ARTICLES
PUBLISHED ONLINE: 26 SEPTEMBER 2010 | DOI: 10.1038/NNANO.2010.175
Direct nanoprinting by liquid-bridge-mediated
nanotransfer moulding
Jae K. Hwang1, Sangho Cho1, Jeong M. Dang1, Eun B. Kwak1, Keunkyu Song2, Jooho Moon2
and Myung M. Sung1 *
Several techniques for the direct printing of functional materials have been developed to fabricate micro- and nanoscale
structures and devices. We report a new direct patterning method, liquid-bridge-mediated nanotransfer moulding, for the
formation of two- or three-dimensional structures with feature sizes as small as tens of nanometres over large areas up to
4 inches across. Liquid-bridge-mediated nanotransfer moulding is based on the direct transfer of various materials from a
mould to a substrate through a liquid bridge between them. We demonstrate its usefulness by fabricating nanowire fieldeffect transistors and arrays of pentacene thin-film transistors.
T
he fabrication of micro- and nanoscale structures is essential
for electronics1, micro/nanoelectromechanical systems2–4,
biological and chemical sensors5–8, microfluidics9–12, display
units, and optoelectronic devices13. Of existing patterning
methods, the direct printing of functional materials is the most efficient method for the fabrication of new types of structures and
devices at low cost and low environmental impact. Direct printing
includes a number of non-photolithographic techniques that
directly transfer the functional materials to the substrates: ink-jet
printing14, screen printing15, flexographic printing16, gravure printing17,18, offset printing19–21, and microtransfer moulding22–27.
Microtransfer moulding is the most versatile and cost-effective
method for the fabrication of functional microstructures over a
large area, but it suffers from problems such as poor edge resolution
(due to the lateral diffusion of the liquid inks), residues between
patterns, and difficulty in multi-alignment.
Several alternative residue-free direct printing methods have
been developed for patterning at the nanoscale, such as nanoimprint
lithography28–32, capillary force lithography33,34, and nanotransfer
printing28,35–39. Recently, nanoimprint lithography and capillary
force lithography have been used with selective dewetting to fabricate residue-free patterns of functional polymers. However, imprinting methods suffer from residues and difficulty in multi-alignment.
Nanotransfer printing is based on the adhesive transfer of a patterned metal thin film from a stamp to a substrate with tailored
surface chemistries35–37, but it also suffers from problems. For
instance, it only works with a limited number of materials
(mainly metals), it only works in a small range of processing conditions, and continuous operation can be difficult because vacuum
conditions are required.
We have developed a direct printing technique that is based on a
liquid-bridge-mediated transfer moulding process. The polar liquid
layer serves as an adhesion layer that provides good conformal
contact between the functional materials and the substrate38,39.
Unlike microtransfer moulding, our technique is not subject to
surface diffusion and can generate complex nanostructures with
minimum feature sizes below 60 nm with an edge resolution of
2–6 nm. The new technique allows two- or three-dimensional
complex nanostructures to be directly fabricated over a large area
using many types of inks.
Liquid-bridge-mediated transfer moulding
Figure 1 illustrates the procedure for patterning functional materials
using liquid-bridge-mediated nanotransfer moulding (LB-nTM). In
a first step, patterned hard and soft moulds were fabricated by using
polyurethane acrylate (PUA) and polydimethylsiloxane (PDMS),
respectively. These two materials have very low surface free energies
(PUA, 25 mJ m22, PDMS, 20 mJ m22). The patterned mould
was then filled with an ink solution using selective inking.
Discontinuous dewetting40 was used to fill only the recessed areas
of the mould with the ink solution. By dragging a deposited ink
solution over the patterned mould with a glass stick or a needle,
the meniscus of the ink solution moves over the surface of the
mould to fill inside the features without leaving any residues on
the raised surface (Fig. 1b). Discontinuous dewetting takes advantage of the interfacial free energy between the mould and the ink solution, and the ink solution must have a surface free energy (between
30 mJ m22 and 70 mJ m22) appropriate to the PDMS and PUA
moulds. The rate of dragging the solution, the aspect ratio of the
features in the mould (depth/width ≥ 1/20), and the viscosity of
the ink solution (,500 cP) also determine the success of the
discontinuous dewetting process40.
