Infrared Photodetection Based on Colloidal
Quantum-Dot Films with High Mobility and Optical
Absorption up to THz
Emmanuel Lhuillier, Marion Scarafagio, Patrick Hease, Brice Nadal, Herve
Aubin, Xiang Zhen Xu, Nicolas Lequeux, Gilles Patriarche, Sandrine Ithurria,
Benoit Dubertret
To cite this version:
Emmanuel Lhuillier, Marion Scarafagio, Patrick Hease, Brice Nadal, Herve Aubin, et al.. Infrared Photodetection Based on Colloidal Quantum-Dot Films with High Mobility and Optical
Absorption up to THz. Nano Letters, American Chemical Society, 2016, 16 (2), pp.1282-1286.
10.1021/acs.nanolett.5b04616. hal-01418828
HAL Id: hal-01418828
https://hal.archives-ouvertes.fr/hal-01418828
Submitted on 17 Dec 2016
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
This is an open access art icle published under an ACS Aut horChoice License, which permit s
copying and redist ribut ion of t he art icle or any adapt at ions for non-commercial purposes.
Letter
pubs.acs.org/NanoLett
Infrared Photodetection Based on Colloidal Quantum-Dot Films with
High Mobility and Optical Absorption up to THz
Emmanuel Lhuillier,*,†,‡ Marion Scarafagio,†,§ Patrick Hease,§ Brice Nadal,† Hervé Aubin,§
Xiang Zhen Xu,§ Nicolas Lequeux,§ Gilles Patriarche,∥ Sandrine Ithurria,§ and Benoit Dubertret*,§
†
Nexdot, 10 rue Vauquelin, 75005 Paris, France
Institut des NanoSciences de Paris, UPMC-UMR CNRS 7588, 4 place Jussieu, 75252 Paris CEDEX 05, France
§
Laboratoire de Physique et d’Etude des Matériaux, ESPCI-ParisTech, PSL Research University, Sorbonne Université UPMC Univ
Paris 06, CNRS, 10 rue Vauquelin 75005 Paris, France
∥
Laboratoire de Photonique et de Nanostructures, LPN/UPR20-CNRS, Route de Nozay, 91460 Marcoussis, France
‡
S Supporting Information
*
ABSTRACT: Infrared thermal imaging devices rely on
narrow band gap semiconductors grown by physical methods
such as molecular beam epitaxy and chemical vapor deposition.
These technologies are expensive, and infrared detectors
remain limited to defense and scientific applications. Colloidal
quantum dots (QDs) offer a low cost alternative to infrared
detector by combining inexpensive synthesis and an ease of
processing, but their performances are so far limited, in terms
of both wavelength and sensitivity. Herein we propose a new
generation of colloidal QD-based photodetectors, which
demonstrate detectivity improved by 2 orders of magnitude,
and optical absorption that can be continuously tuned between
3 and 20 μm. These photodetectors are based on the novel
synthesis of n-doped HgSe colloidal QDs whose size can be tuned continuously between 5 and 40 nm, and on their assembly
into solid nanocrystal films with mobilities that can reach up to 100 cm2 V−1 s−1. These devices can be operated at room
temperature with the same level of performance as the previous generation of devices when operated at liquid nitrogen
temperature. HgSe QDs can be synthesized in large scale (>10 g per batch), and we show that HgSe films can be processed to
form a large scale array of pixels. Taken together, these results pave the way for the development of the next generation mid- and
far-infrared low-cost detectors and camera.
KEYWORDS: HgSe, colloidal quantum dot, transistor, electrolyte gating, photoresponse, mid- and far-infrared
C
design new generation of bolometer;5 however, its low
absorption limits its practical use. CQD films achieve
absorption coefficients almost as large as the bulk values. As
a result they may become a low-cost infrared alternative to
current technologies as long as they can address the mid- and
far-IR.
