Cantilever Deflection Research Articles

Terahertz Photoacoustic Spectroscopy Using an MEMS Cantilever Sensor

In this paper, a microelectromechanical systems cantilever sensor was designed, modeled, and fabricated to measure the photoacoustic (PA) response of gases under very low vacuum conditions. The micromachined devices were fabricated using silicon-on-insulator wafers and then tested in a custom-built, miniature, vacuum chamber during this first-ever demonstration. Terahertz radiation was amplitude modulated to excite the gas under test and perform PA molecular spectroscopy. Experimental data show a predominantly linear response that directly correlates measured cantilever deflection to PA signals. Excellent low pressure (i.e., 2-40 mTorr) methyl cyanide PA spectral data were collected resulting in a system sensitivity of 1.97 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and a normalized noise equivalent absorption coefficient of 1.39 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> W Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1/2</sup> .

Comparative study on friction force pattern anisotropy of graphite

In this paper, the experimental and theoretical studies on the atomic-scale two-dimensional friction force pattern are presented. Atomic-scale friction experiments were conducted on graphite surfaces with the atomic force microscopy (AFM) under ambient conditions. Owing to the dimensionality reduction effect of optical method detecting the probe cantilever deflection, the friction force patterns were revealed in these experiments. The friction phenomenon was analyzed theoretically in the framework of Prandtl–Tomlinson model in two dimensions. The dimensionality reduction effect was formulated and involved in the model. The comparison shows the good quantitative agreement between experimental and simulation results, suggesting that the friction force pattern can be interpreted reliably using the model. Meanwhile atomic arrangement was obtained in friction force pattern, the origin and variation of which were also analyzed. The condition for appearance of atomic arrangement was determined qualitatively. By means of band-pass filtering, hexagonal rings or crystal lattices images of graphite were obtained.

G0200201 静電容量を利用した生体組織の3次元形状および局所力学特性検出法

In this study, an experimental system is developed to detect three-dimensional shape and local mechanical properties. The three-dimensional shape is detected by a contact sensor and sequentially controlled three stepping motors for x, y and z axis displacement. A motor-controller circuit for the stepping motor is newly designed and controlled by a microcontroller device. From coordinate data of contact points between the sensor tip and a sample, the three-dimensional shape is reconstructed with a computer. From results of some experiments, it is confirmed that the system passably detects cartilage tissue's three-dimensional shape. On the other hand, the system has another sensor to evaluate mechanical properties based on the principle of electrostatic capacitance. Mechanical properties are estimate by amount of cantilever's deflection, and the amount of deflection was measured by the capacitance meter. The experimental result shows that the developed system can detect difference in mechanical properties between fatty white part and red lean part on a sliced meat.

Giant magnetic moment at open ends of multiwalled carbon nanotubes**Project supported by the National Natural Science Foundation of China (Grant Nos. 10774032 and 51472057) and the Instrument Developing Project of the Chinese Academy of Sciences (Grant No. Y2010031).

The attractions of cantilevers made of multiwalled carbon nanotubes (MWNTs) and secured on one end are studied in the non-uniform magnetic field of a permanent magnet. Under an optical microscope, the positions and the corresponding deflections of the original cantilevers (with iron catalytic nanoparticles at the free end) and corresponding cut-off cantilevers (the free ends consisting of open ends of MWNTs) are studied. Both kinds of CNT cantilevers are found to be attracted by the magnet, and the point of application of force is proven to be at the tip of the cantilever. By measuring and comparing deflections between these two kinds of cantilevers, the magnetic moment at the open ends of the CNTs can be quantified. Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes, it is called giant magnetic moment, and its possible mechanisms are proposed and discussed.

The mechanical characterization of stacked, multilayer graphene cantilevers and plates

ABSTRACTThe mechanical properties of stacked graphene sheets with varying number of layers are examined. The stacked sheets are assembled by manually combining single layer CVD-grown graphene monolayers, resulting in a turbostratic multilayer graphene with irregular layer spacings greater than crystalline graphite. Due to the presence of multiple layers, the material is analyzed as a plate rather than a membrane. Bending stiffness is determined via the deflection of micron-scale cantilevers, prepared using focused ion beam milling, while in-plane tensile stiffness is characterized through center-loading of edge-supported circular specimens. Computational modeling and established analytical solutions are used to extract material and structural property information, and benchmark measured properties relative to complementary results from indentation tests. Stacked, few-layer CVD-grown graphene retains an in-plane elastic modulus of 350N/m/layer (corresponding to 1.04 TPa for an inter-layer spacing of 0.335nm), suggesting good load-sharing between stacked layers. Width-normalized bending stiffness was unmeasurable for cantilevers of 1 and 3 layers, while cantilevers of 5 and 10 layers had values of 11,100nN·nm and 1.3×106nN·nm respectively.

