Probe Deflection Research Articles

Atomic force microscope method for sidewall measurement through carbon nanotube probe deformation correction

To use atomic force microscope to measure narrow vertical features is challenging. Using carbon nanotube (CNT) probes is a possible remedy. However, even with its extremely high stiffness, van der Waals attractive force from steep sidewalls bends CNT probes. This probe deflection effect causes deformation (or "swelling") of the measured profile. When measuring 100-nm-high vertical sidewalls with a 27-nm-diameter and 265-nm-long CNT probe, the probe deflection at the bottom is estimated as large as 5.8 nm. This phenomenon is inevitable when using long and thin probes. We proposed a method to correct this probe deflection effect. Detecting torsional motion of the base cantilever of the CNT probe makes it possible to estimate the CNT probe deflection. Using this information, we have developed a technique for correcting the probe deformation effect from measured profiles. This technique, in combination with correction of the probe shape effect, enables vertical sidewall profile measurement with AFM.

Nanofibrous poly(lactide-co-glycolide) membranes loaded with diamond nanoparticles as promising substrates for bone tissue engineering

Nanofibrous scaffolds loaded with bioactive nanoparticles are promising materials for bone tissue engineering. In this study, composite nanofibrous membranes containing a copolymer of L-lactide and glycolide (PLGA) and diamond nanoparticles were fabricated by an electrospinning technique. PLGA was dissolved in a mixture of methylene chloride and dimethyl formamide (2:3) at a concentration of 2.3 wt%, and nanodiamond (ND) powder was added at a concentration of 0.7 wt% (about 23 wt% in dry PLGA). In the composite scaffolds, the ND particles were either arranged like beads in the central part of the fibers or formed clusters protruding from the fibers. In the PLGA-ND membranes, the fibers were thicker (diameter 270 ± 9 nm) than in pure PLGA meshes (diameter 218 ± 4 nm), but the areas of pores among these fibers were smaller than in pure PLGA samples (0.46 ± 0.02 μm(2) versus 1.28 ± 0.09 μm(2) in pure PLGA samples). The PLGA-ND membranes showed higher mechanical resistance, as demonstrated by rupture tests of load and deflection of rupture probe at failure. Both types of membranes enabled the attachment, spreading, and subsequent proliferation of human osteoblast-like MG-63 cells to a similar extent, although these values were usually lower than on polystyrene dishes. Nevertheless, the cells on both types of membranes were polygonal or spindle-like in shape, and were distributed homogeneously on the samples. From days 1-7 after seeding, their number rose continuously, and at the end of the experiment, these cells were able to create a confluent layer. At the same time, the cell viability, evaluated by a LIVE/DEAD viability/cytotoxicity kit, ranged from 92% to 97% on both types of membranes. In addition, on PLGA-ND membranes, the cells formed well developed talin-containing focal adhesion plaques. As estimated by the determination of tumor necrosis factor-alpha levels in the culture medium and concentration of intercellular adhesion molecule-1, MG-63 cells, and RAW 264.7 macrophages on these membranes did not show considerable inflammatory activity. This study shows that nanofibrous PLGA membranes loaded with diamond nanoparticles have interesting potential for use in bone tissue engineering.

Design of a Flexible Imaging Probe for Robotics Surgery

Minimally invasive surgery assisted by robots has shown higher efficiency and precision. In spite of the good performance of the state of the art surgery robotics systems, the size and number of external incisions required by instruments should be reduced to lower the scarring and incisional pain experienced by the patient. Other important improvement derived from the use of smaller incisions is the diminishment of time required for recovery. This research develops a flexible scope of small diameter driven by segmented multiple actuators to produce a deflection of the imaging probe at its distal end providing better visualization than the current rigid cameras. The research is conducted in cooperation with the Biorobotics Laboratory at the University of Washington USA, where our scope will be incorporated to Raven, a 7-DOF cable-actuated surgical robot. The flexible scope is composed of three segments as illustrated in Figure 1, where it is possible to see that the device contains a ring of cables enclosed externally and internally by two different springs and a semi rigid covering. The main mechanism of bending is the compression and extension of the external spring at the distal end. The change of length in this spring is controlled by an active system that combines pulling and releasing actions through the ring of cables. The device has advantages in its simplicity of actuation and the high elasticity and flexibility at the distal end. In the current state of the project, a testing system is under construction.

