Thickness Of SiC Layer Research Articles

Surface phonon resonance: A new mechanism for enhancing photonic spin Hall effect and refractive index sensor

Abstract Metal-based surface plasmon resonance (SPR) plays an important role in enhancing the photonic spin Hall effect (SHE) and developing sensitive optical sensors. However, the very large negative permittivities of metals limit their applications beyond the near-infrared regime. In this work, we theoretically present a new mechanism to enhance the photonic SHE by taking advantage of SiC-supported surface phonon resonance (SPhR) in the mid-infrared regime. The transverse displacement of photonic SHE is very sensitive to the wavelength of incident light and the thickness of SiC layer. Under the optimal parameter setup, the calculated largest transverse displacement of SiC-based SPhR structure reaches up to 163.8 μm, which is much larger than the condition of SPR. Moreover, an NO2 gas sensor based on the SPhR-enhanced photonic SHE is theoretically proposed with the superior sensing performance. Both the intensity and angle sensitivity of this sensor can be effectively manipulated by varying the damping rate of SiC. The results may provide a promising paradigm to enhance the photonic SHE in the mid-infrared region and open up new opportunity of highly sensitive refractive index sensors.

Mechanical degradation of duplex SiC-fiber reinforced SiC matrix composite tubes under a controlled high-temperature steam environment

This paper describes results from the mechanical evaluation of unirradiated SiC fiber–reinforced SiC matrix composite tubes under a controlled high-temperature steam environment. The experiments were aimed at identifying key material degradation behavior under environments relevant to loss-of-coolant accidents of light water reactors. Mechanical tests of the SiC composite tubes at 1000 °C under steam and inert environments were conducted using a unique test capability. The material tested was a duplex tube with a thick monolithic SiC layer on the outer surface. The tubes were subjected to preloading at ∼100 MPa in tension before exposure to high-temperature steam with up to 75 % of the preload at a constant displacement. In the presence of matrix cracks, the steam exposure caused embrittlement of the SiC composite tubes and failure at a stress level below the pretest stress. The material degradation was explained by a fiber oxidation model, which can be applied to various SiC cladding concepts. The embrittlement could be a limiting factor for using SiC cladding subjected to loss-of-coolant accident conditions.

Imaging and spectrometric performance of SiC Timepix3 radiation camera

A Schottky barrier radiation detector and pixel imaging sensor fabricated from epitaxially grown SiC semiconductor were analyzed. The detector was based on an 80 μm thick epitaxial SiC layer. Capacitance-voltage measurement was performed to study the thickness of the space charge region of the detector as a function of applied bias. The results showed that the detector was completely depleted at a reverse bias higher than 300 V. The impurity concentration profile was also calculated, which indicated a net impurity concentration below 1.5×1014 cm-3. A prototype of a SiC Timpix3 radiation camera was fabricated, and its energy resolution was investigated using the 241Am radioisotope. The camera exhibited an energy resolution of 4.5 keV for 60 keV gamma photons. X-ray fluorescence photons (from 14 keV to 22 keV) were detected with a resolution below 2.0 keV. The imaging quality of the camera was investigated using a test object. The prototype showed a high-quality image performance with a stable count rate, which was determined from uniform intensity profiles extracted from parts of the test object image. A disadvantage of this prototype is that the radiation hits the detector from the side of the substrate and only then it reaches its active SiC epitaxial layer. This represents a dead layer that reduced the detection efficiency of X-rays below 10 keV.

Effect of SiC layer on microwave absorption properties of novel three-dimensional interconnected SiC foam with double-layer hollow skeleton

To design a lightweight and high-performance absorber, this work introduced a novel three-dimensional interconnected SiC foam with double-layer hollow skeleton (3D-ISF), which was prepared by depositing SiC, pyrolytic carbon, and SiC layer on interconnected carbon foam, followed by oxidation of carbon. SEM results showed the interconnected hollow structure had been successfully synthesized, which was beneficial for microwave absorbing efficiency, and numerous columnar SiC defects were observed and played a critical role in the microwave absorption properties. The electromagnetic performances of 3D-ISF-I and 3D-ISF-II were investigated in depth. With the increase of thickness of SiC layer, 3D-ISF-II exhibited a better microwave absorption property, which could be ascribed to the higher impedance matching ratio (Zr) and attenuation constant (α). The optimum reflection loss value of 3D-ISF-II could reach −45.649 dB while that of 3D-ISF-I was just −32.070 dB. There is no doubt that the prepared materials have tunable microwave absorbing properties, which can promote the development of SiC-based absorbing materials to a certain extent. Finally, it was confirmed that the Zr played a dominant role in 3D-ISF, which provided practical guidance for the design of porous materials.

