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Silicon carbide (SiC) is a candidate structural material for fission and fusion reactors as well as an important wide band-gap semiconductor for electronic devices. Using first-principles calculations, we systemically investigate the energetics and stability of helium (He) atoms and intrinsic point defects inside single-crystalline 3C-SiC. We find that the formation energy of interstitial He is lower than those of point defects. Inside 3C-SiC, the He-C interaction is stronger than He-Si. Hence, the interstitial He atom in the Si tetrahedral site has a stronger interaction with the six C atoms in the second nearest neighbor than the four nearest neighboring Si atoms. For interstitial He atoms, the equilibrium He-He distance is about 1.81 Å with a weak attraction of 0.09 eV. According to the binding energies of Hen (n = 2–4) clusters, He interstitials can form He bubbles without involving other types of structural defects. Moreover, a Si (C) monovacancy can accommodate up to 11 (9) He atoms. The Hen clusters trapped in the Si or C monovacancy induce large internal pressure in the order of magnitude of GPa and thus facilitate the creation of a new vacancy at the nearby lattice site. [ABSTRACT FROM AUTHOR]

As a wide band gap semiconductor material silicon carbide, with a stable chemical properties and good thermal conductivity of physical properties, in addition to the mechanical properties of the material also has a strong advantage. In order to explore more scientific and practical nanomaterials, this paper studies the preparation process of silicon carbide nanomaterials and the optical characterization of the materials, and analyzes the properties of the materials, 3C-SiC nanowires and 3C-SiC micron polyhedra, XRD patterns, infrared spectra, Raman spectra, thermogravimetric curves and room temperature photoluminescence spectra. By studying the experimental results of optical properties, it is concluded that silicon carbide products have great application prospect in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract The production of fully dense Mg-SiC nanocomposites with a homogeneous distribution of SiC nanoparticles through powder metallurgy techniques is still a challenging issue. We propose to combine sintering and hot extrusion of mechanically milled composite powders to encompass the known difficulties of conventional processing. Here, we report on the effect of SiC nanoparticle content on the compressibility, microstructure and hardness of SiC-Mg nanocomposites during the different consolidation steps. Cold-isostatic pressing, sintering and indirect hot extrusion were used for compaction and consolidation. Near dense Mg-SiC nanocomposites with 1 and 10 vol% SiC nanoparticles were successfully produced with a homogeneous distribution of the nanoparticles. Scanning electron microscopy, X-ray diffraction and transmission electron microscopy were used to characterise the microstructure of the powders and of the sintered and extruded Mg-SiC nanocomposites. Vickers microhardness tests were done to reveal the hardening effect after sintering and extrusion. The nanoparticles pin the grain boundaries and foster dynamic recrystallisation, so that a nanograined Mg matrix develops and is preserved even after the final consolidation step. The results further show a very good interface adherence between nanoparticles and matrix contributing to the high hardness of the nanocomposites. [ABSTRACT FROM AUTHOR]

Graphical abstract A 3 × 3 × 1 supercell model of 4H-SiC with 72 atoms. One of the two Ni dopants is fixed at the position labeled Ni 0 , The Si atoms labeled by 1–10 are the sites to be replaced by the other doped Ni atoms. Abstract Based on density functional theory (DFT) first-principles method, we have investigated the electronic structures and magnetic properties of (Ni,Al) co-doped 4H-SiC system. Various configurations of Ni sites have been considered to confirm the most stable geometric construction. Comparing with pure 4H-SiC, the magnetic moment of Ni-doped 4H-SiC is increased, which is attributed to the hybridization of Ni:4 s and C:2 p orbitals. Moreover, we found that it is the 3 d orbital of Ni that induces the spin-polarized state in Ni-doped 4H-SiC. In addition, the origin of ferromagnetic coupling between Ni-doped 4H-SiC has been predicted to be the ferromagnetic orders activated by the Ni 0 :3 d -C:2 p -Ni 2 :3 d coupling chains. For (Ni,Al) co-doped system, we found that ferromagnetic stability is reduced significantly. For (2Ni, V Si ) co-doped 4H-SiC system, the antiferromagnetic state is more stable than ferromagnetic state with △ E FM of 97.2 meV, and the system changes from ferromagnetism to anti-ferromagnetism. These results provide a new route for the potential applications of dilute magnetic semiconductors in spintronic devices by employing doped 4H-SiC. [ABSTRACT FROM AUTHOR]

Ni-14 at.% W/SiC nanocomposite coatings containing 0-6 vol.% of submicron size (0.35 μm) SiC particles were obtained using pulsed electrodeposition technique on mild steel substrate. The coatings were subsequently characterized for uniformity of SiC distribution, grain size and mechanical properties (hardness and elastic modulus) using SEM, XRD and nanoindentation techniques, respectively. It was observed that the SiC particulates were uniformly distributed within the coating. The coating matrix (Ni-W) also exhibited nanograin size. Tribological behavior of Ni-14 W/SiC nanocomposite was analyzed under dry sliding wear test conditions using pin on disk method. The interrelationship between SiC content, interparticle spacing, mechanical properties and wear behavior was analyzed. The results suggest that whereas hardness and modulus of nanocomposite coatings varied with SiC content as per Rule of Mixtures, wear mechanism can be best explained on the basis of Inverse Rule of Mixtures. [ABSTRACT FROM AUTHOR]

