Search Results (27)

Copper-doped hydrogenated amorphous carbon (Cu-doped a-C:H) films were synthesized using copper as the cathode and C₂H₂ as the precursor. The result shows that the negative bias voltage can affect the composition and microstructure of nanocomposite films. With bias voltage increasing, Cu content first increases in the range of 50~300 V and then declines with higher voltage, while the deposition rate decreases continuously. The stress and sp³ content present a similar trend with the bias voltage, increasing during the range from 50 V to 200 V and then decreasing with higher voltage. Full article

Hydrogenated amorphous carbon (a-C:H) has been considered a promising biocompatible coating to protect metallic alloys against corrosion for medical applications, namely orthodontics. However, there is still no optimal solution for this biomedical field; hence, the investigation remains open. In this work, the effect of a nonmetallic doping element (N) on sputter-deposited a-C:H coatings was studied concerning both salivary corrosion and cytotoxicity behavior. After a 30-day corrosion test in an acidic modified Fusayama-Meyer artificial saliva, metal release from both coated and uncoated 316L stainless steel (SS) substrates was quantified. Tests on the corrosion extracts were then performed by using monocultures of macrophages and fibroblasts, and their coculture; and cell viability was evaluated via the MTT test. Results show an overall inhibition of the SS corrosion, which enhanced the in vitro biocompatibility with a minimal effect on the coatings’ microstructure. Among all the coatings tested, the undoped a-C:H coating performed the best, whereas an increase in N doping led to poorer protection against metal dissolution and a subsequent slightly lower biocompatibility. The findings corroborate that selecting the nonmetallic element N for doping C-based coatings is not a good choice for this biomedical field, even at low contents up to 10 at.%. Full article

Amorphous carbon is recognized as an excellent lubricating material; however, its tribological properties are significantly influenced by humidity. To elucidate the mechanism underlying this humidity dependence and to propose a novel enhancement method, we investigated and compared the tribological properties of hydrogenated amorphous carbon (a-C:H) and amorphous carbon/gold (a-C/Au) composite films. First, the friction coefficient of these carbon films under different humidity conditions was tested using a rotational ball-on-disk tribometer. Subsequently, we analyzed the morphology and structure of the sliding interface employing optical microscopy (OM), Raman spectroscopy, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Finally, first-principle calculations were carried out to calculate the adsorption energy of water molecules on different surfaces. The results indicate that the friction coefficient of a-C:H film and the area of transfer film increase with the increase of humidity. This phenomenon can be attributed to the fact that water molecules enhance the interaction between the a-C:H film and steel counterfaces. Notably, in contrast, the friction coefficient of a-C/Au film demonstrates low sensitivity to humidity due to the formation of an Au transfer film that exhibits weak interaction with water molecules. These findings provide a promising strategy for developing environment-adaptive amorphous carbon films and play an important role in promoting the development of intelligent lubricating film. Full article

Sulfuric acid is a concern for contacts within electronic devices, and the application of amorphous carbon films as thin electrical insulating coatings for small coils requires full investigation of its effects. Five types of amorphous carbon films were fabricated on Si substrates under different deposition conditions using vacuum coating systems. Based on their optical constants (ISO 23216:2021(E)), the films were classified into three types: hydrogenated amorphous carbon (a-C:H), polymer-like carbon (PLC), and graphite-like carbon (GLC). The structure, surface composition, and electrical insulation properties of the films were evaluated before and after immersion in sulfuric acid. Although the PLC and a-C:H showed progression of surface oxidation due to sulfuric acid immersion, none showed obvious changes in their structure or DC dielectric breakdown field strength due to sulfuric acid immersion, proving their stability. Furthermore, the PLC and a-C:H, which had a relatively low extinction coefficient, exhibited excellent insulation properties. Our results suggest that amorphous carbon films can be useful as thin insulating films for small coils that may come in contact with sulfuric acid. Our study offers a valuable tool for general users in the industry to facilitate selection of electrical insulating amorphous carbon films based on optical constants, such as extinction coefficients. Full article

