Stresses in diamond-like carbon films

Internal stresses have been measured in diamond-like carbon (DLC) films deposited by d.c. plasma assisted chemical vapor deposition from methane, acetylene, or cyclohexane, and in nitrogen containing DLC films deposited from acetylene, or cyclohexane and nitrogen. The total hydrogen content in the films and the fraction of bound hydrogen have been analyzed by forward recoil elastic scattering and Fourier transform infrared spectroscopy respectively. It was found that in pure DLC films the stresses increase with increasing fraction of unbound hydrogen. The highest compressive stresses were obtained in the films deposited from methane and the lowest stresses in films deposited from cyclohexane. In the nitrogen containing DLC films the stresses decrease with increasing nitrogen content in the films. Stresses as low as 0.22 GPa were obtained in the films deposited from cyclohexane and nitrogen at a ratio of 1/15 in the plasma.     

X-Ray reflectometry study of diamond-like carbon films obtained by plasma-assisted chemical vapor deposition

X-Ray reflectivity is used to determine the electron density profiles normal to the surface of diamond-like carbon (DLC) films prepared by plasma-enhanced chemical vapor deposition (PE-CVD). Average values of the scattering lengths obtained from the specular reflection data and elastic recoil detection analysis (ERDA) hydrogen measurements are used to calculate the average mass density of the films. The density is shown to be strongly dependent on the hydrogen content. This depends on the plasma parameters. Argon diluted methane plasma produces homogeneous DLC films but generally with a lower density than the films prepared from pure or He diluted plasmas. These later plasmas produce films with a high density contrast and higher densities.     

Effect of N doping on properties of diamond-like carbon thin films produced by RF capacitively coupled chemical vapor deposition from different precursors

In this paper, we report results concerning properties of diamond-like carbon (DLC) thin films obtained in different experimental conditions: various RF power values and different precursors (methane, acetone and toluene or in combination with nitrogen). The deposition rate of DLC thin films obtained from precursors with low ionizing energy and high number of carbon atoms in molecule as acetone and toluene was higher (142 nm/min for acetone and 607 nm/min for toluene as compared with 79 nm/min for methane at 400 W input power). The highest value of hardness was obtained from methane (18 GPa). In the case of acetone and toluene precursors, the hardness increased with input power to the highest values of 16.8 and 14.8 GPa. By utilizing nitrogen as doping element, the resistivity of DLC thin films obtained from methane and acetone decreased from values higher than 10⁷ Ω cm to lower values of 12.5×10³ Ω cm for 3.79% nitrogen atomic concentration in the case of films obtained from methane and 40×10³ Ω cm for 4.26% nitrogen atomic concentration in the case of films obtained from acetone.     

A study of hard diamond-like carbon films in mid-frequency dual-magnetron sputtering

A series of hydrogen-free diamond-like carbon (DLC) films were deposited by a mid-frequency dual-magnetron sputtering under basic conditions of Cr and C target power density between 6 and 18 W/cm², bias voltage in a range of − 100 V to − 200 V, and a pure argon atmosphere. Microstructure, microhardness, adhesion, friction and wear properties were investigated for the DLC films to be used as protective films on cutting tools and forming dies, etc. The DLC films exhibited some combined superior properties: high hardness of 30–46 GPa, good adhesion of critical load of 50–65 N, and friction coefficient about 0.1 in air condition. Properties of the magnetron-sputtered carbon films showed a strong dependence on flux and energy of ion bombardment during growth of the films.     

A method of determining the elastic properties of diamond-like carbon films

The elastic properties of diamond-like carbon (DLC) films were measured by a simple method using DLC bridges which are free from the mechanical constraints of the substrate. The DLC films were deposited on a Si wafer by radio frequency (RF) glow discharge at a deposition pressure of 1.33 Pa. Because of the high residual compressive stress of the film, the bridge exhibited a sinusoidal displacement on removing the substrate constraint. By measuring the amplitude with a known bridge length, we could determine the strain of the film which occurred by stress relaxation. Combined with independent stress measurement using the laser reflection method, this method allows the calculation of the biaxial elastic modulus, E/(1−ν), where E is the elastic modulus and ν is Poisson's ratio of the DLC film. The biaxial elastic modulus increased from 10 to 150 GPa with increasing negative bias voltage from 100 to 550 V. By comparing the biaxial elastic modulus with the plane–strain modulus, E/(1−ν²), measured by nano-indentation, we could further determine the elastic modulus and Poisson's ratio, independently. The elastic modulus, E, ranged from 16 to 133 GPa in this range of the negative bias voltage. However, large errors were incorporated in the calculation of Poisson's ratio due to the pile up of errors in the measurements of the elastic properties and the residual compressive stress.     

