Thermal conductivity of bio-SiC and the Si embedded in cellular pores of the SiC/Si biomorphic composite

The thermal conductivity of bio-SiC, a heavily defected material with specific cellular pores (channels), was studied in the temperature range 5–300 K. The bio-SiC sample was prepared from the SiC/Si biomorphic composite through the chemical removal of silicon. The thermal conductivity of silicon embedded in cellular pores of the SiC/Si biomorphic composite was determined.     

Heat capacity and velocity of sound in the SiC/Si biomorphic composite

The specific heat at constant pressure and the velocity of sound in the SiC/Si biomorphic composite prepared from white eucalyptus wood are measured in the range 3.5–65 K and at 77 K, respectively. The heat capacity of the SiC/Si sample under investigation is calculated within three proposed models according to the Kopp-Neumann additivity rule.     

Elastic and inelastic properties of SiC/Si biomorphic composites and biomorphic SiC based on oak and eucalyptus

This paper reports on the results of a comparative investigation into the elastic and microplastic properties of biomorphic SiC/Si composites and biomorphic SiC prepared by pyrolysis of oak and eucalyptus with subsequent infiltration of molten silicon into a carbon matrix and additional chemical treatment to remove excess silicon. The acoustic studies were performed by the composite oscillator technique using resonant longitudinal vibrations at frequencies of about 100 kHz. It is shown that, in biomorphic SiC (as in biomorphic SiC/Si) at small-amplitude strains ε, adsorption and desorption of the environmental (air) molecules determine to a considerable extent the Young’s modulus E and the internal friction (decrement of acoustic vibrations δ) and that the changes in E and δ at these amplitudes are irreversible. The stress-microplastic strain curves are constructed from the acoustic data for the materials under study at temperatures of 100 and 290 K.     

Anisotropy of the thermal conductivity and electrical resistivity of the SiC/Si biomorphic composite based on a white-eucalyptus biocarbon template

The thermal conductivity κ and electrical resistivity ρ of a cellular ecoceramic, namely, the SiC/Si biomorphic composite, are measured in the temperature range 5–300 K. The SiC/Si biomorphic composite is fabricated using a cellular biocarbon template prepared from white eucalyptus wood by pyrolysis in an argon atmosphere with subsequent infiltration of molten silicon into empty through cellular channels of the template. The temperature dependences κ(T) and ρ(T) of the 3C-SiC/Si biomorphic composite at a silicon content of ～30 vol % are measured for samples cut out parallel and perpendicular to the direction of tree growth. Data on the anisotropy of the thermal conductivity κ are presented. The behavior of the dependences κ(T) and ρ(T) of the SiC/Si biomorphic composite at different silicon contents is discussed in terms of the results obtained and data available in the literature.     

Electrical properties of bio-SiC and Si components of the SiC/Si biomorphic composite

The electrical resistivity ρ of bio-SiC, a highly porous cellular material prepared from a biomorphic composite SiC/Si based on white eucalyptus wood through the chemical removal of silicon, was measured in the temperature range 5–100 K. The electrical resistivity of bio-SiC was found to be anisotropic along and across the cellular pores. The activation energy of charge transfer in bio-SiC was estimated. The measured values of ρ for the SiC/Si biomorphic composite and bio-SiC were used to determine the electrical resistivity ρ and the carrier concentration in silicon, which is one of the constituents of the composite.     

Elasticity and inelasticity of biomorphic carbon,silicon carbide,and SiC/Si composite produced on the basis of medium density fiberboard

The amplitude and temperature dependences of the Young’s modulus and the internal friction (ultrasonic absorption) of biomorphic carbon, silicon carbide, and SiC/Si composite produced from medium density fiberboard (MDF) by pyrolysis (carbonization), followed by infiltration of molten silicon into the prepared carbon preform have been studied in the temperature range 100–293 K in air and under vacuum. The measurements have been performed by the acoustic resonance method with the use of a composite vibrator for longitudinal vibrations at frequencies of approximately 100 kHz. The data obtained by acoustic measurements of the amplitude dependences of the elastic modulus have been used for evaluating the microplastic properties of samples under study. It has been shown that the Young’s modulus, the decrement of elastic vibrations, and the conventional microyield strength of the MDF samples differ from the corresponding data for previously studied similar materials produced from natural eucalyptus, beech, sapele, and pine woods. In particular, the desorption of environmental molecules at small amplitudes of vibrations, which is typical of biomorphic materials based on natural wood, is almost absent for the MDF samples. The results obtained have been explained by different structures and the influence of pores and other defects, which, to a large extent, determine the mechanical characteristics of the biomaterials under investigation.     

