压电微悬臂梁气体传感器静态弯曲模型的研究

压电微悬臂梁是一种灵敏度高、尺寸小的生化传感器.分子或原子在压电微悬臂梁功能化表面的吸附会引起悬臂梁的静态弯曲,通过静态变形可以得到微悬臂梁的表面应力.将表面应力引起的微悬臂梁中性层位置的变化引入建模过程,并与能量法相结合,建立了压电微悬臂梁在单分子层吸附稳定后的静态弯曲理论模型.结果发现在相同吸附表面积和吸附量条件下...     

基于弯曲测试的纳结构机械力学特性的表征

利用原子力显微镜对聚焦离子束刻蚀技术制备的不同纵横比的氮化硅纳米梁结构进行了弯曲测试,并讨论了一种标定原子力显微镜微悬臂梁弹簧常数的方法.实验中严格界定了欧拉细长梁的条件,在分析了纳米梁组纵横比对测试结果影响的基础上,讨论了如何修正弯曲测试结果.弯曲测试得到了纳米梁的平面模数,并进一步推算氮化硅材料的杨氏模量.测试结果验证了基于原子力显微镜系统的弯曲方法测试纳米薄膜材料杨氏模量的可行性.     

硅纳米悬臂梁传感结构压阻特性的试验研究

为了研究拉伸和大形变弯曲共存状态下硅纳米悬臂梁传感结构的压阻特性,采用CMOS工艺制作了硅纳米悬臂梁传感测试结构,结合原子力显微镜和半导体参数测试仪对其电学参数进行了测量,其位移灵敏度高达1.58216×10-4/nm。在电阻相对变化率实验测量和ANSYS有限元平均应力仿真的基础之上,进而提出了一个非线性压阻模型来提取大弯曲硅纳米悬臂梁的一阶和二阶压阻系数。研究结果表明:其一阶压阻系数约为体硅的5倍,该巨压阻效应为利用硅纳米压阻传感结构来实现超高灵敏度的纳米压力传感器提供了可能的途径。研究结果同时也揭示了要获得高的灵敏度和好的可靠性,硅纳米悬臂梁的长度设计需要折衷考虑。     

微机械悬臂梁中的机械噪声机制分析

本文采用能量统计分布方法研究微机械悬臂梁的噪声模型,对热机械噪声理论模型进行了拓展和修正,使之适用于低温和高频条件.研究了温度、压力和频率对热机械噪声、温漂噪声和吸附-脱附噪声的影响.根据研究结果对静态检测悬臂梁和动态频率响应悬臂梁传感器进行了具体分析.对于静态下工作的微机械悬臂梁,振幅的随机变化取决于热机械噪声.对于工作在谐振状态的微米尺度悬臂梁,在室温常压下热机械噪声是主要的噪声机制;当尺寸进一步缩小至纳米尺度时,表面效应变得显著,吸附-脱附噪声成为主要的噪声机制.基于对不同情况下噪声特性的分析,对微机械悬臂梁传感器的优化设计规则进行了探讨.     

光致硅微悬臂梁形变理论研究

研究了硅悬臂梁的光致应变效应的基本理论.从力学和半导体物理学基本理论出发,考虑了光生载流子的空间分布以及载流子表面复合,提出了一种新的光致悬臂梁弯曲的模型和计算光致应变效应引起的悬臂梁弯曲量的方法.模型更为合理的解释了光致悬臂梁弯曲的根本动力,其计算结果和实验测量结果与文献报道相比更为接近.研究为基于光致应变效应的硅悬臂梁传感器打下了理论基础.     

DNA在SiO2纳米粒子薄膜表面的单分子行为研究

基于应用全内反射荧光显微镜,利用YOYO-1标记的λ-DNA分子作为探针研究了SiO2纳米粒子薄膜的表面性质,在不同的pH值下,考察了pH值对单个DNA分子在其表面行为(自由运动和吸附)的影响,并采用接触角(CA)和原子力显微镜(Atomic Force Microscope,AFM)表征了SiO2纳米粒子薄膜表面的性质.实验表明,随着pH值的降低,DNA分子在其表面的吸附率随之增大.DNA分子在SiO2纳米粒子薄膜表面的吸附行为是静电作用和疏水作用共同作用的结果,但是起主导作用的是疏水作用.此外,相同pH值下,与文献中报道的DNA在玻片上的吸附率相比,DNA在SiO2纳米粒子薄膜表面的吸附率要大得多,这是由于SiO2纳米粒子的比表面积大,表面活性位点多,且疏水性能强的缘故.     

