Surface Of Diamond-like Carbon Films Research Articles

Effect of H 2 and O 2 plasma etching treatment on the surface of diamond-like carbon thin film

In this study, we investigated the surface properties of diamond-like carbon (DLC) films for biomedical applications through plasma etching treatment using oxygen (O 2) and hydrogen (H 2) gas. The synthesis and post-plasma etching treatment of DLC films were carried out by 13.56 MHz RF plasma enhanced chemical vapor deposition (PECVD) system. In order to characterize the surface of DLC films, they were etched to a thickness of approximately 100 nm and were compared with an as-deposited DLC film. We obtained the optimum condition through power variation, at which the etching rate by H 2 and O 2 was 30 and 80 nm/min, respectively. The structural and chemical properties of these thin films after the plasma etching treatment were evaluated by Raman and Fourier transform infrared (FT-IR) spectroscopy. In the case of as-deposited and H 2 plasma etching-treated DLC film, the contact angle was 86.4° and 83.7°, respectively, whereas it was reduced to 35.5° in the etching-treated DLC film in O 2 plasma. The surface roughness of plasma etching-treated DLC with H 2 or O 2 was maintained smooth at 0.1 nm. These results indicated that the surface of the etching-treated DLC film in O 2 plasma was hydrophilic as well as smooth.

Boundary Lubrication Characteristic of Metal-Containing Diamond-Like Carbon (DLC) Films with Poly Alpha Olefin (PAO) Lubricant

The effects of metals such as cobalt (Co), cerium (Ce), magnesium (Mg), nickel (Ni) and titanium (Ti) added to diamond-like carbon (DLC) films on boundary lubrication properties were investigated using a ball-on disk tribometer. The boundary lubrication properties of metal-containing DLC films are improved compared with those of DLC films without metal under poly alpha olefin (PAO) lubricant with and without glycerol mono-oleate (GMO) additives. Moreover, under boundary lubrication using PAO with GMO, DLC films with an appropriate quantity of Co-added show the lowest friction coefficient of μ= 0.02 among all the tested metal-containing DLC films. The friction product layers were formed on the sliding surface of Co-containing DLC films. Lower-nanofriction layers formed on the sliding surface were observed by force modulation methods of atomic force microscopy (AFM).

Influence of sulfidation treatment on the structure and tribological properties of nitrogen-doped diamond-like carbon films

The nitrogen-doped diamond-like carbon (DLC) films were deposited on high speed steel (HSS) substrates in the direct current unbalanced magnetron sputtering system. Sulphurized layer was formed on the surface of DLC films by means of liquid sulfidation in the intermixture of urea and thiourea solution in order to improve the tribological properties of DLC films. The influence of sulfidation treatment on the structure and tribological properties of DLC films was investigated in this work. The structure and wear surface morphology of DLC films were analyzed by Raman spectroscopy, XPS and SEM, respectively. It reveals that the treated films are smooth and uniform; and sulfur atoms are bonded chemically. The treated films have broader distribution of Raman spectra in the range of 1000–1800 cm −1 and higher I D/ I G ratio than the untreated films as a result of the appearance of the crystalline graphite structure after the sulfidation treatment. It is showed that the sp 2 relative content increase in the treated films from the XPS measurement. The Raman results are consistent with the XPS results. The tribological properties of DLC films were investigated using a ball-on-disk rotating friction and wear tester under dry friction conditions. It is found that the sulfidation concentration plays an important part in the tribological properties of the treated DLC films. The results showed the treated films with low sulfidation concentration have a lower friction coefficient (0.1) than the treated films with high sulfidation concentration (0.26) and the untreated films (0.27) under the same friction testing conditions, which can be attributed to both the presence of sulfur-containing materials and the forming of the mechanical alloyed layer on the wear surface. Adding the dry nitrogen to the sliding surface in the testing system helps the friction coefficient of the treated films with low sulfidation concentration to decrease to 0.04 further in this work. On the basis of the experimental results, it is indicated that the liquid sulfidation technique, which is low-cost, non-polluting and convenience, would be an appropriate method for the surface treatment of DLC films.

