Synthesis And Electron Field Emission Properties Of ZnO/Diamond Doublelayered Structure

Zinc oxide(ZnO)and diamond are very important wide bandgap semiconductor materials,have excellent physicochemical properties.At present,new composite structures prepared by combining ZnO and diamond have been widely studied in fields such as field emission display cold cathode materials,semiconductor heterojunctions,and surface acoustic wave devices.By depositing ZnO on diamond substrates,the performance of ZnO/diamond as field emission display cold cathode materials can be significantly improved.Therefore,in this paper,ZnO grown on chemical vapor deposited free-standing diamond(FSD)films and nanocrystalline diamond by low-temperature hydrothermal method.And the reaction time,reactant concentration,diamond substrate and B doping on the growth morphology and field emission performance of ZnO were systematically studied,in order to improve the electron field emission properties of ZnO/diamond doublelayered structure.The microstructure of the samples was characterized by field emission scanning electron microscope,grazing incidence X-ray diffractometry,laser Raman spectroscopy,and photoluminescence spectrometer.The field emission characteristics of the samples were studied by high vacuum field emission testing.The effects of different reaction time,different reactant concentrations,diamond grain size and ZnO doping on the microstructure and field emission properties of ZnO/diamond composites were systematically studied.The main research contents and results are as follows:(1)ZnO nanorods were prepared on a self-supporting diamond film with the hydrothermal reaction time of 1.5 h,3 h,6 h and 8 h,respectively.And compared with the ZnO nanorod/Si composite structure prepared under the same conditions.The results show that the ZnO nanorods prepared on the free-standing diamond films have has the cutting-gathering phenomenon,better crystallinity,higher purity and less structure defect.The feature of the ZnO nanorods grown on free-standing diamond films played an important role in further enhancing the electron field emission performances.Experimentally,the ZnO nanorods/free-standing diamond films with 6 hours reaction time are generally vertical grown on the free-standing diamond films,it also shows the highest aspect ratio and cutting-edge gathered phenomenon and those properties enable nanorods/diamond nanostructures to have a high emission density.The EFE behavior of the ZnO nanorods/free-standing diamond films can be turned on at E0= 6.8 V/?m,attaining a current density of 0.20 mA/cm2 at an applied field of 11.9 V/?m.(2)ZnO nanorods were grown on nanocrystalline diamond with the reactant concentrations of 0.1 M,0.05 M,0.025 M,and 0.01 M,respectively.We studied the effects of nanocrystalline diamond substrates and reactant concentration on the microstructure and field emission performance of ZnO nanorods.The experimental results show that the nanocrystalline diamond can significantly improve the conductivity of the ZnO/nanocrystalline diamond composite structure,and is more conducive to the electron transport from the diamond conduction band to the ZnO conduction band.In addition,the nanocrystalline diamond grain size is smaller,contains more grain boundaries,and is more conducive to electron transfer during field emission.The ZnO nanorods grown on the nanocrystalline diamond substrates with the reactant concentration of 0.025 M have better crystallinity,higher purity and less structure defect.The field enhancement factor is about 5277.7.The turn on field of the ZnO nanorods is 2.9 V/?m,attaining a current density of 0.48 mA/cm2 at an applied field of 8.7 V/?m.(3)B-doped ZnO thin films were grown on the nanocrystalline diamond substrate with the reaction time of 1.5 h,3 h,6 h and 8 h,respectively.The effects of different reaction times on the surface morphology,grain quality and field emission performance of ZnO sheets were systematically studied.The doping of B atoms suppresses the growth of ZnO along the[0001]direction,thus forming a two-dimensional ZnO structure-ZnO sheets.Nano-diamonds have good conductivity,small crystal grains,and many grain boundaries.The morphology of ZnO sheets is conducive to the transmission of electrons.In the field emission process,the electron conductivity is high,so that the field emission performance of ZnO sheets/nanodiamonds is significantly improved.With a reaction time of 8 h,the opening electric field of the ZnO sheets prepared on the nanodiamond substrate can be as low as 2.3 V/?m,and at a 4.0 V/?m electric field,the emission current density can reach 0.53 mA/cm.