SiC System Research Articles

Highly Efficient Optical Pumping of Spin Defects in Silicon Carbide for Stimulated Microwave Emission

Microwaves (MWs) are at the heart of many technologies, $e.g.$ for communication, timekeeping, remote sensing, and quantum information processing. Masers can boost faint MW signals quite nicely, but not under real-world conditions. The authors demonstrate efficient population inversion of optically pumped vacancy-related spins in SiC, at room temperature, and find realistic operating conditions for a SiC maser to serve as a continuous-wave amplifier. These spins can also be coherently coupled to superconducting cavities efficiently at cryogenic temperatures. These findings suggest this SiC system as a promising platform for MW photonics and quantum electronics.

Surface Metallization of SiC Ceramic by Mo-Ni-Si Coatings for Improving Its Wettability by Molten Ag

Abstract Three kinds of Mo-Ni-Si metallized coatings with various chemical compositions were deposited on SiC ceramic substrates by vacuum fusion sintering process, and the phase compositions of the coatings and their interface microstructures were analyzed. The wetting and spreading properties of molten Ag on the coated SiC ceramic substrates were investigated by the sessile drop technique, and the interfacial behavior of the Ag/coated SiC systems was analyzed. The results show that the coatings are mainly composed of Mo5Si3, MoSi2, Ni2Si, NiSi2 and MoNiSi. The tetragonal MoSi2 grains on the coating surface disappear gradually with the concentration of Mo increasing from 20 at% to 40 at%. The final contact angles of Ag/coated SiC systems at 1000 °C for holding 30 min are 45°, 79° and 85° for the coating compositions of Mo20-Ni32-Si48, Mo30-Ni28-Si42 and Mo40-Ni24-Si36, respectively. This result could be closely related to the interactions between the Ag drop and the microstructures of the three Mo-Ni-Si coatings. No obvious reaction layers are found at all the coating/substrate interfaces before and after the wetting tests.

Influences of surface polarity and Pd ion implantation on the wettability of Al-12Si(-2 Mg)/SiC systems

N-type 6H-SiC (0001) single crystals were implanted with 20 keV Pd ions at three doses of 5 × 1015, 5 × 1016 and 5 × 1017 ions/cm2 at room temperature. The wetting of SiC single crystal by molten Al-12Si and Al-12Si-2Mg were performed by using the sessile drop method in a high vacuum at 1323 K. The influences of surface polarity and Pd ion implantation on the wettability of Al-12Si(-2 Mg)/SiC systems were investigated. The experimental results showed that the equilibrium contact angles of molten Al-12Si and Al-12Si-2Mg on the C-terminated SiC were respectively lower than those on the Si-terminated SiC, which can be related to the formation of Al4C3 at the interface. The wettability of Al-12Si/C(Si)-terminated SiC systems was improved with the 2 wt% Mg addition due to the decrease of the solid-liquid surface energy (σSL) originated from the enhancement of interfacial interactions. Moreover, the equilibrium contact angles of Al-12Si/C(Si)-terminated SiC systems decreased more or less with the Pd implantation dose increasing, while those of Al-12Si-2Mg/C(Si)-terminated SiC systems gradually increased, which can be mainly attributed to the variation of interfacial interactions of Al-12Si(-Mg)/SiC systems.

Selective 6H-SiC White Light Emission by Picosecond Laser Direct Writing

Displaying a full or tuneable emission spectrum with highly efficient is significant for luminescent materials used in solid-state lighting. Silicon carbide (SiC) has potential for use in photoelectric devices that operate under extreme conditions. In this paper, we present a method to selectively modify the photoluminescence (PL) properties of SiC by ultrafast laser direct writing. Based on this method, visible white PL could be observed by the naked eye at room temperature under ultraviolet excitation. By increasing the laser power intensity from 40 to 80 MW/cm2, the PL of the irradiated samples increased and pure white sunlight-like emission with controlled colour temperature was realised. The optimised laser power intensity of 65 MW/cm2 achieved a desirable colour temperature similar to that of sunlight (x = 0.33, y = 0.33 and colour temperature of 5500 K) and suppressed blue emission. By direct laser irradiation along designed scanning path, a large-scale and arbitrary pattern white emission was fabricated. The origin of the white luminescence was a mixture of multiple luminescent transitions of oxygen-related centres that turned the Si-C system into silicon oxycarbide. This work sheds light on new luminescent materials and a preparation technique for next-generation lighting devices.

