Silicon-containing Diamond-like Carbon Research Articles

Study of the Influence of Silicon-Containing Diamond-like Carbon Coatings on the Wear Resistance of SiAlON Tool Ceramics

DLC coatings have low adhesive bond strength with the substrate and a high level of residual stresses. This paper is devoted to researching a complex of characteristics of a DLC-Si coating deposited on samples of SiAlON ceramics with intermediate coatings (CrAlSi)N pre-formed to improve the adhesive bond strength employing vacuum-plasma spraying. DLC-Si coatings were formed by chemical vapor deposition in a gas mixture of acetylene, argon, and tetramethylsilane supplied through a multichannel gas purge system controlling the tetramethylsilane volume by 1, 4, 7, and 10%. The SiAlON samples with deposited (CrAlSi)N/DLC-Si coatings with different silicon content in the DLC layer were subjected to XPS and EDX analyses. Tribological tests were carried out under conditions of high-temperature heating at 800C. The nanohardness and elasticity modulus of the rational (CrAlSi)N/DLC-Si coating with Si-content of 4.1% wt. were 26 ± 1.5 GPa and 238 ± 6 GPa, correspondingly. The rational composition of (CrAlSi)N/DLC-Si coating was deposited on cutters made of SiAlON ceramics and tested in high-speed machining of aircraft nickel-chromium alloy compared to uncoated and DLC-coated samples. The average operating time (wear resistance) of (CrAlSi)N/DLC-Si(4.1% wt.)-coated end mills before reaching the accepted failure criterion was 15.5 min when it was 10.5 min for the original cutters.

Effect of tribologically-induced changes in surface termination of silicon-containing diamond-like carbon coatings on the resistance to biomolecule adsorption

Silicon-containing diamond-like carbon (DLC) is a class of thin-film materials with excellent mechanical properties, high thermal stability, and good tribological performance over a wide range of environmental conditions. While non-alloyed/non-doped DLCs also exhibit good biocompatibility and bioinertness, our understanding of the effect of silicon in DLCs on biomolecules/DLC interactions is still elusive. Here, we evaluated the structural, mechanical, and tribological properties of Si-containing DLC coatings with silicon content fraction of 11% and 16%. Tribological tests, performed by sliding a stainless steel pin on the coatings in water, indicated a low friction response (steady-state coefficient of friction <0.11), while quartz crystal microbalance experiments indicated no adsorption of a model biomolecule, namely adenosine triphosphate (ATP), on Si-containing DLCs. Near-edge X-ray absorption fine structure spectromicroscopy analyses performed after tribological experiments provided evidence for an increase in the fraction of silanol surface terminal groups formed in the worn region upon sliding in water without any significant sp3-to-sp2 rehybridization of carbon atoms. The fraction of surface hydroxyl groups in the worn region increases with the silicon content in Si-containing DLC, which leads to a decrease in friction. This tribologically-induced change in surface termination did not lead to the adsorption of ATP upon incubation of tribotested samples in ATP solutions for several hours. These findings open the path for the use of Si-containing DLC in applications requiring good tribological properties in aqueous solution and an excellent resistance to biomolecule surface adsorption that is maintained even after tribologically-induced variations in surface termination.

Effect of Soft X-ray Irradiation on Film Properties of a Hydrogenated Si-Containing DLC Film.

The effect of soft X-ray irradiation on hydrogenated silicon-containing diamond-like carbon (Si-DLC) films intended for outer space applications was investigated by using synchrotron radiation (SR). We found that the reduction in film thickness was about 60 nm after 1600 mA·h SR exposure, whereas there was little change in their elemental composition. The reduction in volume was attributable to photoetching caused by SR, unlike the desorption of hydrogen in the case of exposure of hydrogenated DLC (H-DLC) film to soft X-rays. The ratio of the sp2 hybridization carbon and sp3 hybridization carbon in the hydrogenated Si-DLC films, sp2/(sp2 + sp3) ratio, increased rapidly from ~0.2 to ~0.5 for SR doses of less than 20 mA·h. SR exposure significantly changed the local structure of carbon atoms near the surface of the hydrogenated Si-DLC film. The rate of volume reduction in the irradiated hydrogenated Si-DLC film was 80 times less than that of the H-DLC film. Doping DLC film with Si thus suppresses the volume reduction caused by exposure to soft X-rays.

