基于迟滞行为的2D-SiC/SiC复合材料组份力学性能分析

基于剪滞理论, 建立了单向纤维增强陶瓷基复合材料的加卸载理论模型, 分析了基体长碎块和短碎块对材料迟滞力学行为的不同影响. 通过拉伸循环加卸载试验, 获得了2D-SiC/SiC 复合材料的迟滞应力—应变行为.依据材料基体损伤特点, 将试验结果代入长碎块对应理论推导结果, 计算得到了4 个表征材料组份性能的参数:基体开裂应力为90 MPa, 热残余应力为19 MPa, 界面脱粘能为3.1 Jm2, 界面滑移力为74 MPa. 最后结合少量短碎块的存在对试验结果的影响, 定性分析了计算结果的偏差. 结果表明, 获得的材料组分性能参数具有较小的分散性, 并能够准确表征材料整体的力学行为.      

Synthesis of a composite consisting of carbon nanotubes and graphite shell-encapsulated cobalt nanoparticles using plasma-enhanced chemical vapor deposition

We report a simple and effective one-step synthesis route for synthesizing a composite consisted of carbon nanotubes (CNTs) and graphite shell-encapsulated cobalt nanoparticles using plasma-enhanced chemical vapor deposition on Si (1 0 0) substrate covered with catalyst Co particles, discharging a mixture of H₂ and CH₄ gas, and characterize the obtained composite by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscope, and X-ray photoelectron spectroscopy. The results show that CNTs align perpendicularly to the substrate and graphite shell-encapsulated Co nanoparticles clung to the external surfaces of aligned CNTs. The diameter of the graphite shell-encapsulated Co nanoparticles increases with increasing the H₂ content in H₂ and CH₄ carbonaceous gas. A possible growth mechanism of the CNTs and graphite shell-encapsulated cobalt nanoparticles composite has been explored.     

SiC纳米棒的紫外发光研究

采用聚硅氮烷前驱体在高温常压下热裂解的方法制备了3C-SiC纳米棒,在室温下观察到来自纳米棒的378 nm（33?eV） 强紫外发射. 利用扫描电子显微镜、透射电子显微镜、高分辨透射电子显微镜和X射线衍射对样品的形貌和结构进行表征,观察到在该结构中存在类似6H-SiC结构的三层堆垛层错. 利用室温荧光光谱和室温荧光衰减曲线研究了强紫外发射的产生机理,紫外发射来源于3C-SiC纳米棒中的三层堆垛层错的发光. 关键词： 碳化硅 纳米棒 光致发光     

聚合物前驱体衍生SiC纳米棒的光学性质

采用聚硅氮烷前驱体热裂解方法制备SiC纳米棒,并利用SEM、XRD和EDX表征了SiC纳米棒的结构和组成,表明得到的SiC的组分比C：Si接近1：1。用微区Raman和光致发光方法研究了纳米棒的光学性质。观测到SiC的TO模式对应的Raman峰和相邻肩峰。对SiC纳米棒观测到其紫外3．25eV附近强的光致发光峰,我们认为它归结为α型SiC带间的跃迁。通过XRD、Raman和光发射谱,我们推测前驱体热裂解得到的SiC纳米棒是一个混晶,纳米棒的表层是立方晶,而内层主要为a—SiC。     

Barrier height homogeneity for 4.5 kV 4H-SiC Schottky diodes

4.5 kV SiC Schottky diodes have been fabricated using Ni as the Schottky contact. A manufacturing yield of 40% is reached for the bigger area diodes (1.6×1.6 mm²) and of 70% for the smaller ones (0.4×0.4 mm²). The measured variations of barrier height and ideality factor with temperature do not agree with the thermionic model. This has been interpreted in terms of barrier height inhomogeneities using the Werner model. We extracted an average barrier height and its standard deviation . These two parameters are almost independent of the diode size. The variation of the barrier height distribution with field has also been investigated and shows a dependence similar to that of Schottky diodes realized from other semiconductor materials.     

