Increasing Substrate Bias Voltage Research Articles

Reactive remote plasma sputtering of TiOx thin films and controlled growth of textured single-phase rutile using rf substrate biasing

Titanium oxide (TiOx) thin films were deposited by remote plasma sputtering (RPS) with the use of rf substrate bias onto unheated and water-cooled glass, Si, and Kapton substrates. The rf remote plasma power was kept constant (2.0 kW) and the properties of the films were studied as a function of deposition rate and substrate bias voltage. Four different reactive processes at four different deposition rates were developed under zero bias conditions by altering the target bias voltage and the flow of oxygen to give highly transparent TiOx films. These processes were studied with varying substrate bias voltage and the film structural, optical, and surface properties were investigated by GI-XRD, SEM, transmission, and sessile drop measurements. The changes in film structure and properties observed were related to the plasma conditions of the RPS system, investigated by dc electrical probe and OES measurements, and compared with other observations for films deposited under energetic conditions in the literature. All films deposited under zero bias conditions exhibited amorphous structures in GI-XRD and SEM images. Sufficient application of substrate bias was seen to promote columnar growth in cross-sectional SEM images and to crystallise phase pure rutile with no detection of the anatase phase in GI-XRD. Rutile bearing films were noted for their change in optical properties. Further increase of the substrate bias voltage caused a change in the texture of the rutile films from a low-energy [110] preferred orientation to a high-energy [101] and [002] preferred orientation. Contact angles of water with deposited films were found to increase with increasing substrate bias voltage and decreasing deposition rate. Film stress was also found to be influenced mainly by the substrate bias voltage process parameter.

Influence of substrate bias voltage on microstructure and mechanical characteristics of TiAlSiN coating deposited by High Power Impulse Magnetron Sputtering (HiPIMS)

Substrate bias voltage has a presumably predominant and significant influence on the microstructural morphology and mechanical properties of HiPIMS deposited coatings. In the present investigation, it has been investigated in depth for a quaternary coating, TiAlSiN coating, which was deposited on the cemented carbide (WC-10 wt% Co) substrates. In this HiPIMS process, a pair of TiAl60 and a pair of TiSi34 targets were used. Four different substrate biases were set, i.e., −60, −90, −120, and −150 V to explore the difference in the coating characteristics. In every case, the substrate bias was also applied in pulsed mode but with an offset of 40 μs to the cathode pulse. Both cathode current and bias current were observed to increase from 87 to 98 A and 19 to 23 A, respectively, with increase of substrate bias voltage. As the bias voltage increased, the surface morphology became finer, and the cross-section morphology turned to be highly denser. The minimum and maximum grain sizes were estimated to be 7.23 nm and 9.90 nm at a substrate bias of −60 V and −150 V, respectively. Variation of Ti content (at.%) was noticed in the range of 28.35 to 30.71 with the increase of bias voltage. The maximum hardness of the coating was recorded to be 42.95 GPa at the bias voltage of −150 V. The adhesion level has been classified under HF1 in all deposition cases, as investigated by Rockwell indentation method, whereas the scratch test results suggest that a load range between 154 and 161 N is required for the complete delamination of the coating. Spallation and edge-chipping were the primary failure mechanisms during the scratching of the TiAlSiN coating.

Graphitic regulation of C/Cr composite film for 304 stainless steels bipolar plates

This work aims to deposit conductive and corrosion-resistant protective coatings for bipolar plates in proton exchange membrane fuel cells. The films' graphitization degree is regulated to obtain excellent conductivity and corrosion-resistance. A series of Cr-doped graphite-like carbon films with different substrate bias voltages and deposition times (600 V 2 h, 900 V, 2 h, 900 V, 3 h; and 1200 V, 2 h) were prepared on 304 stainless steels by plasma enhanced chemical vapour deposition method combined with magnetron sputtering technique. The results showed that an increase of substrate bias voltage increased substrate current density. The substrate current density was the highest when the substrate bias voltage was 1200 V at 400 °C. Subsequently high substrate bias voltage caused ID/IG to increase, indicating that the increase of energy contributes to graphitisation of the films. The particle size of the films decreased with increasing bias voltage, and the cross section showed that the prepared films were homogeneous and distinctive. The interface contact resistance (ICR) of the films at 1.4 MPa decreased with an increase of substrate bias voltage, showing that deeper graphitisation improves the conductivity of the films. The coated 304 stainless steels showed a considerable decrease in self-corrosion current density in comparison to the 304 stainless steel substrate. According to the VDI-3198 indentation test, the adhesion of the films and substrate belongs to the HF1 level. After long-term service, chromium oxides, iron oxides, and defects were formed on the surface, leading to an increase in ICR. The study revealed that the optimum technical parameters were 1200 V and 2 h.

