Diamond-like Carbon Surface Research Articles

Direct silanol analysis of tribological surfaces using synchrotron radiation

A new direct detection technique for silanol is needed for tribological materials containing silicon. We focused on near-edge X-ray absorption fine structure (NEXAFS), which uses synchrotron radiation as a method for directly detecting silanol. Model samples were prepared, and their spectra were obtained by NEXAFS. The Si and the O K-edge spectra of silanol exhibited peaks at approximately 1843 eV and 535 eV, respectively. Then the surfaces of silicon-containing diamond-like carbon (DLC-Si) films were measured. The amount of silanol on high-silicon-doped DLC, which had a low friction coefficient, was found to be greater than that on low-silicon-doped DLC. In this research, we demonstrated that the silanol on the surface of DLC-Si films can be directly detected and identified by NEXAFS.

Using Textured-DLC Coating to Improve the Wear Resistance of Stainless Steel Plate Under Dust-Containing Lubricant Condition

Sliding mechanical parts working under heavy loads and at high speeds in harsh environments are often subjected to sand and dust, leading to abnormal wear and seizing. Although sliding surfaces can be hardened and textured, there is a need for even higher wear and seizure resistance. We therefore did this study to confirm the trapping effect of surface texturing on dust by finding a way to visualize the dust. As a result, we confirmed that the dust became trapped in the grooves of the texture during the sliding. In addition, to produce a sliding surface having both seizure and wear resistance, we produced a surface combining a diamond-like carbon (DLC) film and surface texturing, and we evaluated its tribological characteristics. In dusty conditions, the specific wear rate was about 1/20 on surfaces where DLC film and the surface texturing were used in conjunction, and its wear resistance was higher than that of a non-treated stainless steel substrate. On the other hand, a rise in the coefficient of friction due to a rise in contact stress on the corners of the texturing grooves was confirmed. Therefore, when the tribological characteristics were evaluated by changing the radii of the groove corners and the parameters of the groove depth, the coefficient of friction was the lowest, decreasing about 50% for the test sample with a corner radius of 7.1 μm.

Friction properties of carbon nanoparticles (nanodiamond and nanoscroll) confined between DLC and a-SiO2 surfaces

Friction properties of carbon nanodiamond (CND) and nanoscroll (CNS formed from graphene patch wrapping around nanodiamond) were studied by nonequilibrium molecular dynamic simulation of sliding diamond-like carbon (DLC) over the nanoparticles supported by amorphous silica (a-SiO2) slabs. CNS reduces friction coefficient (COF) by 72% relative to CND and superlubricity (COF ≤ 0.01) is enabled by CNS, which agrees well with experimental observations. Due to the wrapping graphene patch, the DLC-CNS contact area is smaller than the DLC-CND contact area and the CNS motion is repressed. Contrary to the rolling motion of ball bearings at the macroscale, the repressed motion of nanoparticles reduces the system friction dissipation. These make CNS a more effective solid lubricant compared with CND.

Non-corrosive Green Lubricant With Dissolved Lignin in Ionic Liquids Behave as Ideal Lubricants for Steel-DLC Applications.

Diamond-like carbon (DLC)–steel contacts become more and more popular in the industry now. Since the surface chemical properties of DLC are quite different from those of iron, traditional formulated lubricants have problems to form tribo-chemical films, which are effective to improve the tribological performance for steel-steel contacts, on the surface of DLC. Thus, new lubricants formulation strategies are needed to be considered for steel-DLC applications. A kind of green lubricant (lignin-[Choline][L-Proline] (L-[CH][Pro])) without any traditional tribo-chemical active element, i.e., free of P, S, B, etc., was studied in this paper for the steel-DLC contact. To find the difference between this new ILs and the traditional lubricants, a commercially available fully formulated lubricant was used as a reference. An Optimol SRV-III oscillating friction and wear tester was used to evaluate the tribological performance. Three different kinds of commercially available DLC coatings (Tribobond 40(Cr + a-C:H:W), Tribobond 43 [(Cr+) a-C:H), and Tribobond 44(a-C:Cr)] were investigated. The results show that the ILs exhibit an obviously lower friction coefficient than that of the traditional commercially available fully formulated lubricant. Among those three DLC coatings, the (Cr+) a-C:H DLC coating exhibits the biggest improvement of wear resistance lubricated with the new ILs than that of the commercially available fully formulated lubricant. It's expected that its excellent tribological properties are attributed to the affinity of the ILs to the metal surface and the strength of the ionic liquids interactions by hydrogen bonding. Thus, forming strong physical adsorption strategy, instead of forming chemical tribo-films, is recommended to enhance the lubricating performance of lubricants for DLC.