Asymmetric and tunable infrared emission in metamaterials composed by oriented air voids into a polar material

ABSTRACTWe numerically investigated the asymmetric spectral emissivity in the mid- to long-infrared range of a metamaterial composed by subwavelength oriented air inclusions into a polar (SiC) matrix. The longitudinal phononic resonance can be excited and tuned as a function of the inclusions content and orientation, within the application limits of the effective medium homogenization technique. Furthermore, our numerical results show that it is possible to enhance the emissivity in a given direction rather than in the opposite one by continuously varying the inclusions filling factor along the film thickness. As an example, we design a graded air inclusion pattern starting from a few microns thick SiC layer. We show that a strongly asymmetric (forward vs. backward) emission along the normal direction to the surface can be achieved.

Development, Characterization, and Testing of a SiC-Based Material for Flow Channel Inserts in High-Temperature DCLL Blankets

Flow channel inserts (FCIs) are the key elements in the high-temperature dual-coolant lead-lithium blanket, since in this concept the flowing PbLi reaches temperatures near 700 °C and FCIs should provide the necessary thermal and electrical insulations to assure a safe blanket performance. In this paper, the use of a SiC-sandwich material for FCIs consisting of a porous SiC core covered by a dense chemical vapor deposition-SiC layer is studied. A fabrication procedure for porous SiC is proposed and the resulting materials are characterized in terms of thermal and electrical conductivities (the latter before and after being subjected to ionizing radiation) and flexural strength. SiC materials with a wide range of porosities are produced; in addition, preliminary results using an alternative route based on the gel-casting technique are also presented, including the fabrication of hollow samples to be part of future lab-scale FCI prototypes. Finally, to study the corrosion resistance of the material in hot PbLi, corrosion tests under static PbLi at 700 °C and under flowing PbLi at ~10 cm/s and 550 °C, with and without a 1.8–2T magnetic field, were performed to materials coated with a 200–400- $\mu \text{m}$ -thick dense SiC layer, obtaining promising results.

Three-Dimensional Intercalated Porous Graphene on Si(111)

Three-dimensional intercalated porous graphene has been formed on Si(111) by electron beam evaporation under appropriate conditions and its structural and electronic properties investigated in detail by reflection high-energy electron diffraction, x-ray photoemission spectroscopy, Raman spectroscopy, high-resolution scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. The results show that the crystalline quality of the porous graphene depended not only on the substrate temperature but also on the SiC layer thickness during carbon atom deposition.

The Gorsky effect in the synthesis of silicon-carbide films from silicon by topochemical substitution of atoms

The mechanisms of evaporation of silicon from the surface of silicon carbide (SiC) grown by atomic substitution are studied. It is assumed that the emergence of elastic deformations at the stage of cooling of the sample with a SiC film is one of the causes of Si evaporation. It is demonstrated theoretically that elastic stresses induce the mechanochemical Gorsky effect in the SiC layer. This effect initiates redistribution of Si and C atoms in the SiC layer, which results in violation of the stoichiometry of films and asymmetry of their composition over the SiC-layer thickness. A method for growing epitaxial SiC films with a homogeneous composition and a low density of silicon vacancies from a gas mixture of carbon monoxide and trichlorosilane is proposed.

Synthesis of an oxidation-resistant SiC coating on graphite and modeling analysis with thermodynamics calculations

AbstractA graded SiC coating was prepared on a graphite substrate by a pack cementation technique at 1 873 K to improve the oxidation resistance. The HSC Chemistry software was used for thermodynamics calculations. The coating was characterized by means of X-ray diffraction and scanning electron microscopy. Isothermal oxidation testing of the samples was performed at 1 773 K in air. The modeling analysis indicated that aluminum oxide can be reduced and an SiC coating can be formed due to the reaction of silicon with CO and carbon with SiO. The growth of the SiC nanofibers was attributed to the gaseous reaction of SiO with CO. A 600 μm thick SiC layer can be observed at the graphite–coating interface. The simulation and experimental results were consistent with each other. The mass loss of the SiC coated sample was 1.1 % after oxidation for 10 h, whereas the graphite was fully oxidized after 1 h.

