Types Of Diamond-like Carbon Films Research Articles

Tribological and corrosive behavior under HCl corrosive environment of diamond-like carbon films with doped H, Cr and WC

Diamond-like carbon films exhibit low friction and strong wear resistance under various conditions. In order to evaluate tribological and corrosion resistant performance of different types of diamond-like carbon films in hydrochloric acid (HCl) environment, DLC, Cr/DLC, H/DLC and WC/DLC films were prepared by unbalanced magnetron sputtering technology. Their microstructure, mechanical properties, tribological properties and corrosion resistance were characterized and studied. The results show that the prepared DLC film exhibits the lowest wear rate in 1 M HCl solution. H/DLC film has an obvious corrosion resistance due to its high sp3 C bond and dense structure. Cr/DLC and WC/DLC films show a lower friction coefficient. In general, tribological failure of DLC film is mainly due to ordinary mechanical wear; while that of Cr/DLC film is mainly attributed to abrasive wear caused by, for example, hard particles and wear products; adhesive wear is found to be responsible for H/DLC film, which is caused by transformation of CH bond to oxygen group at the friction interface. The WC/DLC film is experienced with both local degradation and low resistance to elastic/plastic changes (H/E and H3/E2), and therefore both granular and chemical failures occurred. This study provides a complete and comprehensive understanding of tribological and anti-corrosive performance of diamond-like carbon films in hydrochloric acid environment, and can be used further as a reference for industrial applications.

Classification of DLC films for cell proliferation based on optical constants

Nine types of diamond-like carbon (DLC) films were prepared on 316L stainless steel by physical vapor deposition and chemical vapor deposition under different plasma processing conditions. The refractive index and extinction coefficient of the DLC films were evaluated with a spectroscopic ellipsometer. The DLC samples were classified into 4 types of films: a-C, a-C:H, polymer-like, and graphite-like types. In addition, the surface functions of the DLC films were analyzed by X-ray photoelectron spectroscopy and cell culture. DLC films on which high levels of cell proliferation were observed had relative high extinction coefficients and CO bond ratios. The extinction coefficient was related to cell proliferation on the DLC films and depended on the film structure and deposition methods. Using optical properties, such as the extinction coefficient, it is possible to distinguish various types of DLC films on which cells can be grown as a biointerface.

Colorful Diamond‐Like Carbon Films from Different Micro/Nanostructures

AbstractThe coloration is one kind of interesting and important properties of diamond‐like carbon (DLC) films, but lack of in‐depth study. The micro/nanostructure composition of material determines its macroscopic properties. Here, the Commission Internationale de I'Eclairage (CIE) color space, quantitative micro/nanostructure composition analysis, and ab initio molecular‐dynamics simulations are used to quantitatively analyze the generation mechanism for coloration of DLC films. It is found that as a typical amorphous thin film, the generation of DLC film coloration can be explained by the thin film interference and amorphous photonic crystal structural color theory, but the generation mechanisms of coloration for different types of DLC films are not the same. The micro/nanostructure in terms of hydrogen content and carbon atom state plays vital roles in the generation of DLC film structural colors and even determines whether the noniridescent structure color exists or not. These results demonstrate the possibility of utilizing the human eyes to directly distinguish different types of DLC films and accelerate the application of DLC film in energy saving, optical filter, sensor, color gradient coating, advanced luxury products, and bionics fields.

Morphological and Chemical Evolution of Gradually Deposited Diamond-Like Carbon Films on Polyethylene Terephthalate: From Subplantation Processes to Structural Reorganization by Intrinsic Stress Release Phenomena.

Diamond-like carbon (DLC) films on polyethylene terephthalate (PET) are nowadays intensively studied composites due to their excellent gas barrier properties and biocompatibility. Despite their applicative features being highly explored, the interface properties and structural film evolution of DLC coatings on PET during deposition processes are still sparsely investigated. In this study two different types of DLC films were gradually deposited on PET by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using acetylene plasma. The surface morphology of the deposited samples has been analyzed by atomic force microscopy (AFM). Their chemical composition was investigated by diffusive reflectance infrared Fourier transform (DRIFT) and Raman spectroscopy analysis and the surface wettability by contact angle measurements. Subplantation processes and interface effects are revealed through the morphological and chemical analysis of both types. During plasma deposition processes the increasing carbon load causes the rise of intrinsic film stress. It is proven that stress release phenomena cause the transition between polymer-like to a more cross-linked DLC network by folding dehydrogenated chains into closed 6-fold rings. These findings significantly lead to an enhanced understanding in DLC film growth mechanism by RF-PECVD processes.

