Nitrogen-doped Diamond-like Carbon Research Articles

Localized corrosion of nitrogen-doped diamond-like carbon films on the surface of 304 stainless steel

Nitrogen-doped diamond-like carbon (N-DLC) films with different nitrogen content were prepared on the surface of 304 stainless steel (SS) using plasma-enhanced chemical vapour deposition technology. Localized failure mechanisms of the N-DLC films under long-term exposure to sodium chloride solutions have been investigated. The results demonstrated that nitrogen doping significantly affected the failure behavior of the N-DLC films. When undoped, the number of pore defects in the film is high, providing a channel for the corrosive medium to attack the substrate metal. Meanwhile, due to the high internal stress within the undoped film, extensive exfoliation of the film occurred under the effect of the growth of oxides at the film-substrate interface. The DLC film on 304 SS is subject to stress corrosion cracking failure during long-term service in sodium chloride solution. However, when nitrogen doping is 10 sccm, the pH of the micro-zone solution was highly variable due to the dissolution of nitrogen in the film and the processes of formation and hydrolysis of NH4+. A large number of residual metal cations dissolved from the substrate combine with oxygen at the corrosion pits mouth to form oxides. This can aggravate the occlusion effect of the pits and severe pitting corrosion of 304 SS occurs under autocatalytic effects. The N-DLC film with 5 sccm nitrogen addition showed the excellent durability properties. The evolution mechanism of oxidation and dissolution behaviors in the presence of variations in local hydrochemistry is also discussed.

Nitrogen-Doped Diamond-like Carbon Buffer Layer Enhances the Mechanical and Tribological Properties of Diamond-like Carbon Films Deposited on Nitrile Rubber Substrate

The poor adhesion between the DLC film and rubber restricts its application of seals. Introducing a suitable interlayer can bolster the adhesion of the coating or film. In this study, nitrogen-doped diamond-like carbon (N-DLC) emerged as the optimal intermediate layer between rubber and DLC. A series of N-DLC/DLC multilayer films were fabricated via DC magnetron sputtering on nitrile rubber (NBR) substrates, varying the substrate bias voltage (0 V, 100 V, 200 V). A scanning electron microscopy analysis revealed that the composite film surface was smoother than the DLC film alone. The results of Raman spectroscopy and X-ray photoelectron spectroscopy indicated a robust bond between nitrogen and carbon atoms in the composite film, with nitrogen facilitating the conversion of sp3C-C bonds into sp2C=C. Mechanical tests demonstrated that the N-DLC interlayer improved film adhesion and reduced the CoF of the composite film to 0.2–0.3. Specifically, the CoF of the N-DLC/DLC film prepared at 100 V was as low as 0.20, with a wear amount of 1.13 mg. Consequently, the inclusion of the N-DLC interlayer substantially enhanced the mechanical and tribological properties of DLC-coated NBR, rendering this coating highly advantageous for various applications.

Optimized Tribological Performance of Nitrogen-Doped Diamond-like Carbon Films on NBR: Influence of Bias Voltage of DC Magnetron Sputtering.

In this research, nitrogen-doped diamond-like carbon (N-DLC) coatings were deposited on Nitrile Butadiene Rubber (NBR) substrates using direct current magnetron sputtering (DC-MS) under varying bias voltages. This study aimed to explore environmentally friendly, low-wear, and non-lubricating seal coatings to enhance the durability of rubber sealing products, which predominantly operate under dynamic sliding conditions. By reducing the coefficient of friction (CoF), the friction and wear on rubber products can be significantly minimized, extending their lifespan. This investigation thoroughly examined the microstructure, mechanical properties, and tribological behavior of the N-DLC films. Among the coatings, the one produced at a bias voltage of -50 V demonstrated superior hardness, elastic modulus, and the lowest CoF in comparison to those prepared with 0, -100, and -200 bias voltages. This optimal combination of properties resulted in an exceptionally low wear rate of 10-9 for the film deposited at -50 V, indicating its outstanding wear resistance.