Ring oscillators (ROs) are used to study the high-temperature characteristics of an in-house silicon carbide (SiC) technology. Design and successful operation of the in-house-fabricated 4H-SiC n-p-n bipolar transistors and TTL inverter-based 11-stage RO are reported from 25 °C to 600 °C. Non-monotonous temperature dependence was observed for the oscillator frequency; in the range of 25 °C to 300 °C, it increased with the temperature (1.33 MHz at 300 °C and $V_{CC} =15$ V), while it decreased in the range of 300 °C–600 °C. The oscillator output frequency and delay were also characterized over a wide range of supply voltage (10 to 20 V). The noise margins of the TTL inverter were also measured; noise margin low ($\text {NM}_{L}$) decreases with the temperature, whereas noise margin high ($\text {NM}_{H}$) increases with the temperature. The measured power-delay product (${P}_{D} \cdot {T}_{P}$) of the TTL inverter and 11-stage RO was ≈ 4.5 and ≈285 nJ, respectively, at ${V}_{\text {CC}} =15$ V. Reliability testing indicated that the RO frequency of oscillation decreased 16% after HT characterization. [ABSTRACT FROM AUTHOR]

In this study, C f /SiC composite was modified with SiC nanowires (SiC nws ) grown in-situ in SiC matrix. Effects of SiC nw on bending strength and fracture toughness were investigated by comparison with conventional C f /SiC. Results showed that SiC nw significantly improved both strength and fracture toughness of C f /SiC. Compared to C f /SiC, flexural strengths of C f /SiC-SiC nw /PyC and C f /SiC-SiC nw composites increased from 363.1 MPa to 375 MPa and 466.9 MPa, respectively. Bending strength and fracture toughness were estimated to 565 MPa and 20.30 MPa m 1/2 for C f /SiC containing SiC nw at high temperature (1000 °C), respectively. These values were 13.2% and 16.1% higher than that of conventional C f /SiC. The latter was attributed to deflection, bridging, and pull-out of SiC nanowires to cracks. Improvements in mechanical properties of modified C/SiC composites were mainly attributed to deflection and bridging of SiC nanowires on cracks and pulling out of SiC nanowires from the matrix. [ABSTRACT FROM AUTHOR]

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The investigations of pure and heteroatom doped carbon clusters have created great interest because of their enormous prospective applications in various research zones, for example, optoelectronics, semiconductors, material science, energy storage devices, astro-science and so on. In this article, the interaction of molecular oxygen ( O 2 ) with C 3 Si has explored within a density functional theory (DFT). Different possible types of structure for C 3 S i O 2 have collected. Among five different kinds of structure, the structure- 1a , A 1 1 is more energetically stable. The nature of the bonding of O 2 and C 3 Si, in C 3 S i O 2 has been studied by using Bader's topological analysis of the electron charge density distribution ρ ( r ) , Laplacian ∇ 2 ρ ( r ) and total energy density H ( r ) at the bond critical points (BCPs) of the structures within the framework of the atoms in molecules theory (AIM). The bonding mechanism of O 2 and C 3 Si in C 3 S i O 2 prompts to the fundamental understanding of the interaction of C 3 Si with oxygen molecule. It is interesting to note that, two types of bonding mechanism are established in same C 3 S i O 2 system such as (i) shared-kind interactions (ii) closed-shell interactions. From various kinds of structure, C C bonds in all structures are shown as shared-kind interactions whereas C Si, O O bonds are classified as closed-shell type interactions with a certain degree of covalent character. [ABSTRACT FROM AUTHOR]

Many interesting studies on composites with nano or submicron SiCp have been performed since the size advantages of fine SiC particles. However, it is extremely hard to disperse fine particles in metal melts due to their poor wettability and large surface-to-volume ratio, especially the fabrication of composites with multisized SiCp (5 µm, 0.5 µm, and ∼60 nm) is very difficult. The use of multisized reinforcements is required to solve the dispersion problem. The stir casting technology and hot extrusion method could be used to disperse the multisized SiCp in the matrix. The effects of multisized SiCp on the dynamic recrystallization behavior of the composites are discussed. The large-scale dynamic recrystallization caused by adding multisized SiCp results in a fine matrix microstructure. Compared with the as-accepted AZ31B alloy (YS: 195 MPa, UTS: 277 MPa), the yield strength and ultimate tensile strength of the AZ31B/SiCp/n-1 + S-4 + 5-10 composite were enhanced to 73.8 and 44.8%, respectively. The better tensile properties were attributed to the uniform distribution of reinforcement, strengthening effect of multisized SiCp, and grain refinement of magnesium matrix. [ABSTRACT FROM AUTHOR]

Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 °C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiC-sandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 °C and under flowing PbLi at ~10 cm/s and 550 °C, with and without a 1.8–2T magnetic field, were performed to materials coated with a 200–400- $\mu \text{m}$ -thick dense SiC layer, obtaining promising results. [ABSTRACT FROM AUTHOR]

