范德华力对硅基微悬臂梁抗粘附稳定性的影响

通过在硅微悬臂梁与基底表面上涂覆低表面能的憎水性OTS(CH3(CH2)17SiCl3)膜,以除去接触面间的表面张力;把梁与基底均接地,以除去接触面间的静电力,研究仅有范德华力作用时,硅微悬臂梁结构的抗粘附稳定性.根据两接触面均为粗糙表面的微观实际接触模型,在接触表面产生塑性变形的情况下,计算范德华粘附能大小,并分析表面形貌对其影响,得到粗糙表面接触的微梁抗粘附临界长度.     

多晶硅微机械抗粘附结构参数设计

讨论了在大气环境或有液体的环境下，表面张力对微加工悬臂梁结构粘附的影响，以及真空条件下Casimir量子力对微机械薄膜微腔结构的稳定性和粘附的影响。建立了Casimir量子力作用下粘附问题的实际粗糙模型理论。对不同表面力作用下的抗粘附结构研究结果表明，微悬臂梁和薄膜微腔结构的稳定性和粘附与材料的弹性特性，材料的表面特性、结构的长度、厚度以及构件与基本之间的间隙有关，而与结构的宽度无关。给出了抗粘附结构参数设计的对数坐标图。     

压电微悬臂梁传感器性能的数值模拟研究

基于力-电双向耦合理论,采用有限元方法,数值模拟研究压电微悬臂梁的灵敏度,并进行参数分析,为设计性能优良的悬臂梁提供理论依据。理论分析微悬臂梁在空气和液体中的共振频率和自身结构参数的定量关系,灵敏度与共振频率变化量、被测物质量的关系,通过数值模拟得到悬臂梁长度、宽度、厚度及共振阶数对微质量检测压电悬臂梁灵敏度的影响。在长期研究OPCM压电传感材料的基础上,进一步提出纵向振动的OPCM材料制作悬臂梁,数值模拟结果表明OPCM比PZT悬臂梁具有更高的灵敏度。数值模拟结果为设计性能优良的悬臂梁提供理论依据。     

微悬臂梁长度对梁末端与底座粗糙面间接触的影响

将磁致伸缩效应等效为材料的热膨胀效应,考虑微梁末端与底座粗糙面微凸体间的相互作用、材料弹塑性变形及微梁弹性恢复力等影响,利用ABAQUS动态模拟了磁致伸缩薄膜悬臂梁末端与底座粗糙面间的接触,分析了不同长度悬臂梁对接触特性的影响。结果表明,重复加卸载过程中,接触面积、法向接触力随着微梁长度的增加呈近似线性增长,而最大等效塑性应变值随微梁长度的增加呈非线性关系,说明微梁长度对梁与底座粗糙面间接触特性的影响十分重要,进而影响到系统工作的可靠性。     

粗糙表面分形接触模型的研究进展

工程表面具有分形特征,利用分形参数对表面形貌进行表征不受仪器分辨率和取样长度的影响。2个粗糙表面之间的接触行为对摩擦、磨损、润滑、密封和传热等均有着重要的影响,因而一直是摩擦学研究的重要课题之一。基于表面的分形特性而建立的接触模型,可使表面接触的分析结果具有确定性和唯一性。介绍分形表面形貌的Weierstrass-Mandelbrot函数生成方法并给出利用MATLAB程序生成的分形曲线和曲面,分析和评述近二十年来分形接触模型中单个微凸体的接触行为、接触面积分布与真实接触面积、接触变形方式与接触载荷以及总的真实接触面积与接触载荷之间的关系等方面的研究情况,并简单列举分形接触模型在机械学科中的应用情况。指出结合分形理论对表面接触行为进行研究是接触理论发展的必然趋势,为摩擦学研究提供新的思路。     

