The tendency of smooth surfaces to stick spontaneously to each other is becoming a serious problem, with: a) the increasing quality in surface finish for many components and systems, b) on miniaturization in mechanical components, and c) in demanded precision of positioning of parts in high-end equipment machines and systems. Surfaces tend to be made smoother in order to gain flatness or in order to fulfill the need for more precise and reproducible positioning of parts. Adhesion or even sticking of the surfaces is a major showstopper for these applications. There are several measures that can be taken in order to reduce spontaneous adhesion. Quantification of the effectiveness of the chosen solution is most often done using an AFM with probes varying from 1 nm to 8 micron of contact diameter. A serious disadvantage in measuring adhesion by sharp tips is the wear of the tips. Sharp tips wear easily, resulting in undefined contact areas. When the real area of contact is not well defined, the quantification of the adhesion force is not significant. In the current study results of AFM measurements from literature with different tip diameters of colloidal probes are compared with measurements we performed using AFM cantilevers with a plateau tip and using probes from large spheres using an alternative setup (UNAT). These methods give results that are in good agreement with values found in literature. Large contacting surface enhance the quality of the measured adhesion values. Another part of the study deals with a deliberately roughening of smooth surfaces to minimize (spontaneous) adhesion. Good agreement has been found with existing results. For the use of larger surfaces it is important that the surfaces to be tested are extremely clean. Particles on smooth surface do influence the measurements quite easily. Especially for larger areas, the possibility of encountering particles on the surface are more likely, when particles are present. For the measurements in this study a lot of care has been taken therefore to remove contamination: particles as well as contamination of organic origin.

In many tribological applications, such as journal bearings and gears, a fluid film is used to accommodate velocity between moving surfaces. To model the behavior of this film and to predict its ability to carry load, the Reynolds equation is predominantly employed. As computational processing power continues to increase, computational fluid dynamics (CFD) is increasingly being employed to predict the fluid behavior in lubrication environments. Using CFD is advantageous in that it can provide a more general approximation to the Navier-Stokes equations than the Reynolds equation. Moreover, using CFD allows for the simulation of multiphase flows as could occur during bearing contamination and bearing exit conditions. Because the bearing surfaces move relative to each other as they obtain equilibrium with the fluid pressure, there is a need to incorporate the moving boundary into the CFD calculation, which is a non-trivial task. In this work, a fluid-structure interaction (FSI) technique is explored as an approach to model the dynamic coupling between the moving bearing surfaces and the lubricant. The benefits of using an FSI approach are discussed and the results of its implementation in a lubricated sliding contact model are presented.

Energy and environment are of major concern in internal combustion engine component design. The piston ring-cylinder liner (PRCL) contact plays an essential part in design and is highlighted in this study. In fact, the rings ensure the sealing property, reducing the environmental impact by avoiding lubricant contamination (blow-by) and lubricant consumption. Unfortunately, when sealing, the rings generate between 11 to 24% of the friction losses in an internal combustion engine [1], thus reducing the energy efficiency of the engine. The cylinder liner surface features a special micro-geometry, a classical one is the cross-hatching pattern, obtained by honing. This texturing acts as a micro-bearing, oil reservoir and debris trap. Understanding the influence of texture parameters as groove depth and width or angle, will allow tribological improvements of the PRCL contact. The 2D transient Reynolds equation has to be solved for this kind of surface. The statistical method using the Patir and Cheng [2] flow factors is widely used. This approach lumps the different components of the surface (grooves and plateaux) and does not consider the roughness directionality. Methods decoupling both components, like the homogenization method [3] are also used. Another alternative is to use a deterministic model on measured surfaces, but this is a “hugely” expensive approach. Multigrid methods [4] are used to drastically reduce the calculational cost. The aim of the current study is to facilitate the understanding of measured surface calculations. Hence, analytical surfaces are used. They allow a flexible handling of the cross-hatching parameters. The plateaux are perfectly smooth and the grooves are sinusoidally shaped. The top ring is modelled using a parabolic profile. Periodic boundary conditions are used in the orthoradial direction and zero pressure conditions (Dirichlet) in the axial direction. To investigate the effect of different parameters, various imposed film thicknesses are applied and the mean load carrying capacity (LCC) over time is calculated. When representing the LCC corresponding to each parameter compared to the smooth LCC, as a function of the logarithm of the minimum film thickness, the curves are quite linear for small values of the film thickness and then for larger values they converge to 1.