Silver-based antibacterial coatings limit the spread of hospital-acquired infections. Indeed, the use of silver and silver oxide nanoparticles (Ag and AgO NPs) incorporated in amorphous hydrogenated carbon (a-C:H) as a matrix demonstrates a promising approach to reduce microbial contamination on environmental surfaces. However, its success as an antibacterial coating hinges on the control of Ag⁺ release. In this sense, if a continuous release is required, an additional barrier is needed to extend the release time of Ag⁺. Thus, this research investigated the use of a plasma fluoropolymer (CF_x) as an additional top layer to elongate Ag⁺ release and increase the antibacterial activity due to its high hydrophobic nature. Herein, a porous CF_x film was deposited on a-C:H containing Ag and AgO NPs using pulsed afterglow low pressure plasma polymerization. The chemical composition, surface wettability and morphology, release profile, and antibacterial activity were analyzed. Overall, the combination of a-C:H:Ag (12.1 at. % of Ag) and CF_x film (120.0°, F/C = 0.8) successfully inactivated 88% of E. coli and delayed biofilm formation after 12 h. Thus, using a hybrid approach composed of Ag NPs and a hydrophobic polymeric layer, it was possible to increase the overall antibacterial activity of the coating. Full article

Hydrogenated amorphous carbon (a-C:H) films were deposited on the sidewall of 3-mm-wide stainless steel or Si trench, and the adhesion strength of the films was evaluated using a micro-scratch tester. Particularly, the effects of carbon ion implantation and Si-containing interlayer (a-SiCx:H) as the pretreatments on the adhesion strength of the a-C:H films prepared on the trench sidewall were investigated. It was found that both carbon ion implantation and interlayer improved the adhesion strength of the a-C:H films deposited on the trench sidewalls. In addition, the carbon ion implantation dominated the adhesion strength of the a-C:H films for the Si substrates, and the interlayer for the stainless steel substrates. In the case of the stainless steel substrates, the carbon was accumulated on the surface of the trench sidewall instead of implantation, whereas the carbon ions were implanted to the Si substrates on the trench sidewall to form a mixing layer. The a-SiCx:H interlayer forms Fe–Si bonds between the stainless steel substrate and the interlayer, which is thought to improve the adhesion strength. It was also found that there is a negative correlation between the trench depth and the adhesion strength regardless of the pretreatment methods. Full article

A single beam plasma source was used to deposit hydrogenated amorphous carbon (a-C:H) coatings at room temperature. Using methane source gas, a-C:H coatings were deposited at different radio frequency (RF) power to fabricate transparent and durable coatings. The film deposition rate was almost linearly proportional to the ion source power. Hydrogenated amorphous carbon films of ~100 nm thickness appeared to be highly transparent from UV to the infrared range with a transmittance of ~90% and optical bandgap of ~3.7 eV. The coatings also possess desirable mechanical properties with Young’s modulus of ~78 GPa and density of ~1.9 g/cm³. The combined material properties of high transmittance and high durability make the ion-source-deposited a-C:H coatings attractive for many applications. Full article

Polycarbonate (PC) is a material that is used in many areas: automotive, aerospace engineering and data storage industries. Its hardness is of particular importance, but some applications are affected by its low wettability or scratch susceptibility. This can be changed either by blending with other polymers, or by surface modifications, such as the application of an amorphous hydrogenated carbon layer (a-C:H). In this study, individual a-C:H layers of different thicknesses (10–2000 nm) were deposited on PC by RF PECVD. Both the layer morphology with AFM and SEM and the bonding states of the carbon on the surface with synchrotron-assisted XPS and NEXAFS were studied. The aim was to investigate the coatability of PC and the stability of the a-C:H. Special attention was paid to the interlayer region from 0 to 100 nm, since this is responsible for the layer to base material bonding, and to the zone of dehydrogenation (from about 1000 nm), since this changes the surface composition considerably. For PC, the interlayer was relatively small with a thickness of only 20 nm. Additionally, a correlation was found between the evolving grain structure and the development of the C?H peak according to NEXAFS C K-edge measurements. Full article

