Nanoscale Silicon Carbide Research Articles

Evaluation of the Mechanical Properties of Aluminium Hybrid Nano Composites Using Ultrasonic-Assisted Stir Casting Method and Reinforced with Nano-scale SiC and MoS2 Particles

The purpose of this research is to investigate the effects of adding large quantities of reinforcing agents specifically, 3% MoS2 along with different SiC concentrations 5%, 10%, and 15% to LM25 aluminium alloys. The goal of producing these composites was to improve the material characteristics of hybrid metal matrix composites (HMMCs) by the use of ultrasonic-assisted stir casting. The study looks at the possible benefits of using particulate materials to improve the mechanical properties of metallic composites, such as silicon carbide (SiC) and molybdenum disulphide (Mo­S2). The research assesses the impact of SiC and MoS2 Nano scale additions on the mechanical and structural characteristics of LM25 composites by experimental analysis. The results of mechanical property testing show significant improvements, especially when 15% of Nano-scale SiC is included. This is mainly because the Nano-scale SiC is evenly distributed throughout the host metal.

Synthesis of embedded ZrC-SiC-C microspheres via carbothermal reduction for thermal stability and electromagnetic wave absorption

Development of a novel material with electromagnetic wave (EMW) absorbing capability and high-temperature resistance is a definite trend. As an ultra-high temperature ceramic, zirconium carbide (ZrC) can be used in a harsh high-temperature environment. However, ZrC has high electrical conductivity and poor low-temperature oxidation resistance. The introduction of silicon carbide (SiC) and carbon (C) into ZrC to modulate its phase composition and microstructure is a feasible method that can improve the sensitivity of ZrC to oxidizing atmospheres and electromagnetic wave absorption properties. In this study, submicron ZrC-SiC-C microspheres were successfully synthesized by the carbothermal reduction reaction combined with the template method, in which nanoscale ZrC and SiC were uniformly embedded in unreacted C. The results exhibit that nano-sized SiC and ZrC grains nucleate and grow on carbon microspheres successively, forming unique interlocking structures. The minimum reflection coefficient (RCmin) of ZrC-SiC-C microspheres attains −34.8 dB with a thickness of 1.65 mm at 13.8 GHz and the RC is below −10 dB from 12.0 to 16.0 GHz. The structure that nano-sized ZrC, SiC, and unreacted C are embedded into each other leads to dramatic increase in the heterogeneous interface, which is conducive to the loss of EMW. The incipient oxidation temperature of the ZrC-SiC-C microspheres is 411 °C, which is much higher than that of ZrC particles. The unique structure and composition increase the oxygen diffusion path and improve the oxidation resistance of ZrC. The results indicate that ZrC-SiC-C microspheres can be promisingly used as EMW absorbents in ultra-high temperature environments.

Synthesis of SiC/SiO2 core\u2013shell nanowires with good optical properties on Ni/SiO2/Si substrate via ferrocene pyrolysis at low temperature

In this study, the high-density SiC/SiO2 core–shell nanowires were synthesized on the nickel coated SiO2 (100 nm)/Si substrate by chemical vapor deposition (CVD) method with ferrocene precursor at temperature 1000 °C compared to previous studies (1300–1600 °C). The present work provides an efficient strategy for the production of SiC/SiO2 nanowires with uniform morphology and good optical properties, where the Ni layer plays important roles for this fabrication at low temperature which reduces the decomposition temperature of hydrocarbon gases and improves the growth quality of SiC nanowires. The as-synthesized SiC/SiO2 nanowires consist of single crystal 3C structures as well as 3C structures with defects along [111] direction. In the photoluminescence (PL) spectrum, the SiC/SiO2 core–shell nanowires revealed an obvious blueshift. The blueshift is due to the formation of nanoscale silicon carbide polytypism caused by the stacking faults in 3C–SiC and the nanoscale polytypism also caused the transition from indirect to direct bandgap which explains why the stacking faults percentage in SiC confirmed from X-ray diffraction (XRD) is 19%, but ultimately makes the strongest emission intensity. Finally, the PL characteristics are further improved by changing the diameter of the SiC nanowire and etching and an approximate model followed by the vapor–liquid–solid (VLS) mechanism was proposed to explain the possible growth mechanism of the SiC/SiO2 nanowires.

