Controllable modification of the conduction properties of carbon nanotube devices through deposition of a metal overlayer onto the sidewalls

The effects of metal contacts and metal overlayers on the electrical properties of carbon nanotubes (CNTs) were studied. We show that the conduction properties of a CNT device can be controllably designed through metal depositions on the sidewall even though the conduction type is not clearly defined by the work function of the contact metal. The conversion from an n-type to a p-type conductor was observed with deposition of an overlayer using a large work function metal (Pd), whereas a p-type to n-type conversion was observed with deposition of an overlayer using a low work function metal (Ti). This behavior was attributed to charge transfer doping or the local bending of nanotube bands beneath the metal overlayer. First-principle calculations revealed that charge transfer doping may be uniquely defined by the work function difference if a metal layer forms a weak contact with the sidewall of a CNT.