~ ·The Journal of
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`EXHIBIT 1014
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`

`

`Physical Chemistry®
`
`~ ------------------------------------------------------------------------------~----------~
`Volume JOO, Number 2 January 11, 1996
`·;, R
`·siered in U.S. Parent and Trademark Office
`'·· egi
`-~ C .nvrighr 1996 by rhe American Chemical Sociecy
`JPCHAx 100(2) 441-928 (1996)
`-..:J Or.
`::•
`ISSN 0022-3654
`·Jl
`.fj.
`-'.~£
`;;~
`' ·•;-r
`~~
`;\-.
`'
`:J
`::1
`~ , Editorial
`.. _i
`<
`.~!~~
`~~,
`~ Kinetics of Alignment and Decay in a Highly Entangled Transient Threadlike Micellar Network Studied by Small-Angle
`'.~E
`·~
`P. D. Butler,* L. J . Magid, W. A. Hamilton, J.B. Hayter, B. Hammouda, and P. J. Kreke
`_:;~Orientation of Toluene and Effect of the Photochromic Fulgide. (E)-[a-(2,5-Dimethyl-3-furyl)ethylidene](dicyclopropylmethyl-
`;~.
`JI"
`.) Determination of the Structure of Distorted Ti06 Units i."l the Titanosilicate ETS-10 by a Combination of X-ray Absorption
`· ~
`Spectroscopy and Computer Modeling
`,
`·~-~ Gopinathan Sankar,* Robert G. Bell, J ohn Meurig Thomas,* l'vl:ichael W. Anderson, Panl A. Wright, and Joao Rocha
`
`Neutron Scattering
`
`LETTERS
`
`M. A. El-Sayed
`
`441
`
`442
`
`ene)-2.5-furandione at the Airffoluene Interface
`
`D. T. Cramb, S. C. Martin, and S. C. Wallace*
`
`446
`
`;z1
`·'
`s .. 409
`'o .• 409
`[95
`201
`ii., 294
`' 1t. 184
`63
`, , ~01
`i
`18
`'· 368
`1~ s .. 180
`'LJ.. 47
`'t. 307 p20
`
`11
`
`IJ1
`i 224
`1'
`1409
`}.., 155
`15
`.P. F., 85
`•, 170
`,265
`lj
`,'II .. 190
`~207
`iS5
`l
`)68, 374
`\274
`P .. 130
`133
`1. 331
`l. S., 207
`I
`i
`1
`""· 397
`
`' I
`
`339
`'3
`!
`i90
`;.4-03
`·, 138
`
`t Observation of a New Absorption Band of HOBr and Its Atmospheric Implications
`Rhett J. Barnes, Michael Lock, Jack Coleman, and Amitabha Sinha"'
`·;
`.lJ Probing DNA's Dynamics and Conformational Substates by Enthalpy Relaxation and Its Recovery
`-,~ Vi~osicy Effects of a Graft Copolymer ~ill a Hydrophobic Back::o::::::~::::: :h::~::e::t:::: Mayer*
`i NMR Study
`.•
`;~~ Influence of Adsorbed Molecules on the Configuration of Framework Aluminum Atoms in Acidic Zcolite-tl. A 27 Al MAS
`L. C. de Menorval,* W. Buckermann. F. Figueras, and F. Fajula
`t:: Synthesis and Characterization of Strongly Luminescing ZnS-Capped CdSe Nanocrystals
`_;§
`'-~ ·1 Macrodipole Generated by Symmetry Breaking due to Phase Separation in Mixed Lipid Vesicles
`-~1
`:~
`}j Uni.molecular Reaction of N02: Overlapping Resonances, Fluctuations, and the Transi tion State
`
`".
`
`Cyc!ohexane Oil-Continuous Microemulsion
`
`.
`Anna Holmberg, Lennart Piculell, * and Bengt Wesslen
`
`1,J
`
`Dietmar Porschke
`
`FEATURE ARTICLE
`
`Margaret A. Hines and Philippe Guyot-Sioonest*
`
`Scott A. Reid and Hanna Reisler
`
`-~!
