Study On Preparation And Field Emission Properties Of Silicon Carbide Nano Wires Synthesized Via High-Energy Microwave Irradiation

Silicon carbide?SiC?materials have been widely used in many fields because of their unique structure and excellent properties covering mechanical,optical,electrical,field emission and photocatalytic.As an important part of SiC material,SiC nanomaterials not only have the excellent properties of the SiC bulk materials,but also have their own special functional characeristics.Such as specific optical,electrical,magnetic,field effect properties,they have a very broad application prospect in fields like vacuum microelectronics,micro-nanostructured devices and so on.On the base of these,in this paper,SiC nanowires synthesized by high-energy microwave technology are used to improve the field emission properties.The optimal properties of SiC are obtained by the join of catalysts in the process of synthesis.At the same time,the growth process and the influence factors of field emission are investigated.The main results of this study are as follws:?1?Numbers of silicon carbide?SiC?nanowires can be obtained by high-energy microwave technology directly irradiate the raw materials covering artificial graphite,silica powders and silicon powders.The sample are component of nanowires,nanorods,microcrystallines and some unreacted raw materials.After detection,it can be confirmed that the nanowire showing a cylindrical SiC/SiO_x coaxial structure.Plenties of structural faults such as stacking faults and vacancy oxygens are existed in the core SiC.The result of photoluminescence properties shows that a strong brosd photoluminescence peak at wavelength of 390nm can be achieved by the excitation light with wavelength of 240nm at room temperature.It shows obviously blue-shift.For the field emission properties,the current value and voltage value are recorded under the conditions of high voltage,then drawing J-E curve through F-N formula.The Eto value can reach to 0.25V/?m.All of this indicated that the cylindrical SiC/SiO_x coaxial nanowires synthesized by high-energy microwave irradiation have excellent photoluminescence and field emission properties.?2?Synthesis of SiC nanowires by catalyst assisted high-energy microwave irradiation.The catalyst is added in two ways:one is directly adding the metal powders into raw materials,the other is immersing a substrate through a metal salt solution for a period of time,then take it from the solution and naturally dry in the air condition,so a metal salt film will be formed on the surface of the substrate,place this substrate above the crucible which containing the raw materials.The results show that the properties of the sample can be improve due to the existion of the catalyst.Under the condition of substrate with(Fe?NO₃?₃,the products can obtain the optimal morphology,structure and performance.Only nanowires are existed in the products,those nanowires have uniform size and same morphology with the diameter about 100nm.The result of photoluminescence properties shows that when the catalyst was metal powders,the photoluminescence peak was detected at wavelength of 387nm,while replace by the substrate with metal salt film the emission peak will move to 380nm.The reason might attributed to the increases of contact area between SiC and SiO_x,more structural defects and hanging bonds at the interface.The result of field emission properties shows different phenomenon.For metal powder catalyst,the Eto value shows increase compaired with noncatalyst,the reason of this might attribute to the metal existed in the top of the nanowires,causing shielding effect on the process of electrons emission.For substrate with metal salt film,the Eto and Ethr values are 0.2 and 2.1V/?m,respectively.Such low Eto and Ethr values indicate that the tube-brush-like SiC/SiO_x coaxial nanowires have excellent field emission properties.?3?The synthesis process of the novle tube-brush-like SiC/SiO_x coaxial nanowires and the movement of the iron-containing materials are investigated.Under the action of microwave plasma,the state of the Fe was constant changed during the forming of nanowires.Fe has two places to go,one is diffusing and volatilizing into the resonator of the microwave oven,the other is to combining and precipitating to form liquid Fe?L?and work as catalyst.The liquid Fe?L?will gradual disappear during the cycle process of the formation of nanowires until clearly depletion,achieving the self-purification of catalyst.The characteristions of the tube-brush-like SiC/SiO_x coaxial nanowires are large number of emission sites,large aspect ratio,small radius of curvature and SiC/SiO_x heterojunction.In addition,the self-purification of catalyst effective solve the shielding effect causing by metal elements.All of these factures provide favorable conditions for electron emission,so the tube-brush-like SiC/SiO_x coaxial nanowires have excellent FE properties.