Study of film thickness effect on carbon nanotube based field emission devices

Carbon nanotube (CNT) has been considered as an ideal cathode material for field emission application for a long time. To improve field emission properties, coating CNT films to form a composite cathode is an effective approach. However, few reports have studied and revealed the effect of coated layer thickness. Hence, in this study, we employed an Au layer to coat CNT cathodes with 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. A nonmonotonic relationship between field emission performances and cathode film thickness was observed, and a high performance with a rather low turn-on field of 0.60 V/μm and an ultrahigh field enhancement factor near to 20000 was optimally demonstrated for the CNT composite cathode with an Au layer thickness of 3 nm. Based on experimental data and analysis, the nonmonotonic tendency was found mainly due to effective field emitter density, and the cathode conductivity works only for ultrathin films. Besides, the CNT composite cathode had good stability and uniformity for low heat contact resistant. The superior performance of the CNT cathode composited with a proper Au layer demonstrated potential applications in vacuum electronic devices and an optimized thickness of the coated layer was important for field emission enhancement of composite cathodes.