Properties Of Diamond-like Carbon Films Research Articles

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.

Effect of Silver Clusters Deposition on Wettability and Optical Properties of Diamond-like Carbon Films

In this study, the effect of silver clusters deposition was investigated on optical, wettability and surface properties of diamond-like carbon (DLC) films. Silver clusters and DLC films were deposited on Ni-Cu (70.4-29.6;W/W) alloy substrates by ion beam sputtering deposition (IBSD) technique. Optical and structural properties were measured using UV-visible spectroscopy and Raman spectroscopy, respectively. The wettability and surface free energy of films were determined by the contact angle (CA) measurements. Raman spectra of DLC thin film with 121±6nm thickness without accumulated Ag showed that the size of the graphite crystallites with sp 2 bands (La) was 3.36A by the ID/IG ratio equal to 0.062 with large optical band gap equal 3eV extracted from Tauc relation. The results of the deposition Ag in the various ion beam energy between 0.6 to 2keV showed the Ag clusters were accumulated uniformity on the surface of DLC films at 0.9keV. The volume percentage of silver clusters was varied from 5.0±2.01 to 16.3±1.4. The variation was caused by controlling the screen voltage and the deposition time. The CA of the deposited films increases from 79°±2 to 95°±2 as well as the reflection values in the visible and near-infrared region due to the increase in the Ag concentration in the surface of DLC films; while the surface free energy decrease from 86±1 to 66±2mJ/m2 and the optical transmittance is almost constant. Our results demonstrate that the deposition of silver particles on DLC films is potentially useful for biomedical applications having good hydrophobic characteristics without causing a destructive effect on the optical properties of DLC films.

High temperature solid/liquid lubrication behaviours of DLC films

AbstractThe high temperature solid/liquid lubrication performances of DLC (diamond like carbon) films were investigated by a ball‐on‐disc tribometer under perfluoropolyether (PFPE) oil. The friction and wear behaviours of DLC films sliding against a Si3N4 ball at different friction pairs, sliding speeds and temperatures were evaluated systematically under dry friction. Moreover, tribological properties of DLC films were investigated under PFPE oils lubrication at elevated temperature. The experimental results show that the solid–liquid synergy lubrication is beneficial to improve the tribological properties of the steel‐related friction system and the tribological properties of the friction pair are significantly influenced by lubrication modes under PFPE oil lubrication, especially at high temperature. Tribotests show that the friction system exhibited low friction behaviours under PFPE oil due to the excellent thermal stability of PFPE oil. Coefficient of friction (CoF) of the friction system is as super low as 0.029 under PFPE oil.

Tailoring the mechanical properties of diamond-like carbon film by doping of trace nonmetal elements: A first-principles study

In order to reflect the regulation mechanism of nonmetal elements on the local mechanical properties of diamond-like carbon (DLC) film, the structure stability, mechanical properties and bonding characteristic of DLC film with nonmetal elements (H, N, O, S, P and Se) were investigated using first-principles calculation. The results show that, in all C-Nonmetal models, the phonon spectrum has no imaginary frequency and elastic constants meet the three Born stability criteria, which indicates that all configurations have dynamic and mechanical stability. In addition, based on the calculation of formation energy and the relaxation of tetrahedral configuration, it is found that compared with the other five nonmetallic atoms, N atom is the most stable in carbon structure. In elastic regime, the maximum elastic modulus and hardness are obtained by C-O model, which is due to the strong electronegativity between C and O. While in plastic range, C-P model has the maximum ideal tensile and shear strength (170.21 and 78.70 GPa). According to the magnitude of the ideal tensile strength (σ) in different directions, the order of σ is as follow: σ<100>>σ<110>>σ<111>. Furthermore, the electron localization between P and the surrounding carbon atoms is the strongest in all models and the C-P bond (ICOHP = −5.41 eV) is largest among all C-Nonmetal bonds, which may result in the maximum tensile and shear strength of C–P model in plastic range.