Hydrogenated amorphous carbon (a-C:H) coatings are attractive materials for protecting metallic surfaces in extreme biological environments like the human oral cavity, due to the unusual combination of mechanical properties, superior bioinertness, and relative easier and cheaper production. In this work, two a-C:H coatings were deposited on AISI 316L substrates by reactive magnetron sputtering with two CH₄ flows to assess if this outstanding system could extend its application range to orthodontics. A 30-day immersion test in Fusayama-Meyer artificial saliva was conducted to mimic an extreme acidic intraoral pH. Extracts were quantified and used to perform in vitro assays with mono- and co-cultures of macrophages and fibroblast to assess cell viability, while mechanical and structural behaviors were studied by nanoindentation and visible Raman. The empirically estimated H contents of ~28 and 40 at.% matched the hard and soft a-C:H coating regimes of 18 and 7 GPa, respectively. After immersion, no important structural/mechanical modifications occurred, regardless of the H content, without corrosion signs, delamination, or coating detachment. However, the adhesion-promoting Cr-based interlayer seems to reduce corrosion resistance via galvanic coupling. The highest biocompatibility was found for a-C:H coatings with the lowest H content. This study indicates that sputtered a-C:H are promising surface materials in orthodontics. Full article

Diamond-like carbon (DLC) coatings have the potential to reduce implant wear and thus to contribute to avoiding premature failure and increase service life of total knee replacements (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt–chromium–molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While a detailed characterization of the tribological behavior is the subject of part II, part I focusses on the deposition of pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coatings (a-C:H:W) and the detailed characterization of their chemical, cytological, mechanical and adhesion behavior. The coatings are fabricated by physical vapor deposition (PVD) and display typical DLC morphology and composition, as verified by focused ion beam scanning electron microscopy and Raman spectroscopy. Their roughness is higher than that of the plain substrates. Initial screening with contact angle and surface tension as well as in vitro testing by indirect and direct application indicate favorable cytocompatibility. The DLC coatings feature excellent mechanical properties with a substantial enhancement of indentation hardness and elastic modulus ratios. The adhesion of the coatings as determined in modified scratch tests can be considered as sufficient for the use in TKAs. Full article

Polyamide 6 (PA6) is a commonly used material in many different sectors of modern industry. Herein, PA6 samples were coated with amorphous carbon layers (a-C:H) with increasing thickness up to 2 µm using radio frequency plasma enhanced chemical vapor deposition for surface adjustment. The morphology of the carbon coatings was inspected by ex situ atomic force microscopy and scanning electron microscopy. Surface wettability was checked by contact angle measurements. The chemical composition was analyzed using the surface sensitive synchrotron X-ray-based techniques near-edge X-ray absorption fine structure and X-ray photoelectron spectroscopy, supported by diffuse reflectance infrared Fourier transform spectroscopy. Particular attention was paid to the coating interval from 0 to 100 nm, to specify the interlayer thickness between the PA6 polymer and a-C:H coating, and the region between 1000 and 2000 nm, where dehydrogenation of the a-C:H layer occurs. The interlayer is decisive for the linkage of the deposited carbon layer on the polymer: the more pronounced it is, the better the adhesion. The thickness of the interlayer could be narrowed down to 40 nm in all used methods, and the dehydrogenation process takes place at a layer thickness of 1500 nm. Full article

Diamond-like carbon coatings may decrease implant wear, therefore, they are helping to reduce aseptic loosening and increase service life of total knee arthroplasties (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While the deposition of a pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coating (a-C:H:W) as well as the detailed characterization of mechanical and adhesion properties were the subject of Part I, the tribological behavior is studied in Part II. Pin-on-disk tests are performed under artificial synovial fluid lubrication. Numerical elastohydrodynamic lubrication modeling is used to show the representability of contact conditions for TKAs and to assess the influence of coatings on lubrication conditions. The wear behavior is characterized by means of light and laser scanning microscopy, Raman spectroscopy, scanning electron microscopy and particle analyses. Although the coating leads to an increase in friction due to the considerably higher roughness, especially the UHMWPE wear is significantly reduced up to a factor of 49% (CoCr) and 77% (Ti64). Thereby, the coating shows continuous wear and no sudden failure or spallation of larger wear particles. This demonstrated the great potential of amorphous carbon coatings for knee replacements. Full article