基底与微悬臂梁间接触-分离的动态分析

将基底与微悬臂梁间的接触简化为一理想平面基底与微悬臂梁粗糙面间的接触,在考虑微悬臂梁的弹性恢复、两接触体的弹塑性变形以及粗糙面微凸体间相互粘着作用的基础上,运用ABAQUS大型有限元软件实现了微悬臂梁与基底的接触-分离动态分析。结果表明,该撞击过程实际上是一个复杂的多次弹塑性撞击过程,一般存在2个以上的明显撞击区,每个撞击区包含了形式多样的复杂的次生撞击过程,并且每次撞击力较静态接触力大很多,因此造成的影响很大。其对今后的材料摩擦磨损具有一定的理论指导意义。     

MEMS微悬臂梁构件变形规律的AFM试验研究

采用原子力显微镜测试了微悬臂梁构件的弯曲变形规律。发现构件的弹性支撑是试验数据和理论计算出现误差的主要原因。引入支撑扭转等效刚度对探针-样品等效刚度计算公式进行修正。修正结果对大有效长度的构件与实测结果吻合良好。对短有效长度微悬臂梁,其误差原因主要为支撑的影响以及测试探针的大变形,论文进一步提出研究的建议。     

表面粗糙度对悬臂梁小试样蠕变性能评价的影响研究

小试样试验方法在材料蠕变性能评估中具有节省材料、快捷等优点.但在小试样蠕变试验过程中,加载压头与试样接触产生的摩擦会对试验结果产生影响.悬臂梁小试样因载荷点位置偏置,压头与试样之间容易发生相对滑移,进而受到接触摩擦的影响,目前尚未有相关试验研究表面粗糙度对悬臂梁小试样蠕变性能评价的影响.通过选取不同表面粗糙度的悬臂梁小...     

塔式起重机回转运动引起起重臂振动响应分析

塔式起重机的回转惯性力将引起起重臂水平面内的振动,这一振动是起重机产生疲劳破坏的主要原因之一。文中根据塔式起重机在回转运动过程中的运动特性,将其简化为悬臂梁,再建立移动质量—悬臂梁系统运动微分方程,仿真分析了回转运动对起重臂振动的影响规律。仿真结果表明:回转加速度的增加将使起重臂的振动幅值增加;回转机构在加、减速运动过程中,起重臂的振动幅值和周期以及振动的平衡位置随着钢丝绳长度和起重量的增加而增加;回转机构在匀速运动过程中,起重臂振动幅值和周期以及振动的平衡位置随着钢丝绳长度和起重量的增加而减小。     

悬臂梁式压电发电结构理论模型及其仿真研究

为提高压电悬臂梁发电能力以及将压电发电技术应用到日常生活中,开展了压电振动理论分析,建立了压电装置的发电能力与压电材料的厚度比、长度以及悬臂梁的材料、长度等之间的关系,提出了数学建模的分析方法,在理论上对压电悬臂梁的发电能力进行了评价,并进行了Matlab仿真实验.其结果表明:悬臂梁压电发电模型中,压电材料存在最佳厚度...     

High resolution non-contact AFM imaging of liquids condensed onto chemically nanopatterned surfaces

The wetting of ethanol and octane on chemically nanopatterned surfaces has been investigated using Atomic Force Microscopy (AFM) under controlled environmental conditions. The patterns were generated on a methyl-terminated, organic monolayer using an AFM electro-oxidation process. The subsequent wetting of the organic liquids was studied using non-contact mode AFM under equilibrium conditions with the vapor. This study of condensed nanoliquids provides the first reliable measurements of sub 100 nm liquid profile shapes. The derived contact angles give an estimate of the line tension.     

