Deflection Sensitivity Research Articles

Investigation of Mechanical Properties of Insulin Crystals by Atomic Force Microscopy

Mechanical properties of protein crystals and aggregates depend on the conformational and structural properties of individual protein molecules as well as on the packing density and structure within solid materials. An atomic force microscopy (AFM)-based approach is developed to measure the elastic modulus of small protein crystals by nanoindentation and is applied to measure the elasticity of insulin crystals. The top face of the crystals deposited on mica substrates is identified as the (001) face. Insulin crystals exhibit a nearly elastic response during the compression cycle. The elastic modulus measured on the top face has asymmetric distribution with a significant width. This width is related to the uncertainty in the deflection sensitivity. A model that takes into account the distribution of the sensitivity values is used to correct the elastic modulus. Measurements performed in aqueous buffer on several crystals at different locations with three different AFM probes give a mean elastic modulus of 164 +/- 10 MPa. This value is close to the static elastic moduli of other protein crystals measured by different techniques that are usually measured in the range from 100 MPa to 1 GPa. The measured modulus of insulin crystals falls between the elastic modulus values of insulin amyloid fibrils measured previously at two orthogonal directions (a modulus of 14 MPa was measured by compressing the fibril in the direction perpendicular to the fibril axis, and a modulus of 3.3 GPa was measured in the direction along the fibril axis). This comparison indicates the heterogeneous structure of fibrils in the direction perpendicular to the fibril axis, with a packing density of the amyloid fibril core that is higher than the average packing density in insulin crystals. The mechanical wear of insulin crystals is detected during AFM measurements. In nanoindentation experiments on insulin crystal, the compressive load by the AFM tip ( approximately 1 nN, corresponding to a pressure of around 5 MPa) occasionally removes protein molecules from the top or the second top layer of insulin crystal in a sequential manner. The molecular model of this surface damage is proposed. In addition, the removal of the multiple layers of molecules is observed during the AC-mode imaging in aqueous buffer. The number of removed layers depends on the scan size.

Microcantilever hotplates with temperature-compensated piezoresistive strain sensors

This paper describes the design, fabrication, and characterization of microcantilever hotplates having both a resistive heater and temperature-compensated piezoresistive strain gauges. The heater was defined near the cantilever free end and the piezoresistive strain gauges were integrated near the clamped base. To realize temperature compensation, a pair of identical piezoresistors was defined in close proximity. One piezoresistor was aligned to the 〈1 1 0〉 crystal direction where the piezoresistive coefficient is maximized and the other one was aligned to the 〈1 0 0〉 crystal direction where the piezoresistive coefficient is nearly zero. The fabricated devices exhibit excellent temperature compensation, with a 20× reduction in temperature sensitivity. The deflection sensitivity shifted only 10% for heating to 200 °C and cantilever deflection ∼10 μm. This work enables cantilever strain sensors that could measure temperature-dependant phenomena.

Micromachined Shear Stress Sensors for Characterization of Surface Forces During Chemical Mechanical Polishing

ABSTRACTThis paper describes the fabrication and calibration of micromachined shear stress sensors intended for characterization of the local pad-wafer contact forces present during chemical-mechanical polishing. Sensors consist of arrays of microfabricated poly-dimethyl-siloxane (PDMS) posts and are able to measure forces ranging from 2 to 200 μN. The posts are 100 μm high and have diameters of 40-100 μm. Calibrated post deflection sensitivities are linear and lie between 0.2 μm/μN and 1.3μm/μN. Sensor design, fabrication, and calibration are detailed. Feasibility is established for sensor integration into a CMP scale model test setup, including an optical viewing method for observing post deflection during polishing. Initial micrographs of post deflection during polishing do not yet have sufficient resolution to determine the microscale forces during polishing.