Preadsorption of Serum Proteins Regulates Bacterial Infections and Subsequent Macrophage Phagocytosis on Biomaterial Surfaces.

Bacterial infection has been one of the main obstacles for extensive biomedical applications of biomaterial films. Understanding the interactions among macromolecules, cells, and bacteria in the microenvironment located on the film surface at the molecular level is essential for developing antibacterial films. Here we report the distinct influence of several key serum proteins adsorbed on diamond-like carbon (DLC) and traditional Ti films on initial bacterial adhesion, biofilm formation, and corresponding immune responses. Type I collagen, Fn, and IgG were selected as the typical serum proteins. Gram-positive bacterium Staphylococcus epidermidis and Gram-negative bacterium Escherichia coli were used as the model bacteria. Macrophage phagocytosis tests were carried out to examine the impact of adsorbed proteins on the ability of macrophages to clear the adhered pathogens. Results show that it was the specific molecular recognition between adsorbed proteins and bacteria, not the surface physiochemical properties such as surface wettability, surface roughness, and surfaces charge, that decisively affected bacterial adhesion and following biofilm formation. Collagen resisted bacterial adhesion on both DLC and Ti films, even though the molecules exhibited distinct conformations on the two surfaces, whereas for Fn and IgG, the specific molecular recognition was closely related to protein conformations. Fn molecules formed globular aggregates on Ti surfaces that greatly enhanced bacterial adhesion but exhibited a fibril conformation on DLC surfaces that inhibited bacterial adhesion. IgG showed an end-on orientation with free F(ab)2 domains on Ti surfaces, facilitating bacterial adhesion and biofilm formation, while the flattened orientation on DLC films showed little effect on bacterial behaviors. Furthermore, preadsorption of Fn and IgG significantly promoted the phagocytosis ability of macrophages against S. epidermidis and affected the corresponding secretion of inflammatory cytokine. These results would give insights into understanding protein-surface interactions for developing appropriate surface modification techniques for biomaterials with desired anti-inflammatory functions.

Comparison of Wound-Healing Characteristics with Minimally Invasive Systems in 3D Liver Model

The object of this research was to investigate the thermal injury in the liver after a minimally invasive devices with a titanium dioxide (TiO2), a chromium nitride (CrN) and a diamond-like carbon (DLC) surface modifications. In 3D computer-aided models, needle type monopolar device equipped with TiO2, CrN and DLC thin films were used to simulate cutting livers. Data indicated that the temperature decreased significantly when minimally device with nanostructured TiO2, CrN and DLC thin films were used. Thermography revealed that the surgical temperature was significantly lower in the minimally invasive device with DLC thin film compared to untreated device. On the other hand, DLC device created a relatively small thermal injury and lateral thermal area. This research reveals that the novel nanostructured thin film on electrode substrates is an effective means of improving the performance of reducing excessive thermal injury and uniformly distributing temperature in livers.

