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Directed assembly of solution processed single-walled carbon nanotubes via dielectrophoresis: From aligned array to individual nanotube devices

TL;DR: In this article, the authors demonstrate directed assembly of high quality solution processed single-walled carbon nanotube (SWNT) devices via ac dielectrophoresis using commercially available SWNT solutions.
Abstract: The authors demonstrate directed assembly of high quality solution processed single-walled carbon nanotube (SWNT) devices via ac dielectrophoresis using commercially available SWNT solutions. By controlling the shape of the electrodes, concentration of the solution, and assembly time, the authors are able to control the assembly of SWNTs from dense arrays down to individual SWNT devices. Electronic transport studies of individual SWNT devices show field effect mobilities of up to 1380 cm2/V s for semiconducting SWNTs and saturation currents of up to ∼15 μA for metallic SWNTs. The field effect mobilities are more than an order of magnitude improvement over previous solution processed individual SWNT devices and close to the theoretical limit. Field effect transistors (FET) fabricated from aligned two-dimensional arrays of SWNT show field effect mobility as high as 123 cm2/V s, which is three orders of magnitude higher than the solution processed organic FET devices. This study shows promise for commerciall...

Summary (3 min read)

A. Electrode design and fabrication

  • Devices were fabricated on heavily doped silicon substrates capped with a thermally grown 250 nm thick SiO2 layer.
  • The electrode patterns were fabricated by a combination of optical and electron beam lithography EBL .
  • First, contact pads and electron beam markers were fabricated with optical lithography using double layer resists LOR 3A/ Shipley 1813 developing in CD26, thermal evaporation of 3 nm Cr and 50 nm Au followed by lift-off.
  • Smaller electrode patterns were fabricated with EBL using single layer PMMA resists and then developing in 1:3 methyl isobutyl ketone:isopropal alchohol MIBK:IPA .
  • The electrode patterns for the alignment of individual tubes use a pair of adjacent taper shaped electrodes with sharp tips separated by 1 m, whereas the electrode patters for aligned arrays of SWNTs were done using 200 m long parallel electrodes with 5 m spacing.

B. Solution preparation

  • The authors used three different SWNT solutions for the DEP assembly: i A homemade dimethylformamide DFM solution, ii homemade dichloroethane DCE solution, and iii already suspended, surfactant-free aqueous SWNT solution purchased from Brewer Science Inc.26.
  • The DMF-SWNT suspension was made by ultrasonically dispersing HiPCO grown SWNTs Carbon Nanotechnologies Inc. in 5 ml DMF and 1 ml trifluoroacetic acid TFA .
  • TFA was used to dissolve any unwanted catalytic particles and amorphous carbon from the bulk material.
  • After dissolving the SWNTs in DMF/TFA, the solution was centrifuged, the supernatant was decanted, and the solid is then redispersed for further dispersion/centrifugation/decantation cycles.
  • The DCE mixture was made by simply adding a very small pinch of the HiPCO SWNT soot to 4 ml of DCE and then sonicating for 5–10 min before the assembly.

A. Controlling the assembly of individual SWNTs

  • Figure 2 shows the effect of SWNT concentration on the DEP assembly using the commercial solution diluted in DI water.
  • The authors use a simultaneous deposition technique14,22 in this case, applying the ac field between source and gate for 3 min.
  • Approximately 10% of the diameters are greater than 3.5 nm, which is an indication of the possible presence of some double-walled nanotubes or large diameter SWNTs.
  • It can be seen here that the devices are free of bundles and catalytic particles which stems from the quality of the commercial solution.

B. Comparison of solutions

  • This is done because long trapping times are more complex to use as DMF and DCE evaporate quickly in air.
  • Figure 4 a shows a representative AFM im- age after the assembly for the DMF solution.
  • As can be clearly seen here, the resulting SWNT deposition contains a bundle and catalytic particles shown by the arrows.
  • The commercial solution turned out to be stable for months, therefore increasing the reproducibility.
  • 26 Therefore, although the DMF and DCE solutions may be optimized for further control, however, due to the reproducible and clean device assembly from the stable commercial solution, the authors only continued further investigation of the devices stemming from the commercial solution.

