Effects of Nanoscale Surface Texturing on Self-Healing of Boundary Lubricant Film via Lateral Flow

Surface texturing of silicon substrates with nanowells can change the lubricious performance of cationic polymer lubricant (CPL), a bound-and-mobile lubricant consisting of a polydimethylsiloxane (PDMS) backbone with covalently bonded quaternary ammonium iodide cations. The filled nanowell reservoirs enhance self-healing within the contact track since they can readily provide CPL to near-by regions. However, once this initial reservoir is completely consumed and depleted, the empty nanowells interfere with long-distance lateral flow process since they act as a reservoir that needs to be filled during the flow.     

Surface Energies of Magnetic Recording Head Components

The rate of material removal during fixed abrasive lapping is a function of friction coefficient, the surface tension of the lubricant and of the substrate, and the contact angles between the interfaces. In this study, the authors measured the surface energies of materials typically found in thin film magnetic recording heads using contact angle measurements and the Lifshitz–van der Waals acid/base approach. The different materials tested were Ni_xFe_y, Al₂O₃, and Al₂O₃-TiC. Sample preparation procedures were also considered. The chemical used to wash the surface was observed to affect the measured substrate surface energies. Surface energy values for samples washed with either acetone or hexane showed comparable results. The Ni_xFe_y gave the highest measured surface energy (46.3–48.8 mJ m⁻²) followed by Al₂O₃ (44.1–45.3 mJ m⁻²) and Al₂O₃-TiC (43.3–45.3 mJ m⁻²). In contrast, the oil-washed samples measured generally lower surface energy values. The study characterized the interaction of two lubricant types against the three materials. The oil-based lubricant spreads completely on oil-washed samples mainly because of the low surface tension of the oil (22.0 mJ m⁻²) and did not show measurable contact angles. In comparison, the water-soluble lubricant ethylene glycol, due to its higher surface tension (48.0 mJ m⁻²), formed higher contact angles ranging from 47.2 to 59.6° on the different substrates.     

Fabrication and Tribological Behavior of Patterned Multiply-Alkylated Cyclopentanes (MACs)–Octadecyltrichlorosilane (OTS) Dual-Component Film by a Soft Lithographic Approach

Patterned mixture component surfaces, offering a means for controlling the adhesion and the wetting behavior of materials, have attracted great interest. In this letter, a patterned dual-component lubricant film consisting of multiply-alkylated cyclopentanes (MACs) mobile lubricant trapped and maintained among the patterned octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) network was fabricated on surfaces of silicon using an elastomeric stamp. Tribological behavior of the patterned MACs–OTS dual-component film was investigated, comparing with MAC film and patterned OTS-SAM. The patterned MACs–OTS dual-component film has shown to have improved load-bearing capacity, anti-wear, and self-lubricating ability. It can remain as an effective lubricant layer for more than 3,600 s as the load increased to 0.4 N, and the average friction coefficient is about 0.1. Compared with patterned OTS-SAM and MACs film, patterned MACs–OTS dual-component film showed best load-carrying capacity and durability at applied loads of 0.1–0.5 N.     

Conformation and Fundamental Properties of Novel Lubricant TA-30 for Near Contact Magnetic Recording

A novel perfluoropolyether (PFPE) lubricant called TA-30 has been developed recently. We investigate the conformation of TA-30 on diamond-like carbon (DLC) thin films, by attempting the direct observation of a lubricant film by atomic force microscopy (AFM) using a fluoride probe. We investigate the fundamental properties of a TA-30 lubricant film, such as its spreading characteristics, and the film thickness dependence of surface energy. Considering these experimental results, we conclude that the conformation of TA-30 is considerably different from that of conventional Z-tetraol2000 whose molecular height is 1.7 nm and which was adsorbed on the DLC surface with the random coil. The TA-30 molecules are adsorbed rigidly to the DLC surface with double layers. The thickness of the first TA-30 layer is ~0.9 nm (similar to diameter of the PFPE backbone) and that of the second layer from the DLC surface is 1.4 nm. Since TA-30 has a lower film thickness than Z-tetraol2000 on the DLC surface, it can have two layers, even if the film thickness is approximately of the order of 1 nm, whereas Z-tetraol2000 does not cover the DLC surface and does not form the complete first layer. In addition, we conduct slider touchdown and takeoff hysteresis tests by using TA-30 and Z-tetraol2000. It is confirmed that the use of TA-30 can improve the head–disk interface (HDI) reliability at low-fly-height conditions.     

