Formation Of Silicon Carbide Research Articles

Silicon carbide formation with pulsed laser and electron beams

Poly-crystalline silicon carbide layers were obtained through nanosecond pulse heating of thin carbon films deposited on silicon wafers. The samples were submitted to electron beam pulses (25 kev, 50 ns) at various current densities in vacuum (~10 −4 mbar) and to XeCl excimer laser pulses (308 nm, 15 ns) in air. Rutherford backscattering spectrometry (RBS) evidenced that in the electron beam annealed samples mixing of elements at the C Si interface starts at current densities of about 1200 A/cm 2. The mixed layer thickness increases almost linearly with current density. From the RBS spectra a composition of the intermixed layers close to the SiC compound was deduced. Transmission electron microscopy (TEM) and electron diffraction studies clearly evidenced the formation of SiC poly-crystals. Using the XeCl laser, intermixing of the deposited C film with the Si substrate was observed after a single 0.3 J/cm 2 pulse. Further analysis evidenced the formation of SiC crystals, embedded in a diamond film.

Formation of silicon carbide in the reaction of reduction of silica by carbon

In the initial stages of heat treatment of H2SiO3 and sucrose a mixture of highly dispersed defective SiO2 particles and carbon material is formed. Then as the result of contact interparticle interaction of a radical character disintegration (activation) of the carbon particles and envelopment of them by a layer of SiO2 accompanied by deformation of the Si-O-Si bonds occur. Filling of the pores of the carbon material with silicon oxide creates in subsequent higher temperature treatment favorable conditions for formation of SiC. The particles formed as the result of the relatively low-temperature solid-state reaction are non-uniform in composition. Their core consists of uninteracted carbon and after it follow a layer of silicon carbide and an outer layer of SiO2. A switch to the area of high synthesis temperature makes it possible to approach a stoichiometric composition of the silicon carbide.

Silicon carbide formation with e-beam and laser pulses

Abstract Polycrystalline SiC layers were obtained through pulsed annealing of thin (100 nm) carbon films deposited on single-crystalline silicon wafers. The samples were submitted to electron beam irradiation (25 keV, 50 ns) at various current densities in vacuum (∼10 −4 mbar) and to XeCl excimer laser pulses (308 nm, 15 ns) in air. Rutherford backscattering analysis showed that in the e-beam annealed samples mixing of the elements at the interface starts at current densities of about 1200 A/cm 2 . The mixed layer thickness increases almost linearly with current density. At current densities higher than 2400 A/cm 2 ablation of the C film was always observed. Using the XeCl excimer laser, a good intermixing of the deposited C film with the Si substrate was observed after a single 0.3 J/cm 2 pulse. From the RBS spectra a composition of the intermixed layers close to the SiC compound was deduced. Transmission electron microscopy and electron diffraction studies clearly evidenced the formation of SiC polycrystals.

The control of morphology in silicon nitride powder prepared from rice husk

Abstract α-Silicon nitride powder of high purity has been prepared by nitriding pyrolysed rice husk at temperatures between 1260 and 1450°C under 95% nitrogen-5% hydrogen. Hydrogen addition is beneficial in accelerating the rate of nitride formation. The addition of iron (III) oxide and nickel (II) oxide to the rice husk promotes the competitive formation of silicon carbide at temperature as low as 1300°C. Other transition metal oxides are without catalytic effect on the nitridation reaction, though vanadium (V) oxide favours formation of β-phase silicon nitride. The silicon nitride particle morphology is determined in part by the particle dimension of the milled rice husk. Silicon nitride crystals of hexagonal symmetry are obtained from starting powder of dimension ≤ 53 μm, whereas greater particle dimensions, and lower packing densities, yield silicon nitride of a whiskery morphology. Addition of pre-formed silicon nitride powder results in the formation of fine, equiaxed, silicon nitride particles.

