Diamond-like Carbon Substrate Research Articles

Adsorption of fatty acid potassium salts on diamond-like carbon: Effects of alkyl chain lengths and adsorptive conditions

Organic monolayers on solid substrates have received considerable attention due to their excellent versatilities in many fields. In this paper, molecular dynamics (MD) simulations were performed to study the adsorption of fatty acid potassium salts (FAPS) on diamond-like carbon (DLC) substrates. The results indicated that adsorbed molecules tend to aggregate on DLC surfaces due to the intense attractions between FAPS molecules. In order to obtain evenly distributed molecular films, the external energy input is needed to facilitate molecular adsorption and overcome the potential barriers. Also, the effects of alkyl chain lengths on molecular adsorption were investigated. A positive correlation was observed between the alkyl length and the adsorptive energy exerted by DLC substrates. Furthermore, the Coulomb interaction between adsorbed molecules is the most powerful interaction within the MD system. Affected by the Coulomb interactions, adsorbed molecules would undergo severe deformation. And a net-like structure composed of polar ends is formed in molecular films. The hollow area within the network is full of alkyl chains of molecules. It can be concluded that the powerful Coulomb interactions between adsorbed molecules play a dominant role in determining the adsorption behavior and structural properties of potassium salts on DLC substrates.

Nano-scratch and nano-indentation study of diamond-like carbon/NiP-SiC nanocomposite bilayer

To overcome the poor adhesion of diamond-like carbon (DLC) films to the steel substrate, an interlayer can be used. In this study, the effect of the addition of NiP-SiC nanocomposite coating as an interlayer in comparison to the NiP coating has been investigated on tribological properties of the DLC layer. Using nano-scratch and nano-indentation tests, the mechanical and nanotribological behaviour of the DLC layers, such as scratch resistance, coefficient of friction, interfacial adhesion between DLC layer and substrate, and hardness were characterised. DLC/NiP-SiC samples showed higher adhesion, hardness, elastic modulus, and lower friction coefficient. These results reveal the improved tribological properties of DLC film by applying the NiP-SiC nanocomposite interlayer in comparison to using the pure NiP interlayer.

CVD-diamond nanoparticle synthesis for DLC film application

Diamond-like carbon (DLC) films have been extensively applied as a solid lubricant and as a protective coating due to their attractive chemical, mechanical, and tribological properties. Furthermore, these properties of DLC coatings can be improved with the incorporation of nanoparticles of different materials, especially diamond nanoparticles (DNPs). Herein, the incorporation of chemical vapor deposition (CVD) DNPs was done from a deionized aqueous colloidal solution by using a controlled pulsed valve, which is an innovative aspect of this work. The CVD DNPs were pulverized into the plasma region and incorporated in the DLC films bulk with controllable size particle distribution and density. In addition, an enhanced process to obtain DNPs with suitable size distribution was established by using a high energy ball milling technique, centrifugation, and a special chemical cleaning process. The DLC films were deposited on a metallic substrate via a modified, pulsed DC plasma-enhanced chemical vapor deposition (PECVD) technique, with an additional cathode. X-ray diffractometry (XRD) and scanning electronic microscopy (SEM) techniques showed that an aqueous colloidal solution of high-purity DNPs with a mean diameter of 32 nm was obtained. Dynamic light scattering (DLS) results showed that it is possible to control particle size distribution by varying the milling and centrifugation time lengths. Therefore, a valuable result was that DLC films could be deposited with DNPs by using clean water without affecting deposition rate, the adhesion between the DLC films and substrates, the structural quality of the film, and keeping lower coefficient of friction.

Quantitative Structure-Properties Relationship of Lubricating Oil Additives and Molecular Dynamic Simulations Studies of Diamond-Like-Carbon (DLC)