Preparation and application of the 3C–SiC substrate to piezoelectric micro cantilever transducers

This study examines the fabrication process and mechanical properties of piezoelectric films with the substrate, which is made from silicon carbide. After depositing the PZT thick film on silicon carbide substrate and silicon substrate respectively, it was shown that silicon carbide substrate formed a stable interface with PZT thick film up to 950?°C, compared with silicon substrate. In addition, the dielectric constant of the PZT thick film sintered at 950?°C on a silicon carbide substrate was 843, and this value was about over 25 % improved value compared with that on a silicon substrate. A thick film piezoelectric micro transducer of a micro cantilever type was fabricated by using a multifunctional 3C–SiC substrate. The fabricated micro cantilever was a micro cantilever with multiple thin films on either silicon or silicon carbide substrate. The piezoelectric thick-film micro cantilever that was fabricated by using a SiC substrate showed excellent mechanical and thermal properties. The piezoelectric micro cantilever on the SiC substrate shows an excellent sensitivity towards the change of mass compared with the piezoelectric micro cantilever on the Si substrate.     

Elasticity and inelasticity of the SiC/Al-13Si-9Mg biomorphic metal ceramics

The acoustic investigations of the elastic (Young’s modulus) and microplastic properties of a composite material, the SiC/Al-13Si-9Mg biomorphic metal ceramic, were performed. The ceramic was prepared by infiltration of the Al-13Si-9Mg melt into porous silicon carbide derived from wood of two species of trees, beech and sapele. The measurements were performed with a composite piezoelectric vibrator under resonance conditions, with rod-shaped samples vibrated longitudinally at about 100 kHz over a wide range of vibrational strain amplitudes, which included both the linear (amplitude-independent) and nonlinear (microplastic) regions. It was shown that the Young’s modulus and the microplastic properties of the composite are anisotropic and depend substantially on the tree species, particularly when longitudinal vibrations are excited in samples cut along the tree fibers.     

Elasticity and inelasticity of biomorphic silicon carbide ceramics

The effect of the vibration strain amplitude on the Young modulus and ultrasonic absorption (internal friction) in biomorphic SiC ceramics is investigated in the temperature range 116–296 K. The biomorphic SiC ceramics is prepared through pyrolysis of eucalyptus with subsequent infiltration of silicon. It is demonstrated that the vibration loading of samples in air and under vacuum is accompanied by a number of unexpected effects. The behavior of the studied ceramics is governed by at least two mechanisms, which, to a large extent, are responsible for the elastic and inelastic properties of the material. One mechanism is associated with the adsorption-desorption of environmental molecules (hypothetically, owing to the presence of pores and residual carbon), and the other mechanism involves microplastic deformation due to the motion of dislocations or other (similar) structural units.     

Mechanism of Formation of Carbon–Vacancy Structures in Silicon Carbide during Its Growth by Atomic Substitution

Physics of the Solid State - The mechanism of formation of carbon-vacancy structures in silicon carbide SiC from silicon vacancies that inevitably form during synthesizing SiC from Si by atomic...     

Control of near-field radiative heat transfer via surface phonon–polariton coupling in thin films

The possibility of controlling near-field radiative heat transfer with the use of silicon carbide thin films supporting surface phonon–polaritons in the infrared spectrum is explored. For this purpose, the local density of electromagnetic states is calculated and analyzed within the nanometric gap formed between two SiC films as well as the radiative heat flux exchanged between the thin layers.     

Formation of tubular silicon carbide from a carbon–silica material by using a reactive replica technique: infra-red characterisation

Thermal treatment of carbon fibres covered with silica prepared by a sol–gel technique leads to the formation of a tubular silicon carbide material keeping the morphology of the carbon source. The conversion of silica into silicon carbide, its kinetics and the structure of the final material were mainly determined by infra-red (IR) spectroscopy. The analytical results were crossed examined with those obtained by gravimetric and microscopic methods. In particular, it is shown, here, that IR-spectroscopy is a suitable technique to quantitatively determine the amount of SiC formed during the heat treatment of a C/SiO₂ material.     

The application of PCMMcs and SiC by commercially direct dual-complex coating on textile polymer

To enhance the thermal insulation effect, waterproof/breathable fabrics were directly top dual-coated by the dry coating method with ceramic materials (silicon carbide, SiC). The fabric was base coated by the wet coating method with 5 wt% phase-change material microcapsules (PCMMcs) and tested for the emission of far-infrared (FIR) radiation. With increasing SiC content, the fabric altered some of the physical properties by increasing the FIR emissivity, emission power, water vapor transmission rate (WVTR) and heat release capacity. Scanning electron microscopy (SEM) analysis revealed the presence of the PCMMcs and SiC particles at the cross-section and surface of the coating, respectively, which exhibited a rugged and blocky shape. The results indicated that SiC addition did not affect the water entry pressure (WEP) in the fabric structure, but did alter the following physical properties: WVTR, interactions between the macromolecule chains and the susceptibility to humidity.     

