反式十氢萘类混合液晶物理性能的研究

反式十氢萘类化合物是一类应用前景广泛的液晶材料，能有效改善混合液晶配方的物理性能。依据近似加法规则，考察了A、B系列反式十氢萘类液晶的引入对配方性能的影响规律，结果显示，A系列反式十氢萘类液晶添加到混合液晶基础配方中，能同时改善配方的高温性能和低温性能，拓宽液晶相区间；B系列添加到基础配方中，能明显改善基础配方的低温性能。含氟B系列反式十氢萘类液晶添加到混合液晶配方中，能有效降低配方的△n、Vth、Vsat。     

An adaptive nonlinear diffusion algorithm for filtering medicalimages

The nonlinear anisotropic diffusive process has shown the good property of eliminating noise while preserving the accuracy of edges and has been widely used in image processing. However, filtering depends on the threshold of the diffusion process, i.e., the cut-off contrast of edges. The threshold varies from image to image and even from region to region within an image. The problem compounds with intensity distortion and contrast variation. We have developed an adaptive diffusion scheme by applying the central limit theorem to selecting the threshold. Gaussian distribution and Rayleigh distribution are used to estimate the distributions of visual objects in images. Regression under such distributions separates the distribution of the major object from other visual objects in a single-peak histogram. The separation helps to automatically determine the threshold. A fast algorithm is derived for the regression process. The method has been successfully used in filtering various medical images     

Threshold current density reduction of strained AlInGaAs quantum-well laser

In the last decades, researchers have tried to implement novel optoelectronic devices with new semiconductor material compounds. There are few competitors in the race for more reliable, more efficient, pump sources for solid-state lasers. These diodes should operate at high power, intense brightness, and with low threshold current. The strained AlInGaAs-GaAs quantum-well (QW) laser is a promising candidate. In this study we optimized the growth parameters of strained AlInGaAs quantum wells using a model for linewidth broadening of photoluminescence, which was extended for the first time to handle quaternary alloys. This model enables us to identify the dominant contributions to the broadening. As a result of our growth parameters optimization technique, low threshold current density of simple broad-area lasers has been obtained, indicating a superior material quality. Moreover, we have studied for the first time the effect of indium and aluminum content and QW width on the threshold current density of quaternary AlInGaAs QW lasers. As a result of these studies the lowest known threshold current density for AlInGaAs on GaAs single QW broad-area laser has been achieved.     

新型反式十氢萘衍生物液晶的研究进展

新型的反式十氢萘衍生物液晶具有拓宽混合液晶工作温度区间、降低阈值电压、增大介电各向异性、减小双折射率等优越的光电性能．适用于TFT型液晶显示材料；在合成中运用了立体选择性更好的新方法和新试剂．收效显著，有较高的参考意义。文中就目前已报道的化合物．从性能和合成的角度对该类化合物目前的发展状况进行了综合论述。     

Effect of melting on the acoustic response of CdTe and GaAs subjected to the pulsed laser irradiation

The effect of a threshold process of surface melting on the acoustic response in CdTe and GaAs subjected to pulsed laser radiation is considered and the mechanisms of excitation of sonic signals are analyzed. Melting thresholds of the surface of binary compounds CdTe and GaAs are established under irradiation by pulses of nanosecond duration of ruby and neodymium lasers from measurements of the amplitude of the acoustic response.     

质子转移反应飞行时间质谱的建立与性能研究

介绍了自主研制的质子转移反应飞行时间质谱的基本结构和性能。首先对数据采集卡甄别离子脉冲的阈值电压进行了优化,结果表明当阈值电压为0.33V时,H316O+(m/z 19)与H318O+(m/z 21)的离子计数比约500:1;然后考察了水团簇离子H3O+(H2O)n的分布与漂移管约化电场的关系,结果表明,当E/N为139 Td时,团簇离子得到很好地抑制,质谱观察到的离子主要是H3O+,其纯度可达99%以上;随后考察了质谱的分辨率,结果表明在m/z124处,分辨率最好,达到2653; 采用不同浓度的乙醇标样对仪器的线性范围和检测限性能进行了测试,结果表明该仪器的线性动态范围可达三个数量级,检测限可达3.8 ppb; 最后用该质谱仪检测了实验室空气,得到了实验室空气的质谱图。自主研制的质子转移反应飞行时间质谱可实现对痕量挥发性有机物的实时在线测量,在环境、食品、医学等领域具有重要应用价值。     

Intercalation‐Induced Tunable Stimuli‐Responsive Color‐Change Properties of Crystalline Organic Layered Compound

Layered structures accommodate guest molecules and ions in the interlayer space through intercalation. Organic layered compounds, such as layered polymers, have both intercalation and dynamic properties. Here intercalation‐induced tunable temperature‐ and mechanical‐stress‐responsive color‐change properties of crystalline layered polydiacetylene (PDA) as an organic layered compound are reported. In general, organic materials with stimuli responsivity are developed by molecular design and synthesis. In the present work, intercalation of guest metal cations in the layered PDA directs tuning of the stimuli‐responsive color‐change properties, such as color, responsivity, and reversibility. Whereas PDA without intercalation of metal ions distinctly changes the color from blue to red at the threshold temperature, the PDA with intercalation of the divalent metal ions (PDA‐M²⁺) shows a variety of color‐change properties. The present study indicates that intercalation has versatile potentials for functionalization of organic layered compounds.     