Pneumatic Cylinders are one of major mechanical components which are widely used in various industries such as automobile production line and semiconductor inspection device due to its low contamination and low maintenance cost. Most of existing studies on pneumatic cylinders have focused on their performance improvement such as operating sliding friction measurement, contact stress minimization, appropriate dynamic response, and etc. This research carried out life tests of pneumatic cylinders and the concerned failure mechanism was the degradation of pneumatic polyurethane seal since leakage caused by seal degradation occurs very frequently. The considered operating parameter was environmental temperature. To assess operating temperature as an acceleration parameter, the lifetime of a pneumatic cylinder was tested at high temperature and the degradation mechanism and characteristics of sealing surface were analyzed by statistical Weibull analysis method as well as by surface analysis using pyrolysis gas chromatography. Ultimately this research will help the life prediction of other pneumatic reciprocating machines.

The pumping effect proposed by the authors is used to analyze the contamination of the air bearing in hard disk drive. Three different types of air bearing surface are considered in the focus on the accumulation of the contamination at the rear pad where the minimum spacing is located. It is found that the contamination tends to accumulate at both the front and the rear ends of the air bearing surface pad where the shear stress of air film is interrupted due to due to the dramatic change in the spacing. The accumulation at the tailing edge of the air bearing is the most detrimental. The thickness of adsorbed film at the tailing edge increases suddenly when the terrace length at the tailing edge exceeds a critical value, which is in between 15 μm and 35 μm in this article.

Nanoindentation measurements on TiAlN, CrN, a-C:H:Me, and TiN, deposited on steel substrates have been performed. It was found that the resulting surface roughness/morphology after deposition significantly affects the measurements of nanomechanical properties, while measurements of these properties on the surface may be significantly different than the bulk portion of the coating, exhibiting a lower nanohardness due to the existence of a surface contamination layer. A simple method is proposed for accurately measuring the nanomechanical properties of coatings alleviating the need for excessive statistical analysis and the issues that arise from surface topography and the presence of surface and contamination layers on thin films.

Particulate contaminated lubricants can be detrimental to any tribosystem. Debris can originate from the external environment, be unintentionally introduced during fabrication, or be generated internally during operation. These particles, if not carefully filtered out, can have serious implications on the integrity of a tribosystem. This study focused on the abrasive wear observed from four-ball wear tests in the presence of lubricant with particulate contaminants. The contaminants studied were silicon dioxide sand particles and self generated AISI E-52100 steel particles. The particles were submerged in an industrial EP gear oil. The effects of particle size, composition, and concentration on abrasive wear of sliding interfaces was analyzed.

Lubricating grease is commonly used for lubricating ‘sealed and greased for life’ bearings. This grease lubricates the rolling contacts. It also provides an additional sealing function to protect the bearing against ingress of contamination. The sealing function of lubricating grease in the vicinity of the seal lip contact has been studied experimentally. The effects of the lubricant rheology on the migration of ingress particles has been examined. In grease, experimental results reveal that contaminant particles consistently migrate towards the sealing contact where the shear rate reaches its highest value. In contrast, for a Newtonian base oil and a non shear thinning elastic fluid, it has been observed that the migration effect takes place in the opposite direction, and brings particles away from the sealing contact. It is concluded that the sealing function of grease in the vicinity of the sealing contact is due to the fluid rheology and more specifically to the shear thinning behaviour of the lubricant.

Particle contamination on a slider in a hard disk drive (HDD) affects the HDD’s reliability. With the introduction of the thermal flying-height control (TFC) slider, the temperature in the head-disk interface (HDI) becomes non-uniform, which induces a temperature-gradient dependent force on particles moving in the HDI. This paper investigates the effect of this force, the so called thermophoretic force, on a particle’s motion in the HDI as well as its effect on particle contamination on the TFC slider. By numerical simulation of the particle’s trajectory together with an analytical analysis, we show that the thermophoretic force is always negligible compared to the Saffman lift force, which points to a direction parallel to the thermophoretic force. We conclude that the current particle contamination simulator without any thermophoretic forces included would not be significantly altered by the inclusion of these forces.