Lateral force calibration in atomic force microscopy: A new lateral force calibration method and general guidelines for optimization

Proper force calibration is a critical step in atomic and lateral force microscopies (AFM/LFM). The recently published torsional Sader method [C. P. Green et al., Rev. Sci. Instrum. 75, 1988 (2004)] facilitates the calculation of torsional spring constants of rectangular AFM cantilevers by eliminating the need to obtain information or make assumptions regarding the cantilever’s material properties and thickness, both of which are difficult to measure. Complete force calibration of the lateral signal in LFM requires measurement of the lateral signal deflection sensitivity as well. In this article, we introduce a complete lateral force calibration procedure that employs the torsional Sader method and does not require making contact between the tip and any sample. In this method, a colloidal sphere is attached to a “test” cantilever of the same width, but different length and material as the “target” cantilever of interest. The lateral signal sensitivity is calibrated by loading the colloidal sphere laterally against a vertical sidewall. The signal sensitivity for the target cantilever is then corrected for the tip length, total signal strength, and in-plane bending of the cantilevers. We discuss the advantages and disadvantages of this approach in comparison with the other established lateral force calibration techniques, and make a direct comparison with the “wedge” calibration method. The methods agree to within 5%. The propagation of errors is explicitly considered for both methods and the sources of disagreement discussed. Finally, we show that the lateral signal sensitivity is substantially reduced when the laser spot is not centered on the detector.

Quantifying the Specific Binding between West Nile Virus Envelope Domain III Protein and the Cellular Receptor αVβ3 Integrin

A previous study has illustrated that the alphaVbeta3 integrin served as the functional receptor for West Nile virus (WNV) entry into cells. Domain III (DIII) of WNV envelope protein (E) was postulated to mediate virus binding to the cellular receptor. In this study, the specificity and affinity binding of WNV E DIII protein to alphaVbeta3 integrin was confirmed with co-immunoprecipitation and receptor competition assay. Binding of WNV E DIII protein to alphaVbeta3 integrin induced the phosphorylation of focal adhesion kinase that is required to mediate ligand-receptor internalization into cells. A novel platform was then developed using the atomic force microscopy to measure this specific binding force between WNV E DIII protein and the cellular receptor, alphaVbeta3 integrin. The single protein pair-interacting force measured was in the range of 45 +/- 5 piconewtons. This interacting force was highly specific as minimal force was measured in the WNV E DIII protein interaction with alphaVbeta5 integrin molecules and heparan sulfate. These experiments provided an insight to quantitate virus-receptor interaction. Force measurement using atomic force microscopy can serve to quantitatively analyze the effect of candidate drugs that modulate virus-host receptor affinity.

Static properties of a femtosecond electron diffraction system

Ultrafast electron diffraction is an important technique to study the ultrafast phenomenon in physical, chemical and biological processes. This paper introduces a femtosecond electron diffractometer. The diameter of electron beam and deflection sensitivity of X-Y deflection plates are reported. We also demonstrate the static diffraction pattern of a 300 nm thick gold film taken by the femtosecond electron diffractometer.

Two-dimensional bend sensing with a cantilever-mounted FBG

A technique for simultaneous measurement of a 2D bend by using a cantilever-mounted fibre Bragg grating (FBG) is experimentally demonstrated. The value of the two-dimensional deflections is acquired from the central wavelength and chirp bandwidth of the reflection spectrum via the inverse sensitivity matrix. Moreover, an interrogation system with an intensity modulator and a Mach–Zehnder interferometer structure is demonstrated, not only providing wavelength information, but also distinguishing the direction of the horizontal deflection. The measured vertical deflection sensitivity reaches 0.135 nm mm−1, and its horizontal counterparts along the positive and negative axes achieve 0.602 nm mm−1 and −0.572 nm mm−1, respectively.

