Β-silicon Carbide Research Articles

The adsorption of H-atoms on polycrystalline β-silicon carbide

The adsorption of atomic hydrogen on a polycrystalline β-silicon carbide (SiC) surface has been studied using temperature-programmed desorption (TPD). Atomic hydrogen adsorbs on this surface, whereas molecular hydrogen does not. Upon heating, the hydrogen recombines and desorbs as H 2, producing two peaks in the TPD spectrum at 975 and 1130 K. The unusually broad width of the desorption peaks is attributed to a distribution of surface binding energies for hydrogen atoms. The desorption spectra are fit using a model that assumes two adsorption sites and a Gaussian distribution of binding energies. The average activation energies derived for the two peaks are 63 and 72 kcal/mol.

Ultraviolet reflectance of AlN, diamond-like carbon, and SiC thin films

The vacuum ultraviolet (VUV) (120–200 nm) and extreme ultraviolet (EUV) (80–120 nm) reflectance characteristics of as-deposited films of amorphous aluminum nitride (AlN) and diamond-like carbon (DLC), and of single-crystal β-silicon carbide (SiC) have been measured. AlN and DLC films have been grown by plasma-enhanced chemical vapor deposition (PECVD) and the SiC film by chemical vapor deposition (CVD). The VUV reflectivities of AlN and SiC exceed 50% while the reflectance of DLC film is low (∼10%). Furthermore, DLC and SiC films display EUV reflectance characteristics that are very desirable. The reflectivity of as-deposited SiC is 40% and that of DLC is about 20%.

Development of ceramics from organosilicon polymers by heat treatment

Special heat resistant materials are obtained by heat treatment of organosilicon polymers at atmospheric pressure in a stream of N 2. Organosilicon polymers are made of polycarbosilanes which are referred to as types I and II. Type I is stable up to 450°C and begins to decompose when it reaches this temperature. The first decomposition is completed around 650°C with almost 90% residue up to 1000°C. Type II is stable up to almost 1000°C in an inert atmosphere; however, it begins to decompose in dry air at 550°C with a 90% residue. These polymers may gradually be converted to β-silicon carbide (β-SiC) by further pyrolysis above 1000°C. X-Ray diffraction powder, diffuse reflectance IR Fourier transform (DRIFT), thermogravimetry (TG) analysis, and differential thermal analysis (DTA) have been used for analyses of these polymers. The X-ray diffraction powder of types I and II below 1000°C has shown an amorphous pattern with no existence of free carbon in the polymers.

Mechanical property evaluation at elevated temperature of sintered β-silicon carbide

The mechanical properties at room and elevated temperature of sintered β-silicon carbide were evaluated. Testing included room temperature flexural strength, flexural stress rupture at 1200°C, and stepped temperature stress rupture (STSR) experiments. Fractographic examination identified the strength limiting flaw populations. Properties measured on this material are typical of commercial grades of sintered silicon carbide.

Local structure of silicon films and silicon carbide by surface extended energy loss fine structure

Surface extended energy loss fine structure (SEELFS) has been shown to yield nearest neighbor coordination and bond length for carbon in different structural forms. A standard Auger electron spectrometer(double pass cylindrical mirror analyzer) is used to obtain energy loss spectra in the laboratory. Preliminary work on diamond, graphite and ‘‘Aquadag’’ using spectra in the second derivative mode is now extended to silicon and α- and β-silicon carbide. Silicon has been used as reference for phase and amplitude in the bond length and coordination determination of β-silicon carbide. β-SiC has been used as a standard for α-SiC. The coordination and radius determined agree with known values to within uncertainties estimated. The uncertainties in the determination of bond length and coordination due to the choice of reference phase and amplitude are discussed.

ChemInform Abstract: CHEMICAL VAPOR DEPOSITION OF SINGLE CRYSTALLINE β‐SILICON CARBIDE FILMS ON SILICON SUBSTRATE WITH SPUTTERED SILICON CARBIDE INTERMEDIATE LAYER

Chemischer InformationsdienstVolume 12, Issue 12 Physical Inorganic Chemistry ChemInform Abstract: CHEMICAL VAPOR DEPOSITION OF SINGLE CRYSTALLINE β-SILICON CARBIDE FILMS ON SILICON SUBSTRATE WITH SPUTTERED SILICON CARBIDE INTERMEDIATE LAYER S. NISHINO, S. NISHINOSearch for more papers by this authorY. HAZUKI, Y. HAZUKISearch for more papers by this authorH. MATSUNAMI, H. MATSUNAMISearch for more papers by this authorT. TANAKA, T. TANAKASearch for more papers by this author S. NISHINO, S. NISHINOSearch for more papers by this authorY. HAZUKI, Y. HAZUKISearch for more papers by this authorH. MATSUNAMI, H. MATSUNAMISearch for more papers by this authorT. TANAKA, T. TANAKASearch for more papers by this author First published: March 24, 1981 https://doi.org/10.1002/chin.198112008Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue12March 24, 1981 RelatedInformation

