Probe Shape Research Articles

Scanning probe-based frequency-dependent microrheology of polymer gels and biological cells.

A new scanning probe-based microrheology approach is used to quantify the frequency-dependent viscoelastic behavior of both fibroblast cells and polymer gels. The scanning probe shape was modified using polystyrene beads for a defined surface area nondestructively deforming the sample. An extended Hertz model is introduced to measure the frequency-dependent storage and loss moduli even for thin cell samples. Control measurements of the polyacrylamide gels compare well with conventional rheological data. The cells show a viscoelastic signature similar to in vitro actin gels.

Improved tip performance for scanning near-field optical microscopy by the attachment of a single gold nanoparticle

Nanometer-size optical probes are gaining increasing interest in near-field optical microscopy. Optimization of the probe shape is still a challenging research and development issue. Here, we propose to improve the optical properties of a fiber-based probe by attachment at the tip apex of one single gold particle of 60 nm diameter. This probe produces an enhancement of the light throughput, both in the near and the far fields, a homogenization of the diffracted light polarization, and a higher accuracy of the topographic sensitivity. In this letter, the chemical procedure for the fixation of one single gold particle on the apex of a standard tip for scanning near-field microscopy is described. Far-field as well as near-field measurements with this probe are performed, showing improvement of the light distribution in excellent agreement with the theory.

Silicon-based microelectrodes for neurophysiology, micromachined from silicon-on-insulator wafers.

A process is described for the fabrication of silicon-based microelectrodes for neurophysiology using bonded and etched-back silicon-on-insulator (BESOI) wafers. The probe shapes are defined without high levels of boron doping in the silicon; this is considered as a step towards producing probes with active electronics integrated directly beneath the electrodes. Gold electrodes, of 4 microns by 4 microns to 50 microns by 50 microns are fabricated on shanks (cantilever beams) 6 microns thick and which taper to an area approximately 100 microns wide and 200 microns long, which are inserted into the tissue under investigation. The passive probes fabricated have been successfully employed to make acute recordings from locust peripheral nerve.

Stress intensity in viscoelastic contacts

Dynamic mechanical contacts with nanometer-to-micrometer dimensions are important in scanned probe microscopy, ultra-low load indentation, microelectromechanical systems, compact discs, etc. The response of these contacts is poorly understood if they involve adhesive viscoelastic materials, such as polymers and self-assembled monolayers. We have studied dynamic contacts to styrene–butadiene latex films. Plots of load vs. displacement show substantial adhesion hysteresis between the loading and unloading portions. The hysteresis is at least partially due to creep, as indicated by the continued increase in penetration after the start of unloading. Thermodynamic works of adhesion were estimated from fits to the loading–unloading data obtained at small loading and unloading rates. Theoretical models that include adhesion but neglect long-range creep effects could not fit the data at all loading rates. Creep tests were carried out under constant load. A model due to Hui, Baney, and Kramer (HBK), which predicts the response of an adhesive viscoelastic contact under increasing load, was used to extract a mode I stress-intensity functional from the data. When this functional is normalized by the square root of the displacement rate, it is shown empirically, to have a simple, nearly universal time-dependence. Variations of this universal form due to load, range of interaction potential, glass transition temperature, and probe shape are weak. This result supports the suggestion of HBK that the stress-intensity functional provides a useful way to characterize adhesive contacts to viscoelastic materials.

Towards sub-Å electron beams

The prospects for reaching sub-Å electron probes through aberration correction in the scanning transmission electron microscope (STEM) are evaluated. The design, results and practical experience gained from a working 100 keV STEM C S corrector are presented and discussed. The design of a second-generation quadrupole–octupole C S corrector that pays particular attention to the influence of instabilities is outlined. Probe shapes calculated for the new corrector indicate that it will be able to produce a probe smaller than 1 Å at 100 keV.

Detection of vibration transmitted through an object grasped in the hand.