Confined Li ion migration in the silicon-graphene complex system: An ab initio investigation

Silicon-Carbon complex systems play an important role in enhancing the performance of Si-based anode materials for Li ion batteries. In this work, the Li migration property of the Silicon-Graphene (Si-Gr) complex systems are investigated by using first-principles calculations. Especially, the effects of graphene coating on the migration of Li ions are discussed in detail. The distance between Si surface and graphene in the Si-Gr system significantly affects the lateral migration of Li ions. With the decrease of the distance from 4.715 to 3.844 Å, the energy barrier of Li ion migration also decreases from 0.115 to 0.067 eV, which are all lower than that of the case without graphene d(0.135 eV). However, smaller distance (3.586 Å) brings the high energy barrier (0.237 eV). Through AIMD calculations, it is found that the graphene coating in the Si-Gr complex system would result in the larger intercalation depths, more uniform distributions, and higher migration coefficients of Li ions. Further calculations of migration coefficients of Li ions at different temperature are used to obtained the activation energy for Li ions migration in the Si-Gr system, which is as low as 0.028 eV. This low activation energy shows that it is easy for Li ions migrating in the Si-Gr system. Our study provided the basically information to understand the migration mechanism of Li ions in Si-C system.

Особливості фазо- та структуроутворення при реакційному гарячому пресуванні композитів системи ZrB$_2$–SiC

Особливості фазо- та структуроутворення при реакційному гарячому пресуванні композитів системи ZrB$_2$–SiC

Magnetic properties of nonmetal doped SiC monolayer: Density functional calculations

The structural, electronic and magnetic properties of doped SiC monolayer with a series of nonmetal atoms, including B, Cl, F, N, and O, are systematically investigated using first-principles calculations. Nonmagnetic behavior shows in the B and O-doped systems. The magnetism has been observed in the cases of Cl, F, and N, which is originated from the 2p (3p) electrons of F/N (Cl) and its neighboring C 2p states. Meanwhile, these nonmetal elements can induce impurity channels around Fermi level (EF), which reduce band gap of the systems. It implies that the B- and O-doped SiC monolayers tune into narrow gap semiconductors without magnetic character. The X-doped (X=B, Cl, F, N, and O) SiC systems are promising candidates for spintronic devices in the future.

Over-the-air in-band full-duplex system with hybrid RF optical and baseband digital self-interference cancellation

In this paper, we propose a hybrid analog optical self-interference cancellation (OSIC) and baseband digital SIC (DSIC) system for over-the-air in-band full-duplex (IBFD) wireless communication. Analog OSIC system is based on optical delay line, electro-absorption modulation lasers (EMLs) and balanced photodetector (BPD), which has the properties of high adjusting precision and broad processing bandwidth. With the help of baseband DSIC, the cancellation depth limitation of OSIC can be mitigated so as to achieve deeper total SIC depth. Experimental results show about 20-dB depth by OSIC and 10-dB more depth by DSIC over 1GHz broad baseband, so that the signal of interest (SOI) overlapped by wideband self-interference (SI) signal is better recovered compared to the IBFD system with OSIC or DSIC only. The hybrid of OSIC and DSIC takes advantages of the merits of optical devices and digital processors to achieve deep cancellation depth over broad bandwidth.

Functionally graded ceramic material prepared by spark plasma sintering (SPS)

A procedure for preparing a functionally graded material in the high-temperature ceramic–SiC system with step composition variation profile is considered. Five-layer samples of a functionally graded material (layer arrangement: 100, 75, 50, 25, and 0 vol % high-temperature ceramic) were prepared by spark plasma sintering. No cracks and no delamination were observed in the samples after thermal cycling in an oxidizing atmosphere at 1400 and 1600°С. A study of the properties and heat resistance of the ceramic functionally graded material revealed its high quality at relatively low density; i.e., spark plasma sintering shows promise as a procedure for preparing this material.

Vaporization and condensation in the Al4C3-SiC system

Al4SiC4 is a refractory ceramic with a reported band gap of about 2.5eV, making it an interesting semiconductor material for various applications in the field of energy. However, the synthesis of Al4SiC4 single crystals has so far not been investigated. In this study, the sublimation growth method is explored as a potential route for getting high quality single crystals. Combining a thermodynamic analysis with an extensive experimental approach, the vaporization and condensation phenomena in the Al4C3 – SiC system are described. Experimental conditions, such as initial composition, baking temperature and temperature gradient, are investigated and demonstrated regarding the crystallization of Al4SiC4. From the results obtained, a condensed phase diagram at equilibrium is established for the molar fraction XAl4C3/(Al4C3+SiC)<0.5, which corresponds to the suitable condition for the Al4SiC4 condensation. Indeed, Al4SiC4 single phase could be experimentally condensed either by self-nucleation or as oriented film on SiC substrates.