基于ABAQUS的复合薄膜热结构有限元分析

半导体硅基复合薄膜悬臂梁在温度场、加速度以及二者耦合场作用下,挠度和应力会发生变化.通过加热可使得驱动元件本身的温度升高,结构内部将会产生热应力,会导致两种薄膜各自产生线应变,线膨胀系数小的薄膜受到拉力作用,线膨胀系数大的薄膜受到压力作用,自由端会受到力矩作用而向线膨胀系数小的薄膜方向弯曲,从而导致悬臂梁的挠度发生变化.当弯曲悬臂梁有加速度作用时,会产生一个与加速度方向相同的力作用在悬臂梁上,同样会导致悬臂梁的挠度发生变化[1].通过ABAQUS软件仿真[2],分别给出不同物理场中弯曲悬臂梁相对位移的大小,所得的结论为半导体硅基复合薄膜弯曲悬臂梁的应用装置提供了理论依据.     

基于MC的生物膜多功能压电换能器研究

频率特性与生物膜的位置和大小的关系是设计多功能生物传感器的关键.设计了微悬臂梁MC(Micro Cantilever)、压电元件和生物膜组成的多功能传感器,用有限元方法分析了微悬臂梁的弯曲振动模型的固有频率与节点位置的关系,确定了如何选择固定两种生物膜的位置和大小的方法,实验和模拟结果表明正交节点位置的质量变化使频率具有正交响应.验证了利用有限元的频率振动模型分析设计多功能压电换能器的有效性.进而分析了设计可测量纳米质量的生物膜多功能MC的可能性.     

用于痕量胺类同系物检测的谐振式微悬臂梁传感器

采用化学修饰法,将酸性羧基基团嫁接于高比表面的积的SBA- 15介孔材料中,然后将该功能化介孔材料负载于集成谐振式微悬臂梁表面,制得一种高性能的挥发性胺类同系物传感器.胺类分子的吸附将导致质量型微悬臂梁传感器谐振频率的下降,传感器检测下限可达ppb量级.对一系列胺类同系物的检测结果表明,胺类分子在羧基功能化介孔表面的吸...     

生物分子在Ni纳米膜表面吸附的力学特性： 分子动力学模拟

采用COMPASS力场,通过分子动力学模拟,研究了Ni纳米薄膜的弹性模量的尺寸效应,以及生物分子吸附在Ni表面对其力学性能的影响.计算结果表明,随着厚度的增大,吸附强度也在增强;Ni纳米薄膜的弹性模量随着膜厚的减小而减小.氨基酸在Ni表面的吸附能够提高其弹性模量1～2 GPa,并且表明分子的取向是重要的影响因素.     

HEDP及其取代物对碳酸钙阻垢机理的研究

采用分子动力学方法,模拟计算了阻垢剂HEDP及其取代物与方解石(104,(102),(202),(113)面的相互作用,计算并分析了阻垢剂与方解石(104),(102),(202),(113)面作用的相互作用能,包括结合能,库仑能和范德华作用能.并且分析了方解石(104)晶面上的钙离子与阻垢剂中双键氧原子、整个(104)晶面与阻垢剂中所有氧原子之间和整个(104)晶面与整个阻垢剂分子之间的对关联函数,结果表明:阻垢剂分子中的氧原子与碳酸钙的Ca2+形成的离子键对吸附起到了主要作用,同时阻垢剂与晶面间存在较弱的范德华力相互作用,阻垢剂与各晶面的的结合能强弱顺序为(102)＞(202)≥(113)≈(104).苯环的大π键有利于阻垢效果的提高.     

