SiC Layer Research Articles

High-Modulus Laminated SiC/AZ91 Material with Adjustable Microstructure and Mechanical Properties Based on the Adjustment of the Densities of the Ceramic Layers.

To address the issue of inadequate strength and plasticity in magnesium matrix composites, SiC preforms were prepared using the freeze-casting process. The effects of sintering temperature on the microstructure, mechanical properties, and fracture behavior of SiCp/AZ91 magnesium matrix composites were studied by controlling the density of SiC preforms through low-temperature sintering. The results indicate that as the sintering temperature decreases, the reaction products in the SiC layer decrease, resulting in lower SiC preform density and increased content of AZ91 alloy filling in the layer. The increased alloy content in the ceramic layer not only inhibits crack initiation but also hinders crack propagation, thereby endowing the SiCp/AZ91 laminated material with excellent compressive strength and compressive strain. At the sintering temperature of 900 °C, the SiCp/AZ91 laminated material exhibits impressive compressive strength and strain values of 623 MPa and 8.77%, respectively, which demonstrates an excellent combination of strength and toughness.

Microstructure evolution and ablation mechanism of SiCf/SiC ceramic matrix composite microgrooves processed by pico-second laser

SiCf/SiC ceramic matrix composites have been widely applied in turbine engine aerospace components with high temperature resistance, high strength, and lightweight performances. Due to the high brittleness and anisotropy, laser-assisted machining acts as a feasible process to improve the machinability of the SiCf/SiC composites. A single-factor experiment was designed to understand the microstructure evolution and ablation behaviors of the microgrooves processed by pico-second laser in this study. The high pulse energy/scanning time and low scanning speed had positive impacts on the depth and width, but negative effect on the three-dimensional surface roughness Sa. Besides, the optimal parameter was 200 kHz repetition frequency. In addition, the microstructure evolution and ablation mechanism under different laser parameters were investigated by the HRSEM, EDS, and XRD analysis. These experimental results showed that the machined microgrooves were covered by a large amount flocculent composed of amorphous SiO2 when the oxidation was weak, and the splashes with the form of amorphous SiO2 and crystal SiO2 under strong ablation conditions. This indicated that the plasma effect transformed to the photothermal effect with enough heat. Meanwhile, a condensate layer occurred in all experiments and a recrystallized SiC layer relied on the microgroove depth controlled by adjusting laser parameters. This work will provide a theoretical basis and practice guidance for laser-assisted machining of the SiCf/SiC composites.

Temperature Dependence of 3С-SiC Growth During Rapid Vacuum Thermal Silicon Treatment

The paper presents the results of a study of the structure, phase composition, and growth kinetics of silicon carbide epitaxial layers on silicon substrates during their rapid vacuum thermal treatment. Transmission electron microscopy revealed the formation of layers of the cubic polytype SiC (3C-SiC) on silicon during carbidization in the temperature range of 1000–1300 °C. It was found that the formation of SiC layers proceeds in two stages, characterized by different activation energies. In the lower temperature range from 1000 to 1150 °C, the activation energy of the SiC growth process is Ea = 0.67 eV, while in the temperature range from 1150 to 1300 °C, the activation energy increases by almost an order of magnitude (Ea = 6.3 eV), which indicates a change in the limiting physical process. It has been established that the type of conductivity and the orientation of the substrate affect the thickness of the formed SiC layers. In this case, the greatest thickness of silicon carbide layers is achieved on silicon substrates with (111) orientation of p-type conductivity.

Investigation of SiC formation on the graphite surface by CO-H2-SiO gas

FINEX process, which utilizes hydrogen (H2) as a part of reductants, has emerged as an environmentally sustainable ironmaking process to meet the upcoming carbon-neutral era. In the H2-enriched atmosphere, local slag holdup in the carbonaceous particle bed may increase due to the increased melting temperature of slags by the rapid reduction of iron oxide and the resulting lower wettability of the carbonaceous materials by liquid slag. In-situ SiC formation on the carbon surface gains much attention as a method to reduce the slag holdup. In this study, as a fundamental study, we investigated the SiC formation on the surface of a graphite substrate under a CO-H2-SiO gas environment at 1873 K. It was found that as the partial pressure of H2 increased, the penetration depth of a SiC layer formed on the graphite surface increased, and the surface roughness became enhanced. A reaction rate analysis revealed that the H2-CO gas mixture accelerated the SiC formation on the graphite surface compared to the N2-CO gas mixture. This effect was attributed to the high bimolecular diffusivity of H2-CO. Our results demonstrate that under a CO-H2-SiO gas environment, the fast diffusion of H2 gas through micropores in the graphite significantly enhances the formation of SiC on the graphite surface. The results obtained in this study show that the acceleration of SiC formation under an H2-enriched atmosphere would improve the wettability of molten slag and reduce the slag holdup in the FINEX process.

