Hard Carbon Films Research Articles

Deposition of carbon films by direct ion beam

In this study diamond-like carbon (DLC) films have been grown onto the Si(111) and steel substrates by direct hydrocarbon (hexane, acetylene) ion beam deposition. Raman spectra of the room temperature deposited carbon films were typical of the hard tetrahedral amorphous carbon films. At 500 and 750 K temperatures, polymer-like carbon films have been synthesized. Hydrocarbon gas dilution by nitrogen resulted in growth of the more graphitic films. Increase of the deposition temperature resulted in increased internal stress in carbon films deposited from hexane–hydrogen gas mixture. Thin film stress decreased as a result of the hexane–hydrogen mixture dilution by nitrogen. Stress decreased with increase of the nitrogen concentration. It has been revealed that DLC films can be deposited by direct ion beam onto the AISI 316 steel at room temperature. Ion beam nitridation was the best method for increase of adhesion between the DLC and steel substrate.

Usage of Extending Carbon Films Including DLC

DLC (Diamond-Like Carbon), a kind of the hard carbon film, has such features as the lowest friction coefficient among various ceramic coating materials, high hardness, and less damage in the counterparts. Because of these features, many developments regarding the application for various kinds of sliding parts are in progress. However, people now call other films DLC, too, even though they are different from those defined in ‘80 s. Moreover, new manufacturing methods such as sputtering and cathodic arc ion-plating are now used in addition to the conventional ones such as the radio frequency (rf) plasma assisted chemical vapor deposition (PACVD) and the ion beam deposition. It is required to use these DLCs properly for each usage. Another topic in these days is a flexible DLC film that uses rubber as the substrate material instead of the generally used ones such as metals and ceramics. This new DLC film is applied to the rubber seal ring (O-ring) for zoom lens system of 35 mm compact cameras.

Friction and wear at nanometer scale: a comparative study of hard carbon films

Tribological properties of nanostructured carbon (ns-C) and tetrahedral amorphous carbon (ta-C) thin films were investigated by friction force microscopy. It was found that the ns-C films have a smaller friction coefficient than ta-C films for relative humidity greater than 30%. In particular, at 40% of humidity, ns-C films have lower friction coefficient (0.11±0.02) than the ta-C films (0.13±0.02), which can be attributed to both the presence of closed graphite nanoparticles and the passivation of the dangling bonds at the ns-C surface. The friction coefficient did not vary as a function of the tip scanning velocity for both films. The nanoscale wear was studied in a very low force regime, in the range of nanonewton, using an atomic force microscope (AFM) with a Si 3N 4 tip and with forces in the range of micronewton with the AFM equipped with a stainless still cantilever and a diamond tip. The ns-C provides better wear resistance compared to ta-C films in the range of forces studied. The sp 2-rich ta-C surface layer was easily scratched during the wear test in contrast to the ns-C films. The wear in ta-C in the low forces regime is attributed to the presence of this low density layer at the surface of the film due to subplantation of energetic ions during deposition while the better resistance to wear of ns-C films is attributed to its highly elastic nature.

Correlation between SiO x content and properties of DLC:SiO x films prepared by PECVD

Hard diamond-like carbon (DLC) films with an addition of SiO x were deposited in capacitively coupled r.f. discharges from a mixture of methane and hexamethyldisiloxane (HMDSO). The flow rate of HMDSO was changed in order to vary the SiO x content in the films. Complete atomic composition of the films was determined by Rutherford backscattering spectroscopy combined with elastic recoil detection analysis. The thickness and the optical properties were obtained from the ellipsometric measurements. The mechanical properties were studied by a depth sensing indentation technique using Fischerscope H100 tester. The O/Si ratio in DLC:SiO x films was 0.286±0.008 and the content of SiO x increased with the HMDSO-to-methane flow rate ratio q. The DLC:SiO x films were close to DLC films as concerning the optical properties in the UV/visible and the high hardness if q was maximum 0.25. However, the compressive stress in the films was reduced, the film fracture toughness was improved and the deposition rate increased.

Nanocrystalline diamond films for nanotechnology applications

Nanocrystalline diamond films with rms roughnesses in the order of 50 nm have been prepared by microwave plasma enhanced chemical vapour deposition. Ar-CH4 gas mixtures have been used in a coaxially bladed reactor, and Ar-H2-CH4 gas mixtures have been used in a reactor with a dual mode microwave applicator. These films have been examined by ultraviolet and visible Raman spectroscopy. They have been subjected to nanotribological investigation, with a view to their incorporation into microelectromechanical systems (MEMS). Comparisons with other diamond and hard carbon films are made, and the advantages of nanocrystalline diamond films are discussed.