`~i.
`:$
`:,~I
`MOLECULAR DYNA.!VUCS AND RELAXATION PROCESSES
`1 Topographical Features of Potential Energy Surfaces of the B + Oi Chemical Reaction
`
`'If. Transient EPR Studies of Ion-Paired Metalloporphyrin Hecerodimers
`Muhamad Bugerat, Arthur van der Est," Emmanuel Ojadi, Laszlo Biczok, Henry Linschitz,
`Haim Levanon, and Dietmar Stehlik*
`
`.
`
`.
`
`j
`
`ARTICLES
`
`Kuo-mei Chen,* Kuo-huei Lee, Jia-lin Chang, Chung-hwa Sung, Teng·hui Chung,
`Tai·kang Liu, and Huey-cherng Perng
`
`SPECTROSCOPY, CLUSTERS, AND MOLECULAR BEAMS
`
`~"
`~,
`
`'1
`
`449
`
`453
`
`458
`
`462
`
`465
`
`468
`
`472
`
`474
`
`488
`
`495
`
`2 of 6
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`

`

`-j;
`;~- r,etters
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`::. temperature n
`· /
`in five 0.55 1
`NOTiCE: ~h.is material ;"T'.~·r 'iP. ·r:'}o16lfil<erdile rat
`by copyngnt law (Title J 7 :_, 3 ·CcaoMV1g the r•
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`i. drous methar
` and subsequf
`to rinse an)
`
`1 1:
`
`I dispersed in
`I. centrifuged
`' reagents.
`l
`
`468
`
`J. Phys. Chem. 1996, JOO, 468-471
`
`Synthesis and Characterization of Strongly Luminescing ZnS-Capped CdSe Nanocrystals
`
`Margaret A. Hines and Philippe Guyot-Sionnest*
`James Franck Institute, The University of Chicago. Chicago, Illinois 60637
`
`Received: August JO, 1995; In Final Form: Occober 16, 1995®
`
`We describe the synthesis of ZnS-capped CdSe semiconductor nanocrystals using organometallic reagents
`by a two-step single-flask method. X-ray photoelectron spectroscopy, transmission electron microscopy and
`optical absorption are consistent with nanocrystals containing a core of nearly monodisperse CdSe of 27- 30
`A diameter with a ZnS capping 6 ± 3 A thick. The ZnS capping with a higher bandgap than CdSe passivates
`the core crystallite removing the surface traps. The aanocrystals exhibit strong and stable band-edge
`luminescence with a 50% quantum yield at room temperature.
`
`Introduction
`
`Semiconductor nanocrystals exhibit interesting size-tunable
`optical properties due to the confinement of the electronic wave
`functions. Over the past decade, much progress has been made
`in the synthesis and characterization of monodisperse nano(cid:173)
`crystals of a wide variety of semiconductors, such as II-VI, 1 ·2
`various chalcogenides,2 Si,3•4 and GaAs.s-7 In particular, II(cid:173)
`VI materials have received much attention and a synthesis has
`been recently developed for CdSe that leads to an unprecedented
`degree of monudispersivity and crystalline order,8 allowing
`detailed investigations of the size-dependent optical absorption.9
`,Tue high surface~to-vo!ume ratio of small nanocrystals
`/ suggests that the surface properties should have significant
`effects on their structural and optical properties. While surfaces
`capped by various organic or inorganic layers appear to influence
`only mildly the absorption characteristics, it is well-known that
`the emission efficiency, spectrum, and time evolution are very
`strongly affected by the surface. This is generally understood
`as being due to the presence of gap surface states arising from
`surface nonstoichiometry, unsaturated bonds, etc. Control of
`the surface is in particular the key to highly luminescent nano(cid:173)
`crystals. Organically capped nanocrystals have already a
`quantum yield of ~ 10% at room temperature reaching nearly
`100% at low lemperatures8·9 but at the expense of very long
`(microseconds) fluorescence lifetimes. These nanocrystals do
`not yet have a perfectly passivated surface. They exhibit some
`red-shifted luminescence and complex decay of the excited
`state. '°·11 Inorganic ·capping provides an alternative.