Mechanical and tribological properties of diamond-like carbon films prepared on steel by ECR-CVD process

Diamond-like carbon (DLC) films were prepared on AISI 440C steel substrates at room temperature by the electron cyclotron resonance chemical vapor deposition (ECR-CVD) process in C₂H₂/Ar plasma under different conditions. In order to prevent the inter-diffusion of carbon and improve the adhesion strength of DLC films, functionally gradient Ti/TiN/TiCN/TiC supporting underlayers were deposited on the steel substrates in advance. Using the designed interfacial transition layers, relatively thick DLC films (1–2 μm) were successfully prepared on the steel substrates without delamination. By optimizing the deposition parameters, DLC films with hardness up to 28 GPa and friction coefficients lower than 0.15 against the 100Cr6 steel ball were obtained. In addition, the specific wear rates of the films were found to be extremely low (∼10⁻¹⁷ m³/Nm). The friction-induced graphitization mechanism of DLC was confirmed by micro-Raman analysis.     

Influence of bias voltage on diamond like carbon (DLC) film deposited on polyethylene terephthalate (PET) film surfaces using PECVD and its blood compatibility

In this paper, diamond like carbon (DLC) films were coated on polyethylene terephthalate (PET) film substrate as a function of biasing voltage using plasma enhanced chemical vapour deposition. The surface morphology of the DLC films was analyzed by scanning electron microscopy and atomic force microscopy. The chemical state and structure of the films were analyzed by X-ray photoelectrons spectroscopy and Raman spectroscopy. The micro hardness of the DLC films was also studied. The surface energy of interfacial tension between the DLC and blood protein was investigated using contact angle measurements. In addition, the blood compatibility of the films was examined by in vitro tests. For a higher fraction of sp³ content, maximum hardness and surface smoothness of the DLC films were obtained at an optimized biasing potential of ? 300 V. The in vitro results showed that the blood compatibility of the DLC coated PET film surfaces got enhanced significantly.     

Deposition of diamond-like carbon films on aluminium substrates by RF-PECVD technique: Influence of process parameters

The properties of diamond-like carbon (DLC) films are influenced by both the process parameters and the properties of the substrate on which they are deposited. Deposition of DLC films on aluminium and its alloys has drawn increasing attention owing to its potential applications as wear resistant coatings in automobile pistons, bores, VCR heads, copier machine drums and textile components. In the present study, DLC films have been deposited on commercial pure aluminium (98.9% purity) in a 200 kHz RF glow discharge sustained by methane gas in an asymmetric and capacitively coupled deposition system. Influence of various process parameters such as power density or bias voltage, methane gas pressure and flow rate on deposition kinetics, hardness and elastic modulus of the films has been assessed. Interrelationships between independent process variables like power density, methane gas pressure and flow rate, and dependent process variables like bias voltage and temperature have also been evaluated on the basis of available models.     

A 400 μm thickness diamond-like carbon preparation

A 400 μm thick diamond-like carbon (DLC) film was prepared on an aluminum alloy (A5052) substrate by a hybrid process of plasma-based ion implantation and deposition using toluene as a precursor gas. The plasma-based ion implantation during deposition relaxed the residual stress in DLC film to almost 0, indicating the production of stress-free DLC. The carbon ion implantation from the methane and acetylene plasmas to the substrate surface, prior to deposition, resulted in an interface graded in carbon composition as well as the formation of amorphous-like structure at the carbon ion-implanted layer that should work as a buffer for stress-relaxation. As a result, a supra-thick DLC film more than 400 μm in thickness was prepared on the substrate.     

Comparison of a-C:H films deposited from methane–argon and acetylene–argon mixtures by electron cyclotron resonance–chemical vapor deposition discharges

Hydrogenated amorphous carbon (a-C:H) films are deposited from methane–argon and acetylene–argon gas mixtures in a microwave electron cyclotron resonance plasma reactor. The films deposited with the two different gas mixtures under similar input parameter conditions have substantially different properties, including deposition rate, mass density, optical absorption coefficient, refractive index, optical bandgap and hydrogen content. The deposition parameters varied include rf-induced dc substrate bias voltage (0 to −60 V), pressure (1–5 mTorr) and argon/hydrocarbon gas flow ratio (0–1.0). The discharge properties of the two different gas mixtures, including electron temperature, ion saturation current, and residual gas composition of the exit gas flow, are measured to help explain the different deposition results from the two different gas mixtures. The use of lower pressures is found to be critical for obtaining denser, lower hydrogen content films from acetylene. For the methane-deposited films the addition of argon to the discharge increased the film's mass density and lowered the hydrogen content. In both methane- and acetylene-based deposition processes the rf-induced bias is also a critical determining factor of film properties.     