Tribological behavior of hard carbon coatings on steel substrates

In this work the tribological behavior of hard carbon films on steel substrates has been studied under moderately high contact stress conditions. Diamond-like carbon (DLC) coatings of 1 μm thickness were deposited by a plasma-enhanced chemical vapor deposition (PECVD) process on hardened substrates made from 4140 alloy steel. The coated flat specimens were tested in an oscillatory pin-on-disk configuration in contact with either uncoated or carbon-coated hardened steel balls. Peak Hertzian contact pressures ranged from about 300 to 500 MPa and mean sliding velocity was 50 mm/s. In some tests, the specimens were lubricated with 10W-30 motor oil. It was found that wear of the carbon coatings was approximately linearly proportional to contact force. For unlubricated tests, wear rates of the coated specimens were about 200 times less than rates of wear of uncoated steel specimens for the same contact force. The contacting steel ball (uncoated) showed even greater wear reduction (more than 3 orders of magnitude) when tested against coated substrates. Friction coefficients were four to five times lower for coated specimens. Coating the ball as well as the flat resulted in a further reduction (about 50%) in wear of both ball and flat. Friction and wear reduction brought about by carbon coating in lubricated tests was less than for unlubricated specimens.

DLC films deposited by a neutral beam source: adhesion to biological implant metals

Hard carbon films have been deposited on implant-grade 316L stainless steel using a saddle source neutral beam system. The properties of the films in terms of hardness, intrinsic stress, adhesion and sp 3 content have been investigated as a function of source current, system pressure and process gas mixture. It has been found that there is a strong correlation between the intrinsic stress and the sp 3 content, as measured by Raman spectroscopy whereas there is little variation in hardness. The adhesion, as measured by the pull-off test is inversely proportional to the intrinsic stress. The source current has a significant effect on film stress and sp 3 content.

Microstructure and nanomechanical and optical properties of single- and multi-layer carbon films synthesized by radio frequency sputtering

Submicrometer-thick hard carbon films were deposited on smooth Si(1 0 0) substrates by radio frequency sputtering. To avoid the development of high residual stresses during film growth under energetic ion bombardment, films were synthesized by either sputtering alternating ultrathin layers of soft and hard amorphous carbon (a-C) or by compounding a-C films with small amounts of nitrogen during deposition. Hardness and elastic modulus measurements were obtained from indentation experiments performed with a surface force microscope and a nanoindenter using the slope of the unloading curve and the continuous stiffness method. The thickness and hardness of a multi-layer film consisting of five bilayers of soft/hard ultrathin a-C layers were found to be equal to ∼115 nm and ∼28 GPa, respectively, and the corresponding values of a single-layer nitrogenated amorphous carbon (a-CN x ) film (deposited under conditions similar to those of the hard ultrathin a-C layers) were found to be equal to ∼222 nm and ∼20 GPa. The microstructure and interface roughness of the films were examined by X-ray diffraction (XRD) and X-ray reflectivity (XRR), respectively, and the optical properties by spectroscopic ellipsometry (SE). XRD results showed that the multi-layer film is amorphous, and that some crystalline phases are present in the single-layer a-CN x film. XRR studies revealed that the density of the soft and hard a-C layers and the relatively thick a-CN x film is equal to 2.2, 2.5 and 2.39 g/cm 3, respectively. According to the SE results, the multi-layer a-C film is dense and rich in sp 2 (∼70 at.%) carbon bonds, whereas the single-layer a-CN x film exhibits high optical absorption at low photon energy.

Atomistic study of ion-beam deposition conditions for hard amorphous carbon

The effect of deposition temperature on the formation of hard amorphous carbon (a-C) films from low and medium energy ions was studied by atomic scale simulation. Applying classical molecular dynamics with a modified hydrocarbon potential of Brenner, ion-beam deposition of carbon films with a thickness of ∼3–10 nm was simulated for ion energies E=10–80 eV, and for substrate temperatures ranging from 100 to 900 K. The dependence of the sp3 content and intrinsic stress in the simulated films on substrate temperature was found to agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp3 fraction increases with ion energy, giving at E>30 eV a highly sp3-bonded tetrahedral amorphous carbon (ta-C) with a high compressive stress. This trend also remains at room temperature, however with lower values of the sp3 content and stress, whereas above 500 K simulations with the Brenner potential predict a sharp transition from ta-C to graphitic carbon with dominating sp2 bonding.

