Surface Of Diamond-like Carbon Films Research Articles

Tribological behavior of DLC/IL solid–liquid lubricating coatings in a high-vacuum condition with alternating high and low temperatures

In this paper, ionic liquid (IL) diamond-like carbon (DLC)-based solid–liquid lubricating coatings were used to conduct friction and wear experiments under a high-vacuum condition with alternating temperatures between −100 and 150°C. The results showed that the friction coefficients at 100 and −100°C were the lowest and the largest, respectively. Considering that the mobility, activity, spreadability, and self-repairing capacity of IL were significantly better at high temperatures compared with those at low temperatures, the DLC film surface slightly graphitized at a relatively high temperature. The disc wear rates were the lowest at room temperature and the highest at 150°C because the surface graphitization of the DLC film and the large friction coefficient resulted in an increase in wear rate.

Electron and laser beam-induced current measurements of diamond-like carbon films modified by scanning probe method

A nitrogen-doped diamond-like carbon (DLC) film deposited on n-type silicon is modified by applying an electric field in a vacuum between a tungsten tip and the DLC film surface using a scanning probe field emission current method. The resistance decreases and a Schottky barrier is formed between the modified DLC and the silicon surface, while micro-Raman measurements show a slight nano-crystalline graphitization. The electron beam induced current from the modified area is measured without any metal contact deposition. An infrared laser beam with a wavelength of 1400 nm is scanned across the backside of the silicon, and the induced current from the DLC modified area is measured. It is shown that both infrared laser and electron beam induced current measurements were possible for the modified DLC film on silicon structures.

Analysis on Self-Organized Formation of Nanofibers on Diamond-Like Carbon Film Surface during RF O<sub>2</sub> Plasma Etching

Analysis on Self-Organized Formation of Nanofibers on Diamond-Like Carbon Film Surface during RF O<sub>2</sub> Plasma Etching

Effects of Pre-heat Treatment on Tribological Properties of DLC Film

A diamond-like carbon (DLC) film exhibits excellent tribological properties. This type of film has an amorphous structure that is generally composed of hydrogen and carbon atoms, and it is the structure of sp2- and sp3-hybridized orbital carbon which brings about the extraordinary tribological properties of the DLC film. It is known that heating causes structural changes in a DLC film, and pre-heat treatment greatly affects the various properties of a DLC film. In this study, we focus on the effects of pre-heat treatment on the friction and wear properties of a hydrogenated DLC film and discuss the structural changes in the film. After pre-heat treatment, the tribological properties were evaluated using a ball-on-disk sliding tester. Our findings indicated that the friction and wear properties of the DLC film were improved by pre-heating up to 500 °C. An as-deposited DLC film had a friction coefficient of approximately 0.15, whereas it was approximately 0.03 for a film pre-heated at 500 °C. The structure of the DLC film was analyzed using micro-laser Raman spectroscopy. The analytic results of the Raman spectroscopy of the film surface showed that the G peak position had shifted toward a higher wave number. This result suggested that hydrogen had evolved from the DLC film because of pre-heat treatment. The half bandwidth of the G peak shifted toward a lower wave number with increases in the pre-heating temperature. This indicated that graphitization of the DLC film had been induced by pre-heat treatment. From these findings, we consider that the hydrogen evolution induced structural changes. Line analysis using micro-laser Raman spectroscopy was performed on a cross section of the pre-heated DLC film. The line analysis showed structural changes which were induced by hydrogen evolution, on the top of the DLC film. On the other hand, hydrogen evolution and graphitization were prevented inside the film, indicating that a gradient structure had been generated by pre-heat treatment. The low friction coefficient of the pre-heated DLC film was caused by graphitization of the DLC film surface. The graphite layer on the top of the film would induce lower shearing resistance at the sliding interface. This gradient structure of the DLC film plays an important role in improving the tribological properties of the pre-heated DLC film.

Detecting Method of Bulk Defects in DLC Films Using Light Scattering

Diamond-like carbon (DLC) film has various micro-size defects like pinhole, void and particle. When DLC film is exposed to white light, light is scattered in all direction at defects in DLC film. In this paper, defects in DLC film are detected by observing scattering light from defects under dark-field microscope. DLC film has wavelength dependence of transmittance. Therefore, using its wavelength dependence allows to separate surface and inside defects of DLC film. This paper describes development of bulk defects detecting system using optical filtering and scattering light detecting. Bulk defects of DLC films were successfully separated into surface defects and inside defects. This detecting method of defect is nondestructive and easy, and applicable to DLC films as well as other coating films.

