Doped Diamond-like Carbon Films Research Articles

Tailoring the mechanical and high‐temperature tribological properties of Si‐DLC films by controlling the Si content

The poor high‐temperature tribological performance of diamond‐like carbon (DLC) films severely limits their applications. To address this issue, silicon (Si) doped DLC films with Si content ranging from 0 to 11.52 at.% were synthesized utilizing the plasma‐assisted reactive magnetron sputtering technique. The influence of Si incorporation on the microstructure and mechanical properties was meticulously investigated by Raman spectroscopy, scanning electron microscope (SEM), X‐ray photoelectron spectroscopy (XPS), nanoindentation, and scratch testing. To ascertain the tribological behavior of the Si‐DLC films under elevated temperature conditions, in situ high‐temperature tests were conducted, spanning temperatures from ambient to 500°C. The findings indicated that distinct lubrication mechanisms prevail for Si‐DLC films with varying Si content across different temperature domains. As the test temperature and Si content increased, the lubrication mechanism exhibited a gradual transitions from high‐temperature induced graphitization to a particle wear regime dominated by SiC and formed SiO2 abrasive phases. The comprehensive performance of the films peaked at a Si content of 4.72 at.%, suggesting an optimal composition for high‐temperature applications. It is postulated that the in‐depth investigation presented herein holds considerable value for the design and fabrication of DLC films intended for use in high‐temperature settings, potentially unlocking their full potential in such demanding environments.

Dielectric response and current-voltage characteristic of Mo-doped diamond-like carbon thin films at room temperature

Herein we have reported the effect of molybdenum (Mo) doping and acetylene (C2H2) gas flow rate, during deposition, on the electrical properties of diamond like carbon (DLC) films. The frequency dependent dielectric response of the undoped and doped DLC films has been discussed in details. Mo doping also increases the dielectric constant value owing to interfacial polarization and the corresponding change with C2H2 gas flow rate has been attributed to the formation of sp2 bonding over sp3 bonding, favoring the emergence of a graphite-like phase. The ac conductivity of DLC films has been observed to increase with frequency following a power law behavior. However, with 29 % Mo doping we have noticed two plateau regions having different slopes which has been explained on the basis of the jump relaxation model (JRM). The theoretical fitting of the experimental data indicates occurrence of ionic conduction along with polaron hoping. The dc contribution part (σdc) of the measured ac conductivity is found to vary with the acetylene (C2H2) gas flow dependent sp2 bonding formation. The σdc is extracted to be 2351 S/m for the 29 % Mo doped DLC films. From the Nyquist plot in impedance spectroscopy single relaxation phenomena have been observed for the no or low Mo doping but with 29 % Mo doping both the grain and grain boundary effect are prominent. This also suggests the presence of sp2 hybridization and formation of dangling bonds between the metal carbide and DLC film. From the current voltage characteristics, the development of high sp2 bonding and high electron injection into the DLC matrix with subsequent change in nature of the DLC from semiconducting to metallic with high Mo doping has been reported. From the capacitance voltage characteristics study it has been found that either increase in acetylene gas flow during deposition or Mo doping increases the space charge and trap carrier densities.

Microstructure and properties of Mo doped DLC nanocomposite films deposited by a hybrid sputtering system

A combination of low internal stress and hydrophobic performance for carbon film is crucial in some practical applications. In this work, Mo doped diamond-like carbon (DLC) films were deposited by a hybrid coating system. The designed DLC films with various Mo contents were obtained by adjusting the Mo target powers. The microstructure and comprehensive properties including wettability of Mo-DLC films were analyzed systematically. Results showed that with increasing the Mo target power, Mo content and deposition rate of films were continuously increased, and also the surface roughness slightly increased. At low Mo doping, films mainly exhibited amorphous feature, whereas, the MoC nanocrystallites were found at high Mo doping, implying the nanocomposite structure formed where MoC crystals were embedded in the carbon matrix. The sp3-C bond fraction was decreasing with increasing the Mo content due to the metal catalyst effect, which effectively promoted the sp3-C bonds transforming into sp2-C bonds. Meanwhile, the Mo addition had a significant positive effect on the reduction of residual stress. Moreover, the wettability of films was transferred from hydrophilicity state to hydrophobicity state, and the maximum water contact angle was 94.2° at 20.1 at. % Mo doping, then slightly diminished to 92.7° with further increasing Mo content. The present work would offer an available method to fabricate the DLC film with low internal stress and desirable wettability property.

