Conductivity and field emission enhancement of C-60-encapsulated single-walled carbon nanotubes

Abstract

C60 molecules are encapsulated inside single-walled carbon nanotubes (SWNTs) and resulting charge (electron) transfer from the SWNTs to the C60s is observed. A Raman upshift in the G-band for the C60-encapsulated SWNTs (C60@SWNTs) is indicative of a charge transfer occurred in this system. The observed conductivity enhancements strongly support the p-doping of the SWNTs by C60 encapsulation, implying the electron concentration of the SWNTs is reduced by the insertion of C60. We also observe the significant field emission (FE) enhancement of C60@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 C60 encapsulation induce a Fermi level upshift (i.e. reduced work function). Although the p-doping of SWNT is achieved by C60 encapsulation, the reduced work function of C60@SWNTs provide the electrons a higher probability for tunneling, resulting in both FE and conductivity enhancement.