Carbon nano-/micro-structures in field emission: environmental stability and field enhancement distribution

Abstract The field emission (FE) properties of carbon films can be understood in terms of local field enhancement β( x , y ), which can be determined with x , y -scanning FE. β( x , y )⇒ the spatial distribution of emitting sites, which can be counted as f (β)∝exp(−kβ). f (β) is connected with the presence of sharp protruding objects, whiskers or nanotubes on the surface. Investigations of the current–time (I– t ) characteristics of field emission from single-walled carbon nanotubes (SWNT) do not show any significant dependence on ambient partial pressures of hydrogen or water up to 10 −5 mbar. Oxygen however, causes a substantial reduction of the FE current. Field emission microscopy (FEM) during short-time nanotube annealing (∼1000 K) reveals dim five-fold as well as six-fold feinstructures, which are believed to be nanotube cap states. The nanotube cap states have a short lifetime due to impinging atoms/ions that are adsorbed due to the high local electric field at the cap (∼3000 V/μm) and create resonant tunnelling states. The anode material is believed to be the main source of adsorbed species and not the ambient gas phase.