The production and industrial use of asbestos cement and other asbestos-containing materials have been restricted in most countries because of the potential detrimental effects on human health and the environment. Chrysotile is the most common form of asbestos and investigations into how to recycle this serpentine phyllosilicate mineral have attracted extensive attention. Chrysotile asbestos tailings can be transformed thermally, at high temperature, by in situ carbothermal reduction (CR). The CR method aims to maximize use of the chrysotile available and uses high temperatures and carbon to change the mineral form and structure of the chrysotile asbestos tailings. When chrysotile asbestos is employed as the raw material and coke (carbon) powder is used as the reducing agent for CR transformation, stable, high-temperature composites consisting of forsterite, stishovite, and silicon carbide are formed. Forsterite (Mg2SiO4) was the most abundant crystalline phase formed in samples heat treated below 1500ºC. At 1600ºC, forsterite was exhausted through decomposition and β-SiC formed by reduction of stishovite. A larger proportion of β-SiC was generated as the carbon content was increased. This research revealed that both temperature and carbon addition play key roles in the transformation of chrysotile asbestos tailings.

The 4H-SiC crystal is found to have great potential in terahertz generation via nonlinear optical frequency conversion due to its extremely high optical damage threshold, wide transparent range, etc. In this paper, optical rectification (OR) with tilted-pulse-front (TPF) setting based on the 4H-SiC crystal is proposed. The theory accounts for the optimization of incident pulse pre-chirping in the TPF OR process under high-intensity femtosecond laser pumping. Compared with the currently recognized LiNbO3-based TPF OR, which generates a single-cycle terahertz pulse within 3 THz, 4H-SiC demonstrates a significant advantage in producing ultra-widely tunable (up to over 14 THz, TPF angle 31°–38°) terahertz waves with high efficiency (~10–2) and strong field (~MV/cm). Besides, the spectrum characteristics, as well as the evolution from single- to multi-cycle terahertz pulses can be modulated flexibly by pre-chirping. The simulation results show that 4H-SiC enables terahertz frequency extending to an unprecedent range by OR, which has extremely important potential in strong-field terahertz applications.

This paper presents an investigation on micropipe evolution from hexagonal voids in physical vapor transport-grown 4H-SiC single crystals using the cathodoluminescence (CL) imaging technique. Complementary techniques optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy (EDS) are also used to understand the formation mechanism of hexagonal voids along with the origin of pipes from these voids. The ability of CL to image variations along the depth of the sample provides new insights on how micropipes are attached to hexagonal voids that lie deep within the bulk single crystals. CL imaging confirms that multiple micropipes can originate from a single hexagonal void. EDS mapping shows that the inside of the micropipe walls exhibits higher levels of carbon. Investigation of the seed region by optical imaging shows that improper fixing of the seed to the crucible lid is the root cause for the formation of hexagonal voids that subsequently lead to micropipe formation.

Silicon carbide (SiC) is ideally suitable as a sensor material in harsh environments. Despite the brittleness in the macroscopic scale, plasticity in SiC is observed at small component length-scales. Previous nanoindentation based study combining experiment and numerical approaches of single-crystal 6H-SiC has shown that slip activation is rather complex, and that non-basal slip could potentially dominate the plastic deformation behaviour. In this study, we investigated the local deformation response evolution of shear strain directly under and in the vicinity of the indenter tip. The results show the pyramidal slip families contribute significantly to the deformation process.

A promising candidate to initiate dust formation in oxygen-rich AGB stars is alumina (Al2O3) showing an emission feature around ∼13μm attributed to Al−O stretching and bending modes (Posch+99,Sloan+03). The counterpart to alumina in carbon-rich AGB atmospheres is the highly refractory silicon carbide (SiC) showing a characteristic feature around 11.3μm (Treffers74). Alumina and SiC grains are thought to represent the first condensates to emerge in AGB stellar atmospheres. We follow a bottom-up approach, starting with the smallest stoichiometric clusters (i.e. Al4O6, Si2C2), successively building up larger-sized clusters. We present new results of quantum-mechanical structure calculations of (Al2O3)n, n = 1−10 and (SiC)n clusters with n = 1−16, including potential energies, rotational constants, and structure-specific vibrational spectra. We demonstrate the energetic viability of homogeneous nucleation scenarios where monomers (Al2O3 and SiC) or dimers (Al4O6 and Si2C2) are successively added. We find significant differences between our quantum theory based results and nanoparticle properties derived from (classical) nucleation theory.

In this work, we compare the results of different Cliff–Lorimer (Cliff & Lorimer 1975) based methods in the case of a quantitative energy dispersive spectrometry investigation of light elements in ternary C–O–Si thin films. To determine the Cliff–Lorimer (C–L) k-factors, we fabricated, by focused ion beam, a standard consisting of a wedge lamella with a truncated tip, composed of two parallel SiO2 and 4H-SiC stripes. In 4H-SiC, it was not possible to obtain reliable k-factors from standard extrapolation methods owing to the strong CK-photon absorption. To overcome this problem, an extrapolation method exploiting the shape of the truncated tip of the lamella is proposed herein. The k-factors thus determined, were then used in an application of the C–L quantification procedure to a defect found at the SiO2/4H-SiC interface in the channel region of a metal-oxide field-effect-transistor device. As in this procedure, the sample thickness is required, a method to determine this quantity from the averaged and normalized scanning transmission electron microscopy intensity is also detailed. Monte Carlo simulations were used to investigate the discrepancy between experimental and theoretical k-factors and to bridge the gap between the k-factor and the Watanabe and Williams ζ-factor methods (Watanabe & Williams, 2006).

