1. Electrolyte gating of single- walled carbon nanotubes University of California - Berkeley Materials Science Division, LBNL Jeffrey C. Gore Jiwoong Park 1 Michael Fuhrer 2 Paul McEuen 1 Support: Hertz Foundation, DOE 1 Present address is Cornell 2 Present address is University of Maryland

2. Carbon Nanotube Field-Effect Transistors VgVg Silicon backgate Si0 2 Si p ++ 500 nm VgVg source drain oxide gate Electrolyte gate Si0 2 sourcedrain oxide gate micropipette SiCl electrode

3. Construction of the Device Nanotube bundles 1 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? VgVg C NT CgCg E EFEF N(E) VgVg 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? VgVg C NT CgCg Reference: Schoenenberger et. al. For an electrolyte gate we thus have:

6. Theory of Electrolyte Gating How much does the Fermi energy move in response to a change in the gate voltage? Reference: Schoenenberger et. al. For an electrolyte gate we thus have:

7. Einstein Relation: Nanotube capacitance Watergate capacitance Backgate capacitance

8. Semiconducting Tubes EFEF EFEF E kxkx E kxkx

9. n-type and p-type Nanotube FETs

10. Metallic Tubes EFEF EFEF E kxkx E kxkx

11. EFEF EFEF E kxkx E kxkx

12. Conclusions Both metallic and semiconducting tubes are intrinsically p-type. Electrolyte gating can lead to equal changes in the gate voltage and E F. The bandgap of semiconducting tubes can be crossed using V g < 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