Si离子注入和退火温度对GaN黄光的影响

对光致发光谱中无黄光和有强黄光的两组GaN样品作了Si离子注入 ,研究了Si离子注入及退火温度对其黄光的影响 .当退火温度升高时 ,不管是哪一组样品 ,其黄光强度和黄光强度与带边发光带强度之比都是增强的 .无黄光的GaN样品在注入Si离子并经退火后出现明显的黄光 ;而有强黄光的GaN样品经相同处理后 ,其黄光强度较原生样品大大降低 .实验结果表明离子注入加上适当退火会在GaN中引入与黄光有关的深受主缺陷从而使黄光强度增加 ,此外 ,在离子注入过程中GaN表面不仅可以吸附离子注入引入的点缺陷 ,而且还能够吸附GaN中原有的与黄光有关的点缺陷 ,这种吸附作用随离子注入剂量增加而变强 .     

基于回光强度的平面标靶自动识别方法

平面标靶在中长距离三维激光扫描仪的检校、数据采集、单点测量等环节中发挥着重要作用,而平面标靶的高精度、自动化识别是在其使用中面临的一个关键问题.在分析扫描数据特点的基础上,提出一种基于回光强度的平面标靶自动识别方法.具体的步骤为:改正回光强度以消除距离的影响;基于回光强度进行阈值分割以得到平面标靶点云;提出一种基于扫描...     

受激布里渊散射与激光雷达

1受激布里渊散射阈值 受激布里渊散射的阈值是受激布里渊散射研究中的重要问题.在以往的定义中使利用了一个经验公式,理论不够严格.该定义中含有材料的长度,即,对于同一种材料,长度不同时稳态受激布里渊散射的阈值不同,这显然是不合理的.而在实验测量方面,通常是测量背向散射的强度,当其达到入射光强度的2%,5%或10%时,即认为此时的入射光强度为受激布里渊散射的阈值.这种测量方法因人而异.缺乏统一的标准.另外,在阈值附近,受激布里渊散射非常不稳定,涨落极大,这使得测量精度很低.     

激光波长对Ce:KNSBN晶体非线性特性的影响

采用非同时读出条件下晶体两波耦合实验装置,在相同的入射光参量下,研究了激光波长(λ)对Ce:KNSBN晶体两波耦合增益系数(r)、衍射效率(n)、响应时间及光扇效应入射光强度阈值的影响.结果显示,激光波长不同时,r、n,响应时间随光入射角2θ的演化趋势相同,但不同波长光入射时,对应相同的2θ,r、n及响应时间不同;激光波长不同时,Ce:KNSBN晶体中光扇效应的入射光强度阈值不同,λ为532nm时,阈值为38mW/cm2,λ为632.8nm时,阈值为26mW/cm2.     

退火对a-Si_xC_(1-x):H薄膜光学性质的影响

研究了退火对α-Si_xC_(1-x):H薄膜红外吸收和光致发光性质的影响.实验结果表明:低温退火使与氢有关的红外吸收和积分发光强度增加;而高温退火使与氢有关的红外吸收和积分发光强度减弱;同时,随着退火温度升高,光致发光光谱的峰值能量位置移向低能.文中对退火引起红外吸收和光致发光性质的变化机理进行了讨论。     

热处理硅中缺陷对室温光致发光的影响(详细摘要)

用室温光致发光方法研究了经450～950℃热处理后硅中的热缺陷行为。光致发光强度密切地依赖于热处理的温度条件。在450℃时,光致发光强度增强,热缺陷减少了非辐射复合中心。高于550℃时,光致发光强度减弱,热缺陷增加了非辐射复合中心。光致发光强度与热缺陷腐蚀斑密度有关。     

InGaN光致发光性质与温度的关系

分析了用金属有机物气相外延方法(MOVPE)在蓝宝石衬底上生长的铟镓氮(InGaN)的光致发光(PL)性质.发现在4.7K至300K范围内,随着温度升高,InGaN带边辐射向低能方向移动,峰值变化基本符合Varshni经验公式;同时InGaN发光强度虽有所衰减,但比GaN衰减程度小,分析了导致GaN和InGaN光致发光减弱的可能因素.     