Fibrinogenesis and Fibrinolysis Followed with Nano-Thrombelastography

Hemostasis is a complex process that relies on a sensitive balance between the formation and breakdown of the thrombus, a three-dimensional polymer network of the fibrous protein fibrin. Neither the details of the fibrinogen-fibrin transition, nor the exact mechanisms of thrombus degradation are fully understood at the molecular or supramolecular level. We investigated nanoscale changes in the viscoelasticity of the 3D-fibrin network during fibrinogenesis and streptokinase (STK)-induced fibrinolysis by using a novel, atomic-force-microscope (AFM)-based application of force spectroscopy, named nano-thrombelastography.Clot formation was initiated by adding Ca2+ to fresh, anti-coagulated mixed human plasma droplet on a glass surface. In order to induce fibrinolysis, STK, at a final enzyme activity of up to 10,000 IU was applied in situ. For measuring the nanoscale elastic and viscous properties of the fibrin network, the tip of an AFM cantilever was immersed in the plasma droplet and oscillated vertically with a constant rate. The cantilever bending was correlated with fibrin-clot elasticity and viscosity in time. Morphological changes were followed by scanning AFM on polymerized fibrin deposited on mica surface.Whereas the global features of the time-dependent change in cantilever deflection corresponded well to a macroscopic thrombelastogram, the underlying force spectra revealed large, sample-dependent oscillations in the range of 3-50 nN and allowed the separation of elastic and viscous components of fibrin behavior. Upon STK treatment the nano-thrombelastogram signal decayed gradually. The decay was driven by a decrease in thrombus elasticity, whereas thrombus viscosity decayed with a time delay. In scanning AFM images mature fibrin appeared as 17-nm-high and 12-196-nm-wide filaments. STK-treatment resulted in the decrease of filament height and the appearance of a surface roughness with 23.7 nm discrete steps that corresponds well to the length of a fibrinogen monomer.

Surface Potential Investigation of Fullerene Derivative Film on Platinum Electrode under UV Irradiation by Kelvin Probe Force Microscopy Using a Piezoelectric Cantilever

Dynamic-mode atomic force microscopy (DFM) combined with Kelvin probe force microscopy (KFM) has been a powerful tool not only for imaging surface topography but also for investigating surface potential on a nanometer-scale resolution. We have developed DFM/KFM using a microfabricated cantilever with a lead zirconate titanate (PZT) piezoelectric thin film used as a deflection sensor. The observed sample can be in a completely dark environment because no optics are required for cantilever deflection sensing in our experimental setup, which is also equipped with a mechanism to irradiate ultraviolet (UV) light onto the sample. We prepared a platinum-on-silicon substrate and deposited fullerene-derivative (PCBM; [6,6]-Phenyl-C61-Butyric Acid Methyl Ester) film patterns by vacuum evaporation with two shadow masks in crossed directions. The energy band diagram with band-bending, it was created by simultaneously obtaining topographic and surface potential images of the same area using the developed DFM/KFM. [DOI: 10.1380/ejssnt.2015.102]

High-frequency multimodal atomic force microscopy.

Multifrequency atomic force microscopy imaging has been recently demonstrated as a powerful technique for quickly obtaining information about the mechanical properties of a sample. Combining this development with recent gains in imaging speed through small cantilevers holds the promise of a convenient, high-speed method for obtaining nanoscale topography as well as mechanical properties. Nevertheless, instrument bandwidth limitations on cantilever excitation and readout have restricted the ability of multifrequency techniques to fully benefit from small cantilevers. We present an approach for cantilever excitation and deflection readout with a bandwidth of 20 MHz, enabling multifrequency techniques extended beyond 2 MHz for obtaining materials contrast in liquid and air, as well as soft imaging of delicate biological samples.