The sp²-rich hydrogenated amorphous carbon (a-C:H) is widely adopted as hard masks in semiconductor-device fabrication processes. The ion-enhanced etch characteristics of sp²-rich a-C:H films on ion density and ion energy were investigated in CF₄ plasmas and O₂ plasmas in this work. The etch rate of sp²-rich a-C:H films in O₂ plasmas increased linearly with ion density when no bias power was applied, while the fluorocarbon deposition was observed in CF₄ plasmas instead of etching without bias power. The etch rate was found to be dependent on the half-order curve of ion energy in both CF₄ plasmas and O₂ plasmas when bias power was applied. An ion-enhanced etching model was suggested to fit the etch rates of a-C:H in CF₄ plasmas and O₂ plasmas. Then, the etch yield and the threshold energy for etching were determined based on this model from experimental etch rates in CF₄ plasma and O₂ plasma. The etch yield of 3.45 was observed in CF₄ plasmas, while 12.3 was obtained in O₂ plasmas, owing to the high reactivity of O radicals with carbon atoms. The threshold energy of 12 eV for a-C:H etching was obtained in O₂ plasmas, while the high threshold energy of 156 eV was observed in CF₄ plasmas. This high threshold energy is attributed to the formation of a fluorocarbon layer that protects the a-C:H films from ion-enhanced etching. Full article

Anti-adhesion characteristics are important requirements for diamond-like carbon (DLC) films. The failure load corresponding to the anti-adhesion capacity varies greatly on three types of DLC film (hydrogen-free amorphous carbon film (a-C), hydrogenated amorphous carbon film (a-C:H), and tetrahedral hydrogen-free amorphous carbon film (ta-C)) in the friction and wear test with step loading using a high-frequency, linear-oscillation tribometer. Therefore, a new method that estimates a representative value of the failure load was developed in this study by performing a statistical analysis based on the Weibull distribution based on the assumption that the mechanism of delamination of a DLC film obeys the weakest link model. The failure load at the cumulative failure probabilities of 10% and 50% increased in the order ta-C < a-C:H < a-C and ta-C < a-C < a-C:H, respectively. The variation of the failure load, represented by the Weibull slope, was minimum on ta-C and maximum on a-C:H. The rank of the anti-adhesion capacity of each DLC film with respect to the load obtained by a constant load test agreed with the rank of the failure load on each DLC film at the cumulative failure probability of 10% obtained by Weibull analysis. It was found to be possible to evaluate the anti-adhesion capacity of a DLC film under more practical conditions by combining the step loading test and Weibull analysis. Full article

Hydrogenated amorphous carbon (a-C:H) films have optical and electrical properties that vary widely depending on deposition conditions; however, the electrical conduction mechanism, which is dependent on the film structure, has not yet been fully revealed. To understand the relationship between the film structure and electrical conduction mechanism, three types of a-C:H films were prepared and their film structures and electrical properties were evaluated. The sp²/(sp² + sp³) ratios were measured by a near-edge X-ray absorption fine structure technique. From the conductivity–temperature relationship, variable-range hopping (VRH) conduction was shown to be the dominant conduction mechanism at low temperatures, and the electrical conduction mechanism changed at a transition temperature from VRH conduction to thermally activated band conduction. On the basis of structural analyses, a model of the microstructure of a-C:H that consists of sp² and sp³-bonded carbon clusters, hydrogen atoms and dangling bonds was built. Furthermore, it is explained how several electrical conduction parameters are affected by the carrier transportation path among the clusters. Full article