Papers by Keyword: Silicon Carbide (SiC)

Abstract: Deep-level defects in 4H-SiC Schottky diodes were studied using deep level transient spectroscopy (DLTS). The epitaxial layers, doped with N and grown on standard n+4H-SiC substrates were exposed to aluminium ion implantation process under the Schottky contact and of junction termination extension (JTE). The studies performed within 80-400 K temperature range revealed five deep electron traps, with a dominant double peak at around room temperature related to the Z1/Z2 defect. The thorough analysis of the DLTS-line shape and DLTS-line behaviour on DLTS measurement conditions made possible to distinguish and identify all the observed deep levels.

Abstract: SiC is fabricated by chemical vapor deposition (CVD) on graphite and Si₃N₄ ceramic respectively. The morphology, composition, grain size and electrical conductivity of SiC deposited on graphite (CVD-SiC_(C)) and on Si₃N₄ ceramic (CVD-SiC_(N)) are investigated and compared. The morphology of CVD-SiC_(C) and CVD-SiC_(N) is much different with each other. The grain size of CVD-SiC_(C) is bigger than that of CVD-SiC_(N). It is nearly stoichiometric in CVD-SiC_(C), while carbon-rich in CVD-SiC_(N), so the electrical conductivity and dielectric loss of CVD-SiC_(N) are much higher than that of CVD-SiC_(C). As the annealing temperature increases, the grain size and electrical conductivity of CVD-SiC_(C) and CVD-SiC_(N) both increase.

Abstract: The composite specimens have been prepared using fused corundum, silicon and bauxite-based β-SiAlON powder as starting materials. The physical properties, high temperature modulus of rupture (HMOR), thermal shock resistance (TSR), phase composition and microstructure of the specimens after firing at 1500°C have been studied. The results show: (1) Al₂O₃-SiC-SiAlON composites are sintered well at 1500°C. (2) HMOR and TSR of the specimens increase with increase of Si content, high temperature properties are further increased with appropriate β-SiAlON addition. (3) The in-situ formed SiC and O’-SiAlON fill in the interstices of corundum skeleton structure, forming interlocking network structure, thus creating strengthening and toughening effects.

Abstract: Nanometer-sized β-SiC were synthesized by carbothermal reduction of silica sol with acetylene carbon black at 1600 °C for 2h. Three kinds (straight, bamboo-like, branch-like) of SiC nanowires were deposited on the graphite plate, while SiC particle agglomerates and nanowires were formed in the graphite crucible. All the nanowires were formed via VS mechanism through the reaction between gaseous SiO and CO produced from the process of carbothermal reduction.

Abstract: Wear behaviors of MoSi₂ against Al₂O₃ or SiC under 30N at 1000°C in air have been investigated by using an XP-5 type High Temperature Friction and Wear Tester. The worn surfaces and phases of samples were characterized by scanning electron microscope (SEM) and X-ray diffractometer, respectively. Result shows the wear rate and friction coefficient of MoSi₂ decreases with the increase of sliding speed. SiC is superior to Al₂O₃ as the counter-face materials of MoSi₂. Serious adhesion leads to very high wear rate of Al₂O₃ in this experiment. SiC shows a surprising mass weighing phenomenon, which is caused by oxidation. The main wear mechanism of MoSi₂ against Al₂O₃ is oxidation and adhesion. However when against SiC, it is chiefly controlled by grinding.

Abstract: The dielectric relaxation behavior of poly (vinylidene fluoride) based composites filled with beta silicon carbide nanoparticles were investigated over a wide frequency range and temperature intervals. The composites exhibited dielectric relaxations in the tested frequency range and the relaxations of composites can be well described via the modulus formalism of dielectric spectroscopy. Further, activation energy determined from the isothermal dielectric relaxations tended to decrease with increasing SiC indicating the promotion of SiC to the dipole relaxations of PVDF.