Effect of Gas Flow Rate and Ratio on Structure and Properties of Nitrogen-Doped Diamond-like Carbon Films

Diamond-like carbon (DLC) has attracted much attention due to its unique properties such as high chemical inertness, optical transparency, and high biocompatibility. In this study, the total gas flow rate was kept constant, while the ratio of reactive gases was varied to deposit nitrogen-doped diamond-like carbon thin films on glass substrates using radiofrequency plasma-enhanced chemical vapor deposition. The effects of the gas flow ratio on the composition, microstructure, surface morphology, and optical properties of the thin films were investigated through extended deposition times. It was found that with an increase in the nitrogen-to-methane gas flow ratio, the film surface became smoother and more compact. The maximum transmittance in the visible range reached 90%, and the highest and lowest transmittance in the same ultraviolet wavelength region differed by up to 25.62% among several sample groups. The optical bandgap decreased from 3.58 eV to 3.46 eV, contrary to the trend of the sp2 fraction variation. Compared with other studies, this study considered the preparation of nitrogen-doped diamondoids using a chemical vapor deposition method with a lesser total gas flow rate passed into it, which provides practical data reference value for the preparation of N-DLC.

Effect of deposition temperature on the tribo-mechanical properties of nitrogen doped DLC thin film

The tribomechanical characteristics of diamond-like carbon (DLC) coatings are notably superior to other hard coatings, making them highly desirable for industrial applications. This study focuses on the synthesis of nitrogen-doped DLC (N-DLC) films through chemical vapor deposition (CVD) methods, with an emphasis on varying the deposition temperature. Comprehensive characterization techniques such as atomic force microscopy (AFM), scanning electron microscopy (SEM), and nanoindentation were employed to investigate the morphological and mechanical attributes of these coatings. The thickness of the films, measured using a Dektak profilometer, demonstrated an increase from 1.9 to 2.8 µm as the deposition temperature rose. Nanoindentation testing revealed that the film deposited at 900°C exhibited the highest hardness (H) and modulus of elasticity (E), measuring 21.95 and 208.3 GPa, respectively. Conversely, the film deposited at 1,000°C showed the lowest values, with H and E at 14.23a and 141.9 GPa, respectively. The H/E ratio of the coatings initially rose from 0.096 to 0.106 as the deposition temperature increased from 800°C to 900°C. However, for deposition temperatures exceeding 900°C the H/E ratio began to decline.

Low friction and wear of Nitrogen-doped diamond-like carbon films deposited on NBR with different flows of N2 by DC-MS

Utilizing a diamond-like carbon (DLC) coating on rubber surfaces is an innovative approach to improve the wear resistance and tribological characteristics of rubber. In this paper, a series of N-doped diamond-like thin films (N-DLC) were deposited on the surface of nitrile butadiene rubber (NBR) substrate by varying the flow rate of nitrogen using direct current magnetron sputtering (DC-MS) technology, and the effects of nitrogen flow rate on the surface morphology, structure, surface energy and tribological properties of N-DLC films were systematically investigated. The results show that the friction coefficients of the N-DLC films are all smaller than those of the undoped DLC films, and most importantly, the samples maintain a stable, ultra-low coefficient of friction of about 0.057 and a low wear rate of the order of 10−9 in the tribological tests at a nitrogen flow rate of 3 sccm, exhibiting excellent tribological performance. This is attributed to several key factors: higher hardness, better film-base bonding, lower surface roughness, and lower friction interface adhesion. This recognition provides insight into the preparation of N-DLC films on rubber to achieve low frictional wear.

