扰动法非线性晶体生长过程数值模拟研究

采用扰动法对使用Cz(Czochralski)法非线性晶体生长过程中提拉速度和熔液平均温度场进行了数值模拟研究,实验结果可用于实现晶体等径生长中提拉速度和熔液平均温度的预测控制。研究表明,熔液平均温度(提拉速度)不变时,提拉速度(熔液平均温度)随环境毕奥数的增加和/或熔液毕奥数的减小而增大。进一步研究,熔液若不会组分过冷,可以得到提拉速度的最大值,并在整个生长过程中,必须控制提拉速度小于它的临界上限,否则晶体生长过程将失败。     

初始啁啾补偿光纤色散效应的数值研究

以具有初始啁啾的高斯脉冲在单模光纤中的传输为例,分析、计算了线性初始啁啾对光纤二阶、三阶色散效应的影响,指出了初始啁啾进行色散补偿的适用范围和条件,并对二阶、三阶色散完全补偿光纤链路中40Gbit/s短脉冲传输效果进行了数值计算,结果表明,依据入射功率选择合适的初始啁啾,能使脉冲稳定传输距离大幅提升.     

位相扰动下“热像”规律研究

研究了具有位相扰动的激光束经过非线性介质后的传输情况,用数值模拟的方法着重研究了入射光强(这里以能量来反映)、调制深度、调制宽度等与热像的关系.研究结果表明,在某些条件下,即通常所说的共轭像面处,和振幅调制一样也可以看到明显的热像,但很多情况下其它一些地方峰值很强(例如棒后dO/2处),成为最值得关注的位置.光束演化(光场分布)对位相调制的深度反应较为敏感,某些深度的调制会有更大的危害性.另外,调制宽度、入射光强等对热像形成也有一定的影响.     

大气高阶扰动对傅里叶望远镜成像的影响分析

傅里叶望远镜（FT）综合了激光主动照明和合成孔径的优点,采用相位闭合技术可以消除各发射望远镜间的粗大相位差及大气的低阶扰动对成像的影响,分辨率可突破单一望远镜的衍射极限。为了FT 实际工程系统的实施,需探讨大气高阶扰动对FT 成像质量的影响,文中模拟大气高度36 km,通过等Rytov 指数方法将大气分成40 层并计算得到了每层的上下界限及每层相位屏的高度值。对于3333 T 型均匀间隔发射阵列,每层模拟了1 626 个相位屏。光束传输采用夫琅和费衍射近似。通过计算机模拟,在不考虑噪声的情况下,对于10 cm 的发射口径,得到大气高阶扰动对FT 成像质量有微小影响的结论。重构结果与衍射极限图像的斯托里尔比（Strehl）由无大气时的0.682 1 降低到0.623 6。当信噪比为100 时,Strehl 达到0.452 5,可分辨目标。     

半球形不同聚能装药对射流发电工质影响的数值模拟研究

针对目前聚能装药难以得到均匀射流的问题,运用ANSYS/LS-DYNA软件,建立半球形聚能装药有限元模型,对奥克托今(HMX)、奥梯炸药(Octol)、B炸药、黑索金(RDX)四种典型的半球形聚能装药通过爆轰压垮药型罩形成金属射流发电工质的过程进行数值模拟,对比分析半球形不同聚能装药对射流发电工质的影响。结果表明RDX装药爆轰要压垮药型罩形成的射流发电工质具有较高的头部速度,均匀性最好,可为进一步优化射流发电工质的均匀形态提供一种可借鉴的新型聚能装药方案。     

二维亚波长结构对OLED光抽出特性的FDTD模拟研究

有机发光二极管(OLED)发光效率很大程度上受到器件中高折射率材料(ITO/有机物)对导波光能量的制约.通过使用时域有限差分(FDTD)方法,对在OLED中的氧化铟与氧化锡复合透明阳极ITO结构上覆盖二维正方以及三角排列SiNx圆柱光子晶体厚膜(PCS)的结构进行了数值模拟,并对这种全新结构对于提高束缚于高折射率材料中的光的抽取效率的效果进行了分析,并给出了最优化的几何参数.     

A comparative study on the growth of InAlN films on different substrates

This work investigates the growth of InAlN films on Si (111), sapphire (001), GaAs (100) and glass substrates and compares the structural, morphological, electrical and optical properties of these films. One micron thick InAlN films were synthesized on these substrates at 300 °C by using reactive magnetron co-sputtering system. The structural analysis showed the formation of polycrystalline InAlN films on all the substrates having preferred orientation along (101) plane. The films grown on sapphire and silicon displayed better structural quality than the films grown on GaAs and glass. The morphological results revealed identical granular features on all the substrates with small variation in the grain size. The electrical resistivity of InAlN film on sapphire was the lowest one (8×10⁻³ Ω-cm) whereas the highest carrier concentration (8×10²⁰ cm⁻³) was obtained for the film deposited on glass. The energy band gap of InAlN films was determined through UV–vis absorption and reflectance spectroscopy. The band gap value obtained on the glass was slightly higher as compared to its value on the other substrates. The changes in InAlN properties on different substrates were explained on the basis of lattice mismatch, crystallite size, residual strain and orientation of the substrates.     

