Tribological properties of bio-mimetic nano-patterned polymeric surfaces on silicon wafer

Nano-patterns made of poly(methyl methacrylate) (PMMA) were fabricated on silicon wafer using a capillarity-directed soft lithographic technique. Patterns with three different aspect ratios were investigated for their adhesion and friction properties at nano-scale and for friction at micro-scale. The patterned samples exhibited superior tribological properties, at both these scales when compared to those of flat PMMA thin films.     

Frictional behaviour of Pb‐Sn thin‐film lubrication

The frictional properties of lead‐tin thin films (thickness of 0.05–0.19 μm) with two types of copper interlayer were investigated. The thin film and the interlayer were formed on a silicon wafer surface by vacuum deposition. Friction tests were carried out using a ball‐on‐disc apparatus in a vacuum chamber. The thin copper interlayer reduced the friction coefficient and prolonged the film life. The effect of load on the friction coefficient is explained by an equation derived using the Hertzian contact area between a sphere and a plate. The thicker copper interlayer did not reduce the friction coefficient but markedly extended the life of the film. In this case, the dependence of the friction coefficient on the load is explained by an equation derived using the Hertzian contact area between a sphere with surface roughness of second order and a plate.     

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

Small amplitude (50 μm) reciprocating wear of hydrogen-containing diamond-like carbon (DLC) films of different compositions has been examined against silicon nitride and polymethyl-methacrylate (PMMA) counter-surfaces, and compared with the performance of an uncoated steel substrate. Three films were studied: a DLC film of conventional composition, a fluorine-containing DLC film (F-DLC), and silicon-containing DLC film. The films were deposited on steel substrates from plasmas of organic precursor gases using the Plasma Immersion Ion Implantation and Deposition (PIIID) process, which allows for the non-line-of-sight deposition of films with tailored compositions. The amplitude of the resistive frictional force during the reciprocating wear experiments was monitored in situ, and the magnitude of film damage due to wear was evaluated using optical microscopy, optical profilometry, and atomic force microscopy. Wear debris was analyzed using scanning electron microscopy and energy dispersive spectroscopy. In terms of friction, the DLC and silicon-containing DLC films performed exceptionally well, showing friction coefficients less than 0.1 for both PMMA and silicon nitride counter-surfaces. DLC and silicon-containing DLC films also showed significant reductions in transfer of PMMA compared with the uncoated steel. The softer F-DLC film performed similarly well against PMMA, but against silicon nitride, friction displayed nearly periodic variations indicative of cyclic adhesion and release of worn film material during the wear process. The results demonstrate that the PIIID films achieve the well-known advantageous performance of other DLC films, and furthermore that the film performance can be significantly affected by the addition of dopants. In addition to the well-established reduction of friction and wear that DLC films generally provide, we show here that another property, low adhesiveness with PMMA, is another significant benefit in the use of DLC films.     

Tribological Characteristics of Oxide Layer Formed on TiN Coated Silicon Wafer

The effects of the oxide layer formed on the wear tracks of a titanium nitride (TiN) coated silicon wafer on friction and wear characteristics were investigated. Silicon wafers were used as the substrate of coated disk specimens, which were prepared by depositing TiN coating with 1.74 m in coating thickness using the arc ion-plating method. SAE 52100 steel balls were used as the counter-faces. The tests were performed both in air for forming an oxide layer on the wear track and in nitrogen to avoid oxidation. This paper reports the characterization of the oxide layer and its effects on friction and wear characteristics using Auger electron spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The TiN coating with the oxides shows relatively high friction compared to that without an oxide layer. The thickness of the layer formed on the surfaces of the TiN coated silicon wafer is very thin compared to the thickness of the TiN coating. The oxide layer dominates the frictional characteristics between the two materials and induces a relative high friction.     

HOT EMBOSSING METHODS FOR PLASTIC MICROCHANNEL FABRICATION

Fabrication of microchannels on polymethylmethacrylate (PMMA) substrates using novel microfabrication methods is demonstrated. The image of microchannels is transferred from a silicon master possessing the inverse image of the microchannel to a PMMA plate by using hot embossing methods. The silicon master is electrostatically bonded to a Pyrex 7740 glass wafer, which improves the device yield from about 20 devices to hundreds of devices per master. Effects of embossing temperature, pressure and time on the accuracy of replication are systematically studied using the orthogonal factorial design. According to the suggested experimental model, the time for the whole embossing procedure is shorten from about 20 min to 6 min, and the accuracy of replication is 99.3%. The reproducibility of the hot embossing method is evaluated using 10 channels on different microfluidic devices, with variations of 1.4 % in depth and 1.8% in width.     

