Microelectromechanical Systems for Nanomechanical Testing: Electrostatic Actuation and Capacitive Sensing for High-Strain-Rate Testing

Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices....     

Nonlinear dynamic response of beam and its application in nanomechanical resonator

Nonlinear dynamic response of nanomechanical resonator is of very important characteristics in its application. Two categories of the tension-dominant and curvature-dominant nonlinearities are analyzed. The dynamic nonlinearity of four beam structures of nanomechanical resonator is quantitatively studied via a dimensional analysis approach. The dimensional analysis shows that for the nanomechanical resonator of tension-dominant nonlinearity, its dynamic nonlinearity decreases monotonically with increasing axial loading and increases monotonically with the increasing aspect ratio of length to thickness; the dynamic nonlinearity can only result in the hardening effects. However, for the nanomechanical resonator of the curvature-dominant nonlinearity, its dynamic nonlinearity is only dependent on axial loading. Compared with the tension-dominant nonlinearity, the curvature-dominant nonlinearity increases monotonically with increasing axial loading; its dynamic nonlinearity can result in both hardening and softening effects. The analysis on the dynamic nonlinearity can be very helpful to the tuning application of the nanomechanical resonator.     

Nanomechanical Unfolding of Self-Folded Graphene on Flat Substrate

Experimental Mechanics - We report the nanomechanical unfolding of individual self-folded graphene flakes on a flat substrate by using atomic force microscopy techniques. The nanomechanical...     

基因芯片纳米挠度和表面应力的解析预测

本文利用能量法解析分析了无标记生物检测中基因芯片的纳米力学行为.首先,考虑微悬臂梁机械能和基因层静电能、水合能和构型熵,建立了基因芯片能量模型,并采用泰勒级数展开法.获得了能量势的一阶近似式.其次,利用能量最小原理,得到了芯片稳态弯曲的曲率半径、纳米挠度和表面应力的解析表达式,从而克服了求解多极值能量泛函数值解的困难.最后,预测了DNA的链长和种植密度对芯片纳米力学行为的影响,同时将表面应力的解析预测结果与有关实验数据进行了比较,证明了本文方法的可靠性.     

Two-mode squeezed state of nanomechanical resonators

In this paper, we introduce a flexible model for the control and measurement of NAMRs （nanomechanical resonators）. We obtain the free Hamiltonian of the dcSQUID （direct current superconducting quantum interference device） and the interaction Hamiltonian between these two NAMRs and the dc-SQUID by introducing the annihilation and creation operators under the rotating wave approximation. We can treat the mode of the dc-SQUID as a classical field. In the Heisenberg picture, the generation of two-mode squeezed states of two nanomechanical resonators is shown by their collective coordinate and momentum operators.     

PIEZOELECTRIC PROPERTIES OF SINGLE-STRAND DNA MOLECULAR BRUSH BIOLAYERS

The paper is devoted to investigations on nanomechanical behaviors of biochips in label-free biodetections.The chip consists of Si-layer,Ti-layer,Au-layer and single-strand DNA (ssDNA)molecular brush biolayer immobilized by self-assembly technology of thiol group.Unlike previous viewpoints,such as force-bending,entropy-bending and curvature electricity effect,etc., the piezoelectric effect of the biopolymer brush layer is viewed as the main factor that induces nanomechanical bending of biochips,and a classical macroscopic piezoelectric constitutive rela- tion is used to describe the piezoelectric effect.A new laminated cantilever beam model with a piezoelectric biolayer in continuum mechanics,the linearized Poisson-Boltzmann equation in statistical mechanics and the scaling method in polyelectrolyte brush theory are combined to es- tablish a relationship between the nanomechanical deflection of DNA chips and the factors such as nanoscopic structural features of ssDNA molecules,buffer salt concentration,macroscopic me- chanical/piezoelectric parameters of DNA chips etc.Curve fitting of experimental data shows that the sign of the piezoelectric constant of the biolayer may control the deflection direction of DNA chips during the packaging process.     