A New Self-Converging System with Combination of Magnetic Lens and Uniform Horizontal Deflection Field for Color CRTs

Color CRTs (Cathode Ray Tubes) are still evolving in competition with other display devices in the growing TV markets, with continuing demands for enhanced performance and lower cost. In response to these trends, we have developed a new self-converging system of CRT with simple structure. It offers advantages in terms of high resolution for HDTV and large deflection angle for short depth TV sets. The system realizes less spot distortion at the screen periphery of the CRT and lower horizontal dynamic focus voltage than those in a conventional self-converging system, while keeping the cost just as low. In the system, a uniform horizontal deflection field and a newly-developed magnet lens are utilized. The uniform field reduces the spot distortion in exchange for occurrences of raster distortion and convergence error, both of which can be corrected by the newly-developed magnet lens without additional circuit modifications. As a core part of the new system, the lens power of the newly-developed magnet lens varies along the horizontal axis in order to simultaneously achieve convergence and correct the pincushion distortion of the raster. Furthermore, countermeasures for magnet-related issues are taken from the viewpoints of real operation and mass production. The system with the new DY was evaluated in experiments using 86cm CRTs (16:9), and it has been found that the system realizes substantially smaller spot distortions as well as favorable convergence and raster performances, with a drawback of decrease in horizontal deflection sensitivity. The spot oblateness, defined as horizontal spot diameter divided by vertical spot diameter, has decreased from 2.65 to 1.70 accompanying a 15% reduction of horizontal spot sizes at the comers of the screen with 30% decreased dynamic focus voltages and 10% decreased horizontal deflection sensitivity.

A highly sensitive atomic force microscope for linear measurements of molecular forces in liquids

We describe a highly improved atomic force microscope for quantitative nanomechanical measurements in liquids. The main feature of this microscope is a modified fiber interferometer mounted on a five axis inertial slider which provides a deflection sensitivity that is significantly better than conventional laser deflection based systems. The measured low noise floor of 572.0fm∕Hz provides excellent cantilever amplitude resolution. This allows us to operate the instrument far below resonance at extremely small cantilever amplitudes of less than 1 Å. Thus linear measurements of nanomechanical properties of liquid systems can be performed. In particular, we present measurements of solvation forces in confined octamethylcyclotetrasiloxane and water with amplitudes smaller than the size of the respective molecules. In general, the development of the instrument is important in the context of quantitative nanomechanical measurements in liquid environments.

Focused ion beam fabrication of thermally actuated bimorph cantilevers

Focused ion beam (FIB) technology was used to fabricate thermally actuated cantilever arrays using silicon nitride membrane chips for microelectromechanical systems (MEMS) applications. Sequential modification and test is made possible by the dualbeam FIB/SEM. A fabrication route based largely on the use of FIB etch and deposition steps applied to a silicon nitride membrane chip resulted in the formation of readily released bimorph structures with lengths <10 μm. Device deflection sensitivity better than 500 nm/mW was observed. Short-circuiting and hence non-functionality of some devices was attributed to the platinum halo overlap between deposited tracks, which limits the potential for miniaturisation of FIB-MEMS prototypes. Potential applications for these cantilever arrays include scanning probe microscope (SPM) systems and resonant gas sensors.

Force detection in optical tweezers using backscattered light

In force-measuring optical tweezers applications the position of a trapped bead in the direction perpendicular to the laser beam is usually accurately determined by measuring the deflection of the light transmitted through the bead. In this paper we demonstrate that this position and thus the force exerted on the bead can be determined using the backscattered light. Measuring the deflection for a 2.50 mum polystyrene bead with both a position sensitive detector (PSD) and a quadrant detector (QD) we found that the linear detection range for the PSD is approximately twice that for the QD. In a transmission-based setup no difference was found between both detector types. Using a PSD in both setups the linear detection range for 2.50 mum beads was found to be approximately 0.50 mum in both cases. Finally, for the reflection-based setup, parameters such as deflection sensitivity and linear detection range were considered as a function of bead diameter (in the range of 0.5-2.5 mum). 140pN was the largest force obtained using 2.50 mum beads.

