Needle-shaped 3C–SiC nanowires were grown from commercially available SiC powders in a thermal evaporation process with iron as catalyst. A strong broad photoluminescence peak located around 450 nm was observed at room temperature, which may be ascribed to quantum size effects of nanomaterials. Needle-shaped 3C–SiC nanowires may have great potential applications such as blue-green light-emitting diodes and display devices.

Nanostructured silicon carbide has unique properties that make it useful in microelectronics, optoelectronics, and biomedical engineering. In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed. Silicon carbide nanocrystals are generally produced using two techniques, electrochemical etching of bulk materials to form porous SiC or embedding SiC crystallites in a matrix such as Si. Luminescence from SiC crystallites prepared by these two methods is generally believed to stem from surface or defect states. Stable colloidal 3C-SiC nanocrystals which exhibit intense visible photoluminescence arising from the quantum confinement effects have recently be produced. The field electron emission and photoluminescence characteristics of silicon carbide nanostructures as well as theoretical studies of the structural and electronic properties of the materials are described.

Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors that allow control over their geometry via simple chemical processes. Herein, we present a molecularly seeded synthesis of a complex nanostructure, SiC tetrapods, and report on their structural and optical properties. The SiC tetrapods exhibit narrow line width photoluminescence at wavelengths spanning the visible to near-infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This previously unknown geometry of SiC nanostructures is a compelling platform for biolabeling, sensing, spintronics, and optoelectronics.

β-SiC nanowires are a novel type of photocatalysts. However, they tend to be entangled together especially at high concentrations when dispersed in water, which may reduce the photocatalytic activity. It is reasonable to expect that β-SiC nanowires would provide better photocatalytic activity if they are grown on activated carbon. In the letter we report the successful synthesis of quantities of β-SiC nanowires grown on the surfaces of the activated carbon by pyrolysis of polycarbosilane at 1300 °C. The nanowires, with the diameters of 50–100 nm and the length of tens of micrometers, are composed of single crystal β-SiC along the 〈1 1 1〉 direction. Both the VLS and the VS mechanisms were employed to interpret the nanowires growth.

Silicon carbide (SiC) microtubes have been successfully synthesized from a wood template with unidirectional pores by a vapor–solid (VS) reaction at 1450 °C in a dynamic argon/hydrogen atmosphere (Ar/H₂ = 80/20). Biomorphic wood cells are transformed into carbon preforms by a two-step carbonization process at 500 and 1000 °C. The gaseous Si precursor (SiO_(vapor)) reacts directly with the free surface of the carbon template to form a SiC layer. Further diffusion occurs to permit SiC layer growth into the carbon template. The as-synthesized SiC is mainly β-SiC with a small amount of pseudo α-SiC. The residual free carbon in the as-synthesized SiC volatilizes through a burnout process at 650 °C in air. The synthesized SiC microtubes possess the villus-like and radial grain morphology on the outer surface, and show the fine grains on the inner surface. A model for the formation of SiC microtubes from porous carbon preforms is proposed, and the morphology and mechanism of synthesis of the SiC microtubes in the VS reaction are discussed.

The bamboo-like silicon carbide nanofibers were synthesized by the carbothermal reduction of the carbonaceous silicon xerogel containing lanthanum nitrate. The xerogel was heated to 1300 °C in argon flow in a horizontally tubular reactor and produced as-synthesized sample. The as-synthesized sample was then heated in air at 700 °C for removal of the residual carbon and treated by nitric acid and then hydrofluoric acid for elimination of the unreacted silica and other impurities. The purified product was characterized by XRD, SEM, TEM and HRTEM. The results indicated that the product was bamboo-like β-SiC nanofibers with a diameter of 40–100 nm and a length of tens to hundreds of micrometers and had planar stacking faults perpendicular to the fiber axis.