Water diffusion in polymer nano-films measured with microcantilevers

We present a method to measure the absorption of water molecules from the liquid and the vapour phase into polymer nano-films and the diffusion inside these films. Film thickness can be down to 45 nm. To demonstrate the possibilities of this method we use polymer films that are deposited on the upper side of a silicon cantilever by plasma polymerization of norbornene. When a microdrop of water is deposited onto the initially straight cantilever, the drop causes the cantilever to bend while it evaporates. Evaporation of such small water drops usually takes less than a second. An upwards bending is due to capillary forces and a downwards bending is due to the diffusion of water into the polymer film – and the consequent volume expansion (swelling) of the film. The magnitude of the capillary forces and the extent of swelling continuously change during drop evaporation. When drop evaporation is over the cantilever returns to its initial straight position. We simulate the time dependent bending with a numerical model that qualitatively agrees with the experiment. From the time dependence of cantilever bending we are able to determine the diffusion coefficient of water in the thin polymer film.     

DNA hybridization measurement by self-sensing piezoresistive microcantilevers in CMOS biosensor

Understanding the mechanism of how biological reactions produce mechanical loadings is fundamental to biomedical developments. A CMOS biosensor chip is developed to measure in situ the induced surface stress change by DNA hybridization. For 20-mer thiol-modified single stranded DNA (ssDNA), the mechanism of ssDNA attached to gold surface via a sulfur–gold linkage can be investigated by using the Langmuir adsorption model. Experimental results indicate that the immobilization response is less than 1 s, the total number of ssDNA molecules on the cantilever is about 3 × 10¹¹, and the induced surface stress is 0.15 N/m. The surface stress sensitivity of the sensor is about 3.5 × 10⁻⁵ m/N. The estimated adsorption rate of the ssDNA is 0.005 s⁻¹. The biosensor is capable of discriminating complimentary molecular targets and thus may provide a powerful platform for high throughput real-time analysis of DNA.     

基于GL Studio的航空虚拟仪表的设计与实现

为了实现航空电子仿真系统中各种仪表的快速建模,从GL Studio平台的技术特点出发,设计开发了一个由外部数据源控制的虚拟仪表。首先,用GL Studio设计虚拟仪表的图形界面;然后用VC++6.0开发一个基于MFC的仪表驱动数据编辑器;最后,编写一个管道通信接口将虚拟仪表与数据源进行连接,从而实现外部数据对虚拟仪表的控制。结果表明,该方法具有很好的实用性。     

Fabrication and Characterization of a Polymeric Microcantilever With an Encapsulated Hotwire CVD Polysilicon Piezoresistor

We demonstrate a novel photoplastic nanoelectromechanical device that includes an encapsulated polysilicon piezoresistor. The temperature limitation that typically prevents deposition of polysilicon films on polymers was overcome by employing a hotwire CVD process. In this paper, we report the use of this process to fabricate and characterize a novel polymeric cantilever with an embedded piezoresistor. This device exploits the low Young's modulus of organic polymers and the high gauge factor of polysilicon. The fabricated device fits into the cantilever holder of an atomic force microscope (AFM) and can be used in conjunction with the AFM's liquid cell for detecting the adsorption of biochemicals. It enables differential measurement while preventing biochemicals from interfering with measurements using the piezoresistor. The mechanical and electromechanical characterization of the device is also reported in this paper.$hfill$[2008-0108]      

在晶体表面寻找最佳吸附位点的高通量算法

在研究原子在晶体表面的吸附现象时,研究者们往往需要依赖已有的经验与知识寻找出所有可能的吸附位点,再通过运行基于密度泛函理论 (DFT) 的第一性原理计算模拟软件最终找到最佳吸附位点,这是较为浪费时间的。借助于材料基因组计划 (MGI) 中的高通量筛选这一概念,本文提出了一个寻找晶体表面最佳吸附位点的自动化的高通量计算方法。本文主要阐述了该高通量方法中的一个重要的算法,即如何自动寻找所有可能吸附位点的算法,然后将该算法与第一性原理计算模拟软件整合,它们一起构成了寻找最佳吸附位点的高通量方法。该高通量方法的创新之处在于能够在不依赖于研究者经验与知识的前提下,自动地找出所有可能的吸附位点,并利用第一性原理计算模拟引擎,最终找到最佳吸附位点。此外,这个方法被应用于 MatCloud 平台。MatCloud 平台是一个高通量材料计算平台,它使得整个寻找最佳吸附位点的流程自动化。     

