β-SiC Particles Research Articles

Stability And Precipitation Kinetics In Si1-yCy/Si and Si1-x-yGexC/Si Heterostructures Prepared by Solid Phase Epitaxy

ABSTRACTThis study investigates the stability of Metastable Si1-yCy/Si heterostructures during rapid thermal annealing (RTA) over a temperature range of 1000 – 1150° C Heterostructures of Si1-yCy/Si and Si1-x-yGexCy/Si (x=0.077, y ≤ .0014) were formed by solid phase epitaxy from C implanted, preamorphized substrates using a 30 Minute 700° C anneal in N2. The occupancy of C in substitution lattice sites was monitored by Fourier Transform Infrared Absorption spectroscopy. The layer strain was monitored by rocking curve x-ray diffraction and the structural changes in the layers were determined using plan-view and X-sectional transmission electron Microscopy (TEM). For anneals of 1150° C or above, all the substitutional C was lost from the Si lattice after 30 seconds. TEM verified that the strain relaxation was the result of C precipitating into highly aligned βSiC particles rather than by the formation of extended defects. No nucleation barrier was observed for the loss of substitutional C Preliminary results will also be discussed for Si1-x-yGexCy/Si heterostructures where there is the additional factor of the competition between strain energy and the chemical driving forces.

Transmission electron microscopy study of chemical-vapor-deposited diamond by a side-view method

The initial growth of synthetic diamond by dc plasma-jet chemical vapor deposition was studied with a transmission electron microscope by a side-view method. Both diamond particles and β-SiC particles were observed on the Si substrate. Si atoms in the substrate were etched clearly by the plasma jet except beneath diamond particles.

In Situ Synthesis of A MoSi2/SiC Composite Using Solid State Displacement Reactions

ABSTRACTA high-strengthin situcomposite of MoSi2/SiC was synthesized using a solid state displacement reaction between Mo2C and Si by blending Mo2C and Si powders and vacuum hotpressing the powders at 1350°C for 2 h followed by 1 h at 1700°C. The resulting microstructure consisted of 1-μm diameter β-SiC particles (30 vol%) uniformly dispersed in a fine grained MoSi2matrix. Transmission electron microscopy was used to study the fine-scale morphology and phase distribution of the composite. Evidence for a small amount of grain boundary glass phase was observed using diffuse dark field imaging. The β-SiC particles were distributed mainly on grain boundaries and triple points within the MoSi2matrix. These findings were used to rationalize the observed mechanical property behavior.

Preparation of SiC hollow particles by gas-phase reaction and thermoelectric properties of sintered bodies

The formation of SiC hollow particles by gas-phase reaction in the silane-methane-hydrogen system and thermoelectric properties of the sintered bodies were studied. Synthesized powders were analyzed by means of TG, XRD, TEM, IR, etc. The powders synthesized at 1200–1300°C consisted of β-SiC and Si phases, but they became almost hollow β-SiC particles at 1400°C. The composition, particle size, and shell thickness of the synthesized particles were dependent on the reaction conditions. From lattice parameter measurements, a certain amount of excess silicon was verified to be incorporated into β-SiC lattice. On the other hand, excess carbon existed, for the most part, as an amorphous phase not forming solid solutions with β-SiC. TEM observations and IR absorption measurements have shown that excess carbon is contained within shells of hollow particles, while unreacted excess silicon exists as a crystalline phase mostly in the cores of the particles. Synthesized powders were sintered at 1850–2100°C for 3 h in nitrogen atmosphere. The electrical conductivity and thermoelectromotive force were measured at 400–1500°C in argon atmosphere. The density, average grain size and sintering additives had significant effects on the thermoelectric properties of SiC.

熱フィラメント法によるダイヤモンド膜のSi基板上への成長とその組織

The growth and structure of diamond films deposited on (111) Si substrates by the hot-filament CVD method were investigated by use of transmission electron microscopy. The density and growth rate of diamond particles on scratched (111) Si substrates were extremely high compared with that without any scratching of substrates. Fine β-SiC particles were observed over the whole area of the substrate after deposition in any case of surface condition. The nucleation and growth of diamond particles seem to be independent from the existence of SiC particles on substrates.

溶融アルミニウム中への粒子分散挙動に及ぼす合金元素の影響

The effect of alloying elements on the dispersions of α-SiC, β-SiC, Al2O3 and SiO2 into molten aluminum was investigated. The dispersion time of β-SiC particles in the molten aluminum was considerably longer than that of α-SiC particles at 1073K. However, at higher temperature, it became short and the difference in the dispersion time between α-SiC and β-SiC particles decreased. The dispersion time for β-SiC was decreased by adding the alloying elements such as titanium, zirconium and vanadium. Moreover, the dispersions of α-SiC and β-SiC were improved by adding calcium in aluminum. The dispersions of Al2O3 and SiO2 in aluminum were difficult, but by adding calcum in the aluminum those particles were dispersed easily. The calcium or titanium concentrated layer was detected by EPMA at the interface between particle and metal matrix.