A Theoretical Approach for Detecting the Chikungunya Virus Based on 1D Photonic Crystals

In the current study, it is aimed at using defective 1D photonic crystals (PCs) to detect the chikungunya virus in various healthy and diseased blood samples composed of plasma, platelets, red blood cells, and uric acid. The proposed PC structure has 14 periods and consists of repeating SiC and SiO2 layers with a central cavity layer. When blood samples are injected into the cavity layer, the transmittance spectrum is examined theoretically by using a transfer matrix approach to determine how the wavelength of the defect mode changes. The cavity layer is 540 and 648 nm thick, and the work is carried out at different angles of incidence. The performance of the sensor is quantified by computing the sensitivity, figure of merit, quality factor, and limit of detection values of the sensor for various blood samples. The maximum sensitivity is 1205.5 nm RIU−1 and detection limit of the order is 10−6 in this proposed work. A lower value of sensor resolution of 0.01218 is also achieved. Such a high‐performance sensor is suitable for biosensing applications with better sensing capabilities.

Effect of Adding Intermediate Layers on the Interface Bonding Performance of WC-Co Diamond-Coated Cemented Carbide Tool Materials.

The interface models of diamond-coated WC-Co cemented carbide (DCCC) were constructed without intermediate layers and with different interface terminals, such as intermediate layers of TiC, TiN, CrN, and SiC. The adhesion work of the interface model was calculated based on the first principle. The results show that the adhesion work of the interface was increased after adding four intermediate layers. Their effect on improving the interface adhesion performance of cemented carbide coated with diamond was ranked in descending order as follows: SiC > CrN > TiC > TiN. The charge density difference and the density of states were further analyzed. After adding the intermediate layer, the charge distribution at the interface junction was changed, and the electron cloud at the interface junction overlapped to form a more stable chemical bond. Additionally, after adding the intermediate layer, the density of states of the atoms at the interface increased in the energy overlapping area. The formant formed between the electronic orbitals enhances the bond strength. Thus, the interface bonding performance of DCCC was enhanced. Among them, the most obvious was the interatomic electron cloud overlapping at the diamond/SiCC-Si/WC-Co interface, its bond length was the shortest (1.62 Å), the energy region forming the resonance peak was the largest (-5-20 eV), and the bonding was the strongest. The interatomic bond length at the diamond/TiNTi/WC-Co interface was the longest (4.11 Å), the energy region forming the resonance peak was the smallest (-5-16 eV), and the bonding was the weakest. Comprehensively considering four kinds of intermediate layers, the best intermediate layer for improving the interface bonding performance of DCCC was SiC, and the worst was TiN.

Residual stresses in as-manufactured TRISO Coated Particle Fuel (CPF)

TRistructural ISOtropic coated particle fuels (TRISO CPF) have been developed as a possible fuel solution for high temperature nuclear reactors, which offer the possibility of nuclear cogeneration-powered industrial facilities and hydrogen production. A finite element model was developed to simulate the fabrication process of TRISO particles. Understanding the initial stress and bonding state of the layers is crucial in predicting performance and failure in service, however this factor has not received an in depth consideration in the available literature. The simulations of a fully bonded model of TRISO (layers perfectly attached to each other) revealed the presence of high values of tensile hoop stresses in the inner fuel kernel (up to 250 MPa, sufficient to cause fracture in UO2) and even higher compressive stresses (up to 600 MPa) in the silicon carbide layer. Simulations conducted without bonding between kernel and buffer found the residual stress state to be consistently more relaxed with respect to the fully bonded model. This was most evident in the radial stress, which drops to less than 10 MPa (tensile or compressive) throughout the particle. In the hoop direction, compression of 150 MPa remained in the SiC layer. Such results are consistent with the empirical evidence of the occurrence of kernel-buffer debonding during the fabrication of TRISO particles. Finally, a brief investigation of the effect of ovality on the model with kernel-buffer debonding showed an overall increase in the magnitude of the hoop stress in the SiC and PyC layers in a flat spot caused by reduced buffer material.

Direct synthesis of nanopatterned epitaxial graphene on silicon carbide

This article introduces a straightforward approach for the direct synthesis of transfer-free, nanopatterned epitaxial graphene on silicon carbide on silicon substrates. A catalytic alloy tailored to optimal SiC graphitization is pre-patterned with common lithography and lift-off techniques to form planar graphene structures on top of an unpatterned SiC layer. This method is compatible with both electron-beam lithography and UV-lithography, and graphene gratings down to at least ∼100 nm width/space can be realized at the wafer scale. The minimum pitch is limited by the flow of the metal catalyst during the liquid-phase graphitization process. We expect that the current pitch resolution could be further improved by optimizing the metal deposition method and lift-off process.