Failure mechanisms of nitrogen-doped diamond-like carbon films: Exfoliation or localized attack behaviour of films under hydrochemistry evolution

Nitrogen-doped diamond-like carbon (N-DLC) films with different nitrogen content were prepared on the surface of 2024 aluminium alloy using plasma-enhanced chemical vapour deposition technology. The failure mechanisms of the N-DLC films during seawater exposure have been investigated. The results demonstrated that nitrogen doping significantly affected the failure behaviour of the DLC films in seawater. Extensive exfoliation of the DLC film was found without the addition of nitrogen. However, when the nitrogen flow rate is 10 sccm and 15 sccm, significant localized corrosion of the DLC film and the aluminium alloy substrate occurred. The difference in the thermodynamic process of corrosion of the N-DLC films was mainly due to the changes in pH value on the local solution caused by the formation and hydrolysis of NH4+. In the DLC film without nitrogen additive, large oxide particles were formed at the film-substrate interface due to the acidification of the solution. Meanwhile, the internal stress of the DLC film was high under this condition. The film was easily exfoliated and ultimately lost its protective effect on the substrate. The corrosion products could not grow sustainably due to the variable pH value when excess nitrogen was added to the DLC film. No extensive exfoliation of the DLC films with 10 sccm and 15 sccm nitrogen addition has occurred, but obvious corrosion channels were formed in the substrate because of the localized corrosion. The evolution mechanism of oxidation behaviour in the presence of variations in local hydrochemistry is also discussed.

Effect of external magnetic field on the preparation of nitrogen-doped diamond-like carbon films

Nitrogen-doped diamond-like carbon (DLC) films were prepared on quartz substrates and silicon wafers using the radio-frequency magnetron sputtering technique with high-purity graphite as the target material. Simultaneously, a permanent NdFeB magnet was placed on the substrate site to study the effect of an additional external magnetic field on the film growth. X-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), UV–Vis spectroscopy, and scanning electron microscopy (SEM) were used to characterize the microstructure and surface morphology of the nitrogen-doped DLC films with and without additional magnetic field. The obtained results indicate that the deposited DLC films were amorphous for both conditions. The C1s and N1s core energy levels of the XPS spectrum confirmed the formation of N=C, N≡C, and N–C bonds in the films. With an increasing nitrogen flow rate, the nitrogen content of the DLC films prepared without an additional magnetic field increased. When the nitrogen flow rate was 9 sccm, the maximum nitrogen content in the film prepared without an additional magnetic field was 24.33%. However, the maximum nitrogen content in the film prepared with an additional magnetic field increased to 32.55%, at the nitrogen flow rate of 3 sccm, and the sp3/sp2 ratio reached 1.39. The SEM results showed that the surface of the nitrogen-doped DLC film was smooth, flat, and compact after the application of the additional magnetic field, and the film was closely bonded with the substrate.

Effect of high-speed steel surface nitriding treatment on adhesion and wear resistance properties of nitrogen-doped diamond-like carbon coatings

Based on the principle of hollow cathode, diamond-like carbon (DLC) coatings were deposited on high-speed steel by plasma enhanced chemical vapor deposition (PECVD). The mechanism of the experimental parameters on the adhesion and wear behavior of the multilayer coatings, prepared by plasma nitriding substrate and DLC N-doping, were systematically investigated via Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), micro-Vickers tester, friction and wear tester analysis. It was found that the deposition speed and structure of DLC coatings can be efficiently improved by different contents of N doping. With the increase of nitrogen content, the content of sp3 bond in DLC coating first increased to 60.82 % and then decreased to 58.73 %. Meanwhile, the friction coefficient of DLC coating first decreased and then increased. Combined with plasma nitriding treatment for substrate, the wear resistance of DLC coating was effectively improved by optimizing the hardness gradient between the coating and the substrate. Under the same friction conditions, the wear rate was reduced by about 50 %, while the adhesion of DLC coating was improved from HF4 to HF1 in comparison with non-nitriding and non-N-doping DLC coatings. It was revealed by the mechanistic-based model that the resistance by nitriding layers played a more important role than an increase in coatings thickness due to the reasonable hardness gradient in resisting deformation. Based on the N-doped DLC + DLC structure, the surface hardness of the coating gradually increased to 1970.9 HV. The hard outer layer provided sufficient load-carrying capacity and wear resistance during the friction process, thus decreasing the generation of wear debris and the depletion of coating.