A piezo-thermal probe for thermomechanical analysis.

Thermomechanical analysis (TMA) is widely used to characterize materials and determine transition temperatures and thermal expansion coefficients. Atomic-force microscopy (AFM) microcantilevers have been used for TMA. We have developed a micromachined probe that includes two embedded sensors: one for measuring the mechanical movement of the probe (deflection) and another for providing localized heating. The new probe reduces costs and complexity and allow for portability thereby eliminating the need for an AFM. The sensitivity of the deflection element ((ΔR∕R)∕deflection) is 0.1 ppm∕nm and its gauge factor is 3.24. The melting temperature of naphthalene is measured near 78.5 °C.

Geometric Effects When Measuring Small Holes With Micro Contact Probes.

A coordinate measuring machine with a suitably small probe can be used to measure micro-features such as the diameter and form of small holes (often about 100 μm in diameter). When measuring small holes, the clearance between the probe tip and the part is sometimes nearly as small as other characteristic lengths (such as probe deflection or form errors) associated with the measurement. Under these circumstances, the basic geometry of the measurement is much different than it is for the measurement of a macroscopic object. Various geometric errors are greatly magnified, and consequently sources of error that are totally irrelevant when measuring macroscopic artifacts can become important. In this article we discuss errors associated with misalignment or non-orthogonality of the probe axes, probe-tip radius compensation, and mechanical filtering.

Luminal Esophageal Temperature Monitoring With a Deflectable Esophageal Temperature Probe and Intracardiac Echocardiography May Reduce Esophageal Injury During Atrial Fibrillation Ablation Procedures

Luminal esophageal temperature (LET) monitoring is one strategy to minimize esophageal injury during atrial fibrillation ablation procedures. However, esophageal ulceration and fistulas have been reported despite adequate LET monitoring. The objective of this study was to assess a novel approach to LET monitoring with a deflectable LET probe on the rate of esophageal injury in patients undergoing atrial fibrillation ablation. Forty-five consecutive patients undergoing an atrial fibrillation ablation procedure followed by esophageal endoscopy were included in this prospective observational pilot study. LET monitoring was performed with a 7F deflectable ablation catheter that was positioned as close as possible to the site of left atrial ablation using the deflectable component of the catheter guided by visualization of its position on intracardiac echocardiography. Ablation in the posterior left atrial was limited to 25 W and terminated when the LET increased 2°C from baseline. Endoscopy was performed 1 to 2 days after the procedure. All patients had at least 1 LET elevation >2°C necessitating cessation of ablation. Deflection of the LET probe was needed to accurately measure LET in 5% of patients when ablating near the left pulmonary veins, whereas deflection of the LET probe was necessary in 88% of patients when ablating near the right pulmonary veins. The average maximum increase in LET was 2.5±1.5°C. No patients had esophageal thermal injury on follow-up endoscopy. A strategy of optimal LET probe placement using a deflectable LET probe and intracardiac echocardiography guidance, combined with cessation of radiofrequency ablation with a 2°C rise in LET, may reduce esophageal thermal injury during left atrial ablation procedures.

An interferometric platform for studying AFM probe deflection

This paper describes an interferometric platform for measuring the full-field deflection of atomic force microscope (AFM) probes and generic cantilevers during quasi-static loading. The platform consists of a scanning white light interferometer (SWLI), holders for the cantilevers, a translation stage, a rotation (tip-tilt) stage, and an adapter plate to connect these items to the SWLI table. Visualization of cantilever bending behavior is demonstrated for snap-in against a rigid surface, cantilever-on-cantilever tests, and a damaged AFM probe. A new approach to normal force calculation using a polynomial fit to the cantilever deflection profile is also presented and verified experimentally. The method requires only the coefficient for the third order (cubic) term from the fit to the deflection profile, the elastic modulus, and the area moment of inertia for the cantilever under test.

