Pure Diamond-like Carbon Films Research Articles

Extremely enhanced friction and wear performance of hydrogen-free DLC film at elevated temperatures via Si doping

Hydrogen-free diamond-like carbon (DLC) films have garnered significant attention as a highly efficient solid lubrication material, but poor high-temperature lubrication and wear resistance limit their further application. Here, silicon-doped DLC (Si-DLC) films with different Si contents were deposited using a superimposed HiPIMS-DCMS deposition system to improve their high-temperature lubrication and wear resistance performance. The influence of Si content on the microstructure, mechanical and high-temperature friction and wear behavior of Si-DLC films was investigated. The results showed that Si-DLC films had a dense structure and nanoscale smooth surface. The Si doping enhanced the adhesion strength and relieved the residual stress of Si-DLC films, but decreased the hardness and Young's modulus. Meanwhile, Raman and XPS spectroscopy revealed significant local structural changes in Si-doped DLC films. Furthermore, the results showed that DLC films doped with low Si content displayed excellent tribological performance at elevated temperatures due to the graphite lubricating layer on the surface of wear marks. Specifically, Si-DLC film with 3.31 at% Si had an ultra-low average friction coefficient of 0.04 at 450 °C and still provided effective lubrication at temperatures up to 500 °C. In contrast, pure DLC film failed to lubricate at 450 °C due to the severe graphitization transition and Si-DLC film with 17.47 at% Si quickly failed to lubricate at 200 °C due to the SiC and SiO2. This work sheds light for the high-temperature application of DLC films doped with low Si content by superimposed HiPIMS-DCMS deposition system.

Micro-structural, electrical, and tribological properties of SiC/DLC composite coating grown by PLD on steel

Protective diamond-like carbon (DLC) composite coating was grown on cylindrical steel surface in a simple inclined pulsed laser deposition (PLD) process. Based on this kind of flexible film-synthesis method, mixed deposition was used to generate the gradient interface that could enhance adhesive strength in Ti/SiC interface, and periodic SiC/DLC layers were grown to reduce residual stress of the pure DLC film. This kind of PLD-grown SiC/DLC composite coating on the curved thin steel that was imitated as piston cylinder showed excellent adhesive property and toughness. Compared with the bare steel, DLC-filmed steel strip had a much lower friction coefficient, higher nano-hardness, and enhanced elastic modulus. Raman spectroscopies showed transform of the micro-structure in DLC layers during friction process, revealing the important reason for reducing friction coefficient. Electrical conductivity test displayed the DLC-filmed steel strip was in high resistance state, although its thickness was only 1.27 μm. Further on, good adhesive strength, excellent toughness and high resistance state of SiC/DLC composite coating could be applied in the MEMS advices.

High-temperature tribological properties of diamond-like carbon films: A review

Abstract The rapid development of aerospace industry has made more and more machinery parts of equipment working at high temperature. Due to the lubrication failure of lubricating oil and grease at high temperature, solid lubricant coatings are almost the only effective method to achieve super low friction at high temperature. In recent years, the tribological properties of diamond-like carbon (DLC) films have been extensively studied at high temperature. The present study reviews the microstructure of DLC films and the influence of doping different elements on the structure of DLC films. Second, the mechanical properties and thermal stability of pure DLC films and DLC doped with different elements are also described. DLC films have different microstructures and tribological properties by different preparation methods. Finally, the high-temperature lubrication failure mechanism of DLC films and the tribological properties of DLC films when doped with different elements are discussed from the macro and micro perspectives.

Microstructure and wettability of novel Al-containing diamond-like carbon films deposited by a hybrid sputtering system

Abstract Al-doped diamond-like carbon (DLC) films having various Al contents were fabricated by a co-sputtering system. The designed Al target power was increased from 10 to 70 W to obtain different Al contents. The effect of Al content on the surface morphologies, carbon bonding structure, residual stress, and the wetting property of films was systematically investigated. The results show that the Al content in films increased with increasing the sputtering power of Al target, and the surface roughness of the films increased with increase of Al content. It was also found that the carbon bond, including sp2─C and sp3─C bonds, was a function of the Al content. The sp2─C bond fraction and the ratio of sp2/sp3 increased with increasing Al content, implying more graphitization in the films. Meanwhile, the residual stress of films decreased by adding Al content. In addition, the contact angles of the films increased from 68.8° for the pure DLC film to 107.7° for the film with moderate Al doping, implying that the wettability of the films transformed from the hydrophilicity state to the hydrophobicity state. Accordingly, the surface energy of the films decreased from 42.45 to 18.43 mJ/m2. This change was attributed to the improved sp2-C bond fraction and surface roughness of the films. The findings of this study provide a feasible method of designing and fabricating DLC films with low residual stress and controllable wettability properties.