Dependence of the ZrO2 growth on the crystal orientation: growth simulations and magnetron sputtering

The growth of crystalline ZrO2 is studied by a combined approach of atom-by-atom growth simulations, high-power impulse magnetron sputtering and conventional pulsedmagnetron sputtering. We focus on the energy of arriving atoms of various elements, and investigate how does it affect the growth of ZrO2 crystals of various orientations. Theresults are correlated with quantities such as surface energy and horizontal periodicity of individual orientations. Simulations show that the growth of orientations characterized by high surface energy and short horizontal period, (001)in the first place, requires higher energy delivered by arriving atoms, and that the energy is more effectively delivered by heavy Zr than by light O. Experiments confirm that the relative preference of such orientations increases with increasing substrate bias voltage, increasing concentration of ions which are subsequently accelerated by the bias voltage, and synchronization of the pulsed bias voltage with the arrival of heavy Zr+ ions. The results are important for the preparation of crystalline ZrO2 of various orientations for various technological applications, and the fundamental reasons behind them make them relevant also for the growth of other crystalline materials.

Effects of Substrate Bias Voltage on Structure of Diamond-Like Carbon Films on AISI 316L Stainless Steel: A Molecular Dynamics Simulation Study.

With the recent significant advances in micro- and nanoscale fabrication techniques, deposition of diamond-like carbon films on stainless steel substrates has been experimentally achieved. However, the underlying mechanism for the formation of film microstructures has remained elusive. In this study, the growth processes of diamond-like carbon films on AISI 316L substrate are studied via the molecular dynamics method. Effects of substrate bias voltage on the structure properties and sp3 hybridization ratio are investigated. A diamond-like carbon film with a compact structure and smooth surface is obtained at 120 V bias voltage. Looser structures with high surface roughness are observed in films deposited under bias voltages of 0 V or 300 V. In addition, sp3 fraction increases with increasing substrate bias voltage from 0 V to 120 V, while an opposite trend is obtained when the bias voltage is further increased from 120 V to 300 V. The highest magnitude of sp3 fraction was about 48.5% at 120 V bias voltage. The dependence of sp3 fraction in carbon films on the substrate bias voltage achieves a high consistency within the experiment results. The mechanism for the dependence of diamond-like carbon structures on the substrate bias voltage is discussed as well.

Robust low friction performance of graphene sheets embedded carbon films coated orthodontic stainless steel archwires

Reducing the friction force between the commercial archwire and bracket during the orthodontic treatment in general dental practice has attracted worldwide interest. An investigation on the friction and wear behaviors of the uncoated and carbon film coated stainless steel archwires running against stainless steel brackets was systematically conducted. The carbon films were prepared at substrate bias voltages from +5 to +50 V using an electron cyclotron resonance plasma sputtering system. With increasing substrate bias voltage, local microstructures of the carbon films evolved from amorphous carbon to graphene nanocrystallites. Both static and stable friction coefficients of the archwire-bracket contacts sliding in dry and wet (artificial saliva) conditions decreased with the deposition of carbon films on the archwires. Low friction coefficient of 0.12 was achieved in artificial saliva environment for the graphene sheets embedded carbon (GSEC) film coated archwire. Deterioration of the friction behavior of the GSEC film coated archwire occurred after immersion of the archwire in artificial saliva solution for different periods before friction test. However, moderate friction coefficient of less than 0.30 sustained after 30 days immersion periods. The low friction mechanism is clarified to be the formation of salivary adsorbed layer and graphene sheets containing tribofilm on the contact interfaces. The robust low friction and low wear performances of the GSEC film coated archwires make them good candidates for clinical orthodontic treatment applications.