(Invited) Nano-Precision Deep Reactive Ion Etching of Monocrystalline 4H-SiCOI for Bulk Acoustic Wave Resonators with Ultra-Low Dissipation

Introduction Micromechanical resonators with ultra-low energy dissipation are essential for a wide range of applications, including chemical sensors, and inertial sensors for navigation in GPS-occluded environments [1]. While ease of batch fabrication along with high-fidelity wafer-level processing have made monocrystalline silicon (Si) the preeminent substrate for seamlessly integrated microelectromechanical systems (MEMS), Si may not be suited to address the ever-growing demand for high-precision MEMS instruments robust to harsh environments. As the quest for low dissipation is plateauing with the direct observation of Si’s quantum limit, monocrystalline Silicon Carbide (SiC) is under active investigation for its promise of room-temperature mechanical Qs exceeding 100M at 6 MHz, owing to its extraordinary Akhiezer damping, which sits 30x below that of Si. Such high Qs are critical to demonstrate navigation-grade resonant gyroscopes with Angle Random Walk (ARW) near 0.00017°√hr, matching the performance of ring laser gyroscopes while being potentially vastly more portable and affordable. Ultra-low Dissipation SiC Resonators This paper reports on the implementation of capacitive SiC resonators with micron-scale transduction gaps, exhibiting fQ=1.25x1014 Hz, a 5-fold improvement over Si’s limits which has already been reported in [3]. These results are particularly interesting because SiC is more susceptible to thermoelastic damping (TED) than Si, by a factor near 5x. To break through the barrier set by material properties that grant an inferior Q TED limit, we have fabricated clamped-clamped beam [4], bulk acoustic wave (BAW) disk [5-6], and Lamé mode resonators [3] using high-density plasma etching of monocrystalline 4H-SiC-on-Insulator (SiCOI) fusion-bonded substrates in STS AOE. We have experimentally verified that these resonators have a decreasing susceptibility to TED in accordance with COMSOL simulations. While the volume-preserving Lamé mode is virtually TED-free in a tether-less square configuration, the unavoidable introduction of tethers and sidewall roughness due to the finite precision of deep reactive ion etching (DRIE) of SiC exacerbates TED. Method While the overarching fabrication details have been published elsewhere [3-6], the SiC DRIE optimization in STS AOE is presented here for the fist time. Plasma etching of SiC can be accompanied by the undesired formation of micropillars because the metallofluorinated NiCxFy compound accumulates on the sidewall and flakes off under various conditions. This issue is circumvented by tailoring the DRIE recipe to reduce the growth rate of the passivation layer. With that in mind, we typically flow an excess of Ar compared to SF6 to starve the trenches from F-based species that tend to polymerize with exposed C atoms. We optimize the coil and platen power to generate a self-bias DC voltage of nearly 280V and reduce the pressure to 8mTorr to prevent any sidewall damage due to the lack of passivation on the sidewall. Results and Conclusions Fig. 1 reveals that selecting bulk acoustic wave (BAW) mode resonators and operating deep in their adiabatic regime enables to the barrier set by TED in monocrystalline SiC, unlike for flexural resonator that operate near the Debye peak. However, surface TED can still limit Q if asperities form on the sidewall of the SiC BAW resonators; we prevent their formation by tailoring the DRIE recipe to limit the deposition of the NiCxFy passivation and by intermittently removing the passivation in wet etchants (Fig. 2). Moreover, removing the passivation enables to etch high-aspect-ratio trenches in SiCOI wafers with nanoscale smoothness (Fig. 3). By designing acoustically deaf SiC Lamé resonators [3], we reveal that SiCOI substrates can support ultra-low dissipation resonators, which fQ=1.25x10 14 Hz, 5x improvement over the limit of monocrystalline Si (Fig. 4). Through the development of nano-scale precision SiC DRIE, this paper opens the door to a myriad of high-performance chip-scale SiC instruments that can be deployed in harsh environments.

