Inner tube growth and electronic properties of metallicity-sorted nickelocene-filled semiconducting single-walled carbon nanotubes

Abstract

In the present work, we have obtained metallicity-sorted nickelocene-filled semiconducting single-walled carbon nanotubes (SWCNTs) by density gradient separation of metallicity mixed filled nanotubes. Double-walled carbon nanotubes (DWCNTs) were obtained by annealing of filled SWCNTs in vacuum. The diameter distribution of inner tubes was analyzed by multifrequency Raman spectroscopy. The chemical transformation of nickelocene upon annealing was studied by X-ray photoelectron spectroscopy (XPS) at the Ni 2p core level. The thermally-induced transformation of nickelocene to nickel carbides and metallic nickel was revealed. The electronic properties of the filled SWCNTs and DWCNTs were investigated by XPS at the C 1s core level. By tracing the C 1s binding energy, it was shown that the annealing of nickelocene-filled SWCNTs at low temperatures (360-600 °C) led to electron doping of SWCNTs, whereas annealing at high temperatures and formation of DWCNTs (680-1200 °C) resulted in hole doping of nanotubes.