Fine Particles of Silicon. I. Crystal Growth of Spherical Particles of Si

Fine crystals of Si having spherical shapes of less than 200 nm, as well as hybrid particles of Si and β-SiC were prepared by a gas evaporation method using an arc discharge as the heat source. Si particles always contain stacking faults and twins which are categorized as growth faults. All the planar faults in a particle occur in the same orientation (parallel to a [110] direction). The nature of these planar faults was examined in terms of crystal growth using an electron microscope. As a result, it has been concluded that these spherical Si particles are crystallized from liquid droplets which condense from Si vapors.

Sintering and HIPping of silicon nitride-silicon carbide composite materials

Si 3N 4 composite materials containing up to 60 vol.% of dispersed β-SiC particles were sintered with Y 2O 3 and Al 2O 3 at 1850°C and 0·1 MPa N 2. Fractional density decreased from 0·97 to 0·91 when the SiC content increased from 0 to 60 vol.%. Simultaneously a retardation of grain growth and reduced pore size was found. Subsequent HIPping at 2000°C with N 2-pressure of 100 MPa resulted in almost complete elimination of presintered closed pores and a final density of 0·99 up to 20 vol.% of SiC. During HIPping Si 3N 4 is formed by reaction of SiC or C with the SiO 2 intergranular glass in the presence of high N 2-pressure. While fracture toughness shows no significant influence of SiC content, a reduction of critical defect size with increasing SiC content results in a distinct increase of fracture strength particularly after HIPping.

Formation of elongated particles in β-SiC compacts

The mechanism of bonding of β-SiC particles in a compact in a sintering process at relatively low temperatures has been investigated by TEM. The initial sign of bonding is observed at around 1800°C. At these temperatures, SiC particles are found to bond together only when their mutual orientations are the same. Similarly oriented grains at contact reorient themselves by rotation to the same orientation and then bond, thus forming elongated particles. As the temperature increases, the tendency to form elongated particles increases. The formation of boundaries between differently oriented particles is observed only at around 2100°C and above in similar compacts. The mechanism of bonding of particles in the same orientation at low temperatures is ascribed to high self-energy of dislocations common to covalent-bonded materials and, hence, the high energy of formation of grain boundaries.

Hexagonal β‐SiC Particles

Among small β‐SiC particles (0.2 ∼ 0.4 μm in size) produced by chemical vapor reaction, hexagonal particles having diameters around 0.2 μm are sometimes found. When observed by TEM, they have image contrasts reminiscent of “multiply twinned particles”. Analysis of diffraction patterns and image contrasts observed indicates that these particles consist of multiple twins with twin planes parallel to the basal plane. The characteristics of growth processes of such particles are discussed.

Morphology, Structure and Growth Mechanism of Carbon Fibers Grown in Vapor Phase from Sulfur-containing Aromatic Reactants

Vapor phase growth of carbon fibers by thermal decomposition of 2-thionaphthol, dibenzothiophene, benzothiophene, thiophenol, and a mixture of naphthalene and hydrogen sulfide has been examined at 1100-1400°C to obtain information on the promotive function of sulfur.Two types of carbon fibers of different morphology were grown depending upon the decomposition temperature;thick and relatively straight fibers of 5-30μm diameter and of 10-30 mm length at 1100°C, and very thin (<1μm diameter) and short (2-3 mm) downy fibers at 1200-1400°C.An α-or β-SiC particle or fibril was identified by electron diffraction at the tip or inthe hollow center of almost every carbon fiber.The morphology of the fibers was apparentlydependent on the size and the number of the SiC particles, and the growth was likely to bepromoted by the SiC nuclei.Sulfur was suggested to mainly catalyse the formation of SiCvia the SiS2 intermediate from the SiO2 component in a mullite boat as a substrate or ina silica tube reactor.

Preparation of ultrafine particles of refractory metal carbides by a gas-evaporation method

In an atmosphere of rarefied inactive gas a carbon rod is mounted vertically with its bottom end touching the top surface of a block of refractory metal. By applying a heavy electric current through the carbon-metal junction, a smoke of metal carbide is produced. The smoke particles are examined by electron microscopy and electron diffraction. The particle diameter is always less than 1 μm. In the case of Si, particles of β-SiC (cubic type) are mixed with those of pure Si. For Ti, V and Zr, Debye rings shows that the particles are of NaCl-type. The lattice parameter is 4.27 Å for Ti and 4.21 Å for V, each of which roughly agrees with that of the stoichiometric carbide. The lattice parameter for Zr is found to be 4.47 Å, which is several percent lower than that of stoichiometric ZrC. Particles of chromium carbide have a complex structure which is analysed to be of the form Cr 7 C 3 with hexagonal structure. For Hf, Nb, Mo, Ta and W, crystalline carbide particles are not yet obtained.