Elastic Properties of GaN and AlN Films Formed on SiC/Si Hybrid Substrate, a Porous Basis

The nanoindentation method was used to study the elastic properties of gallium nitride and aluminum nitride films grown on nanoscale silicon carbide on silicon (SiC/Si), a new type of substrate. The values of the Young’s modulus of epitaxial films of such wide-gap semiconductors as GaN and AlN, grown on substrates SiC/Si. were determined for the first time. It was experimentally established using the nanoindentation method that the Young’s modulus of the GaN epitaxial layer on SiC/Si is 265 GPa, and that of the AlN film is 223 GPa. Using atomic force microscopy and spectral ellipsometry, the structural characteristics of gallium nitride and aluminum nitride films have been studied. The thicknesses of the films and the roughness of their surface are determined.

Study of Elastic Properties of SiC Films Synthesized on Si Substrates by the Method of Atomic Substitution

The elastic properties of nanoscale silicon carbide film grown on a silicon substrate by the method of atomic substitution were studied. The Young modulus of nanoscale silicon carbide was for the first time measured by nanoindentation method. The structural characteristics of silicon carbide film on silicon were studied by the optical profilometry and spectral ellipsometry; the roughness and thickness of film were m-easured.

Mechanically robust and abrasion-resistant polymer nanocomposites for potential applications as advanced clearance joints

Despite exceptional dimensional stability, polyamide 6 (PA6) still suffers relatively low mechanical strength and stiffness as compared with metallic and ceramic materials, which thus significantly limits its engineering applications. Herein, we have demonstrated the fabrication of high-performance PA6 composites with excellent mechanical and wear resistance by introducing nanoscale silicon carbide (SiC) as the reinforcer and anti-wear agents. The results show that the addition of 5 wt% nanoscale SiC (NS) increases the tensile strength of PA6 by 54% (reaching 64.8 MPa) while the elongation at break is over 6 times (around 304%) of that of the PA6 matrix, which giving rise to a 9.6 times increase in the fracture toughness. Moreover, the addition of 30 wt% of NS reduces the friction coefficient from 0.31 for the PA6 to 0.12, indicating improved anti-wear performances. Such significant improvements in both mechanical and anti-wear properties are primarily due to the high stiffness of NS and the strong interfacial interactions with the PA6 matrix. In addition, the effects of friction coefficient on dynamic characteristics of mechanism with clearance are also investigated to gain an insightful understanding on the improved anti-wear properties. This work provides a facile approach to the design of advanced polymer composites combining excellent mechanical and anti-wear performances.

Thermoelasticity of Nanoscale Silicon Carbide Membranes Excited by Extreme Ultraviolet Transient Gratings: Implications for Mechanical and Thermal Management

Understanding and controlling the thermal transport at nanoscale is a key ingredient for the development of future nanoelectronical devices. In this study of thin silicon carbide (SiC) membrane we demonstrate the potential of free electron laser extreme ultraviolet (EUV) transient grating (TG) technique as contactless probe for thermoelastic response at length scales of 84 nm, where the Fourier heat diffusion law is no longer valid. The results have revealed that the mechanical behavior of the system can be fully described in the framework of Lamb waves. Moreover, by use of a bidimensional spatial detector to measure the TG signal, a new feature is the observed, time dependence in the emission angle of the transient diffraction, correlated to the transient grating signal intensity.

Исследование упругих свойств пленок SiC, синтезированных на подложках Si методом замещения атомов

The elastic properties of a nanoscale film of silicon carbide grown on a silicon substrate by atom substitution are studied. For the first time, the Young's modulus of nanoscale silicon carbide was measured by nanoindentation. Using optical profilometry and spectral ellipsometry, the structural characteristics of a silicon carbide film on silicon were studied, namely, the film roughness and its thickness were calculated.