Mechanism analysis of improved DLC films friction behaviors with liquid sulfidation treatment

Diamond like carbon (DLC) films were treated by liquid sulfidation to improve their friction behaviors. Friction behaviors of DLC films were experimentally evaluated in ambient air under dry friction using GCr15 steel ball sliding over DLC-coated steel flat in a ball-on-disk tribometer system. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were applied to identify the chemical composition and structure of DLC films. It was found that the content of sp2 carbon bond increased and G peak shifted to high wave number after sulfidation treatment. The measurement results showed that sulfur atoms were chemically bonded and the graphitization occurred in the treated DLC films. It was indicated that the treated DLC films exhibited much better friction behaviors than the untreated films, especially for DLC films deposited with high nitrogen ratio. In this paper, we proposed the possible sulfidation mechanism of sulfurized DLC films. Sulfidation mechanism is postulated that thiourea reacted with oxygen to form sulfur-containing organic compounds which included CSSC, CSOH and (NH2)NHCSO2H and surface diffusion during sulfidation treatment. The anti-friction behaviors of the treated DLC films can be attributed to the production of the compounds containing sulfur on the DLC film surface, the reduce of oxygen content and the presence of graphitization of DLC films.

H plasma processing triggered phase transformation from DLC to diamond nano-particles

Phase transformation from diamond-like carbon (DLC) films to amorphous carbon (a-C) encapsulated diamond nano-particles (a-DNPs) has been realized by using longtime and low power radio frequency (rf, 40–60W) H plasma processing at 1000K. SEM observation showed that a thin film consisted of densely packed nano-particles (NPs) was formed on the surface of DLC films after a longtime H plasma processing. The length of the NPs increased dramatically with the processing time, but the density change was negligible (~3×1011cm−2). Visible and UV Raman revealed that the NPs were consisted of diamond and a-C. XPS showed a processing time dependent content increase of SP3-hybridized carbon, confirming the growth of diamond during the plasma treatment. Based on previous researches, a core (diamond)-shell (a-C) structure and a two-step transforming model were proposed. We conjecture that the SP3-hybridized carbon clusters in DLC behave as the seeds for the DNP growth, and the rf H plasma treatment provides an appropriate driving force for the running of this phase transformation.

Deposition of Diamond-Like Carbon Films on Inner Wall Surfaces of Millimeter-Size-Diameter Steel Tubes by Plasma Source Ion Implantation

Diamond-like carbon (DLC) film deposition on the interior surfaces of steel tubes was carried out by plasma source ion implantation. SUS304 austenitic-type stainless steel tubes with inner diameters of 9, 5, and 4 mm were used as substrate tubes. Acetylene was the working gas for the plasma that was generated by applying a negative pulse voltage of -18 kV to the substrates. The surface morphology of the films and the film thickness were observed by atomic force microscopy and scanning electron microscopy. The composition within the film and at the interface was examined by depth profiling with Auger electron spectroscopy and secondary ion mass spectrometry. The film structure was characterized by Raman spectroscopy. The friction coefficient of the untreated substrate and the DLC films was evaluated by a reciprocating sliding test. The DLC film surfaces were smooth, and no special structure was observed on the surface. The DLC film thicknesses, structure, and composition on the interior surface of the steel tube depend, on the one hand, on the gas and pulse conditions and, on the other hand, on the distance from the end of the tube, as well as on the diameter of the tube. A low friction coefficient of 0.2 was derived for the deposited DLC films.

Formation of Nanofibers on the Surface of Diamond-Like Carbon Films by RF Oxygen Plasma Etching

Diamond-like carbon (DLC) nanosize fibers were formed by etching DLC films using RF O2 plasma. The DLC films were grown on silicon substrates by an RF plasma chemical vapor deposition (CVD) method, and a small amount of Ni was deposited on the DLC films using a DC magnetron sputtering method before the etching. DLC fibers of 20 nm diameter and 600 nm height were found on the etched surfaces of the DLC films. DLC fibers of similar size that were highly insulating were also obtained by O2 etching without the deposition of Ni. It was found that Al from the RF electrode was sputtered and contaminated the DLC surface during etching, which would have affected the formation of fibers. The anisotropic etching of DLC and the ion-induced growth of carbon fibers are discussed as the formation mechanisms of the DLC fibers. The DLC fibers bent and stuck together during a field-emission scanning electron microscope observation, especially in the slow scanning mode. Such soft fibers can exist vertically and straightly throughout the etching in RF plasma.

