Formation Of Silicon Carbide Research Articles

A self-assembly SHS approach to form silicon carbide nanofibres

β-SiC nanofibres were efficiently produced using the thermal-explosion mode of self-propagatinghigh-temperature synthesis from elemental Si and poly(tetrafluoroethylene) powdermixtures combusted under different operational parameters. The averaged combustiontemperatures were evaluated using emission spectroscopy to be above 2000 K. The solidproducts were characterized by scanning and transmission electron microscopy, chemicalanalysis, and x-ray diffraction. Under optimum conditions the conversion of startingelemental Si into products exceeded 90%. To obtain pure (about 90%) SiC nanofibres thesolid products were processed by wet chemistry.

HREELS study of the adsorption and evolution of diethylamine (DEA) on Si(1 0 0) surfaces

The adsorption of diethylamine (DEA) on Si(1 0 0) at 100 K was investigated using high-resolution electron energy loss spectroscopy (HREELS) and electron stimulated desorption (ESD). The thermal evolution of DEA on Si(1 0 0) was studied using temperature programmed desorption (TPD). Our results demonstrate DEA bonds datively to the Si(1 0 0) surface with no dissociation at 100 K. Thermal desorption of DEA takes place via a β-hydride elimination process leaving virtually no carbon behind. Electronic processing of DEA/Si(1 0 0) at 100 K results in desorption of ethyl groups; however, carbon and nitrogen are deposited on the surface as a result of electron irradiation. Thermal removal of carbon and nitrogen was not possible, indicating the formation of silicon carbide and silicon nitride.

Modeling Silicon Carbide Synthesis on a Submicrometric Scale

We build a model, on a mesoscopic, submicrometric scale, describing the formation of silicon carbide during heating at a constant rate and holding at a temperature smaller than the eutectic temperature of carbon and silicon. Simulating a two-dimensional cut of the initial mixture of powders, we show that the mean number of contacts of a carbon plate with silicon increases as the typical size of the silicon grains decreases. We focus on the simulation of the dynamics of the reaction when the melting of silicon and the dissolution of carbon begin until some solid silicon remains. Precipitation of silicon carbide is assumed to obey a heterogeneous nucleation mechanism. The model sheds some light on the dynamics of dissolution−precipitation in self-heated synthesis and on the morphology of the resulting material. In agreement with the experiments, the simulations reproduce larger reaction speeds for smaller silicon grains. Larger silicon carbide grains are obtained when the typical sizes of silicon and carbon...

X-Ray Photoelectron Spectroscopy and Reflection High EnergyElectron Diffraction of Epitaxial Growth SiC on Si(100) Using C60 and Si

The formation of silicon carbide upon deposition of C60 and Si onSi(100) surface at 850°C is studied via x-ray photoelectronspectroscopy and reflection high energy electron diffraction (RHEED).The C 1s, O 1s and Si 2p core-level spectra and theRHEED patterns indicate the formation of 3C–SiC.

Influence of SHI irradiation on the formation of buried SiC

Silicon carbide (SiC) precipitates buried in Si(1 0 0) substrates were synthesized by ion implantation of 50 keV and 150 keV C + ions at different fluences. Two sets of samples were subsequently annealed at 850 °C and 1000 °C for 30 min. Fourier transform infrared (FTIR) spectroscopy studies and X-ray diffraction (XRD) analysis confirmed formation of β-SiC precipitates in the samples. Ion irradiation with 100 MeV Ag 7+ ions at room temperature does not induce significant change in the precipitates. It could be interpreted from the FTIR observations that ion irradiation may induce nucleation in Si + C solution created by ion implantation of C in Si. Modifications induced by swift heavy ion irradiation are found to be dependent on implantation energy of C + ions.

Perchlorosilanes and perchlorocarbosilanes as precursors for SiC synthesis

Homologues with the general stoichiometry a(SiCl4): bSi: cC: d(SiC) are shown to be potential precursors for the low-temperature gas-phase synthesis of silicon carbide. Thermal decomposition of these precursors yields the chemically stable gaseous species SiCl4 and condensed Si, C, SiC, SiC + Si, or SiC + C. We use thermodynamic modeling of the thermal decomposition of octachlorotrisilane, Si3Cl8, to analyze the key features of the thermolysis of perchlorosilanes with the general stoichiometry a(SiCl4): bSi. The equilibrium compositions of reaction products in the Si3Cl8-CO system are determined. This reaction system enables low-temperature (400–1200 K) formation of silicon carbide.

Synthesis and characterization of silicon carbide by reaction milling in a dual-drive planetary mill

The formation of silicon carbide from elemental silicon and graphite powder by reaction milling in a specially designed dual-drive planetary mill is reported. The phase evolutions, particle size distribution, and morphology of particles during milling are studied during a 40-h grinding period. X-ray diffraction study indicates complete conversion of silicon and graphite to silicon carbide. The crystallite size varies from 150 nm from the start to 10 nm after 40 h of milling. The lattice strain increases with milling up to about 20 h when SiC forms and subsequently with the formation of SiC it is reduced. Al–SiC composites are prepared by mixing Al with 40 h milled final SiC powder and sintered in an inert atmosphere. The composites show excellent compatibility between Al and SiC particles, no voids or cracks are present.