Effects of Ti interlayer on adhesion property of DLC films: A first principle study

Diamond like carbon (DLC) films exhibit high hardness and good wear resistance. However, their poor adhesion to the substrates limits their wide applications in the industry. Introducing an interlayer between steel substrate and the DLC film has been proved to be an effective method to overcome this drawback. Hence, the interfacial strength, electron transfer and bonding nature of Fe/C, Fe/Ti and Ti/C interface were investigated through first-principles calculations. Seven interface geometries with different stacking sequences were established. Three most stable interface configurations i.e. Fe/C-OT, Fe/Ti-SL and Ti/C-OT were selected for further investigation on their bonding nature and the electronic characteristic by the charge density difference and partial density of state (PDOS) calculations. The study shows that the bonding strength of the Fe/Ti and Ti/C interface are greater than the Fe/C interface by comparing the work of separation and interfacial energy. In other words, the introduction of Ti interlayer between the steel substrate and DLC film can increase the adhesion strength. According to charge density difference and PDOS analysis, it was demonstrated that FeC and TiC covalent bonds formed in both the Fe/C and Ti/C interfaces and the charge accumulation degree between Ti/C is stronger than that of Fe/C interface. This study provides a better comprehension for the mechanism of introducing Ti interlayer to improve adhesion between steel substrate and DLC film.

Enhancement of hydrogenated graphene on mechanical and adhesive properties of diamond-like carbon films

This paper aims to investigate the mechanical and adhesive properties of diamond-like carbon films substrate covered by hydrogenated graphene (HG) using molecular dynamics simulations. For the mechanical properties, compared with the bare substrate, the HG-covered substrate shows a remarkable reduction on the out-of-plane stiffness, but shows an improvement on the maximum indentation force. For the adhesive properties, the suppression of covalent bond at the contact interface reduces the interfacial adhesion. These properties of the HG-covered substrate are strongly dependent on the hydrogenation degree of HG and its number of layer due to the sp2-sp3 hybridization of carbon atoms and relative motion between the graphene layers. This finding provides a route for designing the novel solid lubricants with excellent wear-resistance performance.

Correlation between Substrate Ion Fluxes and the Properties of Diamond-Like Carbon Films Deposited by Deep Oscillation Magnetron Sputtering in Ar and Ar + Ne Plasmas

Recently, the use of Ne as a processing gas has been shown to increase the ionization degree of carbon in High Power Impulse Magnetron Sputtering (HiPIMS) plasmas. In this work, time-resolved measurements of the substrate’s current density were carried out in order to study the time evolution of the ionic species arriving at the growing film. The addition of Ne to the plasma resulted in a steep increase of the sp3/sp2 ratio in the films once the Ne contents in the processing atmosphere exceeded 26%. Increasing the Ne content is shown to increase both the total number of C ions generated in the plasmas and the ratio of C/gaseous ions. The time-resolved substrate ion current density was used to evaluate the possibility of substrate biasing synchronizing with the discharge pulses in the HiPIMS process. It is shown that in pure Ar plasmas, substrate biasing should be confined to the time interval between 25 and 40 µs after the pulse starts, in order to maximize the C+/Ar+ ratio bombarding the substrate and minimize the formation of film stresses. However, Ne addition to the processing gas shortens the traveling time of the carbon species towards the substrate, reducing the separation between the gaseous and carbon ion arrival times.

Improving the tribological properties of diamond-like carbon film applied under methane by tailoring sliding interface

Methane fuel will be valued as a renewable and alternative energy source in the new future. Nevertheless, during transportation and application of methane, the damage to moving mechanical components results in a huge loss to the society. Diamond-like carbon (DLC) film, with lots of excellent frictional performances, is expected to resolve the above issue. Herein, experiments were performed by tailoring sliding interfaces under methane to explore the tribological mechanism of DLC film under methane atmosphere. It was found that initial tribological interface had an important impact on the frictional performances of DLC film. Raman spectra demonstrated that the reconstruction, which was critical for the tribological performances of DLC film under methane, occurred at the sliding interface with shearing. The first principles calculation result revealed that carbon dangling bonds were passivated with the groups dissociated from methane. Combining with the hardness of wear tracks, an appropriate passivation on the sliding interface and suitable rigidity of the system were found to be great for the low friction of DLC film under methane atmosphere. The results indicate that DLC film exhibits outstanding lubricating and wear-resistant properties under methane by tailoring sliding interface.

