Properties Of Diamond-like Carbon Films Research Articles

Dramatically enhanced mechanical properties of diamond-like carbon films on polymer substrate for flexible display devices via argon plasma pretreatment

Hydrogen-free diamond-like carbon (DLC) films have been deposited on polyimide (PI) substrate at room temperature using the sputtering with a novel nanodiamond target. Also, argon plasma pretreatment procedure for PI substrate was optimized to improve the adhesion and characteristics of the as-prepared DLC film. The deposited DLC film on the PI substrate pretreated with −400 V of bias voltage was found to possess the highest sp3 bonding fraction of 53%, the pencil hardness of 3H, and the optical transmittance of 82%, respectively. The research work demonstrates prosperous applications of DLC films in the protective coating for commercialized optoelectronic devices.

The Friction and Wear Properties of Metal-Doped DLC Films under Current-Carrying Condition

In an effort to improve the surface properties of electrical contact materials in terms of high friction coefficient and wear rate, diamond-like carbon (DLC) films containing different metal elements were prepared on stainless steel substrates using an unbalanced magnetron sputtering system. In the present study, the effect of current-carrying on DLC film, Cu-doped DLC film (Cu/DLC), and Ti-doped DLC film (Ti/DLC) is reported. The structure and mechanical properties of the films were characterized systematically by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectra; these methods were also used to analyze the initial surface of the films. Moreover, the tribological behaviors of the films sliding against AISI 52100 steel with and without an electric current (1 A) applied were investigated using a tribometer with ball-on-disc configuration in an atmospheric environment. The results demonstrated that the friction coefficients of DLC and Cu/DLC under current-carrying condition were decreased, whereas Ti/DLC showed opposite experimental results. The wear rate of the films with a current was higher than that without a current. Therefore, this study is meaningful to understand the tribological behaviors of microelectromechanical systems.

Preparation, Characterization and Tribological Properties of Diamond-Like Carbon Film on AZ31 Magnesium Alloy

In this study, DLC films were deposited using IBED with various CH4/H2 ratio, gas flow rates and accelerating voltages. The composition and mechanical properties of the DLC coatings were characterized using SEM, Raman spectroscopy and nanoindentor. The tribological properties of the coating were also investigated using a frictional surface microscope with an in situ observation system and friction force measurements. The DLC films were characterized by a lower ID/IG, higher hardness, and improved tribological properties when deposited at a lower accelerating voltage (6 kV). At the CH4/H2 ratio of 1:99 and 6 sccm/6 kV, minimum ID/IG values of 0.62, relatively low friction coefficient of 0.12 , and a maximum hardness of 4056 HV were attained respectively.

Influence of particulate on surface energy and mechanical property of diamond-like carbon films synthesized by pulsed laser deposition

We report a detailed structural study of particulate laden diamond-like carbon (DLC) films synthesized by pulsed laser deposition (PLD) and its influence on surface energy and mechanical properties. A detailed analysis of various parameters such as: Dispersion (G), I(D)/I(G), T-peak position and FWHM(G) obtained from UV Raman spectroscopy for flat and particulate region of all DLC specimens indicate that the vibrational properties vary in both the regions depending on growth mechanism and modification of particulates in the plasma, respectively. The influence of these heterogeneous vibrational properties on surface energy and hardness is extensively studied by contact angle measurement and nano-indentation, respectively. DLC surface energy is observed to be influenced by sp2 cluster size, sp3 content, bond length and angle disorder of sp2 clusters found in the particulate regions, whereas indentation hardness (H) and modulus (E) of DLC films at 0.3 mN applied indentation load follows the evolution of sp3 content in the flat region.

Superlow friction and diffusion behaviors of a steel-related system in the presence of nano lubricant additive in PFPE oil

The lubrication performances of diamond like carbon (DLC) films were investigated by a ball-on-disc tribometer under perfluoropolyether (PFPE) oil lubrications. The influence of nano lubricant additives in PFPE oil on the tribological properties of DLC films was evaluated. The experimental results show that the solid-liquid synergy lubrication is beneficial to improve the tribological properties of the steel-related friction system and the tribological properties of the friction pair are significantly influenced by lubrication modes and the types and contents of nano lubricant additives under PFPE oil lubrication. The friction system exhibits super low friction behaviors under PFPE oil with nano MoS2 lubricant additive lubrication due to the excellent compatibility of nano MoS2 additives with PFPE oil. Coefficient of friction (CoF) of the friction system is as super low as 0.02 under PFPE oil with 0.2 wt.% nano MoS2 additive lubrication. Superlow friction mechanism is attributed to the pointlike contact of nano MoS2 additive as soft phase and the excellent diffusion behaviors of nano MoS2 additives in PFPE oil. The potential usefulness of nano MoS2 particles as the lubricant additives in PFPE oil for the steel/DLC films has been demonstrated.

