微机在测定固体表面结构中的应用

比表面积,孔容,物理吸附层数和孔径分布是多孔固体和固体粉末的重要表面结构信息.现在越来越多的人认识到对催化、功能高分子等方面深入了解必须从了解表面积和孔结构信息开始.这些信息已有许多途径可以获得.但是有些方法计算工作量较大.本文编写了 BASIC 程序,利用微机分析处理多孔固体或固体粉末在液氮温度下的吸附和脱附支等温线,具体方法有:二常数 BET 方程,三常数 BET 方程,Pickett 方程,累积孔中表     

一种基于表面等离激元的纳米温度传感器

本文基于表面等离激元(Surface Plasmon Polariton,缩写为SPP)共振腔提出了一种新型纳米温度传感器。随着温度的升高,金属的折射率会发生微小的变化,而且,共振腔的整体结构也会发生热膨胀,这都是共振腔共振波长随温度变化的因素。同时,为了放大温度对共振波长的影响,引入了一个热膨胀系数不同的金属双层膜,随着双层膜的形变,共振腔的共振波长随之发生更明显的变化。这种共振波长移动的大小可用于测量温度的变化。此外,本文采用有限元法(Finite Element Method,简称FEM)来计算共振腔的光学特性。据了解,这是第一个基于SPP共振腔热膨胀的纳米光学温度传感器,而且与同等尺度的传感器相比,其拥有较大的灵敏度。     

基于内窥检测技术的固体推进剂装药缺陷检测方法

为实现固体推进剂装药内表面缺陷的检测,通过内窥镜检测技术对其进行了理论分析与检测试验,着重对定量检测技术在固体推进剂装药内表面缺陷检测中的应用进行了研究;通过对检测结果的分析,验证了采用该方法能够实现固体推进剂装药内表面缺陷的检测,可以很好地控制固体推进剂装药的质量。     

长条形反射镜背部支撑方案研究

在空间微重力和温度载荷的作用下,反射镜及其支撑结构的变形会影响或破坏光学系统的成像质量.从保证反射镜成像质量及功能的角度出发,介绍了某种光学遥感器反射镜及其支撑结构材料的选取原则;探讨厂反射镜的支撑方式,提出了背部单点支撑与两点支撑两种方案;针对面型精度要求较高的反射镜,提出了柔性支撑结构的设计思想.采用有限元方法,埘反射镜结构进行分析,并对采用柔性支撑结构后的反射镜进行静力学分析和模态分析.分析结果表明:两种支撑方案均满足面型要求,且前者优于后者.     

双层厚膜结构改善气敏元件灵敏度和选择性研究

研究了厚膜印刷技术制备的双层膜结构气敏元件的灵敏度和选择性.测量结果表明:在二氧化锡(SnO2)单层膜下再添加一层纳米三氧化钨(WO3)材料厚膜,可以提高气敏元件对酒精、丙酮、甲醛、甲苯还原气体的灵敏度和选择性.当浓度为900×10-6时,将SnO2覆盖在WO3之上形成双层膜时,较两种材料对应的单层膜灵敏度均有所提升.因此,双层厚膜结构为改善元件的灵敏度和选择性提供了一种可行的方法.初步认为,双层膜的作用与膜的上、下排列顺序有很大的关系,也与双层界面间由于扩散效应所形成的过渡层有关.     

基于机器视觉的发动机包覆层表面缺陷检测技术

固体火箭发动机包覆层表面的缺陷检测是保证其使用安全性的重要手段.本文应用机器视觉技术实现发动机包覆层表面缺陷的自动检测.用工业相机采集发动机包覆层表面的图像,结合图像特点,通过多次实验分析,选择中值滤波方法进行滤波,采用图像模式匹配技术将缺陷从图像背景中分割出来,并将以上功能进行整合,设计缺陷自动检测系统.实验结果表明...     

AutoCAD R12／R13for Windows中的表面粗糙度标注方法

随着计算机辅助设计技术的普及和发展,越来越多的专业技术人员以AutoCAD为支撑平台处理日常的设计绘图、开发自己的专用CAD系统,AutoCAD已成为目前国内用户最多的CAD系统之一.但AutoCAD是一种通用的软件平台,对于某些特定专业的CAD应用要求还不能充分满足,需要进行二次开发,增加适合专业需要的应用程序和功能.比如机械专业的工程图纸设计中标注尺寸时,常常需要标注表面粗糙度,而AutoCAD R12/R13版本中均没有表面粗糙度标注功能,用户大都采用手工绘制或定义图形块的方法实现表面粗糙度的工程标注,使用起来十分不便.作者根据国标标注中表面粗糙度标注的规定和机械设计的要求,采用Autolisp编写了AutoCAD环境中对设计图纸进行表面粗糙度标注的应用程序,使用方便灵活,可极大的提高设计     

