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

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successfully repeated for up to three layers of well material. The ‘‘well’’ is thencapped with a redeposited layer of core metal ions to generate the full QD/QW structure. The thickness of the cladding layer could be increased byaddition in several steps (up to five) of the metal and sulfur precursors [35].The nature of the QD/QW structure and its crystalline quality havebeen analyzed by HR TEM. In the CdS(HgS)CdS system, evidence has beenpresented for both approximately spherical particles, as well as facetedparticle shapes such as tetrahedrons and twinned tetrahedrons. In all cases,well and cladding growth is epitaxial, as evidenced by the absence of amorphousregions in the nanocrystals and in the smooth continuation of latticefringes across particles. Analysis of HR TEM micrographs also reveals thatFigure 12 High-resolution TEM study of the structural evolution of a CdS coreparticle to a (CdS)(core)shell particle to the final CdS(HgS)CdS nanostructure. (a1)Molecular model showing that all surfaces are cadmium terminated (111); (a2) TEMof a CdS core that exhibits tetrahedral morphology; (a3) TEM simulation agreeingwith (a2) micrograph. (b) Model of the CdS particle after surface modification withHg. (c1) Model of a tetrahedral CdS(HgS)CdS nanocrystal; (c2) a typical TEM of atetrahedral CdS(HgS)CdS nanocrystal. (d1) Model of a CdS(HgS)CdS nanocrystalafter twinned epitaxial growth, where the arrow indicates the interfacial layerexhibiting increased contrast due to the presence of HgS; (d2) TEM of a CdS(HgS)CdS nanocrystal after twinned epitaxial growth; (d3) simulation agreeing withmodel (d1) and TEM (d2) showing increased contrast due to presence of HgS; (d4)simulation assuming all Hg is replaced by Cd—no contrast is evident. (From Ref. 36,reprinted with permission.)Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
the tetrahedral shapes are terminated by (111) surfaces that can be eithercadmium or sulfur faces [36]. The choice of stabilizing agent—an anionicpolyphosphate ligand—favors cadmium faces and likely supports the facetedtetrahedral structure that exposes exclusively cadmium-dominated surfaces(Fig. 12). In addition, both the spherical particles and the twinned tetrahedralparticles provide evidence for an embedded HgS layer in the presumed QD/QW structure. Due to differences in their relative abilities to interact withelectrons (HgS more strongly than CdS), contrast differences are evident inHR TEM images as bands of HgS surrounded by layers of CdS (Fig. 12).Size dispersions in these low-temperature, ionic-ligand-stabilized reactionsare reasonably good (f20%), as indicated by absorption spectra, butpoor compared to those achieved using higher-temperature pyrolysis andamphiphilic coordinating ligands (4–7%). Nevertheless, the polar-solventbasedreactions give us access to colloidal materials, such as mercurychalcogenides, thus far difficult to prepare using pyrolysis-driven reactions(Sect. II). Further, the ion-exchange method provides the ability to grow welland shell structures that appear to be precisely one, two, or three monolayersdeep. Heterogeneous nucleation provides less control over shell thicknesses,resulting in incomplete and variable multilayers (e.g., 1.3 or 2.7 monolayerson average, etc.). The stability of core–shell materials against solid-statealloying is an issue, at least for the CdS(HgS)CdS system. Specifically, cadmiumin a CdS–HgS structure will, within minutes, diffuse to the surface ofthe nanoparticle, where it is subsequently replaced by a Hg 2+ solvated ion[35]. This process is likely supported by the substantially greater aqueoussolubility of Cd 2+ compared to Hg 2+ , as well as the structural compatibilitybetween the two lattice-matched CdS and HgS crystal structures.IV.SHAPE CONTROLThe nanoparticle growth process described in Section II, where fast nucleationis followed by slower growth, leads to the formation of spherical orapproximately spherical particles. Such essentially isotropic particles representthe thermodynamic, lowest-energy shape for materials having relativelyisotropic underlying crystal structures. For example, under this growthregime, the wurtzite crystal structure of CdSe, having a c/a ratio of f1.6,fosters the growth of slightly prolate particles, typically exhibiting aspectratios of f1.2. Furthermore, even for materials whose underlying crystalstructure is more highly anisotropic, nearly spherical nanoparticles typicallyresult due to the strong influence of the surface in the nano-size regime. Surfaceenergy is minimized in spherical particles, compared to more anisotropicmorphologies.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 26 and 27: Figure 4 Temporal evolution of the
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 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
Page 76 and 77: Figure 36 Transmission electron mic
Page 78 and 79: achieving biological compatibility
Page 80 and 81: 47. Yu H.; Gibbons P.C.; Kelton K.F
Page 82 and 83: 2Electronic Structure inSemiconduct
Page 84 and 85: Figure 2 (a) Simple model of a nano
Page 88 and 89: electron and hole to be treated as
Page 90 and 91:
independently, Eq. (13) is commonly
Page 92:
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 (
Page 219 and 220:
Copyright 2004 by Marcel Dekker, In
Page 221 and 222:
can contribute to the saturation of
Page 223 and 224:
Page 225 and 226:
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
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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,
Page 303 and 304:
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
Page 323 and 324:
Figure 11 Correlation of optical an
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atomistic approach based on pseudop
Page 327 and 328:
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
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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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Figure 18 Transmission electron mic
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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
Page 389 and 390:
(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
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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
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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
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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’
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:
Figure 11 Transmission electron mic
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
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In this model, the electrons couple
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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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