Synthesis Of Silicon Carbide Nanowires Using Thermal Decomposition Of Organic Solvent And Research Of Their Several Properties

In connection with discovering of carbon nanotubes in 1991,one-dimensional nanostructures,such as nanowires,nanobelts,nanorods,and nanocables have attracted much attention in the field of material research owing to their unique structural and physical properties different form the traditional bulk materials.Resent research results show that they are valuable for the fundamental research of materials and possess potential application.Among the several materials,SiC has been focused as potential material because their outstanding properties,such as wide band-gap,high breakdown field,high saturation drift velocity,short carrier lifetime,high thermal conductivity,excellent mechanical and chemical properties,etc.Compared to bulk material,SiC nanostructures reveal outstanding optical and field emission properties caused by quantum confinement effects and novel structures.Therefore,the material studies of SiC 1D structure are of great importance for future nanoscale photonic and electronic devices.In spite of its outstanding material properties,the study of SiC-based 1D nanostructure is in primary stage.Now,exploring of several synthesis methods,characteristics of basic optical and field emission properties have become main contents of their study.Up to now,several methods such as thermal reduction of carbon nanotubes,direct heat method and chemical vapor deposition,etc.For industrial application,it needs to develop a simple method to synthesize large-scale SiC nanostructures uniformly and at low-cost.In this work,we present a simple and low-cost method to synthesize SiC nanostructures in large-scale and uniformly.Our synthesis of SiC 1D nanostructure is based on the thermal decomposition of organic solvents,i.e.,methanol and ethanol.The synthesis of SiC 1D nanostructure was carried out on the common Si substrate.The morphology,microstructure,crystal structure and several physical properties of nanostructures have been studied systematically and discussed their growth mechanisms.Carbon monoxide is a necessary precursor for synthesis of SiC-SiO₂ core-shell nanocables.We use gaseous carbon monoxide produced by thermal decomposition of organic solvents as a precursor.The use of thermal decomposition of organic solvents in the synthesis of SiC nanostructure makes it convenient and simple.Based on this method,it is possible to synthesize high-quality and large-scale SiC-SiO₂ core-shell nanocables at low-cost.In the works for synthesis of SiC-SiO₂ nanocables,we found that the catalyst dispersion on the Si substrate plays key role for uniform distribution of nanocable.For uniform dispersion of catalyst on the whole surface of Si substrate,we explored a noble covering method of catalyst on Si substrate and a new catalyst mixture.The dispersion state of catalyst and the distribution of resultant nanocables on the Si substrate were investigated using scanning electron microscopy and Raman microscopy.Most of nanocables did not exceed 50 nm in diameter and revealed smooth surface morphologies.Some of them were divided into two or four branches. It is found that the dividing of nanocables was due to the simultaneous formation of several crystal seeds in one catalyst droplet.Unordinary carbon-related peaks were appeared in Raman spectra recorded from the surface of Si substrate on which nanocables have been distributed nonuniformly.These unordinary carbon-related peaks were still observed after annealed at 800℃for 30min in the air.Their origins were discussed comparing with the result of SEM observation.We also investigated the possibility of the use of ethanol for synthesis of SiC nanocables.Differing from the case of methanol,several species such as carbon,H₂O, and hydrocarbons are produced in thermal decomposition course.These species affect on the several properties of nanocables.The existence of these species gave us the possibility to control of microstructures of nanocables.By using the thermal decomposition of ethanol,we successfully synthesized SiC-SiO₂ core-shell nanocables, SiC-C-SiO₂ ternary coaxial nanocables,SiC-SiO₂ nanocables decorated with carbon nanoparticles,and SiC-SiO₂-C ternary coaxial nanocables.We also successfully controlled the diameter of SiC core and the thickness of SiO₂ shell by adjusting the flow ratio between Ar and Ar/ethanol.The former three kinds of nanostructures revealed good photoluminescence properties and the later showed potential application for field emission display.At the end,we synthesized a noble SiO₂ hierarchical nanostructure on SiC nanowires by using a mixture of ethanol and titanium tetrachloride as a precursor.On the basis of SEM and HRTEM observation,the growth mechanism of this noble nanostructure was proposed.