Alkali metal fluoride matrix modifiers for the determination of trace levels of silicon by graphite furnace atomic absorption spectrometry

A method is described for the determination of silicon by graphite-furnace atomic absorption spectrometry with alkali metal fluorides as matrix modifiers. Alkali metal fluorides react with silicon to produce metal hexafluorosilicates, which are stable at temperatures as high as 1120– 1300°C, depending on the particular metal used. At higher temperatures, alkali metal hexafluorosilicates decompose into the metal fluoride and silicon tetrafluoride. The subsequent gas-phase atomization of silicon tetrafluoride occurs rapidly, and produces clean, sharp absorption peaks. When used in conjunction with a zirconium-treated graphite tube, this method has a sensitivity of 50 pg Si at a confidence interval of 95%. There is no evidence of silicon carbide formation in the graphite tube, and very little evidence of any deterioration of the zirconium-treated surface, as demonstrated by the fact that more than 200 samples can be processed on a single graphite tube without a decrease in sensitivity or change in the baseline.

ChemInform Abstract: Preparation of Silicon Carbide and Aluminum Silicon Carbide from a Montmorillonite‐Polyacrylonitrile Intercalation Compound by Carbothermal Reduction.

AbstractCarbothermal reduction of a montmorillonite‐polyacrylonitrile intercalation compounds yields α‐SiC and β‐SiC besides Al4Si2C5.

Preparation of Silicon Carbide and Aluminum Silicon Carbide from a Montmorillonite–Polyacrylonitrile Intercalation Compound by Carbothermal Reduction

Both silicon carbide and aluminum silicon carbide have simultaneously been obtained directly from naturally occurring aluminosilicate by carbothermal reduction for the first time. A precursor of a montmorillonite–polyacrylonitrile (PAN) intercalation compound was heated at 1700°C in Ar. For comparison, montmorillonite–carbon mixtures were similarly heated. α‐SiC, β‐SiC, and Al4Si2C5 formed from the montmorillonite–PAN intercalation compound. Mainly α‐Al4SiC4 was obtained with ternary carbides from the montmorillonite–carbon mixtures in addition to a large amount of β‐SiC. Hence, aluminum silicon carbide formation was affected by the mixing condition of the starting materials.

Evaluation of Carbon Behavior in HIP'ed Silicon Nitride

Effects of carbon impurity on HIP'ed silicon nitride under 60 and 200MPa at 1823, 1873 and 1973K were studied. The density, hardness, fracture toughness, α-β phase ratio, heat capacity and thermal diffusivity were evaluated. The results were compared with those of silicon nitride prepared by the normal and hot press sintering. Carbon behavior of grain boundaries was investigated by X-ray diffraction and Auger electron spectroscopy (AES).(1) Silicon carbide was not formed during HIP'ing of silicon nitride powder with carbon film. Thermodynamic analysis showed that carbon is stable as graphite under the HIP'ing conditions studied. Silicon carbide can be produced from silicon nitride during the normal and hot press sintering. The formation of silicon carbide is explained by the free energy change of the related reaction under high pressure (high pressure Ellingham diagrams).(2) Silicon nitride was HIP'ed to full density. But carbon retards α to β phase transformation of silicon nitride in HIP sintering in contrast to normal or hot press sintering.(3) The mechanical properties are not influenced by the carbon content, unlike the cases for normal or hot press sintering. This can be also explained the pressure of gas phase during sintering.(4) Carbon decreases the thermal diffusivity and thermal conductivity. This may be due to the fact that carbon reduces the α to β phase transformation of silicon nitride in HIP'ing. Heat capacity is not influenced by the carbon content for HIP'ed silicon nitride.(5) The thermal conductivity data showed that carbon dissolves into silicon nitride up to 1000ppm between 1823 and 1973K.

Evaluation of amorphous and crystalline SiC by extended energy loss fine structure (EXELFS) analysis

Crystalline as well as amorphous forms of silicon carbide are materials which have important uses in many areas of materials science including structural ceramics, coatings, and semiconductors. The characterization of SiC by the use of the EXELFS technique yields radial distribution functions (RDF) which are sensitive to the structure and composition within near neighbor distances of either C or Si atoms. In this way a quantitative analysis of possible variations in “structure” can be made. EXELFS analyses of crystalline SiC are especially important in order to evaluate the method when comparison with results from the amorphous state are to be made. The EXELFS technique has previously been applied to study both crystalline as well as amorphous materials.Crystalline as well as amorphous SiC was evaluated. One specimen was a commercially available SiC single crystal. Two other specimens utilized a similar SiC starting material which had been made amorphous either by ion implantation with chromium or by irradiation from 300 kV electrons.