Investigation of the 4H-SiC surface

The silicon carbide (SiC) surface is more complex than that of silicon and can be carbon-terminated or silicon-terminated, and can exist as several reconstructions. Investigations of the surface structure as a function of temperature, under ultrahigh vacuum (UHV) conditions using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED), are presented. The 4H-SiC surface can be passivated using a silicon deposition/evaporation technique to reconstruct the surface. This has a significant effect on the electrical behaviour of metal contacts to the silicon carbide surface, critical in any electronic device. Atomic resolution STM studies of the 4H-SiC surface have revealed step features and micropipe defects in unprecedented detail. STM has also been used to image clusters of metal deposited on the 4H-SiC surface. The effect of annealing on the behaviour of these nickel clusters is also presented. The surface of the silicon carbide is extremely important in the fabrication of silicon carbide electronic devices and this paper presents a discussion of the SiC surface with particular reference to its impact on SiC device applications in power electronics.     

Young’s modulus and internal friction of the SiC/Si biomorphic composite based on the sapele wood precursor

The effect of the vibrational strain amplitude on the Young’s modulus and ultrasound absorption (internal friction) of a SiC/Si biomorphic composite prepared by pyrolysis of sapele wood followed by infiltration of silicon were investigated. The studies were conducted in air and in vacuum by the acoustic resonance method with the use of a composite vibrator in longitudinal vibrations at frequencies of about 100 kHz. Measurements performed on sapele wood-based bio-SiC/Si samples revealed a substantial effect of adsorption-desorption of molecules contained in air on the effective elasticity modulus and elastic vibration decrement. Microplastic characteristics of the SiC/Si composites prepared from wood of different tree species were compared.     

Polytypism of silicon carbide and Schottky barriers

The results obtained in our previous work [4] are revised taking into account the dependence of the electron affinity on the polytype of silicon carbide SiC. The dependence of the energy level of vacancies in a polytype of silicon carbide on the band gap is determined from the data on the Schottky barrier height and is explained in the framework of a simple two-band model.     

Classification and structure of silicon carbide phases

Molecular-mechanical and semiempirical quantum-mechanical methods have been applied to simulate and calculate a geometrically optimized structure of clusters of polymorphic types of silicon carbide, and their structural parameters and some properties (densities, sublimation energies) have been determined. A classification of silicon carbide phases has been proposed, which shows the possible existence of twenty one SiC phases whose atoms are at crystallographically equivalent sites. The structures of seventeen proposed silicon carbide phases have been described and studied for silicon carbide for the first time.     

New method for growing silicon carbide on silicon by solid-phase epitaxy: Model and experiment

A new method of solid-state epitaxy of silicon carbide (SiC) on silicon (Si) is proposed theoretically and realized experimentally. Films of various polytypes of SiC on Si(111) grow through a chemical reaction (at T = 1100–1400°C) between single-crystal silicon and gaseous carbon oxide CO (at p = 10–300 Pa). Some silicon atoms transform into gaseous silicon oxide SiO and escape from the system, which brings about the formation of vacancies and pores in the silicon near the interface between the silicon and the silicon carbide. These pores provide significant relaxation of the elastic stresses caused by the lattice misfit between Si and SiC. X-ray diffraction, electron diffraction, and electron microscopy studies and luminescence analysis showed that the silicon carbide layers are epitaxial, homogeneous over the thickness, and can contain various polytypes and a mixture of them, depending on the growth conditions. The typical pore size is 1 to 5 μm at film thicknesses of ～20 to 100 nm. Thermodynamic nucleation theory is generalized to the case where a chemical reaction occurs. Kinetic and thermodynamic theories of this growth mechanism are constructed, and the time dependences of the number of new-phase nuclei, the concentrations of chemical components, and the film thickness are calculated. A model is proposed for relaxation of elastic stresses in a film favored by vacancies and pores in the substrate.     

Heat capacity of Bio-SiC and SiC/Si ecoceramics prepared from white eucalyptus, beech, and sapele tree wood

This paper reports on measurement of the heat capacity at constant pressure C _p of silicon bio-carbide prepared within the 5–300 K temperature interval from beech tree wood (bio-SiC(BE)), and within 80–300 K, from tree wood of sapele (bio-SiC(SA)), as well as SiC/Si ecoceramics of beech, sapele, and white eucalyptus wood. It has been shown that in bio-SiC(BE) the measured heat capacity contains a significant contribution of surface heat capacity, whose magnitude decreases with increasing temperature. Of the ecoceramics, only SiC/Si(SA) characterized by a high enough porosity has revealed a small contribution to the heat capacity coming from its surface component. The experimental results obtained are discussed.     

Synthesis of silicon carbide nanopowders in a two-jet plasma-chemical reactor

Results of experimental studies on production of nanostructured silicon carbide powders in a plasma-chemical reactor based on a two-jet plasmatorch are presented. The conditions of SiC formation as a function of temperature and composition of the initial components are determined by thermodynamic calculations. Possibility of silicon carbide synthesis with the size of particles of 5?20 nm is shown experimentally.