Characterization, Thermodynamics and Mechanism of Formation of SiC-SiOx Core–Shell Nanowires (original) (raw)
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Evolution of SiOx Shell Layers on SiC-SiOx Core-Shell Nanowires
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Composite core-shell SiC-SiOxnanowires can be produced by heating quartz and SiC powders, with addition of Ar(g) or He(g). The two powders are mixed to create pellets, which will react to SiO(g) and CO(g) at elevated temperatures. The two gases will react on a colder surface, producing a web of SiC-SiOxnanowires. The product serves as a precursor for SiC nanowires production. During the process, silicon and oxygen accumulate at high energy points, forming SiOxnodules. Nodules can either generate in proximity of stacking faults, or where two or more nanowires are close to each other. The present work investigates the role of crystal defects in the wettability between silica and silicon carbide. Samples were collected and analyzed under Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The results show that β-SiC grows mainly in the [111] direction. Crystal defects are located in the SiC core-phase. SiOxinitially develops a uniform layer as thick as the co...
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As the field of biotechnology expands and the semiconductor industry approaches the limit of size reduction with conventional materials, these and other fields will increasingly rely on nanomaterials with novel properties. Silicon carbide (SiC) possesses many properties that make it appealing to research and industry: a large band gap, high hardness, high strength, low thermal expansion, chemical inertness, etc. It is known that silicon carbide nanowires can be synthesized through a reaction between silicon vapor and multiwalled carbon nanotubes. This process was refined to produce smaller, straighter nanowires. This was done by analyzing the dependence of the reaction rate on the partial vapor pressure of silicon. The reaction rate was studied by comparison of SiC and multiwalled carbon nanotubes peak intensities in X-ray diffractograms, which produced an estimate of the respective reactions' SiC yields. The particle morphologies were then analyzed with transmission electron mi...
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Beta-SiC/SiO2 core-shell nanowires were obtained in a mullite boat after the reaction between silicon nanopowder and CH4 gas at 1623 K (1350°C), without adding metal catalysts from outside. The as-grown nanowires were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, scanning TEM, and infrared-ray spectroscopy. The results showed that the typical nanowires consisted of single crystalline β-phase SiC core of 50-70 nm in diameter and a uniform wrapping layer of low crystallinity SiO2 of ~15 nm in thickness, and their lengths were up to several tens of micrometers. The nanowires axes lay along the [111] direction of β-SiC. Oxygen from the experimental setup or the raw powder should be a key factor to synthesize the core/shell nanowires.
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Silicon carbide nanowires have been synthesized by carbothermal reduction, from carbon monoxide and single crystal silicon. Transmission electron microscopy and cathodoluminescence studies confirm the growth of a cubic b-SiC core, coated with an amorphous oxide shell. Planar defects, as stacking faults and rotational twins, are present on (1 1 1) planes. The formation of short thick rods or long thin wires, depending on the growth temperature and time, is discussed.
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Journal of the Ceramic Society of Japan, 2009
High-yield SiC/SiO2 core-shell nanowires were synthesized without adding metal catalysts from outside through a simple thermal evaporation of silicon powders during decomposition of methane gas. The influence of three parameters, size of Si raw powder (50 nm and 5 μ m), reaction temperature (1573, 1623 and 1673 K), and soaking time (1, 3 and 6 h), was investigated. The typical synthesized nanowires from different conditions possess the diameter of no thicker than 100 nm with several tens micrometers in length. It was addressed that the condition using the smaller size Si powder, which contained the highest amount of oxygen, at higher temperature lead to more complete reaction to obtain a large quantity of nanowires. The synthesized nanowires at higher reaction temperature and longer soaking time possessed larger core than those nanowires prepared at lower reaction temperature and shorter soaking time. Oxidation of larger size Si powder improved yield of nanowires. Based on these results, it was suggested that the typical nanowires should be grown via the oxide-assisted growth mechanism.