Synthesis, Field Emission Activity And First-Principle Calculations On Electronic Structure Of Nitrogen-Doped One-Dimensional Sic Nanomaterials

In this paper, The high-quality N-doped one-dimensional SiC nanomaterials were synthetized by chemical vapor reaction method based on different C source and N dopants. We explored a simple and new method for the synthesis of β-SiC/SiO2and N doped β-SiC/SiO2coaxial nanocables:polymer pyrolysis. The growth mechanism of synthetic products which were obtained with different process condition were explored. The influence mechanism of N doping on field emission activity of synthetic products had been analyzed by DFT using the CASTEP code. The main research results as follows:The N-doped one-dimensional SiC nanomaterials were obtained by chemical vapor reaction method using milled Si/SiO2mixed powders as Si source and melamine as N dopant which simultaneously C source and N source. We explored the process parameters (The dosages rate of raw materials、synthesis temperature、holding time and so on) which have influence on the field emission activities, The growth mechanism of synthetic products were investigated. The optimized N-doped reaction technics as follow:the dosages rate of raw materials was1:3, the synthesis temperature was1250℃and the holding time was25min. Under the optimization synthesis conditions, the products exhibited high purity, uniform diameter with80nm, the length is up to tens of microns, and the nanowires are single crystalline (3-SiC, the turn-on field and threshold field are1.5and3.5V/μm.The N-doped one-dimensional SiC nanomaterials were obtained by chemical vapor reaction method using milled Si/SiO2mixed powders as Si source and urea as N dopant which simultaneously C source and N source. We explored the process parameters (The dosages rate of raw materials、synthesis temperature、the keeping temperature of urea and so on) which have influence on the field emission activities, The growth mechanism of synthetic products were investigated. The optimized N-doped reaction technics as follow:the dosages rate of raw materials was1:3, the synthesis temperature was1250℃and the the keeping temperature of urea was250℃. Under the optimization synthesis conditions, the products exhibited high purity, uniform diameter with80nm, the length is up to tens of microns, and the nanowires are single crystalline (3-SiC, the turn-on field and threshold field arel.9and4.0V/μm.A new method for the synthesis of β-SiC/SiO2and N doped β-SiC/SiO2coaxial nanocables:polymer pyrolysis were found. The quality of PCS is3g, the quality of PCS and C3H6N6are3g and6g、the synthesis temperature is1200℃、the holding time is2h. This kind of coaxial nanocables have high purity. And they consist of single-crystalline P-SiC cores with diameters of about30-60nm and uniform amorphous SiO2wrapped layers with the thickness of about15-20nm, and their lengths are up to several tens of micrometers. The pyrolysis mechanism of PCS and growth mechanism of the coaxial nanocable were discussed in detail, respectively. Besides, the N-doped β-SiC/SiO2coaxial nanocable exhibited enhanced field emission activity comparing with the un-doped coaxial nanocable, whose turn-on and threshold fields decreased by0.7V/μm and1.2V/μm.The band structure and density of states (DOS) of the doped and un-doped samples had been calculated in the frame of DFT using the CASTEP code. The results showed that band gap of the N-doped SiC reduced, The transition of an electron from valence band to conduction band needs less energy, the concentration of free electron in N-doped SiC is bigger than SiC, which enhanced the emission ability, and explained the reason of enhancement of field emission activity in theory.