End Of Cantilever Research Articles

산화 텅스텐 나노막대의 트라이볼로지 특성

Friction and wear behavior of tungsten oxide nanorods (TONs) was investigated using friction force microscopy(FFM) employing colloidal probes instead of conventional sharp tips. Vertically well-ordered TONs with 40 nm diameter, 130 nm length and 100 nm pitch width were synthesized on an anodic aluminium oxide substrate using two step electrochemical anodizing processes. The colloidal probe (diameter 20 <TEX>${\mu}m$</TEX>) attached at the free end of tipless cantilever was oscillated(scanned) against a stationary surface of vertically aligned TONs with various scan speeds (1.2 <TEX>${\mu}m/s$</TEX>, 3.0 <TEX>${\mu}m/s$</TEX> and 6.0 <TEX>${\mu}m/s$</TEX>) and sliding cycles (100, 200 and 400) under normal load of 800 nN. The friction force and wear depth decreased with the increase of the scan speed. Plastically deformed thin layers were formed and sparsely deposited on the worn nonorod surface. The lower wear rate of the TONs with the longer oscillating cycles was attributed to the decreased real contact pressure due to the increase of real contact area between the colloidal probe and the TONs.

Monitoring of delamination onset and growth during Mode I and Mode II interlaminar fracture tests using guided waves

A delamination monitoring method was proposed to characterize Mode I and Mode II delamination onset in carbon fiber/epoxy (CF/EP) composite laminates through interrogation of guided waves activated and captured using piezoelectric actuators and sensors in a pitch–catch configuration. Mode I and Mode II interlaminar fracture tests were conducted using double cantilever beam (DCB) and end notch flexure (ENF) specimens to evaluate the proposed method. The changes in wave propagation velocity and wave magnitude (or attenuation), and the degree of waveform similarity between excitation and response signals, were calculated as delamination-sensitive wave parameters and plotted versus displacement recorded using a materials testing system. The kink points determined from wave parameter–displacement curves agreed well with the deviation from linearity (NL), visual observation (VIS) and maximum load (Max) points, which are often used in conventional methods for determining interlaminar fracture toughness. The propagation characteristics of the A 0 wave mode in a low frequency range were demonstrated to have high sensitivity to Mode I and in particular Mode II delamination onset in CF/EP composite laminates. It was concluded that the guided waves propagating in the DCB and ENF specimens were capable of determining Mode I and Mode II interlaminar fracture toughness, complementing current practices based on visual inspection or trivial interrogation using load–displacement curve alone.

Effect of Bondline Thickness on Mixed-Mode Fracture of Adhesively Bonded Joints

The effect of bondline thickness on the critical strain energy release rate (CSERR) was investigated using aluminum adherends and an epoxy adhesive. Complete mixed Mode I/II fracture envelopes for adhesive thicknesses ranging from 0.203 to 1.52 mm were developed using double cantilever beam (DCB), mixed-mode bending (MMB), and end notch flexure (ENF) tests methods. Bondline thickness strongly affects the CSERR for different amounts of Mode II component. Pure Mode II had the largest CSERR and showed monotonic increase with bondline thickness, whereas pure Mode I had the lowest CSERR and exhibited non monotonic relationship with bondline thickness. The shape and size of the plastic zone that develops prior to crack propagation was predicted by finite element analysis. Variation of CSERR as a function of adhesive layer thickness was shown to be related to the size of the plastic zone for Mode I and MMB 50% fracture. No correlation was observed for the MMB 75% and Mode II, however.

Experimental determination of validated, critical interfacial modes I and II energy release rates in a composite sandwich panel

A validated experimental approach to obtaining critical mode I and mode II energy release rates for interfacial failure in a sandwich composite panel is outlined in this paper. By modifying the geometry of the sandwich structure to align the face sheet-core interface to coincide with the neutral axis, it is possible to obtain critical mode I and mode II energy release rates by conducting Double Cantilever Beam (DCB) and End Notch Flexure (ENF) tests, respectively. The values so obtained were used to predict the crack growth histories of modified DCB and ENF tests, and a Single Leg Bend (SLB) test, using a discrete cohesive zone method (DCZM). In addition, the influence of material and geometry were also analyzed.