Quantitative Structure-Properties Relationship (QSPR) and molecular dynamics simulations studies were carried out on the 53 lubricating oil additives and hydrogen-containing DLC (a-C: H). Good QSPR model was developed along with squared correlation coefficient (R2), adjusted squared correlation coefficient (R2adj), leave one out cross-validation coefficient (Q2) and the external validation (R2ext) of values 0.807208, 0.763674, 0.68867 and 0.6297 respectively which shows that model I was reliable and satisfactory. Molecular dynamics simulation binding energy calculations between the lubricant additives and the hydrogen-containing DLC (a-C: H) crystals surface revealed that the best molecular dynamic binding energy was found to be -2112.06 kcal/mol and was found to be better than the one reported by other researchers. Moreover, the lubricant additive with compound number 50** (S-(2-(benzo[d]thiazol-2-ylamino)-2-oxoethyl) O-hexyl carbonodithioate) was found to have the best molecular dynamic binding energy of -2112.06 kcal/mol which conformed with excellent best-normalized onset temperature (Tonset) 2.467K of the same compound. Moreover, Table 7 revealed that the time(s) used for every simulation varies from 12683.13s to 138841.09s for all the studied additives. This investigation will help in rational additive design and synthesis of new and better lubricant additives with predetermined promising binding energy and onset temperature (Tonset) and will provide valuable information for the understanding of dynamic binding energy between DLC substrate and the new compounds and will give the way toward the discovery of novel lubricating oil additives that can withstand high dynamic working temperature and also resist wearing and frictions.

Preparation, characterization and investigation of molecular films coated on diamond-like carbon substrate

For the successful application of boundary lubrication, detailed investigations about the influence of preparation process on molecular films are needed. In this paper, a specially designed device was used for the film preparation. The scanning electron microscope (SEM) combined with atomic force microscope (AFM) was employed to characterize the surface morphology and nanotribological behavior of molecular films. After the liquid phase deposition, molecular films are randomly and densely distributed over Ti-doped diamond-like carbon (Ti-DLC) substrates. Through rigorous surface treatments, island-like molecular films were finally achieved on substrate surfaces. The surface friction of molecular films is obviously lower than that of Ti-DLC surfaces. Then, pin-on-disk tribotests were performed to study the macrofriction behavior of molecular films under different preparation parameters. Based on the orthogonal experiment, the effect of five preparation parameters (solution weight percent, smearing force and processing time of three smearing steps) on initial friction coefficient of molecular films was investigated. The results indicated that the order of significance levels is as follows: processing time of the second smearing step > solution weight percent > processing time of step 1 > processing time of step 3 > smearing force. For the purpose of friction reduction, the appropriate level ranges are 0.75% (Solution), 2.5 N–15 N (Force), 1 min–10 min (Step 1), 1 min–2 min (Step 2) and 1 min, 2 min, 5 min and 15 min (Step 3). The initial friction coefficient under the optimized conditions is around 0.112, and the equilibrium friction coefficient is around 0.162, which is lower than that of unlubricated Ti-DLC substrates.

Molecular dynamics research on geometric effect of nanostructured diamond-like carbon substrates on potassium stearate adsorption

Molecular dynamics (MD) simulations were performed to investigate the geometric effect of nanostructured substrates on adsorptive behavior of potassium stearate monolayers. A typical protective coating, diamond-like carbon (DLC), was employed as adsorptive substrates. For the substrates with square grooves, complete penetration of molecules can only occur under large width and small depth. The occurrence of partial penetration would make monolayer atoms away from substrate surfaces and therefore induce weak substrate-molecules interactions. Compared with the square groove bottoms, monolayers are much more strongly adsorbed to the groove concave corners. For substrates with triangle and semi-circle grooves, complete penetrations are achieved in both cases and thus monolayer atoms can interact with the whole groove surface. The effect of substrate morphology on monolayer adsorption would be sufficiently weakened by the decrease of geometric size, and the surface adsorptivity of semi-circle grooves with large radius is similar to that of the smooth surface. The results indicate that the substrates with triangle grooves have better adsorptivity than other morphologies.

Influence of surface morphology on adsorption of potassium stearate molecules on diamond-like carbon substrate: A molecular dynamics study

Molecular dynamics (MD) simulations were used to provide insights into the influence of nano-scale surface morphology on adsorptive behavior of Potassium stearate molecules on diamond-like carbon (DLC) substrates. Particular focus was given to explain that how the distinctive geometric properties of different surface morphologies affect the equilibrium structures and substrate-molecules interactions of monolayers, which was achieved through adsorptive analysis methods including adsorptive process, density profile, density distribution and surface potential energy. Analysis on surface potential energy demonstrated that the adsorptivity of amorphous smooth substrate is uniformly distributed over the surface, while DLC substrates with different surface morphologies appear to be more potentially corrugated, which improves the adsorptivity significantly. Because of the large distance of molecules from carbon atoms located at the square groove bottom, substrate-molecules interactions vanish significantly, and thus potassium stearate molecules cannot penetrate completely into the square groove. It can be observed that the equilibrium substrate-molecules interactions of triangle groove and semi-circle groove are much more powerful than that of square groove due to geometrically advantageous properties. These findings provided key information of optimally design of solid substrates with controllable adsorptivity.

