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Silicon/carbon (Si/C) nanocomposites are considered as one of the most promising anode materials for lithium-ion batteries due to their high capacity and suitable lithiation potential. However, the complex and time-consuming preparation processes of silicon-based nanocomposites and the unexpected silicon carbide generated during high treatment make it difficult to achieve high-performance Si/C nanocomposites for practical applications. Herein, a silicon/carbon nanocomposite is successfully prepared through a facile and eco-friendly molten salt assisted precarbonization–reduction method using palygorskite (PAL) and sodium alginate as raw materials. Based on physical characterizations, it is demonstrated that the sodium alginate plays a key role in the successful preparation of Si/C nanocomposite, which not only boosts uniform embedding of PAL nanoparticles in the carbon matrix but also releases molten sodium salt to suppress the formation of unexpected SiC. When used as an alternative anode material for lithium-ion battery applications, the as-obtained Si/C composite delivers a high reversible specific capacity of 1362.7 mA h g−1 with an initial Coulombic efficiency of 70.3% at a current density of 200 mA g−1 and excellent long-term cycling stability. The findings here provide a facile and eco-friendly molten salt assisted precarbonization–reduction method for high-performance silicon/carbon anode materials. [ABSTRACT FROM AUTHOR]

Point defect color centers acting as single-photon emitters are promising for quantum technology applications and have been extensively studied, e.g., in the 4H polytype of silicon carbide (SiC). However, the physics of such color centers in other SiC polytypes is much less explored. Herein, we study the formation and thermal stability of such color centers in 6H-SiC using photoluminescence spectroscopy. The emissions from typical single-photon emitters, such as silicon vacancies, divacancies, and carbon antisite-vacancy pairs in 6H-SiC, were monitored as a function of the proton irradiation fluence and post-irradiation annealing, and compared to that in 4H-SiC. Overall, at the background of similarities between the emission behavior in 4H- and 6H-SiC polytypes, we observed prominent differences; e.g., for the thermal stability of the carbon antisite-vacancy pair, which exhibited maximized emissions upon 300 and 900 ° C anneals in 4H- and 6H-SiC, respectively. Moreover, we observed a range of defect emission signatures not previously reported for 6H-SiC in the literature and discussed their potential origin in the context of the thermal stability. For example, among the PL-lines in 6H-SiC, we detected periodically repeatable emission signatures, resembling the so-called L-lines recently reported in 4H-SiC, even though their exact origin has not yet been settled in the literature. Thus, we use color centers comparison in different polytypes to better understand the nature of the single-photon emitters in SiC. [ABSTRACT FROM AUTHOR]

4H Silicon carbide (SiC) is widely recognized as one of the most advanced wide bandgap semiconductors used in the production of high-efficiency power electronic devices. Impurities play a crucial role in achieving the desired electrical properties in 4H-SiC, yet the understanding of impurities in this material remains limited. In this study, first-principles formation-energy calculations were employed to establish a comprehensive database of formation-energy diagrams for impurities in 4H-SiC. This database includes valuable information on site preference, lattice distortion, solubility, and charge transition levels (CTLs) of the impurities. The site preference for each impurity is closely related to factors such as the Fermi energy, chemical potential, and the impurity species itself. To assess the lattice distortion caused by each impurity, a comparison was made between the volume changes before and after doping. Moreover, the solubility of each impurity was determined using the detailed balance theory, thereby enabling a direct measure of the maximum impurity concentration achievable in the material. Based on the CTLs, the impurities in 4H-SiC were classified into four categories: n-type impurities, p-type impurities, amphoteric impurities, and non-electroactive impurities. This comprehensive property database for impurities in 4H-SiC provides valuable insights for tailoring the material properties through controlled doping, thereby ultimately leading to enhanced performance of power electronic devices. [ABSTRACT FROM AUTHOR]

Nanophotonic structures have shown promising routes to controlling and enhancing nonlinear optical processes at the nanoscale. However, most nonlinear nanostructures require a handling substrate, reducing their application scope. Due to the underwhelming heat dissipation, it has been a challenge to evaluate the nonlinear optical properties of free-standing nanostructures. Here, we overcome this challenge by performing shot-controlled fifth harmonic generation (FHG) measurements on a SiC meta-membrane - a free-standing transmission metasurface with pronounced optical resonances in the mid-infrared (λ res ≈ 4,000 nm). Back focal plane imaging of the FHG diffraction orders and rigorous finite-difference time-domain simulations reveal at least two orders of magnitude enhancement of the FHG from the meta-membrane, compared to the unstructured SiC film of the same thickness. Single-shot measurements of the meta-membrane with varying resonance positions reveal an unusual spectral behavior that we explain with Kerr-driven intensity-dependent resonance dynamics. This work paves the way for novel substrate-less nanophotonic architectures.