2D-C/SiC复合材料的单轴拉伸力学行为及其强度

通过单调拉伸和循环加卸载试验, 研究了平纹编织C/SiC复合材料的损伤演化过程及其应力-应变行为. 结果表明, 残余应变、卸载模量和外加应力的关系曲线与拉伸应力-应变曲线具有类似的形状. 基于剪滞理论和混合率建立了材料的损伤本构关系和强度模型, 分析计算表明, 残余应变主要由裂纹张开位移和裂纹间距决定, 而卸载模量主要由界面脱粘率决定; 材料的单轴拉伸行为主要由纵向纤维束决定, 横向纤维对材料的整体模量和强度贡献较小. 理论模拟结果与试验值吻合较好.      

Optically controlled SiCGe/SiC heterojunction transistor with charge-compensation layer

A novel optically controlled SiCGe/SiC heterojunction transistor with charge-compensation technique has been simulated by using commercial simulator.This paper discusses the electric field distribution,spectral response and transient response of the device.Due to utilizing p-SiCGe charge-compensation layer,the responsivity increases nearly two times and breakdown voltage increases 33%.The switching characteristic illustrates that the device is latch-free and its fall time is much longer than the rise time.With an increase of the light power density and wavelength,the rise time and fall time will become shorter and longer,respectively.In terms of carrier lifetime,a compromise should be made between the responsivity and switching speed,the ratio of them reaches maximum value when the minority carrier lifetime equals 90 ns.     

Graphene films grown on sapphire substrates via solid source molecular beam epitaxy

A method for growing graphene on a sapphire substrate by depositing an SiC buffer layer and then annealing at high temperature in solid source molecular beam epitaxy (SSMBE) equipment was presented. The structural and electronic properties of the samples were characterized by reflection high energy diffraction (RHEED), X-ray diffraction Φ scans, Raman spectroscopy, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results of the RHEED and Φ scan, as well as the Raman spectra, showed that an epitaxial hexagonal α-SiC layer was grown on the sapphire substrate. The results of the Raman and NEXAFS spectra revealed that the graphene films with the AB Bernal stacking structure were formed on the sapphire substrate after annealing. The layer number of the graphene was between four and five, and the thickness of the unreacted SiC layer was about 1--1.5 nm.     

并联交错PFC技术在磁体电源中的应用

并联交错功率因数校正(powerfactorcorrection,PFC)具有能减小输入电流纹波,减小电感磁芯尺寸,减小输出电容纹波、功率因数高等优点．针对其优点,考虑将该变换器应用到强磁场中心的超导磁体电源的备用方案中,以弥补现在运行电源体积过大的不足．本文主要介绍了并联交错PFC的工作原理,对其参数进行设计和选型,分析了控制方法,利用SiC器件,搭建了１kW 的实验样机,实验验证了方案的可行性,为下一步超导磁体电源的升级改造提供了理论和工程经验。     

Reaching for [6]n SiC‐cyclacenes and [6]n SiC‐acenes: A DFT approach

Density functional theory (DFT) calculations introduced triplet ground states for [6]_n SiC‐cyclacenes and ‐acenes with alternate silabenzene rings including silicon atoms in 2 opposite edges (n = 6, 8, 10, 12). The singlet‐triplet energy gap (ΔE_(S‐T)), binding energy per atom (BE/n), and NBO calculation with very small band gap (ΔE_LUMO‐HOMO) confirmed the triplet ground states. In contrast to polyacenes, the singlet [6]_n SiC‐cyclacenes displayed more stability improvement than triplets, through n increasing. This may open the way for synthesis of larger stable [6]_n SiC‐cyclacenes. The ΔE_(S‐T), BE/n, and the strain energy through homodesmic equations indicated more stability for larger [6]_n SiC‐cyclacenes, which was more noticeable in singlet states. Cyclacenes and acenes with high conductivity and full point charge were introduced as suitable candidates for hydrogen storage.