Lateral Tip Displacement Research Articles

Calibrating lateral displacement sensitivity of AFM by stick-slip on stiff, amorphous surfaces

We calibrate the lateral mode AFM (LFM) by determining the position-sensitive photodetector (PSPD) signal dependency on the lateral tip displacement, which is analogous to the constant-compliance region in normal-force calibration. By stick-slip on stiff, amorphous surfaces (silica or glass), the lateral tip displacement is determined accurately using the feedback loop control of AFM system. The sufficiently high contact stiffness between the Si AFM tip and stiff, amorphous surfaces substantially reduces the error of PSPD signal dependency on the lateral tip displacement. No damage or modification of the AFM probe is involved and only a clean silicon or glass wafer is needed.

The Effects of Structure Thickness, Air Gap Thickness and Silicon Type on the Performance of a Horizontal Electrothermal MEMS Microgripper

The ongoing development of microelectromechanical systems (MEMS) over the past decades has made possible the achievement of high-precision micromanipulation within the micromanufacturing, microassembly and biomedical fields. This paper presents different design variants of a horizontal electrothermally actuated MEMS microgripper that are developed as microsystems to micromanipulate and study the deformability properties of human red blood cells (RBCs). The presented microgripper design variants are all based on the U-shape ‘hot and cold arm’ actuator configuration, and are fabricated using the commercially available Multi-User MEMS Processes (MUMPs®) that are produced by MEMSCAP, Inc. (Durham, NC, USA) and that include both surface micromachined (PolyMUMPs™) and silicon-on-insulator (SOIMUMPs™) MEMS fabrication technologies. The studied microgripper design variants have the same in-plane geometry, with their main differences arising from the thickness of the fabricated structures, the consequent air gap separation between the structure and the substrate surface, as well as the intrinsic nature of the silicon material used. These factors are all inherent characteristics of the specific fabrication technologies used. PolyMUMPs™ utilises polycrystalline silicon structures that are composed of two free-standing, independently stackable structural layers, enabling the user to achieve structure thicknesses of 1.5 μm, 2 μm and 3.5 μm, respectively, whereas SOIMUMPs™ utilises a 25 μm thick single crystal silicon structure having only one free-standing structural layer. The microgripper design variants are presented and compared in this work to investigate the effect of their differences on the temperature distribution and the achieved end-effector displacement. These design variants were analytically studied, as well as numerically modelled using finite element analysis where coupled electrothermomechanical simulations were carried out in CoventorWare® (Version 10, Coventor, Inc., Cary, NC, USA). Experimental results for the microgrippers’ actuation under atmospheric pressure were obtained via optical microscopy studies for the PolyMUMPs™ structures, and they were found to be conforming with the predictions of the analytical and numerical models. The focus of this work is to identify which one of the studied design variants best optimises the microgripper’s electrothermomechanical performance in terms of a sufficient lateral tip displacement, minimum out-of-plane displacement at the arm tips and good heat transfer to limit the temperature at the cell gripping zone, as required for the deformability study of RBCs.

Endpoint Accuracy in Manual Control of a Steerable Needle

PurposeTo study the ability of a human operator to manually correct for errors in the needle insertion path without partial withdrawal of the needle by means of an active, tip-articulated steerable needle. Materials and MethodsThe needle is composed of a 1.32-mm outer-diameter cannula, with a flexure joint near the tip, and a retractable stylet. The bending stiffness of the needle resembles that of a 20-gauge hypodermic needle. The needle functionality was evaluated in manual insertions by steering to predefined targets and a lateral displacement of 20 mm from the straight insertion line. Steering tasks were conducted in 5 directions and 2 tissue simulants under image guidance from a camera. The repeatability in instrument actuations was assessed during 100 mm deep automated insertions with a linear motor. In addition to tip position, tip angles were tracked during the insertions. ResultsThe targeting error (mean absolute error ± standard deviation) during manual steering to 5 different targets in stiff tissue was 0.5 mm ± 1.1. This variability in manual tip placement (1.1 mm) was less than the variability among automated insertions (1.4 mm) in the same tissue type. An increased tissue stiffness resulted in an increased lateral tip displacement. The tip angle was directly controlled by the user interface, and remained unaffected by the tissue stiffness. ConclusionsThis study demonstrates the ability to manually steer needles to predefined target locations under image guidance.