The performance of the CQD-based devices also crucially
depends on their transport properties. The hopping effective
mobility tends to be low (μ < 1 cm2 V−1 s−1). This has led to
the development of alternative device geometries such as
nanotrench6 or hybrid structures with graphene.7 Extensive
efforts have been made to obtain nanocrystal solid with larger
mobility. The latter is obtained using optimized surface
passivation relying on atomically short8−10 or inorganic
ligands.11 Recent progress has pushed the carrier mobility12
olloidal quantum dots (CQD) are excellent building
blocks to develop low cost optoelectronic devices.1 For
applications in the visible wavelength range, CQD face
competition with existing technologies such as CMOS, which
already achieve high performance at low cost. In the infrared
(IR), high performances detectors also exist based on
technologies such as multiquantum well, InSb, HgCdTe, and
type II superlattices. Their detectivities range from 5 × 1010
jones in the LWIR (8−12 μm) to 5 × 1011 jones in the MWIR
(3−5 μm), while their noise equivalent temperature difference
can be as low as 10 mK. However, they remain expensive and
technologically demanding. Uncooled detectors such as the
bolometer offer an interesting alternative to the cooled
quantum detectors, but their performances remain lower (D*
≈ few 109jones). To overcome these limitations, new
technologies that deliver fast,2 high-performing uncooled3
detectors must be developed. Possible strategies rely on the
use of plasmon for light concentration or hot electron
collection.4 Material-like graphene are of utmost interest to
© XXXX American Chemical Society
Received: November 12, 2015
Revised: January 5, 2016
A
DOI: 10.1021/acs.nanolett.5b04616
Nano Lett. XXXX, XXX, XXX−XXX
Nano Letters
Letter
Figure 1. (a) IR absorbance for small and large HgSe CQD. (b) IR absorbance in the intraband peak range of wavenumber for HgSe CQD of
different sizes. (c) Plot of the expected plasmonic peak as a function of the nanocrystal radius for different number of dopants per nanocrystal. The
experimental data and their fit by a k·p model are shown in red and blue, respectively. (d) TEM image of the small HgSe CQD. The inset is a high
resolution image of the nanocrystal. (e) TEM image of the large HgSe CQD. The inset is a high resolution image of the nanocrystal highlighting the
polycrystalline nature of the large HgSe CQD. (f) Image of the resulting material obtained from a large scale synthesis of 10 nm HgSe CQD.
up to 300 cm2 V−1 s−1, which is competitive with values
obtained for epitaxially grown semiconductor. Combining IR
optical features with high mobility is one of the key challenges
for CQD based optoelectronic. In this report we propose a
method to grow CQD with optical absorption up to THz and
mobilities up to 100 cm2 V−1 s−1. These results represent a key
step toward the CQD integration into IR detectors and
cameras.
To address IR optical transition one can use narrow band gap
semiconductors13 (NBGSC) or doped semiconductors for their
plasmonic properties.14,15 However, this second strategy does
not lead to photocurrent generation and is consequently not
suitable for use in photodetectors. Among NBGSC, lead
chalcogenide-based CQD address the near IR,1617 but cannot
be pushed further because of the bulk band gap. For mid-IR,18
HgTe CQD19−21 have attracted most interest because of their
proximity with the bulk HgCdTe alloy, extensively used for
infrared detection. Recent progress has pushed the cutoff
wavelength up to 12 μm using HgTe22 CQD. Unfortunately,
HgTe CQD suffers from a high sensitivity to oxidation23 due to
the low electronegativity of Te, which increases the energy of
the valence band. Other mercury chalcogenides present the key
advantage of being self-n-doped.24,25 As a result, low energy
absorption occurs due to intraband transition, as already
commonly done in multiquantum-well heterostructure.26,27 So
far HgSe CQD has mostly been synthesized with small sizes,28
leading to excitonic features in the visible or near-IR. Aqueous
phase synthesis of HgSe CQD usually lead to a poor control of
the size dispersity.29,30 Howes et al. proposed an organic phase
synthesis31 for this material, but the excitonic feature remains
below 1 μm. Recently, improved synthesis of HgSe CQD has
been proposed25,32 and has pushed the optical properties of
HgSe CQD up to 5 μm. In this report, we propose a new
synthesis for HgSe CQD, which for the first time significantly
expands the range of wavelength of the intraband feature up to
the THz region.
We developed a synthetic method to grow HgSe CQD with
tunable optical properties from 3 to 20 μm. This is the reddest
value reported to date for CQD and covers the mid wave and
long wave atmospheric windows. The synthesis is based on the
reaction of an Hg2+ complex with long amine and carboxylic
acid chains. This precursor is fairly fragile and needs to be
manipulated at low temperature (<120 °C). The HgSe
nanocrystals present optical features in the IR made of a
broad band interband transition and narrow band intraband
transition, see Figure 1a−c. While introducing the Se precursor
under TOPSe form, we obtained small CQD with a tunable size
from 6 to 12 nm, corresponding to intraband peak transition
between 3000 and 1500 cm−1. The intraband absorption
coefficient has been estimated to be 2300 ± 200 cm−1 , which is
consistent with a previous report.25 The peak energy can be
tuned by adjusting the temperature (60 to 120 °C) and the
time of the reaction (1 to 60 min). See the SI for more
information about the synthetic process. The crystalline nature
of the CQD appears clearly on the high resolution TEM images
(see Figure 1d) and X-ray diffraction (see Figures S1 and S2).