Samarium-doped ZrB 2 /SiC (ZBS) coatings possess properties of high emissivity and excellent ablation performance suitable for hypersonic applications. Of interest in the current study is how cyclic ablation affects the scale development on alumina substrates. ZBS coatings with 3, 5 and 8 mol% of samarium (Sm) dopant were prepared via shrouded plasma spray onto alumina substrates and subjected to two 60-s ablation cycles with temperatures reaching up to 1700 °C. Blisters were observed on the Sm-doped coatings after the 1st cycle as a result of a local eutectic reaction between the ablation products and alumina substrate. A Sm-stabilized t -ZrO 2 phase was identified through X-ray diffraction after the ablation of the Sm-doped coatings. The ZBS with 5 mol% of Sm dopant produced a flower-like microstructure after the 2nd cycle due to the formation of convection cells. [ABSTRACT FROM AUTHOR]

The influence of SiC nanoparticles additions on the microstructure and creep behavior of the 2.0Ca + 0.3Sb (wt%) added AZ91 alloy fabricated by squeeze-casting have been investigated. For comparison, the same has also been studied without nanoparticles additions. The α-Mg, β-Mg 17 Al 12 , Al 2 Ca and Ca 2 Sb phases are present in both the alloy and the nanocomposites. The additions of SiC nanoparticles refined the grain size, reduced the volume fraction of the β-Mg 17 Al 12 phase, and increased the amount of Al 2 Ca phase, which is more pronounced with an increase in the nanoparticle content. All the nanocomposites exhibit superior creep resistance than the unreinforced 2.0Ca + 0.3Sb (wt%) added AZ91 alloy. The best creep resistance is obtained in the nanocomposite pertaining 2.0SiC (wt%) nanoparticles. The values of stress exponents and the activation energies are in the range of 4.5–6.2, and 101.9 ± 2.5–115.5 ± 3.2 kJ/mol suggesting the governing creep mechanism for the alloy and the nanocomposites is dislocation climb controlled by pipe diffusion. The post creep microstructural observation confirms that the β-Mg 17 Al 12 phase in the alloy is rigorously fragmented, and aligns in the direction of material flow, which deteriorates its creep resistance. In contrast, the presence of Al 2 Ca phase network and the SiC nanoparticles increase the dislocation pile-ups and dislocation tangling resulting in superior creep resistance of all the nanocomposites. [ABSTRACT FROM AUTHOR]

SiC based refractory is an environment-friendly lining material for high-temperature solid waste gasifier and urgently required longer service life. In this paper, the efficiency of silica sol bonded SiC castables introducing different amounts of Zr combined Si and C was evaluated by considering their sintered properties, mechanical performance, isothermal oxidation behavior, microstructure, and thermodynamics. It was found that the oxidation of SiC castables follows a two-stage kinetic model, controlled by oxidation (rate constant k c ) at an earlier period and diffusion (rate constant k d ) at a later period. Incorporating Zr distinctly slower oxidation rate of the Si containing SiC castables and the k c and k d were reduced by 18.9% and 9.2% with addition of 0.6 wt% Zr, respectively, compared to the unmodified sample. The Zr-modified SiC castables exhibited good mechanical behavior, increased bulk density, and reduced porosity. The oxidation of Zr to ZrO 2 reduced the diffusion path and concentration of O 2 , which prevented the loss of SiC and C by forming SiC fibers and reducing CO(g) to graphite, helped absorb SiO 2 to form ZrSiO 4 . It made the SiC castable a self-repairing and enhanced refractory material. [ABSTRACT FROM AUTHOR]

A comparative study of reactive melt infiltration using Si and Si-Y alloys is presented to provide insight into the governing processes that control the effectiveness of the melt interaction with a carbonaceous preform and the temperature capability of the SiC matrix for ceramic matrix composites. Through experiments on two substantially different scales of capillaries in porous graphite tubes using Si and Si-Y alloys, the current study has characterized the phenomena that play a role in the infiltration of the melt and its reaction with the preform. It is shown that (i) the interface reaction controls wetting in both large and small capillaries and the climb rate is enhanced by the presence of Y; (ii) reaction choking occurs at critical throats within the pore network, usually behind the infiltration front; and (iii) different residual silicides can form during reaction and upon cooling. A potential mechanism for SiC growth is described, and the implications for the interplay between SiC growth and infiltration are discussed. [ABSTRACT FROM AUTHOR]