Fiber deflection probing method based on micro focal-length collimation

In order to improve the low displacement sensitivity in sensing the 2D deflection of a fiber probe used for measurement of micro cavities with high aspect ratio, a fiber stem with a ball mounted on its end is used as a probe and a small segment of it is used as a cylindrical lens to collimate a point light source and image it to a camera. The deflection of the fiber stem can be inferred from the change in image acquired by the camera with ultrahigh displacement sensitivities of 10,000 and 20,000 in two dimensions using a fiber stem of 44 mum in diameter, and the corresponding resolutions are better than 1 nm and 3 nm respectively.

Elastic modulus of low-k dielectric thin films measured by load-dependent contact-resonance atomic force microscopy

Correlated force and contact resonance versus displacement responses have been resolved using load-dependent contact-resonance atomic force microscopy (AFM) to determine the elastic modulus of low-k dielectric thin films. The measurements consisted of recording simultaneously both the deflection and resonance frequency shift of an AFM cantilever probe as the probe was gradually brought in and out of contact. As the applied forces were restricted to the range of adhesive forces, low-k dielectric films of elastic modulus varying from GPa to hundreds of GPa were measurable in this investigation. Over this elastic modulus range, the reliability of load-dependent contact-resonance AFM measurements was confirmed by comparing these results with those from picosecond laser acoustic measurements.

Characterization of Probe Dynamic Behaviors in Critical Dimension Atomic Force Microscopy.

This paper describes a detailed computational model of the interaction between an atomic force microscope probe tip and a sample surface. The model provides analyses of dynamic behaviors of the tip to estimate the probe deflections due to surface intermittent contact and the resulting dimensional biases and uncertainties. Probe tip and cantilever beam responses to intermittent contact between the probe tip and sample surface are computed using the finite element method. Intermittent contacts with a wall and a horizontal surface are computed and modeled, respectively. Using a 75 nm Critical Dimension (CD) tip as an example, the responses of the probe to interaction forces between the sample surface and the probe tip are shown in both time and frequency domains. In particular, interaction forces between the tip and both a vertical wall and a horizontal surface of a silicon sample are modeled using Lennard-Jones theory. The Snap-in and Snap-out of the probe tip in surface scanning are calculated and shown in the time domain. Based on the given tip-sample interaction force model, the calculation includes the compliance of the probe and dynamic forces generated by an excitation. Cantilever and probe tip deflections versus interaction forces in the time domain can be derived for both vertical contact with a plateau and horizontal contact with a side wall. Dynamic analysis using the finite element method and Lennard-Jones model provide a unique means to analyze the interaction of the probe and sample, including calculation of the deflection and the gap between the probe tip and the measured sample surface.

Simultaneous Measurement Of Force And Fluorescence In Single Guinea-pig Cardiac Myofibrils

Kinetic studies of force activation and relaxation in the single myofibril preparation have enhanced our understanding of mechanisms that underlie regulation of muscle force. Likewise, stop-flow and steady-state measurement using fluorescently labeled TnC upon Ca2+ activation in reconstituted protein systems have provided data regarding the kinetics of thin filament regulation. However, to develop a detailed understanding and fully characterize muscle regulation, an integration of mechanical, biochemical, and structural information is necessary. We present the development of a new apparatus which allows simultaneous measurement of florescent probe signals from labeled contractile proteins (such as TnC), and force kinetics under active isometric force development to allow direct correlation between these parameters in a single myofibril. Single guinea-pig cardiac myofibrils were prepared in relaxing solution (PCa8.0) by mechanical homogenization; endogenous TnC was exchanged for recombinant mutant labeled human TnC (2.5 mg/ml; overnight 4°C; Alexa-350 label conjugated to cys-84). Myofibrils were attached to glass micro-tools with one serving as a cantilever of known stiffness to assess force (painted black for improved contrast) and the other attached to a high speed motor. Myofibrils were activated with a Ca2+ pulse delivered via a double barreled perfusion pipette attached to a stepper motor (∼5 ms). Excitation UV-light (270-350 nm), chopped at 52 kHz using a photo-elastic modulator, was projected (400nm DC mirror) onto the attached myofibril. Force probe deflection was measured in bright-field using red light (670nm) while fluorescence emission was measured (420nm LP filter) using a photomultiplier. Data was sampled by a high-speed (2MHZ) A/D converter and demodulated using custom designed software. Preliminary results indicate that using this apparatus and techniques, ultra-low intensity TnC fluorescence signals can be obtained at high temporal resolution in parallel with bright-field optical measurement of force development.