乙炔桥键四环异硫氰酸酯液晶化合物的合成及性能

为了研究液晶材料结构与性能的关系,本文以含乙炔桥键的四环异硫氰酸酯化合物为研究对象,芳基硼酸和3-氟-4-溴碘苯为起始原料,经6步反应合成了12种目标化合物,LC纯度大于99%,采用核磁共振、红外光谱对其结构进行了表征。采用DSC和POM对目标化合物的介晶性进行了研究,采用外推法对其双折射率和介电各向异性值进行了测试。结果表明:目标化合物具有300℃以上高清亮点、150℃以上向列相温度区间、0.40~0.51的双折射率以及大于17的介电各向异性值。对于同一系列化合物,随着末端烷基链的增长,化合物熔点降低,但呈现近晶相的趋势增加。在Y、Z位引入侧向氟取代基,熔点和清亮点均降低;X位再引入侧向氟取代基,熔点上升、清亮点下降。用环己烷替代左边第一个苯环,化合物熔点降低、向列相温度区间变宽。引入侧向氟取代基使双折射率下降0.008~0.036。目标化合物有利于提高混合液晶配方的双折射率、清亮点和降低阈值电压。     

Growth of High-Quality AlxGa1−xAs By OMVPE for laser devices

Optimum conditions are reported for the growth of high-quality Al_xGa_{1_x}As by means of vapor phase epitaxy from organometallic compounds (OMVPE). Typical values of mobili-ty and radiative recombination efficiency are reported, showing that OMVPE material quality is the same as that grown by liquid phase epitaxy (LPE). OMVPE-grown DH narrow-stripe lasers with Al_.06Ga_.94As active layers show minimum threshold currents of85 mÅ, comparable to the best lasers with similar structures produced by LPE.     

Interfacial and interband lasing in an AnAs/InAsSbP heterostructure grown by vapor-phase epitaxy from metal-organic compounds

Sources of coherent radiation are fabricated on the basis of a double InAs/InAsSbP heterostructure, grown by vapor-phase epitaxy from metal-organic compounds, that includes a thick (3.3μm) active region. The spectral characteristics of diodes with various cavity lengths are studied, and light polarization is measured. It is established that the modes that compose the spectrum of radiation are controlled by radiative recombination at the heteroboundary and in the bulk of the active region. A new mode with a wavelength of intermediate value, lying between the wavelengths of the aforementioned kinds of radiation, is observed if the current exceeds the threshold value by 30%. This intermediate mode presumably results from an interaction between the modes related to the interfacial and interband radiative recombination, which are present in the cavity at the same time.     

2.3-2.7-μm room temperature CW operation of InGaAsSb-AlGaAsSbbroad waveguide SCH-QW diode lasers

A new approach in the design of (Al)InGaAsSb-GaSb quantum-well separate confinement heterostructure (QW-SCH) diode lasers has led to continuous-wave (CW) room-temperature lasing up to 2.7 μm. This has been achieved by using quasiternary heavily strained InGaSb(As) QW's inside a broad-waveguide SCH laser structure. The QW compositions are chosen in the region outside the miscibility gap and, as a consequence, do not suffer from clustering and composition inhomogeneity normally found with quaternary InGaAsSb compounds of 2.3-2.7-μm spectral range. Very low threshold current density (~300 A/cm²) and high CW output powers (>100 mW) were obtained from devices operating in the 2.3-2.6-μm wavelength range     

氧化锌与定向碳纳米管复合纳米结构设计与场发射性能研究

考虑到目前方法制备出的氧化锌碳纳米管复合结构多为随机取向,会在一定程度上影响其场发射性能,例如发射电流稳定性、寿命等性能方面,提出了一种氧化锌纳米线与定向碳纳米管复合纳米结构阵列的制备方法,并制备出了相应的结构体.模拟计算和测试结果表明文中制备出的复合纳米结构阵列改善了单一纳米结构的场发射性能.与单纯碳纳米管阵列相比,...     