Proposal of a new formation mechanism for hydrogenated diamond-like carbon transfer films: Hydrocarbon-emission-induced transfer

Diamond-like carbon (DLC) is one of the most promising solid lubricants for sliding against other materials, such as steel, alumina, and silicon carbide (SiC). During sliding, a DLC transfer film is usually formed on the counterpart surface, affording a low friction coefficient. It is well known that hydrogen in DLC strongly promotes the formation of the DLC transfer film. To further improve the lubricity of DLC, we investigate the formation mechanisms of the DLC transfer film on amorphous SiC and the influence of hydrogen on transfer film formation using reactive molecular dynamics simulations. In addition to the conventional transfer mechanism induced by surface adhesion, we herein propose the new transfer mechanism of “hydrocarbon-emission-induced transfer”. In the proposed transfer mechanism, hydrocarbon molecules are emitted from the DLC surface and subsequently adsorb on the counterpart surface during the continuous grinding of the sliding interface, ultimately generating the DLC transfer film. Furthermore, the addition of hydrogen atoms to DLC slightly increases the adhesion-induced transfer and greatly accelerates the “hydrocarbon-emission-induced transfer”, collaboratively contributing to substantial DLC transfer film formation. Thus, we suggest that the experimentally observed promotion of DLC transfer film formation by hydrogen is largely attributable to our proposed mechanism of “hydrocarbon-emission-induced transfer”.

Interactions of Atomic and Molecular Hydrogen with a Diamond-like Carbon Surface: H2 Formation and Desorption

Abstract The interactions of atomic and molecular hydrogen with bare interstellar dust grain surfaces are important for understanding H2 formation at relatively high temperatures (>20 K). We investigate the diffusion of physisorbed H atoms and the desorption energetics of H2 molecules on an amorphous diamond-like carbon (DLC) surface. From temperature-programmed desorption experiments with a resonance-enhanced multiphoton ionization (REMPI) method for H2 detection, the H2 coverage-dependent activation energies for H2 desorption are determined. The activation energies decrease with increasing H2 coverage and are centered at 30 meV with a narrow distribution. Using a combination of photostimulated desorption and REMPI methods, the time variations of the surface number density of H2 following atomic and molecular hydrogen depositions are studied. From these measurements, we show that H2 formation on a DLC surface is quite efficient, even at 20 K. A significant kinetic isotope effect for H2 and D2 recombination reactions suggests that H-atom diffusion on a DLC surface is mediated by quantum mechanical tunneling. In astrophysically relevant conditions, H2 recombination due to physisorbed H-atoms is unlikely to occur at 20 K, suggesting that chemisorbed H atoms might play a role in H2 formation at relatively high temperatures.

Temperature and velocity dependent friction of a microscale graphite-DLC heterostructure

One of the promising approaches to achieving large scale superlubricity is the use of junctions between existing ultra-flat surface together with superlubric graphite mesas. Here we studied the frictional properties of microscale graphite mesa sliding on the diamond-like carbon, a commercially available material with a ultra-flat surface. The interface is composed of a single crystalline graphene and a diamond-like carbon surface with roughness less than 1 nm. Using an integrated approach, which includes Argon plasma irradiation of diamond-like carbon surfaces, X-ray photoelectron spectroscopy analysis and Langmuir adsorption modeling, we found that while the velocity dependence of friction follows a thermally activated sliding mechanism, its temperature dependence is due to the desorption of chemical groups upon heating. These observations indicate that the edges have a significant contribution to the friction. Our results highlight potential factors affecting this type of emerging friction junctions and provide a novel approach for tuning their friction properties through ion irradiation.

Influence of particulate on surface energy and mechanical property of diamond-like carbon films synthesized by pulsed laser deposition

We report a detailed structural study of particulate laden diamond-like carbon (DLC) films synthesized by pulsed laser deposition (PLD) and its influence on surface energy and mechanical properties. A detailed analysis of various parameters such as: Dispersion (G), I(D)/I(G), T-peak position and FWHM(G) obtained from UV Raman spectroscopy for flat and particulate region of all DLC specimens indicate that the vibrational properties vary in both the regions depending on growth mechanism and modification of particulates in the plasma, respectively. The influence of these heterogeneous vibrational properties on surface energy and hardness is extensively studied by contact angle measurement and nano-indentation, respectively. DLC surface energy is observed to be influenced by sp2 cluster size, sp3 content, bond length and angle disorder of sp2 clusters found in the particulate regions, whereas indentation hardness (H) and modulus (E) of DLC films at 0.3 mN applied indentation load follows the evolution of sp3 content in the flat region.