High entropy alloy FeMnNiCoCr coatings: Enhanced hardness and damage-tolerance through a dual-phase structure and nanotwins

Three FeMnNiCoCr high entropy alloy (HEA) coatings were deposited onto M2 steel substrates using a direct current (DC) magnetron sputtering system under a range of substrate bias voltages (−20 V, −60 V and −120 V). The microstructure transformed from a fine elongated structure to coarse V-shaped columnar grains with increasing substrate bias voltage. A high density of nanotwins, together with the presence of a partial fcc-to-hcp transformation, was observed in the coating deposited at −120 V. This was attributed to the introduction of stacking faults whose presence was promoted by preferential re-sputtering effects during the deposition process. A high hardness value of ~9.1 GPa, accompanied by exceptional damage-tolerance, was achieved in the coating deposited at −120 V. Here, the formation of nanotwins and the dual-phase structure was found to contribute to this remarkable combination of hardness and resistance to plastic deformation.

On the adhesion and wear resistance of DLC films deposited on nitrile butadiene rubber: A Ti-C interlayer

To promote the adhesion strength between diamond-like carbon (DLC) films and nitrile butadiene rubber (NBR) substrates, titanium-doped carbon (Ti-C) films prepared by dual-target magnetron sputtering under varied substrate bias voltages were used as an interlayer on the rough NBR. The surface topography and structure of Ti-C films were investigated by atomic force microscopy (AFM) and Raman spectra. Raman analysis indicates that the increase of substrate bias voltage leads to an increase of the number or the size of sp2 clusters in the Ti-C interlayer. The adhesion strength and tribological properties of DLC films coated on NBR substrate were scrutinized by a scratch tester and a ball-on-disk tribometer, respectively. It was found that DLC film with a Ti-C interlayer at a certain bias voltage exhibited superior wear resistance with a low coefficient of friction (CoF) during the sliding of 6000 laps. No clear damages in the coatings were observed from the wear tracks. Besides, the scratch test also revealed a reliable adhesion when the interlayer was prepared at −150 V, as confirmed by a scratch crack width of ~50 μm as compared to that of the pure DLC film increasing to ~ 120 μm. Therefore, a Ti-C interlayer could significantly enhance the adhesion and wear resistance of DLC thin films deposited on NBR.

Substrate Bias Voltage Tailoring the Interfacial Chemistry of a-SiC x:H: A Surprising Improvement in Adhesion of a-C:H Thin Films Deposited on Ferrous Alloys Controlled by Oxygen.

Hydrogenated amorphous carbon thin films (a-C:H) have attracted much attention because of their surprising properties, including ultralow friction coefficients in specific conditions. Adhesion of a-C:H films on ferrous alloys is poor due to chemical and physical aspects, avoiding a widespread application of such a film. One possibility to overcome this drawback is depositing an interlayer-an intermediate thin film-between the carbon-based coating and the substrate to improve chemical interaction and adhesion. Based on this, interlayers play a key role on a-C:H thin-film adhesion through a better chemical network structure at the outermost layer of the a-SiC x:H interlayer, i.e., the a-C:H/a-SiC x:H interface. However, despite the latest important advances on the subject, the coating adhesion continues being a cumbersome problem since it depends on multifactorial causes. Thus, the purpose of this paper is to report a standard protocol leading to surprising good results based on the control of the interfacial chemical bonding by properly biasing the substrate (between 500 and 800 V) during the a-SiC x:H interlayer deposition at an appropriate low temperature, by using hexamethyldisiloxane as precursor. The interlayers and the outermost interfaces were analyzed by a comprehensive set of techniques, including X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, and Fourier transform infrared spectroscopy. Nanoscratch tests, complemented by scanning electron microscopy and energy-dispersive X-ray spectroscopy, were used to evaluate the critical load for delamination to certify and quantify the adhesion improvement. This study was important to identify the chemical local bonding of the elements at the interface and its local environment, including the in-depth chemical composition profile of the coating. An important effect is that the oxygen content decreases on increasing substrate bias voltage, improving the adhesion of the film. This is due to the fact that energetic ion hitting the growing interlayer breaks Si-O and C-O bonds, augmenting the content of Si-C and C-C bonds at the outermost interface of the a-SiC x:H interlayer and enhancing the a-C:H coating adhesion. Moreover, the combination of high bias voltage (800 V) and low temperature (150 °C) during the a-SiC x:H interlayer deposition allows good adhesion of a-C:H thin films due to sputtering of light elements like oxygen. Therefore, an appropriated bias and temperature combination can open new pathways in a-C:H thin-film deposition at low temperatures. These results are particularly interesting for temperature-sensible metal alloys, where well-adhered a-C:H thin films are mandatory for tribological applications.