Transverse piezoelectric properties of {100} – Oriented PLZT[x/65/35] thin films

Preferentially {100}-oriented thin films of lead lanthanum zirconate titanate, (Pb1−xLax) (Zr0.65Ti0.35)1−x/4O3[PLZT(x/65/35)] with compositions near the morphotropic phase boundary (MPB) were prepared on silicon substrates (111)Pt/Ti/SiO2/Si by sol–gel spin coating technique. The structural, micro structural and electrical characteristics have been studied as a function of thin film composition. Crystalline orientation and microstructure of the thin films have been determined by X-ray diffraction, Scanning electron microscopy, respectively. The transverse piezoelectric coefficient, e31∗ of the PLZT thin films have been evaluated by tip deflection of unimorph cantilevers. The influence of thin film composition on e31∗ have been determined. PLZT (7/65/35) thin film exhibited the optimum dielectric and piezoelectric characteristics with a dielectric permittivity, εr = 917; dielectric loss, tan δ = 0.03 and average e31∗ = −4.2 C/m2.

Erratum to: Fe73.5Cu1Nb3 Si 15.5B7 Thin Films Deposited by HiPIMS: Magnetic and Magnetostrictive Behavior

Results concerning the magnetic, magnetostrictive, structural, morphological, and topological properties of amorphous and nanocrystalline Fe 73.5Cu 1Nb 3Si 15.5 B 7 thin films deposited using the high power impulse magnetron sputtering (HiPIMS) technique are reported. In as-deposited state, the samples are amorphous, the nanocrystalline state being achieved for samples isothermally annealed at adequate temperatures, in an electric furnace. For the optimum annealing temperature (475 ∘C), a decrease by about 70 % for the coercive magnetic field (50 A/m) and up to 1 order of magnitude for the saturation magnetostriction (~1×10−6), compared to the as-deposited state, was obtained. The X-ray diffractometry (XRD) and scanning electron microscopy (SEM) results for samples thermally treated at 475 ∘C revealed a 53.6 % crystalline volume fraction of α-Fe(Si) nanograins with an average size of about 15 nm and a Si content of 10.78 %, uniformly dispersed in a residual amorphous matrix. Using the saturation magnetostriction values determined using the cantilever deflection method and the crystalline volume fraction of α-Fe(Si) nanograins, the contribution of crystalline phase to the saturation magnetostriction was also determined.

Effect of p-type and n-type piezoresistors on characteristics of high sensitive silicon piezoresistive microcantilever designs

This study presents four new silicon piezoresistive microcantilevers designs for biosensor application and compares their surface stress sensitivities for p-type and n-type piezoresistors. One basic and three variant designs with the piezoresistor inscribing the rectangular holes are proposed. The piezoresistors are placed in the high stress concentration regions near the cantilever base for achieving maximum sensitivity. Mathematical models for cantilever deflection and piezoresistor stress are derived and verified using finite element software. The designs are studied for operating conditions involving surface stress, ambient temperature and operating voltages. Results show that the average longitudinal stress in the piezoresistor of variant models is more than three times the average transverse ones, and that p-type cantilevers are better than n-type in piezoresistive microcantilever biosensor application.

Photopiezoelectric Composites of Azobenzene‐Functionalized Polyimides and Polyvinylidene Fluoride

Light is a readily available and sustainable energy source. Transduction of light into mechanical work or electricity in functional materials, composites, or systems has other potential advantages derived from the ability to remotely, spatially, and temporally control triggering by light. Toward this end, this work examines photoinduced piezoelectric (photopiezoelectric) effects in laminate composites prepared from photoresponsive polymeric materials and the piezoelectric polymer polyvinylidene fluoride (PVDF). In the geometry studied here, photopiezoelectric conversion is shown to strongly depend on the photomechanical properties inherent to the azobenzene-functionalized polyimides. Based on prior examinations of photomechanical effects in azobenzene-functionalized polyimides, this investigation focuses on amorphous materials and systematically varies the concentration of azobenzene in the copolymers. The baseline photomechanical response of the set of polyimides is characterized in cantilever deflection experiments. To improve the photomechanical response of the materials and enhance the electrical conversion, the polyimides are drawn to increase the magnitude of the deflection as well as photogenerated stress. In laminate composites, the photomechanical response of the materials in sequenced light exposure is shown to transduce light energy into electrical energy. The frequency of the photopiezoelectric response of the composite can match the frequency of the sequenced light exposing the films.