MEMS表面微加工工艺技术

在介绍了北大微电子所开发的两层多晶硅表面微加工工艺和源于加州Berkely传感器与执行器研究中心的三层多晶硅表面微加工工艺的基础上,介绍了美国Sandia国家实验室开发的五层MEMS表面微加工工艺的主要技术特点.给出了利用这三种表面微加工工艺制备的一些微机械表面器件及其技术特点.     

HF在Cu(100)和SiO2(100)晶面吸附的蒙特卡罗模拟

HF 同固体表面的相互作用,在腐蚀、催化和电化学等领域都有重要的意义.为了研究在低温低压条件下,HF 在 Cu 和 SiO2晶体表面的吸附情况,本文采用巨正则蒙特卡罗(GCMC)模拟法,计算模拟 HF 在 Cu(100)和SiO2(100)晶体表面的吸附行为.结果表明:本文所模拟的属于物理吸附.在 150 K、46.62 Pa 以上时,HF 可以在 Cu 晶体表面上发生吸附,如压力降低,则吸附大大降低,在 100 K 以下、1 Pa 以上时,均能发生吸附.在相同条件下,HF 与SiO2 比与 Cu 晶面的吸附能力强,且更易发生物理吸附,在 150 K 以下,1 Pa 以上时,HF均可与SiO2晶面发生吸附.本文的结果为在低温低压下 HF 与 Cu 和SiO2 晶体表面的吸附实验提供一定的理论指导.     

固体入水的边界压力处理及表面粒子位置的修正

基于传统光滑粒子流体动力学(SPH)方法的边界力法、虚粒子法或耦合力法处理固体入水时,流 体与固体交互界面的粒子密度不连续、压力不稳定、固体边界处会发生部分流体粒子穿透或分离等现象,而流 体表面因为受到力的作用,表面破碎后,液面较粗糙。针对上述问题,结合边界力和虚粒子的优点,对耦合力 法进行改进,处理运动固体边界,阻止流体粒子穿透固体边界;改进交互界面的压力计算方法,提高计算精度, 稳定交互界面压力场;对流体表面的粒子位置进行校正,提升流体表面自由流动液面边界的模拟效果。通过经 典的二维固体入水实验,对该方法进行了验证,实验结果表明,本文方法在流体粒子与固体粒子交互后,交互 界面压力稳定,界面分离清晰无穿透,表面流体粒子分布均匀,流场的运动真实自然。     

Polymeric matrices for immobilising zinc tetraphenylporphyrin in absorbance based gas sensors

Zinc tetraphenylporphyrin (ZnTPP) was incorporated in six silicone elastomers and three thermoplastics. The stability of ZnTPP in these membranes on storage under ambient light and in the dark over 35 days period was measured using absorption spectroscopy. The characteristic Soret band absorbance of ZnTPP in all the polymeric membranes stored under ambient light decreased, with the absorbance of ZnTPP in silicone membranes was scarcely measurable after 14 days. However, when stored in the dark, the rate of decrease in the Soret band absorbance of ZnTPP within these membranes appears to be dependent on the concentration of ZnTPP incorporated in them. Possible explanations for this behaviour are discussed.

Ethyl cellulose (EC) and poly(vinyl chloride) (PVC) yielded active membranes with little or no change in their spectral characteristics on storage in the dark. Addition of diethyl phthalate to both thermoplastics reduced response and reversal times of the membranes when exposed to ammonia (NH₃) gas (EC, <120 s; PVC, <10 s). The response characteristics of optimised sensing membranes of PVC exposed to ammonia gas were measured. These membranes responded to ammonia gas in less than 10 s and are capable of detecting ammonia gas at levels less than 0.5 mg m⁻³; however, these membranes were also found to be sensitive to relative humidity.     