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.

Correlation study of structural, optical, and hydrophobicity properties of diamond-like carbon films prepared by an anode layer source

Diamond- like carbon (DLC) thin films were deposited using anode layer source system on glass substrate at substrate temperature ranging from room temperature (RT) to 375 °C. An anode layer source is a specific ion gun, which can be fed with carbon precursors like propane to deposit hard and highly defect-free hydrogenated DLC thin films. The morphological, structural, optical, and hydrophobicity properties of DLC thin films were characterized by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, UV- Vis spectrophotometer, and water contact angle (CA) measurement. The surface roughness was found to increase with substrate temperature. Disorder (D) and graphite (G) peak positions have been observed to respectively move toward 1400 cm−1 and 1546 cm−1, with substrate temperature, indicating a graphitization of DLC thin films, which may probably be ascribed to the sp2 cluster sites growth. The full width at half maximum (FWHM) of G peak increased upon increasing the substrate temperature. From the FWHM values of G peak, the clusters became more ordered with increasing the substrate temperature of DLC thin films. The G peak position changed by increasing the substrate temperature that in turn led to increment in the ID/IG ratio from 0.71 to 0.85, and also the graphite cluster size increased from 1.07 to 1.24 nm. Optical transmittance in UV and near infrared regions of the prepared DLC thin films found to decrease with the increase of substrate temperature. The refractive index (n) and extinction coefficient (k) of the films have been found to increase with substrate temperature. The CA of DLC thin films slightly increased with increasing substrate temperature from 80° at RT to 94° at 300 °C.

Effect of SiNx interlayer thickness on adhesion and friction properties of diamond-like carbon films

A suitable interlayer thickness is critical to reduce film mismatch and roughness. In this text, diamond-like carbon (DLC) films with different SiNx interlayer thicknesses were successfully synthesized on Si (100) substrates by radio frequency (RF) and direct current (DC) magnetron sputtering method. The effect of SiNx interlayer thickness on surface morphology, adhesion, tribological and mechanical properties of DLC films was investigated. The results show that, due to the use of SiNx interlayer in the DLC films, the adhesion is significantly enhanced, the surface roughness is increased, and the sp3 content and modulus are lowered. When the SiNx interlayer is introduced, the internal stress and the roughness decrease first decrease and then increase. The reason may be related to the accumulation of nitrogen vacancy centers (NVC). A sample of about 10 nm SiNx interlayer was found to have the best combination of tribology, mechanical properties, and surface roughness.

Pulsed-DC Discharge for Plasma CVD of Carbon Thin Films

A pulsed-dc discharge method for plasma chemical vapor deposition (CVD) was developed using a constructed versatile pulsed-dc generator and a vacuum discharge chamber. Argon (Ar) gas discharge experiments were performed under a variety of discharge conditions, and plasma conditions were evaluated using optical emission spectroscopy. The developed system can perform glow discharge by employing nearly rectangular, unipolar, and high-voltage negative pulses with a wide variation of voltage amplitudes and a set discharge current, pulse repetition rate, and duty cycle. Plasma conditions could also be tuned by varying the pulse parameters. A preliminary test of the deposition of diamond-like carbon (DLC) films on silicon (Si) substrates and ultrathin pyrolytic carbon (PyC) films on nanothickness metal-catalyzed glass substrates was performed with acetylene (C 2 H 2 ) by selecting some typical deposition conditions based on the gas discharge experiments. The deposited films were characterized via Raman spectroscopy. The characteristic properties of DLC and PyC films were achieved. The DLC films demonstrated conventional hard insulating properties while the ultrathin PyC films exhibited conductive and semitransparent properties. These results revealed that the developed pulsed-dc discharge system for plasma CVD is applicable for the synthesis of insulating hard as well as soft conducting carbon thin films.

