| Owing to the advantage of extremely small grain size,low surface roughness,chemical inertness,high electrical conductivity and excellent field emission properties,ultrananocrystalline diamond(UNCD)films show large potential for applications such as cold cathode field emitters and other vacuum microelectronic devices.During the UNCD deposition process by MPCVD,the change of process parameters plays an important role in the evolution of the microstructure of the film.Ion implantation is a surface modification technology that can effectively improve the electrical properties of diamond films and combined annealing treatment.In the text,Free-standing diamond(FSD),microcrystalline diamond(MCD),and nanocrystalline diamond(NCD)with different grain size were firstly prepared as reference samples and compared with UNCD for analyzing the effects of grain size and surface morphology on field emission properties.Secondly,UNCD films with different parameters were prepared by changing the concentration of H2 in the reaction gas.Finally,the 100 keV,1×1017 ions/cm2 doses of Cu ions were implanted into UNCD films.And they were annealed in Ar atmosphere at 500 ℃ in order to study the microstructure and EFE properties of UNCD films.A variety of test methods were used to characterise the micro-morphology,structural characteristics,and chemical bond structure of the films,while the electric properties were investigated through Hall Effect and field emission test.The main research contents and results are as follows:(1)The effects of grain size on field emission properties of diamond films were investigate by comparing the microstructure and field emission properties of UNCD,FSD,MCD,and NCD films.The results show that the grain size has a significant impact on the field emission properties of diamond film because of proportion of the grain boundary to reduce with the decreasing of grain size.The high grain boundary ratio provides a conductive network that facilitates electron emission.That is,electron emission sites increases with the degree of graphitization.The narrow grain boundary size enhances the electric field between interface and vacuum,leading electron tunneling easier to occur.Therefore,UNCD films exhibit the best field emission properties.(2)diamond samples with different H2 concentrations were prepared to explore the effect of hydrogen atoms on the microstructure and field emission performance of UNCD films.The results show that H2 concentration significantly influences the microstructure and field emission properties of the films.With the decrease of H2 concentration in the CH4/Ar atmosphere,the grain size of the film decreases,the proportion of amorphous carbon and graphite in the film is increased.The enhancement of a large number of sp2 phases and the "local state" electric field in the grain boundary provides a conductive channel for the emission of electrons,which reduces the difficulty of electron tunneling and increases the field emission properties.(3)The effects of 100 keV Cu ion implantation and subsequent annealing(i.e.common annealing or rapid annealing)at 500 ℃ on modifying the surface morphology and the electron field emission(EFE)properties of UNCD films were investigated.The results show that Cu ion implantation causes lattice damage,and nano diamond particles on the surface of the film disappear.After the 500 ℃ common annealing,the lattice damage caused by the implantation process is recovered slightly.The implanted Cu ions migrate to the surface of the film to form Cu NPs and catalyze the formation of a small amount of nano-graphite phases,providing more conducive electron-emitting conductive channels.After rapid annealing,more Cu NPs and a large amount of nano-graphite phases will be formed on the surface of the film.And an interconnected network structure is formed under the catalytic action of Cu.This"conductive island" structure and the nano-graphite phase provide a conductive path for the emission of electrons,significantly reducing the value of E0. |
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