Si-doped Diamond-like Carbon Films Research Articles

Extremely enhanced friction and wear performance of hydrogen-free DLC film at elevated temperatures via Si doping

Hydrogen-free diamond-like carbon (DLC) films have garnered significant attention as a highly efficient solid lubrication material, but poor high-temperature lubrication and wear resistance limit their further application. Here, silicon-doped DLC (Si-DLC) films with different Si contents were deposited using a superimposed HiPIMS-DCMS deposition system to improve their high-temperature lubrication and wear resistance performance. The influence of Si content on the microstructure, mechanical and high-temperature friction and wear behavior of Si-DLC films was investigated. The results showed that Si-DLC films had a dense structure and nanoscale smooth surface. The Si doping enhanced the adhesion strength and relieved the residual stress of Si-DLC films, but decreased the hardness and Young's modulus. Meanwhile, Raman and XPS spectroscopy revealed significant local structural changes in Si-doped DLC films. Furthermore, the results showed that DLC films doped with low Si content displayed excellent tribological performance at elevated temperatures due to the graphite lubricating layer on the surface of wear marks. Specifically, Si-DLC film with 3.31 at% Si had an ultra-low average friction coefficient of 0.04 at 450 °C and still provided effective lubrication at temperatures up to 500 °C. In contrast, pure DLC film failed to lubricate at 450 °C due to the severe graphitization transition and Si-DLC film with 17.47 at% Si quickly failed to lubricate at 200 °C due to the SiC and SiO2. This work sheds light for the high-temperature application of DLC films doped with low Si content by superimposed HiPIMS-DCMS deposition system.

Effect of the Variation of Film Thickness on the Properties of Multilayered Si-Doped Diamond-Like Carbon Films Deposited on SUS 304, Al and Cu Substrates

Multilayered Si-doped DLC film with thicknesses of 5.5, 10.1, 21.8 and 28.3 μm was deposited on stainless steel, aluminum alloy and copper alloy substrates by plasma-enhanced chemical vapor deposition. The mechanical and tribological properties of multilayered Si-doped DLC films deposited on three different substrates were evaluated in this study. The hardness of the multilayered Si-doped DLC film of different substrates is related to the substrate material and internal stress. In a scratch test, the adhesion of the multilayered Si-doped DLC film increased with the film thickness. The multilayered Si-doped DLC film with a thickness of 28.3 μm on stainless steel substrate has the highest adhesion of 31 N. The adhesion of the multilayered Si-doped DLC film with different thicknesses on the copper alloy is relatively poor. The ball-on-disk friction test results show that the multilayered Si-doped DLC film with thicknesses of 5.5 and 10.1 μm is prone to shear deformation and exhibit high friction coefficient. The uneven stress distribution and surface deformation of the multilayered Si-doped film deposited on the aluminum alloy and the copper alloy cause the fluctuation and rise of the friction coefficient. The wear resistance of multilayered Si-doped DLC films on different substrates is related to stress shielding and adhesion strength.

Deformation mechanisms of Si-doped diamond-like carbon films under uniaxial tension conditions

Element-doped diamond-like carbon (DLC) films have been fabricated to achieve excellent mechanical properties but their elastic/plastic deformation mechanisms are unclear due to experimental limitations in characterizing the deformation process. This study investigates the deformation mechanisms of Si-doped DLC films by simulating their uniaxial tensile tests. It is found that these films show many strain-localized regions under tensile deformations. The coordination number (CN) of Si atoms in such regions decreases even with a small tensile strain. The sp3-sp2 bonding transition of C atoms also happen in these regions with a large tensile strain. As a result, these regions show highly-degraded structures with weak mechanical strength and can be regarded as the defects in the Si-DLC films. In this case, the tensile forces are mainly undertaken by the networks formed of both sp3C atoms and Si atoms with large CN, and hence such networks can be regarded as backbones of Si-DLC films. Their fracture finally initiates in the strain-localized regions. Furthermore, Si-DLC films with an increased Si content show large fraction of sp3C atoms but still exhibit a decreased strength due to the rapid presence of strain-localized regions.