C. Electrical transport properties of individual nanotube devices

  • After the DEP assembly, the room temperature dc electrical transport measurements of the devices were done in a probe station using a DL instruments 1211 current preamplifier combined with a high resolution DAC card interfaced with LABVIEW.
  • After two terminal resistance measurements of the as-assembled devices, they were annealed in a tube furnace using ultrahigh purity Ar /H2 1:10 ratio/Ar:H2 at 200 °C for 1 h.
  • During cool down, the gas was left flowing until the sample reached room temperature.
  • Approximately 70% of their devices show metallic or semimetallic behavior with current on-off ratio Ion / Ioff less than 10, and 30% of the devices show semiconducting behavior with on-off ratios 10.
  • The higher percentage of metallic nanotubes during the assembly is expected since, to the first order approximation, DEP tends to attract metallic SWNTs over semiconducting SWNTs because metallic SWNTs have a higher dielectric constant.

1. Metallic nanotube device properties

  • Figure 5 b is a histogram of the contact resistance for the metallic SWNT devices before annealing and after annealing.
  • The average contact resistances before and after annealing are 100 M and 1 M , respectively.
  • The contact resistance is as low as 25 k after annealing for C6B10 Paul Stokes and Saiful I. Khondaker: Directed assembly of solution processed SWNTs C6B10 J. Vac. Sci. Technol.
  • To characterize the quality of the metallic SWNTs and their contact, the authors measured the ID-VDS characteristics at high bias after annealing.

2. Semiconducting nanotube device properties

  • The drain current changes by several orders of magnitude with gate voltage and maintains approximately the same off-current for each VDS.
  • The maximum mobility is 20 times higher than the highest previous reported values for other solution processed devices and close to what is expected in high quality direct growth CVD devices of similar diameter.
  • The authors speculate that the improved device performance stems from the nonexistence of residual surfactant and the cleanliness of the as-assembled devices with the absence of bundles.

D. Large area assembly and device properties

  • Large scale parallel arrays of SWNTs are of considerable interests in order to increase device to device homogeneity and their expected higher performance compared to organic electronic FETs.
  • The authors used diluted commercial solution 1 g /ml for this assembly along with parallel electrode.
  • The array contains a mixture of metallic and semiconducting SWNTs as evident in the I-VG for the asassembled device Fig. 6 b top curve where the device shows semimetallic behavior with an on-off ratio of 3.
  • After the second breakdown, the mobility reduces a small amount to 53 cm2 /V s and the on-off ratio increases to 14.
  • The devices yield median mobility values of 77, 41, and 15 cm2 /V s after the three breakdowns, respectively.

IV. CONCLUSIONS

  • The authors demonstrated directed assembly of high quality solution processed carbon nanotube devices via ac dielectrophoresis using commercially available SWNT solutions.
  • By optimizing the device design, concentration of the solution, and assembly time, the authors are able to control the assembly of SWNTs from dense arrays to clean individual devices.
  • Electronic transport measurements of individual SWNT revealed mobilities more than an order of magnitude improvement over previous solution processed individual SWNT devices and close to the theoretical limit.
  • FETs fabricated from aligned 2D arrays of SWNT show high field effect mobility, up to three orders of magnitude higher than solution processed organic FET devices.
  • This study shows promise for commercially available SWNT solution for the parallel fabrication of high quality nanoelectronic devices.

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University of Central Florida University of Central Florida
STARS STARS
Faculty Bibliography 2010s Faculty Bibliography
1-1-2010
Directed assembly of solution processed single-walled carbon Directed assembly of solution processed single-walled carbon
nanotubes via dielectrophoresis: From aligned array to individual nanotubes via dielectrophoresis: From aligned array to individual
nanotube devices nanotube devices
Paul Stokes
University of Central Florida
Saiful I. Khondaker
University of Central Florida
Find similar works at: https://stars.library.ucf.edu/facultybib2010
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contact STARS@ucf.edu.
Recommended Citation Recommended Citation
Stokes, Paul and Khondaker, Saiful I., "Directed assembly of solution processed single-walled carbon
nanotubes via dielectrophoresis: From aligned array to individual nanotube devices" (2010).
Faculty
Bibliography 2010s
. 828.
https://stars.library.ucf.edu/facultybib2010/828

