SiCf/SiC陶瓷复合材料的研究进展

SiCf/SiC陶瓷复合材料具有良好的力学性能、高温抗氧化性和化学稳定性，是航空航天和原子能等领域理想的新一代高温结构材料。本文概述了增强体SiCt的发展状况及存在的问题，对SiCt/SiC材料的制备工艺、界面相的研究状态、材料的损伤破坏机理和目前的应用研究进展做了综述，并分析了SiCf/SiC陶瓷复合材料的研究重点和发展前景。     

Chemical compositions and optical properties of HfOxNy thin films at different substrate temperatures

High-k HfO_xN_y thin films have been grown by radio frequency (rf) reactive sputtering of metal Hf target in N₂/Ar/O₂ ambient at different substrate temperatures. The chemical compositions of the films have been investigated as a function of substrate temperature by X-ray photoelectron spectroscopy (XPS). XPS measurements showed that nitrogen concentration increases with an increase in substrate temperature. Room-temperature spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV was used to investigate the optical properties of the films. SE results demonstrated that refractive index n increases with an increase in substrate temperature. Based on TL parameters which were obtained from the best fit results used in a simulation of the measured spectra, meanwhile, we conclude that the energy band gap (E_g) decreases with an increase in substrate temperature.     

Conduction band states of transition metal (TM) high-k gate dielectrics as determined from X-ray absorption spectra

This paper uses X-ray absorption spectroscopy to study the electronic structure of the high-k gate dielectrics including TM and RE oxides. The results are applicable to TM and rare earth (RE) silicate and aluminate alloys, as well as complex oxides comprised of mixed TM/TM and TM/RE oxides. These studies identify the nature of the lowest conduction band d^* states, which define the optical band gap, E_g, and the conduction band offset energy with respect to crystalline Si, E_B. E_g and E_B scale with the atomic properties of the TM and RE atoms providing important insights for identification high-k dielectrics that meet performance targets for advanced CMOS devices.     

Intermittent Phenomena in Switched Systems With High Coupling Strengths

In this paper, one kind of intermittency generated by a discontinuous system is studied. Although this system, which is composed of two switched subsystems coupled with a high strength, is nonsmooth, the mechanism of this kind of intermittency can be analyzed with several explicit relations between the intermittency characteristics and the system control parameters. In particular, estimates of "steady-state" values of the system (in the laminar phases) and a critical value for this intermittency can be derived, which are helpful in relevant control systems design. Moreover, some power laws for the observed intermittency are obtained and discussed     

Elastic solutions of a cylindrical rod containing periodically distributed inclusions with axisymmetric eigenstrains

Summary. In this paper, we give the elastic solution for a special type of microstructure – a circular cylindrical rod containing periodically distributed inclusions along its axial direction. Each inclusion has the same uniform axisymmetric transformation strain (eigenstrain). Analytical elastic solutions are obtained for the displacements, stresses and elastic strain energy of the rod. The effects of microstructure and its evolution (growth of inclusions) on the elastic stress and strain fields as well as the strain energy of the rod are quantitatively demonstrated. As a result of such microstructure evolution nominal stress-strain relation with strain softening is derived for a rod under uniaxial tension.     

Programmable group-delay module using binary polarization switching

We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.     

Effect of heat treatments on tensile properties and microstructures of wrought Mg−Zn−Zr-RE alloys

The effect of heat treatments on the tensile properties and microstructures of wrought Mg–Zn–Zr-Rare earth alloys MB25 and MB26 have been studied in this paper. It was shown that the homogenization of the cast ingots decreased the strength of the extruded bars because some grain boundary phases were dissolved during the process of this treatment, while the ageing treatment of the extruded bars increased the strength due to the dispersive precipitation of MgZn₂ phase. The quenching + ageing treatments of the extruded bars decreases the strength and plasticity because of the growing up of the grains.Abbreviations ED electron diffraction - GB grain boundary - RE rare earth - TEM transmission electron microscope     

Large-scale quantum mechanical simulations of high- Z metals

High-Z metals constitute a particular challenge for large-scale ab initio electronic-structure calculations, as they require high resolution due to the presence of strongly localized states and require many eigenstates to be computed due to the large number of electrons and need to accurately resolve the Fermi surface. Here, we report recent findings on high-Z metals, using an efficient massively parallel planewave implementation on some of the largest computational architectures currently available. We discuss the particular architectures employed and methodological advances required to harness them effectively. We present a pair-correlation function for U, calculated using quantum molecular dynamics, and discuss relaxations of Pu atoms in the vicinity of defects in aged and alloyed Pu. We find that the self-irradiation associated with aging has a negligible effect on the compressibility of Pu relative to other factors such as alloying. The US Goverment’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

First-principles study of the tensile and fracture of the Al/TiN interface

Employing the density functional theory, we investigate the tensile and fracture processes of the Al/TiN(0 0 1) interface. The simulation presents directly the strain–stress relationship, the ideal tensile strength and the process of bond breaking of the system. Through the analysis of deformation, we find that the softer Al layers deform larger than the harder TiN layers during the tensile process. And fracture occurs between the interface and the sub-interface Al layers. In addition, the results show that during the tensile process, the ripple of the interfacial TiN layer decreases gradually with the increment of the strain. Charge transfer was detected from the Al to TiN layers near the interface area during the tensile process by means of charge density and density of states analyses. The charge transfer affects the fracture process. Compared to our previous study of the Al/TiN(1 1 1) interface, the Al/TiN(0 0 1) interface has smaller work of adhesion and larger tensile strength than the Al/TiN(1 1 1) interface. Our investigation shows that the fractures of the Al/TiN(0 0 1) and (1 1 1) interface systems both happen in the Al layers near the interface.