-fit line with exponent f 1.6. (d)Average on-time probability distribution for 15-Å-radius CdSe(ZnS) QD (E), 25-A˚ -radius CdSe(ZnS) QD (5) and 25-A˚ -radius CdSe QD (x) at RT, 100 W/cm 2 . Thestraight line here is a guide for the eye. The vertical lines correspond to truncationpoints where the power-law behavior is estimated to end.Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
Figure 10 (a) Time trace of a CdSe(ZnS) QD with increasing excitation intensity in30-s stages. Inset shows that the on–off nature still holds at high excitation intensity.(b) The emitted photon flux at the peak emission intensity (.) and average emissionintensity (4) from the time trace in (a). The average emitted photon flux calculatedfrom power-law histograms (E). More details given in text.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
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
Page 221 and 222: can contribute to the saturation of
Page 223 and 224: Copyright 2004 by Marcel Dekker, In
Page 225 and 226: coupling between ‘‘volume’’
Page 227 and 228: numerous discussions on the photoph
Page 229 and 230: 53. Kang, K.; Kepner, A.; Gaponenko
Page 231 and 232: the ‘‘on-off ’’ emission in
Page 233 and 234: parallel form of data acquisition i
Page 235 and 236: Figure 3 (a) Spectral time trace of
Page 237 and 238: transition energies. In fact, these
Page 239 and 240: distribution (dark line) does not d
Page 241 and 242: exposure to only room light. In our
Page 243 and 244: statistics for the off times are in
Page 245: 230Shimizu and BawendiCopyright 200
Page 249 and 250: and excited QD core states to fluct
Page 251 and 252: arrows indicate the on-time truncat
Page 253 and 254: W. K. Woo and V. C. Sundar for assi
Page 255 and 256: size allows the electron affinity a
Page 257 and 258: II.THEORY OF ELECTRON TRANSFER BETW
Page 259 and 260: For the specific case of charge tra
Page 261 and 262: dominates, the mobility is often fi
Page 263 and 264: where the constant A and the temper
Page 265 and 266: components of modulation which are
Page 267 and 268: nanocrystals [41], understanding ph
Page 269 and 270: and ionization potential through tw
Page 271 and 272: quantum dots. Furthermore, because
Page 273 and 274: For many applications, a host mater
Page 275 and 276: form blends with morphologies that
Page 277 and 278: Figure 11 Photoluminescence efficie
Page 279 and 280: Figure 12 (a) Room-temperature PIA
Page 281 and 282: discussed briefly in Section IV. Ch
Page 283 and 284: dithiolates to thiol-terminated DNA
Page 285 and 286: Films of passivated CdSe nanocrysta
Page 287 and 288: Figure 16 Photocurrent action spect
Page 289 and 290: decay with stretched exponential ki
Page 291 and 292: siderably larger than might be esti
Page 293 and 294: dispersing CdSe nanocrystal chromop
Page 295 and 296: 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-
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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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