Directed assembly of solution processed single-walled carbon nanotubes via
dielectrophoresis: From aligned array to individual nanotube devices
Paul Stokes, and Saiful I. Khondaker
Citation: Journal of Vacuum Science & Technology B 28, C6B7 (2010); doi: 10.1116/1.3501347
View online: https://doi.org/10.1116/1.3501347
View Table of Contents: https://avs.scitation.org/toc/jvb/28/6
Published by the American Vacuum Society
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Directed assembly of solution processed single-walled carbon nanotubes
via dielectrophoresis: From aligned array to individual nanotube
devices
Paul Stokes and Saiful I. Khondaker
a
Nanoscience Technology Center and Department of Physics, University of Central Florida, 12424 Research
Parkway, Orlando, Florida 32826
Received 9 July 2010; accepted 7 September 2010; published 29 November 2010
The authors demonstrate directed assembly of high quality solution processed single-walled carbon
nanotube SWNT devices via ac dielectrophoresis using commercially available SWNT solutions.
By controlling the shape of the electrodes, concentration of the solution, and assembly time, the
authors are able to control the assembly of SWNTs from dense arrays down to individual SWNT
devices. Electronic transport studies of individual SWNT devices show field effect mobilities of up
to 1380 cm
2
/ V s for semiconducting SWNTs and saturation currents of up to 15
A for metallic
SWNTs. The field effect mobilities are more than an order of magnitude improvement over previous
solution processed individual SWNT devices and close to the theoretical limit. Field effect
transistors FET fabricated from aligned two-dimensional arrays of SWNT show field effect
mobility as high as 123 cm
2
/ V s, which is three orders of magnitude higher than the solution
processed organic FET devices. This study shows promise for commercially available SWNT
solution for the parallel fabrication of high quality nanoelectronic devices. © 2010 American
Vacuum Society. DOI: 10.1116/1.3501347
I. INTRODUCTION
The unique electronic properties of single-walled carbon
nanotubes SWNTs make them promising candidates for fu-
ture nanoelectronic devices.
1
For practical applications in na-
noelectronics, it is important that SWNTs are assembled at
selected positions of the circuit with high yield. Chemical
vapor deposition CVD growth of SWNTs using litho-
graphically patterned catalytic islands and then making elec-
trical contact to them has been used for the parallel fabrica-
tion of SWNT devices.
2,3
Although CVD grown SWNT has
shown good device properties, high growth temperature
900 °C is a major bottleneck to make them compatible
with current complementary metal-oxide-semiconductor
CMOS fabrication technologies.
An attractive alternative to CVD growth techniques for
the high throughput assembly of SWNT electronic devices at
selected positions of the circuit is from postsynthesis fabri-
cation using solution processed SWNTs.
4
Solution process-
ing could be advantageous due to its ease of processing at
room temperature, CMOS compatibility, and potential for
scaled up manufacturing of SWNT devices on various sub-
strates. Several assembly techniques from solution include
chemical and biological patterning,
5,6
flow assisted
alignment,
7
Langmuir–Blodgett assembly,
8
bubble blown
films,
9
contact printing,
10
spin coating assisted alignment,
11
and evaporation driven self-assembly.
12
However, most of
these techniques are used either for only large area devices or
only single nanotube devices. In addition, most of these as-
sembly techniques require postetching to remove excess
SWNTs in the circuit.
Dielectrophoresis DEP offers a convenient way in which
SWNTs can be precisely positioned from solution at room
temperature using a nonuniform ac electric field on prepat-
terned electrodes.
1324
DEP can be advantageous over other
solution processed techniques because it allows for the posi-
tioning from large areas to individual SWNTs at predefined
coordinates of the circuit and does not require the need of
postetching or transfer printing. One crucial aspect of the
DEP process is the quality of the SWNT solution. The solu-
tion should be free of catalytic particles, contain mostly in-
dividual SWNTs, and be stable for long periods of time.
Catalytic particles in the solution tend to make their way into
the electrode gap with the SWNTs during assembly process
due to their highly conducive nature which can disrupt their
device performance. Solutions containing bundles make it
difficult to only obtain individual SWNTs reproducibly into
the electrode gap as the DEP force will likely select the
larger bundles due to their higher dielectric constant and con-
ductivity. Additionally, avoiding degradation of the SWNTs
from processing is extremely important to maintain their ex-
cellent electrical properties.
25
In this article, we used a clean commercially available,
surfactant-free SWNT solution combined with the DEP tech-
nique to achieve directed assembly of high quality SWNT
devices with high yield. By optimizing the device design,
concentration of the solution, and assembly time, we are able
to control the assembly of SWNTs from large scale arrays
down to individual devices. Comparison of the assembly
from commercial solution of SWNT with other homemade
solutions in common organic solvents show that the clean
a
Author to whom correspondence should be addressed; electronic mail:
saiful@mail.ucf.edu
C6B7 C6B7J. Vac. Sci. Technol. B 286, Nov/Dec 2010 1071-1023/2010/286/C6B7/6/$30.00 ©2010 American Vacuum Society

