Study Of Field Emission Devices Based On Graphene

Recently,graphene was widely used in energy storage,solar cell,sensors and field emission devices.Especially,in field emission devices,three dimension patterned silicon substrates are the brilliant choice according to their unique structure and compatibility with integrated circuit.Herein,we fabricate two kinds of 3D silicon substrates?silicon-tip and silicon microchannel plates?by MEMS process,semiconductor technology and chemical method.Graphene is prepared and coated on these substrates forming graphene/3D silicon substrates.These innovative structures are characterized in field emission.Firstly,graphene/Ni/Si-tip is fabricated by a series of processes.Graphene is modified by ultrasound process.Modified graphene sheet are deposited on Ni/Si-tip uniformity presenting the petal-like morphology.The results of simulation analysis indicates the top of graphene/Ni/Si-tip can emit lots of electrons.According to field emission test,the single graphene/Ni/Si-tip emits electrons at the current density of 0.32V·?m^-1.The largest current density reaches 24.8?A at the electric field of only 2.13V·?m^-1.These results prove that the graphene/Ni/Si-tip we fabricated shows promise in field emission electron source devices.Secondly,silicon microchannel plates?Si-MCPs?,a kind of 3D silicon substrates,are prepared by MEMS process and photo-assisted electrochemical etching with 5?m×5?m lattice arrays,the length of 250?m,and the thickness of the wall of 1?m.The nickel film is coated well on Si-MCPs by electroless method to be Ni/Si-MCPs.This conductive substrate is called macroporous electrically conductive network?MECN?.Then carbon atoms dope in the Ni film by carbonization hydrothermal method to form Ni₃C.After annealing,Ni₃C is divided into Ni and nanographene.Nanographene/MECN is obtained.This method of preparing and coating nanographene overcome the limitation of the choice of substrate in traditional process.Thirdly,nanographenearemodifiedwithzincoxide.ZnO nanorods/nanographene/MECN is prepared.The length of ZnO nanorods is 600 nm and the diameter is 70 nm.They stand on the surface of nanographene/MECN vertically and uniformly.This ZnO nanorods/nanographene/MECN shows great field emission performance with the turn-on electric field of 0.5 V·?m^-1 and the enhancement factor of 25550.And it shows good stability and sustainability under high,medium and low current densities.For comparisons,ZnO/MECN(E_on=0.7 V·?m^-1,?=25309),nanographene/MECN(E_on=2.1 V·?m^-1,?=324)and MECN(E_on=4.7 V·?m^-1,?=200)is measured.By theoretical analysis and simulated analysis,the reason why this structure shows outstanding field emission performance is explained as follows.Patterned 3D MECN provides more emission edges and avoids the electrostatic shielding effect according to its unique ordered lattice structure.ZnO nanorods and nanographene contacts each other forming metal-semiconductor contact,a heterojunction.The heterojunction reduces the contact barrier between ZnO nanorods and nanographene.Electrons tunnel from nanographene to ZnO nanorods more easily.Compared with former reports,ZnO nanorods/nanographene/MECN prepared in this paper shows greater field emission properties.Last but not least,ZnO and nanographene hybrids are modified with doping indium.In doped ZnO nanoparticles with different doping ratios are coated on nanographene by hydrothermal process.In-ZnO/nanographene/MECN is measured as field emitter.Compared with different ratios,10%is found to be the best ratio.10%In-ZnO/nanographene/MECN shows best field emission properties with the turn-on electric field of 1 V·?m^-1 and the threshold electric field of 3.7 V·?m^-1.The largest current density can reach 2.88 mA·cm^-2 and the estimated?is 27918.10%In-ZnO/nanographene/MECN also shows wonderful stability and sustainability.Under high,medium and low current densities,the average bias is only 2%and the biggest bias is less than 7%.Simulation is adopted for further analysis.The results indicate that doping indium is positive for ZnO and nanographene hybrids.It greatly improves the hybrids'field emission properties and helps the sample reach higher current density.Above all,Si-tip and Si-MCPs are fabricated by MEMS process to be 3D silicon substrate.Graphene is prepared,deposited and modified by nanoscience and nanomaterials process.The combination of Si-tip,Si-MCPs and graphene shows promise in cold cathode field emission electron source devices.This structure realizes the compatibility of field emission devices and integrated circuits.These graphene field emission devices reported in this paper improve the cold cathode field emission electron source devices and scanning electron microscopes in China and overseas.