Study of the mechanical properties of tetrahedral amorphous carbon films by nanoindentation and nanowear measurements

Nanoindentation and nanowear measurements, along with the associated analysis suitable for the mechanical characterization of tetrahedral amorphous carbon (ta-C) films are discussed in this paper. Films of approximately 100-nm thick were deposited on silicon substrates at room temperature in a filtered cathodic vacuum arc evaporation system with an improved S-bend filter that yields films with high values of mass density (3.2 g/cm³) and sp³ content (84–88%) when operating in a broad bias voltage range (−20 V to −350 V). Nanoindentation measurements were carried out on the films with a Berkovich diamond indenter applying loads in the 100 μN–2 mN range, leading to maximum penetration depths between 10 and 60 nm. In this measurement range, the ta-C thin-films present a basically elastic behavior with high hardness (45 GPa) and high Young's modulus (340 GPa) values. Due to the low thickness of the films and the shallow penetration depths involved in the measurement, the substrate influence must be taken into account and the area function of the indenter should be accurately calibrated for determination of both hardness and Young's modulus. Moreover, nanowear measurements were performed on the films with a sharp diamond tip using multiple scans over an area of 3 μm², producing a progressive wear crater with well-defined depth which shows an increasing linear dependence with the number of scans. The wear resistance at nanometric scale is found to be a function of the film hardness.     

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10⁹/cm², 3 × 10⁹/cm², and 7 × 10⁹/cm² by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.     

The effect of annealing on mechanical and tribological properties of diamond-like carbon multilayer films

The diamond-like carbon (DLC) multilayer films have been deposited by plasma CVD deposition onSi wafer substrate. The deposited films have then been post-annealed in vacuum at 250 °C for 2 h. Changes in internal stress, hardness, critical load, friction coefficient and wear have been investigated toassess the influence of annealing on mechanical and tribological properties of DLC multilayer films. At the same time, DLC single layerfilms are also deposited and annealed in the same method for a comparison.The results show that there is 28–33% decrease in internal stress and 10–13% decrease in hardness of theDLC single layer films after the anneal treatment. However, for the DLC multilayer films, there is 41–43% decreasein internal stress and less than 2% decrease in hardness. In addition, the annealed DLC multilayer filmhas the same friction and wear properties as that un-annealed film. This result indicates that the anneal treatment isan effective method for the DLC multilayer films to reduce the internal stress and to increase the critical load.The by-effect of the annealing, decrease of hardness and wear resistance of the multilayer film, can be restrictedby the multilayer structure.     

Microstructure and mechanical properties of Mo/DLC nanocomposite films

Mo-doped diamond-like carbon (Mo/DLC) films were deposited on stainless steel and Si wafer substrates via unbalanced magnetron sputtering of molybdenum combined with inductively coupled radio frequency (RF) plasma chemical vapor deposition of CH₄/Ar. The effects of Mo doping and sputtering current on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM), and nano-indentation. It was found that Mo doping led to increase in the content of sp² carbon, and hence decreased the hardness and elastic modulus of Mo/DLC films as compared with that of DLC films. The content of Mo in the films increased with the increasing sputtering current, and most of Mo reacted with C atoms to form MoC nanocrystallites at a higher sputtering current. Moreover, the Mo-doped DLC films had greatly decreased internal stress and increased adhesion to the substrate than the DLC film, which could be closely related to the unique nanocomposite structure of the Mo-doped films. Namely, the Mo/DLC film was composed of MoC nanoparticles embedded in the cross-linked amorphous carbon matrix, and such a kind of nanostructure was beneficial to retaining the loss of hardness and elastic modulus.     

Preparation of diamond like carbon thin films above room temperature and their properties

Diamond like carbon (DLC) thin films were deposited on p-type silicon (p-Si), quartz and ITO substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at different substrate temperatures (RT ∼ 300 °C). Argon (Ar: 200 sccm) was used as carrier gas while acetylene (C₂H₂: 20 sccm) and nitrogen (N: 5 sccm) were used as plasma source. Analytical methods such as X-ray photoelectron spectroscopy (XPS), FT-IR and UV–visible spectroscopy were employed to investigate the structural and optical properties of the DLC thin films respectively. FT-IR spectra show the structural modification of the DLC thin films with substrate temperatures showing the distinct peak around 3350 cm^− 1 wave number; which may corresponds to the sp² C–H bond. Tauc optical gap and film thickness both decreased with increasing substrate temperature. The peaks of XPS core level C 1 s spectra of the DLC thin films shifted towards lower binding energy with substrate temperature. We also got the small photoconductivity action of the film deposited at 300 °C on ITO substrate.     