Improved Thermal Resistance and Electrical Conductivity of a Boron-Doped DLC Film Using RF-PECVD

Diamond-like carbon (DLC) film doped with boron has unique properties and displays higher thermal resistance, lower internal stress, and better electrical conductivity than un-doped DLC film; this makes it is suitable for various applications, especially in outer space. Radio-frequency plasma-enhanced chemical vacuum deposition of boron-doped DLC film was performed to determine the optimal percentage of boron for improving thermal resistance. Additional heat treatment and 40% B2H6/CH4 yielded the best electrical conductivity. X-ray photoelectron spectroscopy, thermal gravimetric analysis, Raman spectroscopy, and the four-point probe method were utilized to analyze the properties of boron-doped DLC film. The boron-doped DLC film displayed outstanding performance in terms of thermal resistance and electrical conductivity.

The Effects of Magnetic Field on the Properties of Diamond-Like Carbon Films Produced by High-Density Helicon Wave Plasma

Diamond-like carbon (DLC) films were grown on Si substrates by high-density helicon wave plasma (HWP) generated under low pressure, with the help of CH4 as an important single-source precursor. The influence of magnetic field ( ${B}_{0}$ : 1200–2400 Gs) on the film structure, morphology, composition, and mechanical properties has been studied. The high deposition rate of the films exhibits a maximum of 800 nm/min, which is contributed by the high-density plasma generation of HWP. By the X-ray photoelectron spectroscopy (XPS) analysis, the as-deposited DLC film is composed mainly of sp2 C-C. The DLC film deposited at ${B}_{0} =2400$ Gs exhibits that the friction coefficient reaches its minimum value of $5 \times 10^{-3}$ , with small surface roughness (root mean square (RMS) ~ 10 nm). Considering that ${B}_{0}$ can be easily controlled, this article opens up a new approach to achieve ultralow friction coefficient DLC films with a high deposited rate at room temperature.

Influence of RF power and CH4 flow rate on properties of diamond-like carbon films deposited by PECVD technique

In this work, Diamond like carbon (DLC) films were deposited on titanium substrate by plasma enhanced chemical vapor deposition (PECVD) technique. The influences of RF power and CH4 gas flow rate on the properties of the DLC films were studied using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and synchrotron-based near-edge X-ray absorption find structure (NEXAFS) spectroscopy. The results show that the sp3/sp2 ratio decreases, while the ID/IG increases when RF power increases. The sp3/sp2 ratio increases with CH4 flow rate.

Optical properties of diamond-like carbon films prepared by pulsed laser deposition onto 3D surface substrate

ABSTRACT It is difficult to grow uniform film by pulsed laser deposition because the spatial distribution of the laser-induced plume is a forward-directed cone-shape. A 3D-motional deposition setup was founded, and the correlative mathematical model of the film thickness on the 3D curved surface was deduced. Based on simulation and optimization, the diamond-like carbon (DLC) film was grown onto the large curved silicon substrate. According to the infrared transmittance spectra, the optical constants of the DLC film samples at different regions on the curved substrate were similar, indicating that the DLC film prepared onto the curved surface was homogeneous. Meanwhile, the deviation of average transmittance in the medium infrared band was below 2.3%, which could improve the imaging performance of the infrared detection. This research is useful to expand the application of the pulsed laser deposition in the optical field.

Surface modification of 316L stainless steel by diamond-like carbon films

The diamond-like carbon (DLC) film on 316L stainless steel substrate was prepared by pulsed plasma-enhanced chemical vapor deposition, and the performance of the films was optimized by regulating the pulse voltage. Microstructure and properties of DLC film on 316L stainless steel were characterized by atomic force microscopy, field-emission scanning electron microscopy, Raman spectra, nano-indenter and electrochemical workstations. The results showed that DLC films with smooth and dense morphology have a low friction coefficient and high nano-indentation hardness, and the surface hardness of 316L stainless steel substrate was enhanced by more than 3 times. The mechanical properties of DLC films and their bond with 316L stainless steel could be further optimized by increasing pulse voltage. DLC films on 316L stainless steel substrate increased the self-corrosion potential by 0.173 V and decreased self-corrosion current by 99%, which significantly improved the anti-corrosive properties of 316L substrate.