Investigation of the Tribological Behaviors of Polymer Molecular Deposition Films by Tribometer Based on Interferometer

The polymer molecular deposition films including polyelectrolyte molecular deposition (PEMD) film and nanoparticles composite molecular deposition (NPs/MD) film have been prepared using the molecular deposition method and the in situ synthesize method. The polymer molecular deposition films were characterized by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The tribological behaviors of the substrate and polymer molecular deposition films were investigated by a tribometer based on interferometer. It is found that the NPs/MD film has a lower friction force and a better anti-wear property than the PEMD film under the dry friction. The poly alpha olefin (PAO2) and water films confined between samples and steel ball surfaces have been investigated using thin film interferometry. The friction force of substrate was lower than the polymer molecular deposition films under PAO2 lubrication. The friction forces alteration of PEMD film and NPs/MD film were similar and consistent, and lower than that for substrate under water lubrication.     

Optimum film thickness of thin metallic coatings on silicon substrates for low load sliding applications

The frictional behaviour of thin metallic films on silicon substrates sliding against 52100 steel balls is presented. The motivation of this work is to identify an optimum film thickness that will result in low friction under relatively low loads for various metallic films. Dry sliding friction experiments on silicon substrates with soft metallic coatings (silver, copper, tin and zinc) of various thickness (1–2000 nm) were conducted using a reciprocating pin-on-flat type apparatus under a controlled environment. A thermal vapour deposition technique was used to produce pure and smooth coatings. The morphology of the films was examined using an atomic force microscope, a non-contact optical profilometer and a scanning electron microscope. Following the sliding tests, the sliding tracks were examined by various surface characterization techniques and tools. The results indicate that the frictional characteristics of silicon are improved by coating the surface with a thin metallic film, and furthermore, an optimum film thickness can be identified for silver, copper and zinc coatings. In most cases ploughing marks could be found on the film which suggests that plastic deformation of the film is the dominant mode by which frictional energy dissipation occurred. Based on this observation, the frictional behaviour of thin metallic coatings under low loads is discussed and friction coefficients are correlated with an energy based friction model.     

润湿性梯度集油表面制备及摩擦性能研究*

为了解决润滑油发生迁移，使接触面润滑油中断，导致润滑失效的问题，制备一种具有高集油性能的疏油-亲油-疏油的梯度表面。采用化学气相沉积的方法，在硅片表面沉积一层单分子膜，并采用接触角测量仪、UMT摩擦磨损试验机、共聚焦显微镜等对该样品进行表征，研究该类表面在限量供油条件下的润滑性能。结果表明：将油滴滴在疏油/亲油交界处，油滴能够迅速地从疏油区域向亲油区域运动；点接触往复运动摩擦实验结果表明，梯度表面硅片的摩擦因数明显低于原始的硅片，且梯度表面硅片的表面磨痕深度比原始硅片浅。各种实验结果表明，所制备的疏油-亲油-疏油梯度表面能够起到集油的作用，避免了润滑油中断的问题。     

Pad surface and coefficient of friction correlation analysis during friction between felt pad and single-crystal silicon

In wafer polishing pad surface plays a crucial role in the polishing process. With the increase of friction time between pad and wafer, the pad becomes flattened or glazed with particles clogging the pores of the pad and forming a layer of slurry residue and wafer particles, leading to changes of COF, material removal rates and higher defects on the wafer surface. Thus, this study aims to determine the correlation between pad surface deformation, slurry adhesive rate and Coefficient of friction (COF) during friction between felt pad and single -crystal silicon, to analyze the relationship between pad condition and COF. The real-time COF between felt pad and single-crystal silicon wafer are tested which are sorted in groups depending on various loads and oscillation frequencies and surfaces of felt pads measuring by Scanning electron microscope (SEM) are compared. The correlation between pad surface deformation and abrasive adhesion and COF is evaluated through analyzing the experiment results.