Adsorption properties of molybdenum based FMs on boron-doped DLC

Development of low friction surface materials matched with low friction lubricants is an important route to improving engine efficiency and reducing emissions. Diamond-like carbon (DLC) is a material of interest because it combines the durability of diamond with the low friction properties of graphite. Consequently, various forms of DLC have been studied as durable, low friction surface coatings. At the same time, friction modifiers (FMs) are often used in engine lubricants to produce low friction surface layers. Molybdenum-based friction modifiers are commonly used additives that mechanochemically decompose to cover surfaces with MoS2, a solid lubricant. FMs can also reduce friction on DLC surfaces. However, molybdenum can be harmful to DLC and cause rapid degradation and breakthrough of the DLC surface layer. We have found that the wear debit of molybdenum FMs trends with surface affinity of the additive. The adsorption isotherms of 4 Mo-based FMs on boron-doped diamond-like carbon (BDLC) were measured with a quartz crystal microbalance (QCM). The strongest adsorbate, Mo dithiophosphate (MoDTP), which also forms the thickest film, protects the BDLC surface enabling low friction while keeping wear low. Theoretical predictions based on molecular dynamics simulations combined with molecular-thermodynamic theory (MD-MTT) show that adsorption of MoDTP on BDLC deviates significantly from Langmuir behavior and free energy of adsorption for the first monolayer is significantly more negative than the multilayer adsorption free energy observed experimentally. The relationship between wear and adsorption behavior is consistent with experimental observations in the literature. These results also suggest that additive performance in a fully formulated lubricant is related to fundamental adsorption properties measured on the neat additive.

Failure of DLC Films Caused by Cyclic Sphere Indentation and Effects of Film Structures on Failure Mode

As a new strength evaluation method for hard coatings such as diamond-like carbon (DLC), the cyclic indentation test was proposed. Then, a test rig was fabricated and used for the evaluation of DLC. DLC and a Cr/C inclined interlayer for the improvement of the adhesion strength of DLC were prepared by the unbalanced magnetron (UBM) sputtering method on heat-treated and polished JIS SCM415 substrates. Si3N4 spheres having diameters of 10 mm were used for the cyclic indentation test. 10000 cycle indentations brought about DLC fracture and detachment in the indentation impression. Also ring cracks were observed around the impression. I(D)/I(G), which is the ratio of the D to G peak intensities, decreases towards the center of the impression. It was considered to indicate decreasing sp2 cluster size in DLC. On the other hand, compressive stress increased near the surface of DLC in the contact area, as indicated by the change in its G peak position. It seemed to be the cause of the fracture and detachment of DLC in the impression.

Numerical Analysis of Surface Force of Diamond-Like Carbon Surface Coated with Monolayer Lubricant Film

Numerical Analysis of Surface Force of Diamond-Like Carbon Surface Coated with Monolayer Lubricant Film

Wear acceleration mechanism of diamond-like carbon (DLC) films lubricated with MoDTC solution: Roles of tribofilm formation and structural transformation in wear acceleration of DLC films lubricated with MoDTC solution

Abstract The wear acceleration mechanism of DLC films lubricated with MoDTC solution was investigated by using in-situ and ex-situ analytical techniques: Raman spectroscopy, XPS, ToF-SIMS and nano-indenter. Especially, to reveal the role of ZDDPs and ta-C films for inhibiting the wear acceleration, friction tests were carried out using a ball-on-disk setup at a-C:H/steel and ta-C/steel contacts lubricated with PAO, PAO + MoDTC and PAO + MoDTC + ZDDP. All our results suggest that the wear acceleration is caused by hard Mo-carbide containing tribofilms. Therefore, wear acceleration did not occur for the harder DLC, i.e., the ta-C films. Our results also suggest that ZDDPs play important roles in inhibiting the carburization of Mo-compounds involving DLC surfaces at the tribological contact.