Characterization of Si-DLC films synthesized by low cost plasma-enhanced chemical vapor deposition

Diamond-like carbon (DLC) coatings offer versatile applications in surface engineering due to high hardness and strength, chemical and radiation resistance, biocompatibility and low friction coefficient. When doped with Si, such coatings demonstrate even more beneficial properties, such as lower friction coefficient and higher thermal stability. We demonstrate the instrumental developments of a plasma-enhanced chemical vapor deposition (PECVD) method and the use of an original low-cost set-up aimed to synthesize Si-doped DLC films using polyphenylmethylsiloxane (PFMS) precursors. These films on the surface of glass substrate were characterized by means of XPS, AFM, Raman spectroscopy, and nanoindentation. Dry fiction coefficient was found to be reduced for Si-doped DLC for 4–6 times in comparison with glass substrate.

Comparative study on the influence of bias on the properties of Si-DLC film with and without Si interlayer on NBR: The role of Si interlayer

Si doped diamond-like carbon (Si-DLC) film was prepared on nitrile-butadiene rubber (NBR), and the effects of substrate bias on the microstructure, adhesion and tribological properties of Si-DLC films with and without Si interlayer were studied. The principal purpose of this study is to explore how bias leads to structural and performance differences of films with and without interlayer, and to further clarify the role of Si interlayer by comparing the difference in the above obtained results. The results show that bias does not influence the structure of the films without Si interlayer on NBR, but the introduction of Si interlayer has a significant effect on the growth mechanism and microstructure of Si-DLC top layers under the different bias. However, Si interlayer does not play a positive role in improving the adhesion of films in this work. Furthermore, the results of tribological study show that the presence or absence of Si interlayer has little effect on the friction and wear of the films when the bias voltage is low (≤500 V), but the wear mechanism is completely different. However, when the bias voltage is high enough (≥700 V), the friction coefficient and wear of the films with Si interlayer are lower than that of films without Si interlayer. Finally, it must be pointed out that there is a huge risk when the brittle interlayer is chosen once the top layer fails. Therefore, the ductile interlayer should be selected as the load-bearing layer without sacrificing the adhesion, and more efforts should be made to improve the mechanical and tribological properties of the top layer.

Corrosion and wear behaviors of Si-DLC films coated on inner surface of SS304 pipes by hollow cathode PECVD

An integrated technology of hollow cathode plasma enhanced chemical vapor deposition (PECVD) with plasma immersion ion deposition (PIID), promoting the deposition rate ranging from10 to 14 µm h−1, was developed to deposit thick Si-doped diamond-like carbon (Si-DLC) films on the internal surface of 304 stainless steel (SS304) pipes with various inner diameters for corrosion and abrasion protection. After the deposition, the films inside 30 mm and 90 mm diameter pipe have been comprehensively investigated by FESEM, optical 3D profiler, Raman, XPS, nanoindentation, EIS and polarization measurements, salt spray test and friction test. It was found that Si-DLC films were compact and smooth, thick (~11 µm) and hard (~13 GPa). The current density (2.38 × 10−9 A cm−2) of Si-DLC films was 1000 times lower than the uncoated steel pipe through the electrochemical polarization test. The EIS data were analyzed by an equivalent circuit model, which presented a highest charge transfer impedance of ~4.5E7 Ω cm2. Si-DLC films survived 720 h salt spray test without the presence of corrosion pits and exfoliation. The test results confirmed that Si-DLC films possessed superior performances in corrosion resistance, which was not only attributed to the chemical inertness of DLC and Si incorporation, but also to the multilayered film with few defects. Besides, the friction coefficient of Si-DLC films in air, water and oil environments was low at 0.05–0.06, 0.08–0.12 and 0.08–0.09, respectively, in comparison with 0.55, 0.30 and 0.11 for bare steel. The corresponding wear rates of Si-DLC films were much lower than uncoated steel pipe in the three environments as well.

