Meniscus Force Research Articles

Adhesion models: From single to multiple asperity contacts

This review presents a summary of the current adhesion models available to date, between real rough surfaces, starting from single asperity models and expanding to multiple asperity contacts. The focus is made on multi-asperity contact interactions. Both van der Waals and contact mechanics approaches have been considered and relevant adhesion models are reviewed and discussed. The influence of the meniscus forces on adhesion has been considered, along with a summary of the various meniscus models. The effect of surface geometry, its topography and environmental conditions on meniscus action are also discussed along with its integration into multi-asperity adhesion models.

Ageing effect of plasma‐treated wool

Atmospheric pressure plasma treatment of wool fabric, with a relatively short exposure time, effectively removed the covalently bonded lipid layer from the wool surface. The plasma‐treated fabric showed increased wettability and the fibres showed greater roughness. X‐ray photoelectron spectroscopy (XPS) analysis showed a much more hydrophilic surface with significant increases in oxygen and nitrogen concentrations and a decrease in carbon concentration. Adhesion, as measured by scanning probe microscopy (SPM) force volume analysis, also increased, consistent with the more hydrophilic surface leading to a greater meniscus force on the SPM probe. The ageing of fibres from the plasma‐treated fabric was assessed over a period of 28 days. While no physical changes were observed, the chemical nature of the surface changed significantly. XPS showed a decrease in the hydrophilic nature of the surface with time, consistent with the measured decrease in wettability. This change is proposed to be due to the reorientation of proteolipid chains. SPM adhesion studies also showed the surface to be changing with time. After ageing for 28 days, the plasma‐treated surface was relatively stable and still dramatically different from the untreated fibre, suggesting that the oxidation of the surface and modification or removal of the lipid layer were permanent.

Meniscus and Viscous Forces during the Nanoscale Separation of Sphere-on-Sphere Contact Surfaces

When two surfaces are brought into contact or at small separations, the liquid between them forms meniscus, which contributes to adhesion and friction. The increased adhesive force and friction are always the substantial cause leading to micro/nanodevices’s failure. In this study, a dynamic contact model of sphere-on-sphere surfaces during nanoscale separation is presented. A numerical analysis of meniscus and viscous forces based on the dynamic contact model has been carried out. During the separation process, the effects of separation distance, initial meniscus height, surface wettability and separating time on meniscus and viscous forces between the contact surfaces are investigated. The results of numerical solution revealed the adhesion mechanism of sphere-on-sphere surfaces during the separation with liquid mediated. The analyses provide a fundamental understanding of the separating process of two sphere surfaces. It is also useful for the design of the de-wetting and antisticking micro/nanoscale surfaces in various devices.

Effect of Ultraviolet Irradiation on Adhesion of Nanometer-Thick Lubricant Films Coated on Magnetic Disk Surfaces

By measuring force-distance curves with an environmental scanning probe microscope (SPM), we quantitatively evaluated the effect of ultraviolet (UV) irradiation on the adhesive properties of nanometer-thick perfluoropolyether (PFPE) Z03 films coated on magnetic disks. The experimental results indicated that UV irradiation shows negligible influence on the adhesion of the disk surface and on the adhesion of the mobile fraction contained in the UV-irradiated Z03 films. The effect of UV irradiation on the adhesion of Z03 films is essentially achieved by its effect that improves the bonding of the Z03 molecules to the disk surfaces. As the bonding ratio increased with UV irradiation, the adhesive force measured on the 2-nm-thick PFPE Z03 films initially decreased, but it increased after reaching a minimum at a bonding ratio of about 0.6. This is possibly attributed to the increase of the meniscus force caused by decreased mobile lubricant thickness and the decrease of the van der Waals force between the SPM probe and the sample surfaces caused by increased bonded lubricant thickness.

Feedback-induced instability in tapping mode atomic force microscopy: theory and experiment

We investigate a mathematical model of tapping mode atomic force microscopy (AFM), which includes surface interaction via both van der Waals and meniscus forces. We also take particular care to include a realistic representation of the integral control inherent to the real microscope. Varying driving amplitude, amplitude setpoint and driving frequency independently shows that the model can capture the qualitative features observed in AFM experiments on a flat sample and a calibration grid. In particular, the model predicts the onset of an instability, even on a flat sample, in which a large-amplitude beating-type motion is observed. Experimental results confirm this onset and also confirm the qualitative features of the dynamics suggested by the simulations. The simulations also suggest the mechanism behind the beating effect; that the control loop over-compensates for sufficiently high gains. The mathematical model is also used to offer recommendations on the effective use of AFMs in order to avoid unwanted artefacts.