Influence of electrospun Nylon 6,6 nanofibrous mats on the interlaminar properties of Gr–epoxy composite laminates

The present work aims at investigating the influence of electrospun Nylon 6,6 nanofibrous mat to interlaminar strength. Mode I and the Mode II fracture mechanics of virgin and nanomodified laminates are investigated. Nanomodified laminates are fabricated by interleaving an electrospun nanofibrous mats in laminate mid-plane. Double Cantilever Beam (DCB) and End Notched Flexure (ENF) tests are performed on both virgin and nanomodified configuration. Results show that electrospun nanofibrous mat is able to increase by 23.2% the mechanical energy absorbing capability and by about 5% the G IC . ENF tests reveal that the nanofibrous mats contribute to improve the maximum stress before the material crisis (6.5% of increment) and a measurable increment of (8.1%) the maximum mechanical energy that can be absorbed by the material during the crack propagation is registered. The acoustic emission (AE) technique is used to monitor both DCB and ENF tests. The AE information highlight that the nanofibrous mats mitigate the interlaminar matrix failure on both the fracture modes.

Enhancing interlaminar fracture characteristics of woven CFRP prepreg composites through CNT dispersion

The inter-ply characteristics of polymeric prepreg composites influence their interlaminar fracture toughness and the overall performance. This article embarks on engineering the inter-ply interfaces of carbon fiber reinforced polymer (CFRP) composites. A novel and practical technique for dispersion of multi-walled carbon nanotubes (MWCNTs) onto woven CFRP prepreg is presented. The interlaminar fracture toughness of these CFRP lay-ups was evaluated experimentally and compared with the regular (without any CNTs) specimen. Double cantilever beam and end notch flexure tests were conducted for interlaminar fracture studies. It was observed that the addition of MWCNTs in between the CFRP prepreg plies helps in strengthening the interface. There existed an optimum percentage in which these nanofillers should be added. The presence of nanotubes increased fiber bridging within the ply interfaces, which in turn controlled the inter-ply crack propagation. The findings and the mechanisms are discussed using the test data, SEM pictures, schematics, and scans of the fractured surfaces.

Visualization of Recombinant DNA and Protein Complexes Using Atomic Force Microscopy

Atomic force microscopy (AFM) allows for the visualizing of individual proteins, DNA molecules, protein-protein complexes, and DNA-protein complexes. On the end of the microscope's cantilever is a nano-scale probe, which traverses image areas ranging from nanometers to micrometers, measuring the elevation of macromolecules resting on the substrate surface at any given point. Electrostatic forces cause proteins, lipids, and nucleic acids to loosely attach to the substrate in random orientations and permit imaging. The generated data resemble a topographical map, where the macromolecules resolve as three-dimensional particles of discrete sizes (Figure 1) 1,2. Tapping mode AFM involves the repeated oscillation of the cantilever, which permits imaging of relatively soft biomaterials such as DNA and proteins. One of the notable benefits of AFM over other nanoscale microscopy techniques is its relative adaptability to visualize individual proteins and macromolecular complexes in aqueous buffers, including near-physiologic buffered conditions, in real-time, and without staining or coating the sample to be imaged. The method presented here describes the imaging of DNA and an immunoadsorbed transcription factor (i.e. the glucocorticoid receptor, GR) in buffered solution (Figure 2). Immunoadsorbed proteins and protein complexes can be separated from the immunoadsorbing antibody-bead pellet by competition with the antibody epitope and then imaged (Figure 2A). This allows for biochemical manipulation of the biomolecules of interest prior to imaging. Once purified, DNA and proteins can be mixed and the resultant interacting complex can be imaged as well. Binding of DNA to mica requires a divalent cation 3,such as Ni2+ or Mg2+, which can be added to sample buffers yet maintain protein activity. Using a similar approach, AFM has been utilized to visualize individual enzymes, including RNA polymerase 4 and a repair enzyme 5, bound to individual DNA strands. These experiments provide significant insight into the protein-protein and DNA-protein biophysical interactions taking place at the molecular level. Imaging individual macromolecular particles with AFM can be useful for determining particle homogeneity and for identifying the physical arrangement of constituent components of the imaged particles. While the present method was developed for visualization of GR-chaperone protein complexes 1,2 and DNA strands to which the GR can bind, it can be applied broadly to imaging DNA and protein samples from a variety of sources.

