| Diamond is considered as an electron emission source in cold cathode devices due to its negative electron affinity?NEA?.However,diamond itself has high resistivity,the replenishment and transport of electrons in bulk diamond are diminished,which reduce its electronemission.Therefore,the high potential that the diamond bears as a material for the fabrication of coldcathode emitting devices requires the films to be conductive.Actually,metal doping technology is expected to improve its field emission property.In this experiment,different concentrations of Ti,Ag and Ni nanoparticle-doped diamond films were deposited on the titanium matrix by electrophoresis deposition,subsequently,they were annealed at 800?for 10 min in nitrogen atmosphere.Scanning electron microscopy,X-ray diffraction and Raman spectroscopy were used to investigate the morphologies and structures of the composite films.Hall effects was carried out to characterize the electrical properties of the samples and the field emission properties of the composite films was tested by a lab-built high vacuum system.The effect of different doping contents of metal nanoparticles on the emission performance of diamond films was discussed based on F-N equation in this paper.The experimental results are as follows:?1?The electrical properties and field emission performances of diamond films without doping and annealing treatment are not ideal because of their high resistivity.After heat treatment,the electrical properties and field emission performances of diamond films are enhanced clearly.After doping of 2.5 mg,5mg,7.5 mg,10 mg and 12.5 mg Ti metal nanoparticles,Ti-TiC-diamond-TiC-Ti network conductive channels are formed between Ti nanoparticles,nanodiamond and Ti matrix.The field emission performance of the Ti-doped films is greatly enhanced When doping concentration is 5 mg.The turn on field?E0?is 3.04 V/?m,and its current density enhanced to 15.54?A/cm2 at the electric field intensity of 3.69 V/?m and the absolute value of the slope of F-N decreases sharply to 18,However,with the further increase of doping concentration,a large amount of TiC is generated on the surface of the samples,covering part of the diamond material,which reduces the emission sites on the surface of the samples.Therefore,the field emission performance decreases.However,the electrical properties of the material increase with the increase of doping content.At the doping concentration of 12.5 mg,the surface resistivity of the material reduced to 1.041×10-2??cm-2,while the carrier concentration is increased to 8.254×10144 cm-3,and the Hall mobility is obtained at 1.125×103cm2V-1s-1.It indicates that the content of TiC on the surface of the material increases with the increase of doping concentration.?2?The electrical and field emission properties of diamond films doped with Ag nanoparticles of 2.5 mg,5 mg,7.5 mg,10 mg and 12.5 mg by electrophoretic deposition were investigated.The field emission properties increased fistly and the decresed with the increases of Ag content.when the doping concentration was 7.5 mg,the electrical properties and field emission properties of diamond films are the best.The surface resistivity of the diamond films was as low as 9.851×10-2??cm-2,the carrier concentration was as high as4.598×10144 cm-3,and the Hall mobility was 4.125×102 cm2V-1s-1.The turn on field?E0?is as low as 1.55 V/?m,and the field emission current density of 22.69?A/cm2 can be obtained at the electric field intensity of 1.96 V/?m,and the absolute slope of F-N curve reaches the lowest value of 14.The reason for this phenomenon is that Ag is a negative metal,which can form good ohmic contact with diamond material and increase the electron emission source and conductive channel.Since the work function of Ag is lower than that of diamond and different from the dielectric constant of sp3C-C in diamond material,contact electric field and field enhancement effect can occur at the interface of Ag-Diamond,which makes it easier for electrons to move from diamond;Ag nanoparticles doping results in the increase of the number of tip salient,which reduces the difficulty of surface electron emission.However,as Ag nanoparticles continue to be doped,a part of diamond on the surface of the samples are covered and Ag nanoparticles agglomerate,which results in the formation of heterogeneous bonding between diamond and Ag particles similar to Schottky barrier and the reduction of the number of tip salient,which greatly increases the difficulty of electron emission and further reduces the electrical properties and field emission performance of the samples.?3?When 2.5 mg,5 mg,7.5 mg,10 mg and 12.5 mg Ni nanoparticles were doped into the diamond films,the electrical properties and field emission properties of change increases as the content increases initially and decreases afterwards.When the doping content is 5 mg,the electrical properties and the field emission performance achieve the best,the material surface resistivity is as low as 1.026×10-2??cm-2,the carrier concentration is as high as 8.986×10155 cm-3,the Hall mobility is 9.911×102 cm2V-1s-1,the turn on field?E0?is as low as 1.38V/?m,and the stable emission current of 1323.47?A/cm2 can be obtained at the electric field intensity of only 2.94 V/?m,and the absolute slope of F-N curve reaches to 6.When doped properly,Ni particles play the role of conductive channel,electronic source and surface tip protrusion,it make the electrical properties and field emission properties of materials greatly enhanced.In addition,nickel can catalyze sp3 carbon in diamond to form sp2 carbon with excellent conductivity.After heat treatment at 800?and N2 atmosphere,nickel catalyzes the transformation of disordered graphite or amorphous carbon phase into ordered graphite,and forms a network structure with excellent conductivity of Nano-Grained graphite phase,which greatly improves the electric conductivity and field emission performance of the diamond films.With the doping of excessive Ni nanoparticles,the electrical and field emission properties of the samples were reduced due to agglomeration,which resulted in the reduction of surface tip protrusion and the weakening of catalytic effect. |
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