Abstract: Binary poly(vinylidene fluoride)/silicon carbide (PVDF/SiC) composites and its graphite nanosheets (GN) doped ternary hybrids were fabricated using simple solution mixing and hot compression molding process. The dielectric behavior of such hybrids was studied over a wide frequency range. Additions of graphite nanosheets with their concentrations close to the percolation threshold were found to be very effective to enhance the dielectric permittivity of PVDF/SiC system. The dielectric constant for PVDF/SiC/GN 80/20/2 system was ~ 200, being twenty times higher than that of neat PVDF. Furthermore, the dielectric behavior of such hybrid displayed strong frequency dependence.

Abstract: In this study, SiC films were deposited by reactive DC magnetron sputtering of high purity (99.999%) Si target in Ar/CH4 gas mixture. Three types of substrates, AISI M2 grade high speed steel, glass, and Si (100) were used in each deposition. Films were grown with different compositions at 50 oC and 250 oC by varying (0–50 %) CH4/Ar processing gas ratios. Microstructural properties of SiC films were characterized by cross-sectional FE–SEM (Field–Emission Scanning Electron Microscope) observations. XRD (X–Ray Diffractometer) results indicated that films were amorphous. Friction coefficients as low as 0.1 were obtained from SiC coatings against Al2O3 balls, according to the tribological tests. Optical investigations showed that the transparency and opacity of SiC films could easily be tailored by modifying Si and C concentrations in the coatings.

Abstract: This paper reports the influence of sintering additives (RE2O3, Al2O3RE2O3, RE = Yb, Y and Gd, 13 vol%) and mixing effect of 30 nm SiC powder with 800 nm SiC powder on phases of grain boundaries, grain size of SiC, fracture toughness and strength of SiC hot-pressed at 1950°C under 39 MPa of applied pressure. Rare earth ions were uniformly adsorbed on negatively charged SiC particles with 150 nm Al2O3 particles in aqueous suspensions at pH 5. A rapid densification of SiC with one component RE2O3 occurred above 1700°C when a liquid of SiO2 (formed on SiC particles)RE2O3 system was formed. The Al2O3RE2O3 additives lowered a liquid formation temperature to 14001500°C and enhanced the densification rate of SiC. An increased solubility of 30 nm SiC in a liquid during dissolution-precipitation process provided an amorphous phase of SiCSiO2Al2O3RE2O3 system at grain boundaries and suppressed the grain growth of SiC. The fracture toughness of dense SiC was dominated by the grain boundary thickness controlled by grain size of SiC and amount of oxide additives. Mixing of 30 nm SiC with 800 nm SiC improved greatly the strength of SiC with two component oxides and the mean flexural strengths reached 740810 MPa.

Abstract: Effects of simultaneous addition of SiO2 and gadrinium oxide on densification of SiC ceramics were examined, and relation between microstructure and their mechanical properties were discussed. Total 11wt% of Gd2O3 and SiO2 were mixed with fine -SiC powder. The weight of Gd2O3 in (Gd2O3 + SiO2) were set as 0, 20, 40, 60, 80 and 100%. The mixture was hot-pressed at 1950oC under 40 MPa applied pressure for 1 h. In the case of 40Gd2O3 and 80Gd2O3 compositions, the effect of sintering temperature from 1900 to 2000oC was also examined. The bulk density increased with increasing Gd2O3 content at the sintering temperature of 1950oC. Bending strength of the sintered bodies also improved with increasing Gd2O3 content generally, but at 40Gd2O3 composition, the maximum over ~800 MPa was observed. Young’s modulous, Vickers hardness and fracture toughness also increased with increasing Gd2O3 content. The distribution of grain boundary phase was not homogeneous. Evaporation of additives, mainly SiO2, caused non-homogeneous distribution of grain boundary phase between outside and inside of sintered bodies. High temperature bending strength of 80Gd2O3 specimen was superior than that of 40Gd2O3 specimen.