Continuous optical monitoring of aqueous amines in transflectance mode

Derivatives of the chromoreactand 4-trifluoroacetylazobenzene were shown to allow continuous monitoring of amines in aqueous solutions. The optical change was measured by absorbance spectroscopy. The method did not satisfy in view of applications to real food specimens or waste water. In this paper, an optical sensor system based on transflectance measurements is investigated in order to determine the concentration of amines of low molecular mass in a continuous-flow system. For this purpose, solvent polymeric optode membranes selective for amines were modified by using a reflective TiO₂ pigment or an additional white PTFE layer (adlayer).Three different sensor layers were investigated, namely: (a) optode membranes incorporating ETH^T 4001 in plasticized PVC coated with a microporous white PTFE film (membranes M1), (b) membranes incorporating ETH^T 4001 with titanium dioxide dispersed in plasticized PVC (membranes M2), and (c) membranes incorporating a copolymer from ETH^T 4012, methyl methacrylate and butyl acrylate coated with PTFE (membranes M3).Both types of reflective materials were applied to membranes placed within a continuous-flow module. The transducer consisted of a fiber-optical probe, which allowed monitoring of variations in the spectrum of a chromoreactand in the transflectance mode. All three approaches were compared in terms of reproducibility, dynamic range, detection limit, and response time. The free-diffusion membranes M1 and M2 responded faster (30 to 45 s) than membrane M3 (2 to 14 min), which incorporated the reactand covalently linked to the copolymer. Surprisingly, the detection limit of M3 was lower than that of M1 and M2. Due to M3's high mechanical stability, its reproducibility was superior to M1 and M2. In general, the use of reflective material did not affect such sensor characteristics as the selectivity, dynamic range, detection limit and response time of the amine-selective optodes. Thus, it is possible to convert any sensor chemistry based on indicator dyes incorporated into a polymer matrix (optode membranes) into reflectance-based fiber optic sensors without affecting the sensor's performance.     

Microfabrication of palladium-silver alloy membranes for hydrogen separation

In this paper, a process for the microfabrication of a wafer-scale palladium-silver alloy membrane (Pd-Ag) is presented. Pd-Ag alloy films containing 23 wt% Ag were prepared by co-sputtering from pure Pd and Ag targets. The films were deposited on the unetched side of a <110>-oriented silicon wafer in which deep grooves were etched in a concentrated KOH solution, leaving silicon membranes with a thickness of ca. 50 /spl mu/m. After alloy deposition, the silicon membranes were removed by etching, leaving Pd-Ag membranes. Anodic bonding of thick glass plates (containing powder blasted flow channels) to both sides of the silicon substrate was used to package the membranes and create a robust module. The hydrogen permeability of the Pd-Ag membranes was determined to be typically 0.5 mol H/sub 2//m/sup 2//spl middot/s with a minimal selectivity of 550 for H/sub 2/ with respect to He. The mechanical strength of the membrane was found to be adequate, pressures of up to 4 bars at room temperature did not break the membrane. The results indicate that the membranes are suitable for application in hydrogen purification or in dehydrogenation reactors. The presented fabrication method allows the development of a module for industrial applications that consists of a stack of a large number of glass/membrane plates.     

Nanoporous polystyrene fibers functionalized by polyethyleneimine for enhanced formaldehyde sensing

Here we report a novel fabrication approach to highly sensitive formaldehyde sensors by the surface modification of the electrospun nanofibrous membranes. The three-dimensional fibrous membranes comprising nanoporous polystyrene (PS) fibers were electrospun deposition on quartz crystal microbalance (QCM), followed by the functionalization of the sensing polyethyleneimine (PEI) on the membranes. The morphology and Brunauer-Emmett-Teller (BET) surface area of the fibrous PS membranes with fiber diameter of 110-870 nm were controllable by tuning the concentrations of PS solutions. After PEI modification, PEI particles in clusters of varying sizes (50 nm to 1.2 μm) were immobilized onto the surface of the bead-on-string structured nanoporous fibers. The developed formaldehyde-selective sensors exhibited fast response and low detection limit (3 ppm) at room temperature. This high sensitivity is attributed to the high surface-area-to-volume ratio (∼47.25 m²/g) of the electrospun porous PS membranes and efficient nucleophilic addition reaction between formaldehyde molecules and primary amine groups of PEI.     

Identification of mechanical defects in MEMS using dynamic measurements for application in production monitoring

Investigations for non-destructive characterization of MEMS (Micro-Electro-Mechanical-Systems) are presented that can be applied in production monitoring in early stages. Different aspects and experimental results are shown for quadratic and circular silicon membrane structures with artificial structural defects. The quadratic membranes were manufactured with three variations of notches at the edges. The circular membranes had residues on the backside of the membrane resulting from the etching process. The dynamic properties of the structures were measured non-destructively by scanning laser-Doppler vibrometry. The consequences of the generated defects were investigated using the resonant frequencies and mode shapes of the membrane structures in comparison to the dynamic properties of accurate membranes. The results show that the generated defects lead to a variation of the dynamic properties depending on size and position of the defect.     