A differential microcantilever-based system for measuring surface stress changes induced by electrochemical reactions

We report on a differential microcantilever-based system capable of measuring surface stress changes which occur during electrochemical reactions. Surface stress changes induced by sub-monolayer ionic adsorption on metal surfaces and/or by electromechanical transformations in thin films can be measured. Our system is composed of two microcantilever sensors. The first active microcantilever serves as the working electrode (in a conventional three-probe electrochemical cell configuration) and as the mechanical transducer (bending of the microcantilever), yielding simultaneous, real-time, in situ measurements of the current and interfacial stress changes. The second reference microcantilever serves as a reference sensor to detect any unwanted cantilever deflection resulting from temperature variations, mechanical vibrations and/or uncontrolled chemical reactions. A technique for isolating the electrical contact made to the microcantilever from the electrolyte solution is presented. A method for creating a working electrode with a reproducible area of 1.0 mm 2 is also described. This micromechanical cantilever sensor has a deflection sensitivity of 0.2 nm, which translates to a surface stress sensitivity of 1 × 10 −4 N/m with a dynamic range of 5 × 10 5. The differential mode of this system has been characterized by measuring the potential-induced surface stress, at the Au(1 1 1) solid–liquid (HClO 4 electrolyte) interface, during anion (ClO 4 −) adsorption on gold, while varying the solution temperature. Furthermore, we have measured the surface stress induced during ion doping/dedoping of dodecyl benzenesulfonate-doped polypyrrole (PPy(DBS)) films in an aqueous solution of Na(DBS).

Optimization of support positions to minimize the maximal deflection of structures

In this paper, the design sensitivity analysis for the deflection of a beam or plate structure is first investigated with respect to the position of a simple support using the discrete method. Both elastic and rigid supports are taken into account, and closed-form formulae for the deflection sensitivity are developed straightforwardly. Then, on the basis of the design sensitivity analysis, a heuristic optimization algorithm, called the evolutionary shift method, is presented for support position optimization to minimize the maximal deflection of a structure with a fixed grid mesh scheme. In each iterative loop, the support with the highest efficiency is shifted in priority. To facilitate the convergence of the process, a polynomial interpolation technique is employed to evaluate the solution more accurately. The optimal solution is achieved gradually with a minimum modification of the support layout design. Finally, three numerical examples are presented to demonstrate the validities of the sensitivity analysis and the optimization method. Results show that support optimization can improve the structural behavior significantly.

Three-dimensional modeling of melt flow and interface shape in the industrial liquid-encapsulated Czochralski growth of GaAs

The heat transport in the melt and in the crystal including the interface shape was numerically investigated by local, fully three-dimensional (3D), time-dependent simulations for an industrially sized liquid-encapsulated Czochralski setup for growing GaAs crystals with 150 mm diameter. The thermal boundary conditions for the local 3D simulations were obtained from global quasi-steady 2D simulations. It was found that the type of thermal boundary conditions (fixed temperature or heat flux) has a strong influence on the 3D results of the interface shape and on the melt convection. Furthermore, a high sensitivity of the interface deflection on the temperature at the bottom wall of the crucible is observed. For a control of the interface shape the use of two types of magnetic fields (horizontal and vertical) was considered. It was found that a horizontal magnetic field has a bigger influence on the interface shape than a vertical magnetic field.

Direct measurement of tapping force with a cantilever deflection force sensor

An experimental set up dedicated to the measurement of atomic force microscope tapping force was developed. In the set-up, a standard TappingMode™ probe cantilever was used to tap another cantilever equipped with its own low noise and high sensitivity deflection detection system for force measurement. The amplitude and phase change of the tapping lever as well as the deflection of the sensing lever were simultaneously recorded as a function of tip/surface separation. Since the deflection of the sensing cantilever reflects the average force over one interaction cycle, we measured the total average force quantitatively after calibrating the spring constant and deflection sensitivity of the sensing lever. Considerable effort was made to achieve the same force curve in the tapping force measurement as occur during imaging of conventional samples such that the detected tapping force reflects the same interaction of the imaging process.