Platinum-coated probes sliding at up to100 mm s−1 against coated silicon wafers for AFM probe-based recording technology

One of the new alternative information storage technologies being researched is based onthe probe-based recording technique. In one technique, a phase-change medium is used, andthe phase change is accomplished by applying either a high or low magnitude ofcurrent which heats the interface to different temperatures. Tip wear is a seriousconcern. For wear protection of the phase-change chalcogenide medium with asilicon substrate, diamond-like carbon (DLC) film with various lubricant overcoatswas deposited on the recording layer surface. Nanowear properties of platinum(Pt)-coated probes with high electrical conductivity have been investigated in slidingagainst the coated medium using an atomic force microscope (AFM). A silicongrating sample and software to deconvolute tip shape were used to characterize thechange in the tip shape and evaluate the tip radius and its wear volume. Thenanowear experiments were performed at sliding velocities ranging from 0.1 to100 mm s−1. Pt-coated tips on the lubricant-coated DLC film surfaces showed lesssensitivity to the velocity and the load as compared to the unlubricated DLCfilm surfaces. In wear life threshold experiments, the threshold reaches asmaller sliding distance at higher loads. In high-temperature experiments at80 °C, the wear rate is higher compared to that at20 °C. The results suggest that the wear mechanism at low velocity appears to be primarilyadhesive and abrasive. At high velocity, an additional wear mechanism of the tribochemicalreaction is important.

Surface adsorption and wetting properties of amorphous diamond-like carbon thin films for biomedical applications

Diamond-like carbon (DLC) thin films have unique properties for biological and medical applications due to their excellent bio-compatibility, chemical inertness, and superior mechanical properties. It is important to understand the surface properties of DLC thin films for these applications. In this work, we showed that after DLC deposition, NiTi surfaces became much smoother by choosing suitable deposition conditions. Adsorption and wetting properties of DLC films were studied. The adsorption properties of DLC films were unusual in that a hysteresis was found in the adsorption/desorption isotherms, which cannot be interpreted using the conventional theory of capillary condensation in pores. The model proposed in this work for this unusual hysteresis characteristic is that the hysteresis results from the non-wetting property of DLC surfaces in the nano-scale. The nano-sized droplets formed on the DLC surfaces may require significantly higher energy to evaporate than the formation energy. Argon plasma treatment resulted in a small decrease of the contact angles. After oxygen plasma treatment, the wetting contact angles reduced significantly due to the increase of carbon–oxygen sites on the surfaces, suggesting that the low concentration of carbon–oxygen sites on the surfaces of DLC films contributed to the adsorption hysteresis observed in this work.

Friction-induced physical and chemical interactions among diamond-like carbon film, steel ball and water and/or oxygen molecules

Friction and wear behaviors of diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig at different relative humidity (RH) in a nitrogen environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), while the chemical states of some typical elements on the worn surface of DLC film were investigated by means of X-ray photoelectron spectroscopy (XPS). The result showed that the DLC film recorded continuously increased friction coefficient and wear rate with increasing relative humidity from 5% to 100%. In dry nitrogen (RH < 5%), thick and compact transferred carbon-rich layer was observed covering on the worn surface of steel ball, while the chemical states of the original and worn film surface showed no obvious change. In humid nitrogen, distinct changes of the chemical states on the worn surface of DLC film took place, indicating that tribochemical reactions such as the oxidation of DLC film and the interactions between DLC film and steel ball were involved in the friction process. Therefore, it was proposed that the friction and wear behaviors of DLC film were dependent on the friction-induced physical and chemical interactions among DLC film, steel ball and water and/or oxygen molecules. The roles of environment in the friction and wear behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions.

Tribological behavior of nano-undulated surface of diamond-like carbon films

Tribological behavior of nano-undulated diamond-like carbon (DLC) films of the surface roughness ranging from 0.6 to 13.7 nm was investigated in an ambient air of 50% relative humidity. The nano-undulated DLC films were prepared by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) using nanosized Ni dots on a Si (100) substrate. The friction coefficient between the DLC film and the steel ball was characterized by a ball-on-disk type wear rig. Auger and Raman spectroscopy analysis of the debris revealed that the tribochemical reaction with environment was significantly suppressed as the surface roughness increased. Even if the rough surface increased the wear rate of the steel ball and thus the concentration of Fe in the debris, neither the oxidation of Fe nor the graphitization of the carbon in the debris occurred on the rough surface. However, the frictional behavior was affected by several factors: the composition and the size of debris, plowing effect of the rough surface, and the presence of the transfer layer on the wear scar surface.

