Nanometric powder of stoichiometric silicon carbide produced in square-wave modulated RF glow discharges
TL;DR: In this article, a SiC nanometric powder has been obtained in square-wave modulated radiofrequency glow discharges from CH 4 and SiH 4 gas mixtures, and the effects on the structure of the powder were examined by FTIR, EA, XPS and from optical transmittance measurements.
Abstract: SiC nanometric powder has been obtained in square-wave modulated radiofrequency glow discharges from CH 4 and SiH 4 gas mixtures. Chemical and structural characterization revealed that the as-deposited SiC:H powder underwent spontaneous oxidation when exposed to atmosphere. To stabilise the powder chemically, we carried out a thermal treatment under vacuum (10 −4 Pa) consisting of heating to 800°C (20°C/min). The effects on the structure of the powder were examined by FTIR, EA, XPS and from optical transmittance measurements. They can be summarized as follows: dehydrogenation of the powder that induces the formation of a SiC carbidic network and chemical stability under atmospheric conditions, further confirmed by exposure to air for more than 6 months. In addition, TEM images showed that the annealed powder presented a short-range order in β -SiC units, but there was no evidence of size changes due to sinterization or compactaction phenomena.
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TL;DR: In this article, a three-step process is used to fabricate submicron silicon carbide powders in the reaction of silicon with carbon during the third step of thermal treatment.
Abstract: 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.
44 citations
TL;DR: In this paper, a hybrid multilayer nanostructures of ceramic coatings containing Si and SiC were produced to study their structural, mechanical and surface properties, and wear properties were evaluated using an improved pin-on-disc system.
Abstract: Ceramic nanometric multilayer structures of nanostructured particles of SiCx:H layers and amorphous Si films were obtained by chemical vapour deposition using modulated rf plasma This technology has been extensively used for producing ceramic Si-based nanoparticles (SiCxNy) with unique characteristics including spherical morphology, composition and controlled ultrafine particle size in the range 2–100 nm Hybrid multilayer nanostructures of ceramic coatings containing Si and SiC were produced to study their structural, mechanical and surface properties Low densities of crystalline nanoparticles were embedded in a-Si matrix during the growth of these structures and they were intercalated between amorphous Si layers The phase structure, microstructure and morphology of the hybrid multilayered films were examined by transmission electron microscopy and selected area electron diffraction, which revealed the presence and distribution of the nanoparticles in the multilayered structure of the films The hardness and Young's modulus were measured by the nanoindentation technique, and the wear properties were evaluated using an improved pin-on-disc system These results showed that the mechanical properties of the films (hardness, friction, propagation of cracks and wear resistance) were notably enhanced by the presence of the nanoparticles Potential applications of these coatings based on ceramic multilayers include the production of tough and hard coatings, protective and wear-resistant coatings for mechanical tools, gears and mechanical parts, optical surfaces and fibres, corrosion and high temperature-resistant coatings, as well as inorganic membranes, buffer layers for heterogeneous coatings, and coatings with anisotropic properties
19 citations
TL;DR: In this paper , a comprehensive overview on the synthesis, properties and potential applications of SiC nanoparticles is presented, with the classification of solid phase, liquid phase and vapor phase processes.
Abstract: The development of particulate materials is accelerating at a tremendous speed and nanoparticles have gradually gained worldwide attention. Among them, silicon carbide (SiC) nanoparticles have attracted much attention due to their excellent performance and great application potential. This article mainly presents a comprehensive overview on the synthesis, properties and potential applications of SiC nanoparticles. Firstly, various synthesis techniques for SiC nanoparticles were discussed, with the classification of solid phase, liquid phase and vapor phase processes. Subsequently, the unique properties of SiC nanoparticles such as surface properties, thermal properties, electrical properties and biocompatibility properties were highlighted. Thereafter, diversified applications of SiC nanoparticles including composites, catalysts, fluorescent biological labels, bioadhesives and flexible field emitters have been discussed. Finally, contents of the article were summarized and outlooks of future research were stated.
17 citations
TL;DR: In this article, carbon-coated Cu nanopowders with core/shell structure have been successfully fabricated by pulsed wire evaporation (PWE) method, in which a mixed gas of Ar/ (10 vol%) was used as an ambient gas.
Abstract: Carbon-coated Cu nanopowders with core/shell structure have been successfully fabricated by pulsed wire evaporation (PWE) method, in which a mixed gas of Ar/ (10 vol.%) was used as an ambient gas. The characterization of the samples was carried out using x-ray diffraction (XRD), scanning electron microscope (SEM), and high resolution transmission electron microscope (HRTEM). It was found that the nanoparticles show a spherical morphology with the size ranging of 10-40 nm and are covered with graphite layers of 2-4 nm. When oxygen-passivated Cu nanopowders were annealed under flowing argon gas (600 and 800), the crystallinity of phase and the particle size gradually increased. On the other hand, carbon-coated Cu nanopowders remained similar to as-prepared case with no additional oxide or carbide phases even after the annealing, indicating that the metal nanoparticles are well protected by the carbon-coating layers.
8 citations
TL;DR: In this article, an EG-based copper oxide nanofluids with different volume fraction were prepared by controlling explosion number of copper wire, and it was found that the copper oxide nanoparticles exhibited an average diameter about 100 nm with the oxide layer of 2~3 nm.