`Layered and composite semiconducror nanocrystals have
`already been studied by several groups. Systems studied have
`been (CdS)Cd(OH)z, 12.13 (CdSe)ZnS, 14 (CdSe)ZnSe, 15•16 and
`((CdS)HgS)Cd(OH)2. 17.18 Choosing the relative bandgap posi(cid:173)
`tions leads to enhanced charge transfer or improved lumines(cid:173)
`cence. 2 Ideally, epitaxial encasing would be achieved although
`the similar dielectric constants and bonding characteristics
`introduce additional difficulties to maintain size control or
`prevent alloying. Prior to this work, colloidal CdS capped with
`the inorganic capping Cd(OH)2 displayed the highest room(cid:173)
`temperature quantum yield (20% ).12 At low temperature, the
`quantum yield increases to 80%, and the fluorescence lifetime
`does not increase much. 13 These favorable characteristics have,
`in particular, allowed us to obtain single-clus~er fluorescence
`spectra in a previous experiment. 19 CdSe synthesized by the
`inverse micelle method bas also been successfully capped with
`
`<>Abstract p1iblished in Advance ACS Abstracts, December 15, 1995.
`
`ZnS1 4 and ZnSe.15 The ZnS-capped CdSe exhibit enhanced
`band-edge luniinescence and an order of magnitude increase
`of the quantum yield. M ZnSe-capped CdSe has not been
`discussed for its luminescence properties, but structural studies
`confirmed the shell-core structure.15 Thin film composites of
`CdSe nanocrystals in a ZnSe matrix have also been made by a
`combination of electrospray and organometallic chemical vapor
`deposition, 16 and enhanced luminescence has been reported.
`With the excellent size control that can now be achieved for
`CdSe nanocrystals, the capping of a size-tunable lower bandgap
`core nanocrystal with a higher bandgap shell is an attractive
`possibility that could lead to nanocrystals with improved
`luminescence, higher stability (protected from the surrounding
`matrix), and yet electrically connected (better than with an
`organic capping layer). The (CdSe)ZnS nanocrystals that are
`described here are a step in this direction with the highest
`luminescence quantum yield yet achieved while at tbe same
`time preserving a good degree of monodispersivity. We
`describe the synthesis and provide the results of characterization
`by room-temperature optical absorption and luminescence,
`fluorescence decay, transmission electron microscopy, and X-ray
`photoelectron spectroscopy.
`
`Experimental Section
`
`The nanocrystals were synthesized by using modifications
`of previously reported methods. 8•20 All reagents were used as
`purchased with no additional purification. Tri-n-octylpbosphine
`[TOP], tri-n-octylphosphine oxide [TOPO], selenium shot, 1 .M
`dimethylzinc [Me2Zn) in heptane, and anhydrous methanol and
`chloroform were purchased from Aldrich. Bis(trimethylsilyl)
`sulfide[(TMShS] and d.imethylcadmium [Me2Cd) were pur(cid:173)
`chased from Fluka and Organometallics Inc., respectiveiy.
`Stock soiutions of Cd and Se were prepared in a Nrfilled
`drybox by dissolving 0.2 g (0.0025 mol) of Se in 4.5 mL of
`TOP. MeiCd (0.25 rnL, 0.0035 mol) was added to the TOPSe
`and diluted with 19.5 mL of TOP. The Zn and S stock soMion
`was similarly prepared witb 0.52 mL of (TMS)2S (0.0025 mo!~
`in 4.5 mL of TOP, adding 3.5 mL of Me2Zn solution (0.003)
`mo!), and diluting with 16 rnL of TOP.
