具有超媒体人机接口的纳米操作系统

当利用AFM作为纳米操作工具时,由于其缺乏实时的传感器信息反馈,操作完全在盲目的状态下进行,而使纳米操作难于进行.超媒体接口可以解决这个问题,在纳米操作过程中,超媒体接口不但可以为操作者提供实时动态更新的视觉反馈,还可以为操作者提供实时的三维力反馈,与此同时操作者还可以通过该接口直接控制探针的三维运动,实现人机交互式的纳米操作.纳米刻画以及多壁碳纳米管的推动实验验证了系统的效率和有效性.     

具有超媒体人机接口的纳米操作系统

当利用AFM作为纳米操作工具时,由于其缺乏实时的传感器信息反馈,操作完全在盲目的状态下进行,而使纳米操作难于进行.超媒体接口可以解决这个问题,在纳米操作过程中,超媒体接口不但可以为操作者提供实时动态更新的视觉反馈,还可以为操作者提供实时的三维力反馈,与此同时操作者还可以通过该接口直接控制探针的三维运动,实现人机交互式的纳米操作.纳米刻画以及多壁碳纳米管的推动实验验证了系统的效率和有效性.     

机器人化纳米操作系统驱动器驱动与探针定位研究

对基于AFM的机器人化纳米操作系统而言，一个关键问题是如何实现纳米操作时探针的高精度驱动与定位。对此，本文基于对压电陶瓷驱动器的迟滞／非线性特性及现有驱动方法的详细分析，提出“基于复现扫描轨迹的驱动方法”来对操作时的驱动器进行驱动；另外，还对管式驱动器弯曲运动所产生的运动学耦合误差、探针悬臂变形所引起的针尖偏移误差进行了定量分析与补偿。采用上述驱动方法及进行误差补偿后，可以大大提高探针的定位精度，从而使纳米操作与装配得以高精度进行。纳米刻画实验验证了该新型驱动方法及误差补偿的有效性。     

基于探针定位的原子力显微镜纳米操作虚拟夹具实现

尽管基于原子力显微镜(Atom force microscopy,AFM)的纳米操作在过去10年间取得了极大进展,但依然有两个问题没有得到很好解决:探针的精确定位和稳定性操作。由于压电陶瓷驱动器非线性和温漂的影响,使得探针相对于被操作物体的定位极其困难,从而造成纳米操作任务失败;同时,因为探针仅能对被操作物体施加点式作用力,在操作中经常出现探针滑过被操作物体,或者引起被操作物体的转动、形变等非理想结果,阻碍纳米操作的深入发展。针对上述问题,提出基于概率的虚拟夹具纳米操作方法,其核心思想是在基于路标观测的探针定位基础上,实现基于概率的探针多点并发操作策略—虚拟夹具方法。仿真与试验结果验证该方法可以稳定、长距离的推动纳米颗粒,能够对一维纳米材料(管、线、棒)进行定姿态操作,从而使AFM纳米操作效率得到极大提升。     

基于AFM的虚拟纳米手操作策略研究

针对纳米操作过程中存在的不确定性及AFM单探针带来的纳米粒子的稳定操作问题,提出了虚拟纳米手操作策略.该策略采用蒙特卡洛方法描述粒子的不确定性,在纳米粒子推动操作的运动学模型基础上,对AFM探针的作用参数进行规划,模拟多探针并行操作效果,将粒子的中心位置限制在规定误差范围内,从而可以避免操作过程中粒子的丢失,实现粒子的稳定高精度纳米操作,仿真结果与实验操作结果相对比,验证了虚拟纳米手操作方法的有效性.     

基于AFM推动的纳米粒子运动学模型研究

针对纳米操作和装配过程中面临的由AFM单探针带来的物体丢失和操作效率低等问题,通过对纳米粒子推动实验的分析,建立了纳米粒子推动操作的运动学模型.该模型充分考虑了推动速度及探针磨损两个因素,引入了与速度相关的粘滞摩擦力,并利用空间配置的方法解决了探针针尖半径对操作结果的影响.该模型能够预测推动操作后粒子的可能位置,从而可以避免操作过程中粒子丢失的现象,能够提高纳米操作效率.数值模拟结果与多次实验操作结果相对比,验证了所建模型的有效性.     