Kinetics of graphitization of thin diamond-like carbon (DLC) films catalyzed by transition metal

In this paper, we have studied the kinetics of graphitization at 773 K of thin diamond-like carbon (DLC) films coated with minute amount of Ni metallic particles. DLC films are deposited at room temperature by pulsed laser deposition (PLD) on a transparent quartz substrate, and Ni is deposited on the surface of DLC using molecular beam epitaxy technique at room temperature. The ultra-high vacuum thermal (range 573–873 K with 60 min annealing treatments) and kinetic (range 30–3760 min at 773 K) behaviors of the deposited films are investigated. Surface and interface characterizations indicate that the growth of graphitic sp2 clusters starts at temperatures lower than 573 K. The kinetics of graphitization is recorded at 773 K. Thus, the continuous growth of graphitic clusters leads to a long-range kinetics. These clusters are responsible for the increase in the electrical conductivity and carrier mobility, reaching values of 6.103 Siemens/cm and 20 V/cm2 × s, respectively. This continuous change is not only explained by the nucleation and growth of graphitic clusters, but also by some reorientation of them alongside both the surface and the quartz substrate. The obtained results demonstrate that thermally post-treated catalytic metal/DLC films are promising materials for conductive electrodes and sensing applications.Prime novelty and projected interestKinetics of graphitization at 773 K of thin diamond-like carbon (DLC) films coated with minute amount of Ni metallic particles;High surface electrical conductivities, which are quite promising and competitive in comparison to literature data dealing with transparent electrodes.Correlation between conductivity models and Raman measurements in Catalytic Metal/DLC material.

Characterization of DLC-Coated and Uncoated Surfaces by New Directional Blanket Curvature Covering (DBCC) Method

Roughness and curvature of diamond-like carbon (DLC) surface coatings change with both scale and direction of a measurement. However, the changes are not detected by currently used standard parameters which are designed to work with isotropic surfaces at a single scale, thus providing only a limited information about multiscale and directional roughness and curvature. The problem of detailed roughness characterization of DLC-coated surfaces has been addressed in our previous work [Wolski et al. Multiscale characterization of 3D surface topography of DLC-coated and uncoated surfaces by directional blanket covering method. Wear 2017:388–389:47–56]. However, surface curvature description still remains an unresolved issue. To overcome this shortcoming, a directional blanket curvature covering (DBCC) method was developed. The method calculates curvature, peak and valley dimensions which quantify multiscale and directional curvature complexity of surface topography, peaks and valleys, respectively. Higher values of the dimensions represent higher complexity. In the current study, the DBCC method was used to analyse DLC-coated and uncoated bearing steel samples with increasing roughness and curvature. Its ability to discriminate between these two groups of surfaces was evaluated. Results showed that the method could detect minute changes in surface curvature at individual scales and directions. The method would be of interest to those who design wear-resistant systems and surfaces.

Acid Treatment of Diamond-Like Carbon Surfaces for Enhanced Adsorption of Friction Modifiers and Friction Performance

Diamond-like carbon (DLC) is a class of amorphous carbon materials used as wear-resistant coatings in tribo-components. The chemical inertness of DLC surfaces, while important in many applications, makes them incompatible with additives in commercial lubricants. Specifically, DLC surfaces do not permit strong adsorption of friction modifier molecules. This study aims at improving the adsorption of these friction modifier molecules on DLC surfaces through an acid treatment. Water contact angle measurements show that such a treatment results in improved hydrophilicity of the DLC. XPS analysis demonstrates 50% increase in the uptake of ArmeenT, an organic friction modifier, on DLC after the acid treatment. This increased ArmeenT adsorption is accompanied by marked decrease in friction in micro-scale friction experiments.