STRUCTURAL ANALYSIS IN CONTINUOUS SILICON CARBIDE FIBER OF HIGH TENSILE STRENGTH

Abstract The starting material of a continuous silicon carbide fiber with very high tensile strength is a polycarbosilane. It begins to decompose from 300°C in vacuum and is gradually converted into a β-silicon carbide fiber by the heat-treatment at the temperature above 800°C.

CONTINUOUS SILICON CARBIDE FIBER OF HIGH TENSILE STRENGTH

Abstract Continuous silicon carbide fiber of high-tensile strength (about 350 Kg/mm2) was synthesized by means of the heat-treatment of organosilicon polymer obtained from dodecamethylcyclohexasilane. X-ray analysis and high voltage electron microscopic observations revealed that the obtained continuous fiber is an ultrafine grain structure of β-silicon carbide.

A study of pyrotechnic reactions by temperature profile analysis and differential thermal analysis

Nano-sized β-silicon carbide (β-SiC) powder was successfully prepared using the combustion synthesis method in air in combination with a controlled pre-reaction mechanical activation treatment. For the low-exothermic reaction system Si/C, the effect of the mechanical activation time, one crucial processing variable, on the combustion behavior of SiC reactant in air was investigated, and the reaction kinetics parameters were measured and calculated to analyze the reaction mechanism of this combustion reaction. Meanwhile, the reaction mechanism was further approved by the thermodynamic calculation.

A concept for the growth of twinned crystals of fcc structure

Before a twinned crystal of fcc structure can grow by deposition of atoms or molecules at the reetrant edges formed between two crystal matrices, the crystal nucleus has to be twinned. Elastic anisotropy of the fcc structure is introduced as an available cause for twinning on the basis of the observation of the structures of hollow crystals of β-silicon carbide.

Thermal expansivity and conductivity of pure and silicon-alloyed pyrocarbons

Measurements were made of the thermal expansivity (22°–1000°C) and the thermal conductivity (22°–800°C) of isotropic pyrocarbons deposited in fluidized beds and containing up to 34 wt% silicon in the form of β-silicon carbide particles. The thermal expansivity of the pure carbons was proportional to their density, while that of the silicon-alloyed carbons decreased with increasing silicon content, falling from 6·3 × 10 −° C −1 for material containing 4 wt% silicon to 4·6 × 10 −6° C −1 for material with 34 wt% silicon. The thermal conductivity of both pure and silicon-alloyed pyrocarbons increased with increasing temperature up to about 500°C. The room-temperature thermal conductivity of the pure carbons increased with increasing apparent crystallite height ( L c ), and the conductivity of the silicon-alloyed carbons was significantly lower than that of pure pyrocarbon with the same L c . The results suggest that silicon entering substitutionally into the carbon lattice may reduce the conductivity.

Neutron irradiation-induced voids in β-silicon carbide

Pyrolytic β-silicon carbide was irradiated at temperatures between 625°C and 1500°C to neutron fluences up to 12 × 10 21 n/cm 2 ( E > 0.18 MeV). Density changes were measured and the samples were examined by transmission electron microscopy. Irradiation below 1000°C created small Frank dislocation loops on {111} planes. Irradiation at 1250°C and 1500°C produced tetrahedral voids which caused continuing expansion of the samples. Void sizes increased with increasing fluence and with increasing irradiation temperature, while void concentrations decreased with increasing temperature. One-hour post-irradiation anneals at 1700°C to 2100°C reduced the void concentration and total void volume while increasing the maximum void size.

Thermal conductivity of neutron-irradiated pyrolytic β-silicon carbide

Samples of pyrolytic β-silicon carbide deposited at 1400 °C (grain size ∼ 1 μ m ) and at 1750 °C (grain size ∼ 3 μ m ) were irradiated with fast neutrons to 2.7-7.7 × 10 21 n/cm 2 ( E > 0.18 MeV) at 550 °–1100 °C. Irradiation reduced the room-temperature thermal conductivity from ∼0.15 cal/cm · sec · ° C to ∼ 0.02 cal/cm · sec · ° C after irradiation at 550 °C and to ∼ 0.05 cal/cm · sec · ° C for an irradiation temperature of 1100 °C. The thermal conductivity of unirradiated samples decreased with increasing measurement temperature, while that of the irradiated samples was much less temperature dependent. No difference in behaviour was found between the samples with ∼ 1 μ m grain size and the samples with ∼ 3 μ m grain size.