Effect of sp3 Content on Adhesion and Tribological Properties of Non-Hydrogenated DLC Films.

Non-hydrogenated diamond-like carbon (DLC) films with various ratios of sp3/sp2 were prepared on cemented carbide YG8 with DC magnetron sputtering technology. A pure graphite target was selected as the carbon source. Before DLC deposition, a surface etching pretreatment was carried out by mid-frequency magnetron sputtering method, using Ti atoms to improve adhesion strength. The ratios of sp3/sp2 were adjusted by bias voltages. In order to investigate the effect of the ratio of sp3/sp2 on adhesion and tribological properties, Raman spectra, XPS spectra, adhesion scratch test and ball-on-disk dry friction tests were applied. The results indicated that the ratio of sp3/sp2 fluctuated with bias voltage, increasing in the range of 0.74 to 0.98. The adhesion strength decreased from 31.5 to 18.4 N with the increasing ratio of sp3/sp2, while the friction coefficient rose in DLC-Si3N4 and dropped in DLC-Ti6Al4V. For DLC-Ti6Al4V, the oxidation of Ti6Al4V had a greater influence than graphitization of DLC. The hard oxides of Ti6Al4V broke the graphite transfer layer leading to a high friction coefficient. The wear rate was approximately linearly related to bias voltage. The coefficients of the linear regression equation were influenced by different friction materials. The adhesion strength and the friction coefficient were fitted as a function of the ratio of sp3/sp2.

Effects of adding hydrocarbon gas to a high-power impulse magnetron sputtering system on the properties of diamond-like carbon films

Diamond-like carbon (DLC) films were prepared via reactive high-power impulse magnetron sputtering (HiPIMS) using a mixture of argon and a small amount of C2H4 or CH4 gas. Synthesis of the DLC films was based on both plasma-enhanced chemical vapor deposition and physical vapor deposition. At a peak target current of 30 A corresponding to 1.1 A/cm2, the hardness of films prepared with hydrocarbon gas fractions of less than 5% was somewhat higher than the hardness of films prepared via nonreactive Ar HiPIMS. The absence of background due to photoluminescence in the Raman spectra indicated that the hydrogen contents in the films were less than 20%. X-ray photoelectron spectroscopy (XPS) was performed, and the peaks related to the sp3 C in the C 1s core level spectra were investigated. The sp3 C peaks in the C 1s spectra of the films prepared at hydrocarbon gas fractions below 5% were more intense than sp3 C related peaks in the spectra of the films prepared via nonreactive HiPIMS. The sp3 C related peaks accounted for more than 30% of the total at a peak target current of 30 A. The influence of the target current on film properties was also investigated. At peak values of target current exceeding 40 A, the hardness of the films prepared via the nonreactive HiPIMS was somewhat higher than that of the films prepared via reactive HiPIMS. This was predicted from the relationship between the target current and the sp3 C content estimated from the XPS spectra.

Effects of carbide forming elements Me on residual stress and mechanical properties of DLC films by molecular dynamics simulation

In this paper, the structures of diamond-like carbon (DLC) films doped with carbide forming elements Me (MeTi, V, Cr, Zr, Nb, W) were designed firstly by molecular dynamics method. Then, the residual stress and mechanical properties of Me-DLC films were calculated. Meanwhile, the effect of doping carbide forming elements Me on DLC films were analyzed, which indicates the mechanism that the residual stress is decreased. The results show that the residual stress in Me-DLC films is compressive stress. With the increase of Me content, they are decreased firstly and then increased. Meanwhile, the smaller residual compressive stress of the DLC films is, the better their comprehensive mechanical properties are. By the structural analysis, it is found that the carbide forming elements Me are easily combined with the tri-coordinate C to increase the tetra-coordinate C content, which might affect the residual compressive stress. By the bond length and bond angle distribution analysis, it is observed that the CC bond length is relaxed and the CCC bond angle is deformed. By ELF analysis, it is found that a weak covalent bond is formed between the Me atom and the C atom, which lowers the bonding strength.

