Effect of LiAl5O8 additions on the sintering and optical transparency of LiAlON

LiAl₅O₈ (zeta alumina) was reaction sintered with α-Al₂O₃ and AlN to produce γ-LiAlON. Zeta alumina transforms from a primitive to a face-centered cubic structure above 1290 °C with a lattice parameter similar to γ-AlON. Weight loss measurements combined with XRD suggest solubility of Li in the spinel structure at elevated temperatures. The Vickers hardness, at a 1-kg load, of the pressureless sintered LiAlON was 16.5 ± 0.5 GPa, independent of the grain size or amount of zeta alumina added, for LiAl₅O₈ additions ranging between 0 and 16 wt.%. In-line transmission in the visible and near-IR regions increased with increasing grain size, most likely due to pore coalescence.     

Structural and Electric Properties of Sol–Gel-Derived Ba0.9Sr0.1TiO3 Multilayers

Crack-free Ba_0.9Sr_0.1TiO₃ (BST) and Mn-doped Ba_0.9Sr_0.1TiO₃ (BSTM) multilayers with thickness over 2 μm have been prepared by chemical solution deposition based on one single precursor. Both multilayers exhibit good performance as Bragg reflectors. Mn doping tends to suppress the leakage current in BST multilayers effectively by smoothing the layers and the reduction of the charge carries. The Mn-doped BST multilayer displays an excellent ferroelectric property, with an average remnant polarization ( P _r⁺– P _r⁻)/2 of 12.69 μC/cm² and an average coercive field ( E ⁺ – E ⁻ )/2 of about 72.95 kV/cm under an applied field of 440 kV/cm.     

Optical property of amorphous semiconductor mercury cadmium telluride from first-principles study

The structural and optical properties of amorphous semiconductor mercury cadmium telluride (a-MCT) are obtained by the first principles calculations. The total pair distribution functions and the density of states show that the a-MCT has the semiconductor characteristic. The calculated results of dielectric function show that E ₂ peak of the imaginary of dielectric function for the crystal mercury cadmium telluride abruptly disappears in the amorphous case due to the long-range disorders. And the imaginary of dielectric function of a-MCT shows a large broad peak, which is in agreement with the available results of other amorphous semiconductors. From the linear extrapolation of the curve ħωɛ ₂(ω)^1/2 versus ħω, it can be obtained that the optical energy gap of amorphous semiconductor Hg_0.5Cd_0.5Te is 0.51±0.05 eV. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2007CB613205), the National Natural Science Foundation of China (Grant Nos.10725418, 10734090, 60576068), the Key Fund of Shanghai Science and Technology Foundation (Grant No. 08JC1421100) and the Knowledge Innovation Program of the Chinese Academy of Sciences     

Organic–inorganic hybrids containing polyimide,organically modified clay and in situ formed polydimethylsiloxane

A series of organic–inorganic hybrid consisting of polyimide (PI) prepared from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA), organically modified montmorillonite (OMMT) and polydimethylsiloxane (PDMS) were successfully prepared by in situ sol–gel process. OMMT was prepared by surface treatment of montmorillonite (MMT) with hexadecyltrimethylammonium bromide. X-ray diffraction (XRD) analysis showed that the OMMT layers were exfoliated into the polymer matrix at 2% of OMMT content. The PI–OMMT–PDMS hybrids at 2% of OMMT content were transparent when PDMS content was less than 5%. The PI–OMMT–PDMS hybrid showed better tensile modulus, strength and elongation at break than that of pristine PI due to the reinforcement effect of OMMT and toughening effect of PDMS. The thermal stability of hybrids such as the decomposition temperature and weight residue at 800 °C also increased with the increase of PDMS content as evidenced by thermogravimetric analysis (TGA).     

Effects of ZrO2 on the structure and magnetic properties of CoPt thin films

[CoPt 1.5 ml/ZrO2 xnm]10 multilayer films were deposited on glass substrates by magnetron sputtering and then annealed in vacuum at 600℃ for 30 min. Their structures and magnetic properties were investigated as a function of ZrO2 content. The results show that the grain size and coercivity first increase and then decrease with the increase in ZrO2 content. The maximum coercivity and grain size are obtained at 37 vol.% of ZrO2. The content of ZrO2 in the film plays an important role in the separation of CoPt grains and in the reduction of intergrain exchange interaction. On the basis of the studies of angular dependent coercivity, it is found that the magnetization reversal of CoPt films with （111 ） texture is different from either the domain wall motion or the S-W type of rotation mode.     

