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SiC is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Si4+ is bonded to four equivalent C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. C4- is bonded to four equivalent Si4+ atoms to form corner-sharing CSi4 tetrahedra.
SiC is Wurtzite structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. Si4+ is bonded to four equivalent C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.91 Å) Si–C bond length. C4- is bonded to four equivalent Si4+ atoms to form corner-sharing CSi4 tetrahedra.
SiC is Moissanite-6H structured and crystallizes in the hexagonal P6_3mc space group. The structure is three-dimensional. there are three inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. There are three inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.
SiC is Moissanite-6H-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are thirteen inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the second Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.90 Å. In the third Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.91 Å) Si–C bond length. In the fourth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the fifth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. All Si–C bond lengths are 1.89 Å. In the sixth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the seventh Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the eighth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the ninth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the tenth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the eleventh Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the twelfth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.90 Å) Si–C bond length. In the thirteenth Si4+ site, Si4+ is bonded to four C4- atoms to form corner-sharing SiC4 tetrahedra. There is three shorter (1.89 Å) and one longer (1.91 Å) Si–C bond length. There are thirteen inequivalent C4- sites. In the first C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the second C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the third C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fourth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the fifth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the sixth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.89 Å. In the seventh C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the eighth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the ninth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the tenth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. All C–Si bond lengths are 1.89 Å. In the eleventh C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the twelfth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra. In the thirteenth C4- site, C4- is bonded to four Si4+ atoms to form corner-sharing CSi4 tetrahedra.
The purpose of this project was to develop a new breed of Power Conversion Systems (PCS) for PV integration that is enabled by the newly developed 4-Quadrant Single Die SiC Power Semiconductor Switches (4-QPS) or also referred to as “Bidirectional FET (BIDFET)”. This work includes semiconductor die development, advanced packaging, converter design, development, and testing of 4-QPS enabled hardware prototypes at 1 kW (for single phase residential application) and 10 kW (for three phase commercial application). The BiDirectional Field-Effect Transistor (BiDFET) can enable circuit topologies requiring four-quadrant switches, that were earlier designed using discrete combinations of MOSFETs, IGBTs, GaN HEMTs, and PiN diodes. The monolithic nature of the BiDFET allows lower device count, smaller switch volume, lower inductance, and simpler packaging, and hence more reliable and commercially viable implementation in power electronics converters. The matrix converter topologies, now feasible using BiDFETs, can eliminate the bulky and unreliable dc link capacitors or inductors required for conventional voltage-source or current-source converters in ac–ac and ac–dc applications. The 1.2 kV BiDFET has the potential to disrupt all the applications utilizing 1.2 kV switches, including electric vehicle (EV) drivetrain, bidirectional EV chargers, industrial motor drives, solid-state transformers, datacenter power supplies, elevator drives, dc microgrids, energy storage grid integration, solid-state breakers, etc.
We propose neutral defects in 4H-SiC comprising a silicon vacancy and a sulfur atom dopant substituting a carbon atom as an optically controllable spin qubit with application in quantum computing and quantum telecommunications. According to our state-of-the-art first-principles calculation, the proposed defect possess very promising qubit functionalities. This system once again confirms our hypothesis for the rational design of spin qubits and single-photon emitters. Importantly, the atoms of this system have high-abundance isotopes with zero nuclear spin ensuring high spin-coherence time of the qubit.
Poster presentation on HOTSSTAR concept, design and initial on-sun test and evaluation of SiC air receiver design.
Stainless steel is used throughout the world as a structural material. However, it undergoes corrosion damage when exposed to extremely corrosive media, such as the marine environment. An alternative to solve this problem lies in the development of coatings that can withstand extreme conditions but also be easily deposited with inherently corrosion-resistant materials such as silicon carbide (SiC). The present study shows a simple method to produce Al/SiC cermet powders by attrition milling. The resulting cermet powders with a metallic matrix and hemispherical morphology, were employed as fillers in polycarbosilane (PCS) solutions that were sprayed on A304 stainless steel substrates. Al/SiC composite coatings were produced after heating the sprayed suspensions at 700 °C for 1 h in Ar atmosphere. The resulting composite coatings exhibited low surface energies (< 35 mN/m), water contact angles of 53°, and adhesion strength of up to 30 MPa. Finally, corrosion tests were performed in a cyclic corrosion test chamber, showing that these coatings effectively reduced the corrosion rate of stainless steel by 87%, reaching corrosion rate values of 0.007 g/cm 2 year.
