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.

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

0.0

0.2

0.4

0.6

0.8

1.0

Gate Voltage, V

Buffer

1mM K4Fe(CN)6

1mM K4Fe(CN)6

1mM K3Fe(CN)61mM K3Fe(CN)6

Cu

rre

nt,

A

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

0.0

0.2

0.4

0.6

0.8

Cu

rre

nt,

A

1mM K4Fe(CN)6

1mM K3Fe(CN)6

Gate Voltage, V-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

0.0

0.2

0.4

0.6

0.8

Gate Voltage, V

1mM K3Fe(CN)6

1mM K4Fe(CN)6

Cu

rre

nt,

A

Buffer

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.

Charge generation on CNT

J.W. Mintmire and C.T. White, Phys. Rev. Lett., 81, 2506 (1998)

sgn sgn F ntQ q E E F E E E q dE

2 /q ntC R Q

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

Calculate Fermi level: close enough to last step?

Calculate gate voltage

Calculate the conductance

Calculate the source-drain current

Y

N

Example

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.80

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8x 10

-7

Vg (V)

I sd (

A)

experimental data for [Ox]/[Red] = 1

fitting using Eo2

= 0.25 V, = 2.5e-5 m2/ V-s and R

c = 7.5h/e2

Shift Log([Ox]/[Red])

Radius: 1 nm; Length 2 μm

Debye length 2 nm.

q dlC C nt s

Shift in Vg for one order of magnitude change in

[Ox]/[Red]

ln10 / 0.06 VBk T e

.

Larrimore et al. Nano Lett. 6, 1329 (2006).

Effect of salt concentration

Radius: 1 nm; Length 2 μm

Varying Debye length/ 2dl sQ C R nt s

Effect of NT diameter & length

-6 -5 -4 -3 -2 -1 0 10

0.2

0.4

0.6

0.8

1

Vg (V)

G (

q2 /h

)

R = 0.5 nmR = 1 nmR = 1.5 nmR = 2 nm

-0.4 -0.2 0 0.20

0.1

0.2

0.3

0.4

0.5

-6 -5 -4 -3 -2 -1 0 10

0.2

0.4

0.6

0.8

1

Vg (V)

G (

q2 /h

)

R = 0.5 nmR = 1 nmR = 1.5 nmR = 2 nm

-0.4 -0.2 0 0.20

0.1

0.2

0.3

0.4

0.5

Length 2 μm

Debye length 2 nm [Ox]/[Red] = 1

Radius 1nmDebye length 2 nm [Ox]/[Red] = 1

biotinylated probe oligo attached to streptavidin

S D

S D

Laccase with attached oligo probe

ABTS-2

ABTS-1

Hybridized target oligo

Liquid Gate

Liquid Gate

2,2’Azino-di-(3-ethylbenzthiazoline-sulfonate)(ABTS)

Em = 680 mV vs NHE

Redox sensing using laccase bound by hybridizationto surface coated with streptavidin

•Time [Ox]

•Time G

0 5 10 15 20 25 30 35 40 450.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

B C

Isd

(u

A)

at V

g=

-0.1

V

time (min)

100 amole non-complementary target ssDNA (Ol73)

100 amole complementary target ssDNA (Ol63)

Isd at -0.1V gate voltage as a function of time with target at 100 amoles

Facile detection of 100 attomoles target

• 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)

• Support: NASA, NSF.

Summary

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

patterned chip

sensing chamber (4.4 μl)

o-ring

in out

Gate electrode(negative Vg)

Liquid flow cell

Zoom

Zoom

7 x 5 um 12 um

2nd generation CNT device custom made by Molecular Nanosystems Inc.

Pad for gate electrode

2 um

Pads for drain electrodes

Pads for source electrodes

Overcoated catalyst pads