Comparison of thermal-hydraulic calculation in 100 MWt thorium-based HTGR using SiC and ZrC TRISO coated fuel particle

The High-Temperature Gas-cooled Reactor (HTGR) uses Tri-structural Isotropic (TRISO) coated fuel, the first barrier to fission products with unique ruggedness. One of the layers of TRISO is a SiC layer, which maintains the fuel's dimensional stability and mechanical integrity and acts as a fission product barrier. At extremely high temperatures, the SiC layer in the TRISO coating system tends to decompose, vaporizing silicon elements and forming a porous carbon structure. The weakness of the SiC layer leads to more expensive and difficult maintenance processes. ZrC is considered the primary alternative to replace the SiC layer due to its superior stability at high temperatures and more resistance to fission products especially palladium. Previous research has shown that from a neutronic perspective, the performance of ZrC and SiC layers is equally good with insignificant differences. The following research step analyzes the temperature distribution in the hot spot channel of the fuel and the overall core using both types of layers. The temperature analysis is essential to ensure that the maximum fuel temperature during normal operation does not exceed the thermal design target of 1495 °C. This research also simulates the temperature of both layers above the fuel design limit of 1600 °C. In addition to thermal–hydraulic analysis, calculations were also conducted to determine the coolant pressure drop caused by friction, elevation and form. The calculation showed that the peak temperature value during normal operation for TRISO with SiC and ZrC layer is below the thermal design target value. Both temperatures are not significantly different, with the TRISO (ZrC) temperature being higher during normal operation and the TRISO (SiC) temperature being higher during accident/high-temperature conditions. The pressure drop profile indicates that both coated fuel particles do not exhibit significant differences.

SiC/Si Hybrid Substrate Synthesized by the Method of Coordinated Substitution of Atoms: A New Type of Substrate for LEDs

This paper proposes a new type of substrate for manufacturing LEDs based on AlInGaN heterostructures. Instead of depositing SiC layers on the surface of Si using the conventional method, a new method involving the coordinated substitution of atoms (MCSA) to form the SiC layer is proposed. This new approach enables the growth of epitaxial GaN layers with low defect content and facilitates transfer to any surface. The paper details the technology of manufacturing LEDs on SiC/Si substrates obtained by the MCSA and elaborates on the benefits of using these substrates in LED production. Additionally, the advantages of the growth interface between SiC and Si materials are discussed. Moreover, it is found that thinner SiC layers (<200 nm) contribute to the scattering of the LED’s own radiation in the heterostructure waveguide, which decreases its absorption by silicon. For flip-chip LEDs with the substrate removed, substrates with thicker SiC layers (~400 nm) and a growth porous layer of several microns at the SiC-Si interface is utilized to simplify Si substrate removal and enhance the manufacturing process’s cost-effectiveness.

A hybrid graphite powder PFC@G for reserving higher carbon content of self‐lubrication graphite/SiC composites by RMI

AbstractThe appropriate carbon content is indispensable for the application of self‐lubricating graphite/SiC composites. However, it is a big challenge to retain high carbon content in the reaction‐formed graphite/SiC composites because of drastic consumption of carbon by violent reaction with liquid silicon. In this study, a hybrid powder constructed by graphite particles (G) and glassy carbon derived from phenolic resin (PFC) was used as carbon sources, or PFC@G for short, to reserve higher content of carbon in the reaction‐formed composites. The weight ratio of phenolic resin to graphite particles was adjusted to obtain an appropriate PFC@G with dense microstructure and close‐grained surface. Compared with the graphite/SiC composites only using raw graphite particles as carbon sources, the carbon content of the composites fabricated with compact and large PFC@G has obviously increased (up to 172%). In particular, the carbon content of the composites fabricated with the weight ratio = 0.8 reached a high value of 44.26 vol.%, which exhibited outstanding self‐lubrication properties among the four kinds of the composites. The mechanism of reserving higher content of carbon in the graphite/SiC composites by constructing PFC@G is investigated, revealing that a continuous SiC layer formed on the surface of the larger size PFC@G and most closely packed graphite particles inside of PFC@G were insulate from liquid silicon by the layer.

Evolution of the Microstructure and Mechanical Performance of As-Sprayed and Annealed Silicon Coating on Melt-Infiltrated Silicon Carbide Composites.

