  A series of solid organic acids were used to p-dope carbon nanotubes. The
extent of doping is shown to be dependent on the pKa value of the acids. Highly
fluorinated carboxylic acids and sulfonic acids are very effective in shifting
the threshold voltage and making carbon nanotube field effect transistors to be
more p-type devices. Weaker acids like phosphonic or hydroxamic acids had less
effect. The doping of the devices was accompanied by a reduction of the
hysteresis in the transfer characteristics. In-solution doping survives
standard fabrication processes and renders p-doped carbon nanotube field effect
transistors with good transport characteristics.