某微波混频器振动故障的力学仿真及分析

混频器是微波系统中的一个重要器件。某混频器在振动试验中损坏,需要对其进行分析,找出损坏机理并提出改进方法。因混频器尺寸过小无法进行试验,所以需要通过力学仿真方法来分析故障原因。相对于一般结构,该混频器力学仿真的关键在于内部微小元件的等效建模。通过分析可知,损坏的原因是内部磁环无固定措施,在振动过程中位移过大,造成连接导线受力过大,从而导致导线损坏。此结论不仅可以指导混频器的后续改进,还提供了此类微波器件振动条件下的变形特点和敏感频率范围,可作为解决类似问题的参考。     

接触测量中的微探球力变形研究

随着微纳米测量系统中测头微探球尺寸的不断减小和测量不确定度要求的不断提高,测力所引起的力变形误差对测量系统不确定度有着不可忽略的影响。根据Hertz理论,构建了微探球与工件接触时的接触模型、微探球与试样力变形模型,给出了最大允许测力估计方法和力变形计算方法。以现有的3种微纳米三坐标测量机微探球为参考,分别估计了允许最大测力及引起的力变形。结果表明,对于纳米量级测量不确定要求,接触式测量中微探球的受力变形误差是不可忽略的。     

剪料模具的改进

原采用的剪料模具在剪料时所产生的轴向力均作用在压力机的导轨及滑块上,致使导轨及滑块因呈悬臂状态而产生倾斜,这样不仅容易损坏导轨及滑块,且料段剪断面不平整.现采用导轨模座(如图1所示)后,不仅防止了因轴向力引起的导轨及滑块的倾斜,且保证了料段剪断面的平整,下料重量误差可控制在1.5%以内.     

内高压成形机可变合模力系统研究

主要研究如何实现根据内高压成形过程的内压变化施加相应的合模力,使总合模力中平衡内压反力的部分随内压的增大而增加的系统组成,避免模具在内压较低时受到过大的合模力作用造成变形和损坏。     

Sensitivity analysis of nanoparticles pushing critical conditions in 2-D controlled nanomanipulation based on AFM

This paper investigates the sensitivity of critical parameters in AFM-based nanomanipulation, including the nanoparticle pushing force and time versus changing all parameters of the nanomanipulation process. The presented model includes both adhesional and normal friction forces. Also, pull-off forces are modeled by using the Johnson–Kendall–Roberts (JKR) contact mechanics model. Dynamic equations are developed based on the free body diagram of the pushing system, including AFM cantilever and probe, nanoparticle, and substrate. Dynamic simulation of gold particle manipulation on a silicon substrate is performed. In this model, the nanoparticle can be traced at every moment and at the same time all the dynamics and deformations of nanoparticle can be achieved from numerical simulation. Depending on obtained diagrams for parameters sensitivity, the suggested behavior will be followed by the particle such as rolling, sliding, stick-slip, and rotation. Its novelty is that the sensitivity of critical force and critical time for particle pushing on the substrate are obtained for all parameters. This is important for designing and choosing of geometry and materials of AFM, nanoparticle, and substrate. Also this is effective on choosing of proper initial condition in pushing purposes. Finally, it can be used to adjust proper pushing time and force for an accurate and successful pushing and assembly, and real-time visualization during micro/nanomanipulation using real-time force data.     

The effect of off-end tip distance on the nanomanipulation based on rectangular and V-shape cantilevered AFMs

The AFM system, which is used as a nanomanipulator, includes a probe consistent of a cantilever and a tapered tip. In cantilevers, the tip can be located in different distances from the cantilever free end. This causes to change in stiffness of the cantilever and therefore changing in pushing force of the nanomanipulation. In this paper, the effect of the tip distance on the cantilever stiffness is studied using the equations of Hazel, and Neumeister and Ducker (ND), and a new equation to correct the torsional stiffness of V-shaped cantilevers (VSC) is proposed, which is based on the ND equation. Then, the effect of distance on pushing force of AFM-based nanomanipulations with rectangular cantilevered (RC) and VSC AFMs is simulated. The obtained results using proposed equation show that increasing of distance causes to non-linear increment of torsional stiffness of VSC. Error of the proposed equation is achieved less than 3% in comparison with result of torsional stiffness equation of ND. Moreover, it is observed that the torsional stiffness of VSC predicted by Hazel’s equation is considerably inaccurate. In nanomanipulation studies, the necessary pushing forces of nanoparticle motion are increased by increment of distance, for both types of cantilevers (RC and VSC). Moreover, critical time for RC AFM increases, but in the case of VSC AFM, the critical time decreases at first, then it is almost constant at a limited range of d, and finally it starts to increase by increasing the distance.     