Different Cr Contents on the Microstructure and Tribomechanical Properties of Multi-Layered Diamond-Like Carbon Films Prepared by Unbalanced Magnetron Sputtering

To investigate the effects of Cr doping on the microstructure and tribological properties of multi-layered diamond-like carbon (DLC) films, Cr-DLC films with Cr contents ranging from 0 to 22 at.% were deposited on 0Cr19Ni10 stainless steel and Si wafer surfaces by unbalanced magnetron sputtering. The thickness of the transition layer is 180 nm and the Cr-DLC film ranging from 1.3 to 1.5 µm. The microstructure, mechanical and tribological properties of the films were systematically investigated at room temperature in atmospheric environment. Results show that increasing the Cr target current can effectively improve the incident particle density and reduce surface roughness. As a strong carbon metal, Cr has significant influence on the structure and properties of the film for bonding with carbon atoms during deposition. High-energy Cr particles are favorable for films to increase the sp3 hybrid bond ratio and reduce internal stress. The high-hardness sp3 hybrid phase, Cr carbide, oxide dispersion can effectively improve the mechanical properties of the film, but overdoping is detrimental for mechanical properties of the film. The internal stress shows a continuous trend of decreasing with the increasing Cr content and it reduced up to 80% compared with pure DLC films. The films prepared with Cr sputtering current of 0.4 A demonstrate the best tribological properties, and the friction coefficient and wear rate are 0.15 and 2.9 × 10−7 mm3/Nm, respectively.

Electrodeposition and biocompatibility of palladium and phosphorus doped amorphous hydrogenated carbon films

Diamond like carbon (DLC) films are considered as exciting candidates for biomaterials owing to high hardness and chemical inertness. However, the high resistivity of pure DLC films limited further applications in bioelectronic field. The palladium and phosphorus doped DLC film was fabricated by electrochemical deposition from the ethanol solution of Tetrakis (triphenylphosphine) platinum. The structure of the film was composed of CP, CP, CH, sp2–C, sp3–C bonds and Pd nanoparticles. The resistivity was evidently reduced due to the introduction of palladium and phosphorus, and the biocompatibility simultaneously enhanced. It will open up a new application direction for bioelectronic devices.

Mechanical and tribological behaviors of Ti-DLC films deposited on 304 stainless steel: Exploration with Ti doping from micro to macro

Diamond-like carbon (DLC) films with different Ti doping contents from micro amount to a relatively macro level on a 304 stainless steel substrate were prepared by ion beam assisted enhanced unbalanced magnetron sputtering. The evolution of microstructure, mechanical and tribological behaviors of DLC and Ti-DLC films were systematically investigated, and the wear mechanism of the films with different Ti doping stages was also contrastively discussed. Results revealed that the mechanical behaviors of the Ti-DLC films with micro Ti doping content (1.82 wt%) exhibit a better performance than those of pure DLC film and Ti-DLC films with a relatively macro Ti doping content, which can be attributed to the change of CC sp3 bond content. The suitable size and content of TiC nanocrystallites can regulate the carbon matrix and improve the tribological behaviors of the film. While when the larger and more TiC nanocrystallites gradually form with the increased Ti doping content, the 3D structure of the carbon matrix and the surface smoothness could be destroyed and much more TiC involved in the friction process resulting in the high and fluctuating friction coefficients of the Ti-DLC films.

Influence of currents on tribological behavior of diamond-like carbon films

The diamond-like carbon (DLC) film is vastly applied for low-friction protective films at contact sliding surfaces. This work reported the characteristics and tribological properties of DLC, Cu-doped DLC (Cu-DLC) film and Ti-doped DLC (Ti-DLC) film formed by unbalanced magnetron sputtering system and analyzed the frictional tests and the morphology of wear scars. The current intensity at the sliding interface was set to a constant value in the whole current circuit for exploring the influence of current, including 0 A, 0.5 A, 1 A, 1.5 A and 2 A. The results showed the friction coefficient of DLC film decreased from 0.12 to 0.06–0.08 and then increases rapidly to 0.26 when the current increased to 2 A. The change in trend of friction coefficient of Cu-DLC film with the increase in current was the same with the DLC film. The minimum value was 0.12 at 1 A current. In the case of Ti-DLC film, when the current intensity enhanced from 0 to 2 A, the friction coefficient monotonically increased from 0.06 to 0.29. Furthermore, the wear rate of the films under higher current was larger than the wear rate of the films under lower current. This is due to the fact that frictional heat and Joule heat are generated at a relatively large current to make the surface of the film more susceptible to wear. The wear rate of Ti-DLC film is relatively larger as the arc ablation is the main wear mechanism of Ti-DLC film compared with pure DLC film and Cu-DLC film.