The filled ink is next solidified by drying it at mild temperatures
(,100 8C). Almost no residue remains on the protruding surfaces of
the mould as a result of the selective inking (Fig. 1c). The very small
amount of excess residue can be removed by application of a brisk
stream of nitrogen, because the mould has a very low surface free
energy. The absence of residue was confirmed by analysis of the patterns using energy dispersive X-ray analysis and a cross-sectional
view obtained by means of scanning electron microscopy (SEM;
Supplementary Fig. S1). Because of the solidification of the ink
solution, LB-nTM does not suffer from surface diffusion and can
generate nanostructures on a scale well below 100 nm.
The mould with the solidified ink was then brought into contact
with a substrate surface covered by a thin polar liquid layer. A substrate of area 1 × 1 cm2 can be uniformly covered with a 100-mmthick liquid layer by using 10 ml of a polar liquid. The polar liquid
layer on the substrate forms a liquid bridge (a capillary bridge)
between the substrate and a mould containing recessed patterns
(Fig. 1d). The liquid bridge allows good conformal contact
between the solidified ink and the substrate38. The substrate must
1
Department of Chemistry, Hanyang University, Seoul 133-791, Korea, 2 Department of Materials Science and Engineering, Yonsei University, Seoul 120-749,
Korea. *e-mail: [email protected]
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© 2010 Macmillan Publishers Limited. All rights reserved.
NATURE NANOTECHNOLOGY
DOI: 10.1038/NNANO.2010.175
a
b
Mould
500 nm
Fill channels with an ink solution
by selective inking
Ink
Mould
Solidify the ink
Solidified ink
c
Mould
500 nm
Contact
d
Liquid
layer
Subst
rate
Laplace
force
Substrate
Dry the liquid layer
and remove the mould
e
ate
range of materials, and we have made various functional structures
using many types of inks (liquid prepolymers, metal particle solutions, molecular precursors, and so on). It can also be used to fabricate nanometre-sized structures without leaving any residue on the
regions of the substrates not to be coated. In contrast to other direct
patterning methods using liquid inks, such as microtransfer moulding and gravure printing, here, the filled inks are solidified before
transfer onto the substrate to prevent lateral diffusion. The nanometre-sized patterns can be made on diverse substrates as long as
their surface free energies are high enough to exhibit strong capillary
action with a polar liquid layer. In fact, by using LB-nTM with UV
activation of the substrates, complex structures can be patterned on
various substrates including silicon, TiO2 , polyethersulphone (PES)
and gold (Supplementary Fig. S2). LB-nTM can be used to create
complex two- or three-dimensional nanostructures over a large
area in a repetitive, continuous process. The mould can be aligned
easily on complex structures because, before the polar liquid layer
is dried, it acts as an adhesive lubricant, enabling the mould to be
moved over the substrate. Furthermore, deformation and distortion
of the polymer mould can result in errors in the replicated patterns,
as well as misalignment of the patterns. Such problems are difficult
to correct in direct printing methods because the pattern transfer
occurs immediately at the time of contact. In the LB-nTM
method, however, the position of the mould can be adjusted even
after contact with the substrate, because the pattern is not transferred to the substrate before drying of the liquid layer.
Nanoscale patterns
Mould
Solidified ink
Substr
ARTICLES
Pattern
500 nm
Figure 1 | Liquid-bridge-mediated nanotransfer moulding. a, Schematic
illustration of LB-nTM. b, SEM image of the PUA mould. c, SEM image of
the mould filled with ZTO ink. d, Schematic illustration of a liquid bridge
formed by a polar liquid layer between a solidified ink and a substrate.
e, SEM image of ZTO patterns on a silicon substrate.
have a high surface free energy ( 40 mJ m22) to exhibit strong
capillary action as the two surfaces come into contact with the
polar liquid layer. As the liquid evaporates, the attractive capillary
force gradually increases, pulling the two surfaces into contact, providing good conformal contact between them with no additional
pressure to the mould. The majority of the liquid layer initially evaporates through the open sides between the mould and the substrate;
the remainder, which is confined in the features, is absorbed or
evaporates and permeates through the mould41,42. According to
our experiment, the PUA mould can absorb 5.6% of its weight in
ethanol at 70 8C. About 99 wt% of the absorbed ethanol diffuses
into the air in 10 min at 70 8C (Supplementary Table S1). After
drying, the separation of the mould from the substrate then
results in the formation of the patterns.