Local Structure Analysis on Si-Containing DLC Films Based on the Measurement of C K-Edge and Si K-Edge X-ray Absorption Spectra

In this paper, the local structure of silicon-containing diamond-like carbon (Si-DLC) films is discussed based on the measurement of C K-edge and Si K-edge near-edge x-ray absorption fine structure (NEXAFS) spectra using the synchrotron radiation of 11 types of Si-DLC film fabricated with various synthesis methods and having different elemental compositions. In the C K-edge NEXAFS spectra of the Si-DLC films, the σ* band shrunk and shifted to the lower-energy side, and the π* peak broadened with an increase in the Si content in the Si-DLC films. However, there were no significant changes observed in the Si K-edge NEXAFS spectra with an increase in the Si content. These results indicate that Si–Si bonding is not formed with precedence in Si-DLC film.

Direct silanol analysis of tribological surfaces using synchrotron radiation

A new direct detection technique for silanol is needed for tribological materials containing silicon. We focused on near-edge X-ray absorption fine structure (NEXAFS), which uses synchrotron radiation as a method for directly detecting silanol. Model samples were prepared, and their spectra were obtained by NEXAFS. The Si and the O K-edge spectra of silanol exhibited peaks at approximately 1843 eV and 535 eV, respectively. Then the surfaces of silicon-containing diamond-like carbon (DLC-Si) films were measured. The amount of silanol on high-silicon-doped DLC, which had a low friction coefficient, was found to be greater than that on low-silicon-doped DLC. In this research, we demonstrated that the silanol on the surface of DLC-Si films can be directly detected and identified by NEXAFS.

Enhancing the adhesion and tribological performance of Si-DLC film on NBR by Ar plasma pretreatment under a high bias

Silicon-containing diamond-like carbon (Si-DLC) films were successfully deposited on nitrile-butadiene rubber (NBR) via magnetron sputtering Si target in Ar and CH4 mixture atmosphere. The influence of Ar plasma pretreatment bias on the adhesion and tribological properties of the Si-DLC coated NBR were investigated systematically. The results indicated that the surface roughness of NBR substrate decreased monotonously with the increase of bias. Compared with the virgin NBR, the surface topography did not change significantly under a low bias, but a shallow layer and considerable chain scission could be observed by SEM and FTIR analysis under a high bias. As a consequence, the excellent adhesion could be obtained by Ar plasma pretreatment under a high bias (&amp;gt;-500 V), while the adhesion of the samples pretreated by a low bias (≤-500 V) were even worse than that of untreated samples. Furthermore, the samples pretreated at a relatively high bias of -1000 V exhibited the lowest and stable friction coefficient of 0.25 and outstanding wear resistance, while the tribological performance of the samples pretreated with a low bias (≤-500V) were even worse than that of untreated ones. The research results of this work are of great surface engineering significance for the design and fabrication of hard films with a high adhesion and excellent tribological performance on rubber substrates.

The effect of fluoroalkylsilanes on tribological properties and wettability of Si-DLC coatings

Silicon-containing diamond-like carbon (Si-DLC) coatings were prepared on silicon wafers by Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) method using methane/hexamethyl-disiloxane atmosphere. Herein, we report that Si-DLC coatings can be effectively modified by fluoroalkylsilanes which results in significant enhancement of frictional and wettability properties. Two types of fluoroalkylsilanes differing in the length of fluorocarbon chains were deposited on Si-DLC coatings with the use of Vapor Phase Deposition (VPD) method. The chemical composition of Si-DLC coatings and effectiveness of modification with fluoroalkylsilanes were confirmed by Fourier Transform Infrared Spectroscopy (FTIR) and x-ray Photoelectron Spectroscopy (XPS). Frictional properties in microscale were investigated with the use of ball-on-flat apparatus operating at millinewton (mN) load range. It was found that the presence of silicon enhances the chemisorption of fluoroalkylsilanes on Si-DLC coatings by creating adsorption anchoring centers. In consequence, a decrease of adhesion and an increase of hydrophobicity along with a decrease of coefficient of friction were observed. Experimental results indicate, that tribological properties are correlated with dispersive and acid-base components of the surface free energy as well as with the work of adhesion.

