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Figure 12 Tunneling spectra measured for InAs nanocrystals with ligands (uppercurve) and after pyridine treatment (partly removing TOP ligands). Subgap peaks,marked by the circles, appear close to the CB edge, associated with surface states.QDs and the relative intensity of the peaks increased with the surface-tovolumeratio, as shown by Alperson et al. [85].IV.JUNCTION SYMMETRY EFFECTS ON THE TUNNELINGSPECTRAA detailed understanding of the role played by the DBTJ geometry and theability to control it are essential for the correct interpretation of tunnelingcharacteristics of semiconductor QDs, as well as for their implementation inelectronic nanoarchitectures.The tunneling data presented in Section III were acquired on InAsnanocrystals linked to gold by hexane–dithiol molecules realizing a capacitivelyhighly asymmetric DBTJ (C 2 /C 1f 10). The observation of QDCopyright 2004 by Marcel Dekker, Inc. All Rights Reserved.
charging indicated that the tunneling rate G 2 ~ 1/R 2 was on the order of orsmaller than G 1 ~ 1/R 1 . Otherwise, for positive sample bias, an electrontunneling from the tip to the QD would escape to the substrate before the nextelectron could tunnel into the QD. Consequently, merely resonant tunnelingthrough the QD states without charging would take place. By varying the tip–QD distance, we were able to modify the voltage division between junctionsup to the distance that allowed us to obtain meaningful (well above the noiselevel) tunneling spectra. Bakkers and Vanmaekelbergh also reported an STMstudy of CdS and CdSe QDs, focusing on the role of voltage division [64]. Wedemonstrated that by working without linker molecules, charging-free resonanttunneling, as well as a transition back to tunneling accompanied by QDcharging can be achieved for a single QD by controlling R 2 [20].Figure 13 shows InAs nanocrystals deposited without any linker moleculesdirectly on highly oriented pyrolitic graphite (HOPG) [86]. In Fig. 14a,we plot a tunneling spectrum measured on an InAs QD, f2 nm in radius,along with a representative spectrum measured on a QD of similar radius,but anchored to a gold substrate via linker molecules, as described in theprevious section (dashed line). There is a profound difference between thesetwo spectra. In the spectrum measured in the QD/linker molecule/Au geometry,resonant tunneling accompanied by QD charging is clearly seen, as discussedearlier. In contrast, the charging multiplets are absent in the spectrummeasured in the QD/HOPG geometry, and each multiplet is replaced by asingle peak, indicating charging-free resonant tunneling through the s- andp-like CB states. Typically, the peaks observed in the QD/HOPG configurationare broadened as compared to those seen for the QD/DT/AuFigure 13 A 30-nm 30-nm STM topographic showing two single InAs QDspositioned near a monolayer step on HOPG. In this case, no linker molecules separatethe QD from the substrate, thus reducing the QD–substrate tunneling barrier.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
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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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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 [
Page 297 and 298: all) of the optically excited elect
Page 299 and 300: composites of nanocrystals and conj
Page 301 and 302: 55. Asbury, J.B.; Hao, E.C.; Wang,
Page 303 and 304: 108. Morgan, N.Y.; Leatherdale, C.A
Page 305 and 306: The approaches to fabrication of se
Page 307 and 308: Figure 1 Experimental realization o
Page 309 and 310: Due to this voltage division, the m
Page 311 and 312: Figure 3 Simulated tunneling spectr
Page 313 and 314: electron charging. In both positive
Page 315 and 316: Figure 5 shows the typical features
Page 317 and 318: Figure 7 Map of levels for InAs nan
Page 319 and 320: Figure 8 Scanning electron microsco
Page 321 and 322: D CB = 0.31 eV is thus obtained. On
Page 323 and 324: Figure 11 Correlation of optical an
Page 325: atomistic approach based on pseudop
Page 329 and 330: capacitance values were also kept t
Page 331 and 332: could not be detected in the QD/DT/
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
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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
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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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