Sensitivity of the Neuromagnetic N100m Deflection to Spectral Bandwidth: A Function of the Auditory Periphery?

The amplitude of the auditory evoked field (AEF) component N100m in response to tonal stimuli of varying spectral bandwidth and periodicity was compared with simulated peripheral activity patterns of the auditory nerve (AN). The AEF of ten subjects was recorded with a 37-channel axial gradiometer system (four independent measurement sessions per hemisphere). The simulated peripheral activity was characterized using measures derived from spike probabilities of the AN. Stimuli were pure tones, narrow-band harmonic complex tones (spectrum: 4–4.8 kHz), and broad-band harmonic complex tones (spectrum: 800 Hz–4.8 kHz) with periodicities of 100, 200, and 400 Hz. The intensity of all stimuli was set to 65 dB above the absolute thresholds. Both the simulated AN activity and measured cortical response amplitudes increased consistently with spectral bandwidth. This suggests that the enhanced sensitivity of the N100m amplitude to broad-band complex tones is to some extent a function of the auditory periphery.

Micromachined III–V cantilevers for AFM-tracking scanning Hall probe microscopy

In this paper we report the development of a new III–V cantilever-based atomic force sensor with piezoresistive detection and an integrated Hall probe for scanning Hall probe microscopy. We give detailed descriptions of the fabrication process and characterization of the new integrated sensor, which will allow the investigation of magnetic samples with no sample preparation at both room and cryogenic temperatures. We also introduce a novel piezoresistive material based on the ternary alloy n+-Al0.4Ga0.6As which allows us to achieve a cantilever deflection sensitivity ΔR/(R Δz) = 2 × 10−6 Å−1 at room temperature.

Micromechanical cantilever as an ultrasensitive pH microsensor

We report on a pH sensor with ultrahigh sensitivity based on a microcantilever structure with a lithographically-defined crosslinked copolymeric hydrogel. Silicon-on-insulator wafers were used to fabricate cantilevers on which a polymer consisting of poly(methacrylic acid) (PMAA) with poly(ethylene glycol) dimethacrylate was patterned using free-radical UV polymerization. As the pH around the cantilever was increased above the pKa of PMAA, the polymer network expanded and resulted in a reversible change in surface stress causing the microcantilever to bend. Excellent mechanical amplification of polymer swelling as a function of pH change within the dynamic range was obtained, with a maximum deflection sensitivity of 1 nm/5×10−5 ΔpH.

High‐deflection‐sensitivity CRTs with filled yoke

Abstract—The trend towards slim CRTs requires deflection yokes (DYs) with an improved deflection sensitivity. We present a new method to improve the deflection sensitivity by 15–25% by filling the space between the ferrite core and deflection coils with a soft magnetic material. The effect was analyzed in terms of a simplified two‐dimensional model. These model calculations were confirmed by three‐dimensional simulations and by experiments on a DY design for the Philips 29‐in. Real Flat CRT.

An efficient backcalculation algorithm of time domain for large-scale pavement structures using Ritz vectors

This paper describes a backcalculation algorithm to determine the layer moduli and damping coefficients in the time domain for large-scale pavement structures. Pavement is modeled by three-dimensional finite element (3D FE). The parameter identification procedure makes use of Ritz vectors to reduce the size of matrices involved in the forward dynamic response analysis and the deflection sensitivity analysis. An exact complex mode superposition technique is used to obtain the dynamic response of the reduced equation system in the time domain. This method is more efficient, accurate and stable. The parameter estimates are improved iteratively by means of an algorithm that calls the finite element program of dynamic response analysis as a subroutine combining truncated singular value decomposition (TSVD) method. Simulation of a numerical solution validates the efficiency of the proposed method. Finally, the method is implemented for two experimentally tested sections of semiflexible pavement. All parameters are determined using the surface deflections of pavement experimentally recorded at the sensor locations of falling weight deflectometer (FWD).