Sintering of SiC Coating Layer on Graphite Spheres Prepared by Pack Cementation

Pack cementation is an effective method in the manufacture of SiC coating on carbon material substrate surface, which is a controllable and simple process. Meanwhile, due to the reactive infiltration process of powder mixture into the substrate, a gradient transition structure layer is formed between the substrate and outer layer. In this paper, SiC was coated on the spherical substrates taken from the matrix graphite pebbles of high temperature gas-cooled reactor (HTR) fuel element. Relations between the Si/C content ratio of the pack mixture and the thickness of SiC layer were studied. Analysis found that Si/C content ratio, powder size and sintering time are factors influenced the thickness of the coating layers. When the Si/C content ratio was higher than 3:1, a uniform thickness coating bonded well with the substrate was obtained. The composition phases and thickness of coating layer etc. also had obvious changes along with the change of the Si/C content ratio in this research.Results also show that sintering atmosphere and particle size of powders are important factors affecting coating microstructure, while a vacuum atmosphere can smaller powder size can help to get a dense structure.

SiC protective coating for photovoltaic retinal prosthesis

Objective. To evaluate plasma-enhanced, chemically vapor deposited (PECVD) amorphous silicon carbide (α-SiC:H) as a protective coating for retinal prostheses and other implantable devices, and to study their failure mechanisms in vivo. Approach. Retinal prostheses were implanted in rats sub-retinally for up to 1 year. Degradation of implants was characterized by optical and scanning electron microscopy. Dissolution rates of SiC, SiNx and thermal SiO2 were measured in accelerated soaking tests in saline at 87 °C. Defects in SiC films were revealed and analyzed by selectively removing the materials underneath those defects. Main results. At 87 °C SiNx dissolved at 18.3 ± 0.3 nm d−1, while SiO2 grown at high temperature (1000 °C) dissolved at 0.104 ± 0.008 nm d−1. SiC films demonstrated the best stability, with no quantifiable change after 112 d. Defects in thin SiC films appeared primarily over complicated topography and rough surfaces. Significance. SiC coatings demonstrating no erosion in accelerated aging test for 112 d at 87 °C, equivalent to about 10 years in vivo, can offer effective protection of the implants. Photovoltaic retinal prostheses with PECVD SiC coatings exhibited effective protection from erosion during the 4 month follow-up in vivo. The optimal thickness of SiC layers is about 560 nm, as defined by anti-reflective properties and by sufficient coverage to eliminate defects.

Growth optimization and applicability of thick on-axis SiC layers using sublimation epitaxy in vacuum

We demonstrate growth of thick SiC layers (100–200µm) on nominally on-axis hexagonal substrates using sublimation epitaxy in vacuum (10−5mbar) at temperatures varying from 1700 to 1975°C with growth rates up to 270µm/h and 70µm/h for 6H- and 4H–SiC, respectively. The stability of hexagonal polytypes are related to process growth parameters and temperature profile which can be engineered using different thermal insulation materials and adjustment of the induction coil position with respect to the graphite crucible. We show that there exists a range of growth rates for which single-hexagonal polytype free of foreign polytype inclusions can be maintained. Further on, foreign polytypes like 3C–SiC can be stabilized by moving out of the process window. The applicability of on-axis growth is demonstrated by growing a 200µm thick homoepitaxial 6H–SiC layer co-doped with nitrogen and boron in a range of 1018cm−3 at a growth rate of about 270µm/h. Such layers are of interest as a near UV to visible light converters in a monolithic white light emitting diode concept, where subsequent nitride-stack growth benefits from the on-axis orientation of the SiC layer.

Fabrication and characterization of HfC/SiC nanomultilayered films with enhanced mechanical properties

A series of HfC/SiC nanomultilayered films with different SiC layer thickness were synthesized by reactive magnetron sputtering. The effect of SiC layer thickness on the microstructure and mechanical properties of HfC/SiC nanomultilayered films were studied. When SiC layer thickness was less than 0.9 nm, originally amorphous SiC layers were forced to crystallize and grow epitaxially with HfC layers, resulting in the improvement of crystallization integrality and enhancement in hardness and elastic modulus. The maximum hardness and elastic modulus could reach 36.2 GPa and 419 GPa, respectively. With further increase of SiC layer thickness, SiC layers changed back to amorphous state and damaged the epitaxial growth structure, leading to deterioration of mechanical properties.

Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers.

Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%.PACS81.07.Ta; 78.67.Pt; 88.40.jj

Novel Electrical Characterization of Thin 3C-SiC Films on Si Substrates

Thin semiconductor films provide many functional uses in the fields of electronics, sensors, optics, and microelectro-mechanical systems (MEMS). A prime example is the case of thin film 3C-Silicon Carbide epitaxially grown on standard silicon wafers. The required SiC layer thickness for these applications ranges from a few nanometers to a few microns, and process conditions that control film stress, doping type and concentration, crystal orientation, and surface roughness need to be developed along with accurate physical and electrical characterization techniques. In this paper, we present two novel variations on established measurement techniques. Firstly, the hotprobe technique is used as a simple, non-destructive method to monitor film doping and crystal quality based on the open circuit voltage and short circuit currents. Results are presented for both ntype and p-type films grown on (100) and (111) silicon orientations, and supported by transmission electron micrographs and X-ray diffraction data. Secondly, a technique based on the four point resistivity measurement is used to determine film resistivity while eliminating the errors introduced by substrate leakage.