Electron Spin Resonance Study of Hydrogen‐Free Germanium‐Doped Diamond‐Like Carbon Films

Hydrogen‐free germanium (Ge)‐doped diamond‐like carbon (DLC) films deposited on SiO2 substrates are studied by electron spin resonance (ESR) technique at T = 5–295 K. The Ge‐free and DLC films with 1 and 2.5 at% Ge content having low cytotoxicity are investigated. A single Lorentzian ESR line resulting from exchange interaction between localized (LE) and nonlocalized electrons (NE) is observed. The spin susceptibility temperature dependence deviates from the Curie–Weiss law at T > 75 K due to Pauli contribution caused by NE. The antiferromagnetic low‐temperature spin ordering in DLC films, decreasing with Ge content, is observed. The LE contribution is significant for Ge‐free and DLC:1%Ge, whereas NE makes the main contribution to DLC:2.5%Ge. The LEs are related to sp 2/sp carbon‐related centers, while the NEs are assigned with electrons in the sp 3 orbital. The correlation between the sp 3/sp 2 ratio and the shift of g‐factor for NE to lower values with Ge doping is established. The Korringa relaxation model is provided for the ESR linewidth temperature dependence. The higher density of LE states on Fermi energy level caused by Ge doping of DLC films is proposed.

Characteristics of DLC films doped with multi-element alloy

Multi-element alloy doped diamond-like carbon (DLC) films were coated using sputtering with a (AlCrNbSiTiV) target. TEM and XRD results indicated DLC film had an amorphous compound feature incorporating polycrystalline phases around the face-centered cubic structure, which were embedded into the amorphous carbon matrix. The Raman spectra and mechanical characteristics of the DLC film sample were associated with concentration changes in the carbon and the multi-element alloy doped in the DLC films, which depended on the DC power. This investigation indicated that improved mechanical properties, including hardness and the elastic recovery rate, can be obtained from the multi-element alloy doped DLC film coated with proper DC sputtering power. These results demonstrated a proper DC power modifies the structure of multi-element alloy doped DLC film and improves its mechanical performance. This study should pave the way for the development of DLC film and elevate its application in various industries.

Microstructure, wear and corrosion behavior of nano-CeO2 doped diamond-like carbon (DLC) composite films

Diamond-like carbon (DLC) composite films doped with ceria were synthesized on LY-12 aluminum alloys by electrodeposition. The effects of ceria concentration on the microstructure, microhardness, wear and corrosion behavior of the composite film were investigated via Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), micro-Vickers tester, friction and wear tester and electrochemical workstation. Meanwhile, the growth mechanism of the films was explored. Results proclaimed that the loose honeycomb structure of the films was replaced by a compact granular structure as the ceria concentration increased to 1.16 ×10−3 mol/L. Raman spectra showed the typical amorphous characteristics of DLC film. The intensity ratio of G-line and D-line (ID/IG) diminished from 0.59 to 0.47, the G-line shifted to the lower frequency and the GFWHM increased, demonstrating that the CeO2/DLC composite film deposited at optimal ceria contains the higher sp3-C content. XPS analysis revealed that the binding mode of ceria is physically doped. Furthermore, the CeO2/DLC composite film exhibits superior anti-wear and anti-corrosion ability, which is primarily due to the compact structure and high microhardness. The statement of the new informationDouble Ni-Cu interlayer are prepared and CeO2 nanoparticles were successfully encapsulated in diamond-like carbon (DLC) films on LY-12 aluminum alloy substrates by electrodeposition.