S型折叠式微悬臂梁刚度计算

针对目前没有成熟的设计计算S型折叠式悬臂梁刚度公式的问题,本文利用能量法和胡克定律推导了S型折叠悬臂梁x向、y向和z向的刚度计算公式。推导过程中发现对于复杂的微悬臂梁结构,其转角处的弯矩对最终结果影响较大,不可忽略。在ANSYS中对S型折叠悬臂梁建模,应用有限元法计算了S型悬臂梁的刚度,并和理论公式进行了对比。与有限元法对比显示,公式计算值的相对误差分别为0.67%、1.09%和2.95%,均小于3%。应用图像测位移法对S型悬臂梁进行了x、y向的拉伸实验,实验显示得到的实验值和理论值吻合,表明本文推导的 S型悬臂梁的刚度计算公式合理,能够为该类型悬臂梁的设计和计算提供理论依据。     

Prediction of atomic force microscope probe dynamics through the receptance coupling method

The increased growth in the use of tip-based sensing, manipulations, and fabrication of devices in atomic force microscopy (AFM) necessitates the accurate prediction of the dynamic behavior of the AFM probe. The chip holder, to which the micro-sensing device is attached, and the rest of the AFM system can affect the overall dynamics of the probe. In order to consider these boundary effects, we propose a novel receptance coupling method to mathematically combine the dynamics of the AFM setup and probe, based on the equilibrium and compatibility conditions at the joint. Once the frequency response functions of displacement over force at the tool tip are obtained, the dynamic interaction forces between the tip and the sample in nanoscale can be determined by measuring the probe tip displacement.     

A femtogram resolution mass sensor platform based on SOI electrostatically driven resonant cantilever. Part II: sensor calibration and glycerine evaporation rate measurement

This paper presents mass measurements of glycerine beads performed by means of laterally resonant micro-cantilevers. The transducer architecture is based on a resonant cantilever electrostatically coupled by two parallel placed electrodes. Previous to glycerine measurements, a calibration of the mass sensor has been performed by measuring a standard mass based on latex spheres. From these measurements, a value of the mass responsivity is deduced. In addition, a study of the transducer phase noise has been carried out in order to determine the minimum detectable mass. Mass measurements experiments have been performed by detecting the change on the resonance frequency of the on-plane cantilever resonant mode, produced by locally deposited mass. Additionally, the mass losses detected on the calibrated transducer after glycerine drop deposition allowed determining its evaporation rate.     

微机电系统应用中的非线性力学问题分析

微机电系统（MEMS）中常作为和力有关的传感器使用的悬臂梁类型结构，在使用过程中经常会出现淖变形、大位移的情况，这时传统的线性分析方法会导致较大的系统误差。本文基于二次梁理论给出了该几何非线性问题的理论解，其正确性通过有限元的数值计算结果得到验证。这个通过非线性分析得到的理论解不但校正了线性分析方法的系统误差，提高了系统精度，而且扩大了系统的有效使用范围。     

3-D morphological characterization of the liver parenchyma by atomic force microscopy and by scanning electron microscopy

A comparative study of atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging of the healthy human liver parenchyma was carried out to determine the similarities and the differences. In this study, we compared the fine hepatic structures as observed by SEM and AFM. Although AFM revealed such typical hepatic structures as bile canaliculi and hepatocytes, it also showed the location of the nucleus and chromatin granules in rough relief structure, which was not visible by SEM. By contrast, SEM visualized other structures, such as microvilli, the central vein, and collagenous fibers, none of which was visualized by AFM. For better orientation and confirmation of most of the structures imaged by SEM and AFM, Congo Red-stained specimens were also examined. Amyloid deposits in the Disse's spaces were shown especially clearly in these images. The differences between the SEM and AFM images reflected the characteristics of the detection systems and methods used for sample preparation. Our results reveal that more detailed information on hepatic morphology is obtained by exploiting the advantages of both SEM and AFM.     

