Diamond-like Carbon Surface Research Articles

Hydrophobic carbonaceous materials obtained by covalent bonding of perfluorocarbon and perfluoropolyether chains

Perfluorocarbon residues, i.e. perfluoroethyl (PFE), CF3CF2–, perfluoro-n-propyl (PFnP), CF3CF2CF2–, perfluoro-isopropyl (PFiP), (CF3)2CF–, and perfluoropolyether (PFPE) chains, e.g. (CF2CF2O)m(CF2O)n, were covalently bonded on the surface of carbon black (CB) and diamond-like carbon (DLC) using PFPE and perfluorodiacyl (PFDA) peroxides. The thermal decomposition of the peroxidic moieties of these perfluorinated peroxides generated reactive perfluorinated radicals. The perfluorinated free radicals could directly bond to the sp2 sites avoiding any spacer, which usually decreases both thermal and chemical stabilities of the resulting materials. The effects of chemical treatment on the carbonaceous materials were studied using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Contact Angle (CA) measurements. The surface areas of CB powders were determined by the BET technique; the morphology of the DLC coatings was evaluated by Atomic Force Microscopy (AFM) and the friction forces were measured by means of Lateral Force Microscopy (LFM).

Tribological performance of hydrophilic diamond-like carbon coatings on Ti–6Al–4V in biological environment

Tribological performance of diamond-like carbon (DLC) and Si doped DLC (Si-DLC) films on Ti–6Al–4V under bovine serum as well as water and ambient air condition has been studied in terms of surface modification with O 2 plasma treatment for superhydrophilic surface. A tribo-test revealed that bovine serum significantly enhanced the tribological performance on all DLC surfaces in comparison with those under water or in air medium. Especially, O 2 plasma treated Si-DLC coatings with superhydrophilic nature were found to lower the wear and increase coating stability associated with macromolecules especially proteins in the bovine serum and their interactions with surfaces.

Influence of silicon contamination on tribology in low earth orbit

To investigate the silicon contamination effects on tribology in low earth orbit, diamond-like carbon (DLC) film, Ti plate, and single crystal MoS 2 were exposed to dimethylsilicone (PDMS) in an ultra high vacuum (UHV) facility equipped with a tribometer and X-ray photoelectron spectroscopy (XPS). In-situ tribological tests and surface analyses were conducted without ambient air exposure. The PDMS exposure led to their adsorptions on the DLC and Ti sample surfaces and did not affect the friction property of the DLC samples. The friction of the Ti sample became low due to the PDMS adsorption. A little of PDMS were adsorbed on the MoS 2 sample. The hyperthermal atomic oxygen (AO) irradiation broke C–O and C–Si bonds included in PDMS that adsorbed on the DLC and Ti surfaces. The low friction due to the PDMS adsorption for the Ti sample disappeared due to the hyperthermal AO irradiation.

Scattering of neutral hydrogen at energies less than 1 keV from tungsten and diamondlike carbon surfaces

Neutral atom to negative ion conversion efficiencies were studied for polished tungsten and diamondlike carbon surfaces using a beam of incident hydrogen atoms. Neutral atoms at energies below 1 keV were scattered from the surfaces using incident angles between 6° and 20° measured from the surface plane. The angular and energy distributions of negative ions backscattering from the surfaces were measured and used to calculate the fraction of the incident beam that was converted to negative ions. The highest number and the lowest overall energy loss of backscattered ions were both observed near the specular reflection angle of the incident beam for the two surface materials studied. The total conversion efficiency was calculated to be near 2% for the tungsten and diamondlike carbon surfaces. Measurements taken while the surfaces were heated show a significant reduction in conversion efficiency, which is credited to the removal of adsorbates from the top layers of the surfaces.