In this study, silicon coating was deposited on melt-infiltrated SiC composites using atmospheric plasma spraying and then annealed at 1100 and 1250 °C for 1-10 h to investigate the effect of annealing on the layer. The microstructure and mechanical properties were evaluated using scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, nano-indentation, and bond strength tests. A silicon layer with a homogeneous polycrystalline cubic structure was obtained without phase transition after annealing. After annealing, three features were observed at the interface, namely β-SiC/nano-oxide film/Si, Si-rich SiC/Si, and residual Si/nano-oxide film/Si. The nano-oxide film thickness was ≤100 nm and was well combined with SiC and silicon. Additionally, a good bond was formed between the silicon-rich SiC and silicon layer, resulting in a significant bond strength improvement from 11 to >30 MPa.

Synthesizing SiC layer on diamond by heat treatment and its effects on density and thermal conductivity of diamond/W composite

In order to improve the thermal conductivity of W composites as plasma-facing materials, the interface bonding and interfacial thermal resistance of the composites are the key issues to be solved. Based on our previous study, although Si coating on diamond surface can improve the interface bonding and thermal conductivity of the composite, there still existed the interfacial reaction between W and diamond, which produced more low thermal conductivity compounds (WC/W2C) and added the interfacial thermal resistance of the composites. To further improve the interface bonding and increased the thermal conductivity of diamond/W composites, the Si-coated diamonds were used to prepare the Si-SiC dual layer on diamond via vacuum heat treatment and then to fabricate diamond/W composites (HT-coated diamond/W composite). The effects of temperature and holding time of the heat treatment on coating and its interface bonding with the composites were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that a stable and dense Si-SiC-diamond structure was formed after heat treatment at 1200 °C for 1 h, and the thickness of SiC transition layer was about 20 nm. Thermodynamic analysis demonstrated the reaction rate of SiC increased gradually first and then sharply from 1000 °C to 1400 °C. The integrity of the coating on the diamond surface was strongly impacted by residual compressive stress of the SiC layer, and its value increased with the SiC thickness. The Si-SiC dual layer evidently improved the interface bonding and thermal conductivity of diamond/W composite under the combined influence of reaction diffusion at SiC-W interface, inter-diffusion at W-Si interface, and the orientation relationship at diamond-SiC interface. Theoretical thermal analysis proved that HT-coated diamond/W composite possessing lower interface thermal resistance than that of Si-coated diamond/W composite and raw diamond/W composite achieved higher thermal conductivity of 205 W m−1 K−1.

Proven Power Cycling Reliability of Ohmic Annealing Free SiC Power Device through the Use of SmartSiC<sup>TM</sup> Substrate

The Smart CutTM technology enables the combination of a high quality single crystal SiC layer onto a low resistivity handle wafer (<5mOhm.cm), allowing device optimization as well as the reduction of device’s conduction and switching losses. On this new SmartSiCTM substrate, the sheet resistance of the back side contact after metal deposition, without anneal, is about 10x lower than the annealed back side contact on 4H-SiC. Schottky-barrier vertical structures thinned down to 250μm were prepared for power cycling tests (PCT) measurements. Up to 250 k cycles, the devices remained within the specifications of AQG324 for samples prepared from SmartSiCTM substrates. We are demonstrating here that in addition to a higher current rating (up to 20%), the SmartSiCTM substrate enables a device fabrication simplification by skipping the annealing of the back-side ohmic contact, without compromising either the back-side contact resistance or the assembly PCsec reliability.

Structural characterization and reaction mechanism of the Ti/SiC gradient material with Mg2Si additive fabricated by reaction sintering

The Ti/SiC gradient material with Mg2Si additive was designed and fabricated by reaction sintering. The structure, microstructure and properties were investigated systematically. The result indicated that the Ti/SiC gradient material contained six layers with Ti-rich and Si-rich regions. The relative density decreased from 98.32% to 88.73%, and it increased to 97.28%. Besides, the harness increased from 532.97 HV to 571.32 HV and reduced to 228.14 HV with the increase of Ti content. The fracture toughness of the SiC layer was 6.74 MPa m1/2, and it decreased to 4.91–5.39 MPa m1/2 at the layers containing Ti. The shrinkage rates increased during heating, and it slowed down at the holding stage. The densification primarily occurred at the heating and holding stages. The densification mechanism is the pore displacement controlled by lattice diffusion. Ti5Si3 synthesized by the reaction between Ti and SiC shows the incoherent interface to the Ti grain.