Formation of Nanofibers on the Surface of Diamond-Like Carbon Films by RF Oxygen Plasma Etching

Formation of Nanofibers on the Surface of Diamond-Like Carbon Films by RF Oxygen Plasma Etching

Diamond-like Carbon Films Deposited at Room Temperature on Flexible Plastics Substrates for Antireflection Coating

In this present work, diamond-like carbon (DLC) films were coated onto polycarbonate (PC) substrates as a protective layer at room temperature by radio frequency (rf) magnetron sputtering technique. The ID/IG ratio, roughness (Ra), and contact angle of amorphous DLC films could be controlled by regulating deposition power. The DLC films deposited at 150 W with a good hardness of as high as 13.74 GPa were realized with a surface roughness and contact angle of 0.63 nm (Ra) and 103°, respectively. Ultraviolet/visible (UV/vis) spectrophotometry of single-layer DLC films showed a high transmissive ability (>80%) in the visible wavelengths. No cracks occurred on the surface of DLC films after the flexibility test 500 times at a frequency of 8.6 min-1. This confirms the excellent adhesion of DLC films on PC plastic substrates with potential applications in flexible optoelectronic devices.

Tribological effect of iron oxide residual on the DLC film surface under seawater and saline solutions

This paper discusses the seawater and saline solutions effects on the tribological behavior of diamond-like carbon (DLC) films. The adsorption of Fe on DLC surface is one of the mechanisms that is believed to be the cause of the decrease in dispersive component of the surface energy and increase of the I D/I G ratio leading to low friction coefficient and wear rate under corrosive environments. Tribological behaviors DLC films were experimentally evaluated under corrosive environments by using steel ball and DLC coated steel flat under rotational sliding conditions. The DLC films were prepared on 440 stainless steel disks by DC-pulsed PECVD using methane as a precursor gas. Two different set of tribological system was assembled, one when the liquids and the pairs were put inside of a stainless steel vessel and others inside of a PTFE. Every tribological test was performed under 10 N normal load120 mms − 1 of sliding speed. The friction coefficients were evaluated during 1000 cycles.

Control of Surface Shape in Nanostructure Formed with Femtosecond Laser Pulses

This paper reports the experimental results demonstrating that the nanostructured surface of diamondlike carbon film can be shaped so as to have a sawlike pattern with obliquely incident ppolarized femtosecond laser pulses. The nanoscale surface shape was observed as functions of incident angle, superimposed number and fluence of laser pulses and characterized with height and slope angle of the inclined surface. This results show that the inclined shape is formed with the non-uniform spatial distribution of local field enhanced on the nanostructured surface.

MNM-2B-6 フェムト秒レーザによるナノ周期構造付与DLC膜のトライボロジー特性(セッション 2B マイクロ・ナノトライボロジー)

Higher performance hard coatings such as diamond-like carbon (DLC) films and improved surfaces are being investigated for their friction reduction properties. In the present study, the frictional properties of DLC films with the periodic structures were investigated using a block-on-ring type friction tester under lubrication. These periodic structures have been generated on the surface of DLC films by means of a polarized femtosecond (fs) laser of energies near the ablation threshold. Periodic structures have a mean spacing of about 100 nm with a length of 200-2000nm. Worn surfaces were observed by using an AFM. The steady-state friction coefficient and the running-in distance of the DLC with periodic structures was lower than that of the DLC without periodic structures.

Shaping of nanostructured surface in femtosecond laser ablation of thin films

We report that the nanostructured surface of diamondlike carbon films can be shaped so as to have a sawlike pattern with obliquely incident p-polarized femtosecond laser pulses. The nanoscale surface shape was observed as functions of incident angle, superimposed number and fluence of laser pulses and characterized with height and slope angle of the inclined surface. It is shown that the inclined shape is formed with the non-uniform spatial distribution of the local field enhanced on the nanostructured surface.

Study on tribological behavior and cutting performance of CVD diamond and DLC films on Co-cemented tungsten carbide substrates