     

干摩擦和水润滑条件下单晶硅的摩擦磨损性能研究

在UMT-2微摩擦试验机上,对单晶硅片进行了干摩擦和水润滑两种状态下的摩擦磨损试验,分析讨论了载荷和滑动速度对单晶硅片的摩擦因数和磨损率的影响规律;运用扫描电子显微镜,观察和分析了其磨损表面形貌。结果表明:干摩擦条件下的磨损机理主要表现为黏着磨损,水润滑条件下的磨损机理主要表现为机械控制化学作用下的原子/分子去除过程;水润滑条件下的摩擦因数和磨损量均较小,最小磨损率仅为10μm3/s;在水润滑条件下,载荷和滑动速度达到一定值时,硅片表面将发生摩擦化学反应,生成具有润滑作用的Si(OH)4膜,即机械作用在一定条件下对化学反应具有促进作用。     

Investigations on the friction force anisotropy of the silicon lattice

State of the art thin film technologies allow silicon, the material of choice in semiconductor applications, to be used for micro-electro-mechanical systems (MEMS) type microactuators. To investigate the suitability of silicon for these applications, friction force tests for a silicon-silicon interface were performed. For microactuators using friction bearings there is a great need for a general understanding of friction and wear phenomena. Since silicon wafers in general exhibit a single crystalline structure, the investigations included activities regarding the influence of the single crystal silicon’s orientation. The test result shows a periodic change in the coefficient of friction depending on the slider’s rotational position. For instance, a single crystal silicon disk with a {1 1 1} surface crystal orientation exhibits six recurring maxima of the friction force per rotation when tested against a specimen with the same crystal orientation. The contact between wafer and specimen results in a coefficient of friction μ reaching its maximal value of 0.5 every 60° of rotation. To find the root cause for this repetitive behavior, the sliding directions for maximal friction values were compared to the wafer’s respective crystal orientation. For a {1 1 1} silicon wafer, the atoms at the surface are arranged in equilateral triangles. The angle of 60° between the atoms in these triangles corresponds with the periodicity of the friction force. It therefore may be concluded that the coefficient of friction follows the crystal structure. Depending on the lattice orientation, the friction force varies by more than 50%. This information is crucial for designing a micro-slide bearing as well as choosing a combination of lattice orientations that yield minimal friction.     

Effect of Impregnation of Iodine Complex on Friction of Anodic Oxide of Aluminum

Polyvinyl pyrrolidone-Iodine complex (PVP-I) molecules were impregnated into the anodic oxide of an aluminum disk specimen. It was rubbed against a silicon nitride ball specimen using a ball-on-disk type friction test rig. Over the limited range of parameters studied (load: 0.2-1.0 N, sliding velocity: 0.6 mm/s, and sliding distance: 1-7 m), the coefficient of friction decreased to a value as low as 0.01 from values of 0.3 to 0.7 for the anodic oxide surface. Single-crystal iodine rubbed against silicon nitride showed a coefficient of friction of 0.1. The low coefficient of friction is attributed to the thin PVP-I film on the relatively hard anodic oxide. The mechanism of coefficient of friction reduction is the same as that of a thin soft film on a hard substrate.     

Friction and Wear Studies of Octadecyltrichlorosilane SAM on Silicon

A self-assembled monolayer of octadecyltrichlorosilane (OTS) was prepared on a single-crystal silicon wafer (111) and its tribological properties were examined with a one-way reciprocating tribometer. The worn surfaces and transfer film on the counterface were analyzed by means of scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that, due to the wear of the OTS monolayer and the formation of the transfer film on the counterpart ball, the friction coefficient gradually increases from 0.06 to 0.13 with increasing sliding cycles and then keeps stable at a normal load of 0.5N. The transfer film is characterized by deposition, accumulation, and spalling at extended test duration. Though low friction coefficients of the monolayer in sliding against steel or ceramic counterfaces are recorded, poor load-carrying capacity and antiwear ability are also shown. Moreover, the monolayer itself or the corresponding transfer film on the counterface fails to lubricate even at a normal load of 1.0N. Thus, the self-assembled monolayer of octadecyltrichlorosilane can be a potential boundary lubricant only at very low loads.     

SiC抛光片表面氧化行为的XPSS、EM研究

本文利用扫描电子显微镜和X光电子能谱研究SiC抛光片表面氧化行为,发现Si面比C面的氧化更显著,产生更多的氧化产物,提出利用扫描电子显微镜和X光电子能谱来鉴别SiC晶片的Si面和C面的新方法。     

Press molding of a Si–HDPE hybrid lens substrate and evaluation of its infrared optical properties

A hybrid structure of single-crystal silicon (Si) and high-density polyethylene (HDPE) was developed as a new substrate for infrared lenses by using precision press molding. A thin HDPE film was used to laminate a silicon wafer and their interface was directly bonded by the silane cross-link. The HDPE film is easy to be hot-embossed to form three-dimensional surface microstructures and the silicon wafer provides a high stiffness for the hybrid substrate. The infrared (IR) optical properties of the hybrid substrate were examined by two kinds of measurements, transmittance and image sharpness. Interestingly, the transmittance measurement result shows that the IR transmittance of the hybrid substrate is higher than that of Si itself in some region of wavelength. The imaging test result shows that the hybrid substrate is capable to produce similar image quality as Si itself. These results strongly demonstrate that the developed Si–HDPE hybrid substrate is a promising alternative substrate material for IR lens.     

