A Comparative Study of Field Emission From Semiconducting and Metallic Single-Walled Carbon Nanotube Planar Emitters

Field electron emission from thin films composed of solely metallic or semiconducting single-walled carbon nanotubes is investigated using a scanning tip anode technique. Metallic and semiconducting nanotubes are separated by aqueous two-phase extraction. Local field emission centers observed on nanotube films of both types showed non-linear Fowler-Nordheim (FN) plots bent downwards. The curving of FN plots is much stronger for semiconducting nanotubes which is explained by their higher electrical resistance and stronger field penetration effect compared to metallic nanotubes. Particular nanotubes of both types revealed oscillations in current-voltage characteristics. The periodic oscillations indicated that the field emission current is modulated either by resonant tunnelling from confinement states in nano-objects formed by adsorbates or by the Coulomb blockade effect that can occur for emission from short carbon nanotubes.