Diamond and hard carbon films for microelectromechanical systems (MEMS)—a nanotribological study

Previously unreported amorphous carbon and nanocrystalline diamond films have been prepared by microwave plasma-enhanced chemical vapour deposition (MPCVD) in two novel reactor designs. Ar–CH 4 gas mixtures were used in a 1 kW coaxial bladed reactor design, and Ar–H 2–CH 4 gas mixtures were used in a 6 kW reactor with a dual mode applicator. Films were examined by ultra-violet and visible Raman spectroscopy, and subjected to nanotribological investigation by scanning force microscopy (SFM). The results are compared with those from randomly orientated and (100) microcrystalline MPCVD diamond, pulsed laser deposited (PLD) and filtered cathode vacuum arc (FCVA) carbon films, Si wafer and electroformed Ni. A consideration of the relative merits of the various film types for microelectromechanical systems (MEMS) is presented.

Evaluation of tribological properties of DLC films used in sheet forming of aluminum sheet

Diamond-like carbon (DLC) films, i.e. hard carbon films having amorphous structure, are known to have excellent tribological properties against various materials. However, because of its low adhesion strength to a substrate and/or the difficulty of preparing the required thick film, thin films have not been as extensively applied to tools as expected. In this paper, the basic tribological properties of DLC films against aluminum alloys are reported. More specifically, films with different compositions prepared by various techniques and coated onto the forming tools were subjected to tribology tests using aluminum alloys as the counter face material. We constructed a heavy-load friction tester that enables the application of load similar to that in actual metal forming of the material. It was found that among various hydrogenated DLC films with or without inclusion of a silicon element, non-silicon containing films show the best tribological properties.

Femtosecond pulsed laser deposition of diamond-like carbon thin films for tribological applications

Pulsed laser ablation is a well-known technique used for thin film deposition of hard and wear resistant diamond-like carbon (DLC) films. Most of the previous studies were carried out by using pulse duration in the nanosecond range. Compared to conventional nanosecond laser ablation, femtosecond laser allows the production of high energy (up to a few keV) ions in the plasma, which may strongly affect the structure and properties of the deposited films. The present study was achieved by ablating graphite targets with femtosecond (10−15 s range) laser pulses. DLC films were deposited under vacuum onto (100) p-type silicon substrates at room temperature. The laser pulse energy was 1.5 mJ at a repetition rate of 1 kHz. The fluence (or energy density) range was between 1 and 6 J/cm2. The nature and mechanical properties of the films are characterized by X-ray absorption near-edge spectroscopy and nanoindentation techniques. The tribological behavior of the films are also investigated in a pin-on-plate configuration. Correlations between the structure of the films and some of their properties are highlighted, depending on the deposition conditions. Discussion is focused on the comparison between present results obtained using the femtosecond mode, with previously published results related to DLC films deposited using the nanosecond mode.

Thermo-oxidation of hard carbon films with tungsten surface impurity

The removal of codeposited tritiated carbon films from the next generation of fusion reactors may involve baking in an O 2 environment. Experimental results have indicated that thermo-oxidation can be effective in the removal of such films, however, wide variations have been observed in the oxidation rates of various types of carbon films. In the current experiments, we have investigated the role of metallic impurities by sputter-depositing tungsten onto hard a-C:D films, and exposing them to O 2 gas at 623 K. It was found that rather than catalysing the oxidation of the hydrogenated carbon film, the W deposit tended to inhibit the film removal at this temperature. This suggests that film structure is the predominant factor determining the oxidation rate of tokamak codeposits.

Characterization of Hard Diamond-Like Carbon Films Formed by Ar Gas Cluster Ion Beam-Assisted Fullerene Deposition

The coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. With attention to the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital, relative sp2 contents of various DLC films were estimated. The sp2 contents of the DLC films formed by the GCIB-assisted deposition were observed to be lower than those of the DLC films formed by other methods. The hardness value measured with a nano-indentation technique was found to be strongly related to the sp2 content of the DLC film.

Study of the structure of hard graphite-like amorphous carbon films by electron diffraction

The structure of thin hard carbon films was investigated by transmission electron diffraction using a filter of inelastically scattered electrons. It was shown for the first time that in the amorphous graphite-like carbon films under considerable compressive stress the interplane distance d 002 could be shortened down to approximately 0.300 nm. Also, substantiation was given for a simple procedure for the estimation of the first coordination sphere radius in amorphous carbon films. This radius was determined from the maximum of the corresponding diffraction halo. It was shown that this procedure gave the radius of the first coordination sphere very close to its real value for graphite-like structure but did not work so well for a diamond-like structure.