Simultaneous optimization of piezoelectric actuator topology and polarization

This article addresses the problem of piezoelectric actuator design for active structural vibration control. The topology optimization method using the Piezoelectric Material with Penalization and Polarization (PEMAP-P) model is employed in this work to find the optimum actuator layout and polarization profile simultaneously. A coupled finite element model of the structure is derived assuming a two-phase material, and this structural model is written into the state-space representation. The proposed optimization formulation aims to determine the distribution of piezoelectric material which maximizes the controllability for a given vibration mode. The optimization of the layout and poling direction of embedded in-plane piezoelectric actuators are carried out using a Sequential Linear Programming (SLP) algorithm. Numerical examples are presented considering the control of the bending vibration modes for a cantilever and a fixed beam. A Linear-Quadratic Regulator (LQR) is synthesized for each case of controlled structure in order to compare the influence of the polarization profile.     

Elastic–plastic modeling of heat-treated bimorph micro-cantilevers

This paper models the residual stress distributions within micro-fabricated bimorph cantilevers of varying thickness. A contact model is introduced to calculate the influence of contact on the residual stress following a heat treatment process. An analytical modeling approach is adopted to characterize bimorph cantilevers composed of thin Au films deposited on thick poly-silicon or silicon-dioxide beams. A thermal elastic–plastic finite element model (FEM) is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the beam tip deflection following heat treatment. The influences of the beam material and thickness on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a larger beam thickness leads to a greater residual stress difference at the interface between the beam and the film. The residual stress established in the poly-silicon cantilever is greater than that induced in the silicon-dioxide cantilever. The results confirm the ability of the developed thermal elastic–plastic finite element contact model to predict the residual stress distributions within micro-fabricated cantilever structures with high accuracy. As such, the proposed model makes a valuable contribution to the development of micro-cantilevers for sensor and actuator applications.     

Metal (Pd, Pt)-decorated carbon nanotubes for CO and NO sensing

Using the first-principles calculations, we investigated adsorption of CO and NO gas molecules on the Pd- and Pt-decorated single-walled carbon nanotube (SWNT). The metal-decorated SWNTs exhibit strong affinity toward the gas molecules. Our results reveal that the CO and NO gas molecules can be chemisorbed on the Pd or Pt atom, accompanying with the large binding energy and significant charge transfer. Adsorption of these gases would affect the electronic conductance of the materials, which can serve as a signal of gas sensor. In particular, adsorption of NO generates the magnetic properties to the metal-decorated SWNT, which can also serve as a sensitive signal for chemical sensors. After adsorption of CO and NO, the changes in binding energy, charge transfer and conductance may lead to the different response in the metal-doped CNT-based sensors. It is expected that these results could provide helpful information for the design and fabrication of the CO and NO sensing devices.     

Elastic–plastic modeling of heat-treated bimorph micro-cantilevers

This paper models the residual stress distributions within micro-fabricated bimorph cantilevers of varying thickness. A contact model is introduced to calculate the influence of contact on the residual stress following a heat treatment process. An analytical modeling approach is adopted to characterize bimorph cantilevers composed of thin Au films deposited on thick poly-silicon or silicon-dioxide beams. A thermal elastic–plastic finite element model (FEM) is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the beam tip deflection following heat treatment. The influences of the beam material and thickness on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a larger beam thickness leads to a greater residual stress difference at the interface between the beam and the film. The residual stress established in the poly-silicon cantilever is greater than that induced in the silicon-dioxide cantilever. The results confirm the ability of the developed thermal elastic–plastic finite element contact model to predict the residual stress distributions within micro-fabricated cantilever structures with high accuracy. As such, the proposed model makes a valuable contribution to the development of micro-cantilevers for sensor and actuator applications.