Structure Of Diamond-like Carbon Films Research Articles

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.

Reduced Roughness and Enhanced Mechanical Properties of Multilayered Diamond-Like Carbon Films by Periodic Arc Deposition

In this study, very simple periodic cathodic vacuum arc deposition was conducted to prepare multilayered structures of diamond-like carbon films with reduced surface roughness and enhanced mechanical properties compared to conventional unfiltered single-layered films. The roughness of single-layered diamond-like carbon films significantly increased from 23 to 104 nm with increasing thickness from 100 to 800 nm due to the droplet formation in plasma atmosphere. By introducing periodic deposition, the roughness of the multilayered structures with a thickness of 400 nm was reduced from 75 to 37 nm, associated with a much smaller number of surface particles. The hardness of the multilayered structures was enhanced from 27 to 34 GPa, and the interface adhesion was increased from 2.73 to 3.63 J/m2. The single- and multilayered films showed a similar amorphous structure with slightly varied ID/IG ratios from 0.9 to 0.6. The periodic deposition process was the dominant factor for the reduced roughness and enhanced mechanical properties of the unfiltered films.

B-2-4 熱アシスト磁気記録におけるヘッドディスクインターフェイスに関する研究 : DLC保護膜の構造におよぼす加熱の影響(B-2 ヘッド・ディスク・インタフェースに作用する相互作用他,口頭発表:ヘッド・ディスク・インターフェイス)

To further increase recording density of disk storage drives, thermally-assisted magnetic recording can solve the fundamental issues of thermal fluctuation and is regarded as the key technology for achieving recording density of more than 1 Tb/in^2. In this technology, it is suggested that there is critical issues for the ultra-thin liquid lubricant films and diamond-like carbon (DLC) films on the disk surfaces, because they are heated to high temperature with laser beams. In this study, we focused on the thermal stability of the three types of DLC films deposited by chemical vapor deposition (CVD), ion beam deposition (IBD) and filtered cathodic vacuum arc (FCVA) deposition. We also compared the optical properties of heated three DLC films characterized by ellipsometry, electron spectroscopy for chemical analysis and raman spectroscopy. As a result, the effects of heating temperature on the structure of DLC films were clarified.

Structure of diamondlike carbon films deposited by femtosecond and nanosecond pulsed laser ablation

The characterization of diamondlike carbon (DLC) films is a challenging subject, considering the diversity of carbon-based nanostructures depending on the deposition process. We propose to combine multiwavelength (MW) Raman spectroscopy and electron energy-loss spectroscopy (EELS) to probe the structural disorder and the carbon hybridizations of DLC films deposited by pulsed laser ablation performed either with a nanosecond laser (film labeled ns-DLC), either with a femtosecond laser (film labeled fs-DLC). Such deposition methods allow to reach a rather high carbon sp3 hybridization but with some significant differences in terms of structural disorder and carbonaceous chain configurations. MW Raman investigations, both in the UV and visible range, is a popular and nondestructive way to probe the structural disorder and the carbon hybridizations. EELS allows the determination of the carbon plasmon energy in the low-loss energy region of the spectra, as well as the fine structure of the ionization threshold in the high-loss energy region. The paper shows that the combination of MW Raman and EELS is a powerful way to elucidate the nanostructure of DLC films. Complementary nanoindentation investigations allow to correlate the analytical results with the mechanical properties of the films. The ns-DLC film presents a stronger sp3-bonded C character (74%–85%) with a significant content of sp2 chains, whereas the fs-DLC contains less sp3 bonds (35%–50%) with a significant content of sp2-bonded C rings. The ns-DLC film exhibits a higher proportion of disordered sp2 C mainly in the form of chains. Comparatively, the fs-DLC exhibits a predominance of more ordered sp2 C structures in the form of graphitic aggregates whose size has been estimated near three aromatic rings. The film characteristics are in agreement with their mechanical properties. We also propose a correlation between the nanostructure and composition of the films with the deposition mechanisms. The difference in kinetic energy distribution in the plasma plume, together with an absence of interaction between the plasma plume and the femtosecond laser, are responsible for the observed differences in sp3 C content and sp2 C configuration ranging between a predominance of more ordered sp2 rings in the fs-DLC film and a predominance of sp2 chains in the ns-DLC film. These results are consistent with the mechanisms of subplantation occurring during DLC deposition

