A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10⁻⁴ Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm³. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.     

Flexible diamond-like carbon film coated on rubber

Dynamic rubber seals are major sources of friction of lubrication systems and bearings, which may take up to 70% of the total friction. The solution we present is to coat rubbers with diamond-like carbon (DLC) thin films by which the coefficient of friction is reduced to less than one tenth. Coating rubber is very challenging because the film must be flexible and strongly adhered to the surface of rubber substrate. Our novel approach is depositing flexible DLC films on rubbers via self-segmentation. By making use of the substantial thermal mismatch between DLC film and rubber substrates a dense crack network forms in DLC films and contributes to flexibility. The size of film micro-segments can be tuned by varying the bias voltage of pulsed-DC plasma CVD, which governs the amplitude of the substrate temperature variation during deposition. The formation mechanism of crack network and its effect on the flexibility and friction of DLC film coated rubbers are scrutinized. This paper provides generic design rules for the deposition of flexible and ultra-low friction DLC films on rubber seals.     

Characterization of hydrogen-free diamond-like carbon film deposited on cyclic olefin copolymer

In this study, the feasibility of the diamond-like carbon (DLC) film as a viable component for cyclic olefin copolymer (COC) substrate overcoat was assessed. Featured by its advanced physical and chemical properties such as high hardness, chemical stability, and wide band-gap optical transparency, the hydrogen-free DLC exhibits promising characteristics as the overcoat for flexible substrates or other TFT components. Ultra smooth, DLC thin films were synthesized by using a filter arc deposition (FAD) system and a cathodic arc evaporation (CAE) system. Raman spectroscopy, ESCA, Nano-Indentation, and electron microscopy were used to characterize the electronic, morphological, and microstructure properties of the DLC coatings. Results indicate that the device-quality DLC needs to be synthesized at lower substrate bias potential to retain high sp³/sp² ratio. The bending tests demonstrated a 30-fold improvement of the DLC-protected COC over that of the unprotected COC. Water vapor permeability tests demonstrated a 25-fold improvement of the DLC-protected COC over that of unprotected COC.     

Femtosecond-laser-induced nanostructure formation and surface modification of diamond-like carbon film

This paper reports the pump and probe experiment for in situ reflectivity measurements in the femtosecond laser ablation that brings about nanoscale modification of diamond-like carbon (DLC) film. The characteristic reflectivity changes observed demonstrate that the formation of periodic nanostructure is preceded by a change in bonding structure of DLC in the ablation at low fluences. We have observed a coherent nonlinear wave-mixing signal that can resolve the ultrafast interaction processes for the nanoscale modification on the film surface. Based on the results obtained, a model of the interaction process is proposed.     

A diamond-like carbon film as a self-alignment layer for LCDs

Diamond-like carbon (DLC) films without H deposited with a DC magnetron in-line sputtering system have shown sufficient self-alignment properties towards liquid crystals (LC). The DLC film was successfully used as an alignment layer for LC without any alignment processes such as rubbing or atomic beam bombardment or UV irradiation. From the observations of the test cells, the LC director was aligning parallel to the substrate movement direction of the in-line sputtering system. The alignment property of the DLC films has been demonstrated by a contrast ratio value of close to 200. It appears that DLC film may have anisotropic structure that is interacting with LC to align.     

Effect of hydrogen on the UV Raman intensities of diamond-like carbon

UV Raman spectroscopy is a powerful technique for the investigation of diamond-like carbon (DLC) films because it can provide information on the density, mechanical and optical properties.Here we show a detailed analysis of the G and D peak Raman intensity of hydrogenated DLC (a-C:H) with hydrogen (H) content ranging from 25 to 50 at.%. We show that the G peak Raman intensity strongly increases with the H content. This has been attributed to a strong enhancement of the UV Raman cross-section with the H incorporation.     

Effect of oxygen plasma treatment on non-thrombogenicity of diamond-like carbon films

The non-thrombogenicity of oxygen-plasma-treated DLC films was investigated as surface coatings for medical devices. DLC films were deposited on polycarbonate substrates by a radio frequency plasma enhanced chemical vapor deposition method using acetylene gas. The deposited DLC films were then treated with plasma of oxygen gas at powers of 15 W, 50 W, and 200 W. Wettability was evaluated by water contact angle measurements and the changes in surface chemistry and roughness were examined by X-ray photoelectron spectroscopy and atomic force microscope analysis, respectively. Each oxygen-plasma-treated DLC film exhibited a hydrophilic nature with water contact angles of 11.1°, 17.7° and 36.8°. The non-thrombogenicity of the samples was evaluated through the incubation with platelet-rich plasma isolated from human whole blood. Non-thrombogenic properties dramatically improved for both 15 W- and 50 W-oxygen-plasma-treated DLC films. These results demonstrate that the oxygen plasma treatment at lower powers promotes the non-thrombogenicity of DLC films with highly hydrophilic surfaces.     

