Deposited Diamond-like Carbon Coatings Research Articles

Modification of optical and mechanical properties of nitrogen doped diamond-like carbon layers

We have deposited diamond-like carbon (DLC) films on glass and Si substrates with direct ion beam deposition technique and investigated the effect of N2 doping on their structural, mechanical, and optical properties. The DLC coatings were doped with nitrogen under different flow rates of 5, 10, 20, 40, and 50 sccm. Morphological characteristics investigation of the prepared samples showed decrement in their average roughness from 4.1 to 0.68 nm. Raman studies showed that the number of graphitic sp2 bonding increased with N doping. By increasing the N2 content, the graphite cluster size increased. FTIR measurement revealed the functional groups available in the prepared samples. UV–Vis analysis showed that the optical transmission of nitrogen-doped DLC (N-DLC) coatings decreased when N2 content increased from 5 to 40 sccm followed by decrement in both the optical band gap and the internal stress. Finally, the mechanical properties such as hardness and elastic modulus decreased by increasing N2 content from 5 to 40 sccm.

The influence of positive pulses on HiPIMS deposition of hard DLC coatings

Diamond-like Carbon (DLC) coatings were deposited by a novel HiPIMS method that incorporates positive voltage pulses at the end of the conventional HiPIMS discharge. Different positive voltage amplitudes (100, 200, 300, 400 and 500 V) were used to evaluate the effect of this operation mode on the discharge process and the mechanical properties of the deposited DLC coatings. The application of positive pulses was observed to enhance the ionization of both the sputtered carbon and argon species. Mass spectroscopy measurements showed that a larger amount of high-energy C+ ions are generated, with ion energies proportional to the amplitude of the overshoot voltage. The ion bombardment induced by the positive pulses led to higher compressive residual stresses and densification of deposited DLC coatings. Moreover, their Raman spectra exhibited lower D-band and G-band intensity ratios (ID/IG) as the pulses voltage was increased which is indicative of higher sp3 content. Mechanical properties were evaluated by nanoindentation testing and the hardness of the deposited DLC films was observed to increase from 9.6 GPa (for no voltage pulse applied) to 22.5 GPa (for an applied positive pulse voltage of 500 V).

Comparison of the wear particle size distribution of different a-C coatings deposited by vacuum arc

Abstract For biomedical application in the field of artificial hip joints diamond-like carbon (DLC) coatings have been widely studied due to their tribological properties. The wear particles as the main factor limiting the life expectancy of hip joints have attracted more and more interest, not only the number of them, but also the distribution of their size. In this study we have deposited DLC coatings on stainless steel (P2000) by a vacuum arc adjustable from anodic to cathodic operation mode, with the anode–cathode diameter ratio of da/dc = 3/1 at a DC bias of − 250 V to − 1000 V. To improve the adhesion of the DLC coating on P2000, titanium as a metallic interlayer was deposited by cathodic vacuum arc evaporation. The internal structure of the coating was investigated by the visible Raman spectroscopy with the four-Gaussian curve fitting method. Comparing the results with the previous work (coatings deposited with da/dc = 1/1), it was found that the anode–cathode diameter ratio has an effect on the structure (e.g. ID/IG) as well as the wear particle size distribution. It was shown that the maximum of the frequency distribution e.g. at − 1000 V bias can be shifted to below 1 μm with increasing da/dc.

Detailed Raman Study of DLC Coating on Si (100) Made by RF-PECVD

Radio frequency (RF) plasma enhanced chemical vapour deposition (PECVD) technique was used to make a diamond like carbon (DLC) coating on silicon (100) substrate. The deposition was carried out using C2H2 as the process gas, at different temperatures, 25°C (room temperature) and 300°C with constant power and flow rate. Characterization techniques such as ellipsometry and Raman spectroscopy were used to characterize these samples. Raman analysis of DLC coatings at different temperature is carried out in detail for two different excitation wavelengths i.e. 514 and 785nm and, results are presented in the paper. Blue-shiftis observed in both D and G peaks of Raman spectrum with increase in deposition temperature, which indicates the formation of compressive strain in high temperature deposited DLC coatings. Dispersion in both D and G peaks is observed for different excitation wavelength suggesting that the coating is hydrogenated DLC. The degree of hydrogenation of the DLC coating appears to decrease with respect to the deposition temperature. Nano-indentation study shows a marginal increase in hardness with increase in deposition temperature.