In this paper, the significance and contribution of SiC particle size and spark plasma sintering (SPS) parameters on the mean TiB 2 grain size and Vickers hardness of TiB 2 –20 vol% SiC ceramic composites were studied. An L9 orthogonal array was used to design of experiments by the Taguchi method to investigate the effects of four processing parameters including the SPS temperature, SPS soaking time, SPS pressure and SiC particle size. Three levels were selected for each parameter and the analysis of variance (ANOVA) was employed for optimization of processing parameters. The SPS temperature was identified as the most effective parameter on the as-sintered grain size and hardness of TiB 2 –SiC ceramics, but, the SPS soaking time does not have an obvious influence on these characteristics. The presence of SiC together with the in-situ formed nano-sized TiC phases acted as grain growth inhibitors which was helpful to obtain a fine-grained composite microstructure. The ANOVA disclosed that the sintering temperature of 1800 °C, the soaking time of 15 min, the pressure of 30 MPa and the SiC particle size of 200 nm are the optimal processing conditions. A Vickers hardness of 28.5 GPa was predicted at such optimized conditions which is near to the experimentally measured value of 27.4 GPa as the confirmation test. [ABSTRACT FROM AUTHOR]

In order to broaden the application of SiC particle-reinforced aluminum matrix composite in electronics packaging, newly developed ZnAlGaMgTi filler with a low melting point of 418-441 °C was utilized as filler metal for active soldering of aluminum matrix composites (70 vol.%, SiCp/Al-MMCs) for the first time. The effect of loading pressure on joint properties of ZnAlGaMgTi active filler was investigated. The experimental results indicated that novel filler could successfully solder Al-MMCs, and the presence of Mg in the filler enhanced the penetration of Zn, while the forming of Zn-rich barrier layer influenced the active element MPD (melting point depressant) diffusion into parent composite, and the bulk-like (Mg-Si)-rich phase and Ti-containing phase were readily observed at the interface and bond seam. With the increase in loading pressure, the runout phenomenon appeared more significant, and the filler foil thickness and the Zn penetration depth varied pronouncedly. Sound joints with maximum shear strength of 29.6 MPa were produced at 480 °C at 1 MPa, and the crack occurred adjacent to the boundary of SiC particle and then propagated along the interface. A novel model describing the significant mutual diffusion of Al and Zn atoms between the parent material and solder was proposed. [ABSTRACT FROM AUTHOR]

In this study, pure nickel and Ni-SiC composite coatings were prepared by the conventional electrodeposition technique from nickel sulfamate electrolytic bath containing dispersed SiC particles. The samples obtained after the electrodeposition were subjected to the ultrasonic nanocrystal surface modification (UNSM) technique to improve the surface- and interface-related properties of the coatings. The surface morphology, elemental composition, surface roughness, microstructure, and crystallinity were observed and analyzed by using scanning electron microscope, energy-dispersive x-ray spectroscopy, roughness tester, and x-ray diffraction techniques, respectively. Electrochemical corrosion behavior of the obtained samples was evaluated in 3.5 wt.% NaCl solution by using three electrodes configuration. XRD result revealed the enhanced crystallinity of the UNSM-treated samples. A significant improvement in surface morphology, Vickers microhardness, wear and coefficient of friction, and anti-corrosion property was observed in the UNSM-treated nickel and Ni-SiC coatings compared to the UNSM-untreated samples. [ABSTRACT FROM AUTHOR]

Multi-layered SiC composites consisting of monolithic SiC and a SiC f /SiC composite are one of the accident tolerant fuel cladding concepts in pressurized light water reactors. To evaluate the integrity of the SiC fuel cladding under normal operating conditions of a pressurized light water reactor, the hydrothermal corrosion behavior of multi-layered SiC composite tubes was investigated in the simulated primary water environment of a pressurized water reactor without neutron fluence. The results showed that SiC phases with good crystallinity such as Tyranno SA3 SiC fiber and monolithic SiC deposited at 1200 °C had good corrosion resistance. However, the SiC phase deposited at 1000 °C had less crystallinity and severely dissolved in water, particularly the amorphous SiC phase formed along grain boundaries. Dissolved hydrogen did not play a significant role in improving the hydrothermal corrosion resistance of the CVI-processed SiC phases containing amorphous SiC, resulting in a significant weight loss and reduction of hoop strength of the multi-layered SiC composite tubes after corrosion. [ABSTRACT FROM AUTHOR]

SiC nanoparticles reinforced magnesium matrix composite was fabricated by ultrasonic vibration assisted squeeze casting. Since ultrasonic device could meet the use requirements according to theoretic calculation, uniform dispersion of SiC nanoparticles was expected to achieve. The grains of the composite were refined compared with the AZ91 alloy, which was related to the increase of nucleation sites during solidification and Zenner pinning effect caused by SiC nanoparticles. With increasing the ultrasonic power, grain size of the composite changed no obviously while the morphology of β-Mg17Al12 phase was significantly affected. The ultimate tensile strength, yield strength, and elongation to fracture of the composites fabricated under different ultrasonic powers were simultaneously improved compared with the AZ91 alloy. The increase of yield strength could be attributed to Hall-Petch strengthening and Orowan strengthening for the present composites. Theoretical value of the yield strength obtained by the square root method was close to the experimental value. [ABSTRACT FROM AUTHOR]

Characterisation of membranes produced for use as micro-electro-mechanical systems using vibrational techniques can give a measure of their behaviour and suitability for operation in different environments. Two membranes are studied here: germanium (Ge) and cubic silicon carbide (3C-SiC) on a silicon (Si) substrate. When driven at higher displacements, the membranes exhibit self-protecting behaviour. The resonant vibration amplitude is limited to a maximum value of around 10 nm, through dissipation of energy via higher harmonic vibrations. This is observed for both materials, despite their different Young's moduli and defect densities. [ABSTRACT FROM AUTHOR]