Friction Properties of Carbon Nano-Onions from Experiment and Computer Simulations

The carbon nano-onion can be considered as a new kind of interesting lubricating nanoparticle. Used as lubricant additives, carbon nano-onions lead to a strong reduction of both friction and wear, even at low temperature. To better elucidate the mechanisms by which these processes occur, coupled experimental and computational investigations are carried out. In addition, it is found that lubricious iron oxide nanoparticles are generated in the core of the steel contact through mechanisms that are not yet known. The molecular dynamics simulations of carbon onions placed between sliding diamond-like carbon surfaces at high contact pressure indicate that the lubrication mechanism of the onions is based on a coupled process of rolling and sliding inside the contact area. We conclude that most of carbon onions seem to remain intact under friction processes and do not generate graphitic planes, which is in contrast to the previously determined behavior of MoS2 fullerenes that are mainly exfoliated inside the contact area and liberate lubricating lamellar sheets of h-MoS2.

Design and fabrication of ultra broadband infrared antireflection hard coatings on ZnSe in the range from 2 to 16 μm

In conventional infrared multilayer antireflection coatings (MLAR) materials of fluoride and chalcogenide types are used, which are disadvantaged due to their low mechanical strength and poor stability against humidity and environmental impacts. In this paper, we show that high performance ultra broadband and hard infrared multilayer antireflection coatings on ZnSe substrates in the wavelength range from 2 to 16 μm can be designed and fabricated. Diamond-like carbon (DLC) hard coating as a mechanical and environmental protection layer was proposed and deposited onto MLAR surfaces (MLAR + DLC) using a pulsed vacuum arc ion deposition technique. The thickness of the high optical quality DLC can be optimized in the design simulation to achieve a practically best antireflection and surface protection performance. We show that a germanium thin film (15 nm) between the MLAR and DLC surfaces can be used as a transition layer for optical and material match. The average transmission of the fabricated MLAR+DLC surfaces was 93.1% in the wavelength range between 2 and 16 μm. The peak transmission was about 97.6%, close to the simulated values. The durability and stability against mechanical impacts and environmental tests was improved significantly compared with the conventional infrared windows.

Use of near atmospheric pressure and low pressure techniques to modification DLC film surface

Diamond-like carbon (DLC) films have been use in numerous industrial applications due to its mechanical properties such as low friction coefficient, high hardness, and high adherence on different substrate materials. It has been demonstrated that the DLC surface can be modified with oxygen plasma treatment. The purpose of this paper is to study two kinds of surface treatments (atmospheric and low pressures) using oxygen gas for different etching exposure times in DLC films. Plasma durability along the time was also evaluated. DLC films were deposited using plasma enhanced chemical vapor deposition technique. The properties of DLC treated for both techniques in different exposure times were investigated through Raman, AFM and contact angle measurements. D band position slightly shifts toward lower wave numbers after oxygen plasma etching treatment whilst the surface becomes rougher, although the roughness values are still lower. A conventional wetting contact angle method was used to study the surface properties of DLC films with different treatments. The wetting contact angle reduced significantly due to the increase of carbon–oxygen sites on the surface.

Biocompatible PEG Grafting on DLC-coated Nitinol Alloy for Vascular Stents

The surfaces of Nitinol (TiNi), a popular metal alloy for arterial stents were thin-coated with diamond-like carbon (DLC) and then grafted with poly(ethylene glycol) (PEG) to increase biocompatibility. The TiNi control, DLC-coated TiNi (TiNi—DLC), and the PEG-grafted TiNi—DLC (TiNi—DLC—PEG) surface characteristics and biocompatibility were evaluated. The hydrophilicity of the TiNi—DLC—PEG significantly increased and the amount of both oxygen and nitrogen on the TiNi—DLC—PEG also increased compared to the TiNi control and TiNi—DLC due to the grafted PEG. The ratio between albumin and fibrinogen was higher on the PEG-grafted surface than the other surfaces when tested with human blood components; the platelet adhesion decreased the most on the TiNi—DLC—PEG surface, indicating improved blood compatibility. For in vivo tests using a rat model, the samples that were implanted for 6 weeks formed fibrous tissue; the tissue layer was much thinner on the PEG-grafted sample than the other two groups. The present results indicate that PEG-grafted TiNi—DLC surface may be effective in enhancing biocompatibility of blood-contacting biomaterials including vascular stents.

