Modulation of Conductance in a Carbon Nanotube Fi eld Effect Transistor by Electrochemical Gating - Application to the detection of unique sequences of DNA Bruce A. Diner#, Salah Boussaad#, T. Tang + , Anand Jagota* # DuPont CR&D * Lehigh University (Chemical Engineering) + University of Alberta (Mechanical Engineering) Co-workers: Xueping Jiang, Janine Fan and Kristin Ruebling-Jass (DuPont)
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Modulation of Conductance in a Carbon Nanotube Field Effect Transistor by Electrochemical Gating
Modulation of Conductance in a Carbon Nanotube Field Effect Transistor by Electrochemical Gating - A pplication to the detection of unique sequences of DNA Bruce A. Diner#, Salah Boussaad#, T. Tang + , Anand Jagota* # DuPont CR&D * Lehigh University (Chemical Engineering) - PowerPoint PPT Presentation
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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 CR&D* Lehigh University (Chemical Engineering)+ University of Alberta (Mechanical Engineering)
Co-workers: Xueping Jiang, Janine Fan and Kristin Ruebling-Jass (DuPont)
• Introduction
• CNT-FET in water with ions and redox species
• FET gated by electrode in solution
• Model for conductance
• DNA detection scheme (via activity of a redox enzyme)
Outline
Buffer
chamber
CNTVsd
Si/SiO2
Filling port
S D
G
Syringe Reservoir
Au-wireAg/AgCl
Connecting port
17% KNO3
5% KCl
•Choice of 3 gate electrodes
Diameter-dependent oxidation by K2IrCl6 (EmK2IrCl6/K3IrCl6 = 860 mV vs. NHE)
Zheng and Diner (2004) JACS 126, 15490-15494
DNA-dispersed HiPco single-walled carbon nanotubes easier to oxidize than nonionic dispersed nanotubes
The larger the diameter the easier the nanotube is to oxidize
CNT can be readily oxidized bystrong oxidants such as K2IrCl6, and fully reducedback by reductants such as Na2S2O4
800 mV vs NHE for (6,5)
Electrolyte Gated CNT-FET’s
Rosenblatt et al. (2002) Nano Lett. 2, 869
Krüger et al. (2001) Appl. Phys Lett. 78, 1291
• High mobility, low contact-resistance• High capacitance gating
• Gate voltage NT potential Charge Conductance
J. Guo, M. Lundstrom and S. Datta, Appl. Phys., Lett. 80, 3192 (2002)
Larrimore et al. Nano Lett. 6, 1329 (2006).
• Addition of oxidizing molecules causes a +ve shift• Addition of reducing molecules causes a –ve shift
• Electron transfer from CNT? Change in potential? Both?
5
1
2
Distances in µm
13Catalyst
pad
Devices made by Molecular Nanosystems Inc.
AFM image courtesy of Scott Mclean
Chemical vapor deposition (CVD)-grown nanotubes
Metallic CNT
Semiconducting CNT
CVD-grown nanotubes
Drain
SiO2
Si
Source
Vsd
Vg
CNT
CNT-FET
p-type (100) Si wafer
Gate
SiO2
Isd vs.Vg at different Vsd
Post-Burn, Isd vs.Vg at different Vsd
Thinning as described by Ph. Avouris (2002) Chem. Phys. 281, 429
F
+
Vg
-
Vg<0
Buffer
chamber
CNTVsd
Si/SiO2
Filling port
S D
G
Syringe Reservoir
Au-wire
Ag/AgCl
Connecting port
17% KNO3
5% KCl
•Choice of 3 gate electrodes
0 2 4 6 8 10 12
-0.010
-0.005
0.000
0.005
Time, min
0.1 mM K3Fe(CN)
6
1 mM K3Fe(CN)
6
A1
13
8 n
m
1 mM K4Fe(CN)
6
700 800 900 1000 1100 1200 1300
0.20
0.22
0.24
0.26
0.28
3min
Abs,
OD
, nm
8min
Oxidation and reduction by ferri- and ferrocyanide of aqueous dispersions of CNTs
oxidation
reduction
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.
K3Fe(CN)6 and K4Fe(CN)6 in reservoir only K3Fe(CN)6 and K4Fe(CN)6 throughout
K3Fe(CN)6 and K4Fe(CN)6 in reservoir only
Au wire gate in reservoir
Ag/AgCl gate in reservoir
Ag/AgCl gate in reservoir
K3Fe(CN)6 and K4Fe(CN)6 throughout
CNTVsdSi/SiO2
• Vg
EmK3Fe(CN)6/K4Fe(CN)6 = 361 mV
Gate electrodes
Heller et al (2006) JACS 128, 7353-7359
Summary
There are two ways in which swCNT-FETs respond to changes in the redox potential of solution:
1) Response of gold gate electrode to redox couple shifts the electrostatic potential of the solution.
2) 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).
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.
Interface of gate and solution: electrochemical equilibrium
s sRed Oxn
g
en
Oxln
RedB
g s
k TV
ne
o o OxOx Red
Red
1lno
Ben k T
ne
• Gate electrode area dominates• Interfacial resistance dominates
Gate voltage determines potential in solution through the Nernst equation
Interface between solution and CNT: insulated
1/ 2 / 2 / ln 2 /dl s s o o oC RK R K R R :
2 /q ntC R Q
2 1 12 1 q
s nt ntdl q dl dl
CR QR Q
C C C C
For devices in water and for high salt concentrations , the electric potential experienced by the CNT is nearly identical to that in solution.
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)
G - Vg relation
/ / 2NT sd sdR V I L R Q
11 2/ 4 / 2Q C NT CG R R R h q R L R Q
Purewal et al. PRL (2007; Kim group/Columbia)Rosenblatt et al. Nanoletters (2002)
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