Cantilever-based acoustic velocity sensors

This paper discusses progress made on the design of an acoustic velocity sensor. An analytic model was developed for the frequency response of a slender cantilever rod forced by the pressure gradient and particle velocity associated with an acoustic wave propagating in a fluid. The model, validated with acoustic response measurements in air, was used to design cantilever sensors, which respond predominately to acoustic particle velocity. One such design utilizes a short cantilever formed from a 125 μm silica glass fiber immersed in a viscous fill fluid whose lateral tip displacement is detected using a multi-fiber optical probe. This velocity sensor is predicted to be able to detect fairly low acoustic sound levels in water. Progress has been made in instrumenting a large pool at NRL to allow accurate propagating acoustic wave response measurements in water of these new velocity sensors down to frequencies below 5 Hz. Measurements made in this facility on various cantilever sensors will be presented and discussed. [Work supported by ONR.]

Design of a contact probe with high positioning accuracy for plasmonic lithography

Plasmonic lithography with a contact probe records nano-meter scale features and has high-throughput owing to its capability to scan in contact mode. The probe is commonly based on a micrometer-scale cantilever, which leads to the tip-positioning problem due to force-deflection that induces lateral tip displacement. We propose a geometrically modified probe to achieve high positioning accuracy. Contrary to a conventional cantilever-tip probe, we designed a "circular probe" with arc-shaped arms that hold the tip in the center. The mechanism is based on the "fixed-fixed beam" concept in material mechanics. To confirm its positioning accuracy, we used a finite element method (FEM) to calculate the tip displacement for a circular probe and compared the results with those using a conventional cantilever-tip probe. The probe was designed considering a silicon-based micro-fabrication process. The designed probe has a square outline boundary with a length of 50 µm, four arms, and a pyramidal tip with a height of 5 µm. The ratio of the lateral tip displacement to the vertical deflection was evaluated to indicate the accuracy of the probe. The probe has higher positioning accuracy by a factor of 10(3) and 10 in its approach mode and scan mode, respectively, compared with a cantilever-tip probe. We expect that the probe is suitable for the applications that require high positioning accuracy, such as nanolithography in contact mode and applications based on multiple-probe arrays.

Loading rate effect on lateral force measurements on nanostructured Ti and TiN thin films

Tribological properties of titanium and titanium nitride nanostructured thin films as well as of silicon substrate have been studied. We report on the effect of lateral tip displacement direction and normal force loading mode on lateral force measurements. On hard coatings such as titanium nitride thin films, we show that the tip's scratch direction has almost no effect on lateral force measurements. A completely different behaviour has been observed on titanium films. In this last case, the measured lateral force is very dependent on the scratch direction. Concerning the effect of normal force loading mode, we will show how the loading rate, rather than the sliding speed, is a very important parameter in the case of a ramping normal load. For this purpose we have performed two sets of six scratches, for each sample. Scratch length was fixed to 10 μm in all cases. In the first set, the scratch length and duration were kept constant. In the second one, the scratch duration was tuned in order to achieve a constant value of the normal loading rate ⅆ F z ⅆ t . In this last case, the experimental data leads to a unique curve. This means that during nanoscratch measurements, normal tip displacement is controlled by the normal force loading rate. Consequently, lateral displacement speed ⅆ x ⅆ t must be tuned in order to obtain the required value of ⅆ F z ⅆ t . This behaviour seems to be universal and not related to material hardness and Young modulus.

크랙을 가진 회전 외팔보의 동특성 해석

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The equation of motion is derived by using the Lagrange's equation. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip-displacement and the axial tip-deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration. When the crack depth is constant, the natural frequencies of a rotating cantilever beam are proportional to the rotating angular velocity in the each direction.