Characterization of carbon nanotube nanoswitches with gigahertz resonance frequency and low pull-in voltages using electrostatic force microscopy

An electrostatic force microscope (EFM) was used to characterize single-walled carbon nanotube (SWNT)-based nanoswitches in this paper. A conductive atomic force microscopy (AFM) tip acted as a mechanical probe as well as a positioning electrode in the experiment. The resonance frequency of the SWNT beams was computed from the measured SWNTs’ dimension and spring constant. The pull-in voltages and the corresponding gaps were extracted simultaneously from a set of force curves at different EFM probe bias voltages. The adhesive force between the AFM tip and the SWNT beam was measured through the analysis of retract force curves. The relationship between the pull-in voltage and the SWNT nanoswitch gap was in agreement with the electrostatic pull-in theory. Long-range forces such as meniscus force or electrostatic force from surface charges engaged the SWNT beam when the gap was below 6 nm in atmosphere. The SWNT beam with a resonance frequency of 1.1 GHz was actuated by a voltage of 2 V for a gap of 6.5 nm. The average adhesive force between an SWNT beam and a platinum/iridium (PtIr5)-coated tip was found to be about 50 nN. Considering the stiffness of the 1.1 GHz SWNT beam, the elastic restoring force at 6.5 nm exceeds 53 nN, which will overcome the adhesive force and release the 1.1 GHz SWNT beam. Finally, some possible approaches to further improve the behavior of SWNT nanoswitches are discussed.

Lateral capillary forces of cylindrical fluid menisci: a comprehensive quasi-static study

Capillarity is pivotal to many important technologies, including capillary self-alignment and self-assembly for heterogeneous microsystem integration and packaging. Lateral capillary forces ensuing from perturbed fluid menisci were the object of substantial theoretical and numerical modeling in recent years. Anyway, those studies were so far unsatisfactorily supported by direct experimental inspections. In this paper we present a comprehensive quasi-static study of lateral capillary forces arising from a constrained cylindrical fluid meniscus subjected to small lateral perturbations. We describe the novel experimental apparatus that we designed to accurately characterize such a fundamental system. We then reproduce our experimental data on lateral meniscus forces and stiffnesses by means of both a finite element and a novel analytical model. The agreement between our measurements and models, while confirming earlier reports, provides a solid foundation for the applications of lateral capillary forces to microsystem assembly. Moreover, our experimental apparatus may enable the exploitation of Gibbs’ inequality to measure the advancing contact angles of liquids, and it may be used as a reference testbed for further experimental investigations on constrained fluid menisci.

Calculation of meniscus force during separation of microsurfaces

The adhesive force between microsurfaces is very important to microelectric mechanical system (MEMS), being always a key factor that detemines the energy dissipation and even the life span. In MEMS, the meniscus force mainly depends on the meniscus shape formed between the contact surfaces. This paper analyzes the meniscus shape changes during the seperation of two microsurfaces. Different meniscus shapes were obtained as a result of different hydrophilic/hydrophobic properties, initial liquid heights and separate distances and so on. The fracture height, the meniscus force value and their change rules in different initial conditions are obtained by numerical simulation, which provides a basis of the MEMS performance analysis and life span calculation.

MNM-P4-3 付着力の熱的制御を用いたマイクロマニピュレーション(P4 ナノ・マイクロ異相界面センシングと制御)

The objective of this study is the development of meniscus tip thermally controlling mainly the meniscus force which is one of the adhesion forces. The meniscus tip, having small heater on water-filled capillary tube, can control the meniscus force through varying wet state of the tip by supplying or drying water. To evaluate the adhesion characteristics, the measurement of adhesion force between the tip surface and the micro object was conducted and the reduction of adhesion force of 10 μN was indicated by its measurement in the heating rate of 0.9 W. Moreover, it was confirmed by the observation of the tip surface during heating that the increase of adhesion force at 0.25 W in the result of adhesion force measurement was caused by the seeping of the inner liquid. Additionally, the micromanipulation of the glass beads of 100 μm diameter was demonstrated.

Numerical Analysis of Contact Mechanics between a Spherical Slider and a Flat Disk with Low Roughness Considering Lennard–Jones Surface Forces

Although analytical and numerical analyses of the contact mechanics of a completely smooth sphere–flat contact have been done, the analysis of a realistic sphere–flat contact with a surface roughness whose mean height planes have a spacing greater than the atomic equilibrium distance has not been done thoroughly. This paper is a fundamental study of the elastic contact mechanics due to Lennard–Jones (LJ) intermolecular surface forces between a spherical slider and a flat disk with low roughness whose height is larger than equilibrium distance z 0. First, neglecting the effect of the attractive force at contacting asperities, adhesion contact characteristics of a 2-mm-radius glass slider with a magnetic disk are presented in relation to the asperity spacing σ between mean height planes. Results showed that the contact behavior at a small asperity spacing of ∼0.5 nm cannot be predicted either by the Johnson–Kendall–Roberts or Derjaguin–Muller– Toporov theories. Second, contact characteristics of a 1-μm-radius sphere on a flat disk are presented to examine how LJ attractive force at contacting asperities can be evaluated. It was found that the adhesion force of contacting asperity is a function of separation in general, but it becomes almost constant when σ = ∼z 0. A simple equation to evaluate the LJ attractive pressure of contacting asperities is presented for the rough contact analysis. Third, numerical calculation methods for a sphere–flat contact including LJ attractive forces between the mating mean height planes and contacting asperities are presented. Then, adhesion characteristics of a 2-mm-radius glass slider and magnetic disk are calculated and compared with the previous experimental results of dynamic contact test. It is shown that the calculated LJ adhesion force is much smaller than the experimental adhesion force, justifying that the adhesion force observed at the separation of contact is caused by meniscus force rather than by vdW force.