There are several reasons why LB-nTM is well suited for use in
automated printing machines. First, it can be applied to a wide
Nanometre-scale patterns of various materials were made on silicon
substrates using the LB-nTM method with hard moulds (PUA). The
masters used for fabrication of the moulds were silicon wafers with
dense nanoscale patterns, which were made by laser interference
lithography and subsequent dry etching steps, as described previously43. The moulds were fabricated by casting PUA on them.
After UV curing, the PUA moulds were peeled away from the
masters. To pattern an array of zinc–tin oxide (ZTO) on a nanometre scale, the recessed spaces of the patterned PUA moulds
were filled with a 2-methoxyethanol solution of ZTO ink. The
ZTO ink solution in the mould was solidified at 80 8C for 10 min.
The mould was then placed in contact with an oxidized Si(100) substrate covered by a thin ethanol layer. Following drying of the
ethanol layer between the mould and the substrate at 70 8C for
10 min, the mould was peeled away, leaving the ZTO nanopatterns
on the substrate. Scanning electron microscopy (SEM) images of the
representative structures formed in this manner are shown in Fig. 1,
including the PUA mould (Fig. 1a), the mould filled with ZTO ink
(Fig. 1c) and the ZTO patterns fabricated on the substrate (Fig. 1e).
SEM images of the ZTO patterns fabricated using the PUA mould
(140-nm-wide parallel lines, 60-nm-wide spaces) clearly show that
the ZTO patterns retain the x and y dimensions of the mould, as
shown in Fig. 2a. The height of each ZTO pattern, however, is
54 nm, which means that it is reduced by 46% in the z-direction
when compared to the depth of the mould (100 nm). Figure 2b
shows an SEM image of ZTO dots with widths of 165 nm and
depths of 100 nm that were fabricated using the PUA mould. The
height of the ZTO dot is reduced to 50 nm, but it retains a width
of 165 nm. Nanoscale lines and dots of silver and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) were also made using
LB-nTM with PUA moulds (silver lines: line, 95 nm, space,
105 nm, height, 200 nm; silver dots: width, 245 nm, depth, 200 nm;
TIPS-PEN lines: lines, 105 nm, space, 95 nm, height, 200 nm;
TIPS-PEN dots: width, 150 nm, depth, 200 nm). The silver and
TIPS-PEN ink solutions filling the moulds were solidified at 70 8C
and 90 8C, respectively, for 10 min. The moulds with the solidified
inks were then placed in contact with the silicon substrates covered
by thin ethanol layers, which were dried at 70 8C. The silver and
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NATURE NANOTECHNOLOGY
a
DOI: 10.1038/NNANO.2010.175
b
2 µm
1 µm
200 nm
c
d
1 µm
200 nm
e
500 nm
f
4 µm
1 µm
200 nm
Figure 2 | SEM images of nanoscale patterns (white) of different materials fabricated by LB-nTM on silicon substrates (black). a, ZTO line pattern (width,
W, 60 nm; spacing between features, S, 140 nm; height, H, 54 nm). b, ZTO dot pattern (W, 165 nm; H, 54 nm). c, Silver line pattern (W, 105 nm; S, 95 nm;
H, 123 nm). d, Silver dot pattern (W, 245 nm; H, 130 nm). e, TIPS-PEN line pattern (W, 95 nm; S, 105 nm; H, 145 nm). f, TIP-PEN dot pattern (W, 150 nm;
H, 140 nm).
TIPS-PEN patterns prepared in this manner are shown in Fig. 2c–f,
which clearly shows that the patterns retain the x and y dimensions
of the moulds. When compared to the sizes of the moulds, the z
dimensions of the silver and TIPS-PEN patterns are reduced by
35% and 30%, respectively. All these results indicate that the patterns fabricated using LB-nTM retain the x and y dimensions of the
moulds and are only reduced in the z-direction (height) because the
ink solutions locked inside the features are solidified. The shrinkage
of the pattern height mainly depends on the concentration and composition of the ink solutions. The ZTO and silver patterns exhibit
strong adhesion to the substrate surface and, thus, easily pass
Scotch tape adhesion tests. TIPS-PEN, which has low surface free
energy, the adhesion of the patterns is not as strong as those of
ZTO and silver.