Effect of Tribofilm Formation on the Dry Sliding Friction and Wear Properties of Magnetron Sputtered TiAlCrYN Coatings

Nano-structured TiAlCrYN coatings, grown by unbalanced magnetron sputtering on various steel substrates, exhibited friction coefficients 0.6–0.8 and wear coefficients 10⁻¹⁶–10⁻¹⁵ m³ N⁻¹ m⁻¹ in dry sliding wear tests. This article reports comprehensive worn surface analyses using SEM, TEM, EDX, EELS and Raman spectroscopy. A ~80 nm thick tribofilm formed on the TiAlCrYN worn surface was found to have dense amorphous structure and homogeneous oxide composition of Cr_0.39Al_0.19Ti_0.20Y_0.01O_0.21. Viscous flow of the amorphous tribofilm was dominant in causing the high friction coefficient observed. The coatings showed combined wear mechanisms of tribo-oxidation and nano-scale delamination.     

Tribological Properties of Patterned NiFe-Covered Si Surfaces

The tribological properties of patterned surfaces were investigated under lubricated conditions. Micropatterns were fabricated on a Si surface using a combination of photolithography and plasma etching. NiFe film with a 150 nm thickness was then deposited on the patterned Si surface. We prepared four kinds of patterned surfaces: dimple, grating, bump, and mesh patterns. The dimensions of the patterns were: size 30–40 μm, pitch 120 μm, and depth 10–12 μm. Friction tests were carried out using a pin-on-plate tribometer. The pin specimen was made of cast iron and had a flat end. The normal load was varied from 9.8 to 98 mN, and the average sliding speed from 1.0 to 5.0 mm s⁻¹. Slideway lubricating oils or a gear oil were used as the lubricant, and the ISO viscosity grades of these oils were VG32, VG68, and VG320. The results showed that the friction coefficients of the two reverse patterns showed very similar tendencies and that circular patterns had a lower friction coefficient than did the rectangular patterns at a high bearing characteristic number. The surface geometry of the Si surface did not affect the friction coefficients at a low bearing characteristic number.     

Local/global planarization of polysilicon micropatterns by selectivity controlled CMP

The planarization CMP, which is considered as one of the most important ULSI chip, is introduced to make flat surface in patterned areas for multilevel MEMS devices. However, the conventional CMP is limited in its application to MEMS structures, due to their wide patterns of μm to mm order thick film layer of several μm. A new CMP process has been developed for application to MEMS structures by the control of selectivity between polysilicon and silicon oxide. A 30nm thick protective oxide layer is deposited to protect the recessed areas, and then polished with low selectivity slurry to partially remove the protruded area while suppressing the removal rate of the recessed area. During the second step of the new CMP process, high selectivity slurry is used to minimize the dishing amount and the variation in the step height according to pattern size and density. Experimental results showed that dishing amount was less than 30nm at the largest pattern of 1250 μm in width and showed no variation of entire pattern, which meant local and global planarization. This result suggests that the newly developed selectivity controlled CMP process can be successfully applied for fabrication the multilevel MEMS devices.     

Simulation of nanochannel membrane formation

Monte Carlo simulations of atomic processes on the surface of silicon nanochannel membranes during molecular-beam epitaxy and subsequent thermal oxidation are performed. It is demonstrated that silicon deposition on Si(001) wafers with 1–100 nm cylindrical pores results in constriction of channel inlets. The rates of reduction of the nanochannel diameter are estimated as functions of the wafer temperature, silicon deposition rate, and initial nanochannel diameter. Optimal conditions of silicon deposition on nanochannel membranes are determined: the wafer temperature of 250–450°C and silicon flux intensity of 10⁻² to 10 monolayers (ML) per second. Under these conditions, the rate of reduction of the nanochannel inlet diameter is 0.13–0.15 nm/ML, which allows membrane channel modifications over a wide range down to several nanometers. Simulations of nanochannel membrane oxidation in an oxygen flux shows that precise reduction of nanochannel inlet diameters down to complete sealing of the channel due to oxide growth is only possible for small diameters of the initial pores. For channels with large lateral sizes, the effect of reduction of the channel inlet diameter due to oxidation is insignificant. Oxidation of pores enhances their stability to subsequent high-temperature treatment.     