A three-dimensional kinetic Monte Carlo (KMC) model has been developed to study the step instability caused by nucleation during the step-flow growth of 3C-SiC. In the model, a lattice mesh was established to fix the position of atoms and bond partners based on the crystal lattice of 3C-SiC. The events considered in the model were adsorption and diffusion of adatoms on the terraces, attachment, detachment and interlayer transport of adatoms at the step edges, and nucleation of adatoms. Then the effects of nucleation on the instability of step meandering and the coalescence of both islands and steps were simulated by the model. The results showed that the instability of step meandering caused by nucleation was affected by the growth temperature. And the effects of nucleation on the instability was also analyzed. Moreover, the surface roughness as a function of time for different temperatures was discussed. Finally, a phase diagram was presented to predict in which conditions the effects of nucleation on step meandering become significant and the three different regimes, the step-flow (SF), 2D nucleation (2DN), and 3D layer by layer (3DLBL) were determined. [ABSTRACT FROM AUTHOR]

The effects of the size of micron SiC particle (SiCp) on the grain refinement, distribution of particle and tensile properties of as-cast AZ31B (Mg-3Al-1Zn-0.3Mn) magnesium matrix composites have been investigated. As the volume fraction of micron SiCp increases to 15 vol%, excellent grain refinement is achieved. Meanwhile, volume fraction of particle is set as same content, grain size of matrix decreases as the size of micron SiCp decreases. This is due to both the uniform distribution and refining effect of the fine particles. The micron SiCp distributes along the grain boundaries. Because of grain refinement strengthening and ceramic phase strengthening effects, the room temperature tensile property of M5-15 has the optimal value of YS 171MPa-UTS 216MPa-EL 0.87 %. [ABSTRACT FROM AUTHOR]

An edge termination method, referred to as guard-ring-assisted multistep junction termination extension (MS-GR-JTE), is presented for ultrahigh voltage silicon carbide (SiC) power devices. In comparisonwith other JTEs, the MS-GR-JTE creates a step electric field (EF) distribution with greatly reduced peak EF at the corners and edges of the device, resulting in a superior breakdown voltage (BV) performance with wide tolerances to JTE dose and SiC surface charges. According to the numerical simulations based on a 100- \mu \textm -thick epilayer, an optimized MS-GR-JTE shows that the 15-kV BV performance with wide tolerances of 1.3\times 10^12 cm ^-2 to JTE dose and 6.1\times 10^12 cm ^-2 to positive surface charges are obtained, respectively, both superior to other compared JTEs. [ABSTRACT FROM AUTHOR]

We use hybrid-functional density functional theory to study the role of oxygen vacancies in negative bias-and-temperature stress-induced threshold voltage instability in 4H-silicon carbide power MOSFETs. According to our model, certain originally electrically “inactive” oxygen vacancies are structurally transformed into electrically “active” defects in the presence of strong negative bias and temperature. These newly generated defect configurations function as short-lived or long-lived switching oxide hole traps. The transients of their generation process are shown to correlate well with the measured “short-term” threshold voltage instability. Additionally, we show that the long-lived defects continue to degrade the room-temperature reliability of these devices even after stress removal. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to present the results of measurements and calculations illustrating mutual thermal coupling between power Schottky diodes made of silicon carbide situated in the common case.Design/methodology/approach The idea of measurements of mutual transient thermal impedances of the investigated device is described.Findings The results of measurements of mutual transient thermal impedances between the considered diodes are shown. The experimentally verified results of calculations of the internal temperature waveforms of the considered diodes obtained with mutual thermal coupling taken into account are presented and discussed. The influence of mutual thermal coupling and a self-heating phenomenon on the internal temperature of the considered diodes is pointed out.Research limitations/implications The presented methods of measurements and calculations can be used for constructing the investigated diodes made of other semiconductor materials.Originality/value The presented results prove that mutual thermal coupling between diodes mounted in the common case must be taken into account to calculate correctly the waveforms of the device internal temperature. [ABSTRACT FROM AUTHOR]

Raman spectroscopy has been increasingly used, in recent years, to characterize irradiated materials, in particular silicon carbide. The interpretation of the spectra is nevertheless problematic. In this paper, we provide a first step toward a more quantitative interpretation, by providing first-principles calculations of Raman intensities for various polytypes of silicon carbide (SiC) and for point defects in cubic SiC. We consider here, as benchmarks, the carbon antisite, CSi, and the doubly charged carbon vacancy/carbon antisite complex, VCCsi+2. We show that some care is necessary to understand the contribution of point defects on the Raman spectrum of the material, due to supercell size effects. [ABSTRACT FROM AUTHOR]