Raman Spectroscopy of Carbon Based Films – Spectra Interpretation and Selected Applications

The investigation of the film structure of diamond-like carbon films was the main objective of this work. Films within the structural systems of hydrogenated tetrahedral amorphous carbon (ta-C:H), silicon doped hydrogenated amorphous carbon (a-C:H:Si) and nitrogen doped amorphous carbon (a-C:N) were deposited at substrate temperatures of well below 100 °C. As deposition methods ion beam deposition, reactive unbalanced magnetron sputtering of silicon as well as infrared pulsed laser deposition (IR-PLD; λ=1064 nm) were studied. By the use of Raman spectroscopy it was found, that for high kinetic ion energy film deposition processes, i.e. ion beam deposition, the structure and properties of the ta-C:H films can be controlled by the kinetic energy of carbon species involved during film growth. For deposition techniques being typically known for low ion energies like magnetron sputtering or IR-PLD, applied for deposition of a-C:H:Si and a-C:N films, process tuning involves the study of the effects of inert gas/ reactive gas flow and the type of the reactive gas.

Effect of thickness on structures of ultrathin diamond-like carbon films

Diamond-like carbon (DLC) films with different thickness were deposited by filtered cathode vacuum arc (FCVA). Vis-Raman and spectroscopic ellipsometry were employed to analyze the structure of DLC films. The wavelength of Vis-Raman is 514.5 nm. Experimental results show that structures of DLC films are affected by film thicknesses. When the film thickness increases from 2 to 30 nm, the G-peak position (G-pos) shifts to higher wavelength, the intensity ratio ID/IG and the extinction coefficient Ks decrease. It is indicated that the content of sp3 bond increases with film thickness. However, when the film thickness increases from 30 nm to 50 nm, ID/IG and Ks increase. The content of sp3 bonds decreases with film thickness.

Nanoscale Friction Behaviors of Hierarchical Superhydrophobic Structure of Diamond-like Carbon Films with Various Humidity Conditions

Superhydrophobic double roughening structure of DLC film was prepared by 2.45 GHz surface wave-excited plasma CVD with the mixture of methane (CH4) and tetramethylsilane (TMS: Si(CH3)4) gases on the undulated DLC film by a series of plasma Ar etching, coating process and plasma Ar etching. Static wetting angle of water was observed that double roughening structure of DLC was superhydrophobicity such as wetting angle 161°. This approach also increased in air pockets easily trap among the needle-like posts. For the low friction at nanoscale, the surface wettability of the solid lubrication played a significant role, when the DLC film modified from flat to double roughening structure, the friction was constantly inner humidity conditions. Results generally showed that humidity had insignificant effect on the nanoscale friction at superhydrophobic DLC surface. The effect of the superhydrophobic double roughening DLC and friction were discussed with the following factors; the surface morphology affinity to needle-like shape, a reduction of the real area of contact, graphitization and easily occur to slip at small contact interface due to superhydrophobicity.

The influence of the structures and compounds of DLC coatings on the barrier properties of PET bottles

To reduce the oxygen transmission rate through a polyethylene terephthalate (PET) bottle (an organic plastic) diamond-like carbon (DLC) coatings on the inner surface of the PET bottle were deposited by radio frequency plasma-enhanced chemical vapour deposition (RF-PECVD) technology with C2H2 as the source of carbon and Ar as the diluted gas. As the barrier layer to humidity and gas permeation, this paper analyses the DLC film structure, composition, morphology and barrier properties by Fourier transform infrared, atomic force microscopy, scanning electron microscopy and oxygen transmission rate in detail. From the spectrum, it is found that the DLC film mainly consists of sp3 bonds. The barrier property of the films is significantly relevant to the sp3 bond concentration in the coating, the film thickness and morphology. Additionally, it is found that DLC film deposited in an inductively coupled plasma enhanced capacitively coupled plasma source shows a compact, homogeneous and crack-free surface, which is beneficial for a good gas barrier property in PET bottles.