纳米氢氧化镁的结构表征和阻燃特性

采用活性剂包覆的溶液沉淀法制备了不易团聚的纳米氢氧化镁粉体.经透射电镜表征,其形态是短轴方向尺寸为6～9nm,长轴方向尺寸为50～100nm的针状粒子.随着氢氧化镁粒径的减小,光致发光光强度显著增强.同时还制备了氢氧化镁/EVA(1∶1)纳米复合材料,该材料的极限氧指数(LOI)为38.3.高分辨透射电镜照片表明氢氧化镁纳米粒子在EVA基体中分散均匀.     

InGaN光致发光性质与温度的关系

分析了用金属有机物气相外延方法 (MOVPE)在蓝宝石衬底上生长的铟镓氮 (In Ga N)的光致发光 (PL)性质 .发现在 4.7K至 30 0 K范围内 ,随着温度升高 ,In Ga N带边辐射向低能方向移动 ,峰值变化基本符合 Varshni经验公式 ;同时 In Ga N发光强度虽有所衰减 ,但比 Ga N衰减程度小 ,分析了导致 Ga N和 In Ga N光致发光减弱的可能因素 .     

纳米氢氧化镁的结构表征和阻燃特性

采用活性剂包覆的溶液沉淀法制备了不易团聚的纳米氢氧化镁粉体.经透射电镜表征,其形态是短轴方向尺寸为6～9nm,长轴方向尺寸为50～100nm的针状粒子.随着氢氧化镁粒径的减小,光致发光光强度显著增强.同时还制备了氢氧化镁/EVA(1∶1)纳米复合材料,该材料的极限氧指数(LOI)为38.3.高分辨透射电镜照片表明氢氧化镁纳米粒子在EVA基体中分散均匀.     

A new evaluation method of electron optical performance of high beam current probe forming systems

A new numerical simulation method is presented for the electron optical property analysis of probe forming systems with point cathode guns such as cold field emitters and the Schottky emitters. It has long been recognized that the gun aberrations are important parameters to be considered since the intrinsically high brightness of the point cathode gun is reduced due to its spherical aberration. The simulation method can evaluate the 'threshold beam current I(th)' above which the apparent brightness starts to decrease from the intrinsic value. It is found that the threshold depends on the 'electron gun focal length' as well as on the spherical aberration of the gun. Formulas are presented to estimate the brightness reduction as a function of the beam current. The gun brightness reduction must be included when the probe property (the relation between the beam current l(b) and the probe size on the sample, d) of the entire electron optical column is evaluated. Formulas that explicitly consider the gun aberrations into account are presented. It is shown that the probe property curve consists of three segments in the order of increasing beam current: (i) the constant probe size region, (ii) the brightness limited region where the probe size increases as d approximately I(b)(3/8), and (iii) the angular current intensity limited region in which the beam size increases rapidly as d approximately I(b)(3/2). Some strategies are suggested to increase the threshold beam current and to extend the effective beam current range of the point cathode gun into micro ampere regime.     

混沌序列下图像水印的嵌入算法

混沌序列具有易生成性,对初始条件强敏感性,可完全重现性等特点.故采用混沌序列先做加密处理,然后对图像进行分块处理,利用不同块的亮度及纹理局部特性以及人眼的亮度感觉及对比灵敏度阈值等人类视觉系统特性来确定水印嵌入的强度因子,再分别嵌入水印.实验结果表明,算法对图像压缩、滤波,噪声以及图像裁减具有一定的安全性和鲁棒性.     

基于量子多元宇宙算法的磁光成像增强

为了提高磁光成像增强效果,采用量子多元宇宙算法。首先铁磁材料施加磁场时,磁场的N、S级产生的光强差别性使得磁光成像区域的亮度由暗到明逐渐变化,焊缝磁光成像的像素灰度值与焊缝亮度成正比;接着引导滤波减少磁畴区域对磁光成像的影响,atctan函数对磁光成像区域增强;最后给出了算法流程。实验显示磁感应强度变化随着交变电压的增加而变大,霍尔探头离焊缝中心越远,则磁感应强度越小,磁感应强度在焊缝中心呈现对称分布,最小值在焊缝中心处,即磁场N级、S级交接处;磁畴特性随低频交流电压增加表现越明显;本文算法使得磁光成像增强效果清晰,评价指标较优。     

Theoretical Study on Field Emission Patterns of the Nanotube

The distributions of the electrical potential and field have been given from Maxwell‘s field equations. The results show that there exists very strong electric field intensity on the tip of the nanotube,and the intensity decays rapidly as the distance increases away from the tip. The strong electric field intensity on the tip is consistent with the low threshold voltage under the electric field emission from a nanotube. The calculation also revealed that the higher the aspect ratio is, the stronger the electric field intensity on the tip of the nanotube will be,if the distance and voltage between the cathode and the anode do not change, which predicts the lower threshold voltage under the field emission.     

