Preparation And Field Emission Properties Of Ni/graphene Nanocomposite Cathode

With unique structures,graphene is of outstanding electrical,physical and chemical properties,such as excellent conductivity,large specific surface area,good structural stability,and have been considered as an excellent field emission cathode material.Much effort has been made,mainly through the surface modification or building composite cathode,to enhance their field emission properties.In this work,we have fabricated nano-Ni supported graphene oxide(GO)cathode using the electrostatic self-assembly method,and then obtained nano-Ni/reduced GO(rGO)composite cathode by a plasma post-treatment to reduce GO layers.This strategy overcomes the disadvantage of aggregation phenomenon of graphene material during solution process.Moreover,as the graphene coated on the surface of Ni particles with spokewise nanoneedles,the field screen effect caused by the graphene sheet edges that act as electron emission sites has been lowered and thus the field emission properties have been improved.In this work,Ni nanostructures were prepared by liquid phase reduction method.The effects of reductant concentration,reduction temperature on the surface morphologies and field emission properties of Ni nanostructure were investigated.The result showed that,the particle size of nano-Ni was increased from 2 ?m to 6.5?m with increasing the reductant concentrations from 0.1 M to 1 M.The reduction temperature also had a great impact on the morphology of nano-Ni.At temperature of 80 ?,the prepared nano-Ni was spherical in shape,while it showed urchin-like morphology at temperatures higher than 80 ?.The urchin-like nano nickel cathode prepared at a reductant concentration of 0.5 M and reduction temperature of 85 ?exhibited the lowest turn-on field of 8.2 V/?m,and highest field enhancement factor of 1681.Secondly,nano-Ni particles were processed by amino treatment with polyallylamine hydrochloride(PAH)which attracts graphene oxide sheets in the solution via electrostatic attraction to form the nano-Ni/GO composite structure.The effects of PAH concentration on the morphology and field emission properties of nano-Ni/GO composite cathode were studied.The results indicated that the field emission properties of Ni nanostructures was improved and then degraded with increasing the PAH concentrations from 0.05 g/L to 0.5 g/L.The Ni/GO nanocomposite prepared at 0.1 g/L PAH showed a low turn-on field of 4.2 V/?m,a high field enhancement factor of 2253 and good field emission stability,compared with the naked Ni arrays.Nano-Ni/GO composites were exposed to nitrogen plasma treatment to form nano-Ni/rGO composites.The effects of plasma treatment time on the degree of reduction and field emission properties of nano-Ni/rGO were investigated.XPS and FTIR analyses showed that after 5 minutes plasma treatment,most oxygen-containing functional groups had been removed from the surface of graphene oxide.In addition,after 15 minutes of plasma treatment,carbonnitrogen bond was found in the XPS spectra of nano-Ni/rGO composite structure,implying the formation of nitrogen-doped of graphene.Field emission results showed that the nano-Ni/rGO cathode had the best field emission properties when treated for 15 min,which showed a low turn-on field of 3.4 V/?m and a high field enhancement factor of 3051 and the field emission stability was also improved.