Visualization of Recombinant DNA and Protein Complexes Using Atomic Force Microscopy

Atomic force microscopy (AFM) allows for the visualizing of individual proteins, DNA molecules, protein-protein complexes, and DNA-protein complexes. On the end of the microscope's cantilever is a nano-scale probe, which traverses image areas ranging from nanometers to micrometers, measuring the elevation of macromolecules resting on the substrate surface at any given point. Electrostatic forces cause proteins, lipids, and nucleic acids to loosely attach to the substrate in random orientations and permit imaging. The generated data resemble a topographical map, where the macromolecules resolve as three-dimensional particles of discrete sizes (Figure 1) 1,2. Tapping mode AFM involves the repeated oscillation of the cantilever, which permits imaging of relatively soft biomaterials such as DNA and proteins. One of the notable benefits of AFM over other nanoscale microscopy techniques is its relative adaptability to visualize individual proteins and macromolecular complexes in aqueous buffers, including near-physiologic buffered conditions, in real-time, and without staining or coating the sample to be imaged. The method presented here describes the imaging of DNA and an immunoadsorbed transcription factor (i.e. the glucocorticoid receptor, GR) in buffered solution (Figure 2). Immunoadsorbed proteins and protein complexes can be separated from the immunoadsorbing antibody-bead pellet by competition with the antibody epitope and then imaged (Figure 2A). This allows for biochemical manipulation of the biomolecules of interest prior to imaging. Once purified, DNA and proteins can be mixed and the resultant interacting complex can be imaged as well. Binding of DNA to mica requires a divalent cation 3,such as Ni2+ or Mg2+, which can be added to sample buffers yet maintain protein activity. Using a similar approach, AFM has been utilized to visualize individual enzymes, including RNA polymerase 4 and a repair enzyme 5, bound to individual DNA strands. These experiments provide significant insight into the protein-protein and DNA-protein biophysical interactions taking place at the molecular level. Imaging individual macromolecular particles with AFM can be useful for determining particle homogeneity and for identifying the physical arrangement of constituent components of the imaged particles. While the present method was developed for visualization of GR-chaperone protein complexes 1,2 and DNA strands to which the GR can bind, it can be applied broadly to imaging DNA and protein samples from a variety of sources.

Electrothermal Atomic-Force Microscope Cantilever With Integrated Heater and n-p-n Back-to-Back Diodes

This paper reports the integration of both electrical and thermal elements into the free end of an atomic-force microscope cantilever, where the electrode and heater-thermometer are electrically isolated by an NPN semiconductor back-to-back diode. The electrothermal cantilever can be self heated using an integrated solid-state heater to more than 600°C. The tip voltage can be measured or controlled independent of the tip temperature, either in the direct or the alternating current mode. To our knowledge, this setup is the first microcantilever to have a solid-state junction and heater integrated near a scanning probe tip.

Direct nanomechanical measurement of layer thickness and compressibility of smectic liquid crystals

Using an atomic force microscope (AFM) we confined a smectic-A liquid crystal (LC) between a flat glass plate and a 10-μm glass sphere attached to the free end of the AFM cantilever. Both surfaces were treated with a surfactant that induces normal alignment of the LC molecules. We measured the force F acting on the cantilever while varying the plate-sphere distance D with subnanometer precision. For D < 50 nm, the force was periodically oscillating and decayed as D was increased. Analyzing the force in the framework of a simple model of elastic deformation of the smectic layers, we have evaluated the undeformed layer thickness a(0) and compressibility modulus B. Compared to other techniques used to determine a(0) and B, AFM measurements are faster and require a much smaller amount (microliters) of LC. Moreover, they are based on purely mechanical deformations of the LC structure and do not require any static or radiative electromagnetic field.

Ultrashort cantilever probes for high-speed atomic force microscopy

Since its invention in 1986, atomic force microscopy (AFM) has become the most widely used scanning-probe imaging technique.1 The microscope ‘maps’ the topography of the sample by scanning its surface with a small tip integrated near the free end of a flexible cantilever. In contrast to other microscope techniques, it is possible to image the surface of many materials—including electrically isolating ones, such as ceramics and glasses—with a resolution in both the vertical and horizontal direction of below 1nm. Figure 1 shows a typical example of an AFM measurement in vacuum, depicting a cerium oxide surface in true atomic resolution. The inherent mechanical characteristics of AFM requires serial acquisition of data, which limits the speed for obtaining high-resolution images. Using commercially available microscopes, a typical image of 256 256 pixels resolution can be obtained in 1–10min. This is significantly slower than the time resolution required, for example, to resolve biological processes such as the movement of motor proteins in cells.2 Enhancing imaging speed demands improved scanner technology and control electronics. Specifically, several limiting factors with respect to the cantilever probe must be addressed to reduce resolution time. First, the measurement bandwidth of the local interaction between the probe tip and sample, as well as the velocity at which the tip moves, must be increased. Additionally, the tip must be able to follow the sample’s topography at greater speed.3 Ideally, cantilever probes will function at resonance frequencies in the megahertz region with low force constants (approximately a few nano-Newtons per nanometer). Here, we report our progress in fabricating cantilever probes for highspeed imaging in AFM.4 Figure 1. Atomic force micrograph of a cerium oxide surface with true atomic resolution, imaged using a conventional atomic force microscope in noncontact mode.

