Fabrication And Electron Field Emission Performance Of Ti O₂ Nanoarrays And Diamond Composite Structure

Now,the application of traditional cold cathode materials is limited due to their large volume and mass,poor stability in harsh environments and high preparation costs,which requires the design and selection of some new composite structure of cathode materials to meet the needs of integrated circuit emitter devices.TiO2 nanoarrays(TNAs)have a series of excellent physicochemical properties,such as low work function,large aspect ratio,small end curvature radius,environmental protection,etc.They are widely used in the fields of energy,environment,and biology due to their simple process,low cost,and unique geometric characteristics.They are considered potential candidates for cold cathode materials.Diamond,the next-generation semiconductor,possesses high mechanical strength,excellent chemical inertness,large electron-hole mobility,low or even electron affinity,and many other characteristics.It can be used as an ideal material for emitter devices.Therefore,the composite structure combining TNAs and diamond will have more possibilities in the electron field emission(EFE).In this paper,the composite structure of TNAs and diamond is prepared by microwave plasma chemical vapor deposition(MPCVD),impulse magnetron sputtering(IMS),and anodic oxidation techniques.The morphologies,microstructures,phase composition,and electrical properties of composite films are characterized by various testing instruments.The effect of the samples’morphologies and structures on their EFE properties and the enhancement mechanism are discussed.The main research and results are as follows.1.The TNAs are grown on free-standing diamond(FSD)film,the Si wafer substrate is for comparison.The effect of anodizing times(5,15,25,45,and 60 min)on TiO2 films morphologies and EFE performance is studied.The TNAs grown on the FSD substrate undergo a transition from nanorods to nanopores to nanotubes with the increasing anodizing time.The nanotubes with a good structure and grown perpendicularly to diamond grain faces are formed on the FSD film after 45 min anodization,and the TNAs grown on the Si wafers only change in nanopores size within a short oxidation time.The oxidation of the Ti layer on the FSD film is more intense than that of the Si wafer substrate.The phase composition of TiO2 on FSD film and Si wafer is dominated by rutile and anatase,respectively.The composite structure anodized at 30 V,10 wt%H2O,and 45 min shows excellent EFE performance,which can be turned on at a low field of 0.7 V/μm,and attain a high current density of 0.6 m A/cm~2 at an applied field of 1.6 V/μm.The synergistic effect of FSD substrate as electron acceleration layer and TiO2 nanotubes with large aspect ratio and low work function improves the EFE performance.2.The TNAs are grown on nanocrystalline diamond(NCD)film,the Si wafer substrate is also for comparison.The effects of electrolyte water content(0,5,10,and 20 wt%)and oxidation voltage(10,20,30,and 40 V)on the morphologies and EFE performance are investigated respectively.The diameter of TiO2 nanotubes on both substrates increases with the increase of electrolyte water content,while the voltage variation has little effect on the morphologies of nanotubes.The nanotubes with good morphology are formed on NCD under the optimized conditions of the electrolyte water content of 10 wt%,oxidation voltage of 30 V,and oxidation time of 45 min.The TNAs grown on the NCD film shows better EFE performance than that on the Si wafer substrate.The sample under this condition shows a low turn-on field of 5.3 V/μm,attaining a current density of 139.3μA/cm~2 at an applied field of8.7 V/μm.In addition to the tips of nanotubes,the quality of NCD film,i.e.,the large grain boundary density and more sp~2-bonded carbon(C=C)also are important factors to enhance the EFE performance of the composite structure.3.The microcrystalline diamond(MCD)and NCD are deposited on TiO2 nanotubes.The effect of deposition times(MCD:1,3,5,and 7 h.NCD:1,1.5,3,and 5 h)and grain sizes of diamond on the morphologies and EFE performance of samples are examined.The MPCVD plasma can make the diameter of TiO2 nanotubes smaller and the wall thicker.With the increase in deposition time,MCD changes from grains to continuous and compact film(7 h),as does the deposition process of NCD.The uniform and compact NCD film with an average grain size of 4.8 nm is deposited on TiO2 nanotubes after 5 h.Both diamond films have enough bond strength with TiO2 nanotubes substrates,and the EFE performance of the composite structure is enhanced compared with substrates.Moreover,the research on the composite film can be further extended to capacitors,photocatalytic electrodes,and anticorrosion materials.