热氧化多孔硅制备及其干涉特性研究

采用电化学阳极氧化法制备彩色薄层多孔硅,经高温热氧化处理后形成稳定的热氧化多孔硅.研究电化学制备条件对热氧化多孔硅的干涉效应和光学厚度的影响,分析热氧化处理前后多孔硅的稳定性.结果表明,在可见光波长范围内,所制备的热氧化多孔硅反射光谱出现一定规律性的干涉条纹,表现出明显的反射干涉现象;随阳极氧化时间、电流密度和HF浓度增大,热氧化多孔硅光学厚度呈增大趋势,当阳极氧化时间为30s、电流密度为520mA/cm2、v(HF):v(C2H5OH)为2:1～5:2时,制备的热氧化多孔硅干涉条纹均匀且光学厚度较大;热氧化处理后,多孔硅结构中的Si-Hx键被Si-O键所取代,其反射干涉特性非常稳定.     

多孔硅的电化学制备与研究

以电化学方法制备了多孔硅材料并通过表面轮廓测试仪、原子力显微镜、显微拉曼光谱仪等设备对制备多孔硅的孔隙率、厚度、表面形貌、以及热导率进行了表征.结果发现,本实验制备的多孔硅属于介孔硅(15～20nm),其孔隙率随腐蚀时间和腐蚀电流的变化有先增大后减小的趋势.增加多孔硅的厚度和孔隙率,可以使得多孔硅的热导率显著降低(最低可低至0.62W/m·K).     

多孔硅层孔隙率对其热绝缘性能的影响

研究了多孔硅层孔隙率对其热绝缘性能的影响机制.以P 型硅片为基底,通过双槽电化学腐蚀法制备多孔硅.采用微拉曼光谱法对多孔硅的热导系数进行了测量,结果表明,多孔硅的热导系数随其孔隙率的增大而明显下降,实验中热导系数最低可达到0.624W/(m·K),从而通过降低热导系数使多孔硅的绝热性能得到了增强.     

MEMS中多孔硅绝热技术

主要介绍了多孔硅的制备方法(化学法、电化学法及原电池法等)、多孔硅导热系数测试的几种常用手段(温度传感器法、显微拉曼散射法及光声法等)、导热系数的理论模型及影响因素．此外,采用不同方法制备了多孔硅样品,分析了其表面形貌并用显微拉曼光谱法测定了导热系数．结果发现,化学法制备的多孔硅孔径尺寸大于微米量级,而利用大孔硅电化学和原电池法得到的样品孔径尺寸小(约20nm),属于介孔硅．由于腐蚀条件的不同,多孔硅的孔隙率和厚度也不同,多孔硅的导热系数随孔隙率和厚度的增大而迅速减小．     

高度有序多孔阳极氧化铝薄膜光学常数的确定

采用二步阳极氧化法制备了多孔阳极氧化铝(PAA)薄膜,借助于扫描电子显微镜(SEM)分析了多孔阳极氧化铝薄膜的微观形貌,发现在其表面孔径为70～90 nm的六边形孔洞分布均匀,且垂直于表面平行生长.依据PAA反射光谱的实验数据,利用Kramers-Kronig关系计算出PAA薄膜的复折射率、复介电常数以及光学能隙等光学常数.通过分析吸收系数与入射光子能量之间的关系,表明PAA具有直接带隙(能隙约为3.4eV)半导体的光学性质.     

纳米多孔硅的电化学制备及性能研究

纳米多孔硅是一种潜在的化学和生物传感材料,本文采用电化学腐蚀法制备纳米多孔硅。采用SEM技术分析多孔硅的表面形貌,研究了腐蚀条件对多孔硅的孔隙率、厚度、I-V特性的影响。结果表明,多孔硅的孔隙率随着腐蚀电流密度和腐蚀时间的增加而呈线性增大趋势;其厚度随着腐蚀电流密度的增加而近似呈线性增大趋势,随腐蚀时间的成倍增加而显著增大;其I-V特性表现出非整流的欧姆接触。     

应用于微电子机械系统中多孔硅的研究

针对多孔硅在MEMS中作为牺牲层和绝热层的应用,主要研究了电化学腐蚀法制备多孔硅的实验条件与多孔硅深度及其孔隙率间的关系,实验发现电化学腐蚀法制备多孔硅的腐蚀速率在腐蚀前期阶段基本是一定值(电流密度为80mA/cm2时为1.3μm/min,电流密度为40 mA/cm2时为0.4μm/min),但到腐蚀后期阶段随着孔深的增加有所下降.同时发现对于不同的腐蚀电流密度,多孔硅的孔隙率都有随腐蚀时间的延长先增加后降低的趋势,用Beale模型可以很好的解释这一现象.最后,针对多孔硅在制备后易发生龟裂的现象,用拉曼光谱分析了多孔硅的内部应力情况,结果表明随多孔硅孔隙率的上升其内部残余应力有增加的趋势.     