Wettability and antibacterial activity of modified diamond-like carbon films

Diamond-like carbon (DLC) films can be used in a numerous industrial applications, including biomedical coatings with bactericidal properties. It has been demonstrated that DLC surface can be modified with oxygen plasma treatment. The purpose of this paper is to study the wettability and bactericidal activity of oxygen plasma-treated DLC films produced by plasma enhanced chemical vapor deposition technique. The sp 3/ sp 2 ratio increased after the treatment due to the increase in the generation of the unstable carbon bonds caused by the energetic ions, especially O–H group. The treated DLC surface becomes superhydrophilic and rougher, although the roughness values are still lower. DLC antibacterial activity did not increased with plasma treatment. Therefore, oxygen plasma treatment can be used to make superhydrophilic DLC but not to increase its bactericidal properties.

The influence of viscosity on the friction in lubricated DLC contacts at various sliding velocities

Diamond-like-carbon (DLC) coatings are one of the promising types of protective coatings for various mechanical applications, including those under lubricated conditions. In recent years the research focus of lubricated DLC contacts has been primarily on the chemical aspects of lubrication, while the physical properties of the oils and the other physical lubrication aspects were to a large extent neglected. In this work we analyse the friction behaviour of self-mated DLC/DLC contacts that use various viscosity grades of polyalphaolefin (PAO) base oils, i.e., 18, 30 and 46 mm 2/s, at a range of velocities from 0.04 to 0.41 m/s. For a comparison, we also investigated some steel/steel contacts. At low velocities (up to 0.08 m/s) we observed almost no effect of the viscosity for the DLC surfaces, suggesting a predominant influence of the DLC “solid–solid” contacts on the friction. However, relatively strong, physically adsorbed oil-film layers were present on the DLC surfaces, which were able to prevent the coatings from wearing out under low-speed conditions, that otherwise occur under dry conditions. In the high-velocity region (above 0.17 m/s), the viscosity has no effect on the steel contacts, but higher-viscosity oils tended to reduce the DLC friction, suggesting that for DLC surfaces, higher viscosities are required for the same film thickness and “quality” of lubrication than for steel surfaces. This is due to the poorer wetting and oil-adsorption properties of DLC compared to steel. However, at the same time, this effect leads to reduced friction in DLC contacts, which was about 15% lower for all the investigated sliding velocities.

Preparation and tribological behaviour of multiply-alkylated cyclopentane-1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane dual-layer film on diamond-like carbon

Hybrid dual-layer film was prepared on diamond-like carbon (DLC) surface by depositing mobile lubricant multiply-alkylated cyclopentane (MAC) on 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane self-assembled monolayers (FDTS-SAMs). The formation of comparatively uniform FDTS-SAMs on DLC surface was verified by static contact angle measurement, X-ray photoelectron spectrometer, and atomic force microscope (AFM). AFM result showed that a high density of regular but discrete nano-scale island-like liquid droplets of MAC were distributed on DLC surface with an interlayer of FDTS-SAMs to form hybrid AC-FDTS dual-layer film. The average diameter and height of MAC droplets on FDTS-SAMs are 30 nm and 35 Å, respectively, and the area covered by MAC droplets is ∼60 per cent. The tribological behaviour of the resulting hybrid film was evaluated on a pin-on-plate test rig using Zdol-2000 film and FDTS-SAMs as reference. The result showed that hybrid MAC-FDTS dual-layer film exhibited the best reducing-friction capability, load-carrying capacity, and durability compared with Zdol-2000 and FDTS-SAMs at applied loads of 50–250 mN. This may be attributed to the self-healing ability of the mobile MAC lubricant to diffuse and cover the damaged or defective areas of the substrates.