Adhesion and corrosion of Al–N doped diamond-like carbon films synthesized by filtered cathodic vacuum arc deposition

Diamond-like carbon (DLC) films (thickness: ∼118 nm) doped with Al and N on AISI 4140 steel were synthesized using a filtered cathodic vacuum arc technique. The adhesion and corrosion of the ta-C, ta-C:N, ta-C:Al, and ta-C:Al:N films were examined in terms of structure and bonding. X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy revealed that the Al-doped and Al and N co-doped films had lower densities and internal stresses than the other films, as indicated by their higher ID/IG ratios and graphite cluster size (La) and lower sp3 relative fractions. All DLC films exhibited improved corrosion resistance as compared to AISI 4140, as indicated by their decreased corrosion rate and increased corrosion potential and polarization resistance. The corrosion resistances of ta-C:Al:N and ta-C:Al films were high owing to the combined effect of sp3 C–N and Al2O3, as confirmed by near-edge X-ray absorption fine structure spectroscopy and XPS. All doped DLC films exhibited improved adhesion performance compared to the ta-C film owing to their improved lubrication performance (increased sp3-hybridized C–N bonds) and improved toughness (formation of Al2O3).

Thermomechanical properties and frictional contact behavior of oxygen doped DLC film through molecular dynamics simulation

Using the MD simulation techniques, we investigated the effects of doped oxygen atoms on the thermomechanical properties and tribological performance of diamond like carbon (DLC). The atomic percentage of oxygen (at.% O) in DLC was varied from 0 to 20.0%. The mechanical stiffness of oxidized DLC samples was evaluated using the nanoindentation simulation, while the coefficient of friction (COF) and the frictional temperature rise were obtained from the sliding contact simulation. From the simulation results, it could be found that the mechanical stiffness and the COF decreased with the at.% O in DLC. The lower COF for the oxidized DLC could be explained by the less covalent interactions with the diamond tip surface. Due to the lower stiffness, the oxidized DLC showed larger surface displacement and wear during the sliding contact. Also, the frictional temperature rise was evaluated with respect to the at.% O in DLC. The higher at.% O in DLC, the lower surface temperature rise. This could be attributed to the lower frictional heat flux and the higher specific heat of the oxidized DLC samples.

High-temperature tribological performance of the Si-gradually doped diamond-like carbon film

Silicon containing diamond-like carbon films is of value for engineering applications operating at the temperature above 200 °C. This work presents a Si-gradually doped diamond-like carbon film with increasing the Si content from outer layer to inner layer deposited by plasma-assisted reactive magnetron sputtering process. The microstructure, chemical bonding state and temperature-dependence tribological properties upto 500 °C of the film are investigated by using focused ion beam/transmission electron microscope (FIB/TEM), X-ray photoelectron spectroscopy (XPS) techniques and ball-on-disk tribometer, respectively. The results show that the as-deposited Si-gradually doped DLC film exhibit amorphous structure. The wear track tested at 500 °C are composed of carbon, SiO2 and silicon oxide. High-temperature tribological tests show that the friction coefficient values are 0.05 ± 0.01, 0.02 ± 0.004 and 0.09 ± 0.04, while the wear rates are 1.17 × 10−7 mm3/N·m, 1.65 × 10−7 mm3/N·m and 1.4 × 10−6 mm3/N·m at 300 °C, 400 °C and 500 °C, respectively. It is proposed that the improved high-temperature tribological properties of the Si-gradually doped DLC film benefit from its special composition structure that the inner layer with high Si content provides the required mechanical properties and the outer layer with low Si content reduces the friction coefficient as well as the wear rate.

The influence of Cr and Ni doping on the microstructure of oxygen containing diamond-like carbon films

Non-hydrogenated diamond-like carbon (DLC) films doped with metals and oxygen were deposited by direct current magnetron sputtering. The influence of chromium and nickel on the surface morphology, elemental composition, bonding structure, adhesion force, optical transmittance and nanohardness of the films was characterized by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), multi-wavelength Raman spectroscopy, UV–VIS–NIR spectrophotometry and nanoindenter. The surface roughness was reduced with the addition of Cr (7.4 at. %) or Ni (8.9 at. %) into DLC films. The EDX measurements indicated that the addition of Cr increased the oxygen content by ~37%, while Ni reduced it by ~50%, compared to the oxygen doped DLC film. The microRaman analysis indicated that the G band shifted to a higher wavenumbers range, became narrower and the sp3/sp2 sites fraction ratio decreased for the metals doped DLC films. The nanohardness values of the sputtered doped DLC films varied in the range of 4.5–7.6 GPa. It was observed that the Ni-DLC film showed the highest adhesion force value and was optically opaque.

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.