The influence of nitrogen on the dielectric constant and surface hardness in diamond-like carbon (DLC) films

In this work a carbon target was sputtered by a methane/argon/nitrogen plasma in order to produce nitrogenated diamond-like carbon films (a-C:H:N). As the N₂ content in the sputtering gas was increased, the deposition rate increased markedly. Rutherford backscattering spectrometry (RBS) was used to investigate the chemical composition of the films. This nitrogen incorporation modifies the chemical bonding structure of the films, as shown by the analysis of the Raman spectra, including the occurrence of two extra peaks at approximately 2200 and 690 cm⁻¹. Electrical properties were measured through capacitance–voltage (C–V) curves. The hardness of the films decreased with the N content as shown by measurements performed by indentation method. A correlation among the Raman studies, the N content in the films, the dielectric constant and the surface hardness is presented.     

Diagnosis of dielectric barrier discharge CH4 plasmas for diamond-like carbon film deposition

Dielectric barrier discharge (DBD) CH₄ plasmas during diamond-like carbon (DLC) film deposition have been characterized in-situ by means of optical emission spectrometry (OES), the Langmuir double probe method and molecular beam mass spectrometry (MBMS). With a 1.4 kHz, 30-kV peak voltage DBD power source, while the Pd-value (the product of CH₄ pressure P, and discharge gas spacing d) decreases from ∼14 to 4 torr mm, the measured electron temperature and the hydrogen atom excitation temperature of the CH₄ plasmas rise from ∼3.0 to 5.8 eV, and from ∼6.3×10³ to 7.8×10³ K, respectively. The higher electron temperature and H excitation temperature of the plasmas at smaller Pd, imply the generation of more energetic ions in the plasma sheath near the film surface, that is confirmed by the MBMS observations. The MBMS experiments also show that the major ions near the coating are CH₃⁺, CH₂⁺, CH⁺ and C⁺, which are mainly produced through the collisions between fast CH_x⁺ (x=1–4) and neutral CH₄ molecules in the plasma sheath region.     

Fabrication of fluorine-terminated diamond-like carbon thin film using a hyperthermal atomic fluorine beam

Surface modification of diamond-like carbon (DLC) film was performed using a hyperthermal atomic fluorine beam on the purpose of production of hydrophobic surface by maintaining the high hardness of DLC film. By the irradiation of atomic fluorine beam of a 1.0 × 10²⁰ atoms/cm², the contact angle of a water drop against the DLC surface increased from 73° to 111°. The formation of CF₃, CF₂ and CF bonding on the modified DLC surface was confirmed from the measurements of X-ray photoelectron spectra and near-edge X-ray absorption fine structure spectra. Irradiation of hyperthermal atomic fluorine beam was concluded to produce insulator fluorine-terminated DLC film, which has high F content on the surface, by the taking of the use of neutral atomic beam as a fluorine source.     

Macro-scale superlow friction enabled when MoS2 flakes lubricate hydrogenated diamond-like carbon film

The achievement of superlow friction in moving parts in air can significantly reduce energy consumption. Hydrogenated diamond-like carbon, the most promising superlubric materials which can be applied in mechanical system, was investigated extensively in the past decades. Nevertheless, it is still challenging for hydrogenated diamond-like carbon to achieve superlow friction in moist air. Moreover, some novel and simple strategies to establish superlow friction are desired to be developed for the film in open air. In this paper, a composite structure was simply obtained by depositing MoS₂ flakes on H-DLC film by means of drop-casting process. The results showed that MoS₂ flakes could effectively suppress the energy dissipation and reduce the friction during the sliding process. Macro-scale superlow friction could be achieved with a coefficient of friction as low as 0.005 in air with a relative humidity of 24 ± 2%. The results indicated that with the introduction of MoS₂ flakes, the carbon transfer film/hydrogenated diamond-like carbon contact was evolved into a self-organized and highly ordered MoS₂ transfer film/hydrogenated diamond-like carbon heterogeneous contact. The heterostructure leaded to incommensurate contact between the frictional interfaces, resulting in reducing the friction in order of magnitude and establishing superlow friction during the rubbing period.     