An optimized tradeoff between blocking voltage and specific ON-resistance for 4H-silicon carbide power vertical double-implanted metal–oxide–semiconductor field-effect transistor (DMOSFET) is exclusively obtained as a function of doping concentration in the drift region. Based on a novel analytical model of the electric field in the gate oxide of 4H-SiC DMOSFETs, we propose a closed-form equation of the Junction FET (JFET) region width and the drift thickness as function of doping concentration without using fitting and empirical parameters to obtain the maximum figure of merit. Model results are successfully verified with TCAD numerical simulations, covering a wide range of device performances, and experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a ground fast cooling simulation device is designed for the thermal testing of the materials and parts on high speed flight vehicles. Experimental investigation is performed to validate the effectiveness of the design and feasibilities of 4 different cooling techniques with both Ti alloy and C/SiC test pieces. The results show that air impingement cooling is the most feasible cooling method because it offers high cooling rates and it’s compatible with Ti alloy and C/SiC. LN and water jet impingement cooling prove to be unfeasible mainly due to the uncontrollability and destruction of thermocouples, respectively. Water spray cooling, however, is found to be feasible only for Ti alloy test pieces and destructions of C/SiC test pieces are observed after the experiment. Based on SEM images of the microstructure, oxidation effects of water spray cooling on C/SiC are briefly analyzed. [ABSTRACT FROM AUTHOR]

Al/SiC-reinforced metal matrix composite is widely used in weight-sensitive applications such as portable and integrated circuit devices. The presence of SiC particles in aluminum alloys enhances material properties like thermal conductivity, density, and tensile strength. Reinforced aluminum matrix composite can be welded by friction stir welding (FSW) process. This investigation mainly focuses on optimizing the welding parameters of friction stir welded AA7075 with SiC reinforcement particle. The welding parameters considered are spindle speed, travelling speed, downward force, and percentage of SiC added to AA7075. The experiments are designed using response surface methodology (RSM). The responses considered are ultimate tensile strength and percentage elongation. Regression models are developed for the single responses and the results are analyzed using analysis of variance. Fuzzy grey relational analysis approach is then used to optimize the FS welding parameters by considering multiresponses. Highest grey fuzzy reasoning grade is obtained at a tool rotational speed of 1150 rpm, welding speed of 40 mm/min, axial force of 6 kN, and percentage of reinforcement of 20 wt% of SiC. The analysis using ANOVA for multiresponse case clearly indicates that the percentage of reinforcement is the most predominant parameter which requires more attention. [ABSTRACT FROM AUTHOR]

An experimental analysis of the behavior under short-circuit conditions of three different silicon-carbide (SiC) 1200-V power devices is presented. It is found that all devices take up a substantial voltage, which is favorable for detection of short circuits. A transient thermal device simulation was performed to determine the temperature stress on the die during a short-circuit event, for the SiC MOSFET. It was found that, for reliability reasons, the short-circuit time should be limited to values well below Si IGBT tolerances. Guidelines toward a rugged design for short-circuit protection (SCP) are presented with an emphasis on improving the reliability and availability of the overall system. A SiC device driver with an integrated SCP is presented for each device-type, respectively, where a short-circuit detection is added to a conventional driver design in a simple way. The SCP driver was experimentally evaluated with a detection time of 180 ns. For all devices, short-circuit times well below 1 \upmu\texts were achieved. [ABSTRACT FROM AUTHOR]

Silicon (Si) insulated-gate bipolar transistors (IGBTs) are widely used in power converters. Silicon carbide (SiC) technology will push the limits of switching devices in three directions: higher blocking voltage, higher operating temperature, and higher switching speed. The first SiC–metal–oxide–semiconductor field-effect transistor (MOSFET) half-bridge modules (SiC HBM) are now commercially available and look promising. Although they are still limited in breakdown voltage, these components should, for instance, improve traction-chain efficiencies. In particular, a significant reduction in switching losses is to be expected which should lead to improvements in power-to-weight ratios—of particular interest for rolling-stock. Nevertheless, because of the high switching speed and the high current levels required by traction applications, the implementation of these modules is critical. In this paper, the authors investigate the parallel connection of SiC HBM with a focus on traction equipment. The key points are underlined and an original approach is proposed to design the bus-bar and the gate-drive circuit. Experimental results performed on an opposition method test bench, valid the correct operation of three SiC modules in parallel. [ABSTRACT FROM AUTHOR]

Investigating stressed oxidation and scale crystallization kinetics of advanced SiC fibers at elevated temperature in steam is a challenging yet essential undertaking for the assessment of the effects of oxidation on mechanical properties of SiC-SiC ceramic matrix composites (CMCs). Moisture in the oxidizing environment is known to change oxidation rates, reduce scale viscosity and lower temperatures for scale crystallization. In order to study these phenomena, a facility for testing SiC fiber tows in creep at elevated temperatures in air, in steam and in steam saturated with silicic acid was developed. The newly constructed test facility was validated through creep testing of Hi-Nicalon?-S fibers at 800°C in steam saturated with silicic acid. Testing in saturated steam resulted in formation of a uniform oxide scale. Details of the test facility design, development and experimental validation are presented. [ABSTRACT FROM AUTHOR]

