Surface Of Diamond-like Carbon Films Research Articles

Enhancing sp3 content in diamond-like carbon thin film electrodes by pulsed laser annealing for durable charge storage performance

In this work, diamond-like carbon (DLC) thin film electrodes were grown on Si substrate by pulsed laser deposition (PLD) technique, and the implication of pulsed laser annealing (PLA) treatment on their electrochemical supercapacitor performance was examined by three electrode systems in 1 M Na2SO4 electrolyte solutions. The SEM micrographs exhibit a sheet-like wrinkled surface of DLC film on Si which later transformed into tiny hierarchical heap-like structures with enhanced surface roughness. The Raman spectra confirm signature of the D and G peaks of pristine DLC film at ∼1352 cm−1 (1356 cm−1 after PLA) and 1591 cm−1 (1589 cm−1 after PLA), and appearance of minor T2g (diamond) (1332 cm−1) peaks with an increment of the sp3 content after PLA treatment. The X-ray photoelectron spectroscopy (XPS) spectra were deconvoluted into three different contributions CC (sp2), CC (sp3), and CO, and their sp3 percentages were estimated ∼48.9 %, and 64.7 % before and after annealing. The area under cyclic voltammetry (CV) curve and galvanostatic charging discharging (GCD) performance of PLA-treated DLC film were improved and the highest areal-specific capacitance was obtained to be ∼48.25 mF/cm2 for scan rate of 5 mV/s and 36.01 mF/cm2 for current density of 2 mA/cm2, respectively. Excellent charging discharging cyclic stability of PLA treated electrode was observed over 5000 cycles, and Coulombic efficiency and capacitance retention were determined to be ∼93.5 % and ∼ 97.3 %, respectively. The electrochemical impedance spectroscopy (EIS) was performed to obtain the Nyquist plot (Z′vs.Z′′) of both electrodes before and after the stability test, and a small degradation in impedance was observed. The Nyquist plots were fitted with the well-known Randles equivalent circuit model Rs(Cdl(RctZw)) and substantial curtailment of Warburg resistance (Zw) in PLA-induced DLC electrode signifies the dominance of the diffusion-controlled region in the charging-discharging process. Minor changes in the Nyquist plot before and after the stability test manifest the enduring charge kinetics of both electrodes and PLA-treated DLC exhibits better cyclic stability. PLA techniques have a great impact on upgrading the areal-specific capacitance, capacitance retention with high Coulombic efficiency, and stability with negligible impedance loss of the DLC film electrodes.

RETRACTED: Molecular Dynamics Simulation of Friction in DLC Films with Different sp3 Contents

Through molecular dynamics simulations, the friction behavior between diamond-like carbon (DLC) films with different sp3 fractions and Si3N4 bulk was studied under various sliding velocities and loads. DLC films with moderate sp3 fractions demonstrated superior tribological properties, with lower frictional forces, smaller shear deformations and wear, and fewer sp3-sp2 transitions under equivalent sliding velocities and loads. Increasing sliding velocity promoted rapid mixing of the contacting interface, reducing shear deformations and adhesive wear. High loads disrupted DLC film surface structure, leading to a lubricating layer that shifted friction behavior from adhesive to abrasive wear, while suppressing sp3-sp2 transitions and releasing internal stress. These findings hold crucial implications for optimizing DLC film friction performance and applications.

Anti-corrosion and erosion properties of multilayers with diamond-like carbon and silicon films deposited on low-carbon steel

A multilayer of diamond-like carbon (DLC) and silicon (Si) films were deposited on low-carbon steel (CS) using a combination of bipolar-pulsed magnetron sputtering (MS) and the radio frequency plasma enhanced chemical deposition (RF-PECVD) methods. Spectroscopic techniques such as Raman spectroscopy, synchrotron-based X-ray photoemission spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy were used to investigate the chemical and structural properties of the film. The mechanical properties were measured using nanoindentation and nano-scratch testers. The films' electrochemical performance and corrosion behavior were evaluated in the 3.5 wt% NaCl solution at room temperature. The erosion resistance of the films was studied under the sand jet impingement apparatus. The results indicate that the 2 Si-layers in the DLC film and CS substrate increase the C‒sp3 content at the DLC film surface resulting in high mechanical hardness. The adhesion of the DLC film on the CS substrate was also improved by adding the Si layer between the CS substrate and DLC film. Consequently, multilayer Si/DLC film resists the elastic deformation of films caused by graphitization.