Alternating-Current White Thin-Film Light-Emitting Diodes Based on Hydrogenated Amorphous Carbon Layer

Alternating-current white thin-film light-emitting diodes (ACW-TFLEDs) have been fabricated and demonstrated with composition-graded hydrogenated intrinsic amorphous silicon carbide (i-a-SiC : H) layers. It was found that H₂-plasma treatment of luminescent i-a-C : H layer played an important role in decreasing the ACW-TFLED electroluminescence (EL) threshold voltage, increasing the brightness, and broadening the EL spectrum. The EL spectra of the ACW-TFLED under either dc forward or reverse bias, or the sinusoidal alternating-current voltage were qualitatively very similar, with a peak wavelength at about 505 nm and a broad full-width at half maximum (FWHM) about 240 nm. This device revealed a brightness about 800(500)cd/m² under dc forward (reverse) bias at an injection current density of 600 mA/cm²     

A nonlinear receptive field model of the visual system

A nonlinear model for the visual system is proposed in relation to the dependence of receptive field size on luminance. The model is constructed based on the fact that the exponent of Stevens' brightness function varies depending on the target size. The model consists of two stages; the mechanism of spatial summation and the mechanism of 0.5-power in cascade. The mechanism of 0.5-power is responsible for an exponent 0.5 of the brightness function for the point target. The extent of the spatial summation changes depending on the luminance so that the model yields a brightness function with exponent 0.33 for the infinite target of uniform luminance distribution. The model predicts well the signal transfer function of vision, the charactreristics of the suprathreshold spatial summation and the mean luminance dependence of the spatial frequency characteristics for threshold contrast.     

Monitoring of low-dose ion implantation in silicon

Monitoring of low-dose arsenic or boron ion implantation (doses: 5×10¹⁰ to 1×10¹³ cm^-2) in silicon, which is required for threshold voltage control of MOS transistors, is studied. The thermal-wave (TW) signal intensity decreases monotonically with decreasing dose. The lowest detection limit for As⁺ and B⁺ implantations is 5×10¹⁰ and 1×10¹¹ cm^-2, respectively. Correlation of the TW signal intensity versus damage density, TW intensity versus dose, and laser Raman intensity versus dose is obtained. The TW intensity is also correlated with the sheet conductance, and the threshold voltage of the transistor. Therefore, this technique is useful as a nondestructive, highly sensitive dose monitor for low-dose implantation to achieve tight threshold voltage control in MOS transistors     

基于数据场的未知雷达信号动态聚类算法

未知雷达信号分选一直是雷达对抗情报处理中的难题。通过引入势和场强的概念,提出了一种基于数据场的未知雷达信号聚类算法。该方法通过设置势值门限来剔除噪声,同时设置场强门限进行聚类。该方法可以达到自动确定聚类数目和聚类中心的目的。仿真试验表明,该方法能够有效适应于未知雷达信号的分选。     

Threshold voltage of narrow channel field effect transistors

A new effect associated with Metal-Oxide-Silicon Field-Effect-Transistors (MOS-FET's) is presented in this paper. MOS-FET's show an increase of threshold voltage with decreasing ratio of channel width to gate depletion width. This narrow channel effect is explained by means of geometrical edge effects. With decreasing channel width the transition from the field oxide depletion region to the gate oxide depletion region becomes comparable to the gate width and cannot be neglected in the derivation of the threshold voltage equation.A theoretical model is given to explain the influence of decreasing channel width on the threshold voltage as well as on other electrical parameters. This theoretical model is in good agreement with experimental results given in this paper.     

Optically excited bulk semiconductor lasers

Optical pump experiments on homogeneous samples provide a method of obtaining a clearer understanding of the details of laser action in semiconductors. For this reason, the quantum-mechanical rate equations for a bulk semiconductor laser that explicitly include a monochromatic light field as a pump source are developed. The theory treats general optical transitions and is valid for both pure and doped homogeneous semiconductors. The developed theory gives the intensity of the laser output in the entire region from below to above threshold as a function of the intensity and frequency of the pump field, the temperature, doping level, and material constants. Also the variation of the laser light frequency at threshold upon these parameters is given by the theory. Information about the dependence of the necessary pump intensity and frequency for threshold is gained. The theoretical calculations are compared with experimental measurements and found to be in general agreement.