Lubricant-Induced Spacing Increases at Slider–Disk Interfaces in Disk Drives

In this article, we explore the physical mechanisms for lubricant migration on recording head slider surfaces and how this migration leads to increased slider–disk spacing during disk drive operations. This is done using both a new experimental methodology, called the “droplet stress test,” and through simulation. In our simulations, we compare the air shear-induced lubricant migration modeled either as viscous flow of a continuum liquid film with zero slip or as wind driven slippage of molecules across the surface. The experimental data are best fitted using the viscous flow model to determine an effective viscosity for the sub-nanometer thick lubricant films. This effective viscosity tends to be somewhat less than the lubricant bulk viscosity due to air shear promoting the slippage of lubricant molecules across the surface. Our experimental results also indicate that the potential spacing increase from the pickup of disk lubricant on the slider is limited by the mobile fraction of the dewetting thickness of the lubricant film on the slider.     

Tribological Properties of Ultra-Thin Functionalized Polyethylene Film Chemisorbed on Si with an Intermediate Benzophenone Layer

In this study, an ultra-thin (~20 nm) functionalized polyethylene (fPE) film is successfully attached to Si substrate via a reactive benzophenone (Ph₂CO) layer. The presence of fPE promotes wear durability of Si/Ph₂CO/fPE to 1,000 cycles compared with 100 cycles for Si/Ph₂CO and nearly zero wear life for bare Si in a ball-on-disk (4-mm-diameter Si₃N₄ ball) wear test under 40 mN applied normal load and 500 rpm sliding speed. As an enhancement to the wear life, perfluoropolyether (PFPE) is applied as a top mobile lubricant layer coated onto Si/Ph₂CO and Si/Ph₂CO/fPE. A significant improvement in the wear durability is observed as Si/Ph₂CO/PFPE fails at 250,000 cycles and Si/Ph₂CO/fPE/PFPE does not fail until one million cycles. Si/Ph₂CO/fPE/PFPE can withstand a minimum applied load of 150 mN at a sliding speed of 0.052 ms⁻¹ without failure, providing a PV (pressure x velocity) limit of greater than 106.6 MPa ms⁻¹.     

The effect of thermal stressing on perfluoropolyalkylethers at elevated temperatures

Fultz et al. have reported that the thermo‐oxidative properties of linear PFPAEs can be improved by stressing the fluid at elevated temperature (371°C) in the presence of air. A study of M‐50 steel coupons exposed to unstressed and stressed linear PFPAE fluids at 260 °C and 330 °C each reveal complex surface layers. For the coupon exposed to the unstressed fluid at 260 °C, a subsurface layer is observed between the iron oxide and iron substrate that has been characterized as being composed of FeF₂. In contrast, the coupon exposed to the stressed fluid has a marked increase in the iron oxide thickness ∼2–3 times) when compared to the unstressed sample and shows no evidence of a buried fluorine‐containing layer. An increase in temperature (330 °C) in the stressed fluid O–C test was required to form a subsurface FeF₂ layer. It is proposed that the elimination of the fluorine layer found on the M‐50 substrate increases the upper temperature limit found from the oxidation–corrosion studies. The increase in the oxide layer thickness implies that the FeF₂ layer found in the unstressed sample acts like a diffusion barrier which inhibits the outward movement of Fe⁰ and the decreased rate of iron oxide growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dependence of surface morphology on molecular structure and its influence on the properties of OLEDs

