The Preparation And Performance Of CuO/Carbon Nanocomposite Cathode

As a typical p-type semiconductor with narrow band gap(about 1.2 eV),copper oxide(CuO)is a potential cathode material because of its good chemical stability and low work function.With unique structures,Carbon nanomaterials are of outstanding electrical,physical and chemical properties,such as large aspect ratio(for CNT)and high body surface ratio(for graphene),and have been considered an ideal cathode material theoretically.Combining CuO nanowire arryas with carbon nanomaterial by coating will hopefully solve some existing problems,such as aggregation of nanomaterials,instability of emission current,short lifetime of field emission for carbon nanomaterial and poor electrical conductivity for copper oxide.Moreover,hydrothermal method is a common method to grow CuO nanostructures directly from the Cu substrate at low tempreture,which has many advantages for device fabrication.In this work,CuO nanostructures were prepared by the hydrothermal method.The effects of oxidant concentration,oxidation time on the surface profile and field emission properties of CuO nanostructure were investigated.The results showed that copper oxides with different structures(nanowire and nanosheet)were fabricated with different oxidant concentrations.The field emission properties of CuO nanostructures was improved and then degradated with increasing oxidants concentrations from 0.05M to 0.6M.The CuO nanowire cathode prepared at an oxidant concentration of 0.3M and an oxidation time of 2h exhibited the lowsst turn-on field of 6.6 V/μm and highest field enhancement factor of 1058.In view of the poor electrical conductivity of copper oxide,graphene oxide coated cooper oxide(GO/CuO)nanocomposite cathode has been proposed to improving field emission properties.The results indicated that,as compared with the naked CuO nano wire arrays,GO/CuO nanocomposite had better field emission properties.The GO/CuO nanocomposite prepared at oxidant concentrations of 0.3M showed a low turn-on field of 3.7 V/μm,a high field enhancement factor of 1521 and good field emission stability.Furthermore,CNT/CuO composites were prepared by coating CNT on the surface of CuO nanowire arrays.By comparison,the CNT/CuO cathode had better filed emission properties than the naked CuO nano wires,the pure CNTs and the GO/CuO composite cathode,with the low turn-on field of 0.9 V/μm.It has been found that the CuO nanowires with sharp tips easily pierce CNT films to make the nanowires tips bare,and the CuO nanowires with large diameter and small density are coated with a thin layer of CNT.For the latter,it was found that the CuO nanowires with modest density had the best field emission property by optimizing the density of CuO nanowires.To further explore the impacts of CNT coverage on field emission of composite cathode,the CNT coverage was decreased and the turn-on field increased slightly from 0.75 V/μm(70%coverage)to 1.07 V/μm(35%coverage),while it greatly lowered the fluctuation and attenuation in emission current.