`The synthesis was performed by the following method: I 2 5
`g of TOPO was heated to 200 °C under vacuum, at which
`temperature it was dried and degassed for approximately 20
`min. The temperature was then raised to 350 °C und~r
`approximately 1 atrn of Ar. Once the temperarure bad stabi(cid:173)
`lized, 0.7 rnL (0.07 mrnol Se, 0. 1 mmol Cd) of Cd/Se/TOP
`stock solution was injected into the reaction flask. and
`
`0022-3654/96/20100-0468$12 .0010
`
`© 1996 American Chemical Society
`
`Dilutions
`for room-ten
`spectra wer1
`the size. Tl
`Elmer UV/\
`acquired at J
`quantum yic
`emission of
`of470 nm'
`Samples:
`using gold l
`Cr adhesion
`inEtOH for
`with EtOH.
`nanocrystal
`rinsed and
`Electronics
`source.
`The TEI
`Philips Clv
`5Qlutions c
`A thick cai
`solution in
`
`Results a1
`
`I:.
`•··
`
`Synthes
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`growth.8
`from the c
`material \
`CdSe nan
`small size
`temperatu
`the condi
`reproduci
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`'.
`their Fig1
`:·· CdSe wit
`critical t<
`
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`
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`

`~ · · J.,elters
`... ~ '.
`
`J. Phys. Chem., Vol. 100, 'No. 2, 1996 469
`
`tbe heat removed. The reaction mixture was allowed to cool
`w approximately 310 °C, and a small aliquor was extracted for
`·characterization of the initial CdSe nanocrystals. When the
`temperature reached 300 °C the Zn/S!TOP solution was injected
`in five 0.55 mL portions at approxi!Dately 20 s intervals. A
`iota! mole ratio of injected reagents was 1:4 Cd/Se:Zn/S. Upon
`cooling the reaction mixture was stirred at 100 °C for 1 h.
`The nanocrystals were purified by precipitation with anhy(cid:173)
`drous methanol The precipitate was collected by centrifuging
`and subsequently washed three times with anhydrous methanol
`to rinse any residual. TOPO. The nanocrystals were then
`dispersed in 10 mL of anhydrous chloroform. The solution was
`centrifuged to remove any residual debris and unreacted
`reagents.
`Dilutions of the concentrated nanocrystal solution were used
`for room-ternperat~e optical characterization. The absorption
`spectra were compared to those in the literature6 to estimate
`the size. The absorption spectra were acquired on a Perkin(cid:173)
`Elmer UV/vis spectrometer. The luminescence spectra were
`acquired al right angle on a SPEX Fluorolog spectrometer. The
`quantum yield was measured by comparison of the integrated
`emission of rhodamioe 560 (exciton) in ethanol at an excitation
`of 470 nm with collection between 480 ~d 850 nm.
`Samples for X-ray photoelectron spectroscopy were prepared
`using gold films (2000 A.) on silicon wafers with a thin (50 AJ
`Cr adhesion layer that were placed into 5 mM 1,6-hexanedithiol
`in EtOH for 2 h.20 The films were removed, rinsed thoroughly
`with EtOH. dried with Ar, and placed into dilute solutions of
`nanocrystals in CHC13 for 12 h. The samples were once again
`rinsed and dried. The spectra were acquired on a Physical
`Electronics 5000 LS ESCA System using an Al Ko. X -ray
`source.
`The TEM images of the nanocrystals were acq uired on a
`Philips CM electron microscope operating at 200 kV. Dilute
`solutions of the nanocrystals in CHCb were dropped onto 50
`A thick carbon coated copper grids (400 mesh) with the excess
`solution immediately wicked away.