Polymer-polymer friction: Adhesion dependence

The friction of pure polyethylene and acrylate grafted films or mixtures of polyethylene and a poly (ethylene-butylacrylate-maleic anhydride) terpolymer is examined at low speed for sliding on a poly(methylmethacrylate)(PMMA) or polyvinylchloride (PVC) substrate. In all cases, the friction coefficient μ at equilibrium is proportional to the adhesion energy of the same films as determined by a peel test. This study shows how much for smooth surfaces, interfacial and mechanical properties intervene simultaneously in polymer-polymer friction.     

Effects of support method and mechanical property of 300 mm silicon wafer on sori measurement

This paper describes the effects of support methods and mechanical properties of 300 mm silicon wafer on sori measurement. A new supporting method, named three-point-support method, used in the sori measurement of a large diameter silicon wafer was proposed in this study to obtain a more stable measuring process. The wafer was supported horizontally by three steel balls on the vertexes of a regular triangle at the wafer edge. The measuring repeatability and anti-disturbance ability were compared between the proposed method and the conventional one-point-support method, in which the wafer is supported with a small-area chuck at the wafer center. The effects of friction between the supports and wafer surface for the three-point-support were also estimated. Finally, the influences of different mechanical characteristics at the front and back surfaces and the crystal orientation on sori measurement were investigated.     

Friction of Poly(n-Alkyl Methacrylates)

The friction coefficient of solid poly(n-alkyl methacrylates) decreases progressively with increasing length of the alkyl group. This behavior parallels the behavior of adsorbed films of these polymers from solution on solid surfaces. Durability of thin films of these polymers (approximately 3,500 Å thick) increases with increasing length of alkyl group. For example, when the alkyl is C₂₂ the durability is four times greater than when the alkyl is C₁₂ (polymer film on a 1020 steel substrate). The film durability is strongly substrate dependent, e.g., durability of poly(n-dodecyl methacrylale) is three times greater on glass than on 1020 steel when rubbed with a 440 C rider. The friction and durability are attributed to side chain crystallinity of the polymer. Side chain crystallinity has been observed by others using x-ray and other techniques when the alkyl group is at least 10 or 12 carbons long. Friction measurements may be a more sensitive way of detecting side chain crystallinity. The friction behavior of adsorbed films from solution of the poly(n-alkyl methacrylates) suggests that side chain crystallinity also pertains to suck adsorbed films.     

Modelling of frictional and adhesive contacts at silicon/polymer interface for nanotechnological applications

Abstract

The minimisation of friction and adhesion during sliding contacts is crucial for the industrial fabrication of many micro/nanodevices (e.g. MEMS/NEMS), as well as in nanotechnological processes, e.g. in nanoimprint lithography where a silicon mould is used to fabricate polymeric nanostructures by imprinting. We have conducted intensive research on the contact between the mould and PMMA polymeric resist film via advanced modelling and computer simulations. The properties of the contacting surfaces have been identified with the atomic force microscope and nanoindentation, as well as wettability tester applied for the identification of the surface free energy. A model of contact has been elaborated and adequate original software was used to calculate the frictional and adhesive forces in particular at the silicon mould/polymeric resist interface.     

DPPC LB膜的摩擦学行为研究

通过LB技术,以镉离子水溶液为亚相在单晶硅表面制备DPPC不同层数的LB膜,并通过AFM、UMT-2对其表面形貌及摩擦学行为进行考察。摩擦学行为研究发现,DPPC LB膜表现出比花生酸(AA)LB膜更为优异的摩擦学性能。同时,DPPC LB膜的摩擦学性能存在最佳层数。分析认为,DPPC LB膜优异的摩擦学性能与DPPC分子有2个亲水极性基团有关,它可使DPPC分子与亲水基底结合更为牢固,而亚相中金属离子的加入使成膜性能有效提高。