Silicon-incorporated Diamond-like Carbon Research Articles

Effects of surface wettability of silicon-incorporated diamond-like carbon films on barnacle larval settlement

The colonization of barnacles on surfaces has detrimental effects on shipping, leisure vessels, heat exchangers, oceanographic sensors, and aquaculture systems. One strategy for avoiding barnacle colonization on surfaces is to utilize surface wettability. Silicone-incorporated diamond-like carbon (Si-DLC) has high hardness and a low friction coefficient, and an increase in the incorporation of Si leads to hydrophobicity. By contrast, oxygen plasma treatment produces hydrophilicity in Si-DLC films. The improved surface wettability of Si-DLC may reduce barnacle colonization. However, few studies have been conducted on barnacle larval settlement in relation to Si-DLC films. The aim of this study is to evaluate barnacle larval settlement on Si-DLC films and on oxygen-plasma-treated Si-DLC films. Si-DLC films were prepared by radio-frequency plasma-enhanced chemical vapor deposition and treated with oxygen plasma. The films were characterized using Raman spectroscopy and X-ray photoelectron spectroscopy. Contact angles of the films were measured to evaluate their hydrophobicity. Barnacle cyprid larva settlement was observed on the Si-DLC and oxygen-plasma-treated Si-DLC films. The contact angle of the Si-DLC-0% film was 69.9 ± 3 . 3 ∘ and increased with Si incorporation. Following oxygen plasma treatment, the contact angle of the Si-DLC-0% films decreased to 10.9 ± 4 . 4 ∘ and gradually increased with Si incorporation. The barnacle cyprid larval settlement ratio for the non-coated stainless plate was 36.4%, whereas that of the DLC films was 15.0%, which decreased with Si incorporation. Following oxygen plasma treatment, the ratio of barnacle cyprid larval settlement in Si-DLC films was lower than for the Si-DLC films. The Si-DLC film was effective in avoiding barnacle adhesion, whereas the oxygen-plasma-treated Si-DLC was even more effective. This study demonstrated the feasibility of Si-DLC for antifouling against barnacles.

Effect of oxygen and fluorine plasma surface treatment of silicon‐incorporated diamond‐like carbon coatings on cellular responses of mouse fibroblasts

AbstractThe surface chemistry of silicon‐incorporated diamond‐like carbon (Si‐DLC) was tailored utilizing oxygen and fluorine plasma treatments. Successful anchoring of oxygen and fluorine functional groups to the surface of Si‐DLC was verified using X‐ray photoelectron spectroscopy. The impact of surface modification of Si‐DLC on hydrophobicity was correlated with the viability of L929 mouse fibroblasts. The confocal microscopy and viability results indicated that oxygen‐treated Si‐DLC showed increased cell viability compared to untreated Si‐DLC and fluorine‐treated Si‐DLC samples 5 days after seeding. The increased cell viability was correlated with the conversion of the hydrophobic surface of Si‐DLC into a hydrophilic surface by oxygen plasma treatment.

Antifungal behavior of silicon‐incorporated diamond‐like carbon by tuning surface hydrophobicity with plasma treatment

Silicon-incorporated diamond-like carbon (Si-DLC), an amorphous material containing Si atoms with sp3- and sp2-hybridized carbon, is a promising biomaterial for versatile biomedical applications due to its excellent mechanical properties, chemical inertness, biocompatibility, and antimicrobial capability. However, the antifungal properties of plasma-treated Si-DLC have not been systematically evaluated. In this study, Si-DLC coatings were deposited by chemical vapor deposition and further treated with either oxygen or fluorine plasma to render the surface anchored with different functional groups and hydrophobicity. Surface roughness was probed with atomic force microscopy, whereas bonding character and surface composition were assessed using Raman and X-ray photoelectron spectroscopy. Wettability and surface charge were investigated via water contact angle and zeta potential measurements. Antifungal assessment was performed using a Candida albicans multi-well plate screening technique and crystal violet biomass quantification. The results demonstrate that oxygen plasma–treated Si-DLC exhibited hydrophilic properties, lower negative zeta potential, and significant antifungal behavior. This material can potentially be applied on surfaces for the prevention of reduced nosocomial infections.