Numerical analysis of the dual actuator load test applied to fracture characterization of bonded joints

The dual actuator load test was numerically analyzed in order to assess its adequacy for fracture characterization of bonded joints under different mixed-mode loading conditions. This test enables asymmetric loading of double cantilever beam specimens, thus providing a large range of mixed-mode combinations. A new data reduction scheme based on specimen compliance, beam theory and crack equivalent concept was proposed to overcome several difficulties inherent to the test. The method assumes that the dual actuator test can be viewed as a combination of the double cantilever beam and end loaded split tests, which are used for pure modes I and II fracture characterization, respectively. A numerical analysis including a cohesive mixed-mode damage model was performed considering different mixed-mode loading conditions to evaluate the test performance. Some conclusions were drawn about the advantages and drawbacks of the test.

Bimorph Cantilevers Actuated by Focused Laser from the Side

The thin and long bimorph cantilever is mechanically responded in motion depending on the position of the heating laser which is focused from the side. The bimorph cantilever was designed in order to detect the heat from a bio cell in liquid. In the calibration process of the cantilever using a focused laser in vacuum and air, we found the quick and interesting responses of bimorph cantilever, which is vibrated and statically deflected due to the position of the local heat source on the cantilever. The deflections of cantilever have been investigated with a developed model. The responses are expressed by the modeled system with heat loss condition into ambient. To define the temperature distributions on the cantilever using a model, the temperature increments at the end of cantilever are successfully estimated to be +20 K in air and +110 K in vacuum with a laser power of 0.17 mW.

Bending of Flexible Joint Driven by Linear Expandable Artificial Muscle

A flexible finger joint is proposed and applied in multi-joint manipulator. The plate-spring composes of a flexible skeleton. The linear expandable elastomeric bellows by air pressure is used as an artificial muscle. Bend angle of the joint is related to air pressure in the bellows. Static model of the joint bend has been created by assuming that the counteracting force from elastic elongation of the bellows is negligible. The problems of pure mechanics and the model have been studied in detail. The numerical solution based on the model is obtained for the case of the large deflection of cantilever beam synchronously acted on cantilever end by a couple in variable scalar along with forces changing in both scalar and direction.

Atomic Force Microscope Pull-off Force Measurements for Insulin in Contact with Acrylonitrile–Butadiene–Styrene and Polypropylene Surfaces at Various Humidities

The interaction of insulin with polymeric coatings, commonly used in devices for insulin storage and administration, is affected by relative humidity (RH). Understanding the effect of RH on adhesion of insulin particles to polymeric surfaces is of particular interest for selecting coating materials and environmental conditions for packaging and storage. A custom humidity control system was constructed for use with the fluid cell cantilever holder for a Nanoscope model II atomic force microscope (AFM). This system was used for controlling the RH with a precision of ±1% over a range of ∼0–100% and for making pull-off force measurements as a function of RH. Pull-off forces were measured between insulin particles attached to the end of an AFM cantilever and acrylonitrile–butadiene–styrene and polypropylene polymers. Two critical transitions indicated by sudden increases in the pull-off force were identified at two RH values. The first transition to higher pull-off force values occurred near 15–25% RH and the second transition occurred near 60 to 65% RH. The increasing adhesion force with increasing RH is mainly attributed to surface roughness effects that facilitate the formation of water bridges between insulin particle and the polymer substrate.

Optimal design of cantilevered elastica for minimum tip deflection under self-weight

The optimal distribution of material to minimize the vertical deflection of the free end of a horizontal cantilever is determined. The beam is only subjected to its own weight. Large deflections ar...