The synthesis has been scaled to greater than 10 g (Figure 1f
B
DOI: 10.1021/acs.nanolett.5b04616
Nano Lett. XXXX, XXX, XXX−XXX
Nano Letters
Letter
Figure 2. (a) Scheme of a dual (bottom and electrolytic) gated transistor based on a thin HgSe CQD film. (b) Transfer curve (drain current vs gate
voltage) for the dual gated transistor made of a thin HgSe CQD film using back and electrolytic gating. In both cases the drain source bias is 10 mV.
(c) Transfer curve for a thin HgSe CQD film using back gate only (i.e., no electrolyte is present). The film mobility is 90 cm2 V−1 s−1.
dependent. Such level of doping tends to confirm the intraband
character of the transition instead of the plasmonic origin. First
(i), because with less than 2 electrons per nanocrystal, a
collective plasmonic feature is not expected to occur.37 Second
(ii), the plasmonic peak consistent with this density (n) of
doping does not match the experimental data. Indeed, the
carrier density is given by n = ηNQD/(4/3πRQD3) with η the
film density taken equal to 0.64 assuming a random close
packing of the CQD, NQD the number of carrier per QD, and
RQD the CQD radius. The plasma frequency38 is then given by
ωp2 = ne2/εm with e the elementary charge, ε the dielectric
constant, and m* the carrier mass. According to the Drude
model, we expect the plasmonic feature to occur at an energy
and S3), which is already sufficient to build a significant
quantity of devices.
The trioctylphosphine acts as a ligand for these CQD and
likely limits the crystal size. To grow larger CQD, we switched
from Se precursor to SeS2, see Figure 1e. However, only the Se
reacts as XRD and energy dispersive X-ray analysis revealed no
sulfur content in the QCD. This result is consistent with our
observation that nanoparticle formation does not take place
when using TOPS instead of TopSe in the synthesis. Using
SeS2 as precursor under otherwise identical reaction conditions,
the intraband feature can now be tuned within the 1500 to 500
cm−1 (15 THz ≈ 60 meV) range, see Figure 1b (and Figures S4
to S7). The material can still absorb at 24 μm (12.5 THz),
which is the limit of our spectrometer.
In the following we focus on the HgSe CQD with optical
features in the 3−8 μm range and investigate their transport
properties. To ensure an efficient conduction into the CQD
array, we exchange the initial long and insulating ligands with
As2S3-based ligands. The motivation for such a choice are (i)
organic ligands are not suitable due to their own absorption in
the targeted range of wavelength, (ii) As2S3 is transparent up to
11 μm, (iii) As2S3 has already proven its ability for high
mobility film when coupled with lead 33 or mercury
chalcogenides CQD.23 Our ligand exchange procedure is
inspired by the procedure of Buckley.34 As2S3 is first dissolved
in a short alkyl-chain amine.35 This mixture is used to perform a
phase transfer ligand exchange.8 As2S3 actually comes under a
complexed form with amine,33,35 see Figure S8. The material is
then deposited at 100 °C on electrodes.
A polymer electrolyte (LiClO4 in polyethylene glycol) is used
to build a dual gated transistor, see Figure 2a. Either the back
gate of the substrate (Si/SiO2, 400 nm of oxide) or the
electrolyte gating can be used. The transfer curves are plotted
on Figure 2b. The material is n-type and already doped under
no gate bias as expected from the presence of intraband feature
in the IR absorption. This doping is preserved even after ligand
exchange (see Figure S8) since the intraband peak is still
observed after the procedure. The on−off ratio is around 100.