4H Silicon carbide (4H-SiC) is widely recognized as a highly promising material for high-voltage and high-power electronic applications due to its exceptional properties. The performance of devices based on 4H-SiC is often weakened by the presence of carbon-related point defects, particularly carbon vacancies (VC). The defects of VC introduce deep-level traps (e.g., Z1/2 and EH6/7) that deteriorate device functionality. Experimental and theoretical studies on VC have led to some conflicting results about the charge states of VC, especially for the charge state ordering of EH6/7. We now employ ab initio metadynamics (META) to systematically investigate configuration space including the direction and magnitude of bond distortion and identify the most stable structures of VC. Eventually, the charge states of VC in 4H-SiC are identified. The Z1 (EH6) and Z2 (EH7) indicate transitions from acceptor (donor) levels of VC, located on the h and k sublattice sites, respectively. Z1 and Z2 demonstrate negative-U ordering, characterized by U values of −0.16 and −0.37 eV, respectively. Conversely, EH6 and EH7 display positive-U ordering, with U values of 0.16 and 0.08 eV, respectively. The current results provide insights into the properties of VC in 4H-SiC, highlighting the effectiveness of META in the exploration of complex potential energy surfaces associated with point defects in solids. [ABSTRACT FROM AUTHOR]

Based on the transport and polarization relaxation theories, the effects of hydrogen, fluorine, and chlorine atom passivation on the conductivity and dielectric properties of silicon carbide nanowires (SiCNWs) were numerically simulated. The results show that passivation can decrease the dark conductivity of SiCNWs and increase its ultraviolet photoconductivity. Among them, the photoconductivity of univalent (H) passivated SiCNWs is better than that of seven-valent (Cl, F) passivated SiCNWs. In terms of dielectric properties, the passivated SiCNWs exhibit a strong dielectric response in both deep ultraviolet and microwave regions. Hydrogen passivation SiCNWs produce the strongest dielectric response in deep ultraviolet, while fluorine passivation SiCNWs produce the strongest dielectric relaxation in the microwave band, which indicates that atomic passivation SiCNWs have a wide range of applications in ultraviolet optoelectronic devices and microwave absorption and shielding. [ABSTRACT FROM AUTHOR]

The article "Biorestorative Modification of White Spot Lesions in Anterior Teeth" explores the causes, diagnosis, and treatment of white spot lesions (WSLs) in teeth, particularly in relation to orthodontic therapy. It discusses various treatment options, including enamel microabrasion, resin infiltration, and bleaching, to address WSLs effectively. The article emphasizes the importance of patient involvement in prevention, management, and treatment decisions, highlighting the need for conservative and minimally invasive approaches to restore tooth aesthetics and function. [Extracted from the article]

A non-destructive method for detecting sub-micrometer-sized micropipes on an entire wafer surface is investigated. Since it is difficult to detect sub-micrometer-sized micropipes due to their small core size, a non-destructively and accurately detecting method is required. To solve the issue, we focus on a characteristic depression generated around micropipes, namely, line-shaped depressions. In this paper, the location of line-shaped depressions is identified by using optical inspection, and the line-shaped depressions are distinguished whether micropipes exhibit line-shaped depression or not by using mirror electron microscope observation as high-resolution inspection. The accuracy of the distinction results is confirmed by scanning electron microscope observation, and electrical characteristics of the P–N diode are fabricated using the inspected wafer. Furthermore, the sub-micrometer-sized micropipes are observed at the sites of leakage current identified by emission microscopy. Additionally, device simulation of the blocking-voltage characteristics of P–N diodes suggests that the increase in leakage current depends on the electric field at the sub-micrometer-sized micropipes, regardless of their core size. [ABSTRACT FROM AUTHOR]