Long-term thermal stability of Si-containing diamond-like carbon films prepared by plasma source ion implantation

The long-term stability of silicon-containing diamond-like carbon films was investigated. The samples were prepared by plasma source ion implantation with a mixture of tetramethylsilane (TMS) and acetylene (C2H2) using negative high voltage pulses. The film composition was changed by varying the flow rates of the TMS and C2H2 gases, resulting in a Si content from 0 to 44 at.%. After deposition the films were annealed at temperatures from 523 K to 773 K for 168 h in ambient air. The effect of the Si content on the structure, the mechanical and tribological properties of the DLC films was investigated. A silicon oxide layer is produced on the surface of the film which improves the thermal stability. Mechanical and friction characteristics of the Si-DLC were not much affected by the long-term thermal annealing if the temperature was kept below 573 K.

Plasma parameter investigation during plasma-enhanced chemical vapor deposition of silicon-containing diamond-like carbon films

In this work, tetramethylsilane-based plasma-enhanced chemical vapor deposition (PECVD) processes were studied, and the deposited silicon-containing diamond-like carbon (DLC) films were analyzed. The main goal was to identify correlations between plasma parameters and the film structure and properties. The electron temperature, gas temperature, and hydrogen and silicon particle densities in these plasmas were calculated using optical emission spectroscopy measurements; the electron density and elastic electron collision rate were determined using self-excited electron resonance spectroscopy. The elemental composition of the films was determined by glow discharge optical emission spectroscopy, and the hardness and Young's modulus were characterized using nanoindentation. The plasma parameters of the gas temperature and electron temperature revealed stringent correlations with the film composition and properties and thus can already monitor the resulting properties during the deposition process. Increasing the gas temperature using power variation leads to reduced incorporation of silicon and hydrogen in the diamond-like carbon films with a simultaneous increase of the film hardness. However, a gas temperature increase using a higher gas flow rate results in a decrease in the film hardness and an increase in the silicon and hydrogen contents. These results are promising concerning the use of plasma parameters for process control of CVD processes.

Comprehensive Classification of Near-Edge X-ray Absorption Fine Structure Spectra of Si-Containing Diamond-Like Carbon Thin Films

Structural analysis by the measurement of carbon K-edge near-edge X-ray absorption fine structure (NEXAFS) using synchrotron radiation was performed on 23 types of silicon-containing diamond-like carbon (Si-DLC) film fabricated by various synthesis methods. In addition, elementary composition in the Si-DLC films was determined by the combination of Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA) using an electrostatic accelerator. In the C K-edge NEXAFS spectra of Si-DLC films, the σ* band shrunk and shifted to the lower-energy side, and the π* peak broadened with increasing silicon content in the Si-DLC film. The observed NEXAFS spectra of Si-DLC films were classified into four types.

The high‐temperature tribological properties of Si‐DLC films

The tribological properties of Silicon‐containing diamond‐like‐carbon (Si‐DLC) films, deposited by magnetron sputtering Si target in methane/argon atmosphere, were studied in comparison with diamond‐like‐carbon (DLC) films. The DLC films disappeared because of the oxidation in the air at 500 °C, whereas the Si‐DLC films still remained, implying that the addition of Si improved significantly the thermal stability of DLC films. Retarded hydrogen release from DLC film at high temperature and silicon oxide on the surface might have contributed to lower friction coefficient of the Si‐DLC films both after annealing treatment and in situ high‐temperature environment. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Temperature dependent properties of silicon containing diamondlike carbon films prepared by plasma source ion implantation