Nanoscale Broadband Viscoelastic Spectroscopy of Soft Materials Using Iterative Control

A novel approach to nanoscale broadband viscoelastic spectroscopy is presented. The proposed approach utilizes the recently developed modeling-free inversion-based iterative control (MIIC) technique to achieve accurate measurement of the material response to the applied excitation force over a broad frequency band. Scanning probe microscope (SPM) and nanoindenter have become enabling tools to quantitatively measure the mechanical properties of a wide variety of materials at nanoscale. Current nanomechanical measurement, however, is limited by the slow measurement speed: the nanomechanical measurement is slow and narrow-banded and thus not capable of measuring rate-dependent phenomena of materials. As a result, large measurement (temporal) errors are generated when material is undergoing dynamic evolution during the measurement. The low-speed operation of SPM is due to the inability of current approaches to (1) rapidly excite the broadband nanomechanical behavior of materials, and (2) compensate for the convolution of the hardware adverse effects with the material response during high-speed measurements. These adverse effects include the hysteresis of the piezo actuator (used to position the probe relative to the sample); the vibrational dynamics of the piezo actuator and the cantilever along with the related mechanical mounting; and the dynamics uncertainties caused by the probe variation and the operation condition. In the proposed approach, an input force signal with frequency characteristics of band-limited white-noise is utilized to rapidly excite the nanomechanical response of materials over a broad frequency range. The MIIC technique is used to compensate for the hardware adverse effects, thereby allowing the precise application of such an excitation force and measurement of the material response (to the applied force). The proposed approach is illustrated by implementing it to measure the frequency-dependent plane-strain modulus of poly(dimethylsiloxane) (PDMS) over a broad frequency range extending over 3 orders of magnitude (~1 Hz to 4.5 kHz).     

基因芯片纳米力学行为的能量模型

本文利用能量法研究了无标记生物检测中基因芯片的纳米力学行为.首先,在考虑微悬臂梁机械能和基因层静电能、构型熵、渗透能的情况下,借助Strey通过实验得到的双链DNA(dsDNA)自由能的经验势,建立了DNA纳观几何、物理、化学特征以及芯片几何尺寸、宏观力学性能等因素与基因芯片总能量之间的关系.其次,利用能量最小原理预测了Wu实验中基因芯片的纳米挠度响应.数值计算结果与Wu的实验数据比较表明,芯片的弯曲挠度随着DNA链长的增长而增加,且数值结果与实验数据吻合良好;同时四层梁模型和两层梁模型的比较表明,金层和铬层对芯片纳米挠度的影响不可忽略.     

Fluidic applications for atomic force microscopy (AFM) with microcantilever sensors

This review presents the fundamentals of atomic force microscopy (AFM) with microcantilever probes and their use as fluidic sensors for the measurement of micro/nanoscale transport properties. Over the last two decades, AFM has been widely used for, among other purposes, nanoscale topography, nanomechanical characterization, and intermolecular force spectroscopy. Furthermore, a microcantilever, an essential part of AFM, has been modified and exploited as a mechanical transducer for various sensing applications. Among many prospective uses, there appears to be great potential for micro/nanoscale sensing of fluid density and viscosity (Sect. 3.1), temperature (Sect. 3.2), pressure (Sect. 3.3), and flow velocity (Sect. 3.4). These micro/nanomechanical measurement techniques are expected to complement the advanced optical and electrical measurement techniques currently employed for micro/nanoscale fluidic sensors and also to fill the gap between microscale and nanoscale fluidic transport property measurements.     

多模态原子力显微术研究进展

材料纳米尺度的各种性能中，纳米力学性能是纳米材料和器件服役所需要保证的最基本性能。因此，发展可靠的定量化纳米力学测试技术就显得尤为关键。原子力显微镜(Atomic Force Microscope，AFM)作为纳米力学测试的重要平台，目前广泛应用于材料纳米尺度形貌和力学性能成像。作为原子力显微术的前沿应用模式之一，多模态原子力显微术通过同时激励探针的两个或多个振动模态对样品进行测试或成像，可实现对被测样品高分辨率、高灵敏度、定量化和无损的纳米力学快速成像及检测，具有极其广泛的应用前景。围绕多模态原子力显微术，首先介绍了多模态原子力显微术的基本成像原理和力学模型基础。随后，综述了多模态原子力显微术探针动力学以及成像技术相关研究的主要进展。然后，对多模态原子力显微术的几类典型应用进行了总结和评述。最后，对多模态原子力显微术未来可能的研究方向进行了展望。     

