Chemical profiling of single nanotubes: Intramolecular p–n–p junctions and on-tube single-electron transistors

Electrical transport properties of intramolecular $\mathrm{p–n–p}$ junctions formed on individual semiconducting carbon nanotubes are reported. Chemical dopant “profiling” along the length of a nanotube divides the nanotube into two p-doped sections and a central n-doped section. The double $\mathrm{p–n}$ junctions formed on the nanotube dictate the electrical characteristics of the system. Well-defined and highly reproducible single-electron transistors with much smaller size than the geometrical length of the nanotube are obtained.