Correlation between Q-Factor and Residual Stress in Epitaxial 3C-SiC Double-Clamped Beam Resonators

In this work, we investigate the correlation between tensile residual stress and Q-factor of double-clamped beams fabricated on epitaxial 3C-SiC layers grown on both <100> and <111> silicon substrates, using a completely optical measurement setup to measure the Q-factor of the resonators and the residual stress of the layers by means of purposely designed micromachined test structures. From the measurements, a clear correlation appears between the residual stress of the SiC layer and the Q-factor of the resonators, with Q-factor values above half a million for resonators fabricated on <111> substrates, showing residual stress around 1 GPa.

Selective Oxidation during AFM Electrical Characterization of Doped SiC Layers

The possibility of anodic oxidation of SiC surfaces by a strong, local electric field applied during Atomic Force Microscopy (AFM) under ambient conditions is an interesting method to achieve nanopatterning of SiC, but is also a side-effect to be well characterized and controlled during this kind of AFM measurements if used to determine the local electric properties. In this contribution, we will analyze the local electric fields by finite element simulations in order to quantify the effect of the presence of a water meniscus and of an oxide layer on the SiC surface. Furthermore, we will experimentally highlight the strong influence of the local doping on the anodization, leading to the formation of thicker oxide layers at the location of highly doped SiC. Therefore, the location of these areas can be determined by a simple AFM topography scan after the application of a high field, allowing to detect highly doped SiC areas in complex structures as for example SiC MOSFETs.

Ionic accelerator based on metal–semiconductor contact for fast electrode kinetics and durable Zn-metal anode

The development of Zn metal anodes with high reversibility and fast kinetics is critical for achieving high-performance aqueous Zn-metal batteries. Herein, we report a Zn@SiC electrode with an Ohmic contact that exhibits excellent durability and enhanced electrode process kinetics. The Ohmic contact barrier (Φb) inhibited electron transfer from the metal to the SiC passivation layer and effectively regulated Zn deposition under the passivation layer, thus suppressing dendrite growth. The built-in potential (Vbi) accelerated the Zn transfer and reaction kinetics and decreased the nucleation energy, thereby enhancing the charge–discharge platform potential (∼40 mV) in full cells. Coupled with the good anti-side reaction ability of the SiC layer, the Zn@SiC electrode successfully delivered a highly reversible stripping/plating process after 3770 h under a 1.0 mA cm−2 current density with a low overpotential of 33.7 mV. Furthermore, by analyzing the energy band structure of the Ohmic contacts, the critical current density was quantitatively determined. This clarified the relationship between the deposition position and the current density, thus providing a standard for practical semiconductor design.

High temperature oxidation and microstructural evolution of SiC layer of TRISO particles in the presence of NaCl

With the different types of advanced nuclear fission reactors, the reliability of the SiC layer in tristructural-isotropic (TRISO) particles exposed to different corrosive environments is of vital important. In the present work, the oxidation behaviors of the SiC layer of TRISO particles exposed in NaCl salts with the concentrations of 0.2–2 wt% at 800–1400 °C were investigated. The effects of NaCl concentration and oxidation temperature on phase composition, microstructure, and chemical composition of the TRISO particle samples were systematically investigated. The results show that, with the increase of oxidation temperature and NaCl concentration, the oxidation rate of SiC layer in TRISO particles was accelerated. However, the effect of NaCl concentration alone on the oxidation rate of SiC layer was not significant. This could be attributed to the volatility of NaCl at high temperature. In addition, just like other halogen salts, NaCl salts also reacted with the oxide layer to form silicate compounds, such as Na2SiO3, which provided a channel for both oxygen and fluoride ions to diffuse into the inner SiC layer. The results obtained in the present work can provide a guide for the application of TRISO particles in molten salt stacks of chlorine salt.

Cracking failure analysis due to fatigue of the Ti-6Al-4V alloy coated with SiC layer and Cr interlayer deposited by magnetron sputtering

This work aimed to study the effects of coating a thin film of Silicon Carbide and chromium interlayer on the fatigue behavior of Ti-6Al-4V alloy and the correspondent failure evaluation. In the characterization of the layer, the roughness, thickness, and adhesion were determined. Uniaxial fatigue tests were performed under R = 0.1 and the fracture surfaces and corresponding failure mechanisms were observed and identified by SEM, respectively. In the specimens coated using the DC source the number of cycles to failure of the fatigue was increased. The fracture surfaces showed that the crack initiation occurred in the internal regions of the specimens and not superficially. In this case, the layer remained adhered to the specimens even after the tests, showing the effectiveness of the film. In specimens coated using the HiPIMS source, the number of cycles to failure decreased, the cracks were mostly superficial, and the deposited film showed low adhesion after the tests. It proved to be ineffective, worsening the material fatigue behavior.