Tribological properties of boron carbonitride coatings sliding against different wood (acerbic, beech, and lauan) balls

Boron carbonitride (BCN) coatings were prepared using radio frequency (RF) magnetron sputtering via adjusting substrate bias voltage from −50 V to −200 V. The mechanical and tribological properties of the coatings were investigated. The coexistence of B–N, B–C, and N–C bonds was detected in coatings according to X-ray photoelectron spectroscopy analysis, indicating the formation of ternary BCN hybridization. The hardness of BCN coatings increased from 14.4 GPa to 24.3 GPa with an increase of substrate bias voltage, while their adhesion strength on substrate decreased. The friction behavior of BCN coatings sliding against different wood (acerbic, beech, and lauan) balls was examined using a ball-on-disk tribometer. The average friction coefficient fluctuated in a range of 0.74–1.02. The wear track of BCN coating sliding against hardwood (acerbic) presented obvious scratches, which were not noted as sliding against other softwood balls in comparison.

Effects of substrate bias and temperature on the structure and dielectric properties of TixZr1−xNy ternary nitride thin films

Transition metal nitrides have become a kind of promising alternative plasmonic materials. TixZr1−xNy ternary nitride films were prepared by magnetron co-sputtering method, and the effects of bias voltage and temperature on the structure and dielectric properties of the films were investigated. The experimental results show that all the films are fcc-structured, and high substrate bias and temperature can significantly improve the N and Ti content. Increasing substrate bias voltage or temperature can reduce the crossover frequency ωc at which the films transit from dielectric to metallic phase. Also, a high bias can greatly influence the energy loss of the films. Furthermore, the plasmonic quality factor can be effectively tailored by bias and temperature. Increasing bias can decrease the quality factor while high temperature (600 °C) can enhance the quality factor significantly. The study demonstrates that the TixZr1−xNy films, as one kind of alternative plamonic materials, have considerable performances, and their dielectric and plasmonic properties can be modulated by varying the bias voltage and temperature in a wide range.

Microstructure and residual stress of TiN films deposited at low temperature by arc ion plating

Abstract The TiN films were deposited on 316L stainless steel substrates at low temperature by arc ion plating. The influences of substrate bias voltage and temperature on microstructure, residual stress and mechanical properties of the films were investigated by EDS, SEM, XRD and nanoindenter tester, respectively. The results showed that the TiN films were highly oriented in (111) orientation with a face-centered cubic structure. With the increase of substrate bias voltage and temperature, the diffraction peak intensity increased sharply with simultaneous peak narrowing, and the small grain sizes increased from 6.2 to 13.8 nm. As the substrate temperature increased from 10 to 300 °C, the residual compressive stress decreased sharply from 10.2 to 7.7 GPa, which caused the hardness to decrease from 33.1 to 30.6 GPa, while the adhesion strength increased sharply from 9.6 to 21 N.