assembly was obtained from the commercial solution. Elec-
tronic transport properties of individual semiconducting
SWNTs show field effect mobilities up to 1380 cm
2
/ V s and
saturation currents up to 15
A for metallic SWNTs. The
field effect mobilities are more than an order of magnitude
improvement over previous solution processed individual
SWNT devices and close to the theoretical limit. Addition-
ally, field effect transistors FET fabricated from aligned
two-dimensional 2D arrays of SWNT show field effect mo-
bilities as high as 123 cm
2
/ V s, which is three orders of
magnitude higher than solution processed organic FET de-
vices.
II. EXPERIMENTAL DETAILS
A. Electrode design and fabrication
Devices were fabricated on heavily doped silicon sub-
strates capped with a thermally grown 250 nm thick SiO
2
layer. The electrode patterns were fabricated by a combina-
tion of optical and electron beam lithography EBL. First,
contact pads and electron beam markers were fabricated with
optical lithography using double layer resists LOR 3A/
Shipley 1813 developing in CD26, thermal evaporation of 3
nm Cr and 50 nm Au followed by lift-off. Smaller electrode
patterns were fabricated with EBL using single layer PMMA
resists and then developing in 1:3 methyl isobutyl keto-
ne:isopropal alchohol MIBK:IPA. After defining the pat-
terns, 2 nm Cr and 25 nm thick Pd were deposited using
electron beam deposition followed by lift-off in warm ac-
etone. Pd was used because it is known to make the best
electrical contact to SWNTs.
3
Figures 1a and 1b show a
cartoon of the electrode patterns for the DEP assembly of
individual SWNTs and parallel arrays of SWNTs, respec-
tively. The electrode patterns for the alignment of individual
tubes use a pair of adjacent taper shaped electrodes with
sharp tips separated by 1
m, whereas the electrode patters
for aligned arrays of SWNTs were done using 200
m long
parallel electrodes with 5
m spacing.
B. Solution preparation
We used three different SWNT solutions for the DEP as-
sembly: i A homemade dimethylformamide DFM solu-
tion, ii homemade dichloroethane DCE solution, and iii
already suspended, surfactant-free aqueous SWNT solution
purchased from Brewer Science Inc.
26
The DMF-SWNT sus-
pension was made by ultrasonically dispersing HiPCO
grown SWNTs Carbon Nanotechnologies Inc. in 5ml
DMF and 1 ml trifluoroacetic acid TFA. TFA was used to
dissolve any unwanted catalytic particles and amorphous car-
bon from the bulk material. After dissolving the SWNTs in
DMF/TFA, the solution was centrifuged, the supernatant was
decanted, and the solid is then redispersed for further
dispersion/centrifugation/decantation cycles. The final solu-
tion was diluted until it became clear and then sonicated for
several minutes before assembly. The DCE mixture was
made by simply adding a very small pinch of the HiPCO
SWNT soot to 4 ml of DCE and then sonicating for
5 10 min before the assembly. The commercial solution
has an original SWNT concentration of 50
g/ ml and was
diluted using de-ionized DI water to a desired concentra-
tion.
C. Dielectrophoretic assembly
The directed assembly of SWNTs at predefined electrode
positions was done in a probe station under ambient condi-
tions. A small drop of SWNT solution was cast onto the chip
containing the electrode pairs. An ac voltage of 1 MHz,
5V
p-p
was applied using a function generator between the
source and drain electrodes or by a simultaneous deposition
technique
14,22
between source and gate to align at several
electrode pairs simultaneously. The ac voltage gives rise to a
time averaged dielectrophoretic force. For an elongated ob-
ject, it is given by F
DEP
⬀␧
m
ReK
f
E
rms
2
, K
f
=
p
m
/
m
,
and
p,m
=
p,m
i
p,m
/
, where
p
and
m
are the permit-
tivities of the nanotube and, solvent respectively, K
f
is the
Claussius–Mossotti factor,
is the conductivity, and
=2
f is the frequency of the applied ac voltage.
27
The in-
duced dipole moment of the nanotube interacting with the
strong electric field causes the nanotubes to move in a trans-
lational motion along the electric field gradient.
Figures 1c and 1d show a simulation of the electric
field around the electrode gap for the adjacent taper shaped
electrode and parallel plate electrode, respectively. The simu-
lations were done using a commercially available software
FLEX PDE assuming that the potential phasor is real and
therefore using the electrostatic form of the Laplace equation
2
=0.
14
Hence we can set the effective potential of the
electrodes to = V
p-p
/ 2 for our simulation. From Fig.
1c, it can be seen that the strongest electric field lines are
confined at the sharp tips. This increases the probability of
aligning individual SWNTs. For the parallel plate geometry,
the electric field is uniform throughout the electrode gap al-
lowing for many nanotubes to align parallel to one another
throughout the gap. After the assembly, the function genera-
FIG.1. Color online兲共a Cartoon of the electrode patterns for DEP assem-
bly of a individual SWNTs and b 2D arrays of SWNTs. 2D simulated
electric field around the electrode gap for c the taper shaped electrodes and
d parallel plate electrodes.
C6B8 Paul Stokes and Saiful I. Khondaker: Directed assembly of solution processed SWNTs C6B8
J. Vac. Sci. Technol. B, Vol. 28, No. 6, Nov/Dec 2010