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.

OPTICAL PROPERTIES OF THE RAPID ANNEALED OXYGEN-DOPED DIAMOND-LIKE CARBON FILM

The amorphous oxygen-doped diamond-like carbon films were prepared by pulsed laser deposition. Compared with the pure diamond-like carbon film, there were much less graphite clusters on the surfaces of the oxygen-doped diamond-like carbon films, and the average transmission of the oxygen-doped diamond-like carbon films in the medium infrared band increased. However, some new absorption peaks in the infrared spectra of the oxygen-doped diamond-like carbon film were generated. Rapid annealing was experimented to remove the absorption peaks. XPS analysis showed that the fractions of the C–O and C=O bonds that generated the new absorption peaks were reduced more than the fractions of [Formula: see text] bonds by rapid annealing at 400[Formula: see text]C, and the absorption peaks in the medium infrared spectra decreased. It indicated that rapid annealing at right temperature during the right time could reduce greatly the absorption in the medium infrared band of oxygen-doped diamond-like carbon films.

Deposition and Thermal Stability of DLC/Si-N Composite Films Synthesized Using a Sputtering-PBII Hybrid System

Diamond-like carbon (DLC) is a metastable amorphous material that exhibits unique properties. However, there are many limitations regarding the use of this material due to factors such as its tribological characteristics at high temperature and limited thermal stability. In this study, the thermal stability and tribological properties of DLC/silicon-nitrogen (DLC/Si-N) composite films were investigated and compared to those of pure DLC films. All the films were synthesized using a combination of radio frequency (RF) magnetron sputtering and plasma-based ion implantation (PBII) (a so-called sputtering-PBII hybrid system) which is newly developed by us. A high purity silicon nitride (99.9%) disk was used as the target, applying an RF power in the range of 500 - 700 W and a negative pulsed bias voltage of 5 kV to the substrate. An Ar-CH4 mixture was used as the reactive gas. The CH4 partial pressure was varied between 0 and 0.15 Pa, while the total gas pressure and total gas flow were fixed at 0.30 Pa and 30 sccm, respectively. The structures of the resulting films were characterized using Raman spectroscopy, while the thermal stabilities were assessed using thermogravimetric-differential thermal analysis (TG-DTA) and friction coefficients were obtained via ball-on-disk friction tests. The results indicate that the DLC/Si-N composite films produced in this work exhibit improved thermal stability relative to that of pure DLC owing to the presence of thermally stable atomic-scale Si-N compound in the carbon main flame networks. A DLC/Si-N film containing approximately 11 at.%Si and 18.5 at.%N shows good thermal stability in air over 800°C up to 1100°C, together with excellent tribological performance at 500°C in air. Overall, the data demonstrate that DLC/Si-N composite films offer improved thermal stability and superior tribological performance at high temperatures.

Diamond-like carbon film with gradient germanium-doped buffer layer by pulsed laser deposition

Germanium-doped diamond-like carbon film with different germanium concentrations on the germanium substrate were prepared by double laser beams emitted from the femtosecond and nanosecond lasers. Diamond-like carbon film with gradient germanium-doped buffer layer, which was named as GDBL-DLC film, was prepared. The germanium concentration could be controlled easily by adjusting the repetition frequency of one of the lasers. Infrared transmission and hardness of the GDBL-DLC film kept high levels of above 60% and 45.4GPa. On the other hand, the critical load of the GDBL-DLC film on the germanium substrate increased to 143.7mN from 65.5mN of the pure diamond-like carbon film. In addition, the GDBL-DLC film had not been damaged after being rubbed by rubber stick and stuck by tape. It was shown that the GDBL-DLC film could be used as protective film for infrared windows.

Synthesis and characterization of boron incorporated diamond-like carbon thin films

Boron incorporated diamond-like carbon (B-DLC) (up to 8wt.% boron) thin films were synthesized on silicon wafers using biased target ion beam deposition technique, where diamond-like carbon (DLC) was deposited by ion beam deposition and boron (B) was simultaneously incorporated by biased target sputtering of a boron carbide (B4C) target under different conditions. Pure DLC films and B–C films were also synthesized by ion beam deposition and biased target sputtering of B4C under similar conditions, respectively, as reference samples. The microstructure and mechanical properties of the synthesized films have been characterized by various technologies. It has been found that B exists in different states in B-DLC, including carbon-rich and B-rich boron carbides, boron suboxide and boron oxide, and the oxidation of B probably occurs during the film deposition. The incorporation of B into DLC leads to the increase of sp3 bonded carbon in the films, the increase of both film hardness and elastic modulus, and the decrease of both surface roughness and friction coefficient. Furthermore, the content of sp3 bonded carbon, film hardness and elastic modulus increase, and the film surface roughness and friction coefficient decrease with the increase of B-rich carbide in the B-DLC films.