Microswitches have the potential to be used in numerous applications [1]. Microswitches are slower and currently less reliable than semiconductor switches. However they have the advantage of reduced power consumption, less insertion loss, and better isolation. The operation of a microswitch involves many interesting phenomena which will be reviewed. In an electrostatically actuated switch a voltage difference is applied between the beam and the gate. The resulting electrostatic force pulls the beam toward the gate such that its tip contacts the drain and completes the circuit. However the momentum of the beam causes it to deflect further, even after the tip is in contact with the drain. This stored elastic energy can be sufficient to cause the tip to separate from the drain resulting in what is often referred to as “contact bounce” [2]. Contact bounce causes several problems. First the switch cannot be used until the bouncing has stopped, thus increasing the effective time-to-closure. Second the tip and drain are subjected to more mechanical open-close contacts than are intended. Third the impact force between the tip and drain can be several times greater than the force in the closed position. These last two phenomena can prematurely degrade the contact surfaces. Attempts have been made to tailor the actuation voltage in order to reduce both the impact force and contact bounce [3]. Switches can fail in either of two failure modes. In one mode the contact resistance decreases with cycling. This behavior, while seemingly not a problem, is symptomatic of the contact being cleaned due to repeated contacts (i.e. “contact scrub” as it is known in the industry). As the resistance decreases the force of adhesion increases between these clean metal-to-metal contacts, eventually causing the switch to stick shut when the restoring force in the beam is insufficient to pull the contacts apart [4]. Another failure mechanism is a steady increase in contact resistance until the point at which the switch is no longer useable. These failures are attributable to the growth of contamination in the form of a friction polymer on the contacting surfaces [5]. Another measure of switch performance is intermodulation distortion which quantifies the distortion of a pair of harmonic RF signals with nearly equal frequencies. The beating between two such components causes the power to vary relatively slowly, i.e. at the beat frequency. This beat frequency may be sufficiently close to the thermal response time of the switch leading to distortion and false signals in the frequency range of interest [6].

CMP process yield depends on effectiveness of a post-CMP cleaning, which should reduce roughness of the polished wafer and leave it defect-free, consistently removing particles, organic residues, and ionic contamination. This paper presents an overview of wafer cleaning attributes, challenges and opportunities. The cleaning effectiveness depends on the stability of brush PVA (Poly Vinyl Alcohol) properties, magnitude of brush-wafer frictional force, and the adhesion forces between the particle and wafer, and the particle and brush.

Wear at the nanoscale is a key limitation of conventional silicon and silicon nitride atomic force microscope (AFM) probe tips. Tip degradation and contamination induced by tip-sample interactions can result in decreased resolution and uncertainty in AFM measurements. Prediction and control of the wear behavior is challenging since there is no rigorous theory for the wear of a <100 nm asperity. However, ultrananocrystalline diamond (UNCD) and diamond-like carbon (DLC) are potentially ideal materials for AFM probe applications because of their high stiffness and hardness, low surface roughness, low macroscale friction coefficient and wear, and chemical inertness. The nanoscale adhesion and wear behavior of UNCD, DLC, silicon, and silicon nitride AFM probes have been characterized through systematic AFM wear tests and characterization of the corresponding nanoscale modification of the tips through transmission electron microscopy (TEM) imaging, AFM-based adhesion measurements, and AFM-based blind reconstruction of the tip shape. Our results demonstrate that significant reductions in the nanoscale wear can be achieved through the use of these carbon-based materials. We will discuss how the nanoscale wear behavior of the tips can be linked to their intrinsic materials properties through consideration of the mechanics and physics of nanoscale contacts.

The degree of acidification is considered a crucial property of lubricating oils for some applications, e.g. gas engines, as corrosive wear of machine components may be caused by acidic contaminations. For this reason, a sensor concept using the effect of material loss of a thin metal film due to corrosion is proposed. The corrosion of these films prepared from lead has been monitored electrically. In laboratory tests, the sensors were immersed in a series of oils characterized by different types and amounts of acidic components. The usefulness of the proposed sensor concept is also illustrated by corrosion tests with used oil samples taken from engines. The experiments clearly showed a correlation of corrosion rate with acidification expressed as TAN.