Analysis of the meniscus and viscous effects in digital micromirror device

Digital micromirror device (DMD) is the core of digital light processing projected display technology wherein the spring tip-landing site adhesion and wear are the substantial clause leading to failure due to frequent contacts. In an attempt to analyze the adhesive force between the spring tip and the landing site, two main aspects are considered: i.e. the meniscus force and the viscous resistance during separation. The simulation results show that the influences of the surface energy, liquid volume and the separate velocity are prominent. The work will provide some hints for control of adhesive force in DMD components.

A high‐throughput method for controlled hot‐spot fabrication in SERS‐active gold nanoparticle dimer arrays

AbstractWe present a high‐throughput method for fabricating large arrays of surface‐enhanced Raman scattering (SERS) active gold dimers. Using a large‐area/low‐cost nanopatterning method in conjunction with a meniscus force deposition technique, we were able to create large arrays of uniformly spaced nanoclusters comprising two 60‐nm gold nanospheres. Raman measurements of a thiophenol monolayer deposited on smaller scale arrays of aligned dimers yielded enhancement factors as high as 109. Polarization‐controlled measurements show spectral peak heights to be 10–100 times smaller when the incident beam is polarized perpendicularly to the dimer axis, confirming that the measured enhancements arise from the ‘hot spots’ between the two nanospheres. Copyright © 2009 John Wiley & Sons, Ltd.

Analysis of liquid mediated friction during alignment in large area UV imprint lithography

Stiction in large area imprint lithography was studied by a microtribological approach. As imprinting area is expanded, fine aligning movement can be hindered by the adhesion or in-plane friction between the mold and the substrate. In this study, an analytical model for stiction force in the alignment process was proposed and evaluated by measuring the friction force between two plates mediated by a thin liquid film. Experimental verification was conducted for various geometries and surface conditions. Analytic and experimental results demonstrated that the meniscus force induced from surface tension was the most critical parameter affecting stiction in an alignment process.

Surface energy approach and AFM verification of the (CF)n treated surface effect and its correlation with adhesion reduction in microvalves

The purpose of this paper is to outline an approach that will determine the optimal surface pairs to use in a MEMS device with demonstrated stiction problems. The approach uses the contact angle and atomic force microscopy (AFM) pull-off measurements to predict adhesion at the solid–solid interface. The results are compared to microvalves that have been fabricated with different surfaces at the seat/membrane interface. For microfabricated mechanical devices with surfaces that touch or have a small gap distance, stiction can occur during fabrication or during use. Fabricating multiple devices with different surfaces to determine the lowest stiction can be costly and time consuming. Identifying the surface pair with the least amount of surface adhesion before fabrication can lead to a reduction in device failure due to stiction, and/or time it takes to find the lowest energy surfaces via trial and error. Surface energies are obtained using the van Oss equation based on the contact angle measurements, and surface energy can be used to show the relative adhesions between two surface pairs. An AFM pull-off test is performed using nano- and micro-sized tips to quantify the effect of the different surfaces on adhesion between the solid–solid surface pairs, including SiO2/PI, CFn/PI, CFn/SiO2 and CFn/CFn. The work of adhesion of the surface pairs is obtained using the Derjaguin–Muller–Toporotov (DMT) and Johnson–Kendall–Roberts (JKR) theories. The surfaces treated with a C4F8/Ar plasma to form a CFn coating showed the least amount of surface adhesion. The CFn surface treatment effects on adhesion are quantified and correlated with the reduction in the opening pressure of the microvalve whose interfaces are coated with a CFn film. The AFM pull-off test was more closely related to adhesive forces between the surfaces of the valves as seen in the opening pressure data. The adhesion calculation based on the contact angle measurements predicts the adhesion force with a similar trend but does not take into account the meniscus forces.