In this paper, the comparison of cyclic hysteresis behavior between cross-ply C/SiC and SiC/SiC ceramic-matrix composites (CMCs) has been investigated. The interface slip between fibers and the matrix existed in the matrix cracking mode 3 and mode 5, in which matrix cracking and interface debonding occurred in the 0° plies are considered as the major reason for hysteresis loops of cross-ply CMCs. The hysteresis loops of cross-ply C/SiC and SiC/SiC composites corresponding to different peak stresses have been predicted using present analysis. The damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire matrix cracking modes of the composite, and the hysteresis dissipated energy increase with increasing peak stress. The damage parameter and hysteresis dissipated energy of C/SiC composite under low peak stress are higher than that of SiC/SiC composite; However, at high peak stress, the damage extent inside of cross-ply SiC/SiC composite is higher than that of C/SiC composite as more transverse cracks and matrix cracks connect together. [ABSTRACT FROM AUTHOR]

Wire saws with fixed diamond abrasive are often used to cut hard and brittle materials owning to the wire saw's narrow keif, low cutting force, and minimal material waste. Typically, the cutting force changes during the operation since the part diameter and the contact length between the wire saw and part (i.e., contact length) continuously change, even if the process parameters (i.e., wire saw velocity, part feed rate, part rotation speed, and wire saw tension) are fixed, leading to wire saw breakage, wafer collapse, and inferior surface roughness. This study addresses this issue by regulating the force via feedback control. The most significant process parameter affecting the normal force, namely, part feed rate, is taken as the control variable. A system identification routine is used to obtain the transfer function relating the normal force and commanded part feed rate and the model parameters are identified online. An adaptive force controller is designed, and simulation and experimental studies for SiC monocrystal wafer wire saw machining are conducted. The results show the dynamic model well characterizes the normal force generated when wire saw machining SiC monocrystal, and the adaptive controller can effectively track various normal reference force trajectories (i.e., constants, ramps, and sine waves). The experimental results demonstrate that the wire saw machining process with adaptive force control can improve the cutting productivity and significantly decrease wafer surface roughness as compared to the cutting process with a constant part feed rate. [ABSTRACT FROM AUTHOR]

Two symmetrically nonequivalent silicon carbide (SiC) substrate orientations, (0001) Si-terminated and $$(000\overline{1} )$$ C-terminated, were used in the physical vapour transport growth of bulk aluminium nitride (AlN) single crystals. The crystals grown on Si-faces always exhibit an Al-polar growth surface. AlN growth on $$(000\overline{1} )$$ C-terminated surfaces of the SiC substrates was performed to obtain N-polar growth surfaces. An abrupt interface was observed between the AlN crystal and the C-face substrate which is in contrast to the growth on Si-faces where hexagonally shaped SiC hillocks are formed. The growth on C-faces is usually dominated by multi-site nucleation. Applying similar supersaturation conditions that led to step-flow growth on Si-faces to the C-faces resulted in a spiral growth mode, even on highly off-oriented substrates. The obtained broad X-ray diffraction rocking curves of such samples (full-width at half-maximum ≈380 arcsec) indicate the presence of more misfit dislocations and significant misfit stress. In addition, polarity inversion is observed in C-face grown crystals. Though the structural properties of the crystals grown on C-face are inferior to that of the crystals grown on Si-face, the incorporation of unintentional Si impurity was found to be lower (<2 wt%). [ABSTRACT FROM AUTHOR]

In this paper, we discuss silicon carbide (SiC) ceramics as potential materials for biomedical applications. SiC samples were prepared without addition of undesired elements that might have adverse health effect and were characterized with respect to mechanical and magnetic properties, bioactivity, wetting behavior, and release of ions. The materials characteristics are compared to those for Ti6Al4V alloy. Among the examined ceramics, SiC with MgO as sintering aid met the expectation to the greatest extent. Elastic modulus of the material with 24 % porosity is 80 GPa, flexural strength 180 MPa, and fracture toughness ~3 MPa m. The material shows good wetting properties and is weakly diamagnetic. On the other hand, bioactivity estimated on the basis of hydroxyapatite formation in simulated body fluid is only achieved by surface modification. Thus, although SiC ceramics show potential for use in biomedical applications, it should be further developed to meet the requirements. [ABSTRACT FROM AUTHOR]

A performance comparison of an interleaved boost converter (IBC) using Si and SiC diodes for photovoltaic (PV) energy conversion systems is presented in this paper. The performance attributes under investigation include the semiconductor device behavior, thermal requirement, system efficiency, and power density. The IBC is designed to sustain the dc-link voltage in the energy conversion system and to provide the maximum power point tracking in the PV system. Due to the absence of reverse recovery current in SiC Schottky diodes, low switching losses are generated in diodes and switches. This benefit results in a higher system efficiency and smaller cooling system design requirement. As a benefit, the volume and weight of the heatsink can be further reduced. Furthermore, behaviors of the power semiconductors, which will impact the performance in the system, are discussed in the paper. The validity of the analysis is confirmed experimentally with a 2.5-kW IBC prototype with relatively wide power and input voltage operating range. The overall performance of the IBC prototype using Si and SiC diodes is summarized in a table for easy comparison. [ABSTRACT FROM AUTHOR]

