Stable, self-ballasting field emission from zinc oxide nanowires grown on an array of vertically aligned carbon nanofibers

A structure composed of zinc oxide nanowires (ZNWs) grown hydrothermally on an array of vertically aligned carbon nanofibers (CNFs) was fabricated and its field emission properties determined and compared with bare CNF arrays. The combination produced a macroscopic turn-on field of 1.2 V/μm which was found to be the lowest reported from ZNWs deposited on a two-dimensional substrate and much less than the equivalent CNFs array (5.2 V/μm). Crucially, field emission was found to be much more stable at higher pressures of 5×10^-6 mbar without exhibiting current degradation for a fixed external field, while emitting with a current density of 1 mA/cm², the current density typically required for backlighting and field emission displays. We propose a self-ballasting mechanism, in which the low carrier density in the zinc oxide prevents current runaway in the presence of adsorbed species.