Quantum dot injection heterolaser with ultrahigh thermal stability of the threshold current up to 50 °C

Gaseous phase epitaxy from metal organic compounds is used to obtain a low-temperature injection laser with an active region based on In_0.5Ga_0.5As/GaAs quantum dots. Optimizing the growth conditions and geometric parameters of the structure has made it possible to increase the range of ultrahigh thermal stability in the threshold current (the characteristic temperature is T ₀=385 K) up to 50 °C. Fiz. Tekh. Poluprovodn. 31, 226–229 (February 1997)     

Non-stoichiometry and problem of heavy doping in semiconductor phases

The experimental results on the influence of non-stoichiometry on defect structure, band structure and physical properties of the IV–VI and I–III–VI₂ semiconductor compounds with wide homogeneity regions were analyzed. It was shown that compositions at which peculiarities in the concentration dependences of properties in the homogeneity region are observed, correspond to the maximum in the melting curves. Using the approach of percolation theory, the transition from weak to heavy self-doping within the homogeneity region was considered, and the percolation threshold under the introduction of non-stoichiometric defects was estimated. Compositions optimal for long-range ordering were determined.     

Memory switching in a type I amorphous chalcogenide

Amorphous chalcogenides may be divided among three classes based upon the changes in local order and bond type on transition from the amorphous to the crystalline phases. These types include: (I) Stoichiometric compounds which do not undergo significant changes in local order on crystallization (e.g., As₂Se₃). (II) Stoichiometric compounds which undergo significant changes in local order on crystallization (e.g., GeTe). (III) Non-stoichiometric alloys which phase separate on crystallization. Previous work on memory switching has been performed primarily on type II and type III chalcogenides. The memory switching process in thin film specimens of a type I chalcogenide, amorphous As₂Se₃, is examined in this paper. Measurements of the threshold voltage distribution for devices of a given thickness display a sharp peak at some value V_O . A plot of V_O as a function of film thickness shows the initiation of switching to be field controlled, suggesting a non-thermal initiation mechanism. Microscopic examination of switched devices yields evidence for Joule heating, which is enchanced by self-capacitive energy released during switching subsequent to formation of the low resistance path. From the thickness dependence of V_O and measurements of the failure time of devices biased below threshold, a switching mechanism for this material is deduced which incorporates spinodal decomposition of metallic As clusters in an insulating matrix. These clusters then chain under the influence of an applied field and form a low resistance filamentary path.     

动态阈值nMOSFET阈值电压随温度退化特性

对动态阈值nMOSFET阈值电压随温度退化特性进行了一阶近似推导和分析。动态阈值nMOSFET较之普通nMOSFET,降低了阈值电压温度特性对温度、沟道掺杂浓度及栅氧厚度等因素的敏感程度。讨论了动态阈值nMOSFET优秀阈值电压温度特性的内在机理。动态阈值nMOSFET优秀的阈值电压随温度退化特性使之非常适合工作于高温恶劣环境。     

灰度图像的二维交叉熵直线型阈值分割法

 一维Otsu法是一个经典的阈值分割方法,遵循该方法的构造思想,Li 与 Lee基于交叉熵提出了一个阈值分割方法.在解释和说明Li 与 Lee的方法的基础上,与二维Otsu直线型阈值分割方法相对应,提出二维灰度直方图上的二维交叉熵直线型阈值分割方法并给出快速递推公式.与二维Otsu直线型阈值分割法相比,新方法能够更好的适应目标和背景方差相差较大的情形,是一个有效的阈值分割方法.     

采用局部动态阈值的图像分割算法

针对图像全局Otsu分割算法和传统的局部闻值分割算法在复杂背景图像分割中的不足,提出了一种采用局部动态阈值的图像分割算法.首先通过分析图像直方图类型对图像进行划分,并使用Otsu算法确定各个子图像的阈值.然后对阈值矩阵进行平滑和插值处理,使之成为和原图像像素数目相等的新阈值矩阵.最终利用此阈值矩阵完成图像分割.实验结果...     

A Computer-Aided Scheme of Threshold Voltage Measurement for Floating-Gate Mos Transistor

In this paper, analog multiplexers, a threshold voltage measurement block, 16-bit analog-to-digital converter, and a computer are employed to achieve a new scheme of threshold voltage measurement for a floating-gate MOS transistor (FGT). Feedback technology is applied so that the threshold voltage can be measured with good accuracy. A threshold voltage measurement with a maximum error equal to 1% can be achieved. The proposed scheme does not require any matched components, and thus it can be applied effectively to threshold voltage measurement for multiple FGTs. The sampling time of the threshold voltage measurement is 3 ms. Dynamic responses and static characteristics are demonstrated with experimental results.     

面积约束下的最优阈值法分割LED像素点阵

针对基于CCD相机采集方式的亮度校正方法需要从采集图像中分割出每颗LED像素的亮度信息的问题,提出面积约束下的最优阈值分割法。在最优阈值分割法的基础上,根据先验信息引入面积约束条件,对阈值的取值范围进行约束。与传统的最优阈值法相比可以避免分割后LED像素区域连接的情况。面积约束下的最优阈值分割法生成采集图像的灰度直方图,利用最优阈值算法结合面积约束生成最优阈值,最后通过图像的阈值分割法将采集图像分割。实验表明,该方法可以比较好地分割出采集图像中的LED像素,并可避免当LED像素点分布密集时应用最优阈值法分割LED像素造成的区域连接问题。