Microscale patterns
Micrometre-scale patterns of various materials were made on silicon
substrates using the LB-nTM method but with soft moulds (PDMS).
The masters used for mould fabrication were silicon wafers with
patterned resists on scales from 2.5 to 200 mm. The moulds were
fabricated by casting PDMS on the masters. After curing, the
PDMS moulds were peeled away from the masters. The PDMS
moulds were then filled with the ZTO, silver and TIPS-PEN ink solutions. The solidified inks in the moulds were transferred to the
silicon substrate surface by the liquid-bridge-mediated transfer
process. Figure 3 presents various patterns with micrometre-scale
744
features formed by applying LB-nTM with PDMS moulds.
Figure 3a,b shows SEM images of ZTO patterns fabricated using
masters having 9-mm-wide parallel lines with 11-mm-wide spaces
and complex features (3–150 mm). These images clearly show that
the transferred patterns retain the features of the masters.
Micrometre-scale line and complex patterns with silver and TIPSPEN are also shown in Fig. 3c–f, demonstrating that they are also
fabricated with high pattern fidelity and structural integrity.
Multilayer structures formed from silver patterns were formed by
consecutive printing of silver line patterns on pre-patterned substrates using LB-nTM (Fig. 3g). The PDMS mould with silver ink
was placed in contact with the silicon substrate, which had
already been patterned with one layer of silver line patterns. The
mould was rotated 908 with respect to the direction of the first
line patterns. A thin ethanol layer on the pre-patterned silicon substrate is able to produce strong capillary action as the mould comes
into contact with it. As the ethanol layer evaporates, the attractive
capillary force strongly pulls the solidified silver ink into contact
with the substrate and provides good conformal contact between
them (Fig. 3h). Through additional printing steps, many more
layered structures can be added (Supplementary Fig. S3).
Nanowire field-effect and TIPS-PEN thin-film transistors
Nanowire field-effect transistors were fabricated on silicon substrates using LB-nTM, as described in Fig. 4a. Nanometre-scale
line patterns of ZTO where the lines have a width of 60 nm and
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NATURE NANOTECHNOLOGY
ARTICLES
DOI: 10.1038/NNANO.2010.175
a
b
10 µm
100 µm
100 µm
c
d
10 µm
500 µm
100 µm
e
f
10 µm
50 µm
100 µm
g
h
10 µm
2 µm
Figure 3 | SEM images of microscale patterns (white) of different materials fabricated by LB-nTM on silicon substrates (black). a, ZTO line pattern
(W, 9 mm; S, 11 mm; H, 430 nm). b, ZTO complex pattern. c, Silver line pattern (W, 11 mm; S, 9 mm; H, 550 nm). d, Silver isolated pattern (10–200 mm).
e, TIPS-PEN line pattern (W, 9.5 mm; S, 10.5 mm; H, 500 nm). f, TIPS-PEN complex pattern. g,h, Image of a two-layer silver nanopattern (g) with and
expanded view (h).
length of 10 mm were created on heavily doped silicon substrates
comprising 200-nm-thick SiO2 by applying LB-nTM with PUA
moulds. The ZTO nanowire arrays were then annealed at 500 8C
in air to achieve complete thermal decomposition of any organic
residues and metal salts44,45. Finally, source and drain electrodes
composed of 200-nm-thick silver were defined on the substrate by
LB-nTM using PDMS moulds. ZTO-nanowire field-effect transistors were thus obtained, with metal contacts functioning as source
and drain electrodes and the silicon substrate as a back-gate.
Figure 4b shows SEM images of field-effect transistors with from
1 to 100 ZTO nanowires. The width of the ZTO nanowire narrowed
to 55 nm, indicating 23% shrinkage in volume, which was due to
the annealing at 500 8C in air. A post-annealing step at 200 8C
under an atmosphere of hydrogen and nitrogen was performed to
improve the electrical performance of the transistors before carrying
out measurements44,45. Figure 4c,d presents the typical drain
current–gate voltage (ID–VG) transfer curves and drain current–
drain voltage (ID–VD) output curves from the field-effect transistors
with 10 ZTO nanowires. The ZTO-nanowire field-effect transistors
were well modulated, depending on the gate voltage, and exhibited
clear saturation behaviour with a field-effect mobility of
0.4 cm2 V21 s21, an on/off current ratio of 1 × 106 and a
threshold voltage of 5 V. This performance is comparable to ZTO
thin-film transistors fabricated by spin-coating with the same
ZTO solution44 (Supplementary Fig. S4).