The synergistic mechanism between transfer layer and surface passivation of diamond-like carbon film under different gas pressure environments

The low friction behavior and mechanism of diamond-like carbon (DLC) film are studied under different gas pressure environments. The results present that DLC film against Al2O3 and steel balls shows a relatively stable friction coefficient in the air environment, but it shows an unstable and relatively low friction coefficient under gas pressure of 5 Pa. Under gas pressure of 10−3 Pa, the DLC film fails rapidly although it achieves a short superlubricity state. With the decrease of gas pressure, the gas passivation effect on the surface of DLC film will be weaker and weaker while the formation degree of transfer layer will be more and more continuous and dense. The first-principles calculations imply that interfacial adhesion has a significant influence on the formation of tribofilms and surface wear. Further analysis shows that the low friction behavior and mechanism of DLC films in air, low vacuum (5 Pa) and high vacuum (10−3 Pa) environment are not controlled by graphitization mechanism, but are caused by the synergistic action of transfer layer mechanism and surface passivation mechanism.

Frictional Properties of Element- and Compound-Doped Diamond-Like Carbon Films under Boundary Lubrication with Synthetic Base Oil

The frictional properties of diamond-like carbon (DLC) films under boundary lubrication with a synthetic base oil were investigated. The specimens tested were a-C:H, Cr-a-C:H, Ti-a-C:H, W-a-C:H, WC-a-C:H, Mo-a-C:H, MoS2-a-C:H, and Sn-a-C:H films. The tribological properties of DLC/steel contacts were evaluated using a reciprocating-type cylinder-on-disk tribotester. The DLC films exhibited different frictional properties depending on the type of doping elements and compounds used. Notably, the Sn-a-C film gave the lowest friction. The friction tests and static contact angle analyses revealed that the average friction coefficient decreased with a decrease in the static contact angle of the worn DLC film surface, demonstrating that the DLC films with relatively high surface wettabilities exhibited relatively low friction properties. Therefore, surface wettability plays an important role in determining the frictional properties of DLC films under boundary lubrication with synthetic base oil..

From pulsed-DCMS and HiPIMS to microwave plasma-assisted sputtering: Their influence on the properties of diamond-like carbon films

The fabrication of high-hardness non-hydrogenated diamond-like carbon (DLC) via standard magnetron sputtering (MS) is often hindered by the low sputtering yields and ionisation rates of carbon, therefore investigations into pulsed alternatives of MS, else sputtered species post-ionisation methods, are of particular interest. This work focuses on investigating the influence of pulsed-direct current MS (pDCMS), high power impulse magnetron sputtering (HiPIMS) and their microwave plasma-assisted (MA-pDCMS, MA-HiPIMS) variants on the properties of the fabricated DLC films. Two setups were used for the pDCMS- and HiPIMS-based methods, respectively. The films were characterised using Raman spectroscopy, nanoindentation, X-ray reflectometry and scanning electron microscopy, where the pDCMS-produced films were additionally characterised by film-stress measurements. Moreover, in situ time-resolved Langmuir probe plasma analysis was performed under HiPIMS and MA-HiPIMS conditions to analyse the influence of the magnetron and microwave plasmas on one another. For both DCMS- and HiPIMS-based procedures, it was found that the addition of microwave plasma did not facilitate attaining hardnesses beyond 30 GPa, however, it did enable modifying the morphology of the films. Furthermore, this study shows the potential of synchronised sputtering with substrate biasing, as well as the importance of microwave plasma source positioning in relation to the substrate. • DLC films produced via pulsed magnetron sputtering and microwave plasma-assisted methods. • In situ plasma diagnostics were used to study magnetron-microwave plasma interactions. • Maximum DLC film hardness did not significantly exceed 30 GPa. • Microwave plasma caused DLC film surface morphology modifications. • Substrate biasing and microwave plasma source positioning affect DLC film tunability.