`
`Results and Discussion
`
`Synthesis of nearly monodisperse nanocrystals is achieved
`by using supersaturation for sudden nucleation and subsequent
`growlh.8 Io this work, we followed more closely a variant20
`from the original method,8 which produces smaller amounts of
`material with a faster turnover but still nearly monodisperse
`CdSe nanocrystals with well-defined absorption features for
`small sizes ( <40 A). Since changes in the amount injected and
`temperature ofTOPO produces variations in the final CdSe size,
`the conditions described in the previous section apply to the
`reproducible synthesis of rather monodisperse nanocrystals
`between 27 and 30 A as shown in their absorption spectrum in
`their Figure 1. The ability to synthesize nearly monodisperse
`CdSe without further size-selective precipitation8 is evidently
`critical to retain a narrow size distribution with an additional
`coating.
`The choice of ZnS for the capping is based on the earlier
`anempts in the literature and is guided by the need for a
`semiconducror with a wider bandgap than the core. It is also
`such that both holes and electron are a priori confined, i.e., the
`need for a normal configuration.22 An advantage is that ZnS
`forms at lower temperatures than CdS and that ZnS and CdSe
`do not alloy well. However this last characteristic is in pan
`due io the large lattice mismatch between the two materials
`In
`Where the CdSe bond is about 12% larger than ZnS.23
`P<lrticular, this prevents growing flat heterostructures. However,
`this difficulty may become relaxed for small nanocrystals with
`
`Figure 1. TEM picture of (CdSe)ZnS nanocrystals. This picture is
`95 x 95 nm.
`
`short facets. Further studies exploring different sizes are in
`progress. The procedure of adding Me2Zn and (TMS)zS in
`several steps at lower temperature was guided by the need to
`minimize separate ZnS nucleation and to avoid growth of the
`CdSe particles themselves.
`The presence of Zn and S on the synthesized (CdSe)ZnS
`nanocrystals is unambiguously confirmed by XPS. The results
`indicate more Zn than C d (approximately 3x) which is due to
`the finite probe depth (~50 A), and further studies are underway;'
`to obtain more quantitative results. TEM images of (CdSe)(cid:173)
`ZnS show also very clearly that these particles are larg~r than
`the starting CdSe nanocryscals. (CdSe)TOP0 and (CdSe)ZnS
`samples of identical reaction batches were analyzed. for particle
`size by visual appreciation as well as computer analysis21 of
`the TEM images. The diameter of the (CdSe)ZnS particles is
`larger by 12 ± 6 A from which we deduce the ZnS capping to
`be 6 ± 3 A thick if, as discussed below, the core size remained
`constant. flg ure l shows a TEM image of the (CdSe)ZnS
`nanocrystals.
`The indication that the capping process has not lead to
`significant modification of the CdSe core comes fro m the
`comparison of the absorption spectra before and after capping.
`As shown in Figure 2, for the (CdSe)ZnS particles, the first
`exciton peak has broadened some but has not shifted ap(cid:173)
`preciably. Only at shorter wavelength does ¢e absorption
`spectrum deviate significantly from the (CdSe)TOPO system.
`This suggests that the firs t electronic ~tates of the CdSe core
`have been little modified. Importantly, this is also consistent
`with no major alloying or incorporation of the Zn or S inside
`the CdSe core.
`Th e central result of this work is that the fluorescence
`efficiency of the ZnS capped clusters is dramatically enh anced.
`As shown in Figure 3, the fluorescence spectrum of (CdSe)(cid:173)
`TOPO has a broad tail due to surface traos (700-800 nm),
`despite having a strong band-edge lumines~ence (530 nm) as
`observed by others.8 The fluorescence spectrum of (CdSe)(cid:173)
`ZnS retains the sharp peak with a small red shift (~5 nm) but
`has a flat baseline to the red of the emission peak. TI1e 50%
`quantwn yield makes the sample solution appear to "glow·• green
`m room light. It is therefore clear that the ZnS capping has
`greatly reduced the traps still present in (CdSe)TOPO.
`
`ixxlifications
`t
`i'ere used as
`j:Ylphosphilie
`:m shot, 1 M
`'.iethanol and · N
`· .::1
`llmethylsilyl)
`'·i
`J were pur-
`·~tively.