Simulation of particle motion in the Head Disk Interface (HDI) helps to understand the contamination process on a slider, which is critical for achieving higher areal density of hard disk drives. In this study, the boundary effect—the presence of the slider and disk—on particle motion in the HDI is investigated. A correction factor to account for this effect is incorporated into the drag force formula for particles in a flow. A contamination criterion is provided to determine when a particle will contaminate a slider. The contamination profile on a specific Air Bearing Surface is obtained, which compares well with experiments.

Template-based high-rate nanomanufacturing and wafer bonding both rely on surface energy to bring the surfaces into intimate contact. In high-rate nanomanufacturing, unlike wafer bonding, the contacting surfaces must be easily separated after the pressure is removed. A common problem in wafer bonding and nanomanufacturing is particle contamination. Trapped particles cause a separation zone that will prevent the intimate contact required to transfer nanoscale devices from the template to the device wafer. This problem is examined here using two different methods. The first method examines the effect of a rigid particle trapped between elastic plates. The second investigates the effect of a plastically deforming particle trapped between two elastic half-spaces.

We performed experiments where the frictional resistance of antimony nanoparticles with varying contact areas is measured in ambient conditions as well as in ultrahigh vacuum while they are pushed by the tip of an atomic force microscope (AFM). Two different procedures have been used in independent studies to investigate the frictional properties of these particles during dislocation using the AFM operated in the contact mode or dynamic (tapping) mode, respectively. Both experimental approaches revealed a linear dependence of the frictional properties on contact area. Moreover, both methods detect a sudden and distinct increase in frictional resistance at around 15000 nm 2 particle size, which coincides with a structural transition of the particles from an amorphous to a crystalline core state and confirms our earlier data showing the same result. Possible reasons for this effect are discussed in terms of both the atomic structure of the antimony particles as well as the interface structure. Some of the observed frictional behaviour of the particles may be explained considering the influence of sample contamination.

In this paper, we present some current research issues in contact failures in ohmic RF MEMS microswitches. Such experimental and modeling research encompasses contact mechanics (including elastic, plastic, and adhesive contacts) and the related phenomena of brittle and ductile separation. Furthermore the contact interface is not static, but rather is known to evolve over the lifetime of the switch. Also discussed are contamination failures.

The Adhesion and removal of small particles to surfaces is very important to many industries such as semiconductor manufacturing, imaging, aerospace, etc. In most cases, particles represents undesirable contaminants that lower product yield and cause defects. These particulate contaminants may be generated by the process or the product environment. The industry sets threshold specification for acceptable contamination for each generation of products.

For some complex slider designs the two dimensional approximation incorporated in the Reynolds equation for determining the airflow in the air bearing is not applicable due to steps in the air bearing surface. A model that incorporates some transverse flow effects is needed to better characterize the airflow between the slider and disk for some applications. In this paper such a model is derived to better predict the paths of contamination particles entrained in the air bearing. The characteristics of airflow and particle flow within the air bearing are then studied. The analysis including the transverse effects reveals that the transverse velocity of the air is not negligible in the geometric transition regions of the slider. This transverse velocity has a significant effect on the flight path of particles, and therefore, on the particle contamination profile on slider surfaces. The assumption of adhesion of the particles upon impact with a surface is used as the contamination criteria, and it is viewed as the worst-case scenario.

The quality of electrical contact resistance is important to the performance and reliability of metal-contact microelectromechanical system (MEMS) relays and switches. The cyclic degradation of contact resistance was examined for a metal multilayer sphere-on-flat contact at low contact force. The relationships between the degradation and underlying mechanisms, particularly surface contamination effects, were investigated through experimentation and analysis. Results indicated that the degradation severity could be significantly decreased with environmental control and contact current reduction. Micro-arcs at very small surface gaps, which can decompose adsorbed contaminants and leave an insulating surface film, were proposed as a cause of the resistance degradation.