Determination of antimony dopant and some ultra-trace elements in semiconductor silicon by atomic absorption spectrometry with introduction of solid samples into the furnace

Antimony as a dopant at a level of ca. 35 atom/10 6 atoms (ppm, atomic) and ultra-trace concentrations of lead and manganese (<0.02 ppm, atomic) are determined in semiconductor silicon by atomic absorption spectrometry after introduction of milligram samples of silicon to a pyrolytically-coated graphite furnace. Calibration was done with standard aqueous solutions. Iron, silver, zinc and cadmium were sought but were at concentrations below the limits of detection. The graphite microboats used for sample introduction were useful for only 3–10 samples because of silicon carbide formation.

Formation of silicon carbide in silicon substrates during CF 4/H 2 dry etching

Silicon specimens which had been reactive ion etched in CF 4/ X%H 2 (0≤ X ≤40) and subsequently air exposed have been characterised by X-ray photoelectron emission spectroscopy. Angular rotation was used to study films deposited by the plasma process onto the Si surface. In agreement with previous studies it is found that plasma exposure of Si specimens leads to the deposition of a fluorocarbon film. An intriguing new finding was the discovery of subsurface silicon carbide. The existence of this carbide layer was found to be independent of gas composition from 0–40% H 2 for a one-minute plasma exposure. Helium ion channeling studies of the same specimens show Si near-surface disorder. A silicon-carbide formation mechanism is suggested according to which carbon is deposited below the Si surface by the bombardment of carbon containing ions, thus enabling silicon-carbon bonding.

Low-Temperature Formation of β-Type Silicon Carbide by Ion-Beam Mixing

This paper reports on the ion mixing of a carbon-silicon system induced by the Ar-ion bombardment of carbon layers deposited by an arc-discharge on single-crystalline silicon substrates. A study using infrared absorption spectroscopy has shown that a disordered carbon-silicon mixture can be obtained immediately after bombardment and that subsequent annealing causes the formation of a crystalline β-type silicon carbide phase at about 800°C. The formation temperature is lower by about 100°C than that for carbon-silicon mixed layers formed by the direct implantation of carbon ions into silicon substrates. Argon-ion bombardment, itself, is found to play an important role in a reduction of the formation temperature.

Study on formation, morphology, and properties of Si3N4 and SiC fibers

AbstractSilicon nitride and silicon carbide fibers were prepared by firing silicon resin mixed with iron under NH3 flow at 1 500°C. The effect of preparation variables, iron content, flow rate of NH3 gas, and time of heating, on the yield and Si3N4/SiC ratio was studied. The yield of reaction increases considerably with increasing the iron content up to 1.7 wt.‐% iron and decreases slightly beyond this value. The Si3N4/SiC ratio in the yield is affected in the same direction. Heating for a longer time at 1 500°C favours the formation of silicon carbide instead of silicon nitride. The conversion reaction remains constant for the gas flow rates greater than 0.5 1/min.The product has grown dominately in the form of smooth and uniform fibers of a mean diameter of less than 0.3 μm. The electrical resistivity and hardness of silicon nitride and carbide composite material were measured and discussed on the basis of its composition.

Technology of corundum-graphite refractories with a combined binder

The technology of corundum-graphite refractories with a combined binder has been developed. The use of coal-tar pitch and ethyl silicate makes it possible to increase the reaction capacity of the C-SiO2-Si composition for formation of silicon carbide.