Microstructure and Nano-wear Property of Si-doped Diamond-like Carbon Films Deposited by a Hybrid Sputtering System

Diamond like carbon (DLC) films have been extensively studied over the past decades due to their unique combination of properties. In particular, silicon-doped DLC (Si-DLC) films have attracted significant attention for their tribological applications. However, most of the efforts were focusing on friction and wear properties in conventional load range, while nano-scale tribological behavior remains being less investigated. In this study, Si-doped DLC films were deposited by a hybrid sputtering system combining high power impulse magnetron sputtering (HiPIMS) and radio frequency (RF) magnetron sputtering. The Si concentration in the films was controlled by altering the Si target power. The influence of the Si target power on the microstructure, mechanical and nano-wear properties of the Si-DLC films were investigated. The influence of the microstrure variation on mechanical and nano-wear property of the films were further studied. The results indicated that the hardness value was significantly influenced by the Raman ID/IG ratio and the ID/IG ratio also played an important role in the nano-wear behavior of the Si-DLC films.

Nanomechanical and nanotribological behavior of ultra-thin silicon-doped diamond-like carbon films

Diamond-like carbon (DLC) film with ultra-thin thickness displays high internal stress, thereby resulting in the failure of protection to the substrate. Incorporation of silicon into DLC films, which has higher adhesion to substrate and extraordinary thermal stability, can be potentially used in heat assisted magnetic recording (HAMR). The nanomechanical and nanotribological behavior of Si doped DLC films is investigated using molecular dynamic simulation method. Effects of the Si content and density of Si-DLC films on the frictional behavior and wear resistance of Si-DLC films are investigated. Surface profiles at the contact interface are identified before and after sliding.

Effects of frequency of pulsed substrate bias on structure and properties of silicon-doped diamond-like carbon films by plasma deposition

We have investigated the effects of the frequency of pulsed substrate bias on the structure and properties of Si-doped diamond-like carbon (Si-DLC) films deposited by radio-frequency plasma-enhanced chemical vapor deposition using CH4, Ar, and monomethylsilane (CH3SiH3) as the Si source. The Si/(Si+C) ratios in the Si-DLC films deposited using pulsed bias were higher than that of the dc-biased Si-DLC film, and the Si fraction increased with decreasing frequency. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that Si–C, Si–Hn, and C–Hn bonds in the Si-DLC films increased with decreasing frequency. The internal stress decreased as the frequency decreased, which is probably due to the increase in Si–C, Si–Hn, and C–Hn bonds in the films. It was found that the wear rate of the pulse-biased Si-DLC film deposited at the highest frequency in this study is comparable to that of the dc-biased, undoped DLC film. Furthermore, the friction coefficient of the former is about one third of that of the latter.

Influence of duty ratio of pulsed bias on structure and properties of silicon-doped diamond-like carbon films by plasma deposition

We have investigated the influence of the duty ratio of pulsed substrate bias on the structure and properties of Si-doped diamond-like carbon (Si-DLC) films deposited by radio frequency plasma-enhanced chemical vapor deposition using CH4, Ar, and monomethylsilane (CH3SiH3) as the Si source. The Si/(Si+C) ratios in the Si-DLC films deposited using pulsed bias were higher than that of the dc-biased Si-DLC film, and the Si fraction increased with decreasing pulse duty ratio. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that Si-C, Si-Hn, and C-Hn bonds in the Si-DLC films increased with decreasing duty ratio. The internal stress decreased as the duty ratio decreased, which is probably due to the increase in Si-C, Si-Hn, and C-Hn bonds in the films. The Si-DLC films deposited using pulsed bias had higher adhesion strength than the dc-biased Si-DLC film because of the further reduction of internal stress. At higher duty ratios, although the Si fractions of the pulse-biased Si-DLC films were higher than that of the dc-biased Si-DLC film, the wear rates of the former were less than that of the latter.