A comparison study of electrode material effects on the molecular single electron transistor

In this paper, the studies of Molecular Single electron Transistor (MSET) is presented. We have used the Extended Huckel Theory (EHT) coupled with non-equilibrium green's function (NEGF) formalism which is implemented in ATOMISTIC TOOLKIT package. The transport properties with different electrode materials have been studied for the first time using pentacene molecule. The presence of Coulomb blockade on I–V characteristics confirmed that our device operates as Single Electron Transistor. The negative differential resistance (NDR) effect and the coulomb Staircase state has been outlined. The transmission Spectra and density of states (DOS) dependence of the electrode has also been explored to analyze the I-V curves. The NDR behavior and size device make our MSET as a good candidate for use in gate logic circuit with low consumption.     

A revew of in situ transmission electron microscopy study on the switching mechanism and packaging reliability in non-volatile memory

Non-volatile memory(NVM)devices with non-volatility and low power consumption properties are important in the data storage field.The switching mechanism and packaging reliability issues in NVMs are of great research interest.The switch-ing process in NVM devices accompanied by the evolution of microstructure and composition is fast and subtle.Transmission electron microscopy(TEM)with high spatial resolution and versatile external fields is widely used in analyzing the evolution of morphology,structures and chemical compositions at atomic scale.The various external stimuli,such as thermal,electrical,mechanical,optical and magnetic fields,provide a platform to probe and engineer NVM devices inside TEM in real-time.Such ad-vanced technologies make it possible for an in situ and interactive manipulation of NVM devices without sacrificing the resolu-tion.This technology facilitates the exploration of the intrinsic structure-switching mechanism of NVMs and the reliability is-sues in the memory package.In this review,the evolution of the functional layers in NVM devices characterized by the ad-vanced in situTEM technology is introduced,with intermetallic compounds forming and degradation process investigated.The principles and challenges of TEM technology on NVM device study are also discussed.     

雷达抗干扰效果评估方法探讨

雷达抗干扰效果评估是雷达作战效能评估的一个重要环节。本文通过对现有雷达抗干扰技术和战术性能指标的深入分析与对比,确立相应的评估指标和评估方法,从而归纳出雷达抗干扰效果评估一般意义下的方法和步骤,使对深入研究这一问题有所启发和帮助。     

A comparative study on the performance of MIMO‐STBC subject to Weibull fading channels

In this paper, we investigate the analytical performance of the multiple‐input multiple‐output system (MIMO) with orthogonal space‐time block codes (STBCs) subject to Weibull fading channels (WFC). Space‐time block code technique provides an efficient pattern for wireless transmission over various fading channels using multiple transmit antennas. Two approximating methods of the sum of independent Weibull random variables are studied. For each approach, we derive accurate approximate expressions for several performance metrics of MIMO‐STBC system operating under independent and nonidentical WFC. The proposed approximations are expressed in terms of 2 generalized hypergeometric functions, namely, Fox's H and Meijer's G functions. All the derived approximate expressions prove high accuracy, while compared with the simulation results established via Monte Carlo method and Kolmogorov‐Smirnov test as well. Although the 2 approaches have approximately the same accuracy, the second method approximate expressions are much less complex than those of the first method.     

A comparative study on the measurement of toughness of stacks containing low-k dielectric films

Good adhesion strength of thin film stack is desirable for the integrated circuits (IC) manufacturing stage such as chemical mechanical planarisation (CMP). The scratch test and four-point bending test are two most commonly used methods to find the adhesion properties of thin film because of their simplicity and quantifiability. In this research, scratch test is used to find the practical adhesion energy (W_pa) of thin film stack and four-point bending test is used to find the critical strain energy release rate (G_c). The comparison of W_pa from scratch test and G_c from four-point bend test reveals that, for the same thin film stack, W_pa value is comparatively higher than G_c. The scratch test is semi-quantitative, in that the normal load at which a predefined failure event or delamination occurs is defined as a measure of adhesion. However, the four-point bending test is more quantitative in finding the adhesion properties. Thus, for practical application, such as CMP process, the G_c measurements from four-point bending test are recommended as references.     

A detailed comparative study on the main electrical parameters of Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes

We have fabricated Au/n-Si and Au/PVA:Zn/n-Si Schottky barrier diodes (SBDs) to investigate the effect of organic interfacial layer on the main electrical characteristics. Zn doped poly(vinyl alcohol) (PVA:Zn) was successfully deposited on n-Si substrate by using the electrospinning system and surface morphology of PVA:Zn was presented by SEM images. The current–voltage (I–V) characteristics of these SBDs have been investigated at room temperature. The experimental results show that interfacial layer enhances the device performance in terms of ideality factor (n), zero-bias barrier height (Φ_B0), series resistance (R_s), and shunt resistance (R_sh) with values of 1.38, 0.75 eV, 97.64 Ω, and 203 MΩ whereas those of Au/n-Si SBD are found as 1.65, 0.62 eV, 164.15 Ω and 0.597 MΩ, respectively. Also, this interfacial layer at metal/semiconductor (M/S) interface leads to a decrease in the magnitude of leakage current and density of interface states (N_ss). The values of N_ss range from 1.36×10¹² at E_c—0.569 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.387 eV for Au/PVA:Zn/n-Si SBD and 3.34×10¹² at E_c—0.560 eV to 1.35×10¹³ eV^?1 cm^?2 at E_c—0.424 eV for Au/n-Si SBD. The analysis of experimental results reveals that the existence of PVA:Zn interfacial layer improves the performance of such devices.