Interestingly the drain current as a function of gate bias
presents two local minima, which we attribute to the complete
depletion and full filling of the 1s state of the conduction
band.36
According to transport measurements, HgSe CQD contains
approximately 0 to 2 electron(s) per nanocrystal. As a result the
relative magnitude of the interband and intraband transition
depends on the doping level. With the higher the doping, the
greater the intraband absorption and the smaller the interband
absorption observed. The doping is also size and surface
given by σplasmon =
1
2π c
3ηNQDe 2
4πme*(ε∞ + 2εm)R QD3
where c is the speed
of light, m*e = 0.05m0 ± 0.02 is the effective mass in HgSe, ε∞ =
16 is the optical frequency dielectric constant, and εm = 2.1 is
the medium dielectric constant measured by ellipsometry. This
plasmonic feature is expected to occur at a frequency five times
lower than the observed experimental data, see Figure 1c.
Moreover (iii), this intraband transition is fairly narrow
compared to a usual plasmonic feature occurring in highly
doped semiconductor nanocrystals.14,39 Finally (iv), we obtain a
good agreement of the energy of the intraband transition with
the computed value using a two bands k·p model40 (Figures 1c
and S9); see the SI for details. With all these elements taken
together, we can confidently attribute the mid- and far-infrared
optical feature to an intraband transition.
The most striking transport property of this system is its
extremely large carrier mobility. To obtain an accurate
estimation of this mobility, we performed a measurement in a
pure back gate configuration (i.e., no electrolyte), see Figure 2c.
We then extracted a mobility μnFET =
∂IDS
L
WC ΣVDS ∂VGS
in the 50
VDS
to 100 cm2 V−1 s−1 range, which is one of the largest values
reported for colloidal based material. Thanks to the high
mobility of the film, the responsivity reaches 0.8 A W−1 (see
Figure S10), meaning that the external quantum efficiency is
around 20−30% for a 6 μm cutoff wavelength sample after
ligand exchange. This value is typically three orders of
magnitude larger than the one previously reported using
HgSe CQD25 and challenges the existing technology in the
mid-infrared (see Figure S11). This improvement is largely
attributed to the larger mobility of our sample, due to our
improved ligand exchange procedure.
To further study the performance of this material for IR
photodetection we have measured its electronic noise. The
C
DOI: 10.1021/acs.nanolett.5b04616
Nano Lett. XXXX, XXX, XXX−XXX
Nano Letters
Letter
Figure 3. (a) Noise current density for a thin HgSe CQD film under three different biases. The inset is an image of the Wheatstone bridge
configuration used to measure the noise. (b) Absolute photoresponse and detectivity as a function of frequency signal, under a 1 V bias at room
temperature. (c) SEM picture of an array of 60 μm large pixels made in a film of HgSe CQD.
measurement is performed using a Wheatstone bridge
configuration (see the inset of Figure 3a and fiugre S12).
This approach reduces most of the DC component of the
signal, which is crucial for “low” resistance sample. As expected
for nanocrystals array, the noise comes under a 1/f form;41 see
Figure 3a. The detectivity26 of the device is given by D* =
R√A/in with R the responsivity, A the optical area, and in the
noise current density of the sample. Its value, at room
temperature, is of the order of 108 jones (NEP ≈ 700 pW
Hz−1/2, under 1 V bias), which is similar to the one of uncooled
DTGS detector. The improved mobility allows operation of the
device at room temperature to achieve similar performance as
at liquid nitrogen temperature of former generation of HgSe
CQD based photodetectors. The 3 dB bandwidth is at 40 Hz,
see Figure 3b.
Finally we investigate the use of this colloidal material as an
active material of an infrared camera. In this sense it is crucial
that the material can withstand the technological clean room
fabrication process required for pixel design. We processed an
array of pixels with sizes ranging from 20 to 60 μm (Figures 3c
and S13) using e-beam lithography. The lithography step is
followed by a mild plasma etching. For such sizes the pixel
presents sharp edges and a high filling factor (∼90%). The
array of pixels can be as large as several millimeters and is only
limited by thickness inhomogeneity of the nanocrystal film.
This result is of significant interest for the design of a focal
plane array based on CQD.
Conclusion. We present a new synthetic procedure for ndoped mercury chalcogenides CQDs that gives access to
absorption in the mid- and far-infrared up to 25 μm. Once
combined with As2S3 as ligand, the material can achieve
mobilities as large as 100 cm2 V−1 s−1. Compared to other
CQD based devices operating at the same wavelength, our
devices have a photoresponse that is three orders of magnitude
larger for similar operating conditions. Alternatively it can
achieve the same performances while increasing the operating
temperature by 200 K. Finally we address two key steps for the
integration of this material for focal plane arrays: the scale up of
the colloidal synthesis (>10 g nanomaterial) and the material
processing by lithography.