Band structure of diamond-like carbon films assessed from optical measurements in wide spectral range

The optical measurements of thin films on substrates, such as ellipsometry and spectrophotometry, can be efficiently used for obtaining information about film material structure if their dielectric function is parametrized by a proper dispersion model. The sample of hydrogenated diamond-like carbon (DLC) film, prepared by plasma enhanced chemical vapor deposition on silicon single crystal substrate, was investigated by ellipsometry in the NIR–UV range (0.6–6.5 eV), synchrotron ellipsometry in the UV–XUV range (4–20 eV) and reflectometry in NIR–UV range (1.24–6.5 eV). Various dispersion models based on the parametrization of density of states (PDOS) were investigated concerning their application in the wide spectral range. The previously used simple PDOS model was found to be insufficient. It resulted in poor separation of π and σ bands in the short spectral range while in the wide range it could not reflect the film optical properties because transitions to higher excited states were neglected. The inclusion of these transitions led to a considerable improvement of the fit above 16 eV. However, the realistic value of the band gap of σ electrons was obtained only after refinement of the previously expected parabolic shape of the DOS of π and σ electrons. The further developed PDOS model can be used for any other disordered material and it will, together with the optical measurements extended to XUV, supply important information about its band structure.

Thickness dependence of the structure of diamond-like carbon films by Raman spectroscopy

The thickness dependence on structure of Diamond-like carbon films of a-C:H deposited by ECR-CVD and ta-C by FCVA has been studied by visible and UV Raman spectroscopy. The results show that the evolution of structure as a function of the thickness for a-C:H films contains two stages: when thickness is less than 50 Å, the film contains less sp 3 sites and not continuous; and when thickness is up to 50 Å, the film contains more sp 3 sites and become continuous. However, for ta-C films, it includes three stages. In the first stage of thickness lower than 20 Å, the film is not continuous, and also contains less sp 3. In the second stage of thickness between 20 Å and 50 Å, the sp 3 site abruptly shifts a higher value in 20 Å and then keeps stable. In the third stage of thickness over 50 Å, the sp 3 site has a little increase and then almost not changed. Thus, the fundamental limitation thickness in using DLC as an ultrathin overcoat for ta-C films is 20 Å (> 10 Å), and for a-C:H films is 50 Å. The implications of result on the mechanisms proposed for the film growth mode were also discussed.

Structure of Diamond-Like Carbon Film Deposited on Aluminum Oxide Surface with Microstructure

We investigated the deposition phenomena of diamond-like carbon (DLC) film on a microstructured Al2O3 surface using an ion-beam technique. In the case of an acceleration voltage of 300 V, the microstructured Al2O3 surface was smoothly coated to have an unevenness of about 200 nm height with DLC film. The hardness of the DLC film indicated maximum values at acceleration voltages of 100–200 V and gradually decreased for acceleration voltages of 300–400 V. By using Raman spectroscopy and Fourier transform infrared spectroscopy, it was shown that the numbers of sp3 bonds in films deposited at acceleration voltages of 100 and 200 V was larger than that of films deposited at acceleration voltages of 300 and 400 V.

The Thermal Annealing Effect on the Residual Stress and Mechanical Property in the Compressive Stressed DLC Film

The thermal annealing effect on the compressive residual stress has been presented in thin diamond-like carbon (DLC) film on Si substrate. Annealing experiments were carried out with Rapid Thermal Procedure system at from 200 to 600 °C, and the variation of residual stress with annealing temperature was investigated by in-situ stress measurement system. The stress reduction occurs as annealing temperature increases, while the change of chemical structure of DLC film is not significantly changed with observation by Raman spectrometer. The elastic modulus and hardness are not deteriorated when annealing temperature is controlled at less than 400 degree of Celsius, where the residual stress is apparently reduced.