Synthesis and Characterization of Silicon Carbide in the Application of High Temperature Solar Surface Receptors

The use of ceramic surfaces for thermal solar concentrators are not new, but the high costs of fabrication and limited thermal properties have banned the application of such at large scale. Silicon carbide (SiC) is well known due to its high thermo-mechanical properties and spectral absorbance. Because of its capacities to enhance the energy transfer and its resistance to high temperatures silicon carbide have been recognized in our group as a possible improvement to increase the efficiency of electric energy production. At nano-scale SiC shows high surface area and porosity that could be tuned, making it a state-of-the-art material to be used in the application of thermal solar receptors in “Central Tower” power plants. Although the advantages are favorable, the high temperature needs for its synthesis have been an issue for its spread. In the present work, we introduce a novel method to synthesize SiC powders at lower temperature (650°C) we present also its characterization for the potential application in the concentration of thermal solar energy at high temperatures.

A Novel Nanoscale 4H-SiC-on-Insulator MOSFET Using Step Doping Channel

In this paper, we present the unique features exhibited by a novel step doping channel technique in nanoscale silicon carbide metal-oxide-semiconductor field-effect transistors (SDC-MOSFETs) for reaching a suitable threshold voltage upon device scaling and reliability improvement. The device demonstrates large enhancements in performance areas such as output resistance, hot-electron reliability, and threshold voltage upon channel-length or drain-voltage variation. Also, we describe an optimization technique in SDC-MOSFET for improving the threshold-voltage characterization. It was also found that the device performance is very much dependent upon the SDC region parameters. Results show that the most difficult problem of using silicon carbide in VLSI circuits could be solved and that the proposed silicon carbide MOSFETs can work very well in the nanoscale regime.

Synthesis of nanostructured SiC using the pulsed laser deposition technique

We report the new results on the direct synthesis of nanostructured silicon carbide (SiC) materials using the pulsed laser deposition technique. Scanning electron microscopy images revealed that SiC nanoholes, nanosprouts, nanowires, and nanoneedles were obtained. The crystallographic structure, chemical composition, and bond structure of the nanoscale SiC materials were investigated using X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy. The transverse optical mode and longitudinal optical mode in Raman spectra were found to become sharper as the substrate temperature was increased, while the material structure evolved from amorphous to crystalline.

Rapid, low temperature microwave synthesis of novel carbon nanotube–silicon carbide composite

Single wall carbon nanotubes (SWNTs) incorporated into ceramic matrices are known to impart enhanced mechanical, thermal and electrical properties to the composites formed. Current procedures for their synthesis face challenges, such as, the non-uniform dispersion of the SWNTs and their damage during high temperature processing in a reactive environment. These have led to poor interfacial matrix to SWNT adhesion and the ineffective utilization of the unique properties of the nanotubes. Here we report a rapid, low temperature microwave-induced reaction to create a novel nanoscale silicon carbide (SiC)–SWNT composite. The reaction, which was completed in 10 min, involves the decomposition of chloro-trimethylsilane and the simultaneous nucleation of nanoscale SiC spheres on the SWNT bundles. The bulk composite is a branched tree-like structure comprised of three-dimensionally arrayed SiC–SWNTs. The uniqueness of this approach lies in the formation of a ceramic directly on the SWNTs, rather than physical mixing, or the growth of nanotubes in a ceramic matrix.

A new sintering additive for silicon carbide ceramic

Silicon carbide (SiC) ceramic with nanoscale silicon carbide powder and oxide (MgO+Al 2O 3+Y 2O 3) or nitrate salt [Mg(NO 3) 2+Al(NO 3) 3+Y(NO 3) 3] additives was hot-pressed at 1800 °C, 25 MPa, for 30 min. All the samples had fine, equiaxed microstructures with an average grain size less than 1 μm. The addition of nanoscale SiC did not effectively improve the relative density. Whether nano-SiC was added or not, the samples with nitrate salt additives had a higher relative density than their counterparts with oxide additives, and the maximum values were as high as 98.1 and 97.7%, respectively. Crystalline YAG phase was detected by XRD only in samples with nitrate salt additives, and the major phases in the oxide additive samples were the same 3C and 4H polytypes as those in the starting powders. Compared with the previous study, the elemental distribution of Y, Al, and Mg was more homogeneous in the oxide additive samples.