In this study, the microstructure and Vickers indentation fracture toughness ( VIF fracture toughness) of three different types of silicon carbide ( SiC) coatings (stoichiometric SiC, SiC with excess silicon and SiC with excess carbon) were investigated. SiC coatings were produced on tri-isotropic fuel particles by fluidized bed chemical vapor deposition ( FBCVD). The microstructure was investigated using a scanning electron microscope ( SEM) and X-ray diffraction, while a transmission electron microscope was used for the analysis of defects and micro-cracks. The VIF fracture toughness was measured using Vickers indentation. The fracture beneath the indenter consists of Palmqvist cracks as observed using SEM. Based on this crack mode, VIF fracture toughness values of 3.51, 4.03, and 4.93 MPa·m1/2 for stoichiometric, extra- C and extra- Si SiC coatings were obtained, respectively. It was found that stress-induced micro-cracks seem to be a mechanism for the fracture behavior, which gave SiC coatings with high VIF fracture toughness. The difference in the VIF fracture toughness of FBCVD SiC coatings is discussed in terms of defects and grain morphology. [ABSTRACT FROM AUTHOR]

Charge injection and transportation process is a fundamental problem to Si nanocrystals (Si-ncs) based electric and photonic devices. In the manuscript, a single layer of Si-ncs sandwiched by amorphous Si carbide (a-SiC) was prepared by excimer laser annealing of a-SiC/a-Si/a-SiC multilayers, and the charging effect was then characterized by Kelvin probe force microscopy (KPFM) on the microscopic scale. Opposite charges were injected into Si-ncs through the biased tip and formed a core-ring or up-down shaped distribution. The decay characteristics showed that these opposite charges would not only vertically tunnel through the bottom a-SiC layer to substrate but also laterally transport and recombine with each other driven by the attractive Coulomb force. Besides, the charge retention time was also found dependent on the injection biases, which is tentatively ascribed to the charge trapping by the Si-ncs/a-SiC interface states under high bias scanning. The analysis was further supported by conductive atomic force microscopy (CAFM) measurement, in which the current-voltage curves gradually shifted during the repetition test, probably because of bias screening by the trapped charges at these interface states. [ABSTRACT FROM AUTHOR]

The cubic form of SiC (β- or 3C-) compared to the hexagonal α-SiC polytypes, primarily 4H- and 6H–SiC, has lower growth cost and can be grown heteroepitaxially in large area silicon (Si) wafers which makes it of special interest. This in conjunction with the recently reported growth of improved quality 3C–SiC, make the development of devices an imminent objective. However, the readiness of models that accurately predict the material characteristics, properties and performance is an imperative requirement for attaining the design and optimization of functional devices. The purpose of this study is to provide and validate a comprehensive set of models alongside with their parameters for bulk 3C–SiC. The validation process revealed that the proposed models are in a very good agreement to experimental data and confidence ranges were identified. This is the first piece of work achieving that for 3C–SiC. Considerably, it constitutes the necessary step for finite element method simulations and technology computer aided design. [ABSTRACT FROM AUTHOR]

The presence of carbon atoms in silicon carbide and diamond makes these materials ideal candidates for direct fast neutron detectors. Furthermore the low atomic number, strong covalent bonds, high displacement energies, wide bandgap and low intrinsic carrier concentrations make these semiconductor detectors potentially suitable for applications where rugged, high-temperature, low-gamma-sensitivity detectors are required, such as active interrogation, electronic personal neutron dosimetry and harsh environment detectors. A thorough direct performance comparison of the detection capabilities of semi-insulating silicon carbide (SiC–SI), single crystal diamond (D–SC), polycrystalline diamond (D–PC) and a self-biased epitaxial silicon carbide (SiC–EP) detector has been conducted and benchmarked against a commercial silicon PIN (Si–PIN) diode, in a wide range of alpha (Am-241), beta (Sr/Y-90), ionizing photon (65 keV to 1332 keV) and neutron radiation fields (including 1.2 MeV to 16.5 MeV mono-energetic neutrons, as well as neutrons from AmBe and Cf-252 sources). All detectors were shown to be able to directly detect and distinguish both the different radiation types and energies by using a simple energy threshold discrimination method. The SiC devices demonstrated the best neutron energy discrimination ratio (( MeV)/( MeV)  ≈5), whereas a superior neutron/photon cross-sensitivity ratio was observed in the D–PC detector ((AmBe)/(Co-60)  ≈16). Further work also demonstrated that the cross-sensitivity ratios can be improved through use of a simple proton-recoil conversion layer. Stability issues were also observed in the D–SC, D–PC and SiC–SI detectors while under irradiation, namely a change of energy peak position and/or count rate with time (often referred to as the polarization effect). This phenomenon within the detectors was non-debilitating over the time period tested (5 h) and, as such, stable operation was possible. Furthermore, the D–SC, self-biased SiC–EP and semi-insulating SiC detectors were shown to operate over the temperature range °C to °C. [ABSTRACT FROM AUTHOR]