Thickness Effect on Field-Emission Properties of Carbon Nanotube Composite Cathode

Although low work function materials have been widely used to coat carbon nanotube (CNT) cathodes for improving field-emission performance, there have been few reports on the effect of coated layer thickness except for a few examples, in which some contradictory observations were reported. Hence, in this paper, we employed a low work function material of LiF/Al to coat CNT cathodes with the capability to precisely control the coated film thickness and systematically investigated the film thickness effect on field-emission properties of the CNT composite field-emission devices (FEDs). A nonmonotonic relationship between field-emission performance and cathode film thickness was observed and the state-of-the-art performance was optimally demonstrated for the CNT composite cathode with Al layer thickness of 1 nm. Based on experimental data and analysis, the nonmonotonic tendency was found to correspond well with the behavior of thickness-dependent resistance and thus was mainly assigned to the conductance of composite cathodes. In addition, the improved stability and lighting uniformity for the FEDs with an Al layer were attributed to the increased effective emission sites and the robust emitters being protected. The superior performance of the CNT cathode composited with a low work function material of LiF/Al demonstrates potential applications in vacuum electronic devices and an optimized thickness of the coated layer is important for field emission enhancement of CNT composite cathodes.