Silicon carbide and its derivatives are promising materials with potential applications in various types of nuclear reactors. To better understand their characteristics, this paper investigates the recrystallization behavior of amorphous SiC prepared through pre-irradiation using 800 keV Kr2+. Following different annealing processes, Raman spectra revealed that recrystallization happened beyond 873 K, and nearly complete recrystallization of the amorphous layer occurs at 1423 K. Afterward, in situ annealing and He+ irradiation experiments were conducted. The results indicate that the recrystallization progress is a layer-by-layer epitaxial regrowth on the amorphous–crystal interface under 873 K annealing, and the epitaxial recrystallization would slow down mainly due to the accumulation of defects and Kr atoms. However, under 30 keV He+ irradiation at 873 K, the interface continues to move. Moreover, when the irradiation dose rises, nanocrystals and helium bubbles appear simultaneously, growing in both size and density. The different recrystallization behaviors caused by irradiation and non-irradiation conditions could be explained by radiation-enhanced atomic diffusion, and helium bubbles are likely to be the by-products of nanocrystal formation. A possible explanation is proposed. This study provides insights into the practical application of amorphous silicon carbide in reactors and other irradiation environments. [ABSTRACT FROM AUTHOR]

The possibility of using axial spin centers with S = 3 / 2 in silicon carbide for all-optical measurement of the projection B z of the external magnetic field onto the c -axis of the SiC crystal, as well as the polar and azimuthal angles of the magnetic field relative to the direction of the c -axis, at room and significantly higher temperatures is shown. Spin centers in SiC, where optically induced spin alignment occurs, have a unique system of spin levels in a magnetic field, caused by the interaction of the fine structure and hyperfine interaction with the 29 Si nuclei. There is a wide range of level anticrossings (LACs) resulting in an extremely strong change in the photoluminescence intensity at LAC. The dependence of the LAC spectrum on the orientation of the external magnetic field is also observed. The proposed magnetometer is based on the compensation of the external magnetic field at the position of the optical excitation spot of the confocal microscope. The sensitivity to a constant magnetic field for the z-component of the magnetic field (B z) is better than 0.1 μ T / Hz in the confocal volume at room temperature. The sensitivity of polar and azimuthal angle determination depends on the sensitivity of the perpendicular component of the magnetic field, which is better than ∼ 0.01 mT / Hz in the range from − 0.4 to 0.4 mT. [ABSTRACT FROM AUTHOR]

Slurry infiltration method has been widely used as a preliminary step in preparing dense and multifunctional fiber reinforced SiC ceramic matrix composites. However, the infiltration efficiency of slurry is low mainly due to its insufficient stability, specifically manifested as the limited weight gain of composite after slurry infiltration. The aim of this study is to improve the infiltration efficiency of slurry by improving its stability, while maintaining its low viscosity and high particle concentration. In this study, by adjusting the particle size, two SiC slurries with identical high particle concentration (50 wt.%) and similar low viscosities (less than 10 mPa·s) but different stabilities were obtained and then applied in the infiltration process of composites. The stability of slurry can be highly improved by decreasing the particle size. The weight gain of composites after infiltration of high stability slurry (sedimentation time exceeding 35 h) is more than twice that of low stability slurry (sedimentation time nearly 1 h). Combined with chemical vapor infiltration method, the final composite using high stability slurry exhibits increased density, reduced porosity and enhanced mechanical performance. [ABSTRACT FROM AUTHOR]

The use of submicron silicon carbide powder as a raw material is crucial for preparing high-performance silicon carbide ceramics. However, its strong absorption of ultraviolet light makes stereolithography of submicron silicon carbide powder challenging. In this study, submicron SiC particles, photosensitive resin, and photoinitiator were used as raw materials to prepare SiC ceramics via stereolithography combined with a pressureless sintering method. The effects of ultraviolet wavelength, type, and content of photoinitiator on the curing properties of submicron SiC ceramic slurry were investigated. The results showed that the curing thickness of the SiC ceramic slurry significantly increased with the increasing ultraviolet wavelength. Compared to photoinitiators TPO and 396, photoinitiator 819 exhibited a better curing effect. Additionally, increasing the photoinitiator content facilitated the generation of more free radicals in the SiC ceramic slurry at low light intensity, thereby improving its ultraviolet absorption characteristics. When the dosage of photoinitiator 819 was 8.8 %, the SiC slurry achieved the best curing performance, with a single-layer curing thickness of 50 μm and a sintering density of 95 % for SiC ceramics. [ABSTRACT FROM AUTHOR]