Hydrogen Permeation, and Mechanical and Tribological Behavior, of CrNx Coatings Deposited at Various Bias Voltages on IN718 by Direct Current Reactive Sputtering

In the current work, the microstructure, hydrogen permeability, and properties of chromium nitride (CrNx) thin films deposited on the Inconel 718 superalloy using direct current reactive sputtering are investigated. The influence of the substrate bias voltage on the crystal structure, mechanical, and tribological properties before and after hydrogen exposure was studied. It was found that increasing the substrate bias voltage leads to densification of the coating. X-ray diffraction (XRD) results reveal a change from mixed fcc-CrN + hcp-Cr2N to the approximately stoichiometric hcp-Cr2N phase with increasing substrate bias confirmed by wavelength-dispersive X-ray spectroscopy (WDS). The texture coefficients of (113), (110), and (111) planes vary significantly with increasing substrate bias voltage. The hydrogen permeability was measured by gas-phase hydrogenation. The CrN coating deposited at 60 V with mixed c-CrN and (113) textured hcp-Cr2N phases exhibits the lowest hydrogen absorption at 873 K. It is suggested that the crystal orientation is only one parameter influencing the permeation resistance of the CrNx coating together with the film structure, the presence of mixing phases, and the packing density of the structure. After hydrogenation, the hardness increased for all coatings, which could be related to the formation of a Cr2O3 oxide film on the surface, as well as the defect formation after hydrogen loading. Tribological tests reveal that hydrogenation leads to a decrease of the friction coefficient by up to 40%. The lowest value of 0.25 ± 0.02 was reached for the CrNx coating deposited at 60 V after hydrogenation.

Variation of local chemical compositions of (Ti, Al)N films on inner wall of small hole deposited by high-power impulse magnetron sputtering

The local chemical composition of (Ti, Al)N thin films grown on the inner-walls of holes by high-power impulse magnetron sputtering (HiPIMS) was analyzed in detail to investigate the transport behavior of ionized and neutral species into small holes. HiPIMS deposition was performed at the floating substrate potential and at −50 and −150V with a fixed pulse length of 100μs and a frequency of 333Hz. The deposition rate on the inner-walls decreased with increasing substrate bias at all hole depth. From the obtained local chemical compositions of (Ti, Al)N films on inner-walls, it was found that the content of the metal elements, Ti and Al, decreases with increasing depth. In addition, the rate of decrease of the Ti content with increasing depth on the inner-walls is greater than that of the Al content. This tendency becomes increasingly significant with increasing substrate bias voltage. These bias dependencies are discussed by considering the degree of thermalization for ionized species from the viewpoint of the difference in the mass number between Ti, Al, and the gas species.

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CNx) coatings are investigated. CNx coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400V 200W, −400V 100W, −800V 200W, and −800V 100W. The deposition rate, N/C atomic ratio, and hardness of CNx coatings as well as friction coefficient of CNx coating sliding against AISI 52100 pin in N2 gas stream decrease, while the residual stress of CNx coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0GPa and lowest residual stress of 3.7GPa of CNx coatings are obtained at −400V 200W, whereas the lowest friction coefficient of 0.12 of CNx coatings is achieved at −800V 100W. Raman and XPS analysis suggest that sp3 carbon bonding decreases and sp2 carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CNx coatings is controlled by the directly sliding between CNx coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp3 carbon bonding in the CNx coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CNx coatings.

Improvement of Thermal Stability of ZrB2/Si3N4 Coatings as High-Temperature Solar Selective Absorbers

ZrB2 thin films were prepared by DC magnetron sputtering technique. The microstructure, thermal stability and optical properties of thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and spectrophotometer. The compactness of ZrB2 thin films was studied to improve the thermal stability by optimizing the deposition parameters. The compactness and thermal stability of the coatings were improved with the increase of substrate temperature. However, these properties of the coatings were enhanced firstly and then weakened with the increase of substrate bias voltage. The selectivity of sample deposited at high substrate temperature and suitable bias voltage degraded slightly after annealing at 500 °C/100 h in air. This provided a new way to improve the thermal stability of high-temperature solar selective absorber.