Diamond-like carbon coatings for the protection of metallic artefacts: effect on the aesthetic appearance

Plasma-enhanced chemical vapour deposition (PECVD) is an environmentally friendly process used to deposit a variety of nano-structured coatings for the protection or the surface modification of metallic artefacts like the SiO2-like films that have been successfully tested on ancient silver, bronze and iron artefacts as barriers against aggressive agents. This paper deals with the preliminary results of a wider investigation aimed to the development of eco-sustainable coatings for the protection of Cu and Ag-based artefacts of archaeological and historic interest. Diamond-like carbon (DLC) coatings have been deposited by PECVD in different experimental conditions, in a capacitively coupled asymmetric plasma reactor, placing the substrates either on electrically powered electrode (cathodic mode) or grounded electrode (anodic mode) with and without hydrogen addition in the gas mixture. The final goal is to develop a coating with good protective effectiveness against aggressive atmospheres and contemporarily with negligible effects on the aesthetic appearance of the artefacts. The evaluation of possible colour changes of the surface patinas, due to coating process, was performed by optical microscopy and colorimetric measurements. Furthermore, to evaluate the reversibility of the thin DLC layer, an etching treatment in oxygen plasma has been successfully carried out and optimized. The chemical-physical characterization of the deposited DLC coatings was performed by means of the combined use of micro-Raman and XPS spectroscopies. The results show that the DLC films obtained in the anodic mode, may be proposed as a viable alternative to polymeric coatings for the protection of metallic ancient objects.

Electrochemical performances of diamond-like carbon coatings on carbon steel, stainless steel, and brass

Diamond-like carbon (DLC) coatings have been deposited onto stainless steel, carbon steel and brass by plasma-enhanced chemical vapor deposition, respectively. Atomic arrangement, chemical structure, surface morphology and cross-section microstructure of the DLC coatings were examined by X-ray diffraction, Raman scattering spectroscopy and scanning electron microscopy. The electrochemical behaviors of the DLC coatings in 3.5wt.% NaCl solution were investigated by performing an open circuit potential (OCP) measurement and a potentiodynamic polarization test. The experimental results showed that properly deposited DLC coatings could cause an increase of OCP by hundreds of millivolts and a reduction of anodic current density by several orders of magnitude as compared to that of the substrate. The results also demonstrated that electrochemical techniques could be used as tools to detect the soundness of the DLC coating by examining OCP and polarization curve, which varied with the form of defect and depended on the type of substrate.

Comparison of the wear particle size distribution of different a-C coatings deposited by vacuum arc

For biomedical application in the field of artificial hip joints diamond-like carbon (DLC) coatings have been widely studied due to their excellent mechanical, tribological and biological properties. The wear particles as the main factor limiting the life expectancy of hip joints have attracted more and more interest, not only the number of them, but also the distribution of their size. In this study we have deposited DLC coatings on stainless steel (P2000) by a vacuum arc adjustable from anodic to cathodic operation mode. To improve the adhesion of the DLC coating on P2000, titanium as a metallic interlayer was deposited by cathodic vacuum arc evaporation. The frequency distribution of wear particles generated using a disc-on-disc test was measured by a particle size analyzer. It was shown that the maximum of the frequency distribution e.g. at —1000 V bias can be shifted to below 1 µm with increasing anode/cathode diameter ratio da/dc.

Tribological performance of DLC coatings on UHMWPE

Diamond like carbon (DLC) coatings were deposited by several methods (ion beam assisted evaporation, magnetron sputtering, filter cathodic arc, and plasma enhanced chemical vapor deposition) onto medical grade ultra-high-molecular weight polyethylene (UHMWPE) discs. The chemical characteristics and mechanical properties of the deposited DLC coatings were studied by Raman spectroscopy and nanoindentation, respectively. In addition, a set of tribological tests was conducted at human body temperature and under bovine serum lubrication against alumina balls. After testing, wear tracks were both visually inspected and documented using confocal microscopy. Visual inspection of the wear tracks confirmed that the DLC coatings were completely removed in all cases, the only exception being the DLC coating prepared by magnetron sputtering with thickness about 0.5 microns. Although this type of DLC coating exhibited the highest friction coefficient, and therefore it suggested a somewhat lower resistance to abrasive/adhesive wear conditions, no evidence of cracking or delamination was observed after the high contact pressure wear testing. This fact points out a good substrate-coating adhesion, and confirms magnetron sputtered DLC as a potential coating for orthopaedic applications.