Most organic light-emitting diodes (OLEDs) have a multilayer structure composed of organic layers such as a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL) and an electron injection layer (EIL) sandwiched between two electrodes. The organic layers are thin solid films with a thickness from a few nano meters to a few tenths nano meter, respectively. Surface morphology of an organic thin solid film in OLEDs depends on the molecular structure of the organic material and has an affect on device performance. To analyze the effect of surface morphology of an organic thin solid film on fluorescence and electroluminescence (EL) properties, thin solid films of 4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2) and new red fluorophores, (2E,2′E)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th) and (2Z,2′Z)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis(2-phenylacrylonitrile) (ABCV-P) were investigated by atomic force microscopy (AFM). The samples for EL and AFM measurement were fabricated by the high-vacuum thermal deposition (8×10⁻⁷ Torr) of organic materials onto the surface of indium tin oxide (ITO)-coated glass substrate, in which the layer structures of samples for AFM measurement and those for EL measurement were ITO/NPB (40 nm)/red emitters (80 nm) and ITO/NPB (40 nm)/red emitters (80 nm)/BCP (30 nm)/Liq (2 nm)/Al (100 nm), respectively. The analysis based on AFM measurements well supported that the photoluminescence properties and the device performance were very much dependent upon surface morphology of an organic thin layer.     

Effects of Self-Assembled Monolayer and PFPE Lubricant on Wear Characteristics of Flat Silicon Tips

The effects of self-assembled monolayer (SAM) and perfluoropolyether (PFPE) lubricant on the wear characteristics of flat silicon tips were investigated. The wear test consisted of sliding the silicon tips fabricated on a flat silicon specimen against SAM and PFPE (Z-tetraol) coated silicon (100) wafer. The tips were slid at a low speed for about 15 km under an applied load of 39.2 μN. The wear volume of the tip was obtained by measuring the tip profile using an Atomic Force Microscope (AFM). It was found that the coatings were effective in reducing the wear of the tips by an order of magnitude from 10⁻⁶ to 10⁻⁷.     

Frictional Properties of a Mesoscopic Contact with Engineered Surface Roughness

Friction between titanium spheres and an artificially structured silicon surface was measured with a friction force microscope. Two spheres with radii of 2.3 μm and 7.9 μm were firmly glued to the tip of the microscope cantilever. A periodic stripe pattern with a groove depth of 26 nm and systematically increasing groove width from 500 nm to 3500 nm was fabricated from a silicon wafer with a focused ion beam. The sphere substrate friction coefficient shows a strong enhancement at a certain groove periodicity, which is related to geometrical interlocking of the two surfaces. This shows that careful modification of the surface roughness can help to control the tribological behavior of mesoscale contacts.     

Comparison of friction measurements using the atomic force microscope and the surface forces apparatus: the issue of scale

Results are presented of lateral force measurements using the atomic force microscope (AFM) and the surface forces apparatus (SFA). Two different probes are used in the AFM measurements; a sharp silicon nitride tip (radius R20 nm) and a glass ball (R15 m). The lateral force is measured between the (silicon nitride or glass) probe and a mica surface which has been coated by a thin lubricant film. In the SFA, a thin lubricant film separates two molecularly smooth mica surfaces (R1 cm) which are slid relative to each other. Perfluoropolyether (PFPE) and polydimethylsiloxane (PDMS) were used as the lubricant films. In the SFA where the contact diameter is largest, the PFPE film shows much lower friction than PDMS. As the size of the probe decreases, the difference in the measured friction decreases. For sharp AFM tips, no clear distinction between the tribological properties of the films can be made. Hence, the measured coefficient of friction varies according to the length scale probed, at least for small dimensions.     

Thin multilayer aluminum structures for superconducting devices

Various aluminum-based thin-film structures were manufactured and investigated at temperatures of 50 mK–3 K. Multilayer films of Al and Si, Al and Cr, and Al in the presence of oxygen were deposited by the thermal evaporation technique. As the thickness of pure-Al films decreases from 20 to 3 nm, the temperature of the superconducting transition increases from 1.30 to 2.45 K. An increase in the oxygen pressure to 5 × 10⁻⁶ mbar during deposition of Al films results in an increase in the critical temperature to 2.4 K. The presence of a chromium sublayer with a thickness of <0.5 nm may lead to complete suppression of superconductivity, whereas a thicker layer, 1–4 nm, deposited at a higher temperature with preliminary sputtering reduces the critical current of Al/Cr two-layer films to a lower degree. An atomic-force microscope was used to study the surface morphology and granularity and the roughness of manufactured film structures. The smallest linear roughness having a size of 0.29 nm for a 3-nm-thick film shows the advantage of using thinner films for creating a homogeneous tunneling barrier.     