Enhanced Vapor Transmission Barrier Properties via Silicon-Incorporated Diamond-Like Carbon Coating.

In this study, we describe reducing the moisture vapor transmission through a commercial polymer bag material using a silicon-incorporated diamond-like carbon (Si-DLC) coating that was deposited using plasma-enhanced chemical vapor deposition. The structure of the Si-DLC coating was analyzed using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, selective area electron diffraction, and electron energy loss spectroscopy. Moisture vapor transmission rate (MVTR) testing was used to understand the moisture transmission barrier properties of Si-DLC-coated polymer bag material; the MVTR values decreased from 10.10 g/m2 24 h for the as-received polymer bag material to 6.31 g/m2 24 h for the Si-DLC-coated polymer bag material. Water stability tests were conducted to understand the resistance of the Si-DLC coatings toward moisture; the results confirmed the stability of Si-DLC coatings in contact with water up to 100 °C for 4 h. A peel-off adhesion test using scotch tape indicated that the good adhesion of the Si-DLC film to the substrate was preserved in contact with water up to 100 °C for 4 h.

Enhanced nucleation and large-scale growth of CVD diamond via surface-modification of silicon-incorporated diamond-like carbon thin films

Herein we report a method to tailor the surface of silicon-incorporated diamond-like carbon (Si-DLC) thin films to enhance the diamond nucleation density and growth. In this technique, the surfaces of Si-DLC films were modified by fluorine and oxygen species utilizing a reactive-ion etching (RIE) method. The surface properties of Si-DLC, oxygen-terminated Si-DLC (O Si-DLC), and fluorine-terminated Si-DLC (F Si-DLC) films were investigated and compared. The analyses depicted that the sp2/sp3 ratio of carbon‑carbon bonds has diminished from 20.28% for Si-DLC film down to 8.96% and 4.41% for O Si-DLC and F Si-DLC films, respectively. Moreover, a significant amount of new sp3 hybridized bonds formed on the surface of the modified Si-DLC thin films, particularly in F Si-DLC film. The deposition of micro-diamond on the films was performed using hot filament chemical vapor deposition (HFCVD). SEM, XRD, and Raman results showed the enhancement in nucleation density and growth of micro-diamond on F Si-DLC and O Si-DLC films and the in-plane stress reduction up to 60%. Owing to the lower number of sp2 bonds and the greater number of new sp3 sites, the F Si-DLC thin film provided a superior platform for diamond nucleation than O Si-DLC film. The continuous diamond coverage on F Si-DLC film was up to ~2 mm2 versus ~0.4 mm2 for O Si-DLC film.

The Effect of Physicochemical Properties of Perfluoroalkylsilanes Solutions on Microtribological Features of Created Self-Assembled Monolayers.

The presented article shows the influence of concentration of perfluoroalkylsilanes in solutions on tribological properties of self-assembled monolayers (SAMs) deposited on three surfaces with different silicon content in the millinewton load range. The SAMs were created using the liquid phase deposition (LPD) method with 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (FDTS) and (3, 3, 3-trifluoropropyl) trichlorosilane (FPTS) solutions, for which viscosity and surface tension were estimated. Deposited layers were analyzed in terms of thickness, coverage, wettability, structure and coefficient of friction. The obtained results demonstrated that SAMs created on the silicon-incorporated diamond-like carbon (Si-DLC) coatings possess the best microtribological properties. Systems composed of perfluoroalkylsilane SAM structures deposited on Si-DLC coatings are highly promising candidates as material for microelectromechanical applications.

Argon and oxygen plasma treatment increases hydrophilicity and reduces adhesion of silicon-incorporated diamond-like coatings.