Comparison between FTIR and XPS characterization of amino acid glycine adsorption onto diamond-like carbon (DLC) and silicon doped DLC

Diamond-like carbon (DLC) coatings are extremely useful for creating biocompatible surfaces on medical implants. DLC and silicon doped DLC synthesized on silicon wafer substrate by using plasma enhanced chemical vapour deposition (PECVD). The adsorption of glycine onto prepared samples has been investigated with a range of surface analysis techniques. The effects of surface morphology on the interaction of glycine with doped and undoped DLC films have been investigated. The chemical composition of the surface before and after adsorption was analyzed using X-ray photoelectron spectroscopy (XPS). For undoped DLC the spectra show peaks at 285eV (C 1s), 532eV (O 1s) and in the case of Si-doped DLC films a band at ∼100eV (Si 2p) is observed. Following exposure to solutions containing (0.001M) glycine, for undoped DLC the peaks at ∼285.0, ∼399 and ∼532eV reduced in intensity and for Si-DLC samples, the peak at 100eV was reduced. This gives an indication of the quantitative change in the amounts of C, N and O on the surfaces. From Fourier transform infrared (FTIR) spectrum, the peaks occur the following functional groups were assigned as COOR, COŌ, NH3+, NH2, CH and CCN. Both XPS and FTIR spectroscopy confirm that glycine was bound onto the surfaces of the DLC and Si-DLC films via interaction of ionized carboxyl groups and the amino group did not play a significant role in the adsorption of glycine. These results from SE show that an adsorbed layer of glycine is higher at low silicon doping whilst increased doping levels led to a reduced adsorption compared to undoped DLC. Therefore doping of DLC may provide an approach to controlling the protein adsorption.

Thermal Stability and High-Temperature Tribological Properties of a-C:H and Si-DLC Deposited by Microwave Sheath Voltage Combination Plasma

In this study, amorphous hydrogenated carbon (a-C:H) and Si-doped diamond-like carbon (Si-DLC) films were prepared using microwave sheath voltage combination plasma (MVP) deposition. The thermal stability of the a-C:H and Si-DLC films were investigated by performing an annealing test (100-700°C) in ambient air. Furthermore, the in situ high-temperature tribological properties on the films were investigated by performing a sliding test against a Si3N4 ball at high temperatures (100, 200, and 300°C). Hardness measurements and a tribological test showed that Si-DLC has better thermal stability than a-C:H; however, Si-DLC has a higher friction coefficient and undergoes more wear than does a-C:H in the in situ high-temperature tribological test. Therefore, the failure of Si-DLC is due to adhesive wear, whereas that of a-C:H is due to abrasive wear.

Surface properties of nano-structural silicon-doped carbon films for biomedical applications

Hydrogenated diamond–like carbon (DLC) containing Si films were synthesised using the radio frequency plasma enhanced chemical vapour deposition. The results show that all Si–doped DLC films exhibited a similar amorphous structure as non–doped DLC films. Doping Si caused graphitisation of C and reduced the surface hardness. Moreover, the surface roughness of the films decreased with the Si content, which consequently decreased the water contact angle of the film surfaces. Such hydrophilic property reveals the possibility of applying Si–doped amorphous diamond–like carbon films as a bioactive treatment on biomedical implant surfaces.

Adhesion and composite micro-hardness of DLC and Si-DLC films deposited on nitrile rubber

Thin films of hydrogenated diamond-like carbon (DLC) and silicon (Si) doped diamond-like carbon (Si-DLC) have been deposited on acrylonitrile butadiene rubber (NBR) using a closed field unbalanced magnetron sputtering ion plating system. A sputter cleaning process was integrated into the deposition process so as to reduce the likelihood of re-contamination between the cleaning and deposition stages. The deposited coatings showed excellent adherence with an adhesion rating of 4A for films with a Si-C interlayer. The composite micro-hardness was highest for DLC films at 15.5GPa for indentation load of 147.1mN using a Vickers micro-hardness tester. Tribological tests undertaken under normal load of 5N using a pin-on-disc tribometer for all of the samples of DLC and Si-DLC films, with and without Si-C interlayer, show a friction increase between 0.25 and 0.4 to between 0.45 and 0.6. This friction increase has been related to the micro-hardness of the films.