Silicon containing diamondlike carbon (Si-DLC) films were prepared on silicon wafer substrates by a plasma source ion implantation method with negative pulses superposed on a negative dc voltage. A mixture of acetylene and tetramethylsilane gas was introduced into the discharge chamber as working gases for plasma formation. Ions produced in the plasma are accelerated toward a substrate holder because of the negative voltage applied directly to it. After deposition, the films were annealed for 0.5 h in ambient air at temperatures up to 923 K in order to evaluate the thermal stability of the Si-DLC films. The films were analyzed by x-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy, and Raman spectroscopy. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The mechanical and tribological properties were investigated by an indentation method and a ball-on-disk test. The results show the silicon containing DLC films were amorphous and the surface roughness of the Si containing DLC films was very smooth and no special structure was observed. Integrated intensity ratios ID/IG of Raman spectroscopy of the Si containing DLC films decreased with Si content. The Raman spectra showed that the structure of the Si-free DLC film changed to a graphitelike structure with increasing annealing temperature, whereas that of the 24 at. % Si containing DLC films did not change at the maximum temperature used in this study. A very low friction coefficient was obtained for the 13 at. % Si containing DLC film. The surface roughness and the hardness of the films changed with increasing annealing temperature. The formation of Si oxide in a near surface layer was confirmed by XPS and it prevents further oxidation of the inside of the film. Heat resistivity of DLC films can be improved by Si addition into the DLC films.

Ultralow nanoscale wear through atom-by-atom attrition in silicon-containing diamond-like carbon

Understanding friction and wear at the nanoscale is important for many applications that involve nanoscale components sliding on a surface, such as nanolithography, nanometrology and nanomanufacturing. Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples. The contact area between the materials must also be described differently at the nanoscale. Diamond-like carbon is routinely used as a surface coating in applications that require low friction and wear because it is resistant to wear at the macroscale, but there has been considerable debate about the wear mechanisms of diamond-like carbon at the nanoscale because it is difficult to fabricate diamond-like carbon structures with nanoscale fidelity. Here, we demonstrate the batch fabrication of ultrasharp diamond-like carbon tips that contain significant amounts of silicon on silicon microcantilevers for use in atomic force microscopy. This material is known to possess low friction in humid conditions, and we find that, at the nanoscale, it is three orders of magnitude more wear-resistant than silicon under ambient conditions. A wear rate of one atom per micrometre of sliding on SiO(2) is demonstrated. We find that the classical wear law of Archard does not hold at the nanoscale; instead, atom-by-atom attrition dominates the wear mechanisms at these length scales. We estimate that the effective energy barrier for the removal of a single atom is approximately 1 eV, with an effective activation volume of approximately 1 x 10(-28) m.

Deposition of silicon-containing diamond-like carbon films by plasma-enhanced chemical vapour deposition

Silicon-containing diamond-like carbon (Si-DLC) films were prepared on silicon wafer substrates by DC glow discharge. Acetylene and mixture with tetramethylsilane gases were used as working gases for the plasma. A negative DC voltage was applied to the substrate holder. The DC voltage was changed in the range from − 1 kV to − 4 kV. The surface morphology of the films and the film thickness were observed by scanning electron microscopy. The compositions of the Si-containing DLC films were examined by X-ray photoelectron spectroscopy. The film structure was characterized by Raman spectroscopy. A ball-on-disc test with 2 N load was employed to obtain information about the friction properties and sliding wear resistance of the films. The films were annealed at 723 K, 773 K and 873 K in ambient air for 30 min in order to estimate the thermal stability of the DLC films. The surface roughness of the Si-containing DLC films was very low and no special structure was observed. The deposition rate increased linearly with Si content. The positions of D- and G-bands in Raman spectra decreased with Si content. The integrated intensity ratios I D/ I G of the Si-containing DLC films decreased with Si content. A very low friction coefficient of 0.03 was obtained for a 24 at.% Si-containing DLC film. The heat resistivity of DLC films can be improved by Si addition into the DLC films.