In this study, the structure, adhesion, and cell viability characteristics of silicon-incorporated diamond-like carbon (Si-DLC) coatings on fused silica substrates were investigated. The effects of argon and oxygen postprocessing plasma treatments on the Si-DLC coatings were also studied. The contact angle results showed that the Si-DLC coatings were more hydrophilic than the uncoated surfaces, and postprocessing plasma treatment increased the hydrophilicity of the Si-DLC coatings. Atomic force microscopy and profilometry confirmed that postprocessing plasma treatment increased the thickness and roughness of the Si-DLC coatings. The results of microscratch testing indicated that the plasma treatments reduced the adhesion of the coatings. The x-ray photoelectron spectroscopy (XPS) showed the presence of carbon, oxygen, and silicon in the Si-DLC coatings before and after the plasma treatments. These results show that the postprocessing plasma treatment significantly reduced the atomic percentage of the carbon in the Si-DLC coatings. XPS also confirmed the presence of carbon in the form of sp3(C-C), sp2(C=C), C-O, and C=O bonds in the Si-DLC coatings; it showed that postprocessing treatments significantly increased the percentage of oxygen in the Si-DLC coatings. Fourier transform infrared spectroscopy (FTIR) analysis showed features associated with C-OH stretching, C-H bending, as well as Si-CH2 and C-H bending in the Si-DLC coating. The XPS and FTIR results confirmed that the plasma treatment caused dissociation of the sp2 and sp3 bonds and formation of C-OH bonds. The contact angle data indicated that postprocessing treatment increased the hydrophilicity of the Si-DLC coating. Similar to the uncoated substrates, L929 cells showed no change in cell viability when cultured on Si-DLC coatings. These results of the study indicate the suitability of Si-DLC coatings as inert coatings for medical and biotechnology applications.

The influence of self-assembled monolayers on tribological properties of Si-DLC coatings

The tribological properties of diamond like carbon (DLC) and silicon-incorporated diamond like carbon (Si-DLC) coatings in contact with Si3N4 counterbody were investigated using a ball-on-disc tribometer. The effect of modification by perfluoro and alkylphosphonic self-assembled monolayers was evaluated in terms of lowering the coefficient of friction (CoF) and wear rate. The tribological tests revealed that the presence of silicon decreases the CoF and slightly increases the wear rate of Si-DLC coatings in comparison with DLC. Further decrease of CoF was achieved for Si-DLC coatings after self-assembled monolayers deposition. The effectiveness of modification, stability on ultraviolet (UV) irradiation and characterization of all coatings was monitored by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy and measurements of the surface free energy (SFE). The obtained study demonstrated that self-assembled monolayers reduce friction and are highly promising candidates as a good lubricant for tribological and mechanical systems.

Impacts of substrate bias and dilution gas on the properties of Si-incorporated diamond-like carbon films by plasma deposition using organosilane as a Si source

We have deposited silicon-incorporated diamond-like carbon (Si-DLC) films by plasma-enhanced chemical vapor deposition using monomethylsilane (CH3SiH3; MMS) as a Si source, and systematically investigated the impacts of substrate bias and dilution gas on the mechanical and tribological properties of the Si-DLC films. The use of a pulse bias and hydrogen dilution is very effective in suppressing the generation of particles during the deposition. The internal stress of the Si-DLC films deposited using the pulse bias tended to be lower than that of the Si-DLC films deposited using a DC bias, while the hydrogen dilution resulted in the increase in the internal stress. On the other hand, the Si-DLC film deposited with H2 using the pulse bias showed the highest adhesion strength and the lowest friction coefficient. The use of the pulse bias resulted in the increase in the wear resistance.

Tribological properties of cross-linked oleophilic polymer brushes on diamond-like carbon films