A tool or probe often functions as an extension of the hand, transmitting vibrations to the hand to produce a percept of the object contacting the tool or probe. This paper reports the psychophysical results of a combined psychophysical and neurophysiological study of the perception of vibration transmitted through a cylinder grasped in the hand. In the first part of the psychophysical study, 19 subjects grasped a cylinder, 32 mm diam, with an embedded motor that caused vibration parallel to the axis of the cylinder. The relationship between threshold and frequency was the traditional U-shaped function with a minimum between 150 and 200 Hz. Except a study by Békésy in which subjects grasped a rod that vibrated parallel to the skin surface, thresholds above 20 Hz were lower and the slopes were steeper than any reported previously. Thresholds were <0.01 microm in some subjects. Data from both the psychophysical and the neurophysiological studies suggest that detection performance at frequencies >20 Hz was based on activity in Pacinian afferents. The extreme sensitivity compared with previous reports may have resulted from differences in contact area, direction of vibration, contact force, and the shape of the stimulus probe. The effects of each of these variables were studied. At 40 and 300 Hz (frequencies near the lower and upper end of the Pacinian range) thresholds were 9.8 and 18.5 dB (68 and 88%) lower, respectively, when subjects grasped the cylinder than when a 1-mm-diam probe vibrated perpendicular to the skin. These differences were accounted for as follows: 1) thresholds at a single fingerpad obtained with the large cylindrical surface were, on average, 20 and 60% lower, respectively, than thresholds with the punctate probe; 2) thresholds at the palm were, on average, 15 and 40% lower, respectively, than at the fingerpads; 3) thresholds obtained when the subjects grasped the cylinder averaged 40 and 20% less, respectively, than when the cylinder contacted only the palm; 4) thresholds with the cylinder contacting two fingers were 10 and 30% lower, respectively, than thresholds with the cylinder contacting a single finger; and 5) thresholds with vibration parallel to the skin surface were, on average, 10 and 30% lower, respectively, than thresholds with vibration perpendicular to the skin. Contact force, which was varied from 0.05 to 1.0 N, had no effect.

Probe translational and rotational diffusion in polymers near Tg: roles of probe size, shape, and secondary bonding in deviations from Debye–Stokes–Einstein scaling

Rotational and translational dynamics of a variety of probes are compared in several polymers near the glass transition temperature, T g. Second harmonic generation was used to measure the rotational relaxation distribution and average rotational relaxation time, 〈 τ〉, and fluorescence nonradiative energy transfer was used to measure D trans, the translational diffusion coefficient. D trans is affected greatly by probe size and shape, typically with a temperature dependence in the rubbery state near T g which violates Debye–Stokes–Einstein (DSE) scaling and an apparent enhancement in translational diffusion; in contrast, 〈 τ〉 is largely unaffected by probe size and shape (for the ranges studied), as long as the probe is sufficiently bulky to have its dynamics coupled to the polymer α-relaxation, and follows DSE scaling. These effects are associated with the short-time side of the distribution of reorientation relaxation times being sensitive to probe size and aspect ratio and the fact that D trans is dominated by short-time relaxations while 〈 τ〉 is dominated by long-time relaxations. With hydrogen bonding between probe and polymer, both D trans and 〈 τ〉 may be affected.

Scanning thermal microscopy using batch fabricated thermocouple probes

We have developed scanning thermal microscopy probes for high resolution analysis of thermal properties in an atomic force microscope (AFM). Electron beam lithography and silicon micromachining have been used to batch fabricate Au/Pd thermocouples situated at the end of Si3N4 cantilevers. The cantilevers are patterned on the side of traditional style pyramidal AFM tips, giving a new shape of probe which is favorable for access to specimens containing significant topographic variation. Tip radius is approximately 50 nm and the probe has a macroscopic opening angle of 70°. The probes were scanned in the repulsive mode using a conventional AFM. Force feedback was optically employed to give topographic and thermal maps simultaneously by maintaining a constant force of approximately 5 nN. During initial scans using a photothermal test specimen, 80 nm period metal gratings were thermally resolved.

Inversion scheme based on optimization for 3-D eddy current flaw reconstruction problems

An inversion scheme based on first-order optimization is developed for eddy current flaw reconstruction problems with arbitrary specimen, probe and defect shapes. As an essential component of this scheme, a new 3-D forward solver is introduced for the purpose of rapid flaw signal prediction in the inversion loop. This forward solver, whose numerical formulation is basically a discrete reaction variational technique, relies on a reaction data set in the form of an equation system, constructed before entering the inversion loop by a finite element electromagnetic field simulator. The anomalous region is subdivided into small subregions, called flaw cells, and a flaw is represented by a complete set of current dipole density pulses defined in these flaw cells. The coefficient matrix of the equation system consists of reactions between the dipole current density pulses while the elements of the right-hand-side vector are reactions between the pulses and the probe coils. The gradient of the error function, which represents the sensitivity with respect to the flaw parameters, can also be computed quickly from the same pre-calculated reaction dataset, thereby ensuring the efficient implementation of a first-order optimization algorithm. In order to avoid being trapped in a local minimum of the error function, good initial flaw estimates are generated by a neural network signal processing system developed recently by the authors. Various reconstruction examples demonstrate the efficiency of the reconstruction system.