Influence of interaction energy between Si‐doped diamond‐like carbon films and bacteria on bacterial adhesion under flow conditions

Diamond-like carbon (DLC) films, especially modified DLC films with doped elements as biomaterials for medical devices have been attracting great interest. In this article, the bacterial adhesion behavior on DLC films, Si-doped DLC films, and stainless steel 316L was investigated with Pseudomonas aeruginosa ATCC 33347, which frequently causes medical device-associated infections. This was done under laminar flow conditions in a flow chamber at 37 degrees C. The contact angles of the coatings and the biofilm were measured. Polar liquids of distilled water and ethylene glycol, and apolar liquid of diiodomethane were used as a probe for surface free energy calculations. The electron donor component gamma(-) of surface energy of Si-doped DLC films increased with increasing the silicon content in the DLC films. The experimental results showed that the surface energy of the coatings and the interaction energy between the coatings and bacteria in water had significant influences on bacterial adhesion. The extended DLVO theory was used to explain the adhesion behavior.

Characteristic of Si-Doped DLC Films on TC4 and Cr12 Substrates

A series of diamond-like carbon (DLC) films with different Si concentration were prepared by changing the ratio of the number of Si-doped graphite target and pure graphite target. As the Si concentration in the thin film keep on increasing, the concentration of C-Si bond will increase leading to decrease of hardness and stress and increase of friction coefficient. In order to synthesize DLC films on metal substrates 3 types of interlayer have been made. The first and second interlayer is made up Ti/TiCx, and the second is thicker, the third interlayer is made up Ti/TiNx/TiNxCy, with the same thickness of the second. We also prepared DLC films with 6.7 at.% Si concentration on TC4 and Cr12 substrates with the third interlayer, and the thickness, hardness and fiction coefficients is about 0.652m, 4200Hv and 0.15, respectively. The adhesion of films had been greatly strengthened with a proper interlayer, and the value is more than 39N/mm2

Evaluation of bacterial adhesion on Si-doped diamond-like carbon films

Diamond-like carbon (DLC) films as biomaterial for medical devices have been attracting great interest due to their excellent properties such as hardness, low friction and chemical inertness. It has been demonstrated that the properties of DLC films can be further improved by the addition of silicon into DLC films, such as thermal stability, compressive stress, etc. However no research work on anti-bacterial properties of silicon-doped diamond-like carbon films has been reported. In this paper the surface physical and chemical properties of Si-doped diamond-like carbon films with various Si contents on 316 stainless steel substrate prepared by a magnetron sputtering technique were investigated, including surface topography, surface chemistry, the sp 3/sp 2 ratio, contact angle, surface free energy, etc. Bacterial adhesion to Si-doped DLC films was evaluated with Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus which frequently cause medical device-associated infections. The experimental results showed that bacterial adhesion decreased with increasing the silicon content in the films. All the Si-doped DLC films performed much better than stainless steel 316L on reducing bacterial attachment.

Investigation of Si-doped diamond-like carbon films synthesized by plasma immersion ion processing

Silicon (Si)-doped diamond-like carbon (DLC) was prepared on Si(100) and polymethyl metha_crylate (PMMA) substrates using a C2H2–SiH4–Ar plasma immersion ion processing (PIIP) method. The chemical composition of the films was varied by adjusting the reactive gas-flow ratio of SiH4 to C2H2 during PIIP depositions. The influence of the Si dopant on the bonding structure, stress, and properties of the DLC films was investigated by using ion beam analysis techniques, Raman shift, ultraviolet/visible spectroscopy, and by analyzing the measured properties. The incorporation of Si up to 17.3 at. % produced a reduction in film stress and increased the density and optical band gap. The Si-doped DLC films also exhibited increased sp3 bonding and higher hardness (25–28 GPa). Further increase in Si dopant, to above 22 at. %, caused a transformation from DLC to amorphous silicon carbide (a-SiC) that showed high hydrogen capacity, low hardness, and low stress. Pin-on-disk tribological tests of Si-doped DLC on PMMA showed greatly improved wear and friction properties related to the uncoated PMMA.