The effect of nitrogen concentration on the properties of N-DLC prepared by helicon wave plasma chemical vapor deposition

Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by helicon wave plasma chemical vapor deposition (HWP-CVD). The mechanism of the plasma influence on the N-DLC structure and properties was revealed by the diagnosis of plasma. The effects of nitrogen doping on the mechanical and hydrophobicity properties of DLC films were studied. The change in the ratio of precursor gas flow reduces the concentration of film-forming groups, resulting in a decrease of growth rate with increasing nitrogen flow rate. The morphology and structure of N-DLC films were characterized by scanning probe microscopy, Raman spectroscopy, and X-ray photoemission spectroscopy. The mechanical properties and wettability of N-DLC were analyzed by an ultra-micro hardness tester and JC2000DM system. The results show that the content ratio of N+ and is positively correlated with the mechanical properties and wettability of N-DLC films. The enhancement hardness and elastic modulus of N-DLC are attributed to the increase in sp3 carbon–nitrogen bond content in the film, reaching 26.5 GPa and 160 GPa respectively. Water contact measurement shows that the increase in the nitrogen-bond structure in N-DLC gives the film excellent hydrophobic properties, and the optimal water contact angle reaches 111.2°. It is shown that HWP technology has unique advantages in the modulation of functional nanomaterials.

Synthesis of Nitrogen-Doped Diamond-Like Carbon Films Produced by Plasma-Enhanced Chemical Vapor Deposition and their Tribocorrosion Behavior in Hanks’ Solution

Synthesis of Nitrogen-Doped Diamond-Like Carbon Films Produced by Plasma-Enhanced Chemical Vapor Deposition and their Tribocorrosion Behavior in Hanks’ Solution

Influence of hydrogen gas flow ratio on the properties of silicon- and nitrogen-doped diamond-like carbon films by plasma-enhanced chemical vapor deposition

We deposited silicon- and nitrogen-doped diamond-like carbon (Si–N–DLC) films by radio frequency (RF) plasma-enhanced chemical vapor deposition using H2 and Ar as dilution gases. We investigated the influence of the H2 flow ratio [H₂/(H₂ + Ar)] on the structure; chemical bonding; and mechanical, tribological, optical, and surface properties of the Si–N–DLC films. The optical bandgap increased from 1.88 eV to 2.06 eV with the H2 flow ratio, and it had a negative correlation with the sp2 CC bonding fraction in the films. When the H2 flow ratio increased from 0% to 100%, the critical load of the Si–N–DLC films increased by ~14% due to a reduction of ~26% in the internal stress of the films. As the H2 flow ratio increased, the friction coefficient and specific wear rate decreased by ~11% and ~35%, respectively, whereas the pure water contact angles of the film surfaces increased from 74.7° to 86.5°. The film surfaces had root mean square roughnesses (RMS) less than 0.2 nm. Therefore, the improvement in their tribological properties and the increase in their contact angles were probably due to the hydrogen termination of dangling bonds. The friction coefficient and wear rate of the Si–N–DLC film deposited at a H2 flow ratio of 0% (100%) changed little (increased) after annealing at 773 K.

Effects of annealing temperature on the mechanical, optical, and electrical properties of hydrogenated, nitrogen-doped diamond-like carbon films

We have deposited nitrogen-doped diamond-like carbon (N-DLC) films by plasma-enhanced chemical vapor deposition using H2 as a dilution gas and investigated the effects of post-deposition annealing in a vacuum on the film properties. It was found that the optical bandgap slightly increased after annealing at 235 °C, whereas it substantially decreased after annealing at 420 and 490 °C. At these temperatures, the critical load increased primarily due to a decrease in internal stress. Simultaneously, the amount of bound hydrogen in the films decreased, whereas sp2 C=C increased and its clustering was accelerated. On the other hand, both friction coefficient and specific wear rate became lowest at 347 °C. We found that the N-DLC/p-type silicon heterojunction annealed at 347 °C exhibited the highest rectification ratio. These results were discussed based on the structure and chemical bonding states of the annealed films.