Thermal shock effect on diamond-like carbon thin films induced by pulsed-laser

When high power laser irradiates the infrared imaging system, the system will be injured or destroyed. The damage to the systems varies for different laser wavelengths. The infrared windows are generally coated with diamond-like carbon(DLC) thin films to protect itself and improve the permeation rate. When the incid ent laser's wavelength lies outside the infrared system response wave band, lase r destroys the DLC films firstly. The DLC films' damage mechanism induced by pul sed laser is studied with the 1.06μm laser. The thermal shock effect model of D LC films is proposed. The temperature and stress distributions are deduced throu gh solving the thermal conduction equation and stress-balance equation. The theo retical analysis shows that thermal stress fracture dominants in the damage mech anism. When the irradiation energy density is E0=100mJ·cm-2 , the pressu re on the surface of DLC films at about 40μm from the center of laser facula ex ceeds the rupture intensity, the film will break and peel off. The theoretical a nalysis matches the experimental results basically, and the correctness of the t hermal shock effect model is confirmed.

Friction behaviors of hydrogenated diamond-like carbon film in different environment sliding against steel ball

Friction behaviors of hydrogenated diamond-like carbon (DLC) film sliding against steel ball were investigated on a ball-on-disk test rig in different environment. The worn surface morphology of the steel ball was observed on a scanning electron microscope (SEM), and the chemical states of some typical elements on the worn surface of DLC film were investigated by means of X-ray photoelectron spectroscopy (XPS). The result showed that the friction behaviors of hydrogenated DLC film were very sensitive to the testing environment. In dry N 2, the film provided a much low and stable friction coefficient of about 0.035. When the friction tests were performed in higher relative humidity and in dry O 2, higher and unstable friction coefficient of more than 0.2 was obtained. It was found that in oxygen and/or water containing environments, the transferred carbon-rich layer on the counterpart steel ball was inhibited, and the friction-induced oxidation of the DLC film surface and the chemical reactions between the DLC film and steel ball were involved in the friction processes, which accounted for the higher friction coefficient of the DLC film. The roles of environment in the friction behaviors of DLC film were discussed in terms of the friction-induced physical and chemical interactions among the DLC film, steel ball and water and/or oxygen molecules.

Fractional Coverage Model for the Adsorption and Removal of Gas Species and Application to Superlow Friction Diamond-Like Carbon

The frictional behavior of diamond-like carbon (DLC) films varies with environmental condition. One theory asserts that the cause of variations in the frictional performance is environmental contaminants adsorbing onto the DLC film surface. Testing of the frictional performance of DLC films in a pin-on-disk contact has mapped the transient behavior of the friction coefficient. A model for fractional coverage, based on the adsorption of environmental contaminants and their removal through the pin contact, is developed. The rate of adsorption is taken from Langmuir’s model [17], which is combined with the removal ratio from Blanchet and Sawyer [18]. The coefficient of friction is based on the average fractional coverage under the pin contact. The model also gives a closed-form expression for the steady-state fractional coverage. Model calculations compared favorably to the time progression of the friction coefficient for a series of earlier experiments on a superlow friction DLC coating [7], when the fractional removal term was allowed to increase with increasing sliding speed.

微細表面制御DLC膜のナノスケール摩擦特性(J23-1 マイクロナノ理工学(1),J23 マイクロナノ理工学)

It is known that the optimum surface roughness is capable of reducing lateral force. In this paper, the frictional properties of the diamond-like carbon (DLC) films with the periodic structures were investigated in nano-scale using a scanning probe microscope (SPM). DLC films were prepared by an unbalanced magnetron sputtering method. The periodic structures have been generated on the surface of DLC films by polarized femtosecond laser (τ=40fs, λ=800nm, F=10Hz) of energies nearby ablasion threshold. The influence of normal load and relative humidity on the lateral forces were confirmed by the SPM. We used a silicon nitride rectangular cantilever with sharpened pyramidal tip or a sperical glass tip. Using the sharpened pyramidal tip, the lateral force of the DLC film with the periodic structures was higher than that of the film without the periodic structures. On the other hand, the lateral force of the DLC film with the periodic structures was lower than that of the film without the periodic structures using a sperical glass tip at low normal load and low relative humidity.

Deposition of diamond-like carbon films by plasma source ion implantation with superposed pulse

Diamond-like carbon (DLC) films were prepared on silicon wafer substrate by plasma source ion implantation with superposed negative pulse. Methane and acetylene gases were used as working gases for plasma. A negative DC voltage and a negative pulse voltage were superposed and applied to the substrate holder. The DC voltage was changed in the range from 0 to −4 kV and the pulse voltage was changed from 0 to −18 kV. The surface of DLC films was very smooth. The deposition rate of DLC films increased with increasing in superposed DC bias voltage. Carbon ion implantation was confirmed for the DLC film deposited from methane plasma with high pulse voltage. I D/ I G ratios of Raman spectroscopy were around 1.5 independent on pulse voltage. The maximum hardness of 20.3 GPa was observed for the film prepared with high DC and high pulse voltage.