The nanogranular nature of C-S-H

Despite its ubiquitous presence as binding phase in all cementitious materials, the mechanical behavior of calcium-silicate-hydrates (C-S-H) is still an enigma that has deceived many decoding attempts from experimental and theoretical sides. In this paper, we propose and validate a new technique and experimental protocol to rationally assess the nanomechanical behavior of C-S-H based on a statistical analysis of hundreds of nanoindentation tests. By means of this grid indentation technique we identify in situ two structurally distinct but compositionally similar C-S-H phases heretofore hypothesized to exist as low density (LD) C-S-H and high density (HD) C-S-H, or outer and inner products. The main finding of this paper is that both phases exhibit a unique nanogranular behavior which is driven by particle-to-particle contact forces rather than by mineral properties. We argue that this nanomechanical blueprint of material invariant behavior of C-S-H is a consequence of the hydration reactions during which precipitating C-S-H nanoparticles percolate generating contact surfaces. As hydration proceeds, these nanoparticles pack closer to center on-average around two characteristic limit packing densities, the random packing limit (η=64%) and the ordered face-centered cubic (fcc) or hexagonal close-packed (hcp) packing limit (η=74%), forming a characteristic LD C-S-H and HD C-S-H phase.     

Investigation on a nanomechanical transistor

In this paper, we propose the mathematical model of a novel device, the nanomechanical transistor, able to control a current through a small drive voltage. The novelty of the device relies in its mechanical working principle where nanopillars vibrate between electrodes under a self-excitation regime which provides a continuative electric charge transportation. The dynamics of the investigated system involves electromechanical phenomena with the addition of quantum effects due to the electron tunneling of charges from pillars to electrodes. The theory here presented is an attempt to build a general model for those multiphysics phenomena (electrical-mechanical with presence of quantum effects) frequently met in nanotechnology that do not fit yet into a systematic frame.     

Nonlinear hardening and softening resonances in micromechanical cantilever-nanotube systems originated from nanoscale geometric nonlinearities

Micro/nanomechanical resonators often exhibit nonlinear behaviors due to their small size and their ease to realize relatively large amplitude oscillation. In this work, we design a nonlinear micromechanical cantilever system with intentionally integrated geometric nonlinearity realized through a nanotube coupling. Multiple scales analysis was applied to study the nonlinear dynamics which was compared favorably with experimental results. The geometrically positioned nanotube introduced nonlinearity efficiently into the otherwise linear micromechanical cantilever oscillator, evident from the acquired responses showing the representative hysteresis loop of a nonlinear dynamic system. It was further shown that a small change in the geometry parameters of the system produced a complete transition of the nonlinear behavior from hardening to softening resonance.     

Numerical model for composite material with polymer matrix reinforced by carbon nanotubes

Due to the high stiffness and strength, as well as their ability to act as conductors, carbon nanotubes are under intense investigation as fillers in polymeric materials. The nature of the carbon nanotube/polymer bonding and the curvature of the carbon nanotubes within the polymer have arisen as particular factors in the efficacy of the carbon nanotubes to actually provide any enhanced stiffness or strength to the nanocomposite. Here the effects of carbon nanotube curvature and interface interaction with the matrix on the nanocomposite stiffness are investigated using nanomechanical analysis. In particular, the effects of poor bonding and thus poor shear lag load transfer to the carbon nanotubes are studied. In the case of poor bonding, carbon nanotubes waviness is shown to enhance the composite stiffness.     

Nanoindentation of Calcified and Non-calcified Components of Atherosclerotic Tissues

Background

Biomechanical models predicting plaque rupture and device-tissue interactions rely on accurate material properties to produce reliable simulation results. However, there is a wide variation in the reported stiffness properties for advanced atherosclerotic lesions.

Objective

The purpose of this study was to characterise isolated calcified and non-calcified portions of ex vivo carotid atherosclerotic tissues using nanomechanical techniques and compare the results against those from previous studies.

Methods

Eleven carotid plaque samples were acquired from patients undergoing endarterectomy. Calcification was characterised using traditional instrumented indentation (TII) (n?=?06). Micro-Computed Tomography was used to identify areas of calcification. Ferrule-top cantilever nanoindentation (FTC) was conducted on non-calcified tissue regions (n?=?05). Adjacent tissue slices were stained with Alizarin Red to select regions of non-calcified tissue for testing. Scanning electron microscopy was employed to qualitatively assess the calcified and non-calcified samples’ surface roughness.