As a kind of metal matrix composites, silicon carbide particulate reinforced aluminum alloy composites (SiCp/Al) have been widely applied in numerous fields. However, it is still difficult to process this composite material with electrical discharge machining (EDM) at present. To address this problem, this study introduces a novel rotary electrochemical discharge – chemical composite machining (RECDM-CM) method. This method uses rotating electrodes and workpieces to improve the flushing effect of working medium and utilizes the electrolysis to reduce the recast layer thickness. The chemical reaction between sodium carbonate (Na2CO3) and aluminum oxide (Al2O3) at high temperatures is used to remove the non-conductive Al2O3 in this composite machining. Rotary electrochemical discharge – chemical composite machining is used to process silicon carbide particulate reinforced AA2009 aluminum alloy composites with the silicon carbide volume fraction of 55%. The experimental results reveal that the material removal rate (MRR) of rotary electrochemical discharge – chemical composite machining is 5.2 times that of rotary electrical discharge machining, and its relative tool wear rate (RTWR) is 37.42% of rotary electrical discharge machining. The recast layer thickness is reduced to less than 13 μm via rotary electrochemical discharge – chemical composite machining. [ABSTRACT FROM AUTHOR]

This study investigates Beam Line Absorbers (BLAs) for the Hefei Advanced Light Facility (HALF). A ferrite-based BLA prototype was developed, demonstrating high-power handling capacity up to 10kW, ultra-high vacuum performance better than 6.5×10−10 mbar, and high absorption efficiency in critical frequency ranges. Subsequently, more compact designs with reduced longitudinal length were explored, investigating ferrite-only, silicon carbide (SiC)-only, and hybrid configurations through RF simulations. Based on preferred absorption efficiency, ferrite-only and hybrid BLA structures were further analyzed under high-power conditions. Referencing test results, multiphysics simulations were conducted under 3kW absorbed power. The hybrid design, comprising two rings of ferrite tiles and one ring of SiC tiles, improved the temperature distribution of the absorbing materials. Extrapolating to 11kW absorbed power, this design reduced the maximum temperatures on absorbing tiles by up to 40°C compared to the ferrite-only design. The hybrid design offers a balanced solution that combines effective HOM damping with enhanced thermal performance, improving the long-term operational stability of BLAs. [ABSTRACT FROM AUTHOR]

The top-seeded solution growth (TSSG) method is an emerging technique for the production of silicon carbide (SiC). Due to its advantage of lower growth temperature compared to the physical vapor transport method, it holds significant potential in the preparation of Al-doped SiC. In this study, a global numerical model calculating heat and mass transfer was established to investigate the impact of solution radius and height, coil position, and rotational speed of the seed crystal on the flow pattern and carbon transport. The results indicated that a meticulous determination of these growth parameters could enhance both carbon transport and growth rate. Furthermore, abundant transient calculation results were utilized to train back-propagation (BP) neural networks to extract the correlation between growth parameters, growth rate, and Al concentration. The optimal parameters were ultimately obtained using the non-dominated sorting genetic algorithm (NSGA-II). The Al concentration calculated in the solution under the optimal growth conditions demonstrated that the evaporation of Al was sufficiently low to satisfy the p-type doping requirement. This study provides valuable insights for the future development of a TSSG system tailored for the rapid growth of Al-doped SiC. [ABSTRACT FROM AUTHOR]

With careful design and integration, microring resonators can serve as a promising foundation for developing compact and scalable sources of non-classical light for quantum information processing. However, the current design flow is hindered by computational challenges and a complex, high-dimensional parameter space with interdependent variables. In this work, we present a knowledge-integrated machine learning framework based on Bayesian Optimization for designing squeezed light sources using microring resonators. Our model, after only 5 optimization rounds, identified two optimal structures with distinct cross-sectional areas and radii (65 and 110 ), achieving escape efficiencies over 90% and on-chip squeezing levels of 7.48 dB and 9.86 dB, respectively. Our results demonstrate that by adaptively finding the coupling coefficient through BO, the model has identified optimal points in the over-coupled regions with superior performance. This optimization model is developed specifically for single resonators made of silicon nitride. However, its applicability extends beyond this, and it can be used to model structures with auxiliary rings or other materials like silicon carbide. Our approach is expected to streamline the design of other integrated photonic components, including Mach-Zehnder interferometers and directional couplers, for applications in quantum photonic circuits and optical neural networks. [ABSTRACT FROM AUTHOR]