Plasma doping processes for CNT devices

A variety of plasmas including positive and negative ions are prepared in gaseous, liquid, and gas–liquid interfacial phases in order to functionalize carbon nanotubes (CNTs) with properties corresponding to electronic and biomedical device applications. In the case of internal doping, alkali metal, alkaline-earth metal, halogen, iron atoms, fullerene, azafullerene, and DNA molecules are encapsulated inside single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) with hollow inner spaces using the plasma-ion irradiation method. The electrical, magnetic, and optical properties of the encapsulated SWNTs and DWNTs are found to be greatly changed compared with those of pristine ones. As a result, a number of significant and nanodevice-applicable transport phenomena are observed, in which air-stable carrier-type control, embedded formation of p–n junction, quantum dot formation, distinct negative differential resistance, magnetic semiconducting behavior, photoinduced electron transfer, and photoelectric conversion are highlighted here. Furthermore, the combination of internal and surface doping processes leads to the creation of Au nanoparticle–DNA_SWNT conjugates toward a nano-biomedical device application.