Structure and properties of DLC–MoS2 thin films synthesized by BTIBD method

Diamond-like carbon (DLC)–MoS2 composite thin films were synthesized using a biased target ion beam deposition (BTIBD) technique in which MoS2 was produced by sputtering a MoS2 target using Ar ion beams while DLC was deposited by ion beam deposition with CH4 gas as carbon source. The structure and properties of the synthesized films were characterized by X-ray diffraction, X-ray absorption near edge structure (XANES), Raman spectroscopy, nanoindentation, ball-on-disk testing, and corrosion testing. The effect of MoS2 target bias voltage, ranging from −200 to −800V, on the structure and properties of the DLC–MoS2 films was further investigated. The results showed that the hardness decreases from 9.1GPa to 7GPa, the Young׳s modulus decreases from 100GPa to 78GPa, the coefficient of friction (COF) increases from 0.02 to 0.17, and the specific wear rate coefficient (k) increases from 5×10−7 to 5×10−6mm3N−1m−1, with increasing the biasing voltage from 200V to 800V. Also, the corrosion resistance of the DLC–MoS2 films decreased with the raise of biasing voltage. Comparing with the pure DLC and pure MoS2 films, the DLC–MoS2 films deposited at low biasing voltages showed better tribological properties including lower COF and k in ambient air environment.

Effect of film gradient profile on adhesion strength, residual stress and effective hardness of functionally graded diamond-like carbon films

• Studied effect of gradient profile on adhesion and residual stress of DLC films. • Investigated DLC films with five polynomial profiles compared with pure DLC films. • Found that adhesion can be greatly improved by optimizing gradient profile. We have studied, for the first time, the effect of continuously-varying film gradient profiles on the adhesion strength, residual stress, and effective film hardness of diamond-like carbon (DLC) films deposited on stainless steel substrates. Precisely graded DLC films with five polynomial profiles (linear, quadratic, cubic, square root and cubic root profiles) were investigated and compared with pure DLC films, and it was shown that by optimizing the film gradient profile the residual stress and adhesion characteristics can be significantly improved but the effective film hardness can be negatively affected.

Characterization of Cr Doped Diamond-Like Carbon Films and Research on Mechanical Properties

Diamond-like carbon (DLC) films have been extensively studied for more than a decade due to their unique combination of properties. The internal compressive stress affects their adhesion and preventing wide usage of these films. Metal-containing DLC films are expected to relax internal stress. The present work focused on the synthesis, chemical bond and mechanical property characterization of Cr-containing DLC films. The films thickness, internal stress and composition were characterized by scanning electron microscopy, optical interferometry and X-ray photoelectron spectroscopy respectively. Incorporation of Cr into DLC causes an initial internal stress reduction and subsequent stabilization around 0.5 GPa. The hardness behavior was found to depend on Cr content. Films with less than 7.36 at.% Cr (no formation of C-Cr bond) showed a dramatically hardness reduction compared to pure DLC films. Above 7.36 at.% Cr (C-Cr bond formed) the hardness increases above 12 GPa.

Deposition and properties of Al-containing diamond-like carbon films by a hybrid ion beam sources

Metal incorporation is one of the most effective methods for relaxing internal stress in diamond-like carbon (DLC) films. It was reported that the chemical state of the incorporated metal atoms has a significant influence on the film internal stress. The doped atoms embedding in the DLC matrix without bonding with C atoms can reduce the structure disorder of the DLC films through bond angle distortion and thus relax the internal stress of the films. In present paper, Al atoms, which are inert to carbon, were incorporated into the DLC films deposited by a hybrid ion beams system comprising an anode-layer ion source and a magnetron sputtering unit. The film composition, microstructure and atomic bond structure were characterized using X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy. The internal stress, mechanical properties and tribogoical behavior were studied as a function of Al concentration using a stress-tester, nanoindentation and ball-on-disc tribo-tester, respectively. The results indicated that the incorporated Al atoms were dissolved in the DLC matrix without bonding with C atoms and the films exhibited the feature of amorphous carbon. The structure disorder of the films tended to decrease with Al atoms incorporation. This resulted in the distinct reduction of the internal stress in the films. All Al-DLC films exhibited a lower friction coefficient compared with pure DLC film. The formation of the transfer layer and the graphitization induced by friction were expected to contribute to the excellent friction performance.