Antibacterial property of F doped DLC film with plasma treatment

Diamond-like carbon (DLC) has excellent biocompatibility and is attracting attention as a means of surface modification to improve the antibacterial properties of biomaterials used in medical devices. In this study, we examined the correlation between the physical and antibacterial properties of a fluorine-containing DLC (F-DLC) that received an atmospheric pressure plasma surface treatment using oxygen gas (O-F-DLC). The antibacterial effect of O-F-DLC was investigated with the ISO 22196 film adhesion method. As a result, we achieved an antibacterial effect approximately 100 times that of the control sample. These results suggest that O-F-DLC is effective as a surface treatment technology that can provide antibacterial properties.

Preliminary Study of Ge-DLC Nanocomposite Biomaterials Prepared by Laser Codeposition.

This paper deals with the synthesis and study of the properties of germanium-doped diamond-like carbon (DLC) films. For deposition of doped DLC films, hybrid laser technology was used. Using two deposition lasers, it was possible to arrange the dopant concentrations by varying the laser repetition rate. Doped films of Ge concentrations from 0 at.% to 12 at.% were prepared on Si (100) and fused silica (FS) substrates at room temperature. Film properties, such as growth rate, roughness, scanning electron microscopy (SEM) morphology, wavelength dependent X-ray spectroscopy (WDS) composition, VIS-near infrared (IR) transmittance, and biological properties (cytotoxicity, effects on cellular morphology, and ability to produce reactive oxygen species (ROS)) were studied in relation to codeposition conditions and dopant concentrations. The analysis showed that Ge-DLC films exhibit cytotoxicity for higher Ge doping.

Bactericidal abilities and in vitro properties of diamond-like carbon films deposited onto MAO-treated titanium

The present work is focused on the antibacterial potentials, tribological properties and corrosion resistances of silver (Ag) or nitrogen (N)-doped diamond-like carbon (DLC) films deposited by a hybrid ion beam deposition system onto titanium substrates that were pretreated by micro arc oxidation (MAO). The results revealed that the DLC and N-DLC films had remarkable sealing effects on the porous MAO-coated substrate. Although the MAO/(Ag:N)-DLC coating still presented porous features, it had the lowest average wear rate of all the samples (4.40 × 10−16 m3/N·m) in an SBF solution and eradicated 100% of the E. coli bacteria. The corrosion current density (1.06 × 10−10 A/cm2) of the MAO/DLC coating was two orders of magnitude greater than that of the other three coatings. It can be speculated that doped DLC films deposited onto MAO-coated substrates could significantly reduce the risk of the titanium implant.

ECR-MPCVD fabricated nitrogen doped DLC films for potential biomedical application

In this work, nitrogen doped diamond like carbon (DLC) films were fabricated on silicon wafers by varying CH4–N2 flow rates in an ECR-MPCVD system. The morphology, roughness and physicochemical nature of as-deposited films were characterized using SEM, AFM and XPS. With the increase of CH4 flow rate from 5 to 20 sccm, the coverage and surface roughness of DLC film have improved, while sp2/sp3 ratio decreases. Subsequently, the in vitro osteogenesis of N doped DLC films with 20 sccm CH4 was evaluated in terms of their apatite forming ability by soaking the samples in simulated body fluid (SBF) at 37 °C. The results show a very fast formation of crystalline apatite coatings on DLC films in 28 days, compared to reported more than 12 weeks. Moreover, the water contact angle (70°), the hemolysis rate (3.63%), the relative growth rate of HEK293T cell (101.2 ∼ 127.96%) and the cytotoxicity level (0) prove its promising potential for biomedical application.

Biomineralization of osteoblasts on DLC coated surfaces for bone implants.

Diamond like carbon (DLC) films were deposited onto Ti6Al4V and Si wafer substrates by RF plasma enhanced chemical vapor deposition. The influence of dopants such as fluorine (F), silicon (Si), and nitrogen (N) on composition, structure, and biocompatibility was investigated. Ion scattering spectroscopy analysis revealed the presence of dopant atoms in the outer-most layers of the films. Raman studies showed that the position of the G-band shifts to higher frequencies with the fluorine and nitrogen content in the DLC film, whereas the incorporation of Si into DLC induces a decrease of the position of the G peak. The corrosion behavior was studied in simulated body fluid. A higher charge transfer resistance (Rct) was observed for the doped DLC films. The indirect cytotoxicity was performed using L929 fibroblast cells. The coated surfaces were hemocompatible when tested with red blood cells. DLC films were noncytotoxic to L929 cells over a 24 h exposure. Saos-2 osteoblast cell response to the doped and undoped DLC coated surfaces was studied in adhesion, proliferation, differentiation, and mineralization assays. The production of calcium and phosphate by cells on doped DLC, particularly, nitrogen doped DLC, was higher than that on undoped DLC.

