Electronic structure and field emission properties of double-walled carbon nanotubes synthesized by hydrogen arc discharge

We have synthesized high-purity double-walled carbon nanotubes (DWCNTs) by an arc-discharge method in hydrogen ambient. The DWCNTs were synthesized using a mixture of Fe catalyst and FeS promoter. Without FeS promoter, we only obtained single-walled carbon nanotubes (SWCNTs). The synthesized DWCNTs had outer diameters in the range of 3.0-3.4 nm and an average interlayer distance of 0.38 nm between graphene layers. The FeS promoter played a key role for the DWCNT growth. The DWCNTs indicated high electronic density of states in the binding energy region between 3.88 and 13.23 eV below Fermi energy, indicating that the DWCNTs had alot of delocalized graphite σ and σlπ electrons. For field emission properties, the typical turn-on field of DWCNTs was about 3.0 V/μm at the emission current density of 0.1 μA/cm², and the emission current density of DWCNTs was about 10 mA/cm² at the applied field of 6.5 W/μm. It is considered that the higher current densities of DWCNTs were mainly attributed to the emitted delocalized graphite σ and σ/π state electrons of DWCNTs. Moreover, DWCNTs have higher emission stability than SWCNTs due to two neighboring graphene layers.