Nonconductive specimens for scanning electron microscopy or X-ray microanalysis are coated with conductive carbon in order to reduce charging. But carbon film absorbs X-ray fluxes causing errors in measuring chemical composition. Especially when the carbon content is measured, carbon coating not only blocks X-rays but also becomes a source of carbon X-rays. It is thus necessary to determine how much errors are induced by carbon coating, and how thick coating is allowed for the accurate measurement. In this study, quantitative analysis of carbon on silicon carbide with carbon coating films was attempted by electron probe microanalyzer. It was found that measured carbon content increased in a nonlinear manner up to 40% with a film thickness, whereas silicon content decreased slightly. Carbon X-ray intensity was determined by computer simulation, which increased in a linear manner with the thickness. The discrepancy was due to a nucleation and growth of islands and thus a change of density with a thickening of coating film.

In this work, the interactions between tungsten (W) and silicon carbide (SiC) in SigmaTM SiC fibers at high temperatures were characterized using scanning and transmission electron microscopy. These fibers could have the potential for use in fusion-related applications owing to their high thermal conductivity compared with pure SiC-based fibers. The as-received fibers were composed of a 100-μm-thick shell of radially textured β-SiC grains and a 15-μm-thick tungsten core, composed of a few hundreds of nm-sized elongated tungsten grains. The interfaces between the tungsten and the SiC and the SiC and the outer coatings were sharp and smooth. After heat treatment at 1,600°C for 3 h in Ar, the tungsten core reacted with SiC to form a rough interface surface. Inside the core, W5Si3, W3Si, and W2C phases were detected using energy-dispersive X-ray spectroscopy and electron-diffraction techniques. The mechanical properties of the fibers deteriorate after the heat treatment.

In this article, the biofunctionalization of 6H–SiC (0001) surfaces via self-assembled monolayers (SAMs) has been studied as a means to modify the in vitro biocompatibility of this semiconductor substrate with H4 (human neuroglioma) and PC12 (rat pheochromocytoma) cells. Silanization with aminopropyldiethoxymethylsilane (APDEMS) and aminopropyltriethoxysilane (APTES), which provided moderately hydrophilic surfaces, and alkylation with 1-octadecene that produced hydrophobic surfaces were used to control the 6H–SiC surface chemistry and evaluate changes in cell viability and morphology due to these surface modifications. The morphology of the cells was evaluated with atomic force microscopy. In addition, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to quantitatively evaluate the cell viability on the SAM-modified surfaces. In all cases, the cell proliferation was observed to improve with respect to untreated 6H–SiC surfaces, with up to a 2x increase in viability on the 1-octadecene-modified surfaces, up to 6x increase with APDEMS-modified surfaces, and up to 8x increase with APTES-modified surfaces. This proves the potential of SiC as a substrate for medical devices given the possibility to tailor its surface chemistry for specific applications.

Silicon carbide (SiC) detectors were used to analyze the multi-MeV ions of the plasma produced by irradiation of various targets with a 300-ps laser at intensity of 1016 W/cm2. The SiC detectors were realized by fabricating Schottky diodes on 80 μm epitaxial layer. The low dopant concentration and defect density of the epilayer allowed the realization of good performance detectors. The use of SiC detectors ensures the cutting of the visible and soft ultraviolet radiation emitted from plasma enhancing the sensitivity to very fast ions. The time-of-flight spectra obtained by irradiating different targets show a peak associated to protons and various peaks relative to different charge states of ions. Processing of the experimental data allows to estimate the energies of the protons and of the different ions emitted from laser-induced plasma. The SiC detector results are compared with the ones obtained by Ion Collector and a Thomson Parabola spectrometer.

The mm-wave as well as avalanche noise properties of IMPATT diode at D-band are efficiently estimated, with different poly-types of silicon carbide (SiC) and GaN as base materials, using advanced computer simulation techniques developed by the authors. The breakdown voltage of 4H-SiC (180 V) is more than the same for 6H-SiC, ZB- and Wz-GaN-based diode of 170,158, and 160 V, respectively. Similarly, the efficiency (14.7%) is also high in the case of 4H-SiC as compared with 6H-SiC and GaN-based diode. The study indicates that 4H-SiC IMPATT diode is capable of generating high RF power of about 8.38 W as compared with GaN IMPATT diode due to high breakdown voltage and negative resistance for the same frequency of operation. It is also observed that Wz-GaN exhibits better noise behavior 7.4 × 10−16 V2 s than SiC (5.16 × 10−15 V2 s) for IMPATT operation at 140 GHz. A comparison between the power output and noise from both the device reveals that Wz-GaN would be a suitable base material for high-power application of IMPATT diode with moderate noise.