UV laser annealing of Diamond-Like Carbon layers obtained by Pulsed Laser Deposition for optical and photovoltaic applications

One of the biggest challenge in optoelectronic devices is the necessity to provide a viable and reliable alternative to Transparent Conducting Oxide (TCO) and especially to Indium Tin Oxide (ITO). Graphene is a widely studied material and one of the best alternative to be used as conductive and transparent electrodes. It is well known that the difficulty to transfer graphene on another substrate is a serious limitation for its use on large scale devices. In this work, we explore Diamond-like Carbon (DLC) thin films prepared by Pulsed Laser Deposition (PLD) to be used as substrate for graphene-like layers. DLC thin films are excellent candidates due to their visible-range transparency being also a very good electrical insulator. Transmission measurements show the UV opaque character of the DLC layers, independently to the experimental parameters used to produce them. Thus, top-hat UV laser surface annealing can strongly modify the DLC thin film structure in order to bring conductivity to the first atomic layers. Raman spectroscopy and X-ray photoemission spectroscopy permit to confirm the graphitic character of the DLC surface. Optimizing PLD as well as laser annealing parameters is explored in detail in order to obtain comparable performances (conductivity and transparency) to ITO typical properties. Moreover, using a full-based laser process offers a complete compatibility with all technical steps of the microelectronic domain.

Impact of modified diamond-like carbon coatings on the spatial organization and disinfection of mixed-biofilms composed of Escherichia coli and Pantoea agglomerans industrial isolates

This work investigated the effects of diamond-like carbon (DLC) coatings on the architecture and biocide reactivity of dual-species biofilms mimicking food processing contaminants. Biofilms were grown using industrial isolates of Escherichia coli and Pantoea agglomerans on bare stainless steel (SST) and on two DLC surface coatings (a-C:H:Si:O designated by SICON® and a-C:H:Si designated by SICAN) in order to evaluate their antifouling activities. Quantification and spatial organization in single- and dual-species biofilms were examined by confocal laser scanning microscopy (CLSM) using a strain specific labelling procedure. Those assays revealed that the E. coli isolate exhibited a higher adhesion to the modified surfaces and a decreased susceptibility to disinfectant in presence of P. agglomerans than alone in axenic culture. While SICON® reduced the short-term growth of E. coli in axenic conditions, both DLC surfaces increased the E. coli colonization in presence of P. agglomerans. However, both modified surfaces triggered a significantly higher log reduction of E. coli cells within mixed-species biofilms, thus the use of SICON® and SICAN surfaces may be a good approach to facilitate the disinfection process in critical areas of food processing plants. This study presents a new illustration of the importance of interspecies interactions in surface-associated community functions, and of the need to evaluate the effectiveness of hygienic strategies with relevant multi-species consortia.

Decreased hydrogen content in diamond-like carbon grown by CH4/Ar photoemission-assisted plasma chemical vapor deposition with CO2 gas

In this study, we tried to decrease the hydrogen content in diamond-like carbon (DLC) grown by photoemission-assisted plasma enhanced chemical vapor deposition (PA-PECVD) using Ar/CH4 mixed with CO2. When the CO2 flux was changed from 0 to 10 sccm with the Ar and CH4 fluxes maintained at 50 and 10 sccm, respectively, the growth rate decreased from 11 to 3 μm/h. Secondary mass spectroscopy measurements confirmed that the amount of O mixed into the DLC was increased through incorporation of CO2 into feed gas flow. The O concentration in the DLC was quantitatively evaluated by X-ray photoelectron spectroscopy (XPS) to be 0.6 atomic % at a CO2 flow ratio of 14%. Raman spectroscopy and XPS revealed that the amount of H trapped in the DLC decreased as the CO2 flow ratio was increased and the sp3/sp2 ratio remained almost unchanged. These results were interpreted by a model involving O radicals acting on the DLC surface associated with CO/CO2 and H2O, resulting in a decrease of the growth rate and H content. A portion of the O radicals also became incorporated into the DLC as COC bonds.