Ultralow Friction of a Tetrahedral Amorphous Carbon Film Lubricated with an Environmentally Friendly Ester-Based Oil

The tribological properties of diamond-like carbon (DLC) films that were lubricated with an environmentally friendly ester-based oil were investigated. Sliding tests were performed on two types of DLC films, hydrogenated amorphous carbon (a-C:H) and tetrahedral amorphous carbon (ta-C) films, using a steel cylinder that was in contact with a steel disk coated with either a-C:H or ta-C under boundary lubrication. To compare the tribological properties of ester-based oils and other based oils, Trimethylolpropane (TMP) ester, polypropylene glycol (PPG), and poly-alpha olefin (PAO) were used as the test lubricants. The ta-C film that was lubricated with TMP ester exhibited the ultralow friction coefficient of 0.015; however, the a-C:H film that was lubricated with TMP ester did not exhibit the ultralow friction. On the other hand, results obtained by a quartz-crystal microbalance with dissipation indicated that the adsorption properties of based oils depended on the type of sensor material (carbon or iron) and the type of based oil used in the measurements. Moreover, the frequency change of based oils increased with decreases in the average frictional coefficients of the steel-steel tribopair and the DLC-steel tribopair. Results of surface analysis indicated that TMP ester formed tribofilms on the ta-C surfaces, which exhibited high viscosity and low friction. All these results suggest that the combination of the ta-C film and TMP ester is the new ultra-low-friction and environmentally friendly sliding system.

Tribological properties of a tetrahedral amorphous carbon (ta-C) film under boundary lubrication in the presence of organic friction modifiers and zinc dialkyldithiophosphate (ZDDP)

Diamond-like carbon (DLC) films provide low friction and high wear resistance under lubricated conditions. In particular, tetrahedral amorphous carbon (ta-C) film has shown ultralow friction behavior under boundary lubrication with an organic friction modifier (FM), such as glycerol mono-oleate (GMO). On the other hand, there are many studies on the tribological properties of DLC films that are lubricated with oils with added zinc dialkyldithiophosphate (ZDDP). ZDDP, however, shows quite different tribological performance, which depends on the type of DLC film. The lubrication mechanism of ZDDP against DLC films has not yet been fully clarified. This research studied the effects of ZDDP additives on the tribological properties of a ta-C film under boundary lubrication with oils that contained organic friction modifiers. The tribological properties were evaluated using the reciprocating type cylinder-on-disk tribo-tester. ZDDP and three types of organic additives (GMO, glycerol mono-oleoyl ether (GME), and tallow diethanol amine (TDEA)) were added to poly-alpha olefin (PAO). Friction tests were carried out for the DLC/DLC tribo-pair under lubrication with PAO and PAO-based oils containing GMO, GME, TDEA, ZDDP, GMO+ZDDP, GME+ZDDP, and TDEA+ZDDP additives. Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM) were used for analyses of the ta-C surface after the friction tests. The ta-C film lubricated with PAO+FMs reached an ultralow friction coefficient of 0.02–0.03. On the other hand, the films with PAO+GMO+ZDDP and PAO+GME+ZDDP had increased friction coefficients and wear volumes compared to the PAO+FMs oils. The ta-C film lubricated with PAO+TDEA+ZDDP reached an ultralow friction coefficient of 0.028. The surface analyses demonstrated that the formation rate and chemical composition of the ZDDP-derived tribofilm depended on the combination of ZDDP and each FM. It was concluded that the formation rate and chemical composition of the ZDDP-derived tribofilm played an important role in the low friction behavior of the ta-C films that were lubricated with any of the oils with added ZDDP.

Relaxation of Cs atomic polarization at surface coatings characterized by X-ray photoelectron spectroscopy

Paraffin coatings on glass slides were investigated through both X-ray photoelectron spectroscopy (XPS) and spin relaxation measurement for cesium (Cs) vapor. The components of the glass substrate, such as silicon and oxygen, existed in the XPS spectra of the coated slides, indicating the imperfection of the prepared paraffin coatings. The substrate was not observed after the annealing of the coatings in Cs vapor, which is known as a “ripening” process for spin relaxation measurement. We found a general trend that effective anti-spin relaxation performance requires high paraffin and low Cs coverage on the surface. We also examined a type of diamond-like carbon film, anticipating the effect of anti-spin relaxation; our attempts have failed to date.

The healing effect of stearic acid applied on amorphous carbon film with dispersed nanodiamonds

Diamond-like carbon (DLC) films have been shown to improve the friction and wear properties of applications with severe loads. Hydrogenated amorphous carbon films (a-C:H), a type of DLC film, were coated onto 440C stainless steel disk surfaces. The plasma enhanced chemical vapour deposition method was used as a coating process, and nanodiamond (ND) particles were dispersed into the film during the deposition process. Stearic acid was expected to affect the lubricating properties of the film because of its reported effectiveness on diamond surfaces. A lubricated reciprocal sliding friction test with 10,000 cycles confirmed that stearic acid improved the friction and wear properties of the ND dispersed a-C:H film. Furthermore, film wear caused by a sliding test without stearic acid could be healed by sliding with stearic acid as long as the level of critical damage was not reached. Raman spectra for the worn tracks revealed the healing effect of the stearic acid on the film because the spectra for the worn tracks after 10,000 cycles were identical to those of the control film, which was not worn. In contrast, the spectra for the worn tracks or debris showed a broad D band peak and no G peak, which was consistent with disordered amorphous carbon.