The tribological behaviors of diamond and diamond-like carbon (DLC) films play a major role on their machining and mechanical applications. In this study, diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC–Co) substrate respectively adopting the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode, and their friction properties are evaluated on a reciprocating ball-on-plate tribometer with counterfaces of silicon nitride (Si 3N 4) ceramic, cemented tungsten carbide (WC) and ball-bearing steel materials, under the ambient air without lubricating condition. Moreover, to evaluate their cutting performance, comparative turning tests are conducted using the uncoated WC–Co and as-fabricated CVD diamond and DLC coated inserts, with glass fiber reinforced plastics (GFRP) composite materials as the workpiece. The as-deposited HFCVD diamond and DLC films are characterized with energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Raman spectroscopy and 3D surface topography based on white-light interferometry. Furthermore, Rocwell C indentation tests are conducted to evaluate the adhesion of HFCVD diamond and DLC films grown onto WC–Co substrates. SEM and 3D surface topography based on white-light interferometry are also used to investigate the worn region on the surfaces of diamond and DLC films. The friction tests suggest that the obtained friction coefficient curves that of various contacts exhibit similar evolution tendency. For a given counterface, DLC films present lower stable friction coefficients than HFCVD diamond films under the same sliding conditions. The cutting tests results indicate that flank wear of the HFCVD diamond coated insert is lower than that of DLC coated insert before diamond films peeling off.

Metallic contacts to nitrogen and boron doped diamond-like carbon films

Hydrogenated diamond-like carbon (DLC) was deposited using a radio-frequency plasma-enhanced chemical vapor deposition method. Electrical properties of Al, Au, Ti, and Zr contacts to nitrogen and boron doped DLC films have been studied, and mechanisms of the observed current–voltage ( I– V) characteristics are investigated. Linear I– V characteristics were observed for Au, Ti, and Zr contacts to both nitrogen and boron doped DLC films. A band structure model for metal–DLC contact is proposed to explain the observed ohmic contacts. Fermi level shifting at the surface of DLC films produces an ohmic resistive layer instead of a Schottky barrier for metal–DLC contacts. Al contacts to both nitrogen and boron doped DLC films show nonlinear I– V characteristics, which are attributed to a dielectric layer of carbide (Al 4C 3) instead of a Schottky barrier suggested by other groups. Inert elements such as Au and Pt, and transition metals such as Ti, Zr and W, which form conductive carbides, are considered good contacting metals for electrical studies of DLC films.

Use of near atmospheric pressure and low pressure techniques to modification DLC film surface

Diamond-like carbon (DLC) films have been use in numerous industrial applications due to its mechanical properties such as low friction coefficient, high hardness, and high adherence on different substrate materials. It has been demonstrated that the DLC surface can be modified with oxygen plasma treatment. The purpose of this paper is to study two kinds of surface treatments (atmospheric and low pressures) using oxygen gas for different etching exposure times in DLC films. Plasma durability along the time was also evaluated. DLC films were deposited using plasma enhanced chemical vapor deposition technique. The properties of DLC treated for both techniques in different exposure times were investigated through Raman, AFM and contact angle measurements. D band position slightly shifts toward lower wave numbers after oxygen plasma etching treatment whilst the surface becomes rougher, although the roughness values are still lower. A conventional wetting contact angle method was used to study the surface properties of DLC films with different treatments. The wetting contact angle reduced significantly due to the increase of carbon–oxygen sites on the surface.

Micro-scale modification of diamond-like carbon and copper electroplating by scanning probe field emission current method

Micro-scale modification of nitrogen-doped diamond-like carbon (DLC) is performed by applying an electric field between a tungsten tip and DLC film surface in vacuum using the scanning probe field emission current (SPFEC) method. The dc voltage ranging from −700 V to −3000 V is applied to the tip. Then, electroplating of Cu is performed on the DLC film surface in CuCl 2 solution by a three electrode-cell. The cathodic polarization curves indicate that the start potential of Cu on modified DLC film is shifted to a lower value than that of Cu on an as-grown DLC film. Cu deposits selectively on the DLC surface modified by an electric field. With this technique, the micro-scale patterning of Cu can be achieved by electroplating without a lithographic process.

Development of DLC Coated Tool for Cutting of Aluminum Alloy －Influence of Deposition Condition on Cutting Characteristic－

Conventional coating tools have a high affinity for ductile materials, like aluminum alloy, so cutting chips tend to adhere to cutting edge and work material surface. Therefore, chipping is caused, and surface texture is degraded. In order to solve these problems, recently, DLC (Diamond-Like-Carbon) has been applied to coating material. In this research, it is curried out cutting of Aluminum alloy by the use of DLC coating tool, and examined influence of DLC coating conditions on cutting characteristics. So far we have been concerned with the effect of type of hydrocarbon gas (acethylene:C2H2, methane:CH4) on cutting. As a result, it is revealed that cohesion of chips decreases, and surface roughness of work material improves in the case of acethylene-DLC. On the other hand, internal stress is produced by deference in hardness between tool surface and DLC film, and which is considered cause of film peeling [1]. Therefore, we examined interlayer between DLC film and tool surface in order to relax of internal stress. As a result, it was cleared that Titanium interlayer excels in adhesion.