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

The field emission (FE) properties of carbon films can be understood in terms of local field enhancement beta (x,y), which can be determined with x,y-scanning FE. beta (x,y) double right arrow the spatial distribution of emitting sites, which can be counted as f(beta) alpha exp(-k beta). f(beta) 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 (similar to 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 (similar to 3000 V/mum) and create resonant tunnelling states. The anode material is believed to be the main source of adsorbed species and not the ambient gas phase. (C) 2001 Elsevier Science B.V. All rights reserved.