Arrays of TIPS-PEN thin-film transistors were fabricated on
4-inch PES substrates using LB-nTM using PDMS moulds
(Fig. 5a). An inverted staggered structure was used in the fabrication
of the thin-film transistor device. A 150-nm-thick indium-tin oxide
(ITO) gate electrode and a 200-nm-thick SiO2 dielectric layer were
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NATURE NANOTECHNOLOGY
a
c
ZTO nanowire
DOI: 10.1038/NNANO.2010.175
1 × 10−5
1.2
1 × 10−6
1.0
1 × 0−7
0.8
1 × 10−9
0.6
−10
1 × 10
Source
ID (µA)
ID (A)
1 × 10−8
0.4
1 × 10−11
Ag metal
Gate
Drain
0.2
1 × 10−12
1 × 10−13
−40 −30 −20 −10
SiO
2
0.0
0
10
VG (V)
20
30
40
1.2
d
VG = 40 V
1.0
b
55 nm
1 µm
ID (µA)
0.8
1 µm
0.4
VG = 20 V
Ag
0.2
VG = 10 V
2 µm
0.0
Ag
1 µm
VG = 30 V
0.6
VG = 0 V
0
10
20
VD (V)
30
40
Figure 4 | ZTO nanowire field-effect transistors. a, Schematic diagram of the procedure for fabricating ZTO nanowire FETs using LB-nTM. b, SEM images of
ZTO nanowire FETs. c, Transfer curve for a ZTO nanowire FET. Drain current ID is plotted as a function of gate voltage VG on a linear scale (red, right axis)
and a logarithmic scale (blue, left axis). Drain voltage VD is 40 V. d, Output curves for a ZTO nanowire FET. Drain current is plotted as a function of drain
voltage for different values of the gate voltage.
a
b 1 × 10−5
2.5
1 × 10−6
2.0
1.5
1 × 10−8
1 × 10−9
1.0
−ID (µA)
−ID (A)
1 × 10−7
1 × 10−10
0.5
1 × 10−11
1 × 10−12
0.0
0
Ag
−10
−20
Ag
c
−1.5
VG = −37.5 V
−1.0
−0.5
Pentacene
−50
VG = −50.0 V
−2.0
ID (µA)
135 µm
−40
−2.5
200 µm
10 µm
−30
VG (V)
VG = −25.0 V
50 µm
VG = −12.5 V
0.0
0
−10
−20
−30
VD (V)
−40
−50
Figure 5 | TIPS-PEN thin-film transistors. a, Photograph and SEM images of TIPS-PEN thin-film transistors. b, Transfer curve for a TIPS-PEN thin-film
transistor on a linear scale (red, right axis) and a logarithmic scale (blue, left axis). VD ¼ 250 V. c, Output curves for a TIPS-PEN thin-film transistor.
746
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NATURE NANOTECHNOLOGY
DOI: 10.1038/NNANO.2010.175
formed on a PES substrate by sputter deposition. An array of TIPSPEN patterns (thickness, 60 nm) acting as active channel layers was
fabricated on the substrate using LB-nTM. The nominal channel
length of the TIPS-PEN thin-film transistor was 10 mm, and the
channel width was 135 mm. Finally, the source and drain electrodes
composed of 200-nm-thick silver were defined on the substrate
using LB-nTM. Figure 5b,c displays the typical drain current–gate
voltage (ID–VG) transfer curves for VD ¼ –50 V and drain
current–drain voltage (ID–VD) output curves for several gate voltages from our TIPS-PEN thin-film transistors prepared on flexible
substrates. The maximum ID level was approximately –2 mA under a
gate bias of –50 V. According to the transfer characteristics (ID–VG)
of Fig. 5b, a field-effect mobility of 0.02 cm2 V21 s21 was achieved
in the saturation regime of VD ¼ –50 V together with an on/off
ratio of 1 × 105 and a threshold voltage of –13 V. In comparison,
thin-film transistors fabricated using the spin-coated TIPS-PEN46
showed a saturation mobility of 0.03 cm2 V21 s21 and an on/off
ratio of 1 ×105 (Supplementary Fig. S5). The TIPS-PEN thinfilm transistors can endure strenuous bending and are also transparent in the visible range (Fig. 5a), and therefore potentially useful for
flexible and invisible electronics.