Deposition of hard amorphous hydrogenated carbon films by radiofrequency parallel-plate hollow-cathode plasmas

Hard amorphous hydrogenated carbon (a-C:H) films were deposited by plasma decomposition of CH₄ gas in a RF parallel-plate hollow-cathode system. The deposition system was built by placing a metallic plate in parallel to and in electrical contact with an usual RF-PECVD planar cathode. Self-bias versus RF power curves were used to make an initial characterization of plasma discharges in nitrogen gas atmospheres, for pressures between 10 and 100 mTorr. The strongly increased power consumption to obtain the same self-bias in the hollow-cathode system evidenced an increase in plasma density. The a-C:H films were deposited onto Si single crystalline substrates, in the − 50 to − 500 V self-bias range, at 5, 10 and 50 mTorr deposition pressures. The film deposition rate was found to be about four times than that usually observed for single-cathode RF-PECVD-deposited films, under methane atmosphere, at similar pressure and self-bias conditions. Characterization of film structure was carried out by Raman spectroscopy on films deposited at 10 and 50 mTorr pressures. Gaussian deconvolution of the Raman spectra in its D and G bands shows a continuous increase in the I_D/I_G integrated band intensity ratio upon self-bias increase, obeying the expected increasing behavior of the sp² carbon atom fraction. The peak position of the G band was found to increase up to − 300 V self-bias, showing a nearly constant behavior for higher self-bias absolute values. On the other hand, the G band width showed a nearly constant behavior within the entire self-bias range. Nanohardness measurements have shown that films deposited with self-bias greater than 300 V are as hard as films obtained by the usual PECVD techniques, showing a maximum hardness of about 18 GPa. Films were also found to develop high internal compressive stress. The stress dependence on self-bias showed a strong maximum at about − 200 V self-bias, with a maximum stress value of about 5 GPa.     

硬质合金刀具类金刚石涂层的摩擦磨损性能

以等离子体化学气相沉积技术在硬质合金刀具表面制备了类金刚石(DLC)涂层.研究了DLC涂层刀具和无涂层刀具的硬度,不同载荷、不同转速下两种刀具的摩擦磨损性能,以及在水润滑和油润滑条件下DLC涂层刀具的滑动摩擦行为.结果表明,DLC涂层刀具的平均硬度为2 099.9 HV,比无涂层刀具提高了48.3%;DLC涂层刀具的摩擦因数明显低于无涂层刀具,其磨损率随着载荷的增加而增大,随转速的增大而减小;油润滑比水润滑能更有效减缓摩擦作用.     

Fast deposition of diamond-like hydrogenated carbon films

Diamond-like hydrogenated carbon films have been formed at low temperatures using methane and acetylene as precursor gases. The source used was of a cascaded arc type employing Ar and Ar/H₂ as carrier gases. Energies of ion species and ion densities in the plasma were measured with a mass energy probe and a Langmuir probe.The films produced were characterized in terms of sp³ content, refractive index, relative hydrogen content, hardness and adhesion. The variation of these parameters is presented as functions of precursor gas flow, process pressure, and surface temperature.Deposition rates up to 30 nm/s have been achieved using acetylene as precursor gas at substrate temperatures below 100 °C. Experiments with acetylene showed deposition rates seven times greater than with methane. The typical sp³ content of 55–78% in the films was determined by X-ray-Excited Auger Electron Spectroscopy (XAES) technique. The hardness and reduced modulus were determined by nanoindentation. Preliminary Atomic Force Microscopy (AFM) studies of the films showed a roughness below 3 nm (R_a).     

Mechanical properties of PECVD thin ceramic films

Silicon dioxide (thickness 350 nm and 969 nm) and silicon nitride (thickness 218 nm) films deposited on silicon substrate using plasma enhanced chemical vapor deposition process were investigated using a Berkovich nanoindenter. The load-depth measurements revealed that the oxide films have lower modulus and hardness compared to the silicon substrate, where as the nitride film has a higher hardness and slightly lower modulus than the substrate. To delineate the substrate effect, a phenomenological model, that captures most of the ‘continuous stiffness measurement’ data, was proposed and then extended on both sides to determine the film and substrate properties. The modulus and hardness of the oxide film were around 53 GPa and 4–8 GPa where as those of the nitride film were around 150 GPa and 19 GPa, respectively. These values compare well with the measurements reported elsewhere in the literature.     

Diamond-like carbon prepared by high density plasma

This paper will present physical and tribological properties of diamond-like carbon (DLC) films deposited by plasma-enhanced chemical vapor deposition using a commercial RF high density plasma (HDP). The films have been prepared from acetylene or acetylene+hydrogen mixtures using a range of HDP conditions. The composition and optical properties of the DLC films have been characterized by forward recoil elastic scattering (FRES) and Fourier transform infrared spectroscopy (FTIR). The tribological properties have been measured in ambient air and in dry nitrogen using a pin-on-flat tribometer. While the friction coefficients in air (<0.14) were mostly independent of the deposition conditions, the friction in dry nitrogen was affected by the deposition conditions, reaching values as low as 0.01. The wear rates of the HDP DLC films were extremely low. This paper will discuss the friction properties of these films in relation to the deposition conditions and their physical properties.