Atomic force microscopy of histological sections using a new electron beam etching method

In order to examine histological sections of the rat vomeronasal epithelium with the atomic force microscope (AFM), we developed an electron beam etching method that improves the resolution of AFM images. This method results in AFM images comparable to those obtained with the transmission electron microscope (TEM). Ultrathin tissue sections embedded in epoxy resin were observed before and after the treatment with electron beam radiation. Before electron beam treatment, epithelial structures such as the microvilli surface, dendritic processes, the supporting cell layers and the neuronal cell layers were all visible using the AFM. However, only a few subcellular structures could also be resolved. The AFM images were not as clear as those obtained with the TEM. After electron beam treatment, however, the resolution of AFM images was greatly improved. Most of the subcellular structures observed in TEM images, including the inner membrane of mitochondria, ciliary-structure precursor body, junctional complexes between the neurons and supporting cells, and individual microvilli were now visible in the AFM images. The electron beam treatment appeared to melt the embedding resin, bringing subcellular structures into high relief. The result of this study suggests that electron beam etching of histological samples may provide a new method for the study of subcellular structure using the AFM.     

A new cantilever system for gas and liquid sensing

A novel setup for gas and liquid sensing was developed and tested. It is based on both detection of frequency shift and of bending of micro-cantilevers to measure mass changes as well as viscosity changes. To drive the cantilevers new electrostatic and magnetic actuations were invented with a closed feed-back loop which forces the cantilever to oscillate always at its resonance frequency. The oscillation is detected via the beam-deflection technique. By measuring the DC signal of the photodiode the static bending of the cantilever can be monitored simultaneously. The closed feed-back loop propagates a very stable oscillation at the resonance frequency and gives a strong increase in the quality factor compared to a system without such feed-back loop. Furthermore, it is possible to operate this cantilever transducer system in liquids.These cantilever sensors hence, show the potential for use in easy-to-use and highly sensitive sensor systems for gas and liquid phase chemical and biochemical sensing.     

Atomic force microscopy of freeze-fracture replicas of rat atrial tissue

Atomic force microscopy (AFM) has provided three-dimensional (3-D) surface images of many biological specimens at molecular resolution. In the absence of spectroscopic capability for AFM, it is often difficult to distinguish individual components if the specimen contains a population of mixed structures such as in a cellular membrane. In an effort to understand the AFM images better, a correlative study between AFM and the well-established technique of transmission electron microscopy (TEM) was performed. Freeze-fractured replicas of adult rat atrial tissue were examined by both TEM and AFM. The same replicas were analysed and the same details were identified, which allowed a critical comparison of surface topography by both techniques. AFM images of large-scale subcellular structures (nuclei, mitochondria, granules) correlated well with TEM images. AFM images of smaller features and surface textures appeared somewhat different from the TEM images. This presumably reflects the difference in the surface sensitivity of AFM versus TEM, as well as the nature of images in AFM (3-D surface contour) and TEM (2-D projection). AFM images also provided new information about the replica itself. Unlike TEM, it was possible to examine both sides of the replica with AFM; the resolution on one side was significantly greater compared with the other side. It was also possible to obtain quantitative height information which is not readily available with TEM.     

Using the atomic force microscope to observe and study the ultrastructure of the living BIU-87 cells of the human bladder cancer

In this study, the ultrastructure of living BIU-87 cells of human bladder cancer was mapped using atomic force microscopy to reveal the dynamic change of single cancerous cell division. Simultaneously, the feasibility and functional reliability of the atomic force microscope (AFM) were established and a laboratory model using AFM to study living cancerous cells was created. In this experiment, BIU-87 cells of human bladder cancer were cultured by conventional methods and grown in gelatin-treated dishes. A thermostat was used for preserving the cell's living temperature. Scanning of these cells using AFM was carried out in physiologic condition. The AFM images of the ultrastructure of living BIU-87 cells as well as those of the cell's membrane and cytoskeleton were very clear. The dynamic phenomenon of single cell division was observed. It was concluded that the AFM was able to observe and depict the ultrastructure of living cells of human bladder cancer directly and in real time. This experimental model is expected to play an important role in elucidating the cancerous mechanism of bladder normal cells at the atomic or nanometer level.