Vaporization Thermodynamics and Enthalpy of Formation of Aluminum Silicon Carbide

The vaporization thermodynamics of aluminum silicon carbide was investigated using Knudsen effusion mass spectrometry. Vaporization occurred incongruently to give Al(g), SiC(s), and graphite as reaction products. The vapor pressure of aluminum above (Al4SiC4+ SiC + C) was measured using graphite effusion cells with orifice areas between 1.1 × 10−2and 3.9X10−4 cm2. The vapor pressure of aluminum obtained between 1427 and 1784 K using an effusion cell with the smallest orifice area, 3.9X10−4 cm2, is expressed aslog p (Pa) =−(18567 ± 86) (K/T) + (12.143 ± 0.054)The third‐law calculation of the enthalpy change for the reaction Al4SiC4(s) = 4Al(g) + SiC(hex) + 3C(s) using the present aluminum pressures gives ΔH°(298.15 K) = (1455 ± 79) kJ·mol−1. The corresponding second‐law result is ΔH°(298.15 K) = (1456 ± 47) kJ·mol−1. The standard enthalpy of formation of Al4SiC4(s) from the elements calculated from the present vaporization enthalpy (third‐law calculation) and the enthalpies of formation of Al(g) and hexagonal SiC is ΔH°f= ‐(221 ± 85) kJ·mol−1. The standard enthalpy of formation of Al4SiC4(s) from its constituent carbides Al4C3(s) and SiC(c, hex) is calculated to be ΔH°(298.15 K) = (38 ± 92) KJ·mol−1.

Conditions of formation of silicon carbide in the surface layer of a glass-reinforced plastic subjected to unidirectional heating

Conditions of formation of silicon carbide in the surface layer of a glass-reinforced plastic subjected to unidirectional heating

Investigations of reactions involved in flameless atomic absorption procedures: Part 7. A Theoretical and Experimental Study of Factors Influencing the Determination of Silicon

The ideal conditions for the determination of silicon by graphite-furnace atomic absorption spectrometry have been investigated by using high-temperature equilibrium calculations. All reasonable reaction products resulting from the reaction between Si, C, O, H, S, N, Ar and Na have been considered. The results show that SiO 2(s) is the stable silicon compound for temperatures below 1500 K. For higher temperatures Si 3N 4(s), SiC(s), SiO(g), SiO 2(s), Si(g), SiN(g), SiCl 2(g) and SiS(g) are the main silicon-containing reaction products. SiO(g) is always formed in the interval 1600–2200 K independently of the partial pressure of oxygen. The basic requirement for the quantitative formation of silicon atoms at 2600 K is that the partial pressure of atomic oxygen is less than 10 -12atm. The main condition for the formation of silicon carbide is an extremely low partial pressure of oxygen. Losses of silicon by the formation of SiO(g) during heating of the graphite tube were experimentally shown to be reduced by using isothermal atomization. An equilibrium model for the formation of silicon atoms is discussed. This model takes into consideration the decrease in the partial pressure of oxygen during the atomization step. The results obtained show that silicon atoms are formed from SiO(g) at the temperatures pertaining to the beginning of the atomization cycle and from SiC(s) at somewhat higher temperatures.

Kinetic and mechanistic study on the formation of silicon carbide from silica flour and coke breeze

Kinetic and mechanistic study on the formation of silicon carbide from silica flour and coke breeze

X-Ray Interferometry of Volume Changes in C+Implanted Silicon

High energy C+ implantation is used to construct a two crystal monolithic X-ray interferometer. The X-ray interferometer technique is applied to in-situ studies of radiation damage annealing in the interferometer. Volume changes in the crystal due to the transformation of single crystal silicon to amorphous silicon and due to the formation of silicon carbide are measured.

A study of silicon distribution in silicon-containing pyrocarbons

The silicon distribution in silicon-containing pyrocarbon obtained by simultaneous pyrolysis of methane and silicon tetrachloride in the temperature range 1160–1630° C was followed by electron-probe microanalyser. Deposits obtained at about 1200° C contain about 4%w/w silicon in the form of silicon carbide. Very fine particles of SiC are homogeneously dispersed over the whole layer. Between 1300 and 1400° C larger lenticular inclusions of silicon carbide are formed which serve as nuclei for further crystallization of both silicon carbide and pyrocarbon. At the highest temperatures used (1600° C) only the solid solution containing 0.2%w/w silicon in pyrocarbon is deposited. It is supposed that the distribution of silicon in pyrocarbon is a result of temperature dependence of the nucleation and growth processes of silicon carbide.