Impurity screening in carbon nanotubes

Nanotube geometry determines electronic structure and thus impurity screening. A metallic carbon nanotube could effectively screen a charged impurity, while a semiconducting carbon nanotube could not. The ability to screen a long-range Coulomb field is mainly determined by whether there are free carriers in the subbands nearest the Fermi level. The detailed screening properties are sensitive to the impurity position, and the tubular structure (such as radius and chiral angle). Strong, short-wavelength Friedel oscillations at long distances are found to exist only in metallic armchair nanotubes. They are relatively obvious for a smaller armchair nanotube, and could survive at room temperature.