Beam Probe Deflection Analysis of Redox Active Species Irreversibly Adsorbed on Electrode Surfaces

Theoretical aspects of probe beam deflection (PBD) as applied to voltammetric studies of redox active species irreversibly adsorbed on a flat electrode surface have been examined using Week’s numerical inverse Laplace transform algorithm. Excellent agreement was found between the time-resolved profiles calculated based on this approach and those obtained via conventional space-time discretization techniques over the interval of relevance to actual experimental measurements. In agreement with the behavior reported elsewhere for related systems, the shape of the PBD response is highly sensitive to the distance between the probing beam and the electrode surface. In particular, plots of the dimensionless derivative of the concentration of the electrolyte with respect to the dimensionless distance normal to the electrode surface, χ (which is proportional to the deflection), ∂θ∕∂χ vs dimensionless time, (or, equivalently, potential, for voltammetric measurements) for small χ, yielded curves similar to the voltammetric behavior of a redox active solution phase species in a thin layer cell configuration (which closely resemble the voltammetry of the actual adsorbed redox couple). As χ was increased, however, the ∂θ∕∂χ vs curves acquired characteristics reminiscent of solution-phase voltammetry recorded with a microelectrode and farther away with a larger electrode. Further evidence of the accuracy of Week’s method was obtained from the analysis of square-wave periodic boundary conditions at the interface, which yielded time-resolved profiles away from the interface, in harmony with the analytical solutions published in the literature.

Welding method for fabricating carbon nanotube probe

Abstract A simple and reliable welding method was developed to fabricate carbon nanotube probe used in atomic force microscopy here. First, apply less than 20 V voltage between silicon probe and carbon nanotube when they were in close proximity under direct view of optical microscope. Then, let carbon nanotube contact with silicon probe and increase the external voltage to 30–60 V until carbon nanotube was divided and attached to the end of silicon probe. The fabricated carbon nanotube probe could be shortened to appropriate length by electron bombard. The weld strength of carbon nanotube probe was calculated by drawing the ordinary AFM probe and measuring the probe's deflections. For one carbon nanotube probe with 75 nm diameter, the weld strength was calculated more than 268 nN. Carbon nanotube probe showed higher aspect ratio and could more accurately reflect the true topography of sample than silicon probe.

Deflection–voltage curve modelling in atomic force microscopy and its use in DCelectrostatic manipulation of gold nanoparticles

A model of deflection–voltage curves in atomic force microscopy and its use in DCelectrostatic nanomanipulation experiments are presented. The proposed model predictsthe deflection of the atomic force microscope probe as a function of the appliedprobe–substrate voltage, as well as the distance and voltage at which the tip collapsesirreversibly onto the substrate due to electrostatic forces. The model is verifiedexperimentally and its use in DC electrostatic manipulation of 25 nm radius goldnanoparticles is demonstrated.

Fabrication and characterization of thermally actuated bimorph probe for living cell measurements with experimental and numerical analysis

This paper deals with a novel structure for single-cell characterization which makes use of bimorph micro thermal actuators combined with electrical sensor device and integrated microfluidic channel. The goal for this device is to capture and characterize individual biocell. Quantitative and qualitative characteristics of bimorph thermal actuator were analyzed with finite element analysis methods. Furthermore, optimization for the dimension of cantilevers and integrated parallel probe systems with microfluidic channels is able to be realized through the virtual simulation for actuation and the practical fabrication of prototype of probes. The experimental value of probe deflection was in accordance with the simulated one.

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.

