Adhesion and Collapse of Carbon Nanotubes

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Modulation of Conductance in a Carbon Nanotube
Field Effect Transistor by Electrochemical Gating
- Application to the detection of unique
sequences of DNA Bruce A. Diner, Salah
Boussaad, T. Tang, Anand Jagota DuPont
CRD Lehigh University (Chemical Engineering)
University of Alberta (Mechanical
Engineering) Co-workers Xueping Jiang, Janine
Fan and Kristin Ruebling-Jass (DuPont)
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Outline
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Diameter-dependent oxidation by K2IrCl6
(EmK2IrCl6/K3IrCl6 860 mV vs. NHE)
CNT can be readily oxidized by strong oxidants
such as K2IrCl6, and fully reduced back by
reductants such as Na2S2O4
The larger the diameter the easier the nanotube
is to oxidize
DNA-dispersed HiPco single-walled carbon
nanotubes easier to oxidize than nonionic
dispersed nanotubes
800 mV vs NHE for (6,5)
Zheng and Diner (2004) JACS 126, 15490-15494
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Electrolyte Gated CNT-FETs

• High mobility, low contact-resistance
• High capacitance gating
• Gate voltage ? NT potential ?Charge ? Conductance

Krüger et al. (2001) Appl. Phys Lett. 78, 1291
Rosenblatt et al. (2002) Nano Lett. 2, 869
J. Guo, M. Lundstrom and S. Datta, Appl. Phys.,
Lett. 80, 3192 (2002)
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• Addition of oxidizing molecules causes a ve
  shift
• Addition of reducing molecules causes a ve
  shift
• Electron transfer from CNT? Change in potential?
  Both?

Larrimore et al. Nano Lett. 6, 1329 (2006).
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Chemical vapor deposition (CVD)-grown nanotubes
AFM image courtesy of Scott Mclean
Distances in µm
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2
Catalyst pad
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5
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Devices made by Molecular Nanosystems Inc.
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CVD-grown nanotubes
Metallic CNT Semiconducting CNT
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CNT-FET
Source
Drain
CNT
Vsd
SiO2
Si
Gate
SiO2
Vg
p-type (100) Si wafer
Thinning as described by Ph. Avouris (2002) Chem.
Phys. 281, 429
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Ag/AgCl
Au-wire
17 KNO3 5 KCl
Reservoir
Syringe
Filling port
Connecting port
Choice of 3 gate electrodes
chamber

Buffer
G
S
D
CNT
Vsd
Si/SiO2
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Oxidation and reduction by ferri- and
ferrocyanide of aqueous dispersions of CNTs
EmK3Fe(CN)6/K4Fe(CN)6 361 mV
3 min and 8 min after the addition of 1 mM
K3Fe(CN)6 in 50 mM glycine pH 9.0.
reduction
oxidation
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Gate electrodes
Vg
Au wire gate in reservoir
EmK3Fe(CN)6/K4Fe(CN)6 361 mV
K3Fe(CN)6 and K4Fe(CN)6 in reservoir only
K3Fe(CN)6 and K4Fe(CN)6 throughout
Ag/AgCl gate in reservoir
Ag/AgCl gate in reservoir
Heller et al (2006) JACS 128, 7353-7359
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• Summary
• There are two ways in which swCNT-FETs respond to
  changes in the redox potential of solution
• Response of gold gate electrode to redox couple
  shifts the electrostatic potential of the
  solution.
• At elevated redox potentials, the nanotubes
  themselves are oxidized by the oxidized member of
  the redox couple raising the concentration of
  p-type charge carriers (holes) which increases
  the nanotube conductance (Isd current).

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Model for modulation of conductance

• Solution Electric potential controlled by the
  applied gate voltage.
• Induces an electric potential on the nanotube.
  (Need solution-CNT quantum capacitance.)
• Potential on the nanotube shifts the band,
  induces carriers, changing conductance.

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Interface of gate and solution electrochemical
equilibrium
Gate voltage determines potential in solution
through the Nernst equation

• Gate electrode area dominates
• Interfacial resistance dominates

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Interface between solution and CNT insulated
For devices in water and for high salt
concentrations , the electric potential
experienced by the CNT is nearly identical to
that in solution.
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Charge generation on CNT
J.W. Mintmire and C.T. White, Phys. Rev. Lett.,
81, 2506 (1998)
J. Guo, M. Lundstrom and S. Datta, Appl. Phys.,
Lett. 80, 3192 (2002)
J. Guo, S. Goasguen, M. Lundstrom and S. Datta,
Appl. Phys. Lett., 81, 1486 (2002)
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G - Vg relation
Purewal et al. PRL (2007 Kim group/Columbia) Rose
nblatt et al. Nanoletters (2002)
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Calculating Conductance
Pick a potential on nanotube
Given an initial guess for the Fermi level
Calculate the charge induced on nanotube
Calculate the potential in solution
Calculate the electrochemical potential in
solution
N
Calculate Fermi level close enough to last step?
Y
Calculate the conductance
Calculate gate voltage
Calculate the source-drain current
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Example
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Shift Log(Ox/Red)
.
Radius 1 nm Length
Shift in Vg for one order of magnitude change in
Debye length 2 nm.
Larrimore et al. Nano Lett. 6, 1329 (2006).
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Effect of salt concentration
Radius 1 nm Length
Varying Debye length
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Effect of NT diameter length
Length
Radius 1nm Debye length 2 nm Ox/Red 1
Debye length 2 nm Ox/Red 1
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Redox sensing using laccase bound by
hybridization to surface coated with streptavidin
biotinylated probe oligo attached to streptavidin
S
D
Liquid Gate
Laccase with attached oligo probe

• Time Ox

Hybridized target oligo

• Time G

2,2Azino-di-(3-ethylbenzthiazoline-sulfonate) (AB
TS)
S
D
Liquid Gate
Em 680 mV vs NHE
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Isd at -0.1V gate voltage as a function of time
with target at 100 amoles
100 amole complementary target ssDNA (Ol63)
Facile detection of 100 attomoles target
100 amole non-complementary target ssDNA (Ol73)
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Summary
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Liquid flow cell
o-ring
patterned chip
sensing chamber (4.4 µl)
Gate electrode (negative Vg)
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Pads for source electrodes
Pads for drain electrodes
Zoom
Pad for gate electrode
2nd generation CNT device custom made by
Molecular Nanosystems Inc.
Zoom
2 um
12 um
7 x 5 um
Overcoated catalyst pads