Conductivity and field emission enhancement of C60-encapsulated single-walled carbon nanotubes

Abstract

Coo molecules are encapsulated inside single-walled carbon nanotubes (SWNTs) and resulting charge (electron) transfer from the SWNTs to the C(60)s is observed. A Raman upshift in the G-band for the C-60-encapsulated SWNTs (C-60@SWNTs) is indicative of a charge transfer occurred in this system. The observed conductivity enhancements strongly support the p-doping of the SWNTs by C-60 encapsulation, implying the electron concentration of the SWNTs is reduced by the insertion of C-60. We also observe the significant field emission (FE) enhancement of C-60@SWNTs, which is not expected since the reduced electron concentration of SWNTs is typically to induce a Fermi level downshift. However, ultraviolet photoelectron spectroscopy results show that C-60 encapsulation induce a Fermi level upshift (i.e. reduced work function). Although the p-doping of SWNT is achieved by C-60 encapsulation, the reduced work function of C-60@SWNTs provide the electrons a higher probability for tunneling, resulting in both FE and conductivity enhancement.