Results

The results from this study demonstrate over 6 orders of magnitude difference in stiffness between the elastic moduli of calcified (22.40 [17.70–27.55] GPa) and non-calcified (8.16 [3.85–14.78] kPa) carotid atherosclerotic tissues. Microscopy analysis indicates a larger variation in surface roughness produced with non-calcified tissue cryosectioning than with calcified tissue metallographic preparation, which may account for the increased amount of indent failures with FTC (32%) than with TII (11%).

Conclusions

Performing high-resolution imaging and nanomechanical approaches in parallel produce results that clarify the wide range in reported properties for advanced atherosclerotic lesions. Future studies should examine the viscoelastic nature of diseased human arterial tissues.

     

Coarse-grained potentials of single-walled carbon nanotubes

We develop the coarse-grained (CG) potentials of single-walled carbon nanotubes (SWCNTs) in CNT bundles and buckypaper for the study of the static and dynamic behaviors. The explicit expressions of the CG stretching, bending and torsion potentials for the nanotubes are obtained by the stick-spiral and the beam models, respectively. The non-bonded CG potentials between two different CG beads are derived from analytical results based on the cohesive energy between two parallel and crossing SWCNTs from the van der Waals interactions. We show that the CG model is applicable to large deformations of complex CNT systems by combining the bonded potentials with non-bonded potentials. Checking against full atom molecular dynamics calculations and our analytical results shows that the present CG potentials have high accuracy. The established CG potentials are used to study the mechanical properties of the CNT bundles and buckypaper efficiently at minor computational cost, which shows great potential for the design of micro- and nanomechanical devices and systems.     

Nanomechanical Property and Nanowear Measurements for Sub-10-nm Thick Films in Magnetic Storage

In the magnetic storage industry, thin film carbon overcoats play a critical role in reducing magnetic and physical spacing between the recording slider and the rotating disk so that the information stored per unit area is maximized. Thin film carbon overcoats have been improved such that they exhibit higher hardness with lower thickness of few nanometers and still being able to perform reliably. In this paper, nanoindentation and nanoscratch techniques to measure nanomechanical properties, namely hardness, elastic modulus and shear strength of thin solid films were presented along with a recently developed high resolution force transducer. Nanowear behavior characterization techniques were also examined and were applied to commercially available magnetic disks to characterize their wear behavior. It was shown that the properties and wear behavior of sub-10-nm thick film carbon overcoats were reliably measured. These techniques could be applied to different thin solid films on substrates, and they are not restricted to magnetic storage systems.     

Closed-form solutions of the pull-in instability in nano-cantilevers under electrostatic and intermolecular surface forces

In this paper, a distributed parameter model is used to study the pull-in instability of cantilever type nanomechanical switches subjected to intermolecular and electrostatic forces. In modeling of the electrostatic force, the fringing field effect is taken into account. The model is nonlinear due to the inherent nonlinearity of the intermolecular and electrostatic forces. The nonlinear differential equation of the model is transformed into the integral form by using the Green’s function of the cantilever beam. Closed-form solutions are obtained by assuming an appropriate shape function for the beam deflection to evaluate the integrals. The pull-in parameters of the switch are computed under the combined effects of electrostatic and intermolecular forces. Electrostatic microactuators and freestanding nanoactuators are considered as special cases of our study. The detachment length and the minimum initial gap of freestanding nano-cantilevers, which are the basic design parameters for NEMS switches, are determined. The results of the distributed parameter model are compared with the lumped parameter model.     

Nonlocal Galerkin Strip Transfer Function Method for Vibration of Double-Layered Graphene Mass Sensor

Double-layered graphene sheets(DLGSs) can be applied to the development of a new generation of nanomechanical sensors due to their unique physical properties. A rectangular DLGS with a nanoparticle randomly located in the upper sheet is modeled as two nonlocal Kirchhoff plates connected by van der Waals forces. The Galerkin strip transfer function method which is a semi-analytical method is developed to compute the natural frequencies of the massplate vibrating system. It can give exact closed-form solutions along the longitudinal direction of the strip. The results obtained from the semi-analytical method are compared with the previous ones, and the differences between the single-layered graphene sheet(SLGS) and the DLGS mass sensors are also investigated. The results demonstrate the similarity of the in-phase mode between the SLGS and DLGS mass sensors. The sensitivity of the DLGS mass sensor can be increased by decreasing the nonlocal parameter, moving the attached nanoparticle closer to the DLGS center and making the DLGS smaller. These conclusions are helpful for the design and application of graphene-sheet-based resonators as nano-mass sensors.