Surface-initiated atom transfer radical copolymerization of hexyl methacrylate (HMA) and 3-ethyl-3-oxetanylmethyl methacrylate (OxMA) was carried out on the surfaces of block- and ring-type steel pieces covered with silicon-incorporated diamond-like carbon (DLC-Si) in order to generate an oleophilic copolymer brush layer at the outermost surface. The sample was then immersed in a 1% BF3OEt2 solution to form cross-linkages between oxetane groups in the polymer brush chains. The thickness of the polymer brush layer was confirmed to be 50 nm through transmission electron microscope images of the focused ion beam (FIB)-fabricated cross section. The friction properties of the composite films were evaluated using block-on-ring tests under a load of 49 N (130 MPa), using a base oil at 353 K for 30 min. Although the brush layer was partially scratched from the substrate surface during the friction test, the polymer brush-immobilized DLC-Si exhibited a low friction coefficient of 0.02, while the friction coefficient of the non-modified steel substrate was 0.12. It is supposed that the oleophilic polymer brush was swollen in the oil to form a stable lubrication layer, thus preventing the direct contact of the DLC-Si substrate. The dependency of the tribological properties on normal load, sliding velocity, wear depth, and the silicon content of the DLC-Si substrate was also investigated.

Microstructure and properties of silicon-incorporated DLC film fabricated using HMDS gas and RF-PECVD process.

The microstructure and characteristics of silicon-incorporated diamond-like carbon film, fabricated using a radio-frequency plasma-enhanced chemical vapor deposition process with hexamethyldisilane [(CH3)3,Si x Si(CH3)3:HMDS] gas as a silicon source, were investigated. Diamond-like carbon films with silicon compositions from 0 to 5 atomic percent were deposited onto ultra-fine grained AZ31 magnesium alloy substrate as buffer layers or multilayers. Si doping led not only to an increase in the bonding ratio (sp3/sp2), but improvements in hardness, critical adhesion, and corrosion resistance. Out of the investigated samples, the multi-deposited silicon diamond-like carbon thin film on magnesium substrate showed the best combination of adhesive, wear resistance, and corrosion resistance properties.

Visible photoluminescence from silicon-incorporated diamond like carbon films synthesized via direct current PECVD technique

Silicon-incorporated diamond like carbon (Si-DLC) films were deposited via DC plasma-enhanced chemical vapor deposition (PECVD) on glass and alumina substrates at a substrate temperature of 473 K. The precursor gas used was acetylene and for silicon incorporation tetraethyl orthosilicate dissolved in methanol was used. Silicon atomic percentage in the films was varied from 0% to 19.3% as measured from energy dispersive X-ray analysis. Fourier transformed infrared spectroscopy studies depicted the presence of Si–C, Si–H and Si–H 2 bonding within the films. The binding energies of C 1s, Si 2s and Si 2p were determined from X-ray photoelectron spectroscopic studies. UV–vis–NIR spectroscopic studies were used to determine the optical gaps as well as the Urbach parameters of the samples. Room temperature photoluminescence study showed a broad peak centered at around 467 nm. Also the peak intensity was found to increase monotonically with Si percentages. The results are discussed in terms of the electronic structure of a-C:H, the doping induced defect states and the enhanced carbon dangling bonds via the formation of more sp 3 hybridized carbon network.

Improvement of corrosion protection property of Mg-alloy by DLC and Si–DLC coatings with PBII technique and multi-target DC–RF magnetron sputtering

Magnesium alloys have been considered as one of the most promising light weight materials with potential applications for automobile and aircraft components. Their poor corrosion resistance, however, has to date prevented wider usage. Diamond-like carbon (DLC) and silicon-incorporated DLC (Si–DLC) coatings are known to provide a high degree of corrosion protection, and hold accordingly promise for enhancing the corrosion resistance of the magnesium alloys. In this work we have studied the effect of coating conditions of DLC coatings as well as Si incorporation into coating on corrosion resistance, deposited onto AZ91 magnesium alloy substrates by plasma based ion implantation (PBII). The influences of a Ti interlayer beneath the DLC, Si–DLC and Ti incorporated DLC (Ti–DLC) coatings fabricated by multi-target direct-current radio-frequency (DC-RF) magnetron sputtering were also examined on both the adhesion strength and corrosion resistance of the materials. We have also examined the effect of the Si content in the Si–DLC coatings made by magnetron sputtering on the alloys’ corrosion resistance. The results of potentiodynamic polarization measurements demonstrate that Si–DLC coating deposited by PBII exhibits the highest corrosion resistance in an aqueous 0.05M NaCl solution. Although Ti layer is helpful in increasing adhesion between DLC coating and AZ91 substrate, it also influences adversely corrosion protection. The ozone treatment of the magnesium alloy’s surface before the formation of coatings has been found to improve both adhesion strength and corrosion resistance.