■
Additional data concerning the chemical preparation and
material characterization of the HgSe CQD, as well as
the device fabrication and optoelectronic characterization
(PDF)
■
AUTHOR INFORMATION
Corresponding Authors
*E-mail: el@insp.upmc.fr.
*E-mail: benoit.dubertret@espci.fr.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank Agence National de la Recherche for funding through
grants SNAP, H2DH, and Nanodose. This work has been
supported by the Region Ile-de-France in the framework of
DIM Nano-K. We thank Pr. Charles Rosenblatt and Dr. Patrick
Brady for careful reading of the manuscript
■
■
REFERENCES
(1) Talapin, D. V.; Lee, J. S.; Kovalenko, M.; Shevchenko, E. Chem.
Rev. 2010, 110, 389−458.
(2) Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Weiss, D.;
Schneider, H.; Helm, M. Appl. Phys. Lett. 2013, 103, 021113.
(3) Herring, P. K.; Hsu, A. L.; Gabor, N. M.; Shin, Y. C.; Kong, J.;
Palacios, T.; Jarillo-Herrero, P. Nano Lett. 2014, 14, 901−907.
(4) Sobhani, A.; Knight, M. W.; Wang, Y.; Zheng, B.; King, N. S.;
Brown, L. V.; Fang, Z.; Nordlander, P.; Halas, N. J. Nat. Commun.
2013, 4, 1643.
(5) Koppens, F. H. L.; Mueller, T.; Avouris, Ph.; Ferrari, A. C.;
Vitiello, M. S.; Polini, M. Nat. Nanotechnol. 2014, 9, 780−793.
(6) Lhuillier, E.; Dayen, J. F.; Thomas, D. O.; Robin, A.; Doudin, B.;
Dubertret, B. Nano Lett. 2015, 15, 1736.
(7) Konstantatos, G.; Badioli, M.; Gaudreau, L.; Osmond, J.;
Bernechea, M.; Pelayo Garcia de Arquer, F.; Gatti, F.; Koppens, F.
H. L. Nat. Nanotechnol. 2012, 7, 363.
(8) Nag, A.; Kovalenko, M. V.; Lee, J. S.; Liu, W.; Spokoyny, N.;
Talapin, D. V. J. Am. Chem. Soc. 2011, 133, 10612.
(9) Koh, W. K.; Saudari, S. R.; Fafarman, A. T.; Kagan, C. R.; Murray,
C. B. Nano Lett. 2011, 11, 4764.
(10) Tang, J.; Kemp, K. W.; Hoogland, S.; Jeong, K. S.; Liu, H.;
Levina, L.; Furukawa, M.; Wang, X.; Debnath, R.; Cha, D.; Chou, K.
W.; Fischer, A.; Amassian, A.; Asbury, J. B.; Sargent, E. H. Nat. Mater.
2011, 10, 765.
(11) Kovalenko, M. V.; Scheele, M.; Talapin, D. V. Science 2009, 324,
1417.
(12) Dolzhnikov, D. S.; Zhang, H.; Jang, J.; Son, J. S.; Panthani, M.
G.; Shibata, T.; Chattopadhyay, S.; Talapin, D. V. Science 2015, 347,
425.
ASSOCIATED CONTENT
S Supporting Information
*
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.nanolett.5b04616.
D
DOI: 10.1021/acs.nanolett.5b04616
Nano Lett. XXXX, XXX, XXX−XXX
Nano Letters
Letter
(13) Kershaw, S. V.; Susha, A. S.; Rogach, A. L. Chem. Soc. Rev. 2013,
42, 3033.
(14) Luther, J. M.; Prashant, K. J.; Ewers, T.; Alivisatos, A. P. Nat.
Mater. 2011, 10, 361.
(15) Sahu, A.; Khare, A.; Deng, D.; Norris, D. J. Chem. Commun.
2012, 48, 5458.
(16) Konstantatos, G.; Sargent, E. H. Nat. Nanotechnol. 2010, 5,
391−400.
(17) Pietryga, J. M.; Schaller, R. D.; Werder, D.; Stewart, M. H.;
Klimov, V. I.; Hollingsworth, J. A. J. Am. Chem. Soc. 2004, 126,
11752−11753.
(18) Lhuillier, E.; Keuleyan, S.; Liu, H.; Guyot-Sionnest, P. Chem.
