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491.
The SiC/SiO2 deposition was performed to improve the oxidation resistive properties of carbon nanofiber (CNF) from electrospinning at elevated temperatures through sol-gel process. The stabilized polyacrylonitrile (PAN) fibers were coated with SiO2 followed by heat treatment up to 1000 and 1400 °C in an inert argon atmosphere. The chemical compositions of the CNFs surface heat-treated were characterized as C, Si and O existing as SiC and SiO2 compounds on the surface. The uniform and continuous coating improved the oxidation resistance of the carbon nanofibers. The residual weight of the composite was 70-80% and mixture of SiC, SiO2 and some residual carbon after exposure to air at 1000 °C. 相似文献
492.
An improved 4H–SiC power MESFET with double source field plates (DSFP) for high-power applications is proposed (DSFP-MESFET). The DSFP structure significantly modifies the electric field in the drift layer. The influence of the DSFP structure on saturation current, breakdown voltage (Vb), and small-signal characteristics of the DSFP-MESFET were studied by numerical device simulation. The Vb of 359 V is obtained for the DSFP-MESFET compared to 301 V of the conventional source field plate MESFET (LSFP-MESFET). Hence, the maximum output power density of 24.7 and 21.8 W/mm are achieved for the DSFP-MESFET and LSFP-MESFET, respectively, which means 13% improvement for the proposed device. Also, the cut-off frequency (fT) of 24.5 and the maximum oscillation frequency (fmax) of 89.1 GHz for the 4H–SiC DSFP-MESFET are obtained compared to 23.1 and 85.3 GHz for that of the LSFP-MESFET structure, respectively. The DSFP-MESFET shows a superior maximum stable gain (MSG) exceeding 23.3 dB at 3.1 GHz, which is presenting the potential of the proposed device for high-power operations. 相似文献
493.
Nanocomposites (SiC-PANI) based on silicon carbide nanoparticles (SiC) encapsulated in conducting polyaniline (PANI) are synthesized by direct polymerization of PANI on the nanoparticle surfaces. The conductivity of PANI and the nanocomposites was modulated by several doping levels of camphor sulfonic acid (CSA). Electron paramagnetic resonance (EPR) investigations were carried out on representative SiC-PANI samples over the temperature range [100–300 K]. The features of the EPR spectra were analyzed taking into account the paramagnetic species such as polarons with spin S=1/2 involved in two main environments realized in the composites as well as their thermal activation. A critical temperature range 200–225 K was revealed through crossover changes in the thermal behavior of the EPR spectral parameters. Insights on the electronic transport properties and their thermal evolutions were inferred from polarons species probed by EPR and the electrical conductivity in doped nanocomposites. 相似文献
494.
Y. Q. Gao X. B. Hu X. G. Xu X. F. Chen Y. Peng S. Song M. H. Jiang W. X. Huang 《Crystal Research and Technology》2011,46(4):357-360
6H‐SiC single crystals have been successfully grown on (1015) plane seed by sublimation method. High density stacking faults (SFs) were observed by transmission synchrotron radiation X‐ray topography. Based on the invisibility criteria of stacking faults, the displacement vectors of most SFs were determined to be the type of 1/6[1120]. Laser scanning confocal microscopy (LSCM) was used to observe the etching morphology of (0115) wafer. The etching steps of SFs were found and their density decreased from 3.6×103 cm‐1 to 2.0×102 cm‐1 along the <0001> projection direction. The inclination angles of the SFs etching step plane to (10‐15) plane were measured by line scanning of LSCM. It was found that the inclination angles decreased from 20° to 10° along the <0001> projection direction. Different etching characteristics of SFs along radial direction of 6H‐SiC (1015) wafer should be attributed to different displacement vectors and different stacking fault energies for these stacking faults. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
495.
Kenneth B. Joelsson Galia Pozina Wei-Xin Ni Chun-Xia Du Gran V. Hansson 《Journal of luminescence》1998,80(1-4):497-501
Near band edge photoluminescence has been obtained from Si1−yCy quantum well (QW) and neighboring Si1−xGex/Si1−yCy double QW (DQW) structures. Enhanced no-phonon recombination is observed from the DQW structures and it is attributed to a breaking of the k-selection rule in the presence of the heterointerface. The luminescence persists for measurement temperatures up to 30–50 K and the intensity exhibits a quenching behavior with an activation energy equal to 8–20 meV. In electroluminescence only recombination in the Si1−xGex layer has been observed from neighboring Si1−xGex and Si1−yCy DQW structures. 相似文献
496.
497.
M.N. Deo 《Journal of Molecular Spectroscopy》2004,228(1):76-82
The gas phase infrared emission spectrum of the A3Σ−-X3Π electronic transition of SiC has been observed using a high resolution Fourier transform spectrometer. Three bands ν′ − ν″ = 0-1, 0-0, and 1-0 have been observed in the 2770, 3723, and 4578 cm−1 regions, where the 0-1 and 0-0 bands were observed for the first time. The SiC radical was generated by a dc discharge in a flowing mixture of hexamethyl disilane [(CH3)6Si2] and He. A total of 1074 rotational transitions assigned to the 0-1, 0-0, and 1-0 bands have been combined in a simultaneous analysis with previously reported pure rotational data to determine the molecular constants for SiC in the two electronic states. The principal equilibrium molecular constants for the A3Σ− state are: Be = 0.6181195(18) cm−1, αe = 0.0051921(20) cm−1, re = 1.8020884(26) Å, and Te = 3773.31(17) cm−1, with one standard deviation given in parentheses. The effect of a perturbation was recognized between the ν = 4 level of X3Π and the ν = 0 level of A3Σ, and the analysis was carried out to determine the interaction parameter between the two states. 相似文献
498.
Fu Zhiqiang Liang Tongxiang Robin Jean-Charles Tang Chunhe 《Applied Surface Science》2005,240(1-4):349-354
The stability of SiC coating in helium with a low concentration of O2, CO2, and H2O is a key factor for their application in improvement of oxidation resistance of graphite for high temperature gas-cooled reactors (HTGRs). Through thermodynamic analysis, it is found that the influence factor controlling the critical temperature of passive oxidation for SiC is partial pressure of active gas in helium; the critical temperature of passive oxidation for SiC increases with the partial pressure of O2, CO2, and H2O, SiC is prone to undergo active oxidation in He–CO2 and He–H2O system. SiO2/SiC multilayer coating can improve the oxidation resistance of graphite at higher temperature than SiC coating does under normal operation condition for HTGRs. 相似文献
499.
500.
As a valuable ultra‐high‐temperature ceramic (UHTC), ZrC was introduced to SiC ceramic for the preparation of high‐temperature‐resistant ZrC/SiC composite by a polymer‐derived method through the reaction between Cp2Zr(CH=CH2)2 and polymethylsilane (PMS). The composition, structure, element distribution and pyrolysis process of the preceramic polymer polyzirconomethylsilane (PZMS) were investigated by nuclear magnetic resonance, infrared, gel permeation chromatography, X‐ray photoelectron spectroscopy, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy and thermogravimetric analysis. The obtained ZrC/SiC ceramic composites had very good high‐temperature resistance with a weight loss of 7.1% after being subjected to temperatures ranging from 1200 to 2200°C, as the introduction of ZrC prevented the fast growth of crystalline β‐SiC. The ceramic composites prepared by this method were homogeneous with well‐distributed element components, and the ceramic yield reached as high as 78.4%. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献