Ultra-nanocrystalline Diamond-graphene Nanowalls Composite Film And Its Application As Field Emission Cold Cathode

Field emission cold cathode materials have important applications in vacuum microelectronic devices such as X-ray tubes and high-power microwaves.Traditional cold cathode materials have problems such as high turn-on field,low emission current density,and poor emission stability,and are not suitable for application in the field of vacuum microelectronics.The diamond-graphene composite material has become a class of field emission cathode materials with excellent performance because of its excellent properties of both diamond and graphene.Therefore,it is of great significance to explore the growth process and mechanism of this composite material to improve its field emission performance.In this paper,nitrogen-doped ultra-nanocrystalline diamond-graphene nanowalls composite films(UNCD-GNWs)were prepared by microwave plasma chemical vapor deposition(MPCVD)technology using liquid nitrogen-containing organic molecules as the reaction source.The effects of process parameters(such as hydrogen flux,growth temperature,etc.)on the phase and morphology of UNCD-GNWs were analyzed by FESEM,HRTEM,Raman,XRD,etc;the field emission properties of UNCD-GNWs were tested by vacuum planar diodes;Plasma optical emission spectroscopy(OES)in situ monitors the plasma composition during the growth of UNCD-GNWs and proposes a possible growth mechanism.Research shows:(1)With the increase of hydrogen flux,the size of the needle-like nanostructures on the surface of the film increased,and the boundary became clearer.At the same time,the crystallinity of graphite decreased and the crystallinity of diamond increased.In addition,the diamond content in the film decreased and the graphite content increased;the use of an excessively high N/C reaction source will lead to a smaller nanowalls size and growth rate in the film.(2)The UNCD-GNWs grown at 750?show the best field emission performance.The opening field was as low as 4.0 V/?m,and the emission current density was as high as 13.0m A/cm~2 under the electric field intensity of 8.8 V/?m.Its excellent field emission performance was attributed to the existence of large-size and highly crystalline multi-layer graphite around acicular nano diamond,which not only ensured good conductivity,but also constructed a good electron transport path from the interior to the surface of the material.(3)OES results showed that C2?CN?H?and CH species existed in the growth of UNCD-GNWs.With the increase of growth temperature,The overall content of C2?CN?H?species increased,but its percentage content showed that C₂ increased only,CN?H?and CH decreased.The mechanism speculated that CH and C₂species were responsible for the formation of diamond and graphene,H?was the main etching species.With the increase of temperature,CN species were activated and induced to form needle-like nanodiamonds.After the synergistic effect of various chemical species,different UNCD-GNWs were finally formed.This growth mechanism provided a theoretical basis for the effective regulation of the morphology,physical phase and field emission performance of UNCD-GNWs,and broadened the application prospect of the field emission field.