tor was turned off and the sample was blown dry by a stream
of nitrogen gas.
III. RESULTS AND DISCUSSIONS
A. Controlling the assembly of individual SWNTs
Figure 2 shows the effect of SWNT concentration on the
DEP assembly using the commercial solution diluted in DI
water. We use a simultaneous deposition technique
14,22
in
this case, applying the ac field between source and gate for 3
min. Figure 2a shows an atomic force microscopy AFM
image of a device after the assembly for a SWNT concentra-
tion of 1000 ng/ml. Dilution of the solution by ten times to
100 ng/ml concentration yield less SWNTs in the gap, as
shown in Fig. 2b. It can be seen here in both cases that the
SWNTs mimic the electric field lines around the electrode
gap, as simulated in Fig. 1c. The yield for the 1000 ng/ml
and 100 ng/ml concentration is 95%. By diluting the solu-
tion to 10 ng/ml, we obtained an individual SWNT in the gap
Fig. 2c. The diameter of this individual SWNT is
2.0 nm, measured by AFM. Figure 2d shows a histogram
of 100 individual SWNTs giving an average diameter of
2.00.2 nm. Approximately 10% of the diameters are
greater than 3.5 nm, which is an indication of the possible
presence of some double-walled nanotubes or large diameter
SWNTs.
28
The total yield of individual SWNTs at low con-
centration is 20% on average and as high as 35% for a
single chip. Figure 3 shows a number of SEM images of
individual nanotubes assembled by this technique. It can be
seen here that the devices are free of bundles and catalytic
particles which stems from the quality of the commercial
solution.
B. Comparison of solutions
We investigated the effect of the different solutions at low
concentration 共⬃10 ng/ ml on the DEP assembly. In con-
trast to the commercial solution in water, for the DMF and
DCE solutions, we apply the ac voltage between one pair at
a time for 5 s. This is done because long trapping times
are more complex to use as DMF and DCE evaporate
quickly in air. Figure 4a shows a representative AFM im-
age after the assembly for the DMF solution. As can be
clearly seen here, the resulting SWNT deposition contains a
bundle and catalytic particles shown by the arrows. At cer-
tain areas along the SWNT, the diameter is as large as 30–40
nm. Figure 4b shows the representative AFM image of a
device after assembling the SWNTs using DCE. The result-
ing device also contains catalytic particles near the electrode
tip on the right and shows diameters up to 10 nm along the
SWNT. Figure 4c shows an AFM image of a device after
assembly by using the Brewer Science SWNT solution. It is
clear from the AFM image that the SWNT is individual and
does not contain any catalytic particles. The commercial so-
lution turned out to be stable for months, therefore increasing
the reproducibility. For the DCE solution we were able to
assemble 10 individual SWNT devices out of 80 tries,
however, all of them contained catalytic particles with
diameter10 nm attached to the tubes. Another problem
that arises when using DCE is that it evaporates in air very
quickly, it is highly toxic, volatile, and did not remain stable
for more than a few hours. In the DMF case, the solutions
also only remained stable for a short period of time and the
results often came with larger diameter bundles 15 nm out
of 50 tries.
As can be concluded here, the commercial solution
yielded the best results for the assembly of clean and indi-
vidual SWNT devices. The good results from the commercial
solution are due to several reasons. First, its very low density
of impurity particles less than 50 ppb
26
is particularly ad-
vantageous in the DEP process because catalytic particles in
the solution tend to make their way into the electrode gap
during DEP due to their high conductivity. This is displayed
FIG.2. Color online AFM image of nanotubes assembled between the
electrodes with SWNT concentrations of a 1000 ng/ml b 100 ng/ml, and
c 10 ng/ml in the solution. Scale bar: 1
m in all images. d Histogram of
diameters for over 100 nanotube devices.
FIG.3. 关共a-l兲兴 SEMs of several individual SWNT assembled via DEP from
commercial solution at a concentration of 10 ng/ml. Gap between the
electrodes is 1
m.
FIG.4. Color online Representative AFM images of SWNTs assembled via
DEP a from DMF solution, b from DCE solution, and c the Brewer
Science solution.
C6B9 Paul Stokes and Saiful I. Khondaker: Directed assembly of solution processed SWNTs C6B9
JVSTB-MicroelectronicsandNanometer Structures