We discuss continuing materials technology improvements that have transformed silicon carbide from an intriguing laboratory material into a premier manufacturable semiconductor technology. This advancement is demonstrated by reduced micropipe densities as low as 0.22 cm−2 on 3-in.-diameter conductive wafers and 16 cm−2 on 100-mm-diameter conductive wafers. For high-purity semi-insulating materials, we confirm that the carbon vacancy is the dominant deep-level trapping state, and we report very consistent cross-wafer activation energies derived from temperature-dependent resistivity.Warm-wall and hot-wall SiC epitaxy platforms are discussed in terms of capability and applications. Specific procedures that essentially eliminate forward-voltage drift in bipolar SiC devices are presented in detail.

The recent discovery of forward-voltage degradation in SiC pin diodes has created an obstacle to the successful commercialization of SiC bipolar power devices. Accordingly, it has attracted intense interest around the world. This article summarizes the progress in both the fundamental understanding of the problem and its elimination.The degradation is due to the formation of Shockley-type stacking faults in the drift layer, which occurs through glide of bounding partial dislocations. The faults gradually cover the diode area, impeding current flow. Since the minimization of stress in the device structure could not prevent this phenomenon, its driving force appears to be intrinsic to the material. Stable devices can be fabricated by eliminating the nucleation sites, namely, dissociated basal-plane dislocations in the drift layer.Their density can be reduced by the conversion of basal-plane dislocations propagating from the substrate into threading dislocations during homoepitaxy.

After substantial investment in research and development over the last decade, silicon carbide materials and devices are coming of age. The concerted efforts that made this possible have resulted in breakthroughs in our understanding of materials issues such as compensation mechanisms in high-purity crystals, dislocation properties, and the formation of SiC/SiO2 interfaces, as well as device design and processing. The progress accomplished over the last eight years in SiC-based electronic materials is summarized in this issue of MRS Bulletin.

Silicon carbide power field-effect transistors, including power vertical-junction FETs (VJFETs) and metal oxide semiconductor FETs (MOSFETs), are unipolar power switches that have been investigated for high-temperature and high-power-density applications. Recent progress and results will be reviewed for different device designs such as normally-OFF and normally-ON VJFETs, double-implanted MOSFETs, and U-shaped-channel MOSFETs. The advantages and disadvantages of SiC VJFETs and MOSFETs will be discussed. Remaining challenges will be identified.

Silicon carbide is a promising semiconductor for advanced power devices that can outperform Si devices in extreme environments (high power, high temperature, and high frequency). In this article, we discuss recent progress in the development of passivation techniques for the SiO2/4H-SiC interface critical to the development of SiC metal oxide semiconductor field-effect transistor (MOSFET) technology. Significant reductions in the interface trap density have been achieved, with corresponding increases in the effective carrier (electron) mobility for inversion-mode 4H-SiC MOSFETs. Advances in interface passivation have revived interest in SiC MOSFETs for a potentially lucrative commercial market for devices that operate at 5 kV and below.

Significant progress has been made in the development of SiC metal semiconductor field-effect transistors (MESFETs) and monolithic microwave integrated-circuit (MMIC) power amplifiers for high-frequency power applications. Three-inch-diameter high-purity semi-insulating 4H-SiC substrates have been used in this development, enabling high-volume fabrication with improved performance by minimizing surface- and substrate-related trapping issues previously observed in MESFETs. These devices exhibit excellent reliability characteristics, with mean time to failure in excess of 500 h at a junction temperature of 410°C. A sampling of these devices has also been running for over 5000 h in an rf high-temperature operating-life test, with negligible changes in performance. High-power SiC MMIC amplifiers have also been demonstrated with excellent yield and repeatability. These MMIC amplifiers show power performance characteristics not previously available with conventional GaAs technology. These developments have led to the commercial availability of SiC rf power MESFETs and to the release of a foundry process for MMIC fabrication.

Impurity atom cluster and nanocrystal formation in Er-implanted hexagonal SiC were studied using TEM and HAADF-STEM. Short interstitial loops were initially observed to form in the as-implanted layers. After annealing at 1600°C extended matrix defects (wide interstitial loops and voids), Er atom clusters and nanocrystals grew. The wide interstitial loops act as strong sinks capturing diffusing dopants that gather first in lines, then planes, and finally in three-dimensional ErSi2 nanocrystals. The unstrained nanocrystals have a hill-like shape and only two polarity-dependent orientations with respect to the matrix. One-, two-, and three-dimensional Er atom clusters were also identified. For the case of Ge implantation, again the wide interstitial loops act as sinks for the implanted Ge, representing the seeds of the nanocrystal.

Gallium nitride films are grown by plasma-assisted molecular beam epitaxy (MBE) on 6H-SiC(0001) substrates with no miscut and with 3.5° miscuts in both the [1 0 0] and [1 1 0] directions. The hydrogen-etched substrates display straight or chevron shaped steps, respectively, and the same morphology is observed on the GaN films. X-ray rocking curves display substantially reduced width for films on the vicinal substrates compared to singular substrates, for the same Ga/N flux ratio used during growth.