Implementation of a piezoresistive MEMS cantilever for nanoscale force measurement in micro/nano robotic applications

The nanoscale sensing and manipulation have become a challenging issue in micro/nanorobotic applications. In particular, a feedback sensor-based manipulation is necessary for realizing an efficient and reliable handling of particles under uncertain environment in a micro/ nano scale. This paper presents a piezoresistive MEMS cantilever for nanoscale force measurement in microrobotics. A piezoresistive MEMS cantilever enables sensing of gripping and contact forces in nanonewton resolution by measuring changes in the stress-induced electrical resistances. The calibration of a piezoresistive MEMS cantilever is experimentally carried out. In addition, as part of the work on nanomanipulation with a piezoresistive MEMS cantilever, the analysis on the interaction forces between a tip and a material, and the associated manipulation strategies are investigated. Experiments and simulations show that a piezoresistive MEMS cantilever integrated into a microrobotic system can be effectively used in nanoscale force measurements and a sensor-based manipulation.     

High-resolution constant-height imaging with apertured silicon cantilever probes

We present high-resolution aperture probes based on non-contact silicon atomic force microscopy (AFM) cantilevers for simultaneous AFM and near-infrared scanning near-field optical microscopy (SNOM). For use in near-field optical microscopy, conventional AFM cantilevers are modified by covering their tip side with an opaque aluminium layer. To fabricate an aperture, this metal layer is opened at the end of the polyhedral probe using focused ion beams (FIB). Here we show that apertures of less than 50 nm can be obtained using this technique, which actually yield a resolution of about 50 nm, corresponding to λ/20 at the wavelength used. To exclude artefacts induced by distance control, we work in constant-height mode. Our attention is particularly focused on the distance dependence of resolution and to the influence of slight cantilever bending on the optical images when scanning at such low scan heights, where first small attractive forces exerted on the cantilever become detectable.     

Influence of Poisson's ratio variation on lateral spring constant of atomic force microscopy cantilevers

Atomic force microscopy (AFM) can be used to measure the surface morphologies and the mechanical properties of nanostructures. The force acting on the AFM cantilever can be obtained by multiplying the spring constant of AFM cantilever and the corresponding deformation. To improve the accuracy of force experiments, the spring constant of AFM cantilever must be calibrated carefully. Many methods, such as theoretical equations, the finite element method, and the use of reference cantilever, were reported to obtain the spring constant of AFM cantilevers. For the cantilever made of single crystal, the Poisson's ratio varies with different cantilever-crystal angles. In this paper, the influences of Poisson's ratio variation on the lateral spring constant and axial spring constant of rectangular and V-shaped AFM cantilevers, with different tilt angles and normal forces, were investigated by the finite element analysis. When the cantilever's tilt angle is 20 degrees and the Poisson's ratio varies from 0.02 to 0.4, the finite element results show that the lateral spring constants decrease 11.75% for the rectangular cantilever with 1muN landing force and decrease 18.60% for the V-shaped cantilever with 50nN landing force, respectively. The influence of Poisson's ratio variation on axial spring constant is less than 3% for both rectangular and V-shaped cantilevers. As the tilt angle increases, the axial spring constants for rectangular and V-shaped cantilevers decrease substantially. The results obtained can be used to improve the accuracy of the lateral force measurement when using atomic force microscopy.     

Facilitating the pickup of individual DNA molecules by AFM nanomanipulation with tips mechanically worn on bare mica

The tip is one of the critical factors to improve the efficiency in picking up individual DNA molecules from solid substrates based on atomic force microscope (AFM) nanomanipulation. We found that wearing AFM tips on certain solid substrates in advance to nanomanipulation operation would largely improve the pickup efficiency, which was ascribed to the increasing affinity of the tip to the DNA molecules along with the increase of the tip radius after wearing. It was demonstrated that bare mica was superior to APTES-modified mica to keep the tip clean while wearing, which was crucial for DNA pickup during AFM nanomanipulation.     