Effect of substrate biasing and temperature on AlN thin film deposited by cathodic arc ion

Aluminum nitride (AlN) films have been grown in pure N2 plasma using cathodic arc ion deposition process. The films were prepared at different substrate bias voltages and temperatures. The aim was to investigate their influence on the Al macro-particles, structural and optical properties of deposited films. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Scanning electron microscope (SEM) and Rutherford backscattering spectrometry (RBS) were employed to characterize AlN thin films. XRD patterns indicated the formation of polycrystalline (hexagonal) films with preferential orientation of (002), which is suppressed at higher substrate bias voltage. FTIR and Raman spectroscopic analysis were used to assess the nature of chemical bonding and vibrational phonon modes of AlN thin films respectively. FTIR spectra depicted a dominant peak around 850cm−1 corresponding to the longitudinal optical (LO) mode of vibration. A shift in this LO mode peak towards higher wavenumbers was observed with the increase of substrate bias voltage and temperature, showing the upsurge of nitrogen concentration in the deposited film. Raman spectra illustrated a peak at 650cm−1 corresponding to E2 (high) phonon mode depicting the c-axis oriented (perpendicular to substrate) AlN film. SEM analysis showed the AlN film deposited at higher substrate bias voltage contains fewer amounts of Al macro-particles.

Stress Induced in Al<sub>2</sub>O<sub>3</sub> Films as Deposited onto Al<sub>2</sub>O<sub>3</sub>TiC Substrate by RF Diode Sputtering

Al2O3 films were deposited onto Al2O3-TiC substrates by RF diode sputtering. The Al2O3 films were deposited at various substrate bias voltages from -80 to -180 V, sputtering powers from 4 to 8 kW and operating pressures from 20 to 30 mTorr. The stress induced in Al2O3 films was measured. The results show that the stress induced in all prepared Al2O3 films is tensile stress. The stress slightly increased with increasing substrate bias voltage whereas it increased linearly with increasing operating pressure. However, the stress was almost constant as the sputtering was increased from 5 to 8 kW and significantly decreased as the sputtering power was decreased below 5 kW.

Influence of substrate bias voltage on structural and optical properties of RF reactive magnetron sputtered WO3 thin films

In this investigation, tungsten oxide (WO3) thin films have been deposited on unheated glass substrates by RF magnetron sputtering of tungsten target at constant oxygen partial pressure of 6×10−2 Pa, sputtering power of 150 W and at different substrate bias voltages in the range from 0 to -150 V. The structural and optical properties of the films were investigated by using X-ray diffraction, Fourier transform infrared spectroscopy and UV-Vis-NIR spectrophotometers. The films formed up to substrate bias voltage of -50 V were found to be amorphous in nature, while those films formed at -100 V showed a weak (200) reflection indicates the presence of monoclinic phase of WO3 in amorphous matrix. The optical transmittance of the films was in the range 78 – 95 % in the wavelength range of 500 – 1200 nm. The absorption band edge was shifted towards higher wavelength side with increasing substrate bias voltage. The optical band gap of the films decrease from 2.81 to 2.69 eV with increase of substrate bias voltage from 0 to -150 V respectively. The refractive index of the films increased from 2.19 to 2.27 with increase of substrate bias voltage from 0 to -150 V respectively.

Optimising deposition parameters of W-DLC coatings for tool materials of high speed steel and cemented carbide

The paper presents the results of investigations on the selection of optimal deposition parameters for W-DLC coatings produced by pulsed reactive magnetron sputtering in order to obtain the coatings with high adhesion to the high speed steel (HSS) and cemented carbide (HM) substrates. To optimise the deposition parameters for W-DLC coatings Taguchi's method was used. An acetylene flow rate, the substrate bias voltage, the thickness of W-DLC coatings and the thickness of chromium sublayer were selected as deposition parameters and for each of them three levels of values were determined. Adhesion, wear resistance and hardness of coatings were chosen as the criteria for selecting the optimum deposition parameters. The test results showed that all the selected parameters have a significant effect on the adhesion of coatings. The thickness of W-DLC coatings has a very significant effect on the adhesion to HSS substrates and in a case of HM substrates the same effect has the thickness of a chromium sublayer. The wear resistance of coatings increases with an increasing acetylene flow rate and decreases with the increasing substrate bias voltage. High correlation was found between the H/E ratio of coatings and their wear resistance as well as toughness. The W-DLC coating showing the best properties (LC3 ≈ 90 N, kV = 3.8 × 10−7 mm3/Nm) was marked by the nanocomposite structure containing about 40% of nanocrystalline tungsten carbide phase and 60% of amorphous carbon matrix.