Characterization Of Diamond-like Carbon Films Research Articles

Characterization of diamond-like carbon films deposited on commercially pure Ti and Ti–6Al–4V

The diamond-like carbon (DLC) films deposited on the articulating surface of medical-grade Ti and Ti–6Al–4V were characterized. The DLC films were synthesized by r.f. plasma assisted chemical vapor deposition (PACVD) using C6H6 at 10 mTorr. For wear tests, the ball-on-disk type wear tester was employed by wearing a 5-mm diameter ruby ball against a rotating metal disk. The DLC coating dramatically improved the wear performance of Ti and Ti–6Al–4V, and protected the substrates from corrosion. The wear behavior of DLC films on the Ti-alloy was that of normal abrasive wear. However, the softer Ti substrate deformed plastically and the films were prefractured. The lifetime of the DLC coating in saline solution was reduced due to the delamination of the coating.

Optical characterization of diamond-like carbon films using multi-sample modification of variable angle spectroscopic ellipsometry

In the first part, thicknesses and spectral dependences of the optical constants of the diamond like carbon (DLC) films were determined without any parameterization in the range 240–830 nm by multi-sample modification of variable angle spectroscopic ellipsometry (VASE). DLC films were prepared by plasma enhanced chemical vapor deposition (PECVD) onto silicon single crystal substrates. It was shown that the influence of some defects of the DLC films on the optical constants is suppressed by applying the method of multi-sample modification of VASE. In the second part, the spectral dependences of the determined optical constants were interpreted using a recently developed model of dispersion based on the modified Lorentz oscillator. Two modified Lorentz oscillators corresponding to both π→π* and σ→σ* interband transitions were taken into account. Within this model of dispersion of the optical constants, the concept of the band gap and the existence of localized energy states within the band gap were taken into account as well.

Tribological Characteristics of Diamond-Like Carbon Films Formed on CP Ti and ELI Ti-6Al-4V

Tribological Characteristics of Diamond-Like Carbon Films Formed on CP Ti and ELI Ti-6Al-4V

Microstructure and adhesion characteristics of diamond-like carbon films deposited on steel substrates

For tribological applications, the low friction coefficient and high microhardness of diamond-like carbon (DLC) films give significant advantages in cutting and forming non-ferrous materials. The inherently large residual stress of DLC films, however, prevents the depositing of thicker films. This study designed and implemented a compound interface, comprising a series of metal, metal nitride, and metal carbonitride interlayers deposited in a graded structure, between the DLC (a metal-doped a-C:H) film and M2 steel substrates. The tribological performance of the interface was evaluated using a scratch tester and ball-on-disk tribometer. Meanwhile, the failure mechanism of DLC deposited on M2 steel substrates was examined using SEM/EDS and TEM microscopy. Experimental results demonstrate an improved DLC hard coating with superior adhesion strength on the steel substrates.

Optical characterization of diamond-like carbon films

In this contribution, the results achieved by the optical characterization of diamond-like carbon (DLC) films are presented. A multi-sample modification of variable angle of incidence spectroscopic ellipsometry (VASE) is used to determine the values of the thicknesses and spectral dependences of the optical constants of these films. It is shown that this optical method is very suitable for characterizing the films studied because the influences of some defects of these films are suppressed within this method. Further, the spectral dependences of the optical constants determined for the DLC films studied are interpreted using a new model of dispersion based on the existence of two oscillators corresponding to both the π→π∗ and σ→σ∗ interband transitions. Within this model of dispersion of the optical constants, the concept of the band gap is respected as well.

Electrical and structural characterization of DLC films deposited by magnetron sputtering

In this work diamond-like carbon (DLC) films were deposited by d.c. magnetron sputtering using a graphite target and argon as the discharge gas. Hydrogen gas was introduced in the discharge chamber to produce hydrogenated DLC films. By increasing the hydrogen flow from zero to 22% of the total flow, the following modifications of the film properties were observed: a decrease in the r.m.s. roughness (from 0.45 to 0.21 nm); an increase in the electrical resistivity (from 5×106Ωcm to 2.55×108Ωcm , while the relative dielectric constant remained almost constant at about 3.3. Increasing the substrate temperature, we observed a logarithmic decrease of the electrical resistivity of the films, caused by a self-annealing process of the DLC film during the deposition. This decrease was faster for the hydrogenated films, due to the additional effect of the dehydrogenation. The Raman spectra analyses of these films are in agreement with these observations.