Tribological and Electrical Properties of Chromium Doped Diamond-Like Carbon Films Deposited by Unbalanced Magnetron Sputtering

Tribological and Electrical Properties of Chromium Doped Diamond-Like Carbon Films Deposited by Unbalanced Magnetron Sputtering

Understanding the friction behavior of sulfur-terminated diamond-like carbon films under high vacuum by first-principles calculations

Generally, the repulsive force was a key factor account for superlow friction of H or F doped diamond-like carbon (DLC) films under high vacuum. As we known, H or F doped DLC usually exhibited superlow friction under high vacuum. However, the superlow friction of S doped DLC under high vacuum was not found so far. This phenomenon was desirable to be well investigated. In this work, S-terminated diamond interfaces also exhibited strong repulsive force, however, the estimated friction coefficient was variable for S-terminated diamond interfaces. The lowest and largest friction coefficient was about 0.003 and 0.4 respectively, which indicated that the superlow friction of S doped DLC could achieve in theory. In order to well probe the unusual friction behavior of S doped DLC under high vacuum, using first-principles method, the repulsive interaction between sliding surfaces was well investigated in order to understand the unusual friction behavior of S doped DLC films.

Phosphorus doping of diamond-like carbon films by radio frequency CVD-cum-evaporation technique

Diamond-like carbon (DLC) films have been deposited by cracking methane gas in radio frequency plasma. Phosphorus was incorporated in DLC films by simultaneously evaporating phosphorus during the synthesis of DLC with methane gas by using capacitatively coupled plasma chemical vapour deposition (CVD) technique. The films were characterized by FESEM, XRD, XPS and Raman studies. The band gap of the pristine DLC films was found to be ~2.61eV and it decreased from 2.61eV to 2.31eV with increased incorporation of P in the DLC films. Raman studies indicated the presence of two broad peaks located at ~1360–1396cm−1 (D-line) and ~1542–1548cm−1 (G-line). The peak positions of the D-lines shifted in towards lower wave number with increased incorporation of phosphorus in them. This indicated that the DLC films became sp2 rich with increased incorporation of phosphorus. Electrical resistivity measurements have been carried out. The films were n-type as indicated by hot-probe technique. The values of electrical resistivity of the undoped and doped DLC films were 2.0×102Ω-cm and 0.7×102Ω-cm, respectively. Value of carrier concentrations (Nd) obtained were 2.5×1015cm−3 and 2.2×1016cm−3 for undoped and phosphorus doped DLC film with 3.4 at.% P in DLC, respectively.

Electrodeposition of Si–DLC nanocomposite film and its electronic application

In this study, a silicon doped diamond-like carbon (DLC) nanocomposite film was deposited electrochemically and it was used to fabricate an Ag/Si–DLC/p-Si metal–interlayer–semiconductor (MIS) Schottky diode. Methanol (CH3OH) was used as carbon and tetraethoxysilane (Si(OC2H5)4) as Si source, respectively. Morphology of the film was observed by scanning electron microscopy and continuous surface with numerous lumps spread randomly was observed. Structural and chemical composition analyses of the film were carried out by Raman and X-ray photoelectron spectroscopy. Typical D and G bands of DLC films were not observed in the Raman spectrum due to abundance of Si–C bonds. Silicon incorporation promoted the film deposition and increased sp3 bonds in the film. Current–Voltage (I–V) measurement was conducted to obtain parameters of the MIS diode. The diode exhibited a good rectifier behavior with ~ 103 rectification ratio. In the forward bias semi-logarithmic I–V plot, two linear regions with different slopes were observed. Such behavior was modelled by two parallel diodes and attributed to different conduction mechanism. The main electrical parameters, such as barrier height, ideality factor and series resistance were calculated by I–V and Cheung–Cheung methods. The Si–DLC nanocomposite film acted as barrier height modifier in the MIS diode.