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TL;DR: These measurements set the upper bound for the performance of nanotube transistors operating in the diffusive regime and are in good agreement with theoretical predictions for acoustic phonon scattering in combination with the unusual band structure ofnanotubes.
Abstract: Semiconducting single-walled carbon nanotubes are studied in the diffusive transport regime. The peak mobility is found to scale with the square of the nanotube diameter and inversely with temperature. The maximum conductance, corrected for the contacts, is linear in the diameter and inverse temperature. These results are in good agreement with theoretical predictions for acoustic phonon scattering in combination with the unusual band structure of nanotubes. These measurements set the upper bound for the performance of nanotube transistors operating in the diffusive regime.

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01 Aug 2006-Small
TL;DR: These results suggest new alternatives for fabricating CNT patterns by simply dispensing/printing the dissolved/dispersed particles on substrates and a cost-effective and scaleable deposition method for generating conductive multi-walled carbon nanotube patterns on paper and polymer surfaces is presented.
Abstract: The advantageous physical properties of carbon nanotubes (CNTs), such as excellent thermal conductivity, good mechanical strength, optional semiconducting/metallic nature, and advanced field-emission behavior, have been utilized in a number of different devices for several years. The area-selective synthesis of well-organized CNTs on prepatterned growth templates using either catalytic or plasma-enhanced chemical vapor deposition methods (CCVD and PECVD, respectively) opens up further novel fields for advanced future applications. However, these promising techniques require complex lithography processes and sophisticated deposition facilities (PECVD) or are limited to thermally durable growth substrates (CCVD). Recent advances in nanotube chemistry enable both the dissolution and dispersion of CNTs in various solvents. These results suggest new alternatives for fabricating CNT patterns by simply dispensing/printing the dissolved/dispersed particles on substrates. Alternatively, controlled flocculation of CNT suspensions in flow channels or on prepatterned stamps can be accomplished to produce patterns of nanotubes on various surfaces. Herein, a cost-effective and scaleable deposition method for generating conductive multi-walled carbon nanotube (MWCNT) patterns on paper and polymer surfaces is presented. MWCNTs grown by CCVD were chemically modified to make the nanotubes dispersible in water, and in turn the aqueous dispersion was dispensed on various substrates using a commercial desktop inkjet printer. The electrical behavior of the printed patterns is investigated and the limitations of the process are discussed. For functionalization (Figure 1a), the MWCNTs were first refluxed in nitric acid to produce carboxyl, hydroxyl, and carbonyl groups at the defect sites of the outer graphene layer of the nanotubes. In a subsequent step, these hydroxyl and carbonyl groups were oxidized further with potassium permanganate solution (in perchloric acid) to achieve additional carboxyl groups on the surfaces of the nanotubes. Modifications of the as-grown CNT structure may be identified by comparison of the Raman spectra ACHTUNGTRENNUNGof the as-produced nanotubes (Figure 1b) and the fully ACHTUNGTRENNUNGfunctionalized nanotubes (Figure 1c) in the vicinity of the

