Synthesis And Properties Of SiC One-dimensional Nanomaterials By Microwave-assisted Method

SiC material is regarded as a very excellent semiconductor, due to its wide bandgap, high work temperature, high thermal conductivity, high saturated drift rate, high critical broken voltage, low intrinsic carrier, high high irradiation, and high chemical stability. It can be used for producing high temperature, high frequency, high pressure resistant, high irradiation, and high power electronic devices, especially those suitable for operation under harsh environment. SiC one dimension (1D) nanomaterials (nanowire, nanotube, nanobelt, nanocable et al.) not only have the above mentioned virtues of bulk SiC but also have many excellent nanomaterial'properties, such as mechanical, optical, field emission properties caused by quantum confinement effects. In addition, SiC 1D nanomaterial can be compatible with the mature silicon planner technology. Thus, we can not only use them to understand the basis concept of low dimension nanomaterial, but also more importantly use them as function module to build nanoelectronic devices. They can be widely used in light emitting diode, high power transistor, field emission materials, photocatalyst, reinforced composites, new type lighting source, sensor and optical-electronic devices field.For the moment, much effort has been devoted to the preparation and characterization of SiC 1D nanomaterials. Although the SiC 1D nanomaterials change with each passing day, it was still in the initial stage for the most study. There are quite many problems, such as most 3C–structure; most nanowire morphology; low yield, long reaction time, high cost, expensive equipment, reaction condition rigour, quantum wire, and so on. The above problems have greatly limited the industry development of SiC 1D nanomaterial and electronic devices applications. Therefore, it is signality to find a method to fabricate SiC 1D nanomaterial by a simple, large-scale and low cost method, and these reasons decide SiC 1D nanomaterial can be widely industry and commercial applications.Compared with the common method, microwave-assisted carbon thermal reduction method (MAXTR) has some merits and can overcome disadvantage of other reported synthesizing methods, such as simple experimental equipment, easy and control experiment parameter, cheap reactive raw materials, and large-scale yield. In this paper, MAXTR was employed to prepare various SiC 1D nanomaterials and the optical and electronic properties of such materials have been primarily studied. SiC 1D nanomaterials, such as ultrathin 3C–SiC nanobelts, 6H–SiC nanowires, 6H–SiC nanobelts, 6H–SiC quantum wire, 3C–SiC-SiO2 nanochain heterojunction, have been prepared by change of experimental conditions. MAXTR has been proved to be a good and efficient method to synthesize SiC 1D nanomaterial with large-scale yield, low cost, short reaction time, size and morphology-controlled and further industry applications. The compositions, morphologies, and microstructures of SiC 1D nanomaterials were successively characterized with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersion spectroscopy (EDS). The optical and electronic properties of the SiC 1D nanomaterials were studied by Raman spectroscopy,photoluminescence spectrum (PL), and the field emission measurements. Based on the investigation, the growth mechanism for different SiC 1D nanomaterials and the relationships between the structure and properties have been studied. Some innovative achievements have been obtained and important conclusions are dawn. We hope that the study of SiC 1D nanomaterials can be used for establishing and supplying a solid foundation for the practical applications of SiC nanowires in nano-devices.The main productions are described as follows:1) By using a simple and low-cost MAXTR, single-crystalline, ultrathin 3C–SiC nanobelts have been synthesized in large scale. Morphological analysis indicates that the nanobelts are tens of micrometers in length, tens of nanometers in width and only several nanometers in thickness. Based on the experimental data, the growth mechanism of 3C–SiC nanobelts was proposed. Under 325 nm excitation, a broad emission peaked at 391 nm has been observed in the spectrum of the nanobelts, which reveals an obvious blueshift of bandgap and direct band gap property. Field-emission (FE) measurements show that the nanobelts are promising field-emitting materials with a low turn-on field of ~3.2 V/μm. The FE properties were also analyzed by applying with the first-order approximation of Fowler-Nordheim (F–N) theory and the electron emission were confirmed by the F–N tunneling emission mechanism. SiC nanobelts can be an excellent blue-light source and field emission material. The interesting photoluminescence and FE properties make the ultrathin nanobelts attractive for photonic and electronic applications.2) Al-doped 6H–SiC nanowires, nanobelts, and quantum wires have been largely synthesized by a novel and low-cost MAXTR. Structural, morphological, and elemental analysis revealed that the products were consisted of Al-doped 6H–SiC nanowires/nanobelts/quantum wires with a diameter of 5-200 nm and a length of tens to hundreds of micrometers. It is noted that the content of quantum wires is more than 20%. Stacking fault, planar defect and twin were also observation in such 6H–SiC nanostructures. Based on the experimental data, V–L–S gorwth mechanism was proposed to elucidate the growth process. We also pointed out that the nano Al powder was the key factor for the 6H–SiC nanostructures. Some unique properties are found in the Raman and photoluminescence spectra of the 6H–SiC nanostructures. An ultraviolet emission band from the 6H–SiC nanostructures and clear evidence of quantum confinement in 6H–SiC nanostructures have been observed. Photoluminescence spectrum shows clear evidence for the quantum confinement of 6H–SiC nanostructures with the emission peak above the energy gap. Moreover, the present results may inspire great interest in exploring other polytypes SiC nanowires, such as 4H–SiC nanowires, 2H–SiC nanowires, 15R–SiC, and so on, and their potential applications in building blocks for nanodevices in the future.3) SiC/SiO2 one-dimensional nanochains and SiC/SiO2 two-dimensional X-junction and Y-junction nanochains were synthesized by using a simple and low-cost MAXTR. Structural, morphological, and elemental analysis revealed that the SiC/SiO2 nanochains were consisted of 3C–SiC strings with diameters of 20-80 nm and periodic SiO2 beads with diameters of 100-400 nm. Based on the experimental characterizations, a two-step growth mechanism of the nanochains was proposed to elucidate the growth process. The nanochains with X-junction or Y-junction are gaining increasing interest as building blocks for two-dimensional or three-dimensional network structure. Theoretically, we can use such junctions to build any complicated form nanostructures. Spectral analysis indicated that both of SiC strings and SiO2 beads produced significant photoluminescence and the presence of SiO2 beads enhanced the emissions from SiC strings. Compared with the PL of SiC-SiO2 nanocables, the current nanochains not only have interesting violet-blue light emission, but also have waveguide properties. The optical properties of SiC nanowires can be tailored by the SiO2 beads because of each SiO2 bead may give off violet-blue light. The SiC/SiO2 nanochains provide periodic semiconductor-oxide units for incorporation of different functionalities into a nanoscale system.The special composite structure accompanied with its optical properties may have some potential applications in photoelectricity and nanodevices. We make sure that our approach presented here would be helpful in designing and preparing other Si-related heterostructures, such as Silicon Nitride and Zinc Silicate nanochain, and it is great meaning to build nanodevices in furture. At the same time, the obtained nanochain heterostructures is the foundation of new complicated systems and SiC nanodevices and could meet the growing demands of optical and electronic nanodevices.