Effect of Carbon Configuration on Mechanical, Friction and Wear Behavior of Nitrogen-Doped Diamond-Like Carbon Films for Magnetic Storage Applications

Effect of Carbon Configuration on Mechanical, Friction and Wear Behavior of Nitrogen-Doped Diamond-Like Carbon Films for Magnetic Storage Applications

Effects of silicon doping on the chemical bonding states and properties of nitrogen-doped diamond-like carbon films by plasma-enhanced chemical vapor deposition

• The properties of Si and N doped diamond-like carbon (Si–N–DLC) have been examined. • The internal stress on Si–N–DLC was lower than that on N doped DLC. • The optical bandgap of Si–N–DLC showed an increasing trend with increasing N content. • Si–N–DLC/p-type Si junctions annealed in a vacuum showed rectifying characteristics. We have investigated the effects of silicon (Si) doping on the chemical bonding states and the electrical, optical, and mechanical properties of nitrogen-doped diamond-like carbon (N−DLC) films prepared via plasma-enhanced chemical vapor deposition using hydrogen as a dilution gas. N doping accelerated the formation of clustered sp 2 C in N−DLC films, whereas the clustering was almost suppressed in Si and N doped DLC (Si−N−DLC) films. Sp 3 C sites in the Si–N–DLC films were higher than those in the N–DLC films. For the Si−N−DLC films, sp 3 C-N bonds were preferentially formed compared with the sp 2 C=N bonds. The internal stress on the Si−N−DLC films was lower than that on the N−DLC films. The Si−N−DLC films exhibited higher optical bandgaps than the N−DLC films. As the N 2 flow ratio increased, the optical bandgap of the Si−N−DLC films showed an increasing trend, whereas that of the N−DLC films showed an opposite trend. The current−voltage characteristics of Si−N−DLC/p-type Si heterojunctions were not rectifying; however, after postdeposition annealing, the heterojunctions exhibited rectifying characteristics.

Elastic loading enhanced NH3 sensing for surface acoustic wave sensor with highly porous nitrogen doped diamond like carbon film

We proposed a surface acoustic wave (SAW) NH3 gas sensor based on nitrogen doped diamond like carbon (N-DLC) film. The N-DLC film, prepared using a microwave electron cyclotron resonance plasma chemical vapor deposition (ECR-PECVD) method, is highly porous and physically and chemically stable, and have active polar groups on its surface, which can selectively absorb polar NH3 gas molecules. These features of the film lead to the high sensitivity, low noise and excellent stability of the sensor. The sensor can achieve capabilities of in-situ monitoring NH3 in a concentration range from 100 ppb to 100 ppm with fast response (∼5 s) and recovery (∼29 s) at room temperature. The NH3 sensing mechanism is attributed to the decreased porosity of the N-DLC film caused by adsorbed NH3 molecules on its polar groups, which leads an increase of the elastic modulus of the film.

High temperature nanomechanical properties of sub-5 nm nitrogen doped diamond-like carbon using nanoindentation and finite element analysis

Nitrogen doped diamond-like carbon (NDLC) is a candidate protective coating in state-of-the-art heat assisted magnetic recording (HAMR) media. To ensure the robustness of the media particularly at higher temperature applications, mechanical properties of ultra-thin sub 5-nm NDLC coatings are of great interest. Due to instrument limitations and very shallow films, it is very challenging to accurately measure sub-5 nm NDLC films and other HAMR components from experiments without substrate effects. In this study, very shallow nanoindentations were performed, and the results were fitted with finite element analysis using a modified indenter geometry to predict the elastic modulus and yield strength of NDLC films of two different thicknesses (3.5 and 4.5 nm) and other components without any substrate effect. Results showed that higher NDLC film thickness led to better elastic modulus and yield strength at 25 °C before and after heating and at 300 °C. Hardness to yield strength ratio (H/Y) for NDLC films was also determined and found within the range of 2.2–2.8, which is higher than the H/Y ratio of DLC films from earlier studies. This implied the dependence of H/Y ratio on the thickness, temperature conditions, and chemical structure of NDLC films. Results also showed that the yield strength of FeCo metal layer and glass substrate in HAMR media decreased at 300 °C, but almost fully recovered to their initial properties after removal of heat.