Diamond as substrate for 3C‐SiC growth: A TEM study

Vapor–liquid–solid (V–L–S) growth of SiC on (100) diamond substrate is reported. The crystalline quality is evaluated by transmission electron microscopy (TEM). Diffraction contrast (CTEM) observations allowed confirming the growth of fully lattice relaxed SiC 3C‐type crystalline structure. Defects as dislocations at the diamond/SiC interface and stacking faults, in the thick SiC layer are revealed by high resolution TEM and CTEM. From the invisibility criteria, using dark field observations, 〈110〉 type Burger vector are identified.

Nanosecond Pulsed Laser Processing of Ion Implanted Single Crystal Silicon Carbide Thin Layers

Abstract The attractiveness of single crystal SiC in a variety of high power, high voltage, and high temperature device applications such as electric vehicles and jet engines is counteracted by the very high cost of substrates. Precision cutting of multiple micrometre thick SiC layers and transferring them to lower cost substrates would drive the cost down and allow expanding the use of single crystal SiC. In this study, laser beam processing has been utilized to exfoliate thin layers from a surface of single crystal SiC that was prepared with hydrogen and boron ion implantation. The layer thickness of 1 μm has been achieved by ion implantation that formed voids and microcracks under the surface at a layer of 150 nm thick. High energy laser pulses provided the layer removal and its transfer to bonded Si substrate has been shown. Exfoliated surfaces and topography have been evaluated with Scanning Electron Microscopy. Furthermore, thermal modelling of pulse laser irradiation of implanted multi-layer SiC material has been conducted and temperature profiles are obtained at different peak pulse intensity settings to optimize exfoliation process parameters. It was found that laser exfoliation mechanism can be further improved by higher optical absorptance of defect rich layer obtained with boron ion implantation.

Improved photovoltaic properties of Si quantum dots/SiC multilayers-based heterojunction solar cells by reducing tunneling barrier thickness

Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC stacked structures prepared in plasma enhanced chemical vapor deposition (PECVD) system. The microstructures were examined by transmission electron microscopy (TEM) and Raman spectroscopy, and results demonstrate the formation of Si QDs. Moreover, p-i-n devices containing Si QDs/SiC multilayers were fabricated, and their photovoltaic property was investigated. It was found that these devices show the good spectral response in a wide wavelength range (400–1200 nm). And it was also observed that by reducing the thickness of SiC layer from 4 to 2 nm, the external quantum efficiency was obviously enhanced and the short circuit current density (Jsc) was increased from 17.5 to 28.3 mA/cm2, indicating the collection efficiency of photo-generated carriers was improved due to the reduced SiC barriers.

The Effect of SiC Coating on the Joint of C/C and LAS

The SiC coating on C/C composites was prepared by CVD and pack-cementation method in this paper, then SiC coated C/C composites was jointed with LAS glass ceramic at 1423K for 30min and the pressure of 15 MPa. The structure and morphology of the SiC coating and as-received joints were analyzed by SEM and XRD; shear strength of joint was examined through the Instron universal testing tensile machine. The results show that the thickness of SiC coating prepared by CVD is about 30μm, while the thickness of SiC layer by pack-cementation is nearly 100μm, and the layer is easier to connect with LAS glass ceramic owing to the rough surface and wedge-shaped structure on the SiC coating; the shear strength of joint between SiC coating coated C/C and LAS by pack-cementation is greater than the joint of C/C- LAS with SiC coating prepared by CVD.

Crystallization of amorphous SiC and superhardness effect in CrAlN/SiC nanomultilayered films

A series of CrAlN/SiC nanomultilayers with different SiC layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The results indicated that, when SiC layer thickness was less than 0.8nm, amorphous SiC layers were forced to crystallize under the template effect of CrAlN layers and grew epitaxially with CrAlN layers, resulting in abnormal enhancement of mechanical properties. The maximum hardness and elastic modulus could respectively reach 35.4GPa and 431GPa when SiC layer thickness was 0.8nm. With further increase of SiC layer thickness, SiC layers changed back to amorphous state and broken coherent growth structure of nanomultilayers, leading to the decrease of hardness and elastic modulus.