Conclusions
We have reported a direct printing method that is based on the
transfer of various materials from a mould to a substrate via a
liquid bridge between them. Ink solution in the mould is solidified
and transferred onto a substrate via a liquid bridge between the
mould and the substrate. The mould can be aligned easily on
complex structures, because it is movable on the substrate
before the polar liquid layer is dried, which acts as an adhesive
lubricant. This procedure is well suited for use in automated
direct printing machines and is capable of generating patterns of
various functional materials with a wide range of feature sizes on
diverse substrates.
Methods
Materials. Unless otherwise noted, all commercial materials were obtained from
Aldrich Chemical Co. and used without further purification. TIPS-PEN was
synthesized following the procedure reported by Anthony et al.47,48, and the resulting
crude product was purified using chromatography on silica gel, first eluting the
excess (triisopropylsily)acetylene with hexane and then eluting a deep blue band
with 90% hexane and 10% dichloromethane. The TIPS-PEN ink solution was
prepared by dissolving 2 wt% TIPS-PEN in tetralin solvent. The ink solution for
printing the ZTO semiconductor was prepared by dissolving zinc acetate dehydrate
[Zn(CH3COO)2.2H2O] and tin acetate [Sn(CH3COO)2] in 2-methoxyethanol44,45.
The silver nanoparticle ink (DGP 40LT-15C) was purchased from Advanced Nano
Products. The ink contained 20 wt% silver nanoparticles, with particle diameters of
40–50 nm, dispersed in methanol solvent. Polyurethane acrylate (MINS-ERM,
Minuta Tech.) was used to prepare the UV-curable hard moulds.
Polydimethylsiloxane (Sylgard 184) was ordered from Dow Corning.
Preparation of substrates. The silicon substrates used in this research were cut from
n-type (100) wafers with resistivity in the range 1–5 V.cm. The silicon substrates
were initially treated by a chemical cleaning process, which involved degreasing,
HNO3 boiling, NH4OH boiling (alkali treatment), HCl boiling (acid treatment),
rinsing in deionized water and blow-drying with nitrogen, as proposed by Ishizaka
and Shiraki, to remove contaminants49. A thin oxide layer was grown by placing the
silicon substrate in a piranha solution (4:1 mixture of H2SO4:H2O2) for 10–15 min.
The substrate was rinsed several times in deionized water (resistivity ¼ 18 MV.cm),
then dried with a stream of nitrogen. The flexible substrates used in this study were
cut from Glastic PES films (i-components Inc.). The PES substrates were cleaned
with methanol and deionized water, and finally blow-dried with nitrogen to remove
the contaminants.
Analysis techniques. The samples were analysed using a Hitachi S4800 SEM. Water
contact angles of the samples were determined on a model A-100 Rame-Hart NRL
goniometer in ambient air by using the sessile drop method. All current–voltage
(I–V ) properties of the field-effect transistors and thin-film transistors were
measured with a semiconductor parameter analyser (HP 4155C, Agilent
Technologies), and C–V measurements were made using a capacitance meter (HP
4284 LCR meter, Agilent Technologies, 1 MHz) in the dark and in air ambient
(relative humidity, 45%) at 20 8C.
ARTICLES
Received 2 June 2010; accepted 21 July 2010;
published online 26 September 2010
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Acknowledgements
This work was supported by the National Research Foundation of Korea (2009-0092807;
2010-0019125; 2009-0086302), the Seoul R&BD programme (ST090839), the IT R&D
program of MKE/KEIT (10030559) and the Korea Research Foundation
(KRF-2007-313-C00383).
Author contributions
M.M.S. conceived and designed the experiments. J.K.H., E.B.K., S.C. and J.M.D. performed
the experiments. K.S. and J.M. contributed to materials and analysis. S.C. and M.M.S.
co-wrote the paper.
Additional information
The authors declare no competing financial interests. Supplementary information
accompanies this paper at www.nature.com/naturenanotechnology. Reprints and
permission information is available online at http://npg.nature.com/reprintsandpermissions/.
Correspondence and requests for materials should be addressed to M.M.S.
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