Key experiments and challenging thermodynamic modeling of the Li-Si-C system

The phase equilibria and thermodynamic properties of the ternary Li-Si-C system are crucial for developing new anode materials containing Si and/or C for Li-ion batteries. We carried out the long time annealing experiments and confirmed the key three-phase equilibrium of βLi2C2+SiC + Li7Si3 at 630 °C–650 °C. A consistent thermodynamic description of the Li-Si-C ternary system has been constructed based on the recently published Li-Si system, and the Li-C and Si-C binary systems that we revised in this work. The revision requires a more negative Gibbs energy for the αLi2C2 and βLi2C2 phases in the Li-C system, and a more positive Gibbs energy for the SiC phase in the Si-C system. The more negative Gibbs energy of the βLi2C2 phase requires an associate solution model to be introduced for the liquid phase. Calculated partial pressures from the revised thermodynamic description of the Li-C binary system show better agreement with the experimental data. The calculated phase diagram sections of the Li-Si-C ternary system are not only in good agreement with the key annealing experiment results, but also with differential scanning calorimetry results.

Electronic structure and magnetic properties of (Cu, N)-codoped 3C-SiC studied by first-principles calculations**Project supported by the Higher School Science Research Outstanding Youth Fund Project of Ningxia, China (Grant No. NGY2015049).

The electronic structures and magnetic properties of the Cu and N codoped 3C-SiC system have been investigated by the first-principles calculation. The results show that the Cu doped SiC system prefers the anti-ferromagnetic (AFM) state. Compared to the Cu doped system, the ionicities of C–Cu and C–Si in Cu and N codoped SiC are respectively enhanced and weakened. Especially, the Cu and N codoped SiC systems favor the ferromagnetic (FM) coupling. The FM interactions can be explained by virtual hopping. However, higher N concentration will weaken the ferromagnetism. In order to keep the FM interaction, the N concentration should be restricted within 9.3% according to our analysis.

Bonding-restricted structure search for novel 2D materials with dispersed C2 dimers.

Currently, the available algorithms for unbiased structure searches are primarily atom-based, where atoms are manipulated as the elementary units, and energy is used as the target function without any restrictions on the bonding of atoms. In fact, in many cases such as nanostructure-assembled materials, the structural units are nanoclusters. We report a study of a bonding-restricted structure search method based on the particle swarm optimization (PSO) for finding the stable structures of two-dimensional (2D) materials containing dispersed C2 dimers rather than individual C atoms. The C2 dimer can be considered as a prototype of nanoclusters. Taking Si-C, B-C and Ti-C systems as test cases, our method combined with density functional theory and phonon calculations uncover new ground state geometrical structures for SiC2, Si2C2, BC2, B2C2, TiC2, and Ti2C2 sheets and their low-lying energy allotropes, as well as their electronic structures. Equally important, this method can be applied to other complex systems even containing f elements and other molecular dimers such as S2, N2, B2 and Si2, where the complex orbital orientations require extensive search for finding the optimal orientations to maximize the bonding with the dimers, predicting new 2D materials beyond MXenes (a family of transition metal carbides or nitrides) and dichalcogenide monolayers.

Wetting and Interfacial Behavior of Molten Al on Mo-Ni(Co)-Si Coated SiC Ceramic

The Mo-Ni (Co)-Si metallizing coatings on the SiC ceramic substrate were prepared by vacuum cladding process. The wetting and spreading of molten Al on coated SiC ceramic substrates at 900 oC were investigated by the sessile drop technique, and the interfacial behavior of the Al/coated SiC wetting couples was analyzed. The experimental results showed that the final contact angle of Al/M20NiSi coated SiC was close to 0o. With the increase of Mo content in the Mo-Ni-Si coating, the shape of the sessile drop became very irregular due to the strong interactions between the Al drop and the coating, so it was unable to precisely characterize the contact angles of Al/Mo30NiSi and Al/Mo40NiSi systems. The final contact angle of Al/Mo10CoSi coated SiC system was also close to 0o, however, the final contact angle of Al/Mo20CoSi coated SiC system climbed to ~42o with the Mo content increasing from 10 at.% to 20 at.%. The significant increase of contact angle may be caused by the accumulation of Mo near the triple line which can impede the spreading of Al drop.

Nanoscale probing of the lateral homogeneity of donors concentration in nitridated SiO2/4H–SiC interfaces

In this paper, nanoscale resolution scanning capacitance microscopy (SCM) and local capacitance–voltage measurements were used to probe the interfacial donor concentration in SiO2/4H–SiC systems annealed in N2O. Such nitrogen-based annealings are commonly employed to passivate SiO2/SiC interface traps, and result both in the incorporation of N-related donors in SiC and in the increase of the mobility in the inversion layer in 4H–SiC MOS-devices. From our SCM measurements, a spatially inhomogeneous donor distribution was observed in the SiO2/4H–SiC system subjected to N2O annealing. Hence, the effect of a phosphorus implantation before the oxide deposition and N2O annealing was also evaluated. In this case, besides an increased average donor concentration, an improvement of the lateral homogeneity of the active doping was also detected. The possible implications of such a pre-implantation doping of the near-interface region on 4H–SiC MOS-devices are discussed.

