Electronic transport modification of single-walled carbon nanotubes by encapsulating alkali-metal ions

We have produced alkali-metal encapsulated single-walled carbon nanotubes using a method of alkali-metal plasma ion irradiation. After plasma ion irradiation, alkali-metal encapsulated single-walled carbon nanotubes are sonicated for several hours in N,N-dimethylformamide to make well dispersed solution, then applied on a field-effect transistor substrate. As a result of measurements, pristine semiconducting single-walled carbon nanotubes show p-type conductivity, but Cs-encapsulated single-walled carbon nanotubes show n-type transport properties. This drastic change can be explained by electron transfer from encapsulated Cs atoms toward the surrounding SWNTs. At 11 K, the Coulomb oscillation is observed, implying that an inhomogeneous encapsulation profile of Cs atoms form several quantum dots. Thus, the electronic properties of SWNTs are found to be successfully controlled by plasma ion irradiation.