The synergistic mechanism between graphitized tribofilm and graphitized surface of diamond-like carbon film under different temperature environments

The tribology characteristics of diamond-like carbon (DLC) film are studied under different experiment temperatures. The outcomes reveal the average COF of DLC film will gradually decrease with the increase of temperature from 25 °C to 225 °C, but its wear rate will gradually increase. Especially at 225 °C, the DLC film is worn through in a very short time. The Raman characterizations imply that the low friction behavior of DLC film may be mainly caused by the synergistic effect of graphitized transfer layer and graphitized worn surface of DLC film as the temperature increases from 25 °C to 175 °C. Further analysis shows that the high wear of DLC film at high temperature may be mainly due to the reduction of wear resistance of worn DLC surface and the formation of soft oxide layer at friction interface.

Effect of Silver Clusters Deposition on Wettability and Optical Properties of Diamond-like Carbon Films

In this study, the effect of silver clusters deposition was investigated on optical, wettability and surface properties of diamond-like carbon (DLC) films. Silver clusters and DLC films were deposited on Ni-Cu (70.4-29.6;W/W) alloy substrates by ion beam sputtering deposition (IBSD) technique. Optical and structural properties were measured using UV-visible spectroscopy and Raman spectroscopy, respectively. The wettability and surface free energy of films were determined by the contact angle (CA) measurements. Raman spectra of DLC thin film with 121±6nm thickness without accumulated Ag showed that the size of the graphite crystallites with sp 2 bands (La) was 3.36A by the ID/IG ratio equal to 0.062 with large optical band gap equal 3eV extracted from Tauc relation. The results of the deposition Ag in the various ion beam energy between 0.6 to 2keV showed the Ag clusters were accumulated uniformity on the surface of DLC films at 0.9keV. The volume percentage of silver clusters was varied from 5.0±2.01 to 16.3±1.4. The variation was caused by controlling the screen voltage and the deposition time. The CA of the deposited films increases from 79°±2 to 95°±2 as well as the reflection values in the visible and near-infrared region due to the increase in the Ag concentration in the surface of DLC films; while the surface free energy decrease from 86±1 to 66±2mJ/m2 and the optical transmittance is almost constant. Our results demonstrate that the deposition of silver particles on DLC films is potentially useful for biomedical applications having good hydrophobic characteristics without causing a destructive effect on the optical properties of DLC films.

Low Friction of Diamond-Like Carbon Film Due to Liquid Hydrocarbon Generated by Laser Heating in a Nitrogen Gas Environment

In this study, we investigated the low friction mechanism of a diamond-like carbon (DLC) film heated by laser irradiation in a nitrogen gas environment. The friction coefficient decreased from 0.5 to 0.06 when the contact area was heated to 250 °C. Subsequently, we heated the DLC film under non-contact conditions (2 μm distance between DLC film and pin surface) and collected the liquid materials adhered on the pin surface. The adhered materials were revealed to be hydrocarbons with –CH2– main-chains, as observed using Raman spectroscopy. On the other hand, thermal desorption gas chromatography with mass spectrometry using helium as a carrier gas demonstrated that hydrocarbons such as alkenes and alkanes with relatively high molecular weight were generated from heated DLC. This agreement between the results of the two analysis techniques suggested that the hydrocarbons in the liquid phase at room temperature were generated from the DLC film heated to a high temperature over 250 °C in an inert gas atmosphere. In addition, we confirmed the reduction in the friction coefficient after pre-heating a different location, as well as the dependence of the friction coefficient on the sliding velocity. The results suggest that hydrocarbons (e.g., alkenes or alkanes) generated upon DLC heating could possibly act as a lubricant to reduce the friction coefficient.

The structure and properties of amorphous diamond-like carbon films deposited by helicon wave plasma chemical vapor deposition