The effect of electrodeposition process parameters on residual stress-induced self-assembly under external load

The authors (Boyd et al 2007 J. Micromech. Microeng. 17 452–61http://iopscience.iop.org/0960-1317/17/3/006/) presented a methodology for using residual stresses due to mismatch strains as a means of self-assembling microstructures under external loading during material deposition. Assembly of two components was considered: one component was subjected to deposition and was modeled as an Euler–Bernoulli beam, and the other component was not deposited and was modeled as a linear spring. This work experimentally extends Boyd et al (2007 J. Micromech. Microeng. 17 452–61http://iopscience.iop.org/0960-1317/17/3/006/) to account for the effects of process conditions, specifically the electrodeposition current density and temperature, which affect both the Young’s modulus and the mismatch strain. First, nickel was electrodeposited onto an atomic force microscope (AFM) cantilever, and the cantilever deflections at various current densities and temperatures were measured by using the resonance method of AFM and the measured deformation of the cantilever was converted into the quantitative mismatch strain by appropriate mechanics. For a given deposition thickness, the magnitude of the mismatch strain increased with increasing current density or plating temperature. The Young’s modulus decreased with increasing current density and increased slightly with increasing temperature. Next, the self-assembly model was experimentally verified by electrodepositing nickel onto an AFM cantilever beam in contact with a second AFM beam, serving as the spring, that does not undergo deposition. For a given deposition thickness, the spring deflection increased with increasing current density and increasing deposition temperature.

Re-evaluation of the widely applied force-frequency relation for frequency-modulation AFM under solution

Frequency-modulation atomic force microscopy (FM-AFM) is a highly versatile tool for surface science. Besides imaging surfaces, FM-AFM is capable of measuring interactions between the AFM probe and the surface with high sensitivity, which can provide chemical information at sub-nanometer resolution. This is achieved by deconvoluting the frequency shift, which is directly measured in experiments, into the force between the probe and sample. At present, the widely used method to perform this deconvolution has been shown to be accurate under high quality (high-Q) factor vacuum conditions. However, under low quality (low-Q) factor conditions, such as in solution, it is not clear if this method is valid. A previous study apparently verified this relation for experiments in solution by comparing the force calculated by this equation with that obtained in separate experiments using the surface force apparatus (SFA). Here we show that, in solution, a more direct comparison of the force calculated by this relation with that directly measured by the cantilever deflection in AFM reveals significant differences, both qualitative and quantitative. However, we also find that there are complications that hinder this comparison. Namely, while contact with the surface is clear in the direct measurements (including the SFA data), it is less certain in the FM-AFM case. Hence, it is not clear if the two methods are measuring the same tip-sample distance regimes. Thus, our results suggest that a more thorough verification of this relation is required, as application of this formulation for experiments in solution may not be valid.

Characterization of Model Uncertainty for Cantilever Deflections in Undrained Clay

AbstractThis work presents a critical evaluation of the model factor for the mobilized strength design (MSD) method for cantilever deflection in undrained soft to medium-stiff clay. The model factor is characterized in two parts. A correction factor η is first defined as the ratio between the wall-top deflection computed from the FEM and its corresponding value computed from the MSD. The hardening soil with a small-strain model is used in FEM. The statistics of η are evaluated using 82 numerical simulations. Because η is not random, and therefore cannot be modeled directly as a random variable, it is decomposed as a product of a systematic part (f) and a random part (η∗). The random part is modeled as a lognormal random variable with a mean of 1.01 and a coefficient of variation (COV) of 0.18. The model factor for FEM (eFEM) is next defined as the ratio between the measured wall-top deflection and the corresponding FEM result. The statistics of eFEM are evaluated using 45 field cases. The ratio eFEM is ra...

High-speed atomic force microscope based on an astigmatic detection system.