Effect of temperature and bias voltage on electrical and electrochemical properties of diamond-like carbon films deposited with HiPIMS

The relatively high electrical resistivity of diamond-like carbon (DLC) film is one of the main drawbacks when applied in electronic device. In this study, DLC films were synthesized on 304 stainless steels by high power impulse magnetron sputtering (HiPIMS) process and the effect of deposition temperature and bias voltage on the microstructure, electrical and electrochemical properties, hardness and adhesion strength of the DLC films were investigated. The sp2/sp3 ratio of DLC films first decreased then increased and the surface became denser as bias voltage increasing from 0 to −400 V. While the film turned into graphite-like structure and became incompact when deposition temperature rose from 100 °C to 300 °C. The interfacial contact resistance (ICR) got reduced by increasing bias voltage and deposition temperature. However, as the deposition temperature increased to 300 °C the anticorrosion ability and hardness of DLC films deteriorated. The DLC films deposited at 300 °C presented soft and had better adhesion strength than hard DLC films deposited at 100 °C. DLC films deposited at −400 V bias and 300 °C had the lowest ICR while DLC films deposited at −400 V bias and 100 °C had the best performance when ICR, corrosion resistance and hardness were all taken into consideration.

Mechanical Properties of Hydrogen Free Diamond-Like Carbon Thin Films Deposited by High Power Impulse Magnetron Sputtering with Ne

Hydrogen-free diamond-like carbon (DLC) thin films are attractive for a wide range of industrial applications. One of the challenges related to the use of hard DLC lies in the high intrinsic compressive stresses that limit the film adhesion. Here, we report on the mechanical and tribological properties of DLC films deposited by High Power Impulse Magnetron Sputtering (HiPIMS) with Ne as the process gas. In contrast to standard magnetron sputtering as well as standard Ar-based HiPIMS process, the Ne-HiPIMS lead to dense DLC films with increased mass density (up to 2.65 g/cm3) and a hardness of 23 GPa when deposited on steel with a Cr + CrN adhesion interlayer. Tribological testing by the pin-on-disk method revealed a friction coefficient of 0.22 against steel and a wear rate of 2 × 10−17 m3/Nm. The wear rate is about an order of magnitude lower than that of the films deposited using Ar. The differences in the film properties are attributed to an enhanced C ionization in the Ne-HiPIMS discharge.

Tribological and Electrical Properties of Diamond-Like Carbon Films Deposited by Filtered Vacuum Arc Method for Medical Guidewire Application.

A good medical guidewires are used to introduce stents, catheters, and other medical devices inside the human body. In this study, diamond-like carbon (DLC) film was proposed to solve the poor adhesion problem of guidewire and to improve the tribological performance of guidewire. DLC films were fabricated on Si substrate by using FVA (Filtered Vacuum Arc) method. In this work, the tribological, structural, and electrical properties of the fabricated DLC films with various arc currents were experimentally investigated. All DLC films showed smooth and uniform surface with increasing applied arc current. The rms surface roughness was increased and the value of contact angle on the film surface was decreased with increasing arc current. The hardness and elastic modulus of DLC films were improved, and the resistivity value of DLC films were decreased with increasing arc current. These results are associated with ion bombardment effects by the applied arc current and bias voltage.

Investigation of Fe3Al-based PVD/HVOF duplex coatings to protect stainless steel from sliding wear against alumina

In this work, the sliding wear properties of several duplex (thin-on-thick) coating systems used to protect stainless steels were evaluated under different loading conditions. The coating systems consisted of a 304-stainless steel (SS304) substrate or the same steel previously coated with a layer of iron aluminide (Fe3Al) based material using the high velocity oxy-fuel (HVOF) technique, onto which a thin film of CrN or DLC (diamond-like carbon) was deposited using the physical vapor deposition (PVD). The mechanical properties of coatings were investigated by indentation, and their wear properties were evaluated using a pin-on-disc tribo-system with alumina as counterpart material in ambient conditions under applied loads between 5 N and 15 N. Wear mechanisms of coatings were assessed by examining the morphology of top surfaces and cross-sections of wear tracks, and by analyzing the counterpart material using scanning electron microscopy, energy dispersive and Raman spectroscopies. Results show that the addition of a top coat significantly enhances the wear resistance of the SS304 substrate and of the HVOF coatings due to the excellent tribological properties of DLC and CrN films. Moreover, the PVD/HVOF/SS304 coating systems exhibit excellent wear properties when compared to PVD/SS304 coatings alone due to the high load bearing capacity of the HVOF layers. The wear resistance of such systems increases with the hardness of the HVOF layer. The DLC/HVOF/SS304 duplex coatings show the best tribo-mechanical performance due to their very low coefficients of friction and good bond strengths between layers. On the contrary, the relatively poor tribological performance of the CrN/HVOF/SS304 duplex coatings can be attributed to the brittle nature of the CrN film. The main degradation mechanisms for the DLC-based duplex coatings were adhesive wear and plastic deformation, while in the case of the CrN-based duplex system, brittle fractures and oxidation wear were predominant. In both coating systems, abrasive wear has also contributed to the material loss.