`•· &~
`!1 a Ni-filled J
`'-l
`In 4.5 mL of
`ll the TOPSe
`· '.J
`'~-
`lrock solution
`, ·j
`1:0.0025 mo!)
`tion (0.0035
`,._;
`I
`.J
`:iethod: 12.5
`lm. at which ":
`hxiinatel y 20 ·: 1
`j 0 °C under
`
`· c ..
`
`lire had stabi- '· .. ·
`
`. Cd/Sef!OP
`· flask, and
`
`·
`; ~
`
`4 of 6
`
`

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`· ·:--·r,etters
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`~.: program of
`« Lucille Pack
`· \1 p.,CS meetin;
`
`.-;
`
`]:leferences
`
`t
`
`(I) Bnis.
`(l) Welle·
`£llgl. 1993, 3;
`(3) Tag$
`Appl. Phys. L•
`(4) Brus,
`(5) Olsha
`:;oc. 1990, 11
`(6) (a) U
`5382. (bl Us
`J. J. Phys. CJ
`(7) Kher
`(8) Mun:
`1993, 115. 8'
`(9) Norr
`Lta. 1994. 7
`(10) Baw
`T. M.; Steig•
`(11) Bav.
`Phys. 1992,
`
`l~
`I I
`I
`
`I
`
`r
`
`' l
`l.
`I
`J
`
`J
`
`r
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`
`j.
`
`·r,,. ,.
`
`.
`.
`.
`
`470 J. Phys. Chem., Vol. JOO, No. 2, 1996
`
`1.0 ~-~--...----.----,---,----., 12
`
`8
`
`0.8
`
`:j .e 0.6
`Ci>
`0 c
`ro
`.0 :s 0.4
`,,.,
`.0
`<C
`
`0.2
`
`0.0
`
`400
`
`600
`500
`Wavelength (nm)
`
`Figure 2. Absorption spectrum of the (CdSe)TOPO (dotted line) and
`the (CdSe)ZnS nanocrystals (solid line). The fluorescence of the
`(CdSe)ZnS is also shown (solid line).
`
`/
`
`4
`
`--:- 3
`=!
`~
`::::-
`·o;
`c 2 ~
`
`<::
`
`x6
`····················
`
`.... ·········
`
`0 1::....'.~-L_l:::::=r=~:::r:=:;::!:;::::.J
`600
`700
`800
`Wavelength (nm)
`
`Figure 3. Fluorescence of the (CdSe)TOPO (dotted line) and (CdSe)(cid:173)
`ZnS (solid line) nanocrystals normalized by their absorption al the
`excitation wavelength (470 nm).
`
`We also note that this fluorescence is stable for months and
`fairly insensitive to the environment, especially as no precautions
`are taken during workup of the reaction solution and subsequent
`manipulations to eliminate oxygen. All products are stored as
`CHCJ3 solutions, and over a,period of months there has been
`no reduction of the quantum yield, W1Jike for the (CdSe)TOPO.
`Regarding this stability, it may be relevant that ZnO remains a
`semiconductor with a wide direct bandgap while CdO has a
`small indirect bandgap,13 but we also verified that solvents such
`as pyridine which tend to quench the fluorescence of (CdSe)(cid:173)
`TOPO, presumably by replacing the TOPO ligands, have little
`effect on the quantum yield of (CdSe)ZnS. Finally, laser
`spectroscopy experiments in progress show a much reduced
`
`I ., ,.
`I I
`I : : !
`I l ;
`
`. I
`
`Modulation Frequency (MHz)
`10
`
`100
`......... •····
`,. _ _,,,..,....,,0.8
`
`•...
`
`80
`
`--(cid:173)Vl
`~ 60
`I....
`Ol
`
`~40
`
`Q)
`
`~ 20
`~ a:
`
`b)
`
`......