Large-scale centimetres-long single-crystal β–SiCnanowires have been prepared using CH₄ as the carbon source and SiO or the mixture of Si and SiO₂ as the silicon source by a simplecatalyst-freeCVD route under superatmospheric pressure conditions. The nanowries grown on ceramic boat or corundum substrates, with lengths of several centimetres and the average diameters of around 40 nm, were composed of single-crystal β–SiC core along the [111] direction and amorphous SiO₂ shell of about 1–30 nm thick depending on the growth position along the flowing direction of the carrier gas. The total gas pressure is an important factor for the synthesis of the large-scale centimetres-long β–SiCnanowires, which can easily adjust the pressure of the vapors to supersaturation condition. The growth of thenanowires was governed by the Vapor-Solid mechanism. The β–SiCnanowires showed an intense blue light emission at room temperature.

In this work, we report on the use of patterned 4H–SiC(0001) substrates for the heteroepitaxial growth of 3C–SiC by vapor–liquid–solid (VLS) mechanism using Ge₅₀Si₅₀ melt. Mesas structures of various size and shape were obtained by standard photolithography and dry etching processes. On the temperature range investigated 1300–1450 °C, 3C–SiC deposit was obtained on top and outside the mesas. Some lateral enlargement of these mesas was observed, but it was systematically homoepitaxial. The lateral growth rate was found rather low compared to other techniques like chemical vapor deposition, with a maximum value of12 μm/h. In addition, elimination of twin boundaries (TBs) inside the 3C–SiC deposit on top of the mesas was observed in the temperature range of 1400–1450 °C and for specific mesa shape or orientation of the sidewalls. The best case for eliminating these TBs was found to be with initially circular mesas, which spontaneously form well orientated hexagonal facets and then lead to TB-free deposit on top after VLS growth.

The crystal growth of 3C-SiC onto silicon substrate by Vapor–Liquid–Solid (VLS) transport, where a SiGe liquid phase is fed with propane, has been investigated. Three sample configurations were used. In a preliminary approach, the VLS growth of SiC was conducted directly onto Si substrate using a Ge film as liquid catalyst. It led to the growth of a thick continuous SiC polycrystalline layer which was floating over a SiGe alloy located between the silicon substrate and the topping SiC layer. In the second configuration, a thin seeding layer of 3C-SiC grown by chemical vapor deposition (CVD) was used and the VLS growth was localized using a SiO₂ mask. The liquid phase was a CVD deposited SiGe alloy. The growth of a few hundred nanometers thick 3C-SiC epitaxial layer was demonstrated but the process was apparently affected by the presence of the oxide which was dramatically etched at the end. In the last configuration, the silicon substrate was patterned down to 10 μm and a thin seeding layer of 3C-SiC was grown by CVD onto this patterned substrate. The liquid phase was again a CVD deposited SiGe alloy. In this last configuration, the presence of epitaxial SiC was evidenced but it grew as trapezoidal islands instead of an uniform layer.

By a vapor−liquid−solid (VLS) mechanism, where a Ge−Si melt is fed by propane, 3C-SiC layers of1.4 μm thickness were grown on 6H-SiC on-axis substrates. These layers were found to be single domain as seen from morphological and electron backscattering diffraction observations. They were free of any hexagonal inclusion. Both transmission electron microscopy and high-resolution X-ray diffraction show the high crystalline quality of the grown material. Nitrogen was found to be the main impurity, at a concentration of (6−7) × 10¹⁷ cm^-3 as estimated by Raman spectroscopy, though Al contamination was also detected by low-temperature photoluminescence. The identification and the quantification of Ge incorporation inside the SiC layers were determined by particle-induced X-ray emission (PIXE). The Ge concentration was calculated to be 5 × 10¹⁸ atoms/cm³.