Formation of hexagonal silicon carbide by high energy ion beam irradiation on Si (1 0 0) substrate

We report the investigation of high energy ion beam irradiation on Si (1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The unexposed and ion exposed substrates were characterized by x-ray diffraction, scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive x-ray analysis and atomic force microscopy (AFM) and the results are reported. The interaction of the pulsed PF ion beams, with characteristic energy in the 60–450 keV range, with the Si surface, results in the formation of a surface layer of hexagonal silicon carbide. The SEM and AFM analyses indicate clear step bunching on the silicon carbide surface with an average step height of 50 nm and a terrace width of 800 nm.

Comprehensive investigations on the influence of gun current of plasma spraying on the properties of silicon carbide films

Polycrystalline silicon carbide films have been prepared by the gas tunnel type plasma spraying method (GTPS). The effect of gun current on microstructure and mechanical properties was investigated. Scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, nanoindentation and abrasive wear were used to characterize the structure, thickness, composition and the mechanical properties of SiC films. Microstructural studies revealed that the formation of cubic silicon carbide (C-SiC) at higher gun currents from 120 to 140 A. The SiC films have good-adhesion, dense, smooth and compact morphology. Hardness of SiC films strongly improved from 23 to 31.5 GPa as the gun current increased from 0 to 140 A. SiC films formed at higher gun current exhibits better wear resistance than that deposited at low gun current, mainly due to SiC films become more hard and more dense. The crystalline cubic silicon carbide films with good morphology and mechanical properties have been obtained from the GTPS method, which makes it a suitable material for high-temperature thermoelectric and mechanical applications.

Synthesis and characterization of embedded SiC phase

Synthesis of embedded silicon carbide (SiC) has been carried out in n-type silicon (Si) samples having (100) and (111) orientations using high dose implantation of 150keV carbon (C+) ions at room temperature. The dose is varied from 4×1017ions-cm−2 to 8×1017ions-cm−2 in different samples of both orientations. Post-implantation annealing at 1000°C is performed in order to anneal out the implantation induced defects and to get a buried silicon carbide layer. Detailed Fourier transform infrared (FTIR) spectroscopy analysis and X-ray diffraction (XRD) studies confirm the formation of cubic SiC precipitates (β-SiC) in the layer. The SiC precipitates have been found to exhibit a better crystalline order in Si (100) samples than in Si (111) samples. X-ray diffraction results also indicate the amorphization of ion beam bombarded region of the Si samples. After annealing the amorphized region is recrystallized into a polycrystalline phase of Si.

Novel Electrochemical Patterning Method of Silicon Carbide

Silicon Carbide (SiC) is the most promising material for the fabrication of a new category of sensors and devices, to be used in very hostile environments (height temperature, corrosive ambient, presence of radiation ...). The fabrication of Silicon Carbide sensors requires new processes able to realize microstructures on bulk material or on the silicon carbide surface. A very promising method to create microstructures in SiC is the electrochemical etch in aqueous solution of hydrofluoric acid. In this paper the bulk micromachining of SiC substrate and the structural and electrical characterization of porous silicon carbide formation are reported. These results were used to create a novel method for the bidimensional pattering of SiC substrate. In particular a novel Si-based hard mask to transfer the design onto the SiC substrate was used. The hard mask is formed by a sandwich structures made by subsequent deposition of VAPOX, POLY Si, SiO2.

Synthesis and characterization of submicron silicon carbide powders with silicon and phenolic resin

A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid–solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders.

Surface structure of SiC formed by C60 molecules on a Si(001)-2×1 surface at 800°C

Formation of silicon carbide upon deposition of C60 onto Si(001) at an elevated temperature of 800°C was studied via synchrotron-radiation photoemission and low electron energy diffraction. The molecules are completely decomposed upon hitting on the hot surface, giving rise to a well-order 2×1 pattern. The C 1s and Si 2p core-level spectra, and valence-band spectra indicate characteristics of a Si-terminated β-SiC(001) 2×1 film. Two surface components corresponding to the terminated and ad-dimer Si atoms are well resolved in the Si 2p cores. By the spectral area ratio of both components, the adlayer atoms cover half of the surface, which agrees with the missing-row structure model [W. Lu et al., Phys. Rev. Lett. 81, 2292 (1998)].

Preparation and properties of C/C–SiC nano-composites

Recently, there seems to be a great emphasis on the development of advanced thermostructural composites such as C/C–SiC. In these composites the core is made of C/C composite and the surface is protected by a layer of SiC. Due to the different thermal expansions of the two materials, cracking occurs in the top SiC layer. The solution to this problem would be the preparation of gradient composite with SiC present in the matrix phase. In this work various options for the production of the C/C composite with SiC nano-particles dispersed in the matrix were investigated. Such material will enable the production of C/C–SiC composites with gradient structure form the carbon in the core to silicon carbide on the surface and consequently with improved mechanical and thermal properties. Two approaches were used to enable the in situ formation of the SiC nano-particles in the carbon matrix: one was the synthesis of SiC precursors by sol–gel and the other was the use of ceramic forming polymers, which after the pyrolysis form silicon carbide. The preparation of the composites and its influence on the microstructure and the mechanical properties of composites were investigated.

