Field emission under extreme conditions from carbon nanopearls in a foam-like arrangement

We studied field emission properties of carbon nanopearls for application as cold cathodes in low vacuum conditions (up to 10(-4) Torr). The nanopearls are spherical in shape, 150 nm in diameter, and composed of both amorphous and nanocrystalline regions. The nanopearls form two-dimensional "strings" which give rise to a macroscopic three-dimensional foam-like material. For this study, we have synthesized uniform layers of nanopearls by chemical vapor deposition directly on the apex of tungsten tips and performed comparative field emission measurements under different gas pressures. We present field emission current stabilities in the mu A range under nitrogen and oxygen atmosphere Up to 10(-4) Torr, which corresponded to field emission current densities up to 1 A/cm(2), and were obtained for hours with a simple "retroaction" voltage control. These results show that field emission with nanopearls is a promising way for applications requiring high current densities in high pressure environment. The long lifetime of nanopearls cathodes at high pressures is a consequence of the foam-like structure of the deposited layers of the nanopearls, leading to a self-healing process of the emission sites that were continuously destroyed by retro-ion sputtering during emission. (c) 2005 American Vacuum Society.