Deposition of amorphous carbon films from C 60 fullerene sublimated in electron beam excited plasma

C 60 fullerene clusters are used as a carbon source for amorphous carbon films deposition in an electron beam excited plasma. C 60 clusters are sublimated by heating a ceramic crucible containing the C 60 powders up to 850 °C, which is located in a highly vacuumed process chamber. The sublimated fullerene powders are injected to the electron beam excited argon plasma and dissociated to be active species that are propelled toward the substrates. Consequently, the carbon species condense as a thin film onto the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 μm/h and the average surface roughness of 0.2 nm over an area of 400 μm 2 are achieved. Decomposition of the C 60 fullerene after injecting into the plasma is confirmed by optical emission spectroscopy that shows existence of small carbon species such as C 2 in the plasma. X-ray diffraction pattern reveals that the microstructure of the film is amorphous, while fullerene films deposited without the plasma show crystalline structure. Raman spectroscopic analysis shows that the films deposited in the plasma are one of the types of diamond-like carbon films. Different negative bias voltages have been applied to the substrate holder to examine the effect of the bias voltage to the properties of the films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 28 GPa. In addition, the films are droplet-free and show superior lubricity.

電子ビーム励起プラズマ中でのＣ６０フラーレン昇華によるアモルファスカーボン膜の作製

C60 fullerene is used as a carbon source for amorphous carbon film deposition in an electron beam excited plasma. C60 powders are sublimated by heating up to 850°C in a highly vacuumed process chamber. The sublimated C60 is injected to the electron beam excited argon plasma and dissociated to be active species that diffuse toward the substrates. Different negative bias voltages have been applied to the substrate holder to examine the effect of the bias voltage to the properties of the films. Consequently, the carbon species condense as a thin film onto the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 μm/h and the average surface roughness of 0.2 nm are achieved. Decomposition of the C60 fullerene after injecting into the plasma is confirmed by optical emission spectroscopy that shows existence of small carbon species such as C2 in the plasma. X-ray diffraction pattern reveals that the microstructure of the film is amorphous, while fullerene film deposited without the plasma shows crystalline structure. Raman spectroscopic analysis shows that the films are one of the types of diamond-like carbon films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 28 GPa.

Atomistic Insights into the Running-in, Lubrication, and Failure of Hydrogenated Diamond-Like Carbon Coatings

The tribological performance of hydrogenated diamond-like carbon (DLC) coatings is studied by molecular dynamics simulations employing a screened reactive bond-order potential that has been adjusted to reliably describe bond-breaking under shear. Two types of DLC films are grown by CH2 deposition on an amorphous substrate with 45 and 60 eV impact energy resulting in 45 and 30% H content as well as 50 and 30% sp3 hybridization of the final films, respectively. By combining two equivalent realizations for both impact energies, a hydrogen-depleted and a hydrogen-rich tribo-contact is formed and studied for a realistic sliding speed of 20 m s−1 and loads of 1 and 5 GPa. While the hydrogen-rich system shows a pronounced drop of the friction coefficient for both loads, the hydrogen-depleted system exhibits such kind of running-in for 1 GPa, only. Chemical passivation of the DLC/DLC interface explains this running-in behavior. Fluctuations in the friction coefficient occurring at the higher load can be traced back to a cold welding of the DLC/DLC tribo-surfaces, leading to the formation of a transfer film (transferred from one DLC partner to the other) and the establishment of a new tribo-interface with a low friction coefficient. The presence of a hexadecane lubricant leads to low friction coefficients without any running-in for low loads. At 10 GPa load, the lubricant starts to degenerate resulting in enhanced friction.

Deposition of unhydrogenated amorphous carbon films by sublimation of C 60 fullerene in electron beam excited plasma

C 60 fullerene clusters are used as a carbon source to deposit unhydrogenated amorphous carbon films. C 60 clusters are sublimated by heating up to 850 °C. The sublimated fullerene powders are injected to an electron beam excited argon plasma and dissociated to be active species. Consequently, the carbon species condense as a thin film on the negatively biased substrates that are immersed in the plasma. Deposition rates of approximately 1.0 µm/h and the average surface roughness of 0.2 nm are achieved. X-ray diffraction pattern reveals that the microstructure of the film is amorphous while fullerene film deposited without the plasma shows crystal structure. Raman spectroscopic analysis shows that the films are one of the types of diamond-like carbon films. The nano-indentation technique is used for hardness measurement of the films and results in hardness up to about 20 GPa.

Diamond-like carbon: state of the art

Abstract Diamond-like carbon films, amorphous hydrogenated or non-hydrogenated forms of carbon, are metastable amorphous materials characterized by attractive mechanical, optical, electrical, chemical and tribological properties. The films can be prepared at low temperatures by different techniques using a large variety of precursors and can be modified by incorporation of different elements such as N, F, Si or metals. The diversity of methods used for the deposition of diamond-like carbon films provides the flexibility to tailor their properties according to specific needs and potential applications. The hydrogenated form of DLC appears to reach a maturity in understanding its properties and finding old and new practical applications for it. The non-hydrogenated diamond-like carbon, or tetrahedral carbon, is at a much younger state of preparation and characterization and practical applications have yet to be proven. The paper will review the state of the art of the preparation of the different types of diamond-like carbon films, the characterization and understanding of their properties, and their practical applications.