Bactericidal silver-doped DLC coatings obtained by pulsed filtered cathodic arc co-deposition

Diamond-like carbon (DLC) coatings have been extensively studied over the last two decades in the field of materials engineering. The addition of effective bactericidal agents like silver suggests the potential application of silver-doped DLC coatings in the biomedical sector. In this paper, DLC coatings containing about 2 at. % Ag were grown on CoCrMo substrates by pulsed filtered cathodic arc co-deposition using pure graphite and silver targets. Morphology, structure and chemical composition of the coatings were characterized by SEM, XPS, XRD, Raman and HRTEM. Wettability and surface free energy were also measured. Mechanical properties were analyzed by means of nanoindentation and Rockwell-C adhesion tests. Corrosion resistance of coated and uncoated samples was determined by potentio-dynamic polarization tests in Hank's solution. Cytotoxicity and antibacterial activity against S. aureus and P. aeruginosa were also studied. For comparative purposes, nitrogen-doped DLC coatings obtained by RF magnetron sputtering were also prepared and characterized. Well-adhered and corrosion resistant Ag-DLC nanostructured coatings of up to 1.5 μm thick and 21 GPa in hardness were obtained. The doping concentration of silver studied in this work seems to be optimal for the preparation of non-cytotoxic coatings with a significant bactericidal activity.

The effect of nitrogen concentration on N-doped diamond-like carbon films prepared by plasma-electrolytic method

Nitrogen-doped diamond-like carbon films were deposited on tool steel substrate througha plasma electrolytic technique. These coatings were fabricated using the hydrocarbons containing nitrogen vapor as a nitrogen and source. The formation of films was proved by Raman spectroscopy, X-ray diffraction patterns, and cross-section scanning electron microscopy. According to the results, by increasing the urea content, the highest amount of Raman intensity ratio for graphite/disordered graphite (ID/IG) was obtained 3.57. On the other hand, N-doped DLC, graphite and nitride phases in X-ray diffraction patterns were observed. The N-doped films had better tribological properties because of significant nitride phases and less surface roughness with an optimum amount of 1.229 μm for the sample with 4 wt. % urea. The friction coefficient of films was obtained as about 0.1–0.25. Subsequently, the sample with 4 wt. % urea indicated the maximum wear resistance by 70 m compared with 10 m resistance for the sample with 0 wt. % urea.

Structural evolution and tribological behavior of nitrogen-doped DLC coatings deposited by pulsed DC PACVD method

In recent years, the stability of wear behavior for diamond-like carbon (DLC) coatings is very crucial and challenging. However, insufficient adhesion of the DLC coating to the substrate makes some problems for its wear application. Nitrogen doped in DLC coatings was prepared by D.C. Pulsed Plasma Assisted Chemical Vapour Deposition (PACVD) technique on the H13 Tool Steel under different conditions to improve the adhesion and finally tribological properties. The coating structure was assessed with Visible Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). The mechanical and tribological properties of the coatings were evaluated by nanoindentation technique and rotational ball-on-disk tribometer. The results revealed that as the nitrogen content in the coatings rises, the friction coefficient of the coatings is more stable, however, it is higher than the other coatings at the beginning of the sliding distance. Therefore, the nitrogen-doped DLC coating deposited with the highest nitrogen gas flow rate (N2 = 10sccm) at 120 °C, demonstrated the best adhesion quality of the coating to the substrate (with a hardness of 15.39 GPa) and a stable friction coefficient of 0.24 at the end of the test and lowest wear rate of 1.15 × 10−6 mm3/Nm.