Magnetic,electrical and thermal transport properties of Al–Cr–Fe approximant phases

Two stable approximant phases in the Al–Cr–Fe system – a gamma-brass phase (γ-AlCrFe) and a mixture of two orthorhombic approximants of the decagonal phase (O₁/O₂-AlCrFe) – were investigated using magnetic susceptibility, electrical resistivity and thermal conductivity measurements, combined with structural investigations using X-ray diffraction, light microscopy (LM) and scanning electron microscopy (SEM). The investigated approximants exhibit physical properties that are in many respects between those of regular metals and quasicrystals (QCs); their electrical resistivities show very weak temperature dependences and the resistivity values are higher than for regular metals and lower than for Al-based QCs. The magnetic susceptibility results show the existence of a small fraction (of about 1% for the γ-AlCrFe and about 10 times less for the O₁/O₂-AlCrFe) of localized magnetic moments with Curie-like temperature dependence. Thermal conductivity measurements show that the electronic and lattice contributions are of comparable size at room temperature. While the electronic contribution can be described by the Wiedemann–Franz law, the lattice contribution can be reproduced by the sum of the Debye term (long-wavelength phonons) and the term due to hopping of localized vibrations. At the lowest measured temperature (8 K), scattering of phonons on stacking-fault-like defects limits the heat transport, and this type of defect has also been observed in the LM and SEM structural investigations.     

Relaxations and bonding mechanism of arsenic in-situ impurities in MCT： first-principles study

1 Introduction Mercury cadmium telluride (Hg1?xCdxTe, MCT) is currently one of the most widely used semiconductor materials for infrared detector arrays. It is well known that the applications of the semiconductor materials, especially for Ⅱ-Ⅵ compound…     

基于载波表的GPS载波跟踪环路研究

实时GPS软件接收机可以使用查找表的方法得到本地复现载波以减少运算量。载波表是由一组具有一定频率间隔和固定初始相位的正弦和余弦信号组成。传统的载波跟踪环路无法使用具有离散频率和不连续相位的复现载波完成GPS载波跟踪。针对这一问题,使用相位补偿算法对载波进行相位补偿,设计了基于载波表的载波跟踪环路。仿真结果表明该载波跟踪环路能有效实现GPS信号的载波跟踪,且与传统的载波跟踪环路相比仅有微小的信噪比损失和频率跟踪精度衰减,可用于实时GPS软件接收机设计。     

基于Linux的内存式WebGIS设计与实现

从计算机存储系统的角度,提出以内存取代硬盘作为运行系统的存储介质,解决磁盘I/O瓶颈,以提升WebGIS响应速度的技术思路。通过分析Linux操作系统上ram disk、ramfs、tmpfs三种内存盘技术和Linux操作系统的组成,针对内存的易失性问题,给出了基于tmpfs和initrd的内存式WebGIS实现方法,并详细阐述了内存式WebGIS的系统组成、系统框架和内存规划。在此基础上,采用64位Debian GNU/Linux操作系统和MapServer WebGIS平台,从构建硬盘WebGIS母系统、构建内存系统镜像文件、重构initrd、内存分配、系统引导和WebGIS应用更新六个方面对内存式WebGIS的实现进行了阐述。实际测试和应用结果表明,应用内存存储提升WebGIS应用响应速度是正确可行的。     

基于时间域读出的大动态范围CMOS图像传感器

设计了一款基于时间域读出的大动态范围CMOS图像传感器。传感器基于一种新型的结构,其可在时间域下探测高输入光强,在模拟域下探测低输入光强。该设计在传统电容反馈式跨阻放大器(CTIA)的基础上,新增了时间域测量电路,在不改变原有积分过程的同时可实现连续的大动态范围。基于0.35μm,5V-CMOS工艺进行了256×1线列CMOS图像传感器流片,光电二极管面积为22.5μm×22.5μm,并对器件的光电特性进行了后仿真验证。仿真测试结果表明,基于时间域读出的图像传感器可实现96dB的大动态范围,且时间域和模拟域的两路输出信号可同步输出,功耗为7.98mW。