Coupling between electronic and nuclear energy dissipation in ion-irradiated, single crystal 4H-SiC has been investigated using Si, Ti, and Ni ions over a range of energies at 300 K, and irradiation damage accumulation is characterized using Rutherford backscattering spectroscopy in channeling geometry. The damage production rate from nuclear energy loss (S n ) is observed to decrease with increasing electronic energy loss (S e ) of the incident ions. A dynamic threshold (S e,th ) in electronic energy loss is determined for each ion species, which defines two regions: i) S e > S e,th , where electronic energy dissipation fully suppresses damage production due to nuclear energy loss along incident ion paths, and ii) S e < S e,th , where simultaneous damage recovery due to Se competes with damage production processes. Here, the electronic energy loss threshold (S e,th ) increases sublinearly with incident ion atomic number. Here, the assessment of S e,th and how it affects damage accumulation is important to advance the understanding of complex processes occurring under ion-solid interactions, as well as in the design of functional materials for opto-electronics and novel structural materials and devices tolerant to harsh thermal and radiation environments.
We describe a novel fusion reactor blanket concept called GAMBL – GA Modular BLanket. This design concept exploits the advantages of SiC-based structures while minimizing their limitations. Material microstructures are tailored for different functions throughout the first wall and blanket, including the use of graded W/SiC composites to enhance heat transfer capabilities and resist erosion at the plasma-facing surface. The design contains a decoupled first wall and breeding blanket, which we show can provide adequate tritium breeding. By decoupling the breeding part of the blanket, we can operate at very low PbLi breeder pressure and support gravity loads in simple, radiatively-cooled structural beams that do not contain coolant. First wall performance capabilities are enhanced by eliminating constraints imposed by the deep blanket. We have performed initial fluid, thermal, mechanical and neutronics analysis of this concept to show its capabilities to meet the design requirements. R&D needs are mostly related to materials development. Except for unique manufacturing needs, no new facilities are required beyond existing or planned facilities for the US base program on steel-based DCLL blankets.
Environmental barrier coatings for SiC/SiC composites are limited by the melting temperature of the Si bond coating near 1414°C. Systems without a bond coating may be required for future turbine applications where material temperatures go beyond 1350 °C. Here, enhanced roughness SiC substrates were developed to assess coating adhesion without the bond coating. Two EBCs with different YbMS/YbDS ratios were produced via modified plasma spraying parameters. Coating microstructure, thermal expansion, and modulus were measured for comparison of coating properties. Cyclic steam exposures at 1350°C were performed to assess oxidation resistance. The EBC with increased concentration of Yb 2 SiO 5 secondary phase displayed a higher CTE, which is typically expected to decrease adhesion lifetimes due to an increase in stress upon thermal cycling. Yet, the EBC chemistry with increased Yb 2 SiO 5 concentration was able to experience longer cycling times prior to coating delamination, likely due to interface interactions with the substrate and the thermally grown oxide.
The influence of implantation-induced point defects (PDs) on SiC oxidation is investigated via molecular dynamics simulations. PDs generally increase the oxidation rate of crystalline grains. Particularly, accelerations caused by Si antisites and vacancies are comparable, and followed by Si interstitials, which are higher than those by C antisites and C interstitials. However, in the grain boundary (GB) region, defect contribution to oxidation is more complex, with C antisites decelerating oxidation. Here, the underlying reason is the formation of a C-rich region along the oxygen diffusion pathway that blocks the access of O to Si and thus reduces the oxidation rate, as compared to the oxidation along a GB without defects.
The coincidence of electronic and damage energy dissipation from energetic ions to an atomic lattice can significantly affect damage production along the ion trajectory due to spatial overlap of inelastic and elastic processes. Damage production and disordering in single crystal 3C-SiC from 5 MeV Si and 10 MeV Au ions is investigated using ion-channeling experiments. While defects are created by damage energy dissipation via elastic scattering, electronic energy dissipation via electron-phonon coupling decreases defect survival along the ion trajectory for Si ions. Finally, the more energetic recoil spectrum for 10 MeV Au ions leads to weaker spatial coupling of electronic and damage energy dissipation processes, and damage production is only weakly affected.