Traction of Lubricated Rolling Contacts between Thin-Film Coatings and Steel

Tribological thin-film coatings can enhance the performance of mechanical components such as bearings and gears. Although a lubricant is present in most applications, the interactions of the lubricant with the coated surfaces are not always well understood. In the present study, Stribeck curves (i.e., traction coefficient vs. dimensionless film thickness λ) were generated for lubricated rolling contact between coated and uncoated surfaces. Chromium nitride, tungsten carbide–reinforced amorphous hydrocarbon, and silicon-incorporated diamond-like carbon coatings were evaluated. Compositions, hydrogen concentrations, Raman spectra, and surface energies are reported for the films. A ball-on-flat test configuration was used in 5%, 50%, and 100% slide-to-roll conditions. The test lubricant was a polyalphaolefin containing rust and oxidation inhibitor additives only. Differences in traction performance were observed for different coating types. Traction coefficients decreased at high λ with increased hydrocarbon content in the coating. Coating micro-texture and composition were believed to influence traction as λ became small.

Atomic hydrogen etching of silicon-incorporated diamond-like carbon films prepared by pulsed laser deposition

We have deposited Si-DLC films by pulsed laser deposition using KrF excimer laser, and have investigated etching of the Si-DLC films by atomic hydrogen. We have examined the structure and chemical bonding of the films by Raman spectroscopy, X-ray photoelectron spectroscopy and photoelectron spectroscopy using synchrotron radiation. Photoelectron spectra of Si 2p with 135 eV photons showed two distinguishing components. The main components were identified with Si–C and silicon oxides. The intensity of the oxide component increased when the detection angle to the surface normal was increased from 0 to 60°, indicating that thin oxide layers were formed at the surface. The oxide component decreased by annealing at a substrate temperature above 850 °C in an ultra-high vacuum and it disappeared at 1050 °C. We found that the etching rate of the films drastically decreased by the incorporation of Si. It was also found that the etching rate of the Si-DLC films markedly increased after dipping in a HF solution, indicating that the hydrogen etching of the Si-DLC films is suppressed by thin oxide layers formed at the surfaces. When the HF-treated Si-DLC films were annealed at a temperature above 400 °C in a high vacuum chamber, the etching rate decreased, suggesting that oxide layers were formed again at the surfaces.

Thin-Film Deposition of Silicon-Incorporated Diamond-Like Carbon by Plasma-Enhanced Chemical Vapor Deposition Using Monomethylsilane as a Silicon Source

We have deposited Si-incorporated diamond-like carbon (DLC) films by radio-frequency plasma-enhanced chemical vapor deposition using methane, argon, and monomethylsilane (MMS; CH3SiH3) as a silicon source, and have investigated the structural and mechanical properties of the films. The deposition rate and Si atomic fraction [Si/(Si+C)] in the DLC films increased with increasing MMS flow ratio. The Si fraction was approximately 13% at a MMS flow ratio [MMS/(MMS+CH4)] of 3%, showing that the deposition using a combination of CH4 and MMS produces films with high Si content compared with those deposited using conventional C and Si sources. The Si fraction was also found to increase with a decrease in Ar flow rate under a constant MMS flow ratio. Many particles composed mainly of Si, whose size was 0.3–1 µm in diameter, were observed on the surface when deposition was carried out at MMS flow ratios of 15 and 30%. Compressive internal stress in the films decreased with the MMS flow ratio and/or with the Ar flow rate. The decrease in internal stress is probably due to the relaxation of a three-dimensional rigid network by the formation of Si–C and Si–H bonds in the films as well as Ar+ ion bombardment.