이동질량을 가진 유체유동 회전 외팔 파이프의 동특성

In this paper, we studied about the effects of the rotating cantilever pipe conveying fluid with a moving mass. The influences of a rotating angular velocity, the velocity of fluid flow and moving mass on the dynamic behavior of a cantilever pipe have been studied by the numerical method. The equation of motion is derived by using the Lagrange`s equation. The cantilever pipe is modeled by the Euler-Bernoulli beam theory. When the velocity of a moving mass is constant, the lateral tip-displacement of a cantilever pipe is proportional to the moving mass and the angular velocity. In the steady state, the lateral tip-displacement of a cantilever pipe is more sensitive to the velocity of fluid than the angular velocity, and the axial deflection of a cantilever pipe is more sensitive to the effect of a angular velocity. Totally, as the moving mass is increased, the frequency of a cantilever pipe is decreased in steady state.

Material anisotropy revealed by phase contrast in intermittent contact atomic force microscopy.

Phase contrast in intermittent-contact atomic force microscopy (AFM) reveals in-plane structural and mechanical properties of polymer monolayers. This is surprising, because measurements of nanoscale in-plane properties typically require contact mode microscopies. Our measurements are possible because the tip oscillates not just perpendicular but also parallel to the sample surface along the long axis of the cantilever. This lateral tip displacement is virtually universal in AFM, implying that any oscillating-tip AFM technique is sensitive to in-plane material properties.

Lateral displacement microscopy of holograms using scanned tip image pairs

Tip displacements associated with lateral forces between specimen and tip can be quite large (e.g. microns in size) during repulsive force microscopy (SFM or AFM) and air-based scanning tunneling microscopy (STM) of soft samples. Both x and y components of the lateral tip displacement due specifically to drag between the specimen and tip, as separated from tfiose components of the tip's displacement due solely to the geometry of mechanical equilibrium between the tip and a tilted surface, may be inferred from STM or SFM image pairs of the same region taken with the tip traveling in different directions (e.g. with the tip fast scan going left versus up). We refer to this process of inferring displacement from image pairs as displacement mapping. By comparison, absolute measurements of lateral force like those obtained by imaging cantilever twists in Digital Instrument's commercial lateral force microscope: (a) don't remove equilibrium (purely geometric) components of the lateral displacement from the often more interesting friction components, (b) measure the lateral force in only one of the two transverse directions, and (c) require special hardware, not available on conventional STM's for example, to measure transverse deflection.

Comment on "Effect of Higher Order Terms in Certain Nonlinear Finite Element Models"

O et al. conclude that convergence will be slowed if terms which characterize nonlinear behavior are approximated by a simpler polynomial than that used for the conventional stiffness matrix. The present Comment offers numerical evidence pertinent to this theoretical conclusion. The problem chosen is of the type used in Ref. 1. A cantilever beam is modeled by ten elements, and at its free end carries an axial compressive load P and a transverse load Q = 0.001. Properties are chosen such that the Euler buckling load is Pcr = 1.000. The solution method is based on convected coordinates, as clearly detailed for plate problems by Murray and Wilson. Thus the technique is pure Newton-Raphson iteration; under-relaxation, convergence-acceleration schemes, etc., were not used. Iterative cycling at a given load level was terminated by a convergence test on displacements. The next load level was then applied, and iteration begun again, starting with the displacements obtained at the previous load level. The conventional stiffness matrix of each element (in its convected coordinate system) was based on a cubic polynomial. Two forms of 'geometric' or 'initial stress' stiffness matrix were considered. The first, [kGC], was based on the cubic polynomial, and the second, [kGL], was based on a linear polynomial. In other words, with reference to Eqs. (3) of Ref. 1, [kcc] was based upon the lateral displacement v(x) = (x) and [kGL] upon v(x) = ^O)v. Let d/L be the ratio of lateral tip displacement to beam length. With P = 0.99, d/L converged to 0.0606 in 9 cycles when [kGL] was used, and to 0.0701 in 15 cycles when [kGC] was used. With the geometric stiffness matrix omitted altogether, d/L reached 0.0257 at 40 cycles but had not converged. The correct result is d/L = 0.0811, which is some 100 times the value produced by lateral load Q acting alone. Table 1 lists tip rotations obtained by progressive increases in load level, with a milder convergence tolerance than used in the preceding paragraph.