Abstract: 【In the present work, ethylene glycol-based (EG) copper oxide nanofluids were synthesized by pulsed wire evaporation method. In order to explode the pure copper wire, high voltage of 23 kV was applied to the both ends of wire and argon/oxygen gas mixture was used as reactant gas. EG-based copper oxide nanofluids with different volume fraction were prepared by controlling explosion number of copper wire. From the transmission electron microscope (TEM) image, it was found that the copper oxide nanoparticles exhibited an average diameter about 100 nm with the oxide layer of 2~3 nm. The synthesized copper oxide consists of CuO/ $Cu_2O$ phases and the Brunauer Emmett Teller (BET) surface area was estimated to be $6.86\;m^2\;g^{-1}$ . From the analyses of thermal properties, it is suggested that viscosity and thermal conductivity of EG-based copper oxide nanofluids do not show temperature-dependent behavior over the range of 20 to $90^{\circ}C$ . On the other hand, the viscosity and thermal conductivity of EG-based copper oxide nanofluids increase with volume fraction due to the active Brownian motion of the nanoparticles, i.e., nanoconvection.】
4 citations
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TL;DR: In this paper, negative ions were only observed over a limited range of power modulation frequency which corresponds to particle-free plasma conditions, and the importance of negative ions regarding particulate formation was demonstrated and commented upon.
Abstract: Negative ions have been clearly identified in silane rf plasmas used for the deposition of amorphous silicon. Mass spectra were measured for monosilicon up to pentasilicon negative ion radical groups in power‐modulated plasmas by means of a mass spectrometer mounted just outside the glow region. Negative ions were only observed over a limited range of power modulation frequency which corresponds to particle‐free plasma conditions. The importance of negative ions regarding particulate formation is demonstrated and commented upon.
109 citations
TL;DR: In this article, the authors used a Brownian free molecule coagulation model to determine the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering.
Abstract: To determine self-consistently the time evolution of particle size and their number density in situ multi-angle polarization-sensitive laser light scattering was used. Cross-polarization intensities (incident and scattered light intensities with opposite polarization) measured at 135 degrees and ex situ transmission electronic microscopy analysis demonstrate the existence of nonspherical agglomerates during the early phase of agglomeration. Later in the particle time development both techniques reveal spherical particles again. The presence of strong cross-polarization intensities is accompanied by low-frequency instabilities detected on the scattered light intensities and plasma emission. It is found that the particle radius and particle number density during the agglomeration phase can be well described by the Brownian free molecule coagulation model. Application of this neutral particle coagulation model is justified by calculation of the particle charge whereby it is shown that particles of a few tens of nanometer can be considered as neutral under our experimental conditions. The measured particle dispersion can be well described by a Brownian free molecule coagulation model including a log-normal particle size distribution. (C) 1996 American Institute of Physics.
90 citations
TL;DR: In this article, different preparation methods of ultrafine powders of high melting point compounds (carbides, borides, nitrides, and oxides with melting temperatures higher than 2000 C) are reviewed and compared.
Abstract: The different preparation methods of ultrafine powders of high melting point compounds (carbides, borides, nitrides, and oxides with melting temperatures higher than 2000‡C) are reviewed. Some properties of these powders are discussed and compared. The consolidation behaviour of these compounds in the nanocrystalline (nc) state is described in detail. Compaction by hot pressing, including high pressures and high temperatures, sintering, and high-energy consolidation methods, is analysed. The microstructure, recrystallization, mechanical and physical properties of nc-carbides, nitrides, and oxides are characterized. Special attention is focused on relationships between structure and properties.
79 citations
TL;DR: The rate of particle generation in a SiH4/NH3 rf discharge has been studied as a function of the discharge operating parameter space, electrode geometry, and power supply coupling mode.
Abstract: The rate of particle generation in a SiH4/NH3 rf discharge has been studied as a function of the discharge operating parameter space, electrode geometry, and power supply coupling mode. Measurements of the bulk quantity of particles produced in the discharge reveal that the mode of coupling (capacitive or dc) as well as the electrode temperature significantly affects particle generation rates. Laser light scattering measurements made as a function of the plasma power density indicate that particle generation abruptly ceases at a threshold value sufficient to induce spark breakdown at the cathode. Based on these observations, it is shown that particle growth in plasmas can be modeled entirely as a heterogeneous process. The initiation of particle growth is shown to be consistent with an electron surface desorption model involving vibrational excitation of surface clusters. Propagation of growth in the gas phase is shown to be consistent with an eliminative ion‐molecular condensation reaction, and the press...
62 citations
TL;DR: In this paper, the discharge power is derived by subtracting losses from the total power reading, which can be used as an aid in the scaling of system sizes, and this discharge power exhibits interesting behavior as the pressure is varied, at constant applied rf voltage.
Abstract: Radio frequency (rf) sputtering is used for the deposition and etching of thin layers. In both cases the target etch rate must be controlled, and often power input has been used as one of the controlling parameters. An earlier paper has shown that the applied rf target voltage (V pp) was a more useful parameter, and here new data is presented which indicates that the peak‐to‐peak voltage remains the preferable parameter for both etch rate control and in transferring between machines. However, a new method is described here which obtains the discharge power by subtracting losses from the total power reading. This discharge power is shown to be related to etch rates, and can thus be used as an aid in the scaling of system sizes. In addition, this discharge power exhibits interesting behavior as the pressure is varied, at constant applied rf voltage. Three main regions are evident when etching Si with CF4: at low pressures directional ion‐induced etching is obtained; in an intermediate region the input power rises rapidly with pressure and the etching is less directional resulting in overhang profiles; and at high pressures an isotropic etching component results in undercut profiles. The two extreme regions correlate with the commonly identified regimes of: (a) low power input, low pressure reactive sputter etching, and (b) high power input, high pressure plasma etching.
51 citations