A Novel Corrosion-Resistant Internal-Coating Method Provides Improved Hardness

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 114020, "A Novel Corrosion-Resistant Internal-Coating Method Using Hollow-Cathode PECVD Technology With Improved Hardness," by Bill Boardman, Karthik Bonapolly, Deepak Upadhayaya, and Tom Casserly, Sub-One Technology, prepared for the 2008 Western Regional and Pacific Section of AAPG Joint Meeting, Bakersfield, California, 31 March-2 April. The paper has not been peer reviewed. A novel technology has been developed for coating the internal surfaces of parts ranging from small components to production pipe. The coating is appropriate for use in many environments for corrosion, erosion, and wear reduction. The process technology that enables the coating of interior surfaces with a hard, wear- and corrosion-resistant silicon-containing diamond-like carbon (DLC-Si) layer is described. Hardness greater than 25 GPa has been achieved while maintaining a high deposition rate. Introduction A new process technology uses a plasma-enhanced chemical-vapor deposition process that has been modified to use a high-density, hollow-cathode plasma that enables a high deposition rate that is generated based on pipe diameter and pressure. In conjunction with DC plasma pulsing, this enables very high deposition rates greater than 0.3 μm/min. Coating properties along the length of a steel pipe are controlled by adjusting process parameters. Ion bombardment improves film quality by biasing the part negative. The process does not require a traditional vacuum chamber, but uses the pipe or part as the vacuum chamber. In addition to improving corrosion resistance, the films are hard, pure, amorphous, dense, and wear resistant. Environmentally friendly precursors such as acetylene or other hydrocarbons are used to deposit inert corrosion-resistant DLC-based films with the potential to replace environmentally damaging precursors such as hexavalent chromium. Adhesion is improved by adding silicon to the DLC layer at the steel interface, and wear resistance and corrosion are improved with a pure-DLC cap layer. The full-length paper reports the results of a study evaluating use of a range of hydrocarbon precursors with respect to hardness, adhesion, and deposition rate. With the optimization of process parameters, the hardness was improved from an average of 15 GPa using acetylene to 25 GPa using butene, while maintaining a high deposition rate. Several authors have reported the effect of ion energy per carbon atom on the hardness of DLC coatings. Optimum ion energy per car-bon atom of approximately 70 eV is reported for high hardness and high sp3 content, with softer films reported at lower or higher energy per carbon atom. The size of the hydrocarbon precursor molecule affects this energy because the molecule will break apart on impact with the substrate. For example, as an acetylene ion is accelerated across the plasma sheath with an energy of 1,000 eV compared to a butene molecule with the same bias, and assuming a collisionless sheath, the acetylene will have an energy of 500 eV per carbon atom and the butene will have an energy of 250 eV per atom.

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

Small amplitude (50 μm) reciprocating wear of hydrogen-containing diamond-like carbon (DLC) films of different compositions has been examined against silicon nitride and polymethyl-methacrylate (PMMA) counter-surfaces, and compared with the performance of an uncoated steel substrate. Three films were studied: a DLC film of conventional composition, a fluorine-containing DLC film (F-DLC), and silicon-containing DLC film. The films were deposited on steel substrates from plasmas of organic precursor gases using the Plasma Immersion Ion Implantation and Deposition (PIIID) process, which allows for the non-line-of-sight deposition of films with tailored compositions. The amplitude of the resistive frictional force during the reciprocating wear experiments was monitored in situ, and the magnitude of film damage due to wear was evaluated using optical microscopy, optical profilometry, and atomic force microscopy. Wear debris was analyzed using scanning electron microscopy and energy dispersive spectroscopy. In terms of friction, the DLC and silicon-containing DLC films performed exceptionally well, showing friction coefficients less than 0.1 for both PMMA and silicon nitride counter-surfaces. DLC and silicon-containing DLC films also showed significant reductions in transfer of PMMA compared with the uncoated steel. The softer F-DLC film performed similarly well against PMMA, but against silicon nitride, friction displayed nearly periodic variations indicative of cyclic adhesion and release of worn film material during the wear process. The results demonstrate that the PIIID films achieve the well-known advantageous performance of other DLC films, and furthermore that the film performance can be significantly affected by the addition of dopants. In addition to the well-established reduction of friction and wear that DLC films generally provide, we show here that another property, low adhesiveness with PMMA, is another significant benefit in the use of DLC films.