Growth mechanism of polycrystalline β-SiC layers on silicon substrate

The surface of monocrystalline silicon was chemically converted with hydrocarbon to polycrystalline β-silicon carbide, and the growth mechanism was investigated by means of 14C tracer method. It is shown that the growth of the silicon carbide layer is due to diffusion of silicon through the SiC layer so that the Si–SiC conversion is taking place at the surface of the sample. Dependence of layer thickness on carbidizing time and on hydrocarbon concentration in the carrier gas hydrogen was measured.

Electron microscopy and diffraction of thermally decomposed β-silicon carbide whiskers

Decomposition of β-silicon carbide whiskers by heating in vacuum results in the formation of highly oriented graphite crystallites with basal planes tangent to the whisker surface but showing no structural relationship to the parent β-silicon carbide. Doubling of the 00.l reflections of graphite is explained by refraction of the electron beam from faces parallel to the basal planes in a direction normal to the whisker axis.

The high temperature reaction between uranium monocarbide and β-silicon carbide

β-Silicon carbide-coated uranium monocarbide granules were heated in the range 1500–1850° to investigate the compatibility of β-silicon carbide and uranium monocarbide. Above 1600° a reaction occurred which can be summarized as: 9UC + 4SiC → 5UC2+ U3C3Si2+ USi2 The reaction appears to involve the formation of a molten shell at the original β-silicon carbide–uranium monocarbide interface. It results in the diffusion of uranium into the β-silicon carbide according to the relation, D= 0·01342 exp (–68,000 ± 20,000/RT).

Effects of fast-neutron irradiation on pyrolytic silicon carbide

Samples of pyrolytic polycrystalline β-silicon carbide were irradiated to 2.0 to 4.2 × 10 21 nvt ( E > 0.18 MeV) at temperatures between 460 and 1040 °C. The samples showed an isotropic linear expansion that decreased with increasing irradiation temperature from 0.35 % at 460 °C to 0.05% at 1040 °C. The lattice parameter changes were equal to the macroscopic dimensional changes within experimental accuracy. Irradiation caused a slight increase in X-ray line broadening that was attributable to the generation of internal strains. There was no significant change in Young's modulus or the modulus of rupture.

Imperfections in Solution-Grown β-Silicon Carbide Crystals

Imperfections in high-purity β-silicon carbide crystal platelets, (111) habit, were studied using Lang x-ray topography, Weissenberg photographs, and etch pitting. Stacking faults on {111} planes with associated partial dislocations of the 〈112〉 type and {111} twinning have been observed. In well-formed platelets, twinning is usually confined to the habit plane. Stacking faults occur parallel with the platelet surface and on {111} planes inclined to the platelet surface, and they tend to cluster in overlapping, closely spaced groups. Etch pits on the surface are caused by emerging 〈112〉 partial dislocations that bound the inclined stacking faults. Partial dislocations in the habit plane have also been identified from diffraction contrast and extinction effects.

Growth and Properties of β-SiC Single Crystals

Chemical, electrical, and optical measurements were performed on n- and p-type β-silicon carbide crystals grown from pure or doped carbon-saturated silicon melts. Pure, transparent yellow crystals showed no detectable impurities and had carrier concentrations in the range of 1016 cm−3. Extensive twinning was observed. Uncorrected electron mobilities of 700–1000 cm2/V·sec were measured at room temperature. Intense injection electroluminescence, peaking at 2.28 eV and 2.0 eV, was observed in many diodes. Strong photoluminescence was observed in aluminum-doped crystals at 77°K and at room temperature when irradiated with uv light.

Cubic β-silicon carbide films on silicon substrates

Highly adherent films of cubic β-silicon carbide have been grown on single-crystal silicon substrates by heating in the presence of graphite in an argon atmosphere. The reaction process and film characteristics were investigated by electron diffraction. Initially, a single-crystal β-silicon carbide film is formed, having an epitaxial relationship to the silicon substrate. Growth proceeds by diffusion of a carbon-bearing species, from the gas phase, inward to the silicon-silicon carbide interface. Beyond a certain thickness, growth becomes polycrystalline. Both n- and p-type films resulted from spontaneous doping, but high resistivities were not observed.