The diamond-like carbon (DLC) films have been synthesized on silicon substrates by using chemical vapor deposition assisted with a high-density m=+1 mode helicon wave-excited plasma in Ar/CH4 gas mixtures. The structure and morphology of the DLC films are characterized by scanning electron microscopy (SEM), Raman spectroscopy and atomic force microscopy (AFM). The surface energies of the DLC films are calculated by the the Owens–Wendt–Rabel–Kaelble (OWRK) method. SEM results show that the surfaces of DLC films are found to be very uniform and dense, and the deposition rate of the film can reach up to 45 μm/h. The Young's modulus of the DLC films reaches the maximum (11 GPa) value at 25 sccm CH4 flow rate. With the increase of CH4 flow rate from 5 sccm to 35 sccm, the surface energy and friction coefficient of the DLC films decrease from 73.5 to 37.6 mJ m − 2 and from 0.56 to 0.25, respectively. It indicates that the deposited DLC films have good friction properties.The Young's modulus value is obtained here using AFM [48]. The results show that the Young's modulus increases from 4.1 to 10. 77 GPa, as the CH4 flow rate increases from 5 to 25 sccm. However, with further increasing the CH4 flow rate, the Young's modulus decreases gradually. This is consistent with the trend of sp3 bond content in Raman results. According to literature [49], CC sp3 bond of DLC films has a certain influence on Young's modulus. The result shows that the CC sp3 content reaches its maximum when the CH4 flow rate reaches 25 sccm. Moreover, the RMS results of DLC films show that the smoother the film is, the higher the Young's modulus is, likewise the rougher the DLC film is, the lower the Young's modulus is. It can be inferred that when DLC film is rough, the accumulated carbon polymer sp3 content in DLC film is low.

Crack evolution in diamond-like carbon films on steel substrates during nano-indentation

Fracture behaviors of thin hard diamond-like carbon (DLC) films were investigated considering the effects of plastic deformation of steel substrates. Nano-indentation tests for DLC films on SUS304 and M50 steels were conducted. The nucleation and propagation of film cracks were analyzed using the extended finite element method (XFEM). The ultimate tensile strength, fracture energy release rate and toughness of the films were evaluated. Results showed that cracks in DLC films on M50 steel substrates nucleated on the top surface of the films during nano-indentation; however, the first crack initiated at the bottom surface of DLC films on SUS304 steel because of its low yield strength. Large plastic deformation of the steel substrate was generated under nano-indentation, leading to consequent high tensile stress that concentrated first at the bottom surface of the films due to the film bending effect.

Comparative Study of Candida albicans Inactivation by Nonthermal Plasma on Stainless Steel with and without Diamond-like Carbon Film

This paper reports the efficacy of nonthermal plasma (NTP) as a biocidal agent to treat 304 stainless steel (SS304) covered with a diamond-like carbon (DLC) film contaminated with Candida albicans biofilms. The association of two techniques using electric plasma was used. The first was plasma-enhanced chemical vapor deposition (PECVD) used to deposit a DLC film on the SS304. The second was NTP used on the surface of the SS304 with and without the DLC film. The combination of the SS304 surface with the DLC film was demonstrated to be effective when using the DLC film as corrosion protection. Comparing the proliferation of Candida species on the DLC film and SS304 surface, it was possible to conclude that Candida species stays longer in the DLC film than in SS304. The reduction of colony numbers was visible after 5 min using plasma on both surfaces; in addition, 99% of Candida species were eliminated after 15 min. Three C. albicans microorganisms were used. Two were from samples of urine and tracheal secret...

Quantifying Macroscopic Friction of Diamond-like Carbon Films by Microscopic Adsorption and Removal of Water Molecules.

The adsorption and desorption of water molecules, which affect the physical and chemical properties of the sliding interface, are critical for the friction behaviors of two solid contacts in atmosphere environment. The amount of water adsorbed on the open surface is a function of gas pressure according to an adsorption equation. However, for a confined sliding interface, the variation of surface fraction covered by gas molecules with water vapor pressure and its induced effects on friction have not been figured out. In this work, the macroscopic friction of diamond-like carbon (DLC) films in a water vapor atmosphere is quantified on the basis of microscopic adsorption and removal of water molecules. The studies correlate the fraction of water molecules adsorbed on the interface of self-mated DLC films with water vapor pressure to illustrate the direct relationship between friction coefficient and gas pressure by first-principles calculations and model fitting. The calculated results revealed that chemisorption and physisorption of water molecules occur on the surfaces of hydrogen-free DLC films (ta-C) and hydrogenated DLC films (HCF). Then, the relation between friction and gas pressure was built by employing a fractional coverage model based on the linear adsorption equation and gas removal. The obtained model agrees well with the typical experimental results about the steady-state friction coefficient of both highly hydrogenated DLC film (HCF) and tetrahedral amorphous carbon (ta-C) film during sliding at various water vapor pressures. In addition, it gave the curves of fractional surface coverage as a function of water vapor pressure. These results show that the frictional coefficient of DLC films could be predicted on the basis of fractional surface coverage as well as the intrinsic characters on surface chemistry. We suggest that the model may be thus extended to understand and predict the friction of DLC films under a specific gas pressure at a low load and speed.