493 citations

Journal ArticleDOI
Ali Javey1, Qian Wang1, Ant Ural1, Yiming Li1, Hongjie Dai1 
TL;DR: In this article, the authors demonstrate multistage complementary NOR, OR, NAND, and AND logic gates and ring oscillators with arrays of p-and n-type nanotube field effect transistors (FETs).
Abstract: This work demonstrates multistage complementary NOR, OR, NAND, and AND logic gates and ring oscillators (frequency ∼220 Hz) with arrays of p- and n-type nanotube field effect transistors (FETs). The demonstration is made possible by progress in three aspects of nanotube synthesis and integration. First, patterned growth leads to large numbers of nanotube FETs in an array, as up to 70% of individual nanotubes are semiconductors. Second, metal electrodes are successfully embedded underneath nanotubes and used as local gates. Third, complementary logic gates are made possible by converting p-type FETs in an array into n-type FETs by a local electrical manipulation and doping approach.

410 citations

Journal ArticleDOI
TL;DR: A general strategy for the parallel and scalable integration of nanowire devices over large areas without the need to register individual nanowires−electrode interconnects has been developed in this paper.
Abstract: A general strategy for the parallel and scalable integration of nanowire devices over large areas without the need to register individual nanowire−electrode interconnects has been developed. The ap...

351 citations

Journal ArticleDOI
TL;DR: It is shown that the dielectrophoretic force fields change incisively as nanotubes assemble into the contact areas, leading to a reproducible directed assembly which is self-limiting in forming single-tube devices.
Abstract: One of the biggest limitations of conventional carbon nanotube device fabrication techniques is the inability to scale up the processes to fabricate a large number of devices on a single chip. In this report, we demonstrate the directed and precise assembly of single-nanotube devices with an integration density of several million devices per square centimeter, using a novel aspect of nanotube dielectrophoresis. We show that the dielectrophoretic force fields change incisively as nanotubes assemble into the contact areas, leading to a reproducible directed assembly which is self-limiting in forming single-tube devices. Their functionality has been tested by random sampling of device characteristics using microprobes.

338 citations

Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Directed assembly of solution processed single-walled carbon nanotubes via dielectrophoresis: from aligned array to individual nanotube devices" ?

In this paper, the authors demonstrated directed assembly of high quality solution processed carbon nanotube devices via ac dielectrophoresis using commercially available SWNT solutions.