Comparative study between erbium and erbium oxide-doped diamondlike carbon films deposited by pulsed laser deposition technique

Diamondlike carbon (DLC) films doped with the same fraction of erbium and erbium oxide were prepared by using 248 nm KrF pulsed laser deposition system. The effects of erbium and erbium oxide on the surface morphology, microstructures, and mechanical property of DLC were investigated. Transmission electron microscopy showed that both erbium and erbium oxide retained their initial oxidation states while embedded as metal or metal-oxide nanoclusters in an amorphous matrix. Atomic force microscopy showed that erbium-doped and erbium oxide-doped DLC films were smooth with rms of less than 0.2 nm and closely resembled pure DLC film. The Raman analysis showed broad peaks centering around 1550 cm−1 on both samples. The deconvoluted Raman spectra showed that the ID/IG value of DLC film increased from 0.38 to ∼0.55 in the presence of erbium and erbium oxide, and the estimated sp3 content for the DLC nanocomposite films was ∼56%–57%. X-ray photoelectron spectroscopy (XPS) confirmed that the C 1s peaks for DLC nanocomposite were slightly shifted from 285.2 eV (diamond) to 284.5 eV (graphite). The deconvolution of XPS spectra further confirmed the amount of sp3 content and revealed the presence of a higher fraction of SiC bonding in erbium oxide-doped DLC film. Microscratch tester results showed that the presence of erbium oxide improved the adhesion strength of DLC film from ∼1.72 to ∼2.19 N, which was more effective than erbium at the same concentration (∼1.89 N). The coefficients of friction of the erbium-doped DLC and erbium oxide-doped DLC films were similar to that of pure DLC. Erbium and erbium oxide showed similar influence on the surface roughness, coefficient of friction, and sp3 content on DLC films, but improved adhesion strength, which was correlated with the SiC bonding states, was observed on erbium oxide-doped DLC.

Composition, microstructure and properties of C-N-V films prepared by pulsed bias arc ion plating

High quality C-N-V films with different compositions were prepared on cemented carbide substrate using pulsed bias arc ion plating. The surface morphology, composition, microstructure and properties of C-N-V films were investigated by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectra, grazing incident X-ray diffraction, and nano-indentation, respectively. The results show that the deposited films were nanocomposite films with VN nanocrystalline phase imbedded within diamond-like carbon(DLC) amorphous matrix. The hardness and elastic modulus, which are closely related to the composition and structure of the film, first increase and then decrease with increasing V and N contents and have the highest values of 368 and 5697 GPa exceeding that of pure DLC film prepared under the same condition when nitrogen content is 204% and vanadium content is 218%. The variation of V and N contents has significant influence on the phase structure, relative concentration of VN crystalline phase and DLC amorphous phase, and induces the formation of nano-diamond phase, hence has great effect on the properties of the films.

Antibacterial activity of DLC films containing TiO 2 nanoparticles

Diamond-like carbon (DLC) films have been the focus of extensive research in recent years due to their potential applications as surface coatings on biomedical devices. Titanium dioxide (TiO 2) in the anatase crystalline form is a strong bactericidal agent when exposed to near-UV light. In this work we investigate the bactericidal activity of DLC films containing TiO 2 nanoparticles. The films were grown on 316L stainless-steel substrates from a dispersion of TiO 2 in hexane using plasma-enhanced chemical vapor deposition. The composition, bonding structure, surface energy, stress, and surface roughness of these films were also evaluated. The antibacterial tests were performed against Escherichia coli ( E. coli) and the results were compared to the bacterial adhesion force to the studied surfaces. The presence of TiO 2 in DLC bulk was confirmed by Raman spectroscopy. As TiO 2 content increased, I D / I G ratio, hydrogen content, and roughness also increased; the films became more hydrophilic, with higher surface free energy and the interfacial energy of bacteria adhesion decreased. Experimental results show that TiO 2 increased DLC bactericidal activity. Pure DLC films were thermodynamically unfavorable to bacterial adhesion. However, the chemical interaction between the E. coli and the studied films increased for the films with higher TiO 2 concentration. As TiO 2 bactericidal activity starts its action by oxidative damage to the bacteria wall, a decrease in the interfacial energy of bacteria adhesion causes an increase in the chemical interaction between E. coli and the films, which is an additional factor for the increasing bactericidal activity. From these results, DLC with TiO 2 nanoparticles can be useful for producing coatings with antibacterial properties.