多孔硅表面氧化钒热敏电阻薄膜的阻温特性

用电化学腐蚀法制备了具有不同导热系数的多孔硅样品(孔隙率为80％±2、厚度为110μm时,导热系数可降低至0．20 W／m·K),并在其表面沉积了氧化钒热敏薄膜,研究了多孔硅样品的热绝缘性能对氧化钒热敏薄膜阻温特性的影响．结果表明:多孔硅良好的热绝缘性使在其表面制备的氧化钒热敏薄膜电阻的灵敏度远高于在硅基底上制备的热敏电阻的(多孔硅和硅片上的氧化钒薄膜电阻随功率变化斜率分别为120 kΩ／μW和2．1 kΩ／μW),且热敏电阻的灵敏度随着多孔硅孔隙率和厚度的增大而升高．     

快压缩P1波在饱和冻土与弹性基岩分界面上的能量传输特性

基于弹性波在冻结饱和多孔介质与单相弹性介质中的传播理论,选取了饱和冻土中传播速度最大的快压缩P₁波入射在饱和冻土与弹性基岩分界面上的能量传输问题。根据分界面上的边界条件,推导出了快压缩P₁波从饱和冻土介质入射到弹性基岩分界面上透反射振幅比和能量率的解析表达式。研究了快压缩P₁波入射在饱和冻土与弹性基岩分界面上的能量与入射角度,入射频率,温度(含冰量),孔隙率,胶结参数以及接触参数的关系。研究结果表明：当入射角度为0°时仅存在压缩波,达到临界角后透射P波消失;各种波在达到临界角时出现不同程度的脉冲,其中反射P₁波最为显著;随着胶结参数,孔隙率,接触参数的增大,临界角越早出现;入射频率仅对反射P₂,P₃和S₂波的能量反射率影响较大;当温度和含冰量较低或较高时,均不利于反射S₂波的能量产生。     

硝酸银水溶液处理新生多孔硅的研究

n型单晶硅经光电化学阳极刻蚀成多孔硅.研究了多孔硅经硝酸银(AgNO3)水溶液浸泡前后样品的光致发光(PL)性质,实验发现,浸泡很短时间内多孔硅发光强度增强,浸泡时间较长的样品发光强度会衰减直至猝灭,且浸泡液浓度越大荧光衰减越明显.通过扫描电子显微镜(SEM),傅立叶红外光谱(FTIR)和X射线光电子能谱(XPS)的检测显示,AgNO3水溶液浸泡的多孔硅样品表面有金属银析出.光致发光增强是多孔硅表面形成Si-O结构所致,荧光猝灭是因为银在多孔硅表面形成大量非辐射复合中心.     

The effective length of subcodes

The effective length distribution (support weight distribution in Kløve's terminology [3]) of a linear code is the set of integers indicating the number of subcodes of the same dimension and the same effective length. A simple proof is presented to MacWilliams type identities relating the effective length distributions of a linear code and its dual.     

Equivalent inclusion approach and effective medium approximations for the effective conductivity of isotropic multicomponent materials

Most effective medium approximations for isotropic inhomogeneous materials are based on dilute solutions of some typical inclusions in an infinite matrix medium, while the simplest approximations are those for the composites with spherical and circular inclusions. Practical particulate composites often involve inhomogeneities of more complicated geometry than that of the spherical (or circular) one. In our approach, those inhomogeneities are supposed to be substituted by simple equivalent spherical (circular) inclusions from a comparison of their respective dilute solution results. Then the available simple approximations for the equivalent spherical (circular) inclusion material can be used to estimate the effective conductivity of the original composite. Numerical illustrations of the approach are performed on some 2D and 3D geometries involving elliptical and ellipsoidal inclusions.     

Estimates of effective characteristics of random cell structures in terms of effective characteristics of periodic structures

The bounds of effective characteristics of random cell structures are obtained in terms of effective characteristics of periodic structures.     

Simple and effective bandwidth reduction algorithm

An automatic algorithm is presented for reducing the bandwidth of symmetric interconnectivity matrices. The technique takes an arbitrary input scheme and reorders the nodes so as to reduce the bandwidth. A large number of examples is presented to illustrate the reliability and cost-effectiveness of the method.     

The design of effective machinery guards

The objectives of this paper are to review the justification for higher standards of machinery guarding as an accident prevention strategy, and to discuss the criteria which determine whether a guard is likely or unlikely to fulfil its function effectively. Part of the paper is devoted to a review of a number of accident case studies which illustrate, and support, the argument for better guarding. Much of this paper is based upon a technical file for Engineering.¹     

Systems engineering effective supply chain innovations

When seeking to adopt innovative supply chain (SC) best practices from apparently better-performing organisations during re-engineering, it is important to acknowledge that context also impacts performance. Hence, the purpose of this study is to evaluate the SC uncertainty circle model for its potential to yield direct performance comparisons even when the benchmarked organisations are located in different business sectors and economic settings. Using a rigorous well-established audit methodology, longitudinal field research with an engineer-to-order SC company demonstrates how highly effective, potentially transferable best practices can be reliably identified when systems thinking is allied to a context-free uncertainty metric, and how reducing product delivery process uncertainty can itself increase innovation capability.     

More effective nanomedicines through particle design

Nanomedicine is an emerging field that applies concepts in nanotechnology to develop novel diagnostics and therapies. Physical and chemical properties of particles, including size, shape, modulus, surface charge and surface chemistry, play an important role in determining particle-cell interactions, cellular trafficking mechanisms, biodistribution, and pharmacokinetics. This discussion focuses on both nanoparticles and microparticles since microparticles can also provide many insights for the development of drug carriers and possess advantages over nanoparticles in certain applications. This review covers recent major advancement in the nanomedicine field and also highlights studies using the PRINT technology.