Properties Oftetrahedralamorphous Carbon Films Deposited By the Filtered Cathodicarc Method

ABSTRACTFirst, we studied the relation between the sp3 bond ratio and the hardness of 100-nm-thick tetrahedral amorphous carbon (ta-C) films deposited by a Filtered Cathodic Arc (FCA) system at different substrate bias voltages. For comparison, sputtered amorphous carbon (a-C) films and Highly Oriented Pyrolytic Graphite (HOPG) were also analyzed. According to the results, ta-C film deposited at a -70 volt substrate bias voltage had high hardness and high sp3 bond ratio of up to 88 GPa and 85%, respectively, whereas those of sputtered a-C were 29 GPa and 28%. Furthermore, we found that the hardness of carbon films, including sputtered a-C and HOPG, increased with increasing sp3 bond ratio. Based on this relation, the chemical bond structures of carbon films are considered to be closely related to their mechanical properties. Secondly, we investigated the relation between sp3 bond ratio and ta-C film thickness, over the range from 1 to 10 nm. The measurements showed that a 2-nm-thick initial layer grown on the surface of CoCrPt magnetic film had low sp3 bond ratios. It is suggested that this reduction in sp3 bond ratio in the initially grown layer seriously degrades the film's performance as a hard disk media overcoat. Further efforts to improve ta-C film processing will be required to improve its mechanical properties.

Halogen lamp-assisted high rate deposition of both hard and elastic carbon films from CH 2I 2

Photo-thermal dissociation of gaseous methylene-iodide (CH 2I 2) by means of a halogen lamp allows the deposition of highly elastic, diamond-like carbon films. This technique combines low cost, easy handling, high flexibility, and high process efficiency. Carbon films may be deposited on even optically transparent materials without a change in film properties being observed. The growth rate obtained is significantly faster than with purely thermal CVD. The present paper presents an analysis of this photo-thermal process, based on the measurement of averaged and instantaneous growth rates as a function of the temperatures induced by the lamp in the substrate. Deposition rates are seen to depend strongly on the ratio between photon flux density and process temperature.

Analysis of chemical vapour deposited diamond films by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) for elemental and phase analysis of diamond surfaces is reviewed, including both single crystal natural diamond and polycrystalline chemical vapour deposition (CVD) films. The core C1s peaks, plasmon losses and valence band spectra of sp 2 graphite are compared with those of sp 3 diamond, and briefly with mixed sp 2/sp 3 hard carbon films. Surface reconstructions are reviewed for diamond in the presence of hydrogen or following thermal annealing. Attention is drawn to the destructive effects of argon ion bombardment ‘cleaning’. The synthesis of CVD diamond, including the initial nucleation process, is described and the significance of hydrogen is explained. Chemical modification of the surface of diamond films is discussed, with relevance to sensors and field electron emission. XPS analysis of (111) polycrystalline films treated by atom beams of N, O, H, Cl is described and the influence of unwanted oxygen is emphasised. For both atom beam and furnace oxidation, the oxygen is incorporated into the (111) diamond surface as bridging C–O–C.

Speeding-up effects of hard carbon films on surface acoustic wave on crystalline quartz

Hard diamond-like carbon (DLC) films and tetrahedral amorphous carbon (Ta-C) films have been deposited on X– Y cut quartz substrates. The 1-μm-thick DLC films prepared by a plasma enhanced CVD system possess typical Young's modulus (and hardness) of approximately 150 (19) GPa, whereas the 0.12-μm-thick Ta-C films grown using filtered cathodic vacuum arc technique have a Young's modulus (and hardness) of 340 (38) GPa. Velocity tests of surface acoustic wave (SAW) were performed by introducing SAW into two delay lines on the quartz; one coated with the carbon films and the other free of the films. It has been confirmed that the DLC and Ta-C films speed up SAW by 2.3% and 3.4%, respectively. These findings are interpreted in terms of the film properties.

Hemocompatibility of DLC coatings synthesized by ion beam assisted deposition

Ion beam-assisted diamond-like carbon (DLC) coatings have been used for growing the human platelet, fibrinogen, and albumin in the control environment in order to assess their hemocompatibility. The hard carbon films were prepared on polymethylmethacrylate (PMMA) at room temperature using ion beam assisted deposition (IBAD). Raman spectroscopic analysis proved that the carbon films on PMMA are diamond-like with a higher fraction of sp3 bonds in the structure of mixed sp2+sp3 bonding. The blood protein adsorption tests showed that DLC coatings can adsorb more albumin and are slightly more fibrinogen than the PMMA chosen as a control sample. The platelets adhered on DLC coatings were reduced significantly in number. These results indicate good hemocompatibility of DLC coatings.