Nitrogen-doped Diamond-like Carbon Films 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.

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.

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.

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.

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.

Interpretation of friction and wear in DLC film: role of surface chemistry and test environment

In spite of the large amount of tribological work carried out to explain the friction and wear mechanism in diamond-like carbon (DLC) films, some of the core issues relating to the evolution of reactive species across sliding interfaces and their role on the friction and wear mechanism remain unclear. The phase composition, film density and hydrogen content present in a DLC film can be tailored by substrate biasing during film deposition to achieve a nearly vanishing friction coefficient. Furthermore, nitrogen doping in DLC films significantly improves wear resistance, and sliding occurs in a nearly wearless regime. Undoped and nitrogen-doped DLC films exhibit a nearly frictionless value with ultra-low wear behavior when tests are performed in argon, nitrogen and methane atmospheres. The antifriction and antiwear properties of the DLC films were improved with the reduction of adsorbed oxygen impurities on the film surface. This behavior was understood by correlating the oxygen impurities present at the surface/subsurface region of the DLC film while using x-ray photoelectron spectroscopy and depth-resolved Auger electron spectroscopy.

Structural and electrical properties and current–voltage characteristics of nitrogen-doped diamond-like carbon films on Si substrates by plasma-enhanced chemical vapor deposition

We have deposited nitrogen-doped diamond-like carbon (N-DLC) films by plasma-enhanced chemical vapor deposition using CH4, N2, and Ar, and investigated the effects of N doping on the structure and the electrical, mechanical, and optical properties of the N-DLC films. We fabricated undoped DLC/p-type Si and N-DLC/p-type Si heterojunctions and examined the current–voltage characteristics of the heterojunctions. When the N2 flow ratio was increased from 0 to 3.64%, the resistivity markedly decreased from the order of 105 Ω·cm to that of 10−2 Ω·cm and the internal stress also decreased. The resistivity gradually increased with increasing N2 flow ratio from 3.64 to 13.6%, and then it decreased at a N2 flow ratio of 13.6%. These behaviors can be explained in terms of the clustering of sp2 carbons and the formation of sp3C–N, sp2C=N, sp1C≡N, and C–Hn bonds. The rectification ratio of the heterojunction using the N-DLC film prepared at 3.64% was 35.8 at ±0.5 V.

Structural characteristics of surface-functionalized nitrogen-doped diamond-like carbon films and effective adjustment to cell attachment**Project supported by the National Natural Science Foundation of China (Grant Nos. 51272237, 51272231, and 51010002) and the China Postdoctoral Science Foundation (Grant Nos. 2012M520063, 2013T60587, and Bsh1201016).

Nitrogen-doped diamond-like carbon (DLC:N) films prepared by the filtered cathodic vacuum arc technology are functionalized with various chemical molecules including dopamine (DA), 3-Aminobenzeneboronic acid (APBA), and adenosine triphosphate (ATP), and the impacts of surface functionalities on the surface morphologies, compositions, microstructures, and cell compatibility of the DLC:N films are systematically investigated. We demonstrate that the surface groups of DLC:N have a significant effect on the surface and structural properties of the film. The activity of PC12 cells depends on the particular type of surface functional groups of DLC:N films regardless of surface roughness and wettability. Our research offers a novel way for designing functionalized carbon films as tailorable substrates for biosensors and biomedical engineering applications.

The study and fabrication of DLC micropattern on roll mold

Diamond-like carbon (DLC) coating is becoming a promising protective coating layers due to its superior properties. In this study, instead of protective coating, DLC film was applied as the only component for micropattern then etched with lithography and lift-off process selectively. Furthermore, DLC film has been fabricated on aluminum roll mold. Then UV curing resin was applied to form the pattern on the polyethylene terephthalate (PET) film. The dimension and formation of the DLC micropattern on roll mold were analyzed. Moreover, the Raman spectroscopic of nitrogen-doped DLC film was analyzed.

Microstructure and electrochemical properties of nitrogen-doped DLC films deposited by PECVD technique

Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by glow discharge plasma enhanced chemical vapor deposition (PECVD) using a hybrid ion beam system. The influence of nitrogen incorporation on the microstructure and electrochemical properties of N-DLC films was investigated by scanning probe microscopy, Raman spectroscopy, X-ray photoemission spectroscopy and cycle voltammetry. Regardless of the deposition parameters, the surface of all the deposited films is very smooth. Raman spectra show that ID/IG increases from 0.6 to 1.04 with the substrate bias voltage increases. XPS results identify that carbon is bonded with nitrogen and the substrate bias makes no distinct contribution to the N content in the films, even the N-DLC film at bias of −550V has the lowest N–O bonds concentration and the highest C–N bonds concentration. The film electrodes show the wide potential windows range over 4V, lower background currents in strong acid media. At the bias of −550V, the N-DLC film electrode not only exhibits the ΔEp at 209mV and Ipox/Ipred at 0.8778 in K3Fe(CN)6 solution, respectively, but also illustrates a nearly reversible electrode reaction. The mechanism of electroproperties is discussed in terms of the atomic bond structures and diffusion process.