T字状フィルタードアーク蒸着装置によるゴム表面への柔軟性DLC膜形成

T-shape filtered arc deposition (T-FAD) is specially designed for removing melted and un-melted macrodroplets from cathodic arc plasma and shows a superior ability to prepare droplet-free thin solid films. Furthermore, T-FAD has a feature that the film formation is done mostly by ions, since the plasma transported magnetically in T-FAD system is ionized nearly 100%. In the present study, by using T-FAD system with graphite cathode, carbon film was deposited on various rubbers. The film was verified as diamond-like carbon (DLC) by Raman spectroscopy. The DLC film was adhered well to the rubber and was not peeled off when the rubber was bended and stretched. The surface morphology, coefficient of friction, and adherence of the prepared DLC film were investigated. The surface of DLC film on rubber was not flat and has random texture structure. The coefficient of friction was lower than 0.2 in most cases. In pulling-off test (JIS K 6256) for adherence evaluation, some rubbers were broken without exfoliation of the DLC film, and the DLC films on other rubbers were peeled off at 1.3-kN/m load.

イオン化蒸着法によるシリコン化合物系傾斜組成薄膜の形成とＤＬＣ中間層への適用

A compositionally graded film (type-G film) that had Si-rich composition near a substrate of Si or Ti alloy and C-rich composition near the surface and a Si-rich monolithic film (type-S film) were prepared by the ionization deposition method using hexamethyldisiloxane and benzene as raw materials. Diamond-like carbon (DLC) films were deposited successively on to the type-G film, type-S film and the substrate directly. These are denoted in this paper as DLC/G, DLC/S and single-DLC, respectively. There was no difference among their Raman spectra, which suggested that existence of the intermediate layers, type-G and type-S films, did not affect the bonding structure of the DLC film surface. The hardness of DLC/G was 30 GPa, being about as high as that of single-DLC (33 GPa). The type-G film was about 1.4 times harder than the type-S film. X-ray photoelectron spectroscopic analysis revealed that a fairly large amount of SiC and graphite components existed on the surface of the type-G film, which increased the film hardness. In the scratching test, the critical load of DLC/G was 3 or more times grater than that of the single-DLC film, and was 1.2 or more times that of the DLC/S. The scratched mark on DLC/G was clearly different from those of other DLC films. The type-G film was proven to be effective as an intermediate layer in obtaining good adhesion between the DLC film and the substrate.

308 水素含有量の異なる DLC 膜の摩擦摩耗特性

DLC (Diamond-like carbon) films have attractive properties that make it a good candidate for a wide range of critical engineering applications. DLC films with different hydrogen contents were deposited using plasma CVD and ion beam deposition methods with different raw materials. The effect of humidity on friction of DLC films differed depending on hydrogen contents, sliding speed, and normal load. The wear of DLC films in dry air was larger than that in humid air. The features of wear surfaces of DLC films varied by changing sliding conditions.

Study of the surface of diamondlike carbon films doped with copper

A study of the surface of copper-doped diamondlike carbon films by the methods of scanning tunneling microscopy and spectroscopy is reported. It is found that the introduction of copper modifes both the microstructure and the electronic properties of the films.

Friction induced phase transformation of pulsed laser deposited diamond-like carbon

Structural transformations in the sliding friction of hydrogen-free diamond-like carbon (DLC) films prepared by pulsed laser deposition are investigated. Stainless steel disks were coated with 0.5 μm thick DLC films, and ball-on-disk sliding experiments were performed with steel and sapphire balls in humid air, a nitrogen atmosphere, and under vacuum. Friction coefficients of about 0.1 are reported. The low friction is related to a friction induced transformation of the surface into a graphite-like phase and the formation of an adherent transfer film of this material on the counterface. Surface enhanced micro-Raman studies of the wear tracks, wear debris and the transfer film demonstrated that an sp 3 to sp 2 phase transition has occurred in the wear tracks on the DLC film surface. The formation of a graphite phase after several thousands of cycles caused a humidity sensitive behavior of the DLC films and an increase in the friction coefficient in high vacuum conditions. A lubricating sp 2-rich layer on the surface of the hydrogen-free DLC films is proposed as the reason for their extremely low wear rates in ambient environments.