Ultrasound probe having interchangeable accessories

In the present invention, an intraoperative ultrasound transducer probe, or intraoperative probe, has a housing, to which, interchangeable accessories may be attached. The interchangeable accessories adapt the intraoperative probe's shape to provide access to a patient's body parts in confined spaces in intraoperative environments. In one embodiment of the present invention a first interchangeable accessory has an extension handle that may be attached to the intraoperative probe to enable an operator to reach into surgical incisions and view the patient's body parts. In an alternate embodiment of the present invention a second interchangeable accessory has a finger cuff for attaching the intraoperative probe to an operator's finger. The finger cuff may be used in place of the extension handle, providing access to a patient's body parts in confined spaces, such as the posterior side of the heart for epicardial imaging during open heart surgery. Since the interchangeable accessories are separable from the intraoperative probe, they are easily sterilized and may be disposed of after use. The interchangeable accessories used to adapt the intraoperative probe's shape have low manufacturing cost relative to the cost of multiple dedicated probes, reducing the overall cost of an ultrasound imaging system.

Fast flaw reconstruction from 3D eddy current data

An eddy current flaw reconstruction strategy based on the minimization of nonlinear least-squares error functionals is developed for problems with arbitrary specimen, probe and defect shapes. A fast 3D forward solver is created to rapidly predict eddy current signals in the inversion shell. The high speed of the signal evaluation comes by utilizing a reaction data set constructed before performing the inversion by a finite element electromagnetic field simulator. The same pre-calculated reaction data set supports the quick evaluation of sensitivity information, thereby ensuring the efficient implementation of an optimization algorithm. This optimization algorithm combines first-order and stochastic optimization strategies and improves the reliability of the reconstruction significantly if the observed data contain large noise components. Examples with tube specimens are presented for different 3D flaw shapes.

Light transmission, linear dichroism and birefringence of nematic/polymer dispersions

A theoretical study of light transmission, linear dichroism and birefringence of partially ordered dispersions of bipolar nematic droplets in a polymer matrix is presented. The treatment rests on the single scattering approach to an ensemble of uncorrelated and noninteracting anisotropic particles. Theoretical evaluations of the extinction cross sections and phase functions are performed in the anomalous diffraction approximation. Four basic model systems are analysed: PDLC and NCAP films in an external electric field, and PDLC and NCAP films under uniaxial mechanical deformation. The calculated dependences of the generalized parameters characterizing the light transmission, dichroism and birefringence on the angle of incidence of the probing light, droplet size and shape, refractive indices of the LC and polymer, and parameters of the external field are presented graphically and discussed in detail.

Near-field optical study of semiconductor photonic devices

A novel-structured semiconductor photonic device is investigated using a near-field scanning optical microscope. By tailoring the shape of the fiber probe, high transmission and collection efficiencies are successfully achieved. Employing optimized fiber tips, multi-diagnostics of lateral p-n junctions is performed with the AFM operation. Measuring the spatially resolved photolumines-cence spectra, we precisely examine the carrier distribution in the transition region of the p-n junctions. Electroluminescence imaging reveals the width and the position of the active region. The slant angle of the p-n interface is determined by applying the multiwavelength near-field photocurrent measurement. We also clarify the mechanism of the mode conversion due to the interaction between the evanescent light on a small aperture and optically dense semiconductors

Examination of Atomic (Scanning) Force Microscopy Probe Tips with the Transmission Electron Microscope

Abstract: We have developed a method for the examination of atomic force microscopy (scanning force microscopy) tips using a high-resolution transmission electron microscope (TEM). The tips can be imaged in a nondestructive way, enabling one to observe the shape of an atomic force microscope probe in the vicinity of the apex with high resolution. We have obtained images of atomic force microscopy probes with a resolution on the order of 1 nm. The tips can be imaged repeatedly, so one can examine tips before and after use. We have found that the tip can become blunted with use, the rate of wear depending upon the sample and tip materials and the scanning conditions. We have also found that the tips easily accrue contamination. We have studied both commercially produced tips, as well as tips grown by electron beam deposition. Direct imaging in the TEM should prove useful for image deconvolution methods because one does not have to make any assumptions concerning the general shape of the tip profile.

Characterization of the PPO dense membrane prepared at different temperatures by ESR, atomic force microscope and gas permeation

Dense (homogeneous) membranes were prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by using 1,1,2-trichloroethylene as a solvent at different solvent evaporation temperatures (22,4 and −10°C). The effect of temperature used during evaporation of solvent on the characteristics of the membrane was studied by using electron spin resonance, atomic force microscopy and gas permeation rate. The morphology of the surfaces of the membrane, the shape of spin probe in the membrane, and the selectivity of gases depend on the temperature of evaporation of solvent. The permeation rate of CO 2 increased with the decrease in the temperature used for the preparation of the membrane. However methane permeation rate increased in the membrane prepared at −10°C. It is suggested that Langmuir sites could be favorable for the CH 4 permeation.