Ultrasonic characterization of mechanical properties of Cr- and W-doped diamond-like carbon hard coatings

Two ultrasonic nondestructive evaluation methods have been applied to systematically characterize the mechanical properties of nano-structured physical vapor deposited diamond-like carbon (DLC) ultra-hard coatings. A photoacoustic guided-wave technique is used to generate broadband surface acoustic waves (SAW) on the coating surfaces, and dispersion relations of the SAW for DLC coatings are measured with frequencies up to about 150 MHz. In addition, line-focus acoustic microscopy is used to investigate the dispersion curves of leaky SAW on coatings in the ultrasonic frequency range from 140 MHz to 240 MHz. A multi-layer material model is used to analyze the wave propagation phenomena in the DLC coating specimens and the transfer matrix method is used to numerically calculate theoretical dispersion curves. The measured acoustic dispersion curves by the two ultrasonic methods are therefore independently analyzed by a nonlinear optimization approach in the inverse problem. The derived Young's moduli using the two ultrasonic techniques are compared with nano-indentation tests and good quantitative agreement is found. An example application of photoacoustic methods to a curved gear component is also shown.

Synthesis of diamond-like-carbon coatings by pulsed laser deposition: optimization of process parameters

In this work, we report on both the microstructural (sp3 carbon atoms content) and the mechanical properties (hardness and elastic modulus) of pulsed laser deposited diamond-like-carbon (DLC) thin films. The sp3 content of the films was determined by analysis of the XPS C 1s core-level signal, and the hardness and elastic modulus were measured by nanoindentation using the continuous stiffness measurement (CSM) technique. By investigating the effect of process parameters, such as deposition temperature and KrF excimer laser intensity on the diamond-like characteristics of the films, we were able to point out that: (1) deposition at 25°C, as opposed to deposition at 300°C, enhances the diamond-like properties of the coatings, (2) the sp3 content increases with laser intensity up to a maximum value of about 60% obtained at 7.0×108 W/cm2 and (3) the hardness and elastic modulus of the coatings both increase with laser intensity as they respectively reach 44 and 375 GPa at 7.0×108 W/cm2. It is finally shown that the observed variations in the hardness value and elastic modulus correlate well with the variations of the sp3 content of the DLC coatings.

Advances in PSII deposited DLC coatings for use as barriers to corrosion

Plasma source ion implantation (PSII) is a non-line of sight process for implanting complex shaped targets without the need for complex fixturing. The breakdown initiation of materials coated with diamondlike carbon (DLC) produced by PSII occurs at defects in the DLC, which expose the underlying material, thus establishing a galvanic couple between the coating and exposed material at the base of the defect. Pitting and oxidation of the base metal leads to the development of mechanical stress in the coating and eventually spallation of the coating. This paper presents current progress in attempting to mitigate the breakdown of these coatings by implanting the parent material before coating with DLC. Ideally the parent material would be implanted with chromium or molybdenum, which are known to improve corrosion resistance, however the necessary organometallics needed to implant these materials with PSII are not yet available. Here the effects of carbon, nitrogen, and boron implantation on the susceptibility of PSII DLC coated mild steel to breakdown are reported.

Material properties and tribological performance of rf-PECVD deposited DLC coatings

Abstract Diamond-like carbon (DLC) coatings were deposited on to silicon, glass and metal substrates, using an rf-plasma enhanced chemical vapour deposition (rf-PECVD) process. The resultant film properties were evaluated in respect of material and interfacial property control, based on bias voltage variation and the introduction of inert (He and Ar) and reactive (N2) diluting gases in a CH4 plasma. The analysis techniques used to assess the material properties of the films included AFM, EELS, RBS/ERDA, spectroscopic, electrical, stress, microhardness, and adhesion. These were correlated to the tribological performance of the coatings using wear measurements. The most important observation is that He dilution (>90%) promotes enhanced adhesion with respect to all substrate materials studied. Coatings typically exhibit a microhardness of the order of 10–20 GPa in films 0.1

Friction and wear performance of diamond-like carbon, boron carbide, and titanium carbide coatings against glass

Protection of glass substrates by direct ion beam deposited diamond-like carbon (DLC) coatings was observed using a commercial pin-on-disk instrument at ambient conditions without lubrication. Ion beam sputter-deposited titanium carbide and boron carbide coatings reduced sliding friction, and provided tribological protection of silicon substrates, but the improvement factor was less than that found for DLC. Observations of unlubricated sliding of hemispherical glass pins at ambient conditions on uncoated glass and silicon substrates, and ion beam deposited coatings showed decreased wear in the order: uncoated glass > uncoated silicon > boron carbide > titanium carbide > DLC > uncoated sapphire. Failure mechanisms varied widely and are discussed. Generally, the amount of wear decreased as the sliding friction decreased, with the exception of uncoated sapphire substrates, for which the wear was low despite very high friction. There is clear evidence that DLC coatings continue to protect the underlying substrate long after the damage first penetrates through the coating. The test results correlate with field use data on commercial products which have shown that the DLC coatings provide substantial extension of the useful lifetime of glass and other substrates.