The unusual tribological behavior of diamond‐like carbon films under high vacuum

We fabricate F‐doped and F‐S‐codoped diamond‐like carbon (DLC) films using plasma‐enhanced chemical vapor deposition system. The hardness, Raman spectra, and high‐vacuum tribological behaviors indicate that the films are DLC films. The hardness is close related to the tribological properties of DLC films under high vacuum. The high hardness of DLC films would be helpful for obtaining the long lifetime under high vacuum. The lifetimes of F‐S‐codoped DLC films are about 120 and 140 seconds, which is attributed to the fast graphitization under high vacuum. The lifetime of F‐doped DLC films is prolonged to the value of around 300 and 440 seconds, X‐ray photoelectron spectroscopy analysis exhibits the existence of the “adsorption” F, and transmission electron microscopy analysis shows that the “adsorption” F could react with Fe to form layered FeF2 nanocrystal at the initial sliding, which could be helpful for prolonging the lifetime of F‐doped DLC films under high vacuum. This investigation opens a new window to overcome the disadvantage of F, S‐doped DLC films under high vacuum.

On the adhesion and wear resistance of DLC films deposited on nitrile butadiene rubber: A Ti-C interlayer

To promote the adhesion strength between diamond-like carbon (DLC) films and nitrile butadiene rubber (NBR) substrates, titanium-doped carbon (Ti-C) films prepared by dual-target magnetron sputtering under varied substrate bias voltages were used as an interlayer on the rough NBR. The surface topography and structure of Ti-C films were investigated by atomic force microscopy (AFM) and Raman spectra. Raman analysis indicates that the increase of substrate bias voltage leads to an increase of the number or the size of sp2 clusters in the Ti-C interlayer. The adhesion strength and tribological properties of DLC films coated on NBR substrate were scrutinized by a scratch tester and a ball-on-disk tribometer, respectively. It was found that DLC film with a Ti-C interlayer at a certain bias voltage exhibited superior wear resistance with a low coefficient of friction (CoF) during the sliding of 6000 laps. No clear damages in the coatings were observed from the wear tracks. Besides, the scratch test also revealed a reliable adhesion when the interlayer was prepared at −150 V, as confirmed by a scratch crack width of ~50 μm as compared to that of the pure DLC film increasing to ~ 120 μm. Therefore, a Ti-C interlayer could significantly enhance the adhesion and wear resistance of DLC thin films deposited on NBR.

A comparative study of surface morphology, mechanical and tribological properties of DLC films deposited on Cr and Ni nanolayers

Applying metallic interlayer between diamond-like carbon (DLC) and substrate is a promising method to improve the adhesion and efficiency of DLC films. Understanding how the interlayer parameters affect the properties of DLC coatings leads to production of long-time excellent performance of them. In this study, DLC films deposited by PECVD and 10, 20 and 40 nm layers of Ni and Cr were sputtered on silicon substrates to use as the adhesion layers. The role of chemical structure and physical parameters (surface roughness) of interlayers on the final properties of DLC films were investigated using atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoscratch and nanoindentation techniques. It was found that a lower surface roughness with a sharp and homogenous distribution of particles sizes (height) results in formation of a smooth DLC film with lower friction coefficient, more stress reduction and better adhesion strength. It was discussed that the chemical structure of the interlayer was important in the solubility and diffusion of carbon atoms and consequently in instability of sp3 and sp2 bonding. Results demonstrated that 40 nm Cr interlayer, not only improved the adhesion of the DLC films but also generated the lowest friction coefficient, better wear resistance and the highest hardness (27 GPa).

Enhancement in the tribological properties of Cr/DLC multilayers in methane: structural transformation induced by sliding

Diamond-like carbon (DLC) films respond as a lubricating material under some atmosphere conditions, such as N2, moisture. Nevertheless, incomplete knowledge about the key factors, which control the performances of film under distinct gases, limits the further use of them. Herein, the tribological properties of DLC film and Cr/DLC multilayers with different modulation periods were studied under methane. Frictional tests conducted under methane show that Cr/DLC film exhibits a great reduction in friction and wear compared to that of DLC film. An interpretation for tribological performances of films was proposed by considering repassivation and structural transformation taking place at the sliding interface. It is chemical passivation that plays a major role in the tribological properties of DLC film, while the Cr/DLC multilayers possess the lower friction coefficient because of the structural transformation induced by shearing. This study is important for broadening applications of DLC film in the industrial field and reducing energy waste.