Tribological properties of diamond-like carbon films deposited by vacuum arc

Abstract Conventional artificial hip joints with metal-on-metal pairings are subject to wear resulting in a large number of metal wear particles, limiting the lifetime of implants. In order to impr...

The friction and wear performance of DLC coatings deposited on plasma nitrided AISI 4140 steel by magnetron sputtering under air and vacuum conditions

Diamond-like-carbon (DLC) coatings with high hardness and low friction coefficient exhibit excellent tribological performance under air and vacuum conditions. However, adhesion and cold welding problems in vacuum conditions lead to increase friction coefficient values. These negative effects can be eliminated by different methods such as forming interlayers between coating and substrate or ion treatment of the substrate. In this work, DLC coatings were deposited on untreated and plasma nitrided (at 400°C, 500°C and 600°C for 1h and 4h) AISI 4140 steel substrates by magnetron sputtering technique. The effects of plasma nitriding treatment on the friction and wear properties of DLC coatings under air and vacuum conditions were investigated. The structural and mechanical properties of DLC films were examined by XRD, SEM, and microhardness tester, respectively. The friction and wear properties were determined by a tribotester under air and vacuum conditions. The microhardness of samples increased after surface treatments and the highest value was obtained from the sample plasma nitrided at 600°C for 4h plus DLC coated sample. The wear resistance of samples increased with increasing plasma nitriding time and temperature. Also, it was observed that the samples tested under vacuum condition showed better wear resistance than the samples tested under ambient air. Furthermore, increasing plasma nitriding time and temperature improved the wear performance of the material regardless of the test environment.

The correlation between optical and mechanical properties of amorphous diamond-like carbon films prepared by pulsed filtered cathodic vacuum arc deposition

Diamond-like carbon (DLC) films were deposited by pulsed filtered cathodic vacuum arc (FCVA) deposition. The microstructure, mechanical and optical properties of DLC films have been investigated as functions of the variation in the substrate negative direct current bias voltage (Vbias) from 0.0 to 1.5 kV. Raman and X-ray photoelectron spectroscopy results show a correlation between the ID/IG ratio and the microstructure in terms of the sp3/sp2 ratio to Vbias. This fact shows that a significant change in the sp3 content, which is attributed to the transformation from graphite-like to diamond-like, is accompanied by a decreasing ID/IG ratio. The relatively high mass density of the films in the range of 2.51 to 2.79 g/cm3 can be obtained with biasing. The mechanical properties, i.e., the hardness and elastic modulus, were 13–25 and 114–145 GPa, respectively. The improvement of the mechanical properties is due to the formation of the compressive residual stress and the local density depending on Vbias. The relationship between the refractive index and the ID/IG ratio agree well with the microstructure and mechanical properties of DLC films. All of these results indicate a vital role of Vbias in determining the DLC properties.

Tribological behavior of DLC films and duplex ceramic coatings under different sliding conditions

Diamond-like carbon (DLC) films are effectively utilized to improve the tribological properties of materials due to their low friction coefficient, good wear resistance and high hardness. In recent years, different pre-treatments such as plasma assisted diffusional processes have been used to increase long-term durability of these coatings. In the present work, DLC films were deposited on untreated and plasma nitrided AISI 4140 low-alloy steel samples using physical vapor deposition method (PVD). The effect of nitride layers on the structural and mechanical properties of DLC films was examined by XRD, SEM, microhardness tester and reciprocating tribotester. The wear tests were performed under dry, saltwater and lubricant environments. The microhardness results indicated that surface hardness considerably increased after duplex treatment and this caused to increase plastic deformation resistance of the material. The reciprocating test results showed that DLC films deposited on untreated and plasma nitrided samples reduced the coefficient of friction because of the formation of transfer film between sliding/mating surfaces. Also, wear rates improved significantly after duplex treatment in consequence of high plastic deformation resistance of duplex treated samples. The highest wear resistance was obtained in lubricated condition while the lowest wear resistance was for the samples tested in dry conditions.