Plasma fluorination of diamond-like carbon surfaces: mechanism and application tonanoimprint lithography

Diamond-like carbon (DLC) films, used as molds for nanoimprint lithography, weretreated with a fluorocarbon-based plasma in order to enhance their anti-adhesionproperties. While ellipsometry and atomic force microscope measurementsshowed negligible changes in thickness and surface roughness after plasmaprocessing, contact angle measurement found fluorine plasma-treated DLCsurfaces to be highly hydrophobic, with surface energy values reduced from∼45 mJ m−2 for untreatedfilms to ∼20–30 mJ m−2 after fluorination. X-ray photoelectron spectroscopy revealed a thin (from∼0.5 to∼3 nm) fluorocarbon layer on the DLC surface. Proposed mechanisms for the formation ofthis layer include two competing processes: etching of DLC and deposition offluorocarbon material, with one or the other mechanism dominant, depending on theplasma conditions. Fluorocarbon plasma-treated DLC molds for nanoimprintlithography were used to pattern sub-20 nm size features with a high degree ofrepeatability, demonstrating an extended lifetime of the anti-adhesion coating.

Micro-scale modification of diamond-like carbon and copper electroplating by scanning probe field emission current method

Micro-scale modification of nitrogen-doped diamond-like carbon (DLC) is performed by applying an electric field between a tungsten tip and DLC film surface in vacuum using the scanning probe field emission current (SPFEC) method. The dc voltage ranging from −700 V to −3000 V is applied to the tip. Then, electroplating of Cu is performed on the DLC film surface in CuCl 2 solution by a three electrode-cell. The cathodic polarization curves indicate that the start potential of Cu on modified DLC film is shifted to a lower value than that of Cu on an as-grown DLC film. Cu deposits selectively on the DLC surface modified by an electric field. With this technique, the micro-scale patterning of Cu can be achieved by electroplating without a lithographic process.

Diamond-like carbon thin films synthesis by low temperature atmospheric pressure plasma method

This study investigated the deposition and field-emission characteristics of diamond-like carbon (DLC) thin films grown on the silicon and indium–tin oxide (ITO) substrates by using a self-designed dielectric barrier discharge (DBD) atmospheric pressure (AP) plasma system with 7 quartz tube jet-electrodes. Helium (He) gas and acetylene (C 2H 2) gas were used as a main plasma working gas and a precursor gas, respectively. Hydrogen gas was adopted to perform etching reaction for obtaining sharper DLC surface. By optimizing the deposition parameters and post-etching process, a turn-on electric field of 7.08 V/μm was achieved for the DLC thin film.

Low friction and protective diamond-like carbon coatings deposited by asymmetric bipolar pulsed plasma

Diamond-like carbon (DLC) thin films have been prepared at room temperature by plasma-enhanced chemical vapour deposition (PECVD) using pulsed-DC power and CH 4 as precursor. Tribological tests of these DLC films have been carried out with a nanotribometer and a calotest instrument adapted for wear measurements. Friction coefficients ranged from 0.15 to 0.20, which differ from values obtained by other techniques. In this study we have systematically measured the abrasive wear rate and friction coefficient of DLC films deposited at different conditions (pulse frequency and peak voltage), and we have discussed the results in terms of DLC structure and surface morphology. These films could find application as ultrathin anti-friction and anti-wear protective coatings, hydrophobic coatings, gas diffusion barriers and dielectric layers in electronic devices.

The Lubrication Properties of Diamond-Like Carbon Coatings in Engine Oil

Ti-doped diamond-like carbon(Ti-DLC) coatings and undoped diamond-like carbon(DLC) coatings were synthesized by unbalanced magnetron sputtering using carburized Chromium Molybdenum Steels (SCM415) as substrates. Nanocomposite structure coatings with metal carbides nanocrystals uniformly dispersing in the amorphous carbon matrix were obtained by the optimization of the kinds of doped metals and deposited parameters. This kind of nanocomposite structure permits improved hardness while maintaining a lower residual stress and getting thick coatings. The friction coefficients of Ti doping DLC coatings are relatively lower compared with undoping DLC coatings in engine oil. The analysis on the wear surface of coatings have indicated that: the surface of DLC doped with metal absorbs more elements from the engine oil, which indicates that the doping of metal can improve the affinity of the coating for the engine oil, enhance the formation of lubrication oil films, and reduce the friction coefficient thereby.