Fabrication of various tip-size AFM probes for evaluating single-molecular retraction force between actin and anti-actin

The authors fabricated a probe tip with various sizes and examined the size dependency of the probe tip on the distribution of retraction forces between actin and anti-actin. Probe tips of various sizes were fabricated by two-photon polymerization methods on a micro cantilever of an atomic force microscope (AFM). The authors succeeded in fabricating a spherical tip having a smooth surface and the tip size varied between φ 0.8 and 5.5 μm. Anti-actin was immobilized on the fabricated probe tips and force curves were measured against an actin-immobilized mica substrate by AFM to analyze the retraction forces. The histograms of retraction forces showed that the single-molecular retraction force between actin and anti-actin was ca. 350–400 pN. It was observed that the average retraction forces for each tip size correlated with the square of the tip radius.     

Hydrodynamic damping of a magnetically oscillated cantilever close to a surface

We studied the frequency response of a magnetically driven atomic force microscope (AFM) cantilever close to a sample surface in liquids. Amplitude–frequency (tuning) curves showed pronounced differences in dependence on the tip–sample separation (from 1 to 50 μm), with significant shifts of the resonance peak. A model was developed in which the cantilever was described in a full shape manner and the hydrodynamic forces acting on the cantilever were approximately calculated. The slight inclination of the cantilever to the surface (15°) leads to a force profile along the cantilever. Therefore, the mathematical problem can be strictly solved only numerically. For an approximate analytical solution, the hydrodynamic force profile was approximated by a constant force along the cantilever for large separations and by a point force acting on the tip of the cantilever for small separations. The theoretical results calculated within this model agreed well with the experimental data and allowed to determine the cantilever mass in liquid M^*, the joint mass at the tip end m_t^*, and the coefficient of viscous interaction of the cantilever with free liquid, γ_∞.     

Molecular dynamics simulation of the contact process in AFM surface observations

In the present work, several molecular dynamics simulations have been performed to clarify dynamically the contact mechanism between the specimen surface and probe tip in surface observations by an atomic force microscope (SFM) or friction force microscope (FFM). In the simulation, a three‐dimensional model is proposed where the specimen and the probe are assumed to consist of monocrystalline copper and rigid diamond or a carbon atom, respectively. The effect of the cantilever stiffness of the AFM/FFM is also taken into consideration. The surface observation process is simulated on a well‐defined Cu{100} surface. From the simulation results it has been verified that the surface images and the two‐dimensional atomic‐scale stick‐slip phenomenon, just as is the case for real AFM/FFM surface observations, can be detected from the spring force acting on the cantilever. From the evaluation of the behaviour of specimen surface atoms, the importance of the specimen stiffness in deciding the cantilever properties can also be understood. The influence of the probe tip shape on the force images is also evaluated. From the results it can be verified that the behaviour of the specimen surface atoms as well as the solid surface images in AFM/FFM surface observations can be understood using the molecular dynamics simulation of the model presented.     

Prototype cantilevers for quantitative lateral force microscopy

Prototype cantilevers are presented that enable quantitative surface force measurements using contact-mode atomic force microscopy (AFM). The "hammerhead" cantilevers facilitate precise optical lever system calibrations for cantilever flexure and torsion, enabling quantifiable adhesion measurements and friction measurements by lateral force microscopy (LFM). Critically, a single hammerhead cantilever of known flexural stiffness and probe length dimension can be used to perform both a system calibration as well as surface force measurements in situ, which greatly increases force measurement precision and accuracy. During LFM calibration mode, a hammerhead cantilever allows an optical lever "torque sensitivity" to be generated for the quantification of LFM friction forces. Precise calibrations were performed on two different AFM instruments, in which torque sensitivity values were specified with sub-percent relative uncertainty. To examine the potential for accurate lateral force measurements using the prototype cantilevers, finite element analysis predicted measurement errors of a few percent or less, which could be reduced via refinement of calibration methodology or cantilever design. The cantilevers are compatible with commercial AFM instrumentation and can be used for other AFM techniques such as contact imaging and dynamic mode measurements.