Study On Synthesis, Properties, Mechanism And Mass Production Technique Of Sic One-dimensional Nanomaterials

As one of the most significant novel semiconductor, SiC is superior to the othersmaterials because of their high band gap, high critical breakdown electric field, lowdielectric constant and outstanding thermal conductivity, which exhibits potentialapplication in blue light emitting diodes (LED), toughening composite, field emissioncathode and photo-catalyst areas. A large number of literatures have pointed out that theperformance of the SiC one-dimensional (1D) depend not only the composition but alsoon their peculiar morphologies and surface structure. Recently, there is increasingattention on the fabrication of SiC1D nanomaterials with different morphology.Researchers hope to achieve the shape-controlled synthesis of SiC1D nanomaterials asthe light, electric, and field emission performances are improved.In this paper, SiC1D nanomaterials with different morphologies were fabricatedusing a simple chemical vapor reaction (CVR) method. In addition, the morphologies,structures, properties and formation mechanism of the as-obtained products wereinvestigated systematically. The main results are summarized as follows:(1) Bamboo-like3C-SiC1D nanomaterials were firstly obtained on6H-SiCsubstrate via CVR method under KI catalyst assist. SEM, EDS and HRTEM equipmentswere employed to test the products, the corresponding results indicated that thenanomaterials with periodic change of diameter grew along [111] direction. A lot ofstacking faults presented in a wide diameter position, and perfect crystal without defectappeared in narrow position. Furthermore, a reasonable growth mechanism was proposedto explain the growth process of the1D nanomaterials.(2) Rod-like1D nanomaterials with ideal morphology were fabricated on the graphite substrate by adjusting the reaction temperature. SEM and XRD were used toevaluate the dependencies between the yield, morphology, crystallinity of products andreaction temperature for the first time. The results indicated that the crystallinity and yieldof the rod-like SiC1D nanomaterials increased with the increase of reaction temperature,and the morphology gradually improved. HRTEM from rod-like SiC1D nanomaterialsobtained at1250℃showed that the SiC core with thin amorphous SiO2layer was cubicstructure which grew along [111] direction.(3) Coaxial3C-SiC1D nanomaterials coated with amorphous carbon coatings wereprepared using Fe-Ni catalyst under extended aeration condition. Three-layer coaxial3C-SiC1D nanomaterials composed of crystalline carbon coating, amorphous SiO2inter-layer and SiC core were prepared using Ni catalyst under extended aerationcondition. An reasonable growth mechanism were put forward felicitously to explain theformation of the two novel SiC1D nanomaterials. The field emission propertiescharacterization results indicated that the lower turn-on field and threshold field ofapproximately0.5V·μm-1and2.1V·μm-1for3C-SiC@a-C nanostructures,0.8V·μm-1and2.6V·μm-1for3C-SiC@SiO2@c-C. The electronic transport process from theproducts internal are investigated in detail. The relevant surface hydrophobic propertiesare explored with contact angles of130°and118°respectively. The remarkable resultspresent guidelines for improving field emission properties and obtaining hydrophobicsurfaces of nanostructures via decorating functional carbon coatings, which show not onlyapplications in cold cathode vacuum microelectronic devices, but also in anti wetting withrespect to water and self-cleaning areas.(4) Milled Si-SiO2mixed powder was used as silicon source, high-purity CH4wasused as carbon source, and graphite wafer was chosen as substrate. The synthesisexperiments of SiC nanowires were carried out in vertical vacuum controlled atmospherefurnace. Based on the previous results, the influence of catalysts, holding time, ventilationrate of CH4on the yield and morphology of SiC1D nanomaterials were investigatedsystematically, the best synthesis process of SiC nanowires was determined.(5) The graphite and single silicon powders were used as the new type carbonsource and silicon source, respectively. The influences of the reaction temperature,preheating temperature, second heating rate and holding time on the yield, morphologyand phase structure of the synthesized SiC nanowires were researched systematically viachemical vapor reaction method. Under the optimum process, the continuous yield of SiC nanowire could achieve gram-scale, which provide material foundation for the applicationand related properties research of SiC nanowire.(6) The influence of the crystalline state and photoluminescence properties of SiCnanomaterials treated with various annealing temperature (400℃-900℃), annealingatmosphere (air, vacuum, Ar, NH3) and annealing time (0.5h,1h,2h,3h,4h) aresystematic investigated in detail, respectively. The characterized results show that: withthe annealing temperature increasing, the luminescent intensity of the specimens increasegradually and tend to be stable. With the increase of treatment time, the luminescentintensity of the specimens present increase to maximum and then decrease gradually. Theluminous intensity annealed in air atmosphere is superior to other conditions. The SiCnanowire annealed in the optimum PL characteristic annealing processair (air atmospherefor2h at900℃), SiC nanowires defect improved, the crystallinity is improved, the lightintensity is greatly enhanced excitation.