Enhancement on the stability of electron field emission behavior of carbon nanotubes by coating ultrananocrystalline diamond films

We report enhanced life-time stability for the carbon nanotubes (CNTs) by coating ultrananocrystalline diamond (UNCD) or hybrid granular structured diamond (HiD) films. Electron field emission (EFE) properties of UNCD/CNTs emitters show a turn-on field of 4.86 V/μm and an emission current density of 0.6 mA/cm2 at an applied field of 8.7 V/μm. There are no notable current degradations or fluctuations over a period of τUNCD/CNTs=228 min for UNCD/CNTs emitters at an applied current of 45 μA. The robustness of UNCD/CNTs emitter is overwhelmingly superior to the lifetime stability of bare CNTs emitters (τCNTs=40 min), even though the bare CNTs possess much better EFE properties (E₀=0.73 V/μm, J_e=1.1 mA/cm2 at 1.05 V/μm, with). The HiD/CNTs emitters exhibited even better EFE properties, i.e., turn-on field of 3.5 V/μm and EFE current density of 0.64 mA/cm² at 5.0 V/μm with longer lifetime of tHiD/CNTs=275 min. Furthermore, the plasma illumination (PI) property of a parallel-plate microplasma device fabricated using the UNCD/CNTs (or HiD/CNTs) as cathode shows a high Ar plasma current density of 1.56 mA/cm² (or 1.56 mA/cm²) at an applied field of 5600 V/cm with lifetime plasma stability of 130 min (or 180 min). The diamond films coated CNTs emitters, which possess marvelous EFE and PI properties with improved lifetime stability, have great potential for the applications as cathodes in flat panel displays and microplasma display devices.