Effects of the methane content on the characteristics of diamond-like carbon films produced by sputtering

In this work, hydrogenated carbon films were sputter deposited at low temperatures using different Ar–CH 4 mixtures. The deposition rate of the films increases by up to a factor of 6 when comparing a CH 4-rich mixture to a pure Ar plasma. At the same time, the sp 3 carbon content is much higher when CH 4 is added to the Ar, and as a consequence the resistivity increases by approximately six orders of magnitude, and the breakdown electric field increases by approximately a factor of three. Another attractive feature of the films deposited with a CH 4-rich plasma is the low dielectric constant, down to 1.8 for a pure CH 4 plasma. The rms roughness of a 1-μm thick film is as low as 1.6 nm. All these features make this technique interesting for depositing intermetallic layers.

Tribological characterization of diamond-like carbon films on nonledeburitic high-speed steels

Hydrogenated diamond-like carbon (DLC) films were deposited on as-tempered nonledeburitic high-speed steel (NHSS) substrates (0–5–1–3Ti–2Nb grade) by capacitively coupled RF glow discharge in a methane atmosphere. The substrates were cleaned with an argon flux before coating deposition. Coatings of 1-μm thickness, good smoothness and adhesion were successfully produced. Microscale abrasive wear tests and field emission scanning electron microscopy were employed to evaluate wear resistance and morphology of the DLC films, substrate–film boundaries and worn components. The wear coefficient of the steel substrates was less than that of M2 tool steel, whereas that for the DLC layer corresponded to the value previously reported for titanium aluminium nitride. Certain decohesion micromechanisms in the NHSS samples after microscale abrasion testing were similar to these found in fractured specimens. Structural influences on the results are discussed.

Structural and tribological characteristics of diamond-like carbon films deposited by pulsed laser ablation

Diamond-like carbon (DLC) films were deposited by pulsed laser ablation (PLA) on Si (100) and Ti–6Al–4V alloy substrates at four different temperatures. The bonding characteristics of the films were studied by X-ray photoelectron (XPS) and Raman spectroscopy techniques. The ratio of tetrahedral to trigonally coordinated carbon atoms was estimated by XPS successfully. The fraction of tetrahedrally bonded atoms in the films deposited on Si at room temperature was estimated to be ∼63 at.% which decreased to ∼33 at.% as the substrate temperature increased to 400°C. The Raman spectroscopy results of these specimens agree qualitatively with these observations. Also, using Raman spectroscopy, the residual compressive stress was also estimated in fully adherent films on Si substrate to be ∼3 GPa with reference to the value of stress present in a free-standing peeled off film from the Ti-alloy substrate. This value is consistent with the residual stresses estimated in the earlier results. The abrasive wear rates have been correlated during the initial stages of the well adhered films with the sp 3/sp 2 ratios. The importance of suitable dopants and the interfacial interlayers in reducing internal compressive stresses in these films is discussed.

Spectroscopic ellipsometry characterization of diamond-like carbon films formed by filtered arc deposition

The properties of diamond-like carbon (DLC) films can vary widely from graphite (sp 2 local bonding) to diamond (sp 3 local bonding), strongly depending on the film preparation conditions. As the optical constants ( n, k) of sp 3 bonded carbon are quite different from those of sp 2 bonded carbon over the visible and near-infrared (VIS–NIR) spectral range, it is possible to provide precise quantitative information on sp 3 C (sp 2 C) fractions using optical characterization methods. In the present work, spectroscopic ellipsometry (SE) using multiple sample analysis method has been applied to study a series of DLC films on silicon substrates