Three-dimensional Observation of Nonmetallic Inclusion Clusters in Solid Metal by X-ray Micro-CT

In this study, we developed a method of observing three-dimensional (3D) inclusion clusters in metal. The theory of X-ray micro-computed tomography (CT) is generally introduced. The criteria on determining the sample size and energy of X-ray beam is set according to the characteristics of the beamline BL20XU available at Spring-8, which is the largest synchrotron radiation facility. The Al–TiB2 and Al–SiC system were measured by the X-ray micro-CT available in beamline BL20XU at Spring-8. The determination of the sample size the energy of X-ray beam are discussed on basis of the X-ray linear attenuation coefficient (LAC) and the transmission rate of Al–TiB2 and Al–SiC system. The limitation of the charge coupled device (CCD) camera, such as spatial resolution and observing field, are taken into consideration as well. Phase retrieval method is applied to reduce the noises of tomographic images for Al–SiC system due to its poor contrast. The 3D particle clusters of TiB2 and SiC are reconstructed by self-developed program. The fractal dimension of TiB2 and SiC clusters are calculated around 2.7. The feasibility of observing alumina cluster in steel is discussed on basis of the latest capability of beamline BL20XU at Spring-8.

Influence of Si addition on thermal conductivity of unidirectional CF/Al-Si composites fabricated by low pressure infiltration process

Unidirectional CF/Al-Si composites were fabricated by low pressure infiltration, permeating molten Al into porous CF-Si preform. In this study, the influences of Si addition in the preforms on the thermal conductivity of obtained CF/Al-Si composites were investigated in terms of the degradation of high thermal conductive CFs by chemical reactions in Si-C and Al-C systems. Comparing with theoretical value, the thermal conductivity of CF/Al-Si composites was extremely low. Although the Si-C reaction led to the decrease of the thermal conductivity, the sintered Si around CF surfaces protected from the significant decrease of the thermal conductivity being attributed to the severe Al and CF reaction. The surface damage of high thermal conductive CFs by Al-C reaction became a main reason for the decrease in the thermal conductivity of CF/Al-Si composites. Especially, the active Al-C reaction in the region of extremely low Si content around CF surfaces affected significant degradation of the CFs.

On the impact of the plasma jet energy on the product of plasmadynamic synthesis in the Si-C system

Silicon carbide (SiC) nanoparticles can be used for ceramics reinforcement, creation of nanostructured ceramics, microelectromechanical systems. The paper presents the results of plasmadynamic synthesis of silicon carbide nanopowders. This method was realized by the synthesis in an electrodischarge plasma jet generated by a high-current pulsed coaxial magnetoplasma accelerator. Powdered carbon and silicon were used as precursors for the reaction. Four experiments with different energy levels (from 10.0 to 30.0 kJ) were carried out. The synthesized products were analysed by several modern techniques including X-ray diffractometry, scanning and transmission electron microscopy. According to analysis results all the products mainly composed of cubic silicon carbide (b-SiC) with a small amount of unreacted precursors. Silicon carbide particles have a clear crystal structure, a triangular shape and sizes to a few hundred nanometers. Comparison of the results of experiments with different energy levels made it possible to draw conclusions on ways to control product phase composition and dispersion. The silicon carbide content and particles sizes increase with increasing the energy level.

Assessment of SiC Crystal Chemistry during the PVT Growth Process: Coupled Numerical Modeling and Thermodynamics Approach

Numerical simulation appeared till now as the only tool able to describe the SiC growth by PVT process, while the chemistry of the Si-C system and its coupling to mass transfer were not considered in a satisfactory way. To assess the chemistry of SiC crystal, the coupling of numerical and thermodynamic calculations computed by FEM, and by treating SiC as a solid solution, respectively, is presented. This enables the possibilities to control the activity of each component in SiC crystal during the growth. The link between growth conditions and SiC crystal chemistry could be one of the key issues to link the growth and the occurrence of cubic or hexagonal polytypes.

Ice templating of ZrB2–SiC systems

Ice templating of a binary ZrB2–SiC system was set to obtain porous architectures with lamellar structure. Two commercial ammonium poly-acrylates, with different molecular weights and pH range of activity, were used as dispersants. Slurries were produced by varying solid loadings (38–48vol%) and/or the dispersant concentrations (from 0.4 to 2wt%). It was found that an excess of dispersant is necessary to achieve a lamellar morphology. The more effective is the dispersant in optimizing electro-steric repulsions between particles, the more effective is in promoting the formation of a lamellar morphology. Preliminary compressive strength tests were carried out.