Characterization of adsorption and lubrication of synovial fluid proteins and HA on DLC joint bearings surface

Adsorption and competitive adsorption behavior of bovine serum albumin (BSA), human γ-globulin (HGG), and hyaluronic acid (HA) molecules on a diamond-like carbon (DLC) film surface were investigated by the means of a quartz crystal microbalance with dissipation (QCM-D), and antigen-antibody reactions. The results showed that a BSA monolayer could be formed on the DLC film surface with side-on orientation and that an HGG monolayer could be formed on the DLC film surface with end-on orientation by using pure BSA or HGG solutions, respectively. HA molecules were hardly adsorbed onto the surface of DLC film or HGG or BSA biomolecular layer. The results of competitive adsorption showed that HGG molecules could displace BSA molecules and that HGG was the dominantly adsorbed molecule on the DLC film surface in a mixture of BSA, HGG, and HA. The frictional behavior of a DLC film sliding against Al2O3 in a mixture of BSA, HGG, and HA, was investigated by means of the friction coefficient and an open circuit potential, which suggested that the HGG molecule was the main component that formed the lubricating film.

Improvement of Hydrophilic Stability of Diamond-Like Carbon Films by O<sub>2</sub>/CF<sub>4</sub> Plasma Post-Treatment

In this article, the results obtained from a study carried out on the plasma post-treatment of diamond-like carbon (DLC) films using an oxygen/tetrafluoromethane (O2/CF4) gas mixture is reported. The surface morphology and chemical bonding of the films before and after the plasma post-treatment were characterized using atomic force microscopy (AFM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The effect of adding CF4 to the O2 plasma on the wettability of the films was also examined using contact angle measurements. The results indicate that the surface roughness increased with the addition of CF4 to the O2 plasma, whereas oxygen-and fluorinated-based functional groups were generated on the surface of the DLC films submitted to O2/CF4 plasma post-treatment. The surface energy also decreased with increasing CF4 fraction, causing the surface of the films to be hydrophobic. Furthermore, the films containing 20% CF4 exhibited higher hydrophilic stability than the others. Thus, the addition of a small amount of CF4 to O2 plasma can be considered beneficial in improving the hydrophilic stability of surface of DLC films.

Atomic Degradation and Wear of Thin Carbon Films Under High-Speed Sliding Contact Using Molecular Dynamics Simulation

The thermomechanical contact behavior and the resulting change in atomic structure of diamond-like carbon (DLC) film were investigated through molecular dynamics simulation. Under the high-speed sliding contact between a diamond asperity and an amorphous DLC film, the atomic stress, temperature rise, and atom coordination number were measured with the elapsed contact time. It was observed that the increase in atomic stress caused higher kinetic energy on the carbon atoms, which accordingly led to the increase in the DLC film temperature. Examining the change in atom coordination number for the carbon atoms in the DLC film, it could be found that the number of sp 2 bonds (i.e., three-fold structure) increased with the contact time, which supported the graphitization process on the DLC film. During the sliding contact, some of the carbon atoms were debonded from the diamond asperity, which were rebonded (or transferred) onto the DLC film surface right after. From the analysis of atomic structural change, it could be concluded that this rebonding process was relying on covalent bonding rather than van der Waals interaction.

Friction at single-asperity contacts between hydrogen-free diamond-like carbon thin film surfaces

This work investigates the friction and adhesive forces at the single-asperity contact between hydrogen-free diamond-like carbon (DLC) coated surfaces in humid air and in argon. High power impulse magnetron sputtering deposition has been used to produce hydrogen-free DLC thin films on commercial silicon AFM tips and silicon wafers. The structure and surface morphology of the deposited DLC films has been investigated by X-ray photoelectron spectroscopy and tapping AFM, investigations that showed very smooth DLC films with about 29% of sp3 C−C bonds. The as-deposited hydrogen-free DLC thin films were hydrophilic (water contact angle about 65°) due to incorporation of a small amount of oxygen (about 9% of C=O bonds) at the film surfaces. The friction force measurements show that at low normal loading force the contact friction is much lower in the humid air than in the argon, while at large values of the loading force the contact friction does not depend on the measurement medium. A qualitative friction model based on the concept of dry and wet friction regimes, when the layer of water adsorbed on DLC film surfaces plays the role of lubricator, is proposed to explain these findings.