Lubricant Depletion and Disk-to-Head Lubricant Transfer at the Head-Disk Interface in Hard Disk Drives

As the head-disk spacing reduces in order to achieve the areal density goal of 1 Tb/in.2, the dynamic stability of the slider is compromised due to a variety of proximity interactions. Lubricant pickup by the slider from the disk is one of the major reasons for the decrease in the stability as it contributes to meniscus forces and contamination. Disk-to-head lubricant transfer leads to lubricant pickup on the slider and also causes depletion of lubricant on the disk. In this paper, we experimentally and numerically investigate the process of disk-to-head lubricant transfer using a half-delubed disk, and we propose a parametric model based on the experimental results. We also investigate the dependence of disk-to-head lubricant transfer on the disk lubricant thickness, lubricant type, and the slider air bearing surface (ABS) design. It is concluded that disk-to-head lubricant transfer occurs without slider-disk contact and there can be more than one timescale associated with the transfer. Furthermore, the transfer increases nonlinearly with increasing disk lubricant thickness. Also, it is seen that the transfer depends on the type of lubricant used and is less for Ztetraol than for Zdol. The slider ABS design also plays an important role, and a few suggestions are made to improve the ABS design for better lubricant performance.

Dynamics of liquid meniscus bridge of a vibrating disk: consideration of flow rheology

A modified Reynolds equation, which includes the effect of flow rheology, is derived to describe the flow behaviour of lubricant between the space of a magnetic head slider and a disk. Under the assumptions of a small vibration of the spacing, and zero contact angle of the liquid–solid interface, the dynamics of a liquid meniscus disk of finite radius is analysed. The time-dependent modified Reynolds equation is linearised, and solved, under the boundary condition considering Laplace pressure. The results show that the pressure and load carrying capacity consist of three terms, that is, the static meniscus force term, the spring term by the dynamic Laplace pressure, and time-dependent damping term by the flow rheology of the fluid. The flow rheology affects the static meniscus forces and the damping forces significantly as compared to the spring forces. The effects of flow rheology on the load carrying capacity are also discussed.

M5-6 マイクロマニピュレータ用メニスカスチップの研究(M5 アクチュエータ/フィジカルセンサ)

With a miniaturization of mechanical parts and devices in the engineering, the manipulation of them becomes more difficult. The change of the object scale from macro to micro requires new micromanipulation technology, fitting to micro physics. In the micromanipulation, the release action of a micro object is more difficult than the pick-up action because of the adhesion force larger than gravitational force. In this study, we focus the meniscus force which is important for the adhesion phenomenon in the micro scale. The purpose of this study is development of the manipulator tip which enables to control adhesion and detachment of the micro object by the control of the meniscus force. Two types of the tip were developed with thin glass pipe. Those Meniscus tip can control dry and wet states of the tip with heating near the tip. The ability of the thermal wetting control was confirmed by adhesion test.

Effect of van der Waals Forces in a Near Contact Head-Disk Interface

The minimum flying height, elastic deformation, and attractive pressure caused by van der Waals force under static air-bearing pressure were analyzed numerically using a spherical pad slider and a flat disk model. Parametric analysis revealed that when the pad radius of curvature was 20 mm, the minimum possible flying height was about 1 nm. The smallest roughness height, for reducing the van der Waals attractive force to less than the meniscus force, is ~ 0.5 nm.

Drag Reduction by Dimples on Surfaces in Plane–Plane Contact Lubrication

An experimental system was designed to evaluate the drag reduction by dimples on surfaces in plane–plane contact lubrication. Because of the dimples on the surfaces, in some of the experiments, it was observed that stable gas bubbles existed in the lubricant film. The results of the experiments showed that the existence of gas was decided by the depth of dimples and the volume of lubricant supply; the deeper the dimples were and the less the lubricant supply, the higher the probability of gas existence. The reason for the existence of gas, based on a model analysis, was the meniscus force of the gas–liquid interface, which caused the gas to be enclosed in the dimples. When a small amount of lubricant was supplied, the friction force was reduced because of a mixed lubrication film of oil and gas. For different amounts of lubricant supply, an optimal depth of dimples existed in plane–plane contact lubrication, which could obviously reduce the friction force. An optimization model for full film lubrication was presented to determine the optimal depth of dimples. Based on the model, the optimal dimple depth is approximately proportional to the distance between the two surfaces. The theoretical analysis agreed with the experiments.

A nanoscale friction investigation during the manipulation of nanoparticles in controlledenvironments

Future micro/nanodevices will contain very small features such that liquidlubrication is not practical and inherent lubricity is needed. In this study, ananoscale friction investigation was carried out during the manipulation of Au andSiO2 nanoparticles on silicon using atomic force microscopy (AFM). Nanoparticle sliding wascharacterized by quantifying the lateral force associated with the AFM tip twisting as ithits the particle edge. The friction force varies with particle area and humidity,illustrating how meniscus forces on nanoparticles affect friction. A large tip slid on thenanoparticle-coated surface exhibited friction reduction due to nanoparticle sliding andcontact area reduction.