The Preparation, Field Emission Characteristics And First-Principles Study Of N-Doped、Ce-Doped And N/Ce-Codoped One-Dimensional SiC Nanomaterials

One-dimensional SiC nanomaterials have potential application as the cold cathode materials in harsh environments, owing to its good field emission (FE) property, chemical stability and electron affinity. The field emission property could be enhanced via the doping of various elements, and the lower turn on field (Eto) and threshold field (Ethr) could be achieved. In this study, the doping process of N-doped, Ce-doped and N/Ce-codoped one-dimensional SiC nanomaterials have been investigated systematically. And we make sure the optimum process parameters via the tests of SEM, TEM, XRD, XPS and FE property. The mechanism of enhancing FE property had been analyzed by DFT using the CASTEP code. And a new model theory of field emission have been proposed and proved according to the analysis of FE property. The main research results as follows:N-doped SiC Nanowires (SiC NWs) at different levels were achieved via annealing with ammonia at different temperatures and different time, and the properties of field emission could be enhanced in varying degrees due to the different concentrations of N-doping. The optimal process parameter was obtained:the reaction temperature was 800℃ and the heat preservation time was 300 min, and in this time, the turn-on field and threshold field were 1.6 V/μm and 5.2 V/μm, respectively. In addition, density functional calculations were performed according to the different concentrations of N-doping. The substitution sites of nitrogen atoms in the 3c-SiC lattices (the N atoms substitute the C sites or Si sites, and they are accumulative or dispersive in SiC lattices) are analyzed according to the field emission test, first principles calculation and the XPS of the products.The N-doped SiC@SiO2 coaxial nanocables (SiC@SiO2 CNCs) have been prepared with the optimum process parameters of N-doped SiC NWs. And it has an excellent FE property that the Eto and Ethr are 0.60 V/μm and 3.38 V/μm, respectively. Whereafter, a tri-segments model theory, corresponding to initiation segment, saturation segment and increasing segment, is put forward based on the analysis of the FN plot of un-doped and N-doped SiC@SiO2 CNCs. This is attributing to that the total field emission currents are divided into CB current and VB current by the band gap and the changing rate of CB current will different from that of VB current with the increase of applied field.The FE properties of Ce-doped SiC NWs could be enhanced in varying degrees due to the different concentrations of Ce-doping. The optimal process parameter was obtained:the quality of the Ce(NO3)3 was 0.66 g, meanwhile the most outstanding FE performance was obtained corresponding to the turn-on field and threshold field being 2.3 V/μm and 4.4 V/μm. The Ce-doped SiC nanowires were also calculated via Castep of material studio on the basis of the first-principle. And the result of theoretical calculation suggest that the narrowed gap could be generated, and the narrowed gap made electronics transfer from VBM to CBM need less energy, and the property of field emission was enhanced.Ce and N Codoped SiC nanowires (Ce, N-SiC NWs) were prepared by the two steps synthesis that are vapor-phase doping method and chemical vapor reaction method. The optimal process parameter was obtained:the quality of the Ce(NO3)3 was 0.66g, meanwhile the reaction temperature was 800℃ and the heat preservation time was 300 min, which corresponds to the turn-on field and threshold field of 0.9 V/μm and 4.4 V/μm. Meanwhile, the cause of the reduction of turn-on field and threshold field is analyzed, respectively.