Structure of diamond-like carbon films containing transition metals deposited by reactive magnetron sputtering

The addition of transition metal (Mo, Nb, Ti, W) atoms within the matrix of diamond-like carbon (DLC) films leads to the improving of their mechanical properties. In this work, we study the effects of the different metal induced structures on the electrical, optical and mechanical properties of DLC thin films. The samples were prepared at room temperature by pulsed-DC reactive magnetron sputtering, as a suitable way to vary their composition. X-ray photoelectron spectroscopy (XPS) evidenced a smooth variation of the composition with relative methane flow. Metal-DLC (Me-DLC) films are generally uniform in composition, as confirmed by secondary ion mass spectrometry (SIMS). Cross-section micrographs of the films, observed by transmission electron microscopy (TEM), showed relevant structural differences, which led to strong variations of physical properties. Among these variations, we can point to a better control of roughness, measured by atomic force microscopy (AFM), and stress. Indentation essays on W-DLC films have been performed in order to obtain the dependence of hardness with W concentration. Optical properties determined by UV–VIS spectroscopic ellipsometry evidenced the influence of methane dilution. The electrical measurements show a thermally activated conductivity, whose range of values and activation energy depend on the metal abundance. Me-DLC films suppose an advance in hard and wear-resistant coatings development.

Structure of Diamondlike Carbon Films Synthesized by the Method of Laser Evaporation of Graphite in a Vacuum

Using the methods of transmission electron diffraction, transmission electron microscopy, and electron paramagnetic resonance, we have analyzed the structure of thin carbon layers deposited on glass substrates, heated to a temperature of T ≈ 473 K, in a vacuum as a result of the exposure of a graphite target to a pulsed laser radiation of nanosecond duration and energy 2–8 J. It is shown that carbon films with an amorphous diamond structure undergo not only graphitization but also crystallization: polycrystalline diamond- and diamond-graphite concretions are formed on their surface.

Application of DLC films as masks for integrated circuit fabrication

In order to evaluate the applicability of diamond-like carbon (DLC) films to the above-mentioned processes, the durability of such films against ion implantation has been investigated. Therefore, DLC films deposited on n-type Si (1 1 1) substrates under varying substrate temperature were exposed to boron (B) ion implantation during the integrated circuit (IC) fabrication process. The implantation of B ions was carried out at an acceleration voltage of 30 keV and a dose volume of 5×10 14 ion cm −2. The surface morphology of DLC films before and after implantation was investigated by atomic force microscopy. IR spectra of the DLC films were obtained with an FTIR spectrometer. Concentration and diffusion depth of the implanted dopants in the films were determined by Auger electron spectroscopy (AES). IR spectra indicate that the structure of DLC films is greatly changed by the implantation process. AES spectra reveal the existence of traces of B at the interface between the DLC film and the Si substrate surface. The yield of excellent pn junctions prepared using DLC films as mask materials was measured as a function of the deposition temperature. From the results of I–V characteristics of pn junction and the yield, the optimum condition of the DLC film is at 400 °C of deposition temperature.

The Thermal Annealing Effect On The Residual Stress And Interface Adhesion In The Compressive Stressed DLC Film.

ABSTRACTWe studied on the thermal annealing effect on the residual stress and the mechanical properties in thin compressive stressed diamond-like carbon film on Si substrate. Annealing experiments were carried out with Rapid Thermal Procedure system at 200–600 °C, and the stress change with annealing temperature was investigated by in-situ stress measurement system. The apparent stress reduction occurred with minimal structure changes. In order to measure the change of chemical structure of diamond-like carbon film by annealing, we used Raman spectrometer. The adhesion deterioration in interface has been detected as annealing temperature increased. In the compressive stressed DLC film, we observed the dramatic evolution of interface delamination at certain high temperature using in-situ heating stage built in Environment SEM. The quantitative change of adhesion affected by annealing process was also measured with scratch testing. For exploring the interface structure affected by the thermal annealing process at high temperature, the cross section of annealed film has been observed with HR TEM.