Tight-Binding Quantum Chemical Molecular Dynamics Study on the Friction and Wear Processes of Diamond-Like Carbon Coatings: Effect of Tensile Stress.

Diamond-like carbon (DLC) coatings have attracted much attention as an excellent solid lubricant due to their low-friction properties. However, wear is still a problem for the durability of DLC coatings. Tensile stress on the surface of DLC coatings has an important effect on the wear behavior during friction. To improve the tribological properties of DLC coatings, we investigate the friction process and wear mechanism under various tensile stresses by using our tight-binding quantum chemical molecular dynamics method. We observe the formation of C-C bonds between two DLC substrates under high tensile stress during friction, leading to a high friction coefficient. Furthermore, under high tensile stress, C-C bond dissociation in the DLC substrates is observed during friction, indicating the atomic-level wear. These dissociations of C-C bonds are caused by the transfer of surface hydrogen atoms during friction. This work provides atomic-scale insights into the friction process and the wear mechanism of DLC coatings during friction under tensile stress.

Deposition of a Diamond-Like-Carbon Film by Ion Plating and Investigation on its Adhesiveness

Diamond-like-carbon (DLC) films are promising as coating materials. Ion plating, an excellent method in terms of adhesiveness, step coverage, and deposition rate, can form not only pure metal films but also oxide films, nitride films, and carbonized films. In this study, which aimed to form a DLC film with good adhesiveness and a diamond crystal structure, a DLC film, with a SiC interlayer formed by ion plating with introduction of tetramethylsilane (TMS), was formed. It was experimentally revealed that as the interlayer thickness increases, the crystal structure in the DLC film becomes more diamond rich, and the adhesiveness of the DLC film and substrate is thereby improved.

An investigation of the adsorption of potassium stearate molecules on diamond-like carbon substrate using molecular dynamics simulation

Molecular dynamics (MD) simulations were performed to investigate the adsorption of potassium stearate molecules on diamond-like carbon (DLC) substrate. The effects of non-bonded interactions and confinement conditions on the adsorption were investigated. The confinement conditions performed herein were achieved by imposing a Z-direction constraint on the movement of molecules in the initial stage of adsorption, and then releasing the molecules from the constraint gradually. Our simulation results show that the polar end groups of molecules tended to accumulate during the adsorption, and the final distribution of adsorptive film without confinement was irregular. Under confinement conditions, the adsorptive film was evenly distributed on the substrate after reaching its equilibrium configuration, and the final inter-subsystem potential of the substrate on adsorptive film was obviously decreased as compared with the results without confinement. These findings provided an effective approach for promoting the adsorption of molecules.

Tribological behavior of diamond-like carbon thin films deposited by the pulse laser technique at different substrate temperatures

Diamond-like carbon (DLC) thin films were deposited by the pulse laser deposition at different substrate temperatures. They were deposited at the temperature range 100–500°C and evaluated for their tribological behavior. The as-synthesized DLC films were characterized by different techniques. Ultrafine nanoparticles were observed in the deposited DLC films. The morphology of the deposited DLC films was significantly modified by increasing the substrate temperature. The particle size was increased from around 10nm to approximately 30nm by increasing the substrate temperature from 100 to 500°C. The surface roughness was also increased, beside a formation of DLC clusters mainly at 500°C. Raman and XPS spectra showed a significant improvement in the graphitization along with pronounced defects in the amorphous carbon structures in these DLC films. These modifications, induced by increasing the DLC substrate temperature have increased values of the friction coefficient and specific wear rate. These results showed that the DLC films with ultrafine nanoparticles have good prospect to be used as protective layers for metallic surfaces as they show low friction property and high wear ability.

Study of Perfluoropolyether Lubricant Consumption and Recovery in Heat Assisted Magnetic Recording Using Molecular Dynamics Simulation Method

Currently, heat-assisted magnetic recording (HAMR) technology has been proposed as a method for enabling higher storage density. In this paper, the molecular dynamic simulation method was used to investigate the consumption and recovery of the lubricant perfluoropolyether (PFPE) layer under rapid heating and cooling through HAMR. A full-atom model for the 3-D slider-lubricants-disk substrate system was built for this paper. The lubricant adheres to the diamond-like carbon substrate, and the space between the slider and the lubricant is filled with helium atoms. It is found that HAMR laser heating results in the gradual consumption of the PFPE lubricant, and that the target operational temperature $T_{0}$ significantly affects the consumption of the PFPE lubricant on the disk substrate. The extent of lubricant consumption increases sharply when $T_{0}$ is above 600 K. The lubricant’s weight percentage on the disk substrate rises up again when cooling occurs. But it cannot be completely recovered. On the other hand, the bearing pressure reduces the degree of consumption of the PFPE lubricant by laser heating. However, the effect of bearing pressure on the amount of remaining PFPE lubricant becomes weak when $T_{0}$ is above 800 K.