Mater. 2013, 25, 1272−1282.
(19) Rauch, T.; Böberl, M.; Tedde, S. F.; Fürst, J.; Kovalenko, M. V.;
Hesser, G.; Lemmer, U.; Heiss, W.; Hayden, O. Nat. Photonics 2009, 3,
332.
(20) Kovalenko, M. V.; Kaufmann, E.; Pachinger, D.; Roither, J.;
Huber, M.; Stangl, J.; Hesser, G.; Schäffler, F.; Heiss, W. J. Am. Chem.
Soc. 2006, 128, 3516.
(21) Keuleyan, S.; Lhuillier, E.; Brajuskovic, V.; Guyot-Sionnest, P.
Nat. Photonics 2011, 5, 489−493.
(22) Keuleyan, S. E.; Guyot-Sionnest, P.; Delerue, C.; Allan, G. ACS
Nano 2014, 8, 8676.
(23) Lhuillier, E.; Keuleyan, S.; Zolotavin, P.; Guyot-Sionnest, P. Adv.
Mater. 2013, 25, 137.
(24) Jeong, K. S.; Deng, Z.; Keuleyan, S.; Liu, H.; Guyot-Sionnest, P.
J. Phys. Chem. Lett. 2014, 5, 1139.
(25) Deng, Z.; Jeong, K. S.; Guyot-Sionnest, P. ACS Nano 2014, 8,
11707.
(26) Rosencher, E. ; Vinter, N. Optoelectronic, 2nd ed; Dunod: Paris,
2002.
(27) Lhuillier, E.; Ribet-Mohamed, I.; Nedelcu, A.; Berger, V.;
Rosencher, E. Phys. Rev. B: Condens. Matter Mater. Phys. 2010, 81,
155305.
(28) Qadri, S. B.; Kuno, M.; Feng, C. R.; Rath, B. B.; Yousuf, M.
Appl. Phys. Lett. 2003, 83, 4011.
(29) Liu, L.; Wu, Q.; Ding, Y.; Liu, H.; Zhang, B. Colloids Surf., A
2004, 240, 135.
(30) (a) Esmaeili-Zarea, M.; Salavati-Niasaria, M.; Sobhanib, A.
Ultrason. Sonochem. 2012, 19, 1079. (b) Salavati-Niasari, M.; EsmaeiliZare, M.; Sobhani, A. Micro Nano Lett. 2012, 7, 1300.
(31) Howes, P.; Green, M.; Johnston, C.; Crossley, A. J. Mater. Chem.
2008, 18, 3474.
(32) Mirzai, H.; Nordin, M. N.; Curry, R. J.; Bouillard, J.-S.; Zayats,
A. V.; Green, M. J. Mater. Chem. C 2014, 2, 2107.
(33) Yakunin, S.; Dirin, D. N.; Protesescu, L.; Sytnyk, M.;
Tollabimazraehno, S.; Humer, M.; Hackl, F.; Fromherz, T.;
Bodnarchuk, M. I.; Kovalenko, M. V.; Heiss, W. ACS Nano 2014, 8,
12883.
(34) Buckley, J. J.; Greaney, M. J.; Brutchey, R. L. Chem. Mater. 2014,
26, 6311−6317.
(35) Kovalenko, M. V.; Schaller, R. D.; Jarzab, D.; Loi, M. A.;
Talapin, D. V. J. Am. Chem. Soc. 2012, 134, 2457−2460.
(36) Yu, D.; Wang, C.; Guyot-Sionnest, P. Science 2003, 300, 1277−
1280.
(37) Pi, X.; Delerue, C. Phys. Rev. Lett. 2013, 111, 177402.
(38) Ashcroft, N. W. ; Mermin, N. D. Solid States Physics; CBS
Publishing Asia: Hong Kong, 1987.
(39) Rowe, D. J.; Jeong, J. S.; Mkhoyan, K. A.; Kortshagen, U. R.
Nano Lett. 2013, 13, 1317.
(40) Lhuillier, E.; Keuleyan, S.; Guyot-Sionnest, P. Nanotechnology
2012, 23, 175705.
(41) Liu, H.; Lhuillier, E.; Guyot-Sionnest, P. J. Appl. Phys. 2014, 115,
154309.
E
DOI: 10.1021/acs.nanolett.5b04616
Nano Lett. XXXX, XXX, XXX−XXX