High-speed atomic force microscopy (HS-AFM) enables visualizing dynamic behaviors of biological molecules under physiological conditions at a temporal resolution of 1s or shorter. A small cantilever with a high resonance frequency is crucial in increasing the scan speed. However, detecting mechanical resonances of small cantilevers is technically challenging. In this study, we constructed an atomic force microscope using a digital versatile disc (DVD) pickup head to detect cantilever deflections. In addition, a flexure-guided scanner and a sinusoidal scan method were implemented. In this work, we imaged a grating sample in air by using a regular cantilever and a small cantilever with a resonance frequency of 5.5 MHz. Poor tracking was seen at the scan rate of 50 line/s when a cantilever for regular AFM imaging was used. Using a small cantilever at the scan rate of 100 line/s revealed no significant degradation in the topographic images. The results indicate that a smaller cantilever can achieve a higher scan rate and superior force sensitivity. This work shows the potential for using a DVD pickup head in future HS-AFM technology.

ChemInform Abstract: A Brief Survey on Basic Properties of Thin Films for Device Application

AbstractReview: 19 refs.

Test and numerical research on wall deflections induced by pre-excavation dewatering

Numerous studies have been devoted to the performance of excavations and adjacent facilities. In contrast, few studies have focused on retaining wall deflections induced by pre-excavation dewatering. However, considerable inward cantilever deflections were observed for a diaphragm wall in a pre-excavation dewatering test based on a long and narrow metro excavation, and the maximum deflection reached 10mm (37.6% of the allowable wall deflection for the project). Based on the test results, a three-dimensional soil–fluid coupled finite element model was established and used to study the mechanism of the dewatering-induced diaphragm wall deflections. Numerical results indicated that the diaphragm wall deflection results from three factors: (1) the seepage force around the dewatering well and the soil–wall interaction caused the inward horizontal displacement of the soil inside the excavation; (2) the reduced total earth pressure on the excavated side of the diaphragm wall above approximately 1/2 of the maximum dewatering depth disequilibrated the original earth pressure on both sides of the diaphragm wall; and (3) the different negative friction on the excavated and retained sides of the diaphragm wall led to the rotation of the diaphragm wall into the excavation.

Solution modification of a piezoelectric bimorph cantilever under loads

Most of the previous investigations on the static performances of piezoelectric bimorph cantilevers are based on the elementary theory of piezo-elasticity. In fact, one fundamental problem has not been solved yet from the view of the theory of piezo-elasticity, that is, a piezoelectric bimorph cantilever covered fully with electrodes on the upper and lower surfaces and subjected to a transversely concentrated load at the free end of the beam. The major obstacle to find the solution is the equipotential conditions on both the upper and lower surfaces of the cantilever. In this article, by establishing suitable boundary conditions and introducing an appropriate Airy stress function, the analytical solutions of a piezoelectric bimorph cantilever under three different loading conditions have been obtained. Numerical analysis is also conducted and the results are consistent with the present theoretical predictions. This investigation amends the corresponding works given by other investigations based on the elementary theory. It is found that the amendments to the end deflections of a PZT-4 piezoelectric bimorph cantilever caused by an end shear force, an end moment, or a voltage difference between the upper and lower surfaces are about 10.46%, 12.78%, and 3.52%, respectively. In addition, it is also found that these amendments depend just on the material parameters, have nothing to do with the geometric parameters of the bimorph cantilever. The Airy stress function proposed in this article can also be used to study other different piezoelectric cantilevers including multilayer piezoelectric cantilevers under corresponding loads.

Miniaturization of Photothermal Cantilever Deflection Spectroscopy with an Electrical Readout

The chemical selectivity challenge of microcantilever sensors can be overcome by photothermal cantilever deflection spectroscopy (PCDS). A bi-material cantilever responds to heat generated by non-radiative decay process when the adsorbed molecules are resonantly excited with infrared (IR) light. The variation in cantilever deflection amplitude as a function of illuminating IR wavelength corresponds to the conventional IR absorption spectrum of the adsorbed molecules. In addition, the mass of the adsorbed molecules can be determined by measuring the resonance frequency shift of the cantilever for the quantitative analysis. This technique offers unprecedented opportunities for highly selective as well as sensitive chemical sensing without relying on chemoselective interfaces. However, conventional optical signal readout schemes employed for microcantilever sensors pose challenges on miniaturization and system level integration. Here, we demonstrate PCDS using a piezoresistive cantilever which can be easily miniaturized and integrated into a portable sensor platform.