1030 軟質材料上へのダイヤモンド状炭素膜コーティングとその摩擦摩耗特性

Diamond-like carbon (DLC) films have been widely recognized as an excellent wear resistant coatings with a low friction coefficient against many kinds of counterparts. The tribological behavior of DLC films depend on not only the quality of the film but also the environmental conditions such as the substrate materials and the pressure applied. Particularly when the DLC films are distorted with the deformation of the soft substrate, the conventional DLC film should be damaged easily. In this study DLC films have been deposited by RF-plasma CVD from methane on the soft material substrates, such as a rubber and aluminum, and the friction and wear tests were conducted using a ball-on-flat configuration under some conditions. In the case of rubber substrate, DLC films show low friction coefficient from 0.2 to 0.3,even if large strain of ε=0.5 was applied to the substrate. A new coating method was proposed in the case of DLC coatings of Al substrate, which employs the segment structure of DLC film. It was found that the wear resistance of the Al substrate was significantly improved in comparison with the conventional DLC coatings.

In situ monitoring of optical characteristics of pulsed picosecond laser-irradiated diamond-like carbon thin films using an optical parametric generator and amplifier

In situ reflectivity measurements were carried out at room temperature and atmospheric pressure to follow dynamic structural variations occurring during pulsed laser irradiation of diamond-like carbon (DLC) thin films. Laser irradiation consisted of second harmonic (λ = 532 nm) picosecond pulses of a Nd-YAG laser, leading to a modification of the carbon layer structure. Irradiation at this wavelength usually leads to graphitization, i.e. an increase of the number and/or size of sp 2 clusters dispersed in the amorphous carbon structure of DLC films. One of the consequences of such a transformation is a pronounced change in the optical properties. Upon graphitization, the optical absorption strongly increases in the near-infrared region. In order to monitor such changes we used a probe beam tunable in this wavelength region. An optical parametric generator (OPG) and amplifier (OPG/OPA) with low energy pulses tunable in the near-infrared range between 700 nm and 2 μm was used to record reflectivity changes at several wavelengths. Such an in situ characterization reveals how the structural transformations proceed in the early phase of graphitization.

The effect of bombardment with carbon ions on the nanostructure of diamond-like films

The effect of irradiation with carbon ions on the nanocluster structure of diamond-like carbon films was studied. It is shown that the electronic properties (optical absorption and electrical conductivity at low temperatures) of the films depend heavily on the ion dose, which is a consequence of the quantum confinement effect. Variations in the optical band gap and in the activation energy for hopping conductivity are indicative of an increase in the size of π clusters whose concentration remains unchanged in the entire range of ion doses of 3×1014–1.2×1017 cm−2. The process of defect production in the clusters is shifted to higher ion doses compared to that in structurally homogeneous materials. The optical absorption in the π clusters, their concentration in the samples, the tunneling parameters for initial and completely “graphitized” films, and the width of the barrier layer between the clusters were estimated; the width of the band of defect states was determined. It is shown that the known dependence of the optical band gap of the π clusters on their size should be modified for large clusters (E g ≤1 eV).

Properties and structures of diamond-like carbon film deposited using He, Ne, Ar/methane mixture by plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films have been deposited by a magnetically enhanced plasma (MEP) chemical vapor deposition (CVD) system. The properties and structures of DLC films deposited by MEP-CVD using various gases (methane, He/methane, Ne/methane, and Ar/methane) were studied. The mechanical properties in terms of hardness, Young’s modulus and stress, and optical properties in terms of optical band gap and refractive index were enhanced by adding inert gas in methane plasma. The magnitude of the effects on the properties for various inert gases was found as Ne, Ar, and He, on the surface roughness was found as Ar, Ne, and He. The Raman characteristic shows a dependence of the bias voltage and inert-gas/methane ratio, as well as the inert gases dilution. The Raman spectroscopy analysis indicates that the changes of properties of the DLC films are due to the structural changes, such as sp2 and sp3 content in the films prepared under various deposition conditions. The films deposited in Ne/methane show the lowest disordered (D) peak to graphitic (G) peak intensity ratio, the D and G peak positions; highest stress, hardness, Young’s modulus, optical band gap, and lowest reflective index. The films deposited in Ar/methane show the lowest surface roughness. This was proposed due to the optimum balance in the inert gas ionization potential and atomic mass.