Correlating local chemistry with conductivity in carbon nanotube transistors

Jason Simmons Dept. of Physics, University of Wisconsin

Numerous studies have shown conductivity changes in nanotube transistors after the introduction of an analyte, suggesting that nanotubes can be used as the active element in chemical and biological sensors. Though products are now coming on the market, in many cases the mechanisms causing the change in conductivity are not fully understood. I will present work in which we directly tie conductivity changes to their underlying molecular causes. For covalent functionalizations, we use a combination of electronic and spectroscopic techniques to explicitly show that disruption of the p-conjugated nanotube orbitals removes electronic states from the Fermi level and leads to a decreased conductance. This is in contrast to reports that propose a charge transfer/doping mechanism on the basis of electronic measurements alone. I will also show experiments using an organic chromophore to optically modulate the conduction in a nanotube transistor. Under illumination, the organic chromophore undergoes a cis-trans isomerization that is accompanied by a change in the molecular dipole moment. Experiments and calculations demonstrate that the changing dipole field modifies the local electrostatic potential, shifting the threshold voltage and causing an increased conductance in the nanotube transistor.

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