Electrolyte gating of single

1
Electrolyte gating of single- walled carbon
nanotubes
Jeffrey C. Gore Jiwoong Park1 Michael
Fuhrer2 Paul McEuen1
University of California - Berkeley Materials
Science Division, LBNL
Support Hertz Foundation, DOE
1 Present address is Cornell 2 Present address is
University of Maryland
2
Carbon Nanotube Field-Effect Transistors
Vg
3
Construction of the Device
Nanotube bundles1 distributed randomly on oxide
surface
Photolithography
1- Tubes courtesy of Richard Smalley
4
Theory of Electrolyte Gating
How much does the Fermi energy move in response
to a change in the gate voltage?
Reference Schoenenberger et. al.
5
Theory of Electrolyte Gating
How much does the Fermi energy move in response
to a change in the gate voltage?
For an electrolyte gate we thus have
Reference Schoenenberger et. al.
6
Theory of Electrolyte Gating
How much does the Fermi energy move in response
to a change in the gate voltage?
For an electrolyte gate we thus have
Reference Schoenenberger et. al.
7
Nanotube capacitance
Einstein Relation
Watergate capacitance
Backgate capacitance
8
Semiconducting Tubes
E
E
EF
kx
kx
EF
9
n-type and p-type Nanotube FETs
10
Metallic Tubes
E
E
EF
kx
kx
EF
11
Metallic Tubes
E
E
EF
kx
kx
EF
12
Conclusions

• Both metallic and semiconducting tubes are
  intrinsically p-type.
• Electrolyte gating can lead to equal changes in
  the gate voltage and EF.
• The bandgap of semiconducting tubes can be
  crossed using Vg lt 1 V.
• A single semiconducting device can be both an n
  and p-type FET.
• Large changes in the conductance of metallic
  tubes are possible.

13
Future Directions

• Explore the origin of conductance change in
  metallic tubes.
• Perform the same experiment with CVD grown
  nanotubes.
• Applications to biosensors