Effect of gold oxide incorporation on electrochemical corrosion resistance of diamond-like carbon

Gold oxide nanoparticles were incorporated into diamond-like carbon (DLC) films in order to improve protection of AISI-1020 from electrochemical corrosion. The AuO_x:DLC films were prepared by plasma enhanced chemical vapor deposition and were subsequently characterized by scanning electron microscopy, Raman spectroscopy and electrochemistry measurements. The electrochemical corrosion performance of the AuO_x:DLC coating was contrasted to AISI-1020 and DLC without AuO_x coating. The electrochemical techniques that were utilized for this investigation were potentiodynamic and electrochemistry impedance spectroscopy. The electrochemical analysis indicated that AuO_x:DLC films presented superior corrosion resistance as compared to DLC. This resulted in 99.8% and 96.8% protection efficiency respectively, when compared to AuO_x:DLC and DLC coatings.     

类金刚石膜的制备及应用

类金刚石膜(DLC)由于其良好的特性被广泛应用于各个领域,文章介绍了类金刚石膜的制备方法及特点,并说明了利用类金刚石膜耐磨损高硬度等特点,将类金刚石薄膜经过特殊的方法形成类金刚石纤维的过程,探讨了其在纤维砂轮中,代替Al2O3纤维作为磨料的应用.     

Lubrication performance of diamond-like carbon and fluorinated diamond-like carbon coatings for intravascular guidewires

Diamond-like carbon (DLC) and fluorinated DLC (F-DLC) films were deposited on SUS316L guidewires using radio frequency (RF) plasma enhanced chemical vapor deposition (CVD), and the lubrication performance of DLC- or F-DLC-coated guidewires was then evaluated under in vitro conditions using a novel friction simulator developed for this study. Scanning electron microscopy (SEM) demonstrated that DLC or F-DLC film completely coated the specimens (SUS316L guidewires) and that polishing scars were substantially reduced. In the torturous vessel model, DLC- or F-DLC-coated guidewires exhibited significantly improved lubrication performance (by approximately 30% over that of uncoated wires). DLC and F-DLC films are thus promising candidates for lubricious coating of intravascular guidewires.     

Effect of nitrogen incorporation into diamond-like carbon films by ECR-CVD

Diamond-like carbon (DLC) and nitrogenated DLC (a-C:N) films were prepared on Si and glass substrates using an electron cyclotron resonance-assisted microwave plasma chemical vapour deposition (ECR-MPCVD) system with radio frequency substrate bias. The hardness and optical bandgap of the resulting films were investigated and correlated to the elemental and phase composition. The a-C:N films, deposited under conditions identical to those for the DLC films except for the introduction of a nitrogen flow, contain nitrogen which partly substitutes for hydrogen and forms carbon–nitrogen triple bonds. These bonds obstruct the formation of carbon–carbon cross-linking, resulting in softer films. These changes can be interpreted with reference to various changes of active vibronic states determined by Raman spectroscopy.     

Humidity dependence on the friction and wear behavior of diamond-like carbon film in air and nitrogen environments

Diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapor deposition (PECVD) technique using CH₄ plus Ar as the feedstock. The friction and wear behaviors of the resulting film sliding against Si₃N₄ balls were investigated on a ball-on-disk test rig in air and nitrogen environments at a relative humidity from 5% to 100%. The worn surface morphologies of the DLC film and the Si₃N₄ counterpart were observed on a scanning electron microscope (SEM), while the chemical states of some typical elements thereon were investigated by means of X-ray photoelectron spectroscopy (XPS). It was found that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity in air. It showed linearly increased friction coefficient with increasing relative humidity in nitrogen, in this case the wear rate sharply decreased and reached the minimum at a relative humidity of 40%, which was followed by an increase with further increase of the relative humidity. The interruption of the transferred carbon-rich layers on the Si₃N₄ balls, and the friction-induced oxidation of the films in higher relative humidity were proposed to be the main reasons for the increases of the friction coefficient and wear rate. Moreover, the oxidation and hydrolysis of the Si₃N₄ ball in higher relative humidity, leading to the formation of a tribochemical film that mainly consists of silica gel on the wearing surface, were also thought to have effects on the friction and wear behaviors of the DLC films.     