`
`·-·-
`·····
`····· -·-····
`·3 '--~~~~~~~~~~-·-·· ·_· ·_··~··~~--'
`Time (ns)
`500
`0
`
`Figure 4. (a) Phase and amplitude of tbe fluorescence decay for
`(CdSe)ZnS (dashed line, filled circles), (CdSe)TOPO (dashed line, open
`circle), and (CdS)Cd(OH}., (dashed line. open diamonds) nanocrvstals
`The lines are four-exponential fits. (b) Reconstructed time decay pl~
`
`tendency to permanent bleaching. This indicates chat the
`capping has the added benefit of protecting the interface.
`The capping also strongly affects the fluorescence decay.
`Room-temperature measurements, on three samples, (CdSe)(cid:173)
`ZnS, (CdSe)TOPO, and (CdS)CdOH2, have been taken with
`the phase method and results, which are fitted well wirh a
`minimum of four exponential components, are shown in Figure
`4. The relative strengths of the four fluorescence decay
`components are (8.5%, 160 ns; 53%, 26 ns; 37%, 12 ns; l.5%,
`1.5 ns) for (CdSe)ZnS, (59.5%, 290 ns; 29%, 49 ns; 10%, 6.1
`us; 1.5%, 0.7 ns) for (CdSe)TOPO, and (54.5%, 203 ns; 38%,
`40 ns; 6%, 7 ns; 1.5%, 0.7 ns) for (CdS)CdOH2. ,. The important
`observation is that 90% of the decay components are in the
`10-30 ns range for (CdSe)ZnS, in sharp conrrast to (CdSe)(cid:173)
`TOPO where 60% of the fluorescence is in the 300 ns range.
`Clearly the capping simplifies the recombination kinetics. If
`the recombination originates from trap states, for example at
`the CdSe!ZnS interface, the overall faster recombination may
`indicate that the trap states are more delocalized. However.
`the nature of the recombination process is a complex issue that
`requires much further investigation.
`
`Conclusion
`
`Nanocrystals of CdSe capped with ZnS have been synthesized
`using organometallic reagents. The higher bandgap ZnS is
`directly grown onto nearly monodisperse CdSe cores with
`retention . of initial core size. The presence of the ZnS was
`confirmed by XPS, and TEM images are consistent with a 6 :±::
`3 A thick capping. The ZnS capping passivates and protects
`the surface as determined by the enhanced and stable room·
`temperature band-edge luminescence with 50% quantum yield.
`These new nanocrystals are being further characterized for their
`low-temperature optical properties and recombination kinetics.
`
`Acknowledgment. ·we thank T. L. Hazlett from the LFD
`at The University of Illinois Urbana-Champaign (NIH RR03155-
`01 and UflJC) for the time-resolved fluorescence data; Stephen
`R. Wasserman, Chemistry Division. Argonne National Labora·
`t0ry, for the XPS data; Robert Josephs, Deparunent of Molecular
`Genetics and Cell Biology, University of Chicago, for the TEN!
`images; and Graham Fleming and Hellmut Fritzsche for the use
`
`5 of 6
`
`

`

`Letters
`
`of their spectrometers. 11ris work was supported by the MR.SEC
`program of NSF und~r. DMR-9_400379 and the David and
`Lucille Packard Founaauon. This work was presented at the
`ACS meeting in Chicago on Aug 20, 1995.
`
`References and Notes
`(l) Brus. L. E. App. Phys. 1991, A53. 465.
`(2) Weller, H. Angew. Chem. 1993, 32, 4l ; Angew. Chem., Int. Ed.
`Engl. 1993, 32_. 41; Adu. Mater. 1993, 5, ~8.
`.
`.
`:· .'
`(3) Tagaki. H.; Ogawa, H.; Yamazaki. Y.; Ish1zaki. A.; Nakagm, T.
`Appl. Phys. Lett. 1990, 56, 2379.
`(4) Brus. L. E. J. Phys. Chem. 1994. 98, 3575.
`(5) Olshavsky, M.A.; Goldstein. A. N .; Alivisams, A . P. J. Am. Chem.
`Soc. 1990, 112, 94 38.