HDI-07 CONFORMATION AND FUNDAMENTAL PROPERTIES OF NOVEL LUBRICANT TA-30 FOR NEAR CONTACT MAGNETIC RECORDING(Head/Disk Interface and Tribology II,Technical Program of Oral Presentations)

A novel perfluoropolyether (PFPE) lubricant called TA-30 has been developed recently. In this study, we have investigated the conformation of TA-30 on diamond-like carbon (DLC) thin films, by attempting the direct observation of a lubricant film by AFM using a fluoride probe. We also investigated the fundamental properties of a TA-30 lubricant film, such as its spreading characteristics, and the film thickness dependency of surface energy. Considering these experimental results, it is estimated that the conformation of TA-30 is quite different from that of conventional Ztetraol2000, and it adsorbs parallelly on the DLC surface with double layers. In addition, it is suggested that TA-30 has a thinner film thickness than Ztetraol2000 on the DLC surface and the second-layer lubricant molecules of TA-30 play a very important role as mobile lubricant fractions, resulting in a very-low-friction and very-low-spacing head-disk interface.

Surface studies of carbon-based ZnO nanocomposite films

The change in the surface and microstructural properties of pure diamond-like carbon (DLC) matrix when small quantities of ZnO were incorporated during deposition process was investigated in this paper. A 248 nm KrF Pulsed Laser Deposition (PLD) technique was used to fabricate these nanocomposite films. AFM showed that the ZnO grain sizes on the films increased with the increase of ZnO in the films, however, the overall film surfaces were still very smooth with RMS roughness <10 nm. XRD detected peaks at 2θ values of 34.4° and 36.4° indicated the presence of (0002) and (0101) planes of ZnO respectively confirming ZnO regions or clusters were present. High resolution XPS confirmed that ZnO and carbon compounds were present, and with an increase in ZnO, the carbon matrix showed a significant decrease in the sp³ content. 514 nm Raman spectroscopy confirmed XPS findings where a single broad peak gradually separated into two separate peaks in the region between 1100 cm−1 and 1700 cm−1 as the amount of ZnO increased. This suggested a transition in the microstructural properties of the carbon network from diamond-like (high sp³ content) to graphite-like (high sp² content).

Fluorinated diamondlike carbon templates for high resolution nanoimprint lithography

Nanoimprint templates were fabricated from diamondlike carbon (DLC) films grown on Si, using negative-tone e-beam lithography and oxygen plasma etching. An antiadhesion coating was provided through fluorocarbon-based plasma treatment, which was found to form a Teflon-like thin layer on the treated DLC surface. The fluorinated templates were used to imprint arrays of dots with diameters down to 10nm in polymethyl-methacrylate. Application of the fluorocarbon plasma treatment was also demonstrated in the antiadhesion treatment of the nanoimprint resist and in elastomer molding.

Comparative surface and nano-tribological characteristics of nanocomposite diamond-like carbon thin films doped by silver

In this study we have deposited silver-containing hydrogenated and hydrogen-free diamond-like carbon (DLC) nanocomposite thin films by plasma immersion ion implantation-deposition methods. The surface and nano-tribological characteristics were studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and nano-scratching experiments. The silver doping was found to have no measurable effect on sp 2–sp 3 hybridization of the hydrogenated DLC matrix and only a slight effect on the hydrogen-free DLC matrix. The surface topography was analyzed by surface imaging. High- and low-order roughness determined by AFM characterization was correlated to the DLC growth mechanism and revealed the smoothing effect of silver. The nano-tribological characteristics were explained in terms of friction mechanisms and mechanical properties in correlation to the surface characteristics. It was discovered that the adhesion friction was the dominant friction mechanism; the adhesion force between the scratching tip and DLC surface was decreased by hydrogenation and increased by silver doping.