Fiber deflection probe for small hole metrology

This paper presents the development of a new probing method for coordinate measuring machines (CMM) to inspect the diameter and form of small holes. The technique, referred to as fiber deflection probing (FDP), can be used for holes of approximately 100 μm nominal diameter. The expanded uncertainty obtained using this method is 0.07 μm (k = 2) on diameter. The probing system consists of a transversely illuminated fiber (with a ball mounted on the end) whose shadows are imaged using a camera. We can infer the deflection of the probe from the motion of the image seen by the camera, and we infer the position of the measured surface by adding the fiber deflection along x- and y-directions to the machine scale readings. The advantage of this technique is the large aspect ratio attainable (5 mm deep for a 100 μm diameter hole). Also, by utilizing the fiber as a cylindrical lens, we obtain sharp crisp images of the fiber position, thus enabling high resolution for measured probe deflection. Another potential advantage of the probe is that it exerts an exceptionally low force (ranging from a few micronewtons down to hundreds of nanonewtons). Furthermore, the probe is relatively robust, capable of surviving more than 1 mm over-travel, and the probe should be inexpensive to replace if it is broken. In this paper, we describe the measurement principle and provide an analysis of the imaging process. Subsequently, we discuss data obtained from characterization and validation experiments. Finally, we demonstrate the utility of this technique for small hole metrology by measuring the internal geometry of a 129 μm diameter fiber ferrule and conclude with an uncertainty budget.

Micro-thermal analysis of NiTi shape memory alloy thin films

A novel technique of micro-thermal analysis (micro-TA) has been used to investigate martensitic to austenitic transformations of near equi-atomic NiTi shape memory alloy (SMA) thin films deposited on silicon wafer by a plasma assisted sputter deposition technique. The results demonstrate that both power and sensor deflection signal of the technique, equivalent to micro-differential thermal analysis (μDTA) and micro-thermomechanical analysis (μTMA), respectively, have a capability of locally characterising transformation temperatures of the SMA films. The phase transition temperatures can be identified as an abrupt deviation of power and thermal expansion from linearity. The change in probe deflection reveals a sample contraction of 0.44% following the martensite to austenitic transformation. This dimension change is consistent with the difference in the unit cell volumes of the different phases. The individual films investigated here show a spatial variation on the micron-scale in the martensite to austenite transition temperatures as the surface is probed. A possible reason for this may lie in the inhomogeneous distribution of Ti and Ni in the film structure as the transition temperature is very sensitive to composition, showing typically a 100 K temperature change between 50 and 51 at.% Ni in Ti. Conventional bulk DSC experiments were carried out on the same materials and the results were compared with those from the micro-TA.

Active Force Generated by the Motility of the Outer Hair Cell.

Although the force production of the outer hair cell (OHC) leads to the fine tuning of the mammalian cochlea, the value of the force generated by the motility of the OHC in vivo has not been clarified yet. In this study, first, the active force generated by the motility of the load-free OHC in response to an electrical stimulation was measured from the deflection of the force probe. Next, to establish cell conditions similar to those of the intact cochlea, a compressive load was applied to the OHC using a force probe driven by a bimorph actuator, and then the active force generated by the motility of the loaded OHC was determined. Comparing the active force generated by the motility of the load-free OHC with that by the motility of the loaded OHC, it was found that the active force decreased due to application of the compressive load.

Reliability theory for receptor–ligand bond dissociation

Cell adhesion in the presence of hydrodynamic forces is a critical factor in inflammation, cancer metastasis, and blood clotting. A number of assays have recently been developed to apply forces to small numbers of the receptor–ligand bonds responsible for adhesion. Examples include assays using hydrodynamic shear in flow chambers or elastic probe deflection assays such as the atomic force microscope or the biomembrane force probe. One wishes to use the data on the time distribution of dissociation from these assays to derive information on the force dependence of reaction rates, an important determinant of cell adhesive behavior. The dissociation process can be described using the theory developed for reliability engineering of electronic components and networks. We use this framework along with the Bell model for the reverse reaction rate (kr=kr0 exp[r0 f/kT], where f is the applied force and kr0 and r0 are Bell model parameters) to write closed form expressions for the probability distribution of break-up with multiple independent or interacting bonds. These expressions show that the average lifetime of n bonds scales with the nth harmonic number multiplied by the lifetime of a single bond. Results from calculation and simulations are used to describe the effect of experimental procedures in forced unbinding assays on the estimation of parameters for the force dependence of reverse reaction rates.