High-aspect-ratio nanoporous membranes made by reactive ion etching and e-beam and interference lithography

Nanoporous membranes engineered to mimic natural filtration systems can be used in “smart” implantable drug delivery systems, hemodialysis membranes, bio-artificial organs, and other novel nano-enabled medical devices. Conventional membranes exhibit several limitations, including broad pore size distributions and low pore densities. To overcome these problems, lithographic approaches were used to develop porous silicon, silicon nitride, ultrananocrystalline diamond (UNCD), and polymer film membranes. Here we report processing of high porosity, high-aspect-ratio membranes by two techniques: UNCD fabricated by reactive ion etching after e-beam lithography and epoxy fabricated by interference lithography.     

On the power and size of extended gemmating P systems

In [3] P systems with gemmation of mobile membranes were examined. It was shown that (extended) systems with eight membranes are as powerful as the Turing machines. Moreover, it was proved that extended gemmating P systems with only pre-dynamical rules are still computationally complete: in this case nine membranes are needed to obtain this computational power. In this paper we improve the above results concerning the size bound of extended gemmating P systems, namely we prove that these systems with at most five membranes (with meta-priority relations and without communication rules) form a class of universal computing devices, while in the case of extended systems with only pre-dynamical rules six membranes are enough to determine any recursively enumerable language.     

A magnetic nano-composite soft polymeric membrane

There is an increased need for low cost actuation technologies at the micro and nanoscale. Magnetically responsive polymer-based materials are good candidates for numerous applications in microsystems for actuation and sensing purposes. In this work, we report on nano-polymer composite magnetic silicone-based membranes, which provide the low elastic modulus needed for magnetic actuation to be effective at small scales. Passivated crystalline cobalt (~37 nm) and water based iron/cobalt (~100 nm) nanoparticles (NPs) have been synthesized using a chemical route at 50 °C and at room temperature, respectively. The NPs were characterized by Fourier Transform Infrared Spectroscopy, X-Ray Diffraction, Atomic Force Microscopy and Vibrating Sample Magnetometry (VSM). The NPs are then uniformly dispersed in a polydimethyl siloxane (PDMS) polymer matrix in order to fabricate smooth and flexible magnetic composite membranes. The magnetic properties of the membranes for different amounts of cobalt and iron NPs (16 and 25 wt%) were characterized by VSM and deflection measurements. Co/Fe PDMS composite membranes of about 50 mm diameter and ~250 μm thickness were used under the application of ~400 Oe magnetic fields. The cobalt-PDMS membrane shows the largest deflection (~900 vs. ~80 μm for an iron-PDMS membrane). The deflections observed on these membranes are found to have a linear dependence on the applied magnetic field.     

Formaldehyde sensors based on nanofibrous polyethyleneimine/bacterial cellulose membranes coated quartz crystal microbalance

A novel formaldehyde sensor based on nanofibrous polyethyleneimine (PEI)/bacterial cellulose (BC) membranes coated quartz crystal microbalance (QCM) has been successfully fabricated. The nanoporous three-dimensional PEI/BC membranes are composed of nanofibers with diameter of 30-60 nm. The sensor showed high sensitivity with good linearity and exhibited a good reversibility and repeatability towards formaldehyde in the concentration range of 1-100 ppm at room temperature. Moreover, the results showed that the sensing properties were mainly affected by the content of PEI component in nanofibrous membranes, concentration of formaldehyde and relative humidity. Additionally, the nanofibrous PEI/BC membrane coated QCM sensors exhibited a good selectivity to formaldehyde when tested with competing vapors. The simple and feasible method to prepare and coat the PEI/BC sensing membranes on QCM makes it promising for mass production at a low cost.     

Super permeable nano-channel membranes defined with laser interferometric lithography

We report the design, fabrication, and testing of super permeable nano-channel membranes, characterized by the absolute control in the pore size at the nano-scale dimensions, large surface area, very high permeability, mechanical stability and durability. The membranes were fabricated using a unique nanotechnology process that combines laser interferometric lithography to define nano-channels (pores) and micro-machining to produce free-standing amorphous silicon membranes, allowing rapid and cost-effective mass production. The suspended membranes were defined as 50 nm thick a-Si, characterized by a very high porosity of approximately 20%, achieved by definition of large arrays of nano-channels. The dimensions of each individual nano-channel was 65 nm wide, 250 nm long. The measured apparent permeability was 0.14 ± 0.05 cm/min for each individual 70 μm × 70 μm membrane, representing one of the highest permeability values ever reported for this scale.