An experimental study on mode I and II fracture toughness of laminates stitched with a one-sided stitching technique

Double cantilever beam (DCB) and end notch flexure (ENF) tests were conducted on laminates stitched using the ITA one-sided technique with two different diameter threads. The DCB results showed the larger diameter produced higher fracture toughness, however, due to the higher stitch loads and variable stitch spacing some rows would break in pairs. This is not preferable for stable crack growth and is a consideration that needs to be taken into account when designing stitch patterns. The ENF tests showed no clear difference in the initial fracture toughness due to the different diameters. At the maximum crack length the larger diameter led to a higher toughness due to the higher residual load and greater saturation length. The cases for with the nap had higher initial fracture toughness, however, the lower residual loads result in lower fracture toughness at higher crack lengths.

Nanoscale Thermal AFM of Polymers: Transient Heat Flow Effects

Thermal transport around the nanoscale contact area between the heated atomic force microscopy (AFM) probe tip and the specimen under investigation is a central issue in scanning thermal microscopy (SThM). Polarized light microscopy and AFM imaging of the temperature-induced crystallization of poly(ethylene terephthalate) (PET) films in the region near the tip were used in this study to unveil the lateral heat transport. The radius of the observed lateral surface isotherm at 133 °C ranged from 2.2 ± 0.5 to 18.7 ± 0.5 μm for tip-polymer interface temperatures between 200 and 300 °C with contact times varying from 20 to 120 s, respectively. In addition, the heat transport into polymer films was assessed by measurements of the thermal expansion of poly(dimethyl siloxane) (PDMS) films with variable thickness on silicon supports. Our data showed that heat transport in the specimen normal (z) direction occurred to depths exceeding 1000 μm using representative non-steady-state SThM conditions (i.e., heating from 40 to 180 °C at a rate of 10 °C s(-1)). On the basis of the experimental results, a 1D steady-state model for heat transport was developed, which shows the temperature profile close to the tip-polymer contact. The model also indicates that ≤1% of the total power generated in the heater area, which is embedded in the cantilever end, is transported into the polymer through the tip-polymer contact interface. Our results complement recent efforts in the evaluation and improvement of existing theoretical models for thermal AFM, as well as advance further developments of SThM for nanoscale thermal materials characterization and/or manipulation via scanning thermal lithography (SThL).

Piezoresistive Microcantilevers From Ultrananocrystalline Diamond

This paper reports on the temperature-dependent electrical resistivity and piezoresistive characteristics of boron-doped ultrananocyrstalline diamond (UNCD) and the fabrication of piezoresistive microcantilevers using boron-doped and undoped UNCD. The devices consist of 1-μm-thick doped UNCD on either 1- or 2-μm-thick undoped UNCD. The electrical resistivity of doped UNCD is 0.1 Ω · cm at room temperature, which is five orders of magnitude smaller than the electrical resistivity of undoped UNCD. Over the temperature range of 25°C-200vC, the doped UNCD has a temperature coefficient of electrical resistance of (-1.4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) per °C. The doped UNCD exhibits a significant piezoresistive effect with a gauge factor of 7.53 ± 0.32 and a piezoresistive coefficient of 8.12 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> Pa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at room temperature. The piezoresistive properties of UNCD are constant over the temperature range of 25°C-200°C. Microcantilevers having a length of 300 μm have a deflection sensitivity of 0.186 mΩ/Ω per micrometer of cantilever end deflection. These measurements of electrical and piezoresistive properties of doped UNCD could aid the design of future diamond microsystems.

Development of a new generation of active AFM tools for applications in liquids

Atomic force microscopy (AFM) is a powerful imaging tool with high-resolution imaging capability. AFM probes consist of a very sharp tip at the end of a silicon cantilever that can respond to surface artefacts to produce an image of the topography or surface features. They are intrinsically passive devices. For imaging soft biological samples, and also for samples in liquid, it is essential to control the AFM tip position, both statically and dynamically, and this is not possible using external actuators mounted on the AFM chip. AFM cantilevers have been fabricated using silicon micromachining to incorporate a piezoelectric thin film actuator for precise control. The piezoelectric thin films have been fully characterized to determine their actuation performance and to characterize the operation of the integrated device. Examples of the spatial and vertical response are presented to illustrate their imaging capability. For operation in a liquid environment, the dynamic behaviour has been modelled and verified experimentally. The optimal drive conditions for the cantilever, along with their dynamic response, including frequency and phase in air and water, are presented.