Effect of various adsorbates on electronic states of the thin diamond-like carbon films

The influence of the adsorbed impurity molecules onto energy spectrum of electronic states of the DLC films deposited on SiO₂/Si substrates by direct ion beam from hydrocarbon IC plasma was studied by charge-based deep level transient spectroscopy (Q-DLTS). The strong sensitivity of Q-DLTS spectra to the presence of the vapor water and alcohol at room temperature was found. The principle is that adsorption of any molecules on the surface of the DLC film results in a change of energy spectrum of the electronic states (or trapping centers) at the DLC film surface. For example, a new peak appeared in Q-DLTS spectra in presence of the vapor water and electron state density increased in several orders. Moreover, the effect of different adsorbed molecules (species) on the surface electron states was different and independent, so that different molecules can be detected separately. It was shown to differentiate a few thousand molecules of virtually any impurity adsorbed by DLC film's surface. Such strong surface phenomena of the thin DLC films may be exploited in novel sensitive and selective chemical sensor devices.     

Bacterial adhesion on silicon-doped diamond-like carbon films

In this paper the surface properties of silicon-doped diamond-like carbon films with various Si contents on 316 stainless steel substrate by a magnetron sputtering technique were investigated. X-ray photoelectron spectroscopy was applied to determine the surface chemical composition of the films. Atomic force microscopy was used for the determination of surface roughness and topography. The sp² contents in the films were determined with Auger electron spectroscopy, which were 67.1%, 34.2% and 25.0% for silicon contents 1%, 2% and 3.8%. The sp³/sp² ratio increases with increasing the silicon contents in the films. Contact angles of three test liquids on the films were obtained with a Dataphysics OCA-20 contact angle analyzer. Surface free energies of the films and their dispersive and polar components were calculated using van Oss acid–base approach. Staphylococcus aureus was used for bacterial adhesion test. The experimental results showed that bacterial adhesion decreased with increasing the silicon content or with increasing sp³/sp² ratio in the films.     

Effect of temperature on sulfur-doped diamond-like carbon films deposited by pulsed laser ablation

In this study, S-DLC films were deposited using pulsed laser ablation of a novel sulfur-graphite (SG) mixture target using an ArF excimer laser (193 nm). The SG targets were made by mixing sulfur and graphite powders at different sulfur molar percentages from 0% to 25%. The S-DLC films were deposited at room temperature, 150 °C and 250 °C. The optical and electronic properties of the doped films were studied. Laser Raman spectroscopy indicated increased graphitic behavior with temperature but decreased with higher sulfur content. Spectroscopic ellipsometry analyses found that the optical band-gap energy, extinction coefficient and reflective index, clearly depended on deposition temperature and sulfur content. Hall Effect measurements indicated n-type carrier with concentration in the range of 1 × 10¹⁴ to 2 × 10¹⁷ cm^− 3, strongly depended upon the deposition temperature and amount of sulfur.     

Substrate surface temperature as a decisive parameter for diamond-like carbon film adhesion to polyethylene substrates

Protective diamond-like carbon coatings (DLCs) deposited on polymer substrates represent a promising means for modification of the substrate surface. Application of strong DLCs on these substrates is rendered difficult due to a large difference in their thermal expansion coefficients, and also to the low heat resistance and thermal conductivity of most polymers. Vacuum pulsed sputtering of graphite is among the methods which show greatest promise for creation of DLCs on such substrates. In this method it is possible to adjust, within broad limits, the mean sputtering rate, and consequently control the thermal load on the substrate during sputtering.We measured the temperature distribution in bulky high-density polyethylene (PE) substrates depending on the pulse repetition rate and the number of pulses in the carbon source. The data were used to determine optimal conditions for deposition of DLCs on PE. DLCs almost 0.1 μm thick were deposited in two stages. In the first stage, when the best adhesion was provided, the source power was a maximum. In the second stage the source power was an order of magnitude lower.Adhesion of the DLCs to the substrates was evaluated using the standard adhesive tape test and by resistance to thermal cycling in the intervals from 77 to 287 K and 77 to 373 K. Adhesion of the DLCs to PE was shown to be strongly dependent on the substrate temperature at the start of sputtering. The best result was achieved when the substrate temperature was nearly equal to, but did not exceed, the PE melting point.