Structural changes of SiC under electron-beam irradiation: Temperature dependence

Electron-beam-irradiation effects on silicon carbide (SiC) was investigated as a function of the irradiated temperatures. Single crystalline 6H-SiC was irradiated with 300kV electrons at temperatures ranging from −170 to 250°C. It was found that amorphous SiC is induced at −170°C and room temperature, while crystalline Si is formed at 250°C with a high electron fluence. It is considered that preferential knock-on displacement of C atoms and damage recovery play an important role in the formation of the amorphous SiC and crystalline Si.

Characterization of the crystalline quality of β-SiC formed by ion beam synthesis

The ion beam synthesis (IBS) technique is applied to form crystalline silicon carbide (SiC) for future optoelectronics applications. Carbon ions at 80 and 40keV were implanted into (100) high-purity p-type silicon wafers at room temperature and 400°C, respectively, to doses in excess of 1017ions/cm2. Subsequent thermal annealing of the implanted samples was performed in a vacuum furnace at temperatures of 800, 900 and 1000°C, respectively. Elastic recoil detection analysis was used to investigate depth distributions of the implanted ions and infrared transmittance (IR) measurement was used to characterize formation of SiC in the implanted Si substrate. Complementary to IR, Raman scattering measurements were also carried out. Levels of the residual damage distribution of the samples annealed at different temperatures were compared with that of the as-implanted one by Rutherford backscattering spectrometry (RBS) in the channeling mode. The results show that C-ion implantation at the elevated temperature, followed by high-temperature annealing, enhances the synthesis of crystalline SiC.

Synthesis of silicon carbide nanofibers from pitch blended with sol–gel derived silica

Silicon carbide nanofibers were synthesized from coal tar pitch blended with sol–gel derived silica. Substituted silicon alkoxide was hydrolyzed to obtain the silica sol, which was blended with the pitch dissolved in a suitable solvent. The pitch silica mixture was heat-treated to 1400 °C followed by oxidation at 700 °C to get silicon carbide nanofibers. IR, Raman and X-ray studies reveal the formation of silicon carbide while SEM and TEM studies show silicon carbide nanofibers having the diameter in the range 45–60 nm.

The mechanism of the solid-state reaction between carbon nanotubes and nanocrystallinesilicon under high pressure and at high temperature

An x-ray powder diffraction method was used to study the reaction between carbonnanotubes (CNT) and silicon (Si) nanosize powder at 2 GPa and temperatures varying from1273 to 1370 K with different sintering times. Samples were obtained using thepiston–cylinder system. On the basis of the Avrami–Erofeev model, we foundthe activation energy of silicon carbide (SiC) formation from CNT and Si to be96 ± 30 kJ mol−1. Analysis of x-ray diffraction patterns provided information on the domain sizes andmicrostrain in SiC. Extending the sintering time increased the grain sizes anddecreased the microstrain in SiC, and increasing the temperature resulted in largercrystallites.

A study of silicon carbide synthesis from waste serpentine

There are 60 000 tons of serpentine wastes produced in year 2004 in Taiwan. This is due to the well-developed joints in the serpentine ore body as well as the stringent requirements of the particle size and chemical composition of serpentine by iron making company. The waste also creates considerable environmental problems. The purpose of this study is reutilization of waste serpentine to produce a high value silica powder after acid leaching. These siliceous microstructure products obtained from serpentine would be responsible for high reactivity and characteristic molecular sieving effect. In this study, the amorphous silica powder was then synthesized to silicon carbide with the C/SiO 2 molar ratio of 3. The experiment results show that silicon carbide can be synthesized in 1550 °C. The formed silicon carbide was whisker β type SiC which can be used as raw materials for industry.

Ceramic Composites Derived from Nb/Al<sub>2</sub>O<sub>3</sub>-Filled Polysilsesquioxane

Ceramic matrix composites (CMC) were prepared by the active-filler-controlled polymer pyrolysis process (AFCOP) using a polysilsesquioxane resin filled with metallic niobium and alumina powders. Samples containing 60 wt% of polysilsesquioxane and 40 wt% of metallic niobium and alumina powders mixtures were homogenized, uniaxially pressed and pyrolysed in an alumina tube furnace up to 1400 °C, under argon flow. The ceramic products were characterized by X-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis (DTA), Fourier transform infrared (FTIR) and energy-dispersive (EDS) spectroscopies. XRD analysis of the products showed the presence of crystalline phases such as NbC, Nb3Si, Nb5Si3, SiC, crystoballite and mullite. Thermogravimetry data of the composites presented low weight losses at 1000 °C. DTA curves showed an endothermic peak at 1350 °C, which was associated to the beginning of carbothermic reduction and/or the formation of silicon oxide and carbide. In addition, an exothermic peak at 1400 °C was associated to the formation of the mullite phase.