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Figure 19 Transmission electron microscopic images of close-packed 3D array of57-A˚ InP QDs showing hexagonal order. The bottom panel is at a lower magnificationand shows a monolayer step between the darker and lighter regions. (TEM by S.P.Ahrenkiel.)Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
QDs, the nature of the QD capping species, QD orientation and packingorder, uniformity of QD size distribution, and the crystallinity and perfectionof the individual QDs in the array. Several studies of electronic coupling incolloidal QD arrays have been reported [37,134–138]. In these arrays, thesemiconductor QD cores are surrounded with insulating organic ligands andcreate a large potential barrier between the QDs. Thus, the electrons andholes are confined to the QD, and very weak electronic communication existsbetween dots in such arrays. Measurements of the photoconductivity ofclose-packed films of colloidally prepared CdSe QDs [137] with diameters>20 A˚ have shown that excitons formed by illumination are confined toindividual QDs and electron transport through the array does not occur.This lack of electronic coupling between QDs is also seen from the fact thatthe absorption spectra are the same for both colloidal solutions and closepackedarrays.However, arrays with very small CdSe QDs with a mean diameter of 16A˚ show that significant electronic coupling between dots in close-packedsolids can occur [138]. Recently, InP QDs with diameters of 15–23 A˚ wereformed into arrays that also show evidence of electronic coupling [139]. Thisconclusion is based on the differences in the optical spectra of isolated colloidalQDs compared to solid films of QD arrays (see Fig. 20). For closepackedQD solids, a large red shift of the excitonic peaks in the absorptionspectrum is expected if the electron or hole wave function extends outside theboundary of the individual QDs as a result of inter-QD electronic coupling.The first indication of a difference in the absorption spectra betweencolloidal QD solutions and QD films appears for 32-A˚ InP QDs with an inter-QD spacing of 11 A˚ (QDs were capped with TOPO); a very small shift ofabout 15 meV was apparent (see Fig. 20a). Above 32 A˚ , no difference wasobserved between the spectra of QD colloidal solutions and solid films.Figures 20b and 20c show results for 18-A˚ -diameter InP QDs, where theinterdot distance was varied between 9 and 18 A˚ by varying the length of alinear alkylamine molecule that was used as the colloidal stabilizer. Thesecolloids were initially prepared in trioctylamine, which was then replaced withhexylamine (interdot distance 9 A˚ ) or oleyamine (interdot distance f18) bya ligand-exchange method. The interdot distance for the different organicligands was estimated from previous published data for close-packed arraysof nanocrystals capped with different organic ligands [140,141]. However,because hexylamine is a weak stabilizer with a relatively low boiling point,QDs may partially lose the organic ligand so that the interdot distance may beshorter.Quantum-dot arrays with an interdot spacing of 9 A˚ have an absorptionspectrum that is relatively smooth with only weak structure (Fig. 20b) andwhich shows a red shift for the first exciton of about 140 meV relative to theCopyright 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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Page 333 and 334: Figure 18 Tunneling conductanceF sp
Page 335 and 336: data in the inset of Fig. 19 repres
Page 337 and 338: corresponding to the s-like wave fu
Page 339 and 340: 7. Grabert, H.; Devoret, M.H., Eds.
Page 341 and 342: 66. Su, B.; Goldman, V.J.; Cunningh
Page 343 and 344: dimensional confinement are created
Page 345 and 346: Figure 1 Transmission electron micr
Page 347 and 348: The room-temperature absorption and
Page 349 and 350: narrower in samples with larger mea
Page 351 and 352: GaInP 2 QDs from a plot of the squa
Page 353 and 354: crystal, indicating lattice-matched
Page 355 and 356: Figure 5 Evolution of Stranski-Kras
Page 357 and 358: Figure 7 Photoluminescence spectra
Page 359 and 360: Figure 8 Photoluminescence spectra
Page 361 and 362: C. Efficient Anti-Stokes Photolumin
Page 363 and 364: Because HF treatment has been shown
Page 365 and 366: Copyright 2004 by Marcel Dekker, In
Page 367 and 368: intensity of the PL when it is on a
Page 369 and 370: eV stems from recombining carriers
Page 371 and 372: Figure 16 Model to explain two-colo
Page 373 and 374: although this term is not rigorousl
Page 375 and 376: 10 ps (about an order of magnitude
Page 377 and 378: electron relaxation is inhibited an
Page 379: Figure 18 Transmission electron mic
Page 383 and 384: QD solution. For an interdot distan
Page 385 and 386: emission spectra of the two individ
Page 387 and 388: Figure 23 Change of the PL intensit
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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
Page 403 and 404: Figure 2 (A-C) Progression of HR-TE
Page 405 and 406: Figure 3 Schematic for gold nanocry
Page 407 and 408: 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
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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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