Small molecule diffusion in a rubbery polymer near Tg: Effects of probe size, shape, and flexibility

Small molecule diffusion in a rubbery polymer near Tg: Effects of probe size, shape, and flexibility

Small molecule diffusion in a rubbery polymer nearTg: Effects of probe size, shape, and flexibility

A novel experimental approach involving fluorescence nonradiative energy transfer (NRET) is employed to study the Fickian diffusion of small molecules in rubbery poly(isobutyl methacrylate) (PiBMA) films near the glass transition, using a formalism that directly relates the small molecule translational diffusion coefficient, D, to changes in the normalized nonradiative energy transfer efficiency, EN. Values of D for pyrene, 1,3-bis-(1-pyrene) propane (BPP), 1,3-bis-(1-pyrene) decane (BPD), 9,10-bis-phenyl ethynyl anthracene (BPEA), diphenyl Disperse Red 4 (DPDR4), and decacyclene in PiBMA are measured over temperatures ranging from approximately Tg to Tg + 25°C. Among these chromophores, significant differences in both the magnitude and temperature dependence of D are observed which are attributed to differences in molecule shape and flexibility, as well as molar volume. Other factors being equal, chromophore flexibility was shown both to increase the magnitude of D and to decrease its dependence on temperature, as does an increase in aspect ratio. For BPD, these effects are attributed to the ability of the flexible molecule to diffuse in a piecewise manner, requiring the cooperative mobility of fewer polymer chain segments than a rigid molecule of the same molar volume. For BPEA and DPDR4, this deviation from D being dominated by molar volume effects is attributed the to high aspect ratio of these elongated molecules. © 1996 John Wiley & Sons, Inc.

Edge-Assignment and Figure–Ground Segmentation in Short-Term Visual Matching

Eight experiments examined the role of edge-assignment in a contour matching task. Subjects judged whether the jagged vertical edge of a probe shape matched the jagged edge that divided two adjoining shapes in an immediately preceding figure–ground display. Segmentation factors biased assignment of this dividing edge toward a figural shape on just one of its sides. Subjects were faster and more accurate at matching when the probe edge had a corresponding assignment. The rapid emergence of this effect provides an on-line analog of the long-term memory advantage for figures over grounds which Rubin (1915/1958) reported. The present on-line advantage was found when figures were defined by relative contrast and size, or by symmetry, and could not be explained solely by the automatic drawing of attention toward the location of the figural region. However, deliberate attention to one region of an otherwise ambiguous figure–ground display did produce the advantage. We propose that one-sided assignment of dividing edges may be obligatory in vision.

Silicon structures for in situ characterization of atomic force microscope probe geometry

Atomic force microscopy (AFM) is increasingly relied on to image and measure micron and submicron scale surface features. Consistent interpretation of AFM information is, however, difficult if the geometry of the probe is not known. In this work, the fabrication of funnel-like structures and their use in probe characterization were developed from a proof of concept to readiness for field testing. The specifications that determine the structure’s sensitivity to probe shape were identified. The fabrication was tailored to yield large reproducible arrays (&amp;gt;100×100 structure). The geometry of the structures was characterized using low voltage scanning electron microscopy (SEM) techniques. Testing in intermittent contact mode has shown that the structures are stable even at high forces for multiple scans under various conditions. An algorithm was developed that calculates the probe geometry from an image of the structure. The sensitivity of the structures to probe shape was tested by comparing SEM images of probe shape to the probe geometry calculated from the AFM images of the structures. From this analysis it was determined that the structures are sensitive to the cone angle of the probe to within 5° and to the probe radius to within 50 nm.

Simulation of geometrical aberration and beam shape of scanning X-ray probe

The scanning X-ray probe has been investigated for application to small area X-ray photoelectron spectroscopy (XPS). The aberration due to the ellipsoidal shape of the diffractor has been calculated as a function of position in the image plane. We find the magnitude of this aberration goes linearly with the diffractor size and the distance from the optical axis. It also depends on the tilt angles for the source and image planes. A practical scanning ESCA microprobe is, therefore, a compromise between sensitivity (diffractor area) and spatial resolution. We chose a geometry that makes the ellipsoid aberration comparable in magnitude to the source size and the crystal aberration over a 250 μm scan field. Experimentally, we find that the X-ray beam is under 10 μm at the center of the scan field. The experimental result is compared with the simulation and some of the influencing factors to experimental result are discussed in detail.