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This book covers several topics of recent, intense interest in the area ofnanocrystals: synthesis and assembly, theory, spectroscopy of interband andintraband optical transitions, single-nanocrystal optical and tunneling spectroscopy,transport properties, and nanocrystal applications. It is written byexperts who have contributed pioneering research in the nanocrystal field andwhose work has led to numerous, impressive advances in this area over thepast several years.This book is organized into two parts: Semiconductor Nanocrystals(Nanocrystal Quantum Dots) and Metal Nanocrystals. The first part beginswith a review of progress in the synthesis and manipulation of colloidalsemiconductor nanoparticles. The topics covered in this first chapter byHollingsworth and Klimov include size and shape control, surface modification,doping, phase control, and assembly of nanocrystals of such compositionsas CdSe, CdS, PbSe, HgTe, and so forth. The second chapter, byNorris, overviews results of spectroscopic studies of the interband (valenceto-conductionband) transitions in semiconductor nanoparticles with a focuson CdSe nanocrystals. Because of a highly developed fabrication technology,these nanocrystals have long been model systems for studies on the effects ofthree-dimensional quantum confinement in semiconductors. As described inthis chapter, the analysis of absorption and emission spectra of CdSe nanocrystalsled to the discovery of a ‘‘dark’’ exciton, a fine structure of band-edgeoptical transitions, and the size-dependent mixing of valence-band states. Thistopic of electronic structures and optical transitions in CdSe nanocrystals iscontinued in Chapter 3 by Efros. This chapter focuses on the theoretical descriptionof electronic states in CdSe nanoparticles using the effective massapproach. Specifically, it reviews the ‘‘dark/bright’’ exciton model and itsapplication for explaining the fine structure of resonantly excited photoluminescence,polarization properties of spherical and ellipsoidal nanocrystals,polarization memory effects, and magneto-optical properties of nanocrystals.Chapter 4, by Guyot-Sionnest, Shim, and Wang, reviews studies of intrabandoptical transitions in nanocrystals performed using methods of infraredspectroscopy. It describes the size-dependent structure and dynamics of thesetransitions as well as the control of intraband absorption using charge carrierinjection. In Chapter 5, Klimov concentrates on the underlying physics ofoptical amplification and lasing in semiconductor nanocrystals. The chapterprovides a description of the concept of optical amplification in ‘‘ultrasmall,’’sub-10-nm particles, discusses the difficulties associated with achieving theoptical gain regime, and gives several examples of recently demonstratedlasing devices based on CdSe nanocrystals. Chapter 6, by Shimizu and Bawendi,overviews the results of single-nanocrystal (single-dot) emissionstudies with focus on CdSe nanoparticles. It discusses such phenomena asspectral diffusion and fluorescence intermittency (‘‘blinking’’). The studies ofCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
these effects provide important insights into the dynamics of charge carriersin a single nanoparticle and interactions between the nanocrystal internal andinterface states. The focus in Chapter 7, written by Ginger and Greenham,switches from spectroscopic to electrical and transport properties of semiconductornanocrystals. This chapter surveys studies of carrier injection intonanocrystals and carrier transport in nanocrystal assemblies and betweennanocrystals and organic molecules. It also describes the potential applicationsof these phenomena in electronic and optoelectronic devices. In Chapter8, Banin and Millo review the work on tunneling and optical spectroscopy ofcolloidal InAs nanocrystals. Single-electron tunneling experiments discussedin this chapter provide unique information on electronic states and the spatialdistribution of electronic wave functions in a single nanoparticle. These dataare further compared with results of more traditional optical spectroscopicstudies. Nozik and Mic´ic´ provide a comprehensive overview of the synthesis,structural, and optical properties of semiconductor nanocrystals of III–Vcompounds (InP, GaP, GaInP 2 , GaAs, and GaN) in Chapter 9. This chapterdiscusses such unique properties of nanocrystals and nanocrystal assembliesas efficient anti-Stokes photoluminescence, photoluminescence intermittency,anomalies between the absorption and the photoluminescence excitationspectra, and long-range energy transfer. Furthermore, it reviews photogeneratedcarrier dynamics in nanocrystals, including the issues and controversiesrelated to the cooling of hot carriers in ‘‘ultrasmall’’ nanoparticles. Finally, itdiscusses the potential applications of nanocrystals in novel photon conversiondevices, such as quantum-dot solar cells and photoelectrochemicalsystems for fuel production and photocatalysis.The next three chapters, which comprise Part II of this book, examinetopics dealing with the chemistry and physics of metal nanoparticles. InChapter 10, Doty et al. describe methods for fabricating metal nanocrystalsand manipulating them into extended arrays (superlattices). They also discussmicrostructural characterization and some physical properties of these metalnanoassemblies, such as electron transport. Chapter 11, by Link and El-Sayed, reviews the size/shape-dependent optical properties of gold nanoparticleswith a focus on the physics of the surface plasmons that leads to theseinteresting properties. In this chapter, the issues of plasmon relaxation andnanoparticle shape transformation indued by intense laser illumination arealso discussed. A review of some recent studies on the ultrafast spectroscopyof mono-component and bicomponent metal nanocrystals is presented inChapter 12 by Hartland. These studies provide important information ontimescales and mechanisms for electron–phonon coupling in nanoscale metalparticles.Of course, the collection of chapters that comprises this book cannotencompass all areas in the rapidly evolving science of nanocrystals. As aCopyright 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 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 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
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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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Copyright 2004 by Marcel Dekker, In
Page 221 and 222:
can contribute to the saturation of
Page 223 and 224:
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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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