Wear stability of polymer nanocomposite coatings with trilayer architecture

A polymer trilayer (sandwiched) film with a thickness of 20–30 nm has been designed to serve as a wear resistant nanoscale coating for silicon surfaces. These surface structures are formed by a multiple grafting technique applied to self-assembled monolayers (SAM) and functionalized tri-block copolymer, followed by the photopolymerization of a topmost polymer layer. The unique design of this layer includes a hard-soft-hard nanoscale architecture with a compliant rubber interlayer mediating localized stresses transferred through the topmost hard layer. This architecture provides a non-linear mechanical response under a normal compression stress and allows additional dissipation of mechanical energy via the highly elastic rubber interlayer. At modest loads, this coating shows friction coefficient against hard steel below 0.06, which is lower than that for a classic molecular lubricant, alkylsilane SAM. At the highest pressure tested in this work, 1.2 GPa, the sandwiched coating possesses four times higher wear resistance than the SAM coating. The wear mechanism for this coating is stress and temperature induced oxidation in the contact area followed by severe plowing wear.     

Self-healing behavior of a polyelectrolyte-based lubricant additive for aqueous lubrication of oxide materials

We report on the self-healing behavior of a polyelectrolyte-based aqueous lubricant additive, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG), during aqueous lubrication of an oxide-based tribosystem. Combined pin-on-disk tribometry and fluorescence microscopy experiments have shown that stable lubricating performance was enabled by means of rapid healing of the worn tribopair surface by polymers dissolved in the adjoining bulk lubricant. This rapid ‘self-healing’ of PLL-g-PEG is attributed to electrostatic interactions between the polycationic poly(l-lysine) (PLL) backbone of the polymer and negatively charged oxide surface. In contrast, a similar healing effect was not readily achievable in the case of methoxy-poly(ethylene glycol)-trimethylsilylether (Sil-PEG), a lubricant additive that is covalently bonded to the surface prior to tribological stress.     

疏水SiO2宽频增透膜的制备与研究

采用溶胶-凝胶浸渍提拉工艺在玻璃表面制备了双层增透膜,该薄膜由折射率分别为1.12和1.33的两层膜构成。薄膜在380~1 100nm和1 100~2 500nm范围内平均透过率较空白玻璃分别提高了7.68%和4.39%。薄膜接触角大约141°,且表层膜在2个月内能保持较高的疏水效果。双层增透膜制备方法简单,在宽光谱耐环境减反射领域有一定的应用潜力。     

Reducing Friction Force of Si Material by Means of Atomic Layer-Deposited ZnO Films

With excellent lubricating property, zinc oxide (ZnO) films are promising candidates to act as protective coatings in Si-based microelectromechanical system devices for the purpose of decreasing friction forces of silicon (Si) material. In this paper, the nanotribological behavior of ZnO films prepared by atomic layer deposition on a Si (100) substrate is investigated by an atomic force microscope. The ZnO films have various thicknesses ranging from 10.0 to 182.1 nm. With the increase of film thickness, the root-mean-square roughness of the films increases, while the ratio of hardness to Young’s modulus (H/E) decreases. Due to their large surface roughness, the thick ZnO films are low in adhesion force. The friction force of the ZnO films is smaller than that of the Si (100) substrate and is greatly influenced by their adhesion force and mechanical property. In a low-load condition, the friction force is dominated by the adhesion force, and thus, the friction force of the ZnO films decreases as film thickness increases. While in a high-load condition, the friction force is dominated by plowing. Films with higher H/E possess smaller friction force, and thus, the friction force increases with the decreasing film thickness.