`·
`(6) (a) Usbida. H.; Curtis, C. J.: Nozik, A. J. J. Phys. Chem. 1991. 95,
`5382. (b) Ushlda, H.; Cunis, C. J.; Kamat, P. V.: Jones, K. M.; Nozik, A.
`J. J. Phys. Chem. 1992, 96. 1156.
`(7) Kher. S. S.; Wells, R. L. Chem. Mater. 1994,,6, 2056.
`(8) Murray, C. B.; Norris. D. J.; Bawendi. M . G. J. Am. Chem. Soc.
`1993. II5. 8706.
`(9) Norris. D. J.; Sacra, A.; Murray, C. B.; Bawendi, M. G. Phys. Reu.
`I.ell. 1994, 72. 2612.
`(10) Bawe!Jdi, M. G.: Wilson, W. L.; Rothberg, L.; Carroll, P. J.; Jedju,
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`J. Phys. Chem., Vol. JOO, No. 2, l996 471
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`(12) Spahnel. L.; Haase. M.; Weller, H.; Henglcin A J Am Ch
`Soc. 1987, 109, 5649.
`'
`·
`·
`·
`em.
`(1_3) Eychmuller, A.; Hasselbarth, A.; Katsikas, L.; Weller, H. J.
`Lummescmce 1991, 48149, 745.
`(14) Kanan, A. R.: Hull, R.; Opila, R. L.; Bawendi, M. G.; Steigerwald,
`M. L.; Carroll, P. J.; Brus, L. E. J. Am. Chem. Soc. 1990, 112, 1327.
`(!5) Hoener, C. P.; Allan. K . A_.; Bard, A- J.; Campion, A.; Fox, M.A.;
`Maliouk, T. E.; Webber, S. E.; White, J.M. J. Phys. Chem. 1992, 96, 3812.
`(16) Eychrnuller. A.; Mews, A.; Weller, H. Chem. Phys. Lerr. 1993, 208,
`.
`~
`~
`(17) Mews, A.; Eychmuller, A.; Giersig, M.: Schoos, D.; Weller, H.J.
`Phys. Chem. 1994, 98, 934.
`(18) Danek. M.; Jensen, K. F .; Murray, C. B.; Bawendi, M. G. Appl.
`Phys. Lett. 1994, 65, 2795; Crysr. Growth 1994. 145, 7 14.
`(19) Blanton, S. A.; Dehestani, A.; Lin, P. C.; Guyot-Sionnest, P. Chem.
`Phys. Lett. 1994, 229, 317.
`(20) Bowen Katari. J. E.; Colvin, V. L.; Alivisatos, A. P. J. Phys. Chem.
`1994, 98, 4 l09.
`(21) Computer software developed by David Grier and John Crocker,
`James Franck Institute, University of Chicago.
`(22) Basic properties of Semiconductors; Moss, T. S., Series Ed.; Nonh
`Holland: Arnsteidam. 1992; Vol. t.
`(23) Semiconducio rs, Data in Science and Technology, Springer(cid:173)
`Verlag: Berlin, 1992.
`
`JP9530562
`
`1~.o
`
`iOO
`decay for
`Hine, open
`~ocrystals.
`/;t;cay plot
`
`. that the
`1ace.
`~ decay.
`I (Cc!Se)(cid:173)
`aken with
`~u with a
`1in Figure
`re decay
`ns; 1.5%,
`'10%, 6.1
`Ins; 38%,
`importaut
`are in the
`o (CdSe)(cid:173)
`•ns range.
`inetics. If
`xample al
`ation may
`However,
`.issue that
`
`ynthesized
`ap ZnS is
`:ores with
`· ZnS was
`with a 6 ±
`1d protects
`Ible room(cid:173)
`llUm yield.
`:cl for their
`•n kinetics.
`
`o the LFD
`RR03I55-
`a; Stephen
`1al Labora(cid:173)
`'Molecular
`irtheTEM
`for the use
`
`6 of 6
`
`