Impact of the difference in power frequency on diamond-like carbon thin film coating over 3-dimensional objects

With a type of capacitatively coupled plasma enhanced chemical vapor deposition (PECVD) technique, where two specially designed electrodes face to each other, the inner surface of hollow 3-dimensional objects such as poly(ethylene terephthalate) (PET) bottles can be coated with diamond-like carbon (DLC) thin film. DLC-coated PET bottles obtained with this technique have an enhanced gas barrier property, and therefore are applicable to industrial use such as for the extension of the shelf-life of contents sensitive to gas permeation. In this paper, the impact of power frequency ranging from 2.5 to 13.56MHz was studied in order to research the behavior of plasma inside PET bottles and resultant properties. Different power frequency turned out to be influential on gas barrier property, the overall and distribution of tint, and adhesion between DLC and PET substrate. In addition, positron annihilation turned out to be powerful tool for the comparison of different coating conditions because it clarifies the homogeneity of DLC thin films through providing information on overall structure and thickness of them. These findings can be used for the optimization not only in the beverage PET bottle application, but also in other capacitatively coupled PECVD devices.

Maintenir au travail les personnes en situation de handicap : nouveaux modèles, nouvelles méthodes pour l’ergonomie

With a type of capacitatively coupled plasma enhanced chemical vapor deposition (PECVD) technique, where two specially designed electrodes face to each other, the inner surface of hollow 3-dimensional objects such as poly(ethylene terephthalate) (PET) bottles can be coated with diamond-like carbon (DLC) thin film. DLC-coated PET bottles obtained with this technique have an enhanced gas barrier property, and therefore are applicable to industrial use such as for the extension of the shelf-life of contents sensitive to gas permeation. In this paper, the impact of power frequency ranging from 2.5 to 13.56 MHz was studied in order to research the behavior of plasma inside PET bottles and resultant properties. Different power frequency turned out to be influential on gas barrier property, the overall and distribution of tint, and adhesion between DLC and PET substrate. In addition, positron annihilation turned out to be powerful tool for the comparison of different coating conditions because it clarifies the homogeneity of DLC thin films through providing information on overall structure and thickness of them. These findings can be used for the optimization not only in the beverage PET bottle application, but also in other capacitatively coupled PECVD devices.

Plasma Modification of DLC Films and the Resulting Surface Biocompatibility

Diamond-like carbon (DLC) films were synthesized on a p-type silicon wafer using radio-frequency plasma composed of a mixture of Ar and C2H2 (ratio of 7 to 28). NH3 plasma treatment of as-grown DLC substrate was carried out to generate surface-terminal amino groups while oxidation of as-grown DLC was performed in O2 plasma. X-ray photoelectron spectroscopy (XPS) was used to characterize the different surface functions formed on DLC surfaces. Water contact angle measurements indicate different wetbility of modified surfaces. The cell (Mouse MC3T3-E1 pre-osteoblasts) morphology and proliferation were monitored to evaluate the biocompatibility of the modified DLC surfaces. A cell count kit-8 (CCK-8 Beyotime) was employed to determine quantitatively the viable pre-osteoblasts. The cell viability assay shows that osteoblast proliferation are improved on NH3 and O2 plasma-treated DLC surface after culturing for 1day, 2days and 3 days. The cell-surface interactions are studied by fluorescence microscopy. There are more osteoblasts as well as better spreading on the aminated and oxidized surfaces after culturing for 3 days. In summary, compared to the as-grown sample, the modified DLC shows better biocompatibility.