Synthesis and electrochemical properties of Ti-doped DLC films by a hybrid PVD/PECVD process

Low electrical conductivity and poor adhesion to metallic substrates are the main drawbacks of diamond-like carbon (DLC) films when used in electrode applications. In this study, Ti-doped DLC films with various Ti contents were synthesized on metal Ti substrates by a hybrid PVD/PECVD process, where PECVD was used for deposition of DLC films and PVD was used for Ti doping. The effects of the Ti doping ratio on the microstructure, adhesion strength, and electrical and electrochemical properties of the DLC films were systematically investigated. An increase in the Ti content led to increased surface roughness and a higher sp2/sp3 ratio of the Ti-DLC films. Ti atoms existed as amorphous-phase Ti carbide when the Ti doping ratio was less than 2.8 at.%, while the nanocrystalline TiC phase was formed in DLC films when the Ti doping ratio was exceeded 4.0 at.%. The adhesion strength, electrical resistivity, electrochemical activity and reversibility of the DLC films were greatly improved by Ti doping. The influence of Ti doping ratio on the electrical and electrochemical properties of the DLC films were also investigated and the best performance was obtained at a Ti content of 2.8 at.%.

Diamond-like carbon layers modified by ion bombardment during growth and researched by Resonant Ultrasound Spectroscopy

Biocompatible Diamond-Like Carbon (DLC) films were prepared by Pulsed Laser Deposition technique using the laser energy density of 10Jcm−2 on the graphite target. The surface of the grown film was modified during the deposition by bombardment with argon, xenon, nitrogen or oxygen ions. The ion energy (up to 150eV) was changed by gun voltage and by ionic current. The films with high and low diamond/graphite content were prepared. Physical and mechanical properties of biocompatible DLC thin layers prepared by hybrid laser technology were studied. The composition of layers and the content trace elements were determined by the methods of Rutherford Backscattering Spectrometry and Particle Induced X-ray Emission. The content of sp2 and sp3 bonds was measured using X-ray Photoelectron Spectroscopy. For different energy of argon and oxygen ions the maximum of sp3 bonds content was found (83.63% of sp3 bonds for argon ions). All films were smooth, which was confirmed by profilometry and Atomic Force Microscopy measurements. Maximum roughness Ra and RMS was did not exceed 1nm. The Younǵs and shear moduli were studied by Resonant Ultrasound Spectroscopy. The Young’s Modulus attained the value of 601GPa and the shear Modulus attained the value of 253GPa at the energy of 30eV of Ar ions. The influence of ion bombardment on DLC film properties is discussed.

Influence of Ne sputtering gas on structure and properties of diamond-like carbon films deposited by pulsed-magnetron sputtering

The key process in diamond-like carbon (DLC) film deposition is the formation of sp3-C hybridized bond, which is believed to significantly link to the ionization degrees of the carbon atoms. Ne has a high ionization energy and can facilitate the ionization degree of sputtered carbon. In this paper, Ne and Ar gas mixture was used as the sputtering gas to prepare DLC film by using a pulsed-magnetron sputter. The influences of the Ne fraction in the sputtering gas mixture on the growth character, carbon bond structure, residual stress and mechanical properties of the as-deposited DLC films were studied carefully by using scanning electron microscope, Raman spectroscopy, stress tester and nano-indentation, respectively. The results reveal that the introduction of Ne in sputtering gas mixture can induce the structure densification of the coatings, and significantly increase the sp3 fraction of the DLC films. However, it was found that the sp3 fraction of the films increased little as the Ne fraction exceeded 25%. This phenomenon might be attributed to the reduction of the electron density of the plasma due to the increase of the Ne fraction in the sputtering gas mixture. The residual stress of the DLC films was believed to depend on the sp3 fraction of the films, and thus exhibited a similar changing trend to sp3 fraction as a function of Ne fraction. However, the hardness and elastic modulus of the films increased continuously as the Ne fraction increased. The structure densification and the increase of the sp3 fraction caused by the addition of Ne may be the main factors contributed to the increase of the hardness and elastic modulus of the films.