Electrical characterization of several 4H-SiC Schottky diodes with Aerosol-Jet printed gold (Au), silver (Ag), and platinum (Pt) contacts was performed using forward and reverse current–voltage (IV) measurements. From these measurements, device parameters such as Schottky barrier height and ideality factor were determined; however, many of the devices exhibited nonideal behavior and inferior performance characterized by ideality factors significantly greater than one, disproportionate low voltage leakage current and low barrier heights. Forward current–voltage (FIV) characteristics were fitted to an inhomogeneous barrier height theory to explain the abnormal behavior exhibited by the printed devices. Here, transmission electron microscopy (TEM) of the device cross-sections was performed to investigate the printed metal and semiconductor epitaxial layer interface, which revealed the imperfections in the metal–semiconductor contact. Despite these irregularities, alpha radiation detection capability of these devices was still achieved with an energy resolution of 1.89% at 5.486 MeV, and the best achievable resolution at 0.51% with no energy degradation of 5.486 MeV.
Chromium deposited by high-power impulse magnetron sputtering (HIPIMS) versus cathodic arc (CA) processes exhibits very different mechanical properties. Combining the two can result in a single-phase with superior performance that can be tailored for use in coating SiC for advanced nuclear fuel cladding. Coating morphology, residual stress, elemental depth profiles, and mechanical testing by scratch, pull-off adhesion, and microcantilevers are shown for HiPIMS, CA, and combined coatings. CA coatings were likely to spall and had lower adhesion strength due to tensile residual stresses but had desirable material properties. Additionally, by depositing an initial layer of Cr by HiPIMS followed by a layer of Cr by CA, a more adherent coating was achieved and some of the stress issues with CA morphology were resolved. Combined coatings withstood at least 80 MPa in pull-off adhesion tests and had maximum failure stress values of 5GPa in microcantilever tests. These results were better than either individual deposition method and point to a hybrid approach being a path forward for a more robust coating.
During aqueous corrosion, atoms in the solid react chemically with oxygen, leading either to the formation of an oxide film or to the dissolution of the host material. Commonly, the first step in corrosion involves an oxygen atom from the dissociated water that reacts with the surface atoms and breaks near-surface bonds. In contrast, hydrogen on the surface often functions as a passivating species. Here, we discovered that the roles of O and H are reversed in the early corrosion stages on a Si-terminated SiC surface. O forms stable species on the surface, and chemical attack occurs by H that breaks the Si–C bonds. Here, this so-called hydrogen scission reaction is enabled by a newly discovered metastable bridging hydroxyl group that can form during water dissociation. The Si atom that is displaced from the surface during water attack subsequently forms H 2 SiO 3 , which is a known precursor to the formation of silica and silicic acid. This study suggests that the roles of H and O in oxidation need to be reconsidered.
In this work, we systematically study the effects of Gd adsorption and intercalation on the electronic band structure of double-layer epitaxial graphene on Si-terminated SiC(0001) by first-principles calculations. We show that Gd adsorption and intercalation exhibit strong effects on the coupling between the graphene layers and between the buffer layer and substrate. Different adsorption/intercalation geometries can result in very different electron band structures. The number of Dirac cones and the positions of the Dirac cones relative to the Fermi level can be effectively manipulated through controlling the Gd adsorption/intercalation geometries. Our calculations provide useful insights to guide the experimental design of graphene-based materials with desirable functionalities for applications.
First-principles density functional theory (DFT) is used to analyze the stability of Pb intercalated phases under buffer layer graphene on SiC(0001) as a function of the supercell size, Pb coverage, and degree of Pb ordering. By comparing the chemical potentials of such two-dimensional Pb structures, here we find that there is a family of structurally distinct thermodynamically preferred Pb subsurface configurations with minute stability differences. These differences are comparable to the thermal energies at about 450 °C, where the Pb intercalated phases are grown. High-resolution surface-diffraction experiments using Spot Profile Analysis Low-Energy Electron Diffraction (SPA-LEED) confirm this high degree of degeneracy of the Pb intercalated phases from broad, low-intensity moiré spots observed exclusively from intercalated Pb. The low intensity of the moiré spots implies the coexistence of structurally different subsurface Pb phases.