Atomistic Molecular Dynamics Study of Structural and Thermomechanical Properties of Zdol Lubricants on Hydrogenated Diamond-Like Carbon

Using atomistic (all-atom) molecular dynamics simulations with COMPASS force-field, we study the structural and thermomechanical properties of Zdol lubricants accommodated on a hydrogenated diamond-like carbon substrate. It is found that the lubricant molecules form a distinct layered structure near the substrate surface. The thickness of each layer and the location of each density maximum depend on temperature. The computed radius of gyration shows a strong anisotropy near the substrate surface and both parallel and perpendicular components of the radius of gyration increase with increasing temperature. In addition, it is found that the lubricant diffusion coefficient is also anisotropic with the component parallel to the surface being larger than the perpendicular one, and both increase with the lubricant film thickness. Using the calculated diffusion coefficients, we extract the activation energies for lubricant diffusion. We also qualitatively compare the present all-atom simulations with the previous coarse-grained simulations.

Novel type of protein chip for multiplex detection of autoantibodies

Evaluation of: Akada J, Kamei S, Ito A et al. A new type of protein chip to detect hepatocellular carcinoma-related autoimmune antibodies in the sera of hepatitis C virus-positive patients. Proteome Sci. 11(1), 33 (2013).Unlocking the proteome and delivering biomarkers to the clinic will be critical for early and improved diagnosis and prognosis. Conventional protein microarrays have evolved as a promising proteomic technology with great potential for protein expression profiling in health and disease. In this study, Akada et al. explore a new type of protein chip, interfaced with a dual-color fluorescence-based read-out, for screening of autoantibodies in serum. Uniquely, the recombinant antigens were microarray adapted by molecular design to contain a five-cysteine tag for immobilization and green fluorescent protein for detection (color 1). The engineered antigens were immobilized on in-house-designed maleimide-incorporated diamond-like carbon substrates and subsequently heat treated in a solution of denaturing and reducing agents before any specifically bound serum autoantibodies were detected (color 2). The authors used a 4-plex array targeting hepatocellular carcinoma-related autoantibodies in the sera of hepatitis C virus-positive patients as model system to demonstrate proof-of-concept.

Frictional and Optical Properties of Diamond-Like-Carbon Coatings on Polycarbonate

In this work, diamond-like-carbon (DLC) films were deposited onto polycarbonate (PC) substrates by radio-frequency plasma-enhanced chemical vapor deposition (RF PECVD), and silicon films were prepared between DLC and PC substrates by magnetron sputtering deposition so as to improve the adhesion of the DLC films. The deposited films were investigated by means of field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Subsequently, the following frictional and optical properties of the films were measured: the friction coefficient by using a ball-on-disk tribometer, the scratch hardness by using a nano-indenter, the optical transmittance by using a UV/visible spectrometer. The effects of incident power upon the frictional and optical properties of the films were investigated. Films deposited at low incident powers showed large optical gaps, which decreased with increasing incident power. The optical properties of DLC films correlated to the sp2 content of the coatings. High anti-scratch properties were obtained at higher values of incident power. The anti-scratch properties of DLC films correlated to the sp3 content of the coatings.

Graphene modulated 2D assembly of plasmonic gold nanostructure on diamond-like carbon substrate for surface-enhanced Raman scattering

A close-packed 2D assembly of plasmonic gold nanostructure was fabricated on a diamond-like carbon film by a two-step electrodeposition via reduced graphene oxide (rGO) modulation. The oxygen functionalities at the rGO surface which were controlled by changing electrochemical reduction time of GO provided reactive sites for nucleation and growth of gold nanoparticles. The Raman intensity of rhodamine B obtained from the gold assembly showed an 860-fold increase compared with that from Si reference, indicating a coupling of localized electromagnetic field enhancement and chemical enhancement. Our research offered a novel way for metallic plasmonic fabrication to realize their potential applications in biochemical analysis, environmental monitoring, disease detection and food safety.

Molecular dynamics investigation of the lubrication mechanism of carbon nano-onions

Carbon nano-onions have been shown to provide exceptional friction and wear reduction through a rolling and sliding mechanism of the nano-onions at the interface, but the influence of this behavior on the their tribological properties is not well documented. Understanding the lubrication mechanisms of such nanostructured materials aids in determining their frictional properties and promotes the use of these materials in tribological applications. Here, we characterize the mechanisms of rolling and sliding through which carbon nano-onions provide low coefficients of friction by performing atomistic molecular dynamics simulations of carbon nano-onions sliding between diamond-like carbon substrates. The results indicate that the ability of the nano-onions to roll is inhibited both by increased contact pressure and the presence of a diamond core within the nanoparticles that enhances the formation of interfacial bonds during friction. The transition from rolling to sliding behavior is accompanied by a significant increase in the coefficient of friction.