Achieving superlubricity in DLC films by controlling bulk, surface, and tribochemistry

Abstract Superlubricity refers to a sliding regime in which contacting surfaces move over one another without generating much adhesion or friction [1]. From a practical application point of view, this will be the most ideal tribological situation for many moving mechanical systems mainly because friction consumes large amounts of energy and causes greenhouse gas emissions [2]. Superlubric sliding can also improve performance and durability of these systems. In this paper, we attempt to provide an overview of how controlled or targeted bulk, surface, or tribochemistry can lead to superlubricity in diamond-like carbon (DLC) films. Specifically, we show that how providing hydrogen into bulk and near surface regions as well as to sliding contact interfaces of DLC films can lead to super-low friction and wear. Incorporation of hydrogen into bulk DLC or near surface regions can be done during deposition or through hydrogen plasma treatment after the deposition. Hydrogen can also be fed into the sliding contact interfaces of DLCs during tribological testing to reduce friction. Due to favorable tribochemical interactions, these interfaces become very rich in hydrogen and thus provide super-low friction after a brief run-in period. Regardless of the method used, when sliding surfaces of DLC films are enriched in hydrogen, they then provide some of the lowest friction coefficients (i.e., down to 0.001). Time-of-flight secondary ion mass spectrometer (TOF-SIMS) is used to gather evidence on the extent and nature of tribochemical interactions with hydrogen. Based on the tribological and surface analytical findings, we provide a mechanistic model for the critical role of hydrogen on superlubricity of DLC films.

A computational chemistry approach for friction reduction of automotive engines

To improve the fuel efficiency of automobile internal combustion engines, the friction reduction of each engine moving part is important. Recently, carbon films have been attracting much interest as surface-coating materials due to its excellent properties such as low friction and good wear resistance. In this study, the low-friction mechanisms of carbon films were analyzed using molecular dynamics simulations and density functional theory calculations. Molecular dynamics simulation results showed that the termination of OH groups on the surface of the diamond substantially reduced the friction coefficient from 0.07 to 0.01. This reduction was achieved because termination of OH groups weakened the covalent interaction between Fe and C atoms, which was indicated by density functional theory calculations. Additionally, based on the concept of terminating the OH groups on the surface of diamond-like carbon films, we carried out the reciprocating friction experiment between hydrogen-free diamond-like carbon surface and glycerin, which contains large number of OH groups. The friction coefficient of the glycerin was 0.028, much lower than that of the base oil, which was 0.075. The experiments confirmed that OH groups on the surface of hydrogen-free diamond-like carbon films greatly improved the friction properties of its films.

Frictional properties of diamond-like carbon coated tool in dry intermittent machining of aluminum alloy 5052

Abstract In this study, an orthogonal intermittent machining test for aluminum alloy 5052 was conducted under dry conditions. By using cutting forces that were measured during the test, the frictional properties of a tool rake face were evaluated during intermittent machining for two types of diamond-like carbon (DLC)-coated tools and an uncoated carbide tool. DLC films used in the test were composed of tetrahedral amorphous carbon (ta-C) deposited by a filtered arc deposition process and hydrogenated amorphous carbon (a-C:H) deposited by a plasma-enhanced chemical vapor deposition process. The test results showed that the initial friction coefficients were approximately 0.8 for all tools. However, with increasing machining time, the friction coefficient of only the ta-C-coated tool decreased remarkably to a lower value of 0.3, whereas those of the a-C:H-coated tool and the uncoated carbide tool remained high. An electron probe micro analyzer (EPMA) analysis revealed an area where no aluminum adhered on the ta-C-coated tool rake face after intermittent machining. This area provided low frictional properties during intermittent machining. An X-ray photoelectron spectroscopy (XPS) analysis showed that the carbon bonding of the DLC film surface in this area had changed from the state before machining.