Hemocompatibility of surface-modified, silicon-incorporated, diamond-like carbon films

The hemocompatibility of plasma-treated, silicon-incorporated, diamond-like carbon (Si-DLC) films was investigated. Si-DLC films with a Si concentration of 2 at.% were prepared on Si (100) or Nitinol substrates using a capacitively coupled radiofrequency plasma-assisted chemical vapor deposition method using a mixed gas of benzene (C 6H 6) and diluted silane (SiH 4:H 2 = 10:90). The Si-DLC films were then treated with O 2, CF 4 or N 2 glow discharge for surface modification. The plasma treatment revealed an intimate relationship between the polar component of the surface energy and its hemocompatibility. All in vitro characterizations, i.e. protein absorption behavior, activated partial thromboplastin time measurement and platelet adhesion behavior, showed improved hemocompatibility of the N 2-- or O 2-plasma-treated surfaces where the polar component of the surface energy was significantly increased. Si–O or Si–N surface bonds played an important role in improving hemocompatibility, as observed in a model experiment. These results support the importance of a negatively charged polar component of the surface in inhibiting fibrinogen adsorption and platelet adhesion.

The effects of Si incorporation on the thermal and tribological properties of DLC films deposited by PBII&D with bipolar pulses

In the present study, the thermal stability and tribological properties of silicon-incorporated diamond-like carbon (DLC) films were investigated. The DLC films were deposited using a bipolar-type plasma based ion implantation and deposition (PBII&D) technique, and the Si contents in the films were varied from 0 to 29 at.%. The deposited DLC films were annealed at 500 °C for 30 min in ambient air. The structure and mechanical properties of the Si-DLC films with a high Si content (≥ 21 at.%) were not affected by the thermal annealing. The 21 at.% Si-DLC film annealed at 500 °C shows low wear as well as low friction, whereas the 29 at.% Si-DLC film exhibited a high friction due to the creation of cracks on the worn surface related to the SiC-like nature. The 11 at.% Si-DLC film annealed at 500 °C shows the lowest friction coefficient at the cost of significant wear in the graphitized film. The formation of a thick silicon oxide layer on the Si-DLC film could be favorable for low friction and wear.

Deposition of Si-DLC film and its microstructural, tribological and corrosion properties

Silicon-incorporated diamond-like carbon (Si-DLC) films were deposited using a bipolar-type plasma based ion implantation and deposition technique, and the effects of Si-incorporation on the microstructural, tribological, anti-corrosion and lubricant bonding properties of the Si-DLC films were investigated. The analysis of Raman spectroscopy exhibited that the sp3 bonds in the DLC film increase due to Si addition. XPS analysis revealed that a thick oxide layer exists on the Si-DLC film surfaces. These explain the high lubricant bonding properties of the Si-DLC films compared to that of the Si-free DLC films. The silicon oxide layer on the Si-DLC film and the transferred silicon oxide layer on the steel ball prevents from the metal/DLC contact between the Si-DLC film and steel ball when sliding, which results in a low friction. Incorporation of Si in DLC films led to significant improvements in the corrosion resistance due to low internal stress and thick insulating oxide layer.

Low-macroscopic field emission from silicon-incorporated diamond-like carbon film synthesized by dc PECVD

Silicon-incorporated diamond-like carbon (Si–DLC) films were deposited via dc plasma-enhanced chemical vapor deposition (PECVD), on glass and alumina substrates at a substrate temperature 300 °C. The precursor gas used was acetylene and for Si incorporation, tetraethyl orthosilicate dissolved in methanol was used. Si atomic percentage in the films was varied from 0% to 19.3% as measured from energy-dispersive X-ray analysis (EDX). The binding energies of C 1s, Si 2s and Si 2p were determined from X-ray photoelectron spectroscopic studies. We have observed low-macroscopic field electron emission from Si–DLC thin films deposited on glass substrates. The emission properties have been studied for a fixed anode–sample separation of 80 μm for different Si atomic percentages in the films. The turn-on field was also found to vary from 16.19 to 3.61 V/μm for a fixed anode–sample separation of 80 μm with a variation of silicon atomic percentage in the films 0% to 19.3%. The turn-on field and approximate work function are calculated and we have tried to explain the emission mechanism there from. It was found that the turn-on field and effective emission barrier were reduced by Si incorporation than undoped DLC.