The electrochemical and wear behaviour of amorphous diamond-like carbon coatings and multilayered coatings in aqueous environments

R.f. plasma CVD deposited diamond-like carbon coatings (DLC) possess interesting wear properties in dry testing conditions or in vacuum applications. Extremely low friction coefficients are displayed in dry test conditions, the friction coefficient being dependent on relative humidity and presence of oxygen. The question arises whether these coatings are equally effective in an aqueous medium. Parameters controlling the through-coating porosity are discussed and their relative importance indicated. A coulometric quantitative porosity measurement has been used. Characterisation by light optical microscopy, profilometric measurements and EPMA suggest the importance of the microstructure of the substrate material. Further, pin-on-disk wear tests in water show a detrimental damage when compared to dry wear tests. De-adhesion of the coating occurs in an early stage with subsequently a rapid destruction of the coating. Important parameters in this failure mechanism are the initial contact stress and the development of this stress by initial wear.

Mechanical and tribological performance of ion-beam deposited diamond-like carbon on polymers

Ion-beam deposited diamond-like carbon (DLC) is an attractive coating material because of its combination of low friction, high hardness and chemical inertness. A nitrogen ion source is used, both to modify the substrate surface and to crack a low vapour pressure oil which is evaporated and condensed onto the substrate surface. Owing to the low deposition temperature—components never exceed 80 °C during the coating process—and the ability to harden and densify the substrate surface in the same process, such DLC coatings are of particular importance for engineering polymers. In this study DLC coatings (approximately 1 μm thick) have been applied to a range of commercially available polymer substrates. Depositions have been carried out with and without surface modification of the polymer by ion bombardment prior to DLC coating. The assessment of the mechanical properties of these coatings is reported, including adhesion, wear resistance and fracture toughness.

Mechanical properties of ion-beam deposited diamond-like carbon on polymers

Ion-beam deposited diamond-like carbon (DLC) is an attractive coating material owing to its combination of low friction, high hardness, and chemical inertness. A 40–80 keV nitrogen bucket ion source is used, both to modify the substrate surface and to crack a low vapour pressure oil which is evaporated and condensed onto the substrate surface. The technique is of special interest owing to the low deposition temperature—components never exceed 80°C during the coating process. Further, the ability to harden and densify the substrate surface in the same process is of particular importance for engineering polymers. Thick DLC coatings (approximately 1 μm) have been applied to a range of polymers, with and without surface modification. The assessment of the mechanical properties of these coatings is reported, including surface roughness, friction hardness, and adhesion. Comparisons are made with untreated polymers and those ion implanted with nitrogen at a range of doses.

Commercial applications of ion beam deposited diamond-like carbon (DLC) coatings

We report the results of applications development by Diamonex on ion beam deposited diamond-like carbon (DLC) coatings. Many of the process scale-up issues for ion beam deposition of DLC coatings have been solved. Commercial applications for abrasion resistant DLC-coated optics take advantage of the transparency, chemical inertness, low friction coefficient, high hardness and excellent adhesion of ion beam deposited DLC coatings. DLC-coated polycarbonate sunglass lenses are more resistant to abrasion by #0000 steel wool than any polycarbonate sunglasses commercially available. Using DLC, highly durable coatings with a variety of iridescent reflected colors can be produced. In addition to providing polycarbonate with substantially improved abrasion and chemical resistance, the ballistic strength of polycarbonate is maintained. DLC-coated float glass windows in supermarket laser bar code scanners demonstrated a projected average lifetime of 9 years, approximately 100 times longer than uncoated glass. ZnS and ZnSe IR windows coated with DLC coatings 1–2 μm thick are highly transparent from 3 to 15 μm wavelength and exhibit large improvements in chemical resistance and abrasion resistance relative to uncoated ZnSe and ZnS. The combination of the high electrical resistivity, relatively high thermal conductivity, low friction coefficient, high hardness and excellent adhesion to metals of ion beam deposited DLC, permits its use as a scratch-resistant dielectric layer for copper heat removal devices in multichip modules.

Diamond-Like Carbon Coating—It'S Application for Polymeric Substrates

ABSTRACTWe report on a recently commercialized Diamond-Like Carbon (DLC) coating that has been deposited on polycarbonate at near room temperature, via a unique ion beam system. Aspects of high speed impact behavior, chemical resistance, abrasion resistance, and thermal stability of the coating are examined. Results of scanning electron microscopy studies indicate that adhesion of the DLC coating is very good; no delamination of the coating was found on ballistically tested specimens. The well-bonded DLC coating did not cause the impact performance of polycarbonate to become brittle. Chemical exposure test results show that the DLC coating is capable of protecting polycarbonate from chemical attack by aggressive organic liquids. These ion beam deposited DLC coatings have considerable potential as protective coatings for optical systems.