采用单质Si粉和酚醛树脂为原料、均混、成型、碳化, 并以10℃/min的升温速率在1300～1400℃/0.5～2h的微波加热条件下制备了SiC纳米线. 用SEM和TEM观察所得SiC纳米线形貌, EDX检测样品成分. 结果发现: 所制备的SiC纳米线具有典型的SiC/SiO₂芯－壳式缆状结构特征, 直径约为20～100nm. 分析认为, 在微波加热条件下, 液态Si在SiC纳米线生长过程中起着至关重要的作用, 既具有催化作用, 同时又是制备SiC纳米线的关键原料.

Silicon carbide has been synthesised from silicon orsilica combined with activated carbon or graphitevia microwave heating over timescales from minutes to seconds without the need for inert atmospheres or subsequentpurification. The carbide morphology and phase purity can be controlled by the microwave cavity used and the power applied and hence by the heating rate. Short irradiation times (ca. 5 minutes) in a multimode cavity using activated carbon produce single phase β-SiCnanofibres as small as 5 nm in diameter while large crystallites of α- and β-SiC can obtained in ≪1 minute using high power, single mode cavity microwave techniques.

The SiC whiskers of good quality are expected to act as the reinforcing element in the ceramic coatings for C/C composites. Using CH₃SiCl₃(MTS) and H₂ as the precursors, SiC whiskers were prepared on the surface of C/C composites by chemical vapor deposition (CVD) at normal atmosphere pressure. XRD, SEM and TEM analyses show that the whiskers are β-SiC structure and their diameters are several-hundred nanometers. With the descending MTS concentration in the depositing room, the purity of the as-prepared whiskers increases and the diameters of the whiskers decrease. The investigation of growth mechanism shows the CVD-SiC whiskers grown up by the vapor–solid (VS) growth process.

Abstract

Field emission property of aligned and random SiC nanowires arrays synthesized by a simple vapor–solid reaction was investigated, respectively. A better field emission property with a turn-on field of ∼10.5 MV/m for oriented nanowires array was obtained while the higher value of ∼29.5 MV/m for disordered nanowires array was received. After comparison, highly aligned and high-quality SiC nanowires with high aspect ratio contributed the better field-emitting property.

Graphical abstract

The bulk-quantity synthesis of coaxial nanowires consisting of a β-phase silicon carbide (β-SiC) core and a silicon oxide (SiO_x) shell has been achieved through a rapid and low-cost microwave heating method. In the preparation process, only silicon, silica, and graphite powders were used, without any metal catalysts or inert protective gas. The microstructures and optical properties of β-SiC/SiO_x nanowires have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), transmission electron microscopy (TEM), and photoluminescence (PL) measurements at room temperature. The nanowires have lengths of several dozens of micrometers and diameters of 20–30 nm, with SiO_x shells exhibiting approximately 30 nm in thickness. They have a growth direction along the<111> planes, with the vapor solid (VS) growth mechanism. The PL spectra, employing a Xe laser (325 nm) as an excitation source, show two emission bands centered at about 444 and 470 nm. The blue-shift phenomenon can be explained by the interface defects and oxygen vacancy defects in the coaxial nanowires.

Silicon carbide (SiC)nanowires were synthesized by a reaction of multiwallcarbon nanotubes (MWCNTs) and silicon vapor from molten salt medium at 1250 °C. The phase, morphology, and microstructure of thenanowires were systemically characterized byX-ray diffraction,field emission scanning electron microscopy, andhigh resolution transmission electron microscopy. The results revealed that thenanowires were of single-crystalline β-SiC phase with the growth direction along [111] and had diameters of 20–80 nm and lengths up to several tens of micrometers. The molten salt introduced facilitated the evaporation of Si (vapor) onto MWCNTs (solid) and the growth of SiCnanowires followed the vapor–solid process. The investigation of microwave absorbability indicated that a minimum reflection loss of −17.4 dB at 11.2 GHz could be achieved with 30 wt% SiCnanowires as the filler in thesilicone matrix. The attenuation of microwave could be attributed to the dielectric loss and a possible absorption mechanism was also discussed.