Structural analysis of Si-containing diamond-like carbon

We have investigated the structures of silicon-containing diamond-like carbon (DLC-Si) films with various silicon contents. The DLC-Si films were deposited on steel substrates at 773 K by direct current plasma-enhanced chemical vapour deposition (DC-PECVD). The Si content in the films was controlled in the range of 4–28 at.% by adjusting the ratio of methane (CH 4) and tetramethylsilane (Si(CH 3) 4) as the precursor gases. Several typical spectroscopic measurements provided the film information: elastic recoil detection analysis (ERDA), hydrogen content; electron probe microanalysis (EPMA), carbon and silicon content; Fourier transform infrared (FT-IR), chemical bonding; and Raman scattering, networking due to the sp 2 carbon (Csp 2). In addition, solid-state 13C nuclear magnetic resonance (NMR) measurements were able to quantify the two types of hybridized carbon atoms, Csp 2 and Csp 3. The cross-polarization technique provided more precise environments for the carbon atoms bonded to hydrogen atoms, suggesting that the environment of Csp 2 is quite different depending on the silicon content. The 29Si NMR measurement was also carried out to provide the circumstance of the four-coordinate Si atoms. In addition, the mechanical property of the films (hardness) was evaluated by the nanoindentation method in order to compare it with the film structure.

Incorporation of Si in a-C:Si:H films monitored by infrared excited Raman scattering

Silicon-containing diamond-like amorphous carbon layers with varying Si content were prepared from methane and tetramethylsilane gas mixture by plasma enhanced CVD. The bonding configuration of the samples was examined by XPS and Raman spectroscopy. By the decomposition of scattering spectra excited by the 488 nm line of an Ar ion laser, it was found that, besides the well-known shift of the G peak to lower wavenumbers with increasing Si content, there is still a contribution to the scattered intensity in the 1550–1600 cm − 1 region even in the spectrum of sample with highest Si content studied. By using near-infrared (785 nm) laser for the Raman probe, we prove the presence of a distinguishable band in the G peak region. Our Raman results show the preservation of sp 2 clusters without any Si incorporation in a-C:Si:H films.

フッ化炭素プラズマ処理シリコン含有ダイヤモンドライクカーボン膜の機械特性

Diamond like carbon (DLC) and silicon containing DLC (Si-DLC) films were deposited by EBEP (electron beam excited plasma)-CVD. The effects of CF4 plasma treatment and Si-inclusion on DLC film on surface energy, nanoindentation hardness and nanoscratching properties were investigated. DLC and Si-DLC films were surface modified by CF4 plasma treatment. CF4 plasma treatment decreases surface energy evaluated by the liquid drop method. Si-inclusion decreases the nanoindentation hardness. CF4 plasma treatment decreases nanoindentaion hardness of DLC film, however increases the hardness of 20% Si containing DLC film. Micro wear depth increases by Si-inclusion evaluated by nanoscratch test. CF4 plasma treatment increases the micro wear of DLC film, however decreases the micro wear of 20% silicon containing DLC film. Friction coefficients of both DLC and Si-DLC films were decreased by CF4 plasma treatment.

X-ray absorption spectroscopy, simulation and modeling of Si-DLC films

Amorphous silicon-containing diamond-like carbon (Si-DLC) films were deposited on silicon wafers by Ar+ Ion Beam Assisted Deposition (IBAD) at various energy conditions. The films were examined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The Si K-edge X-ray Absorption Spectroscopy (XAS) results indicate that Si-DLC films have an amorphous structure, where each Si atom is coordinated to four carbon atoms or CHn groups. This short-range order, where a Si atom is surrounded by four C atoms, was found in all Si-DLC films. The XANES spectra do not indicate Si coordination to oxygen atoms or phenyl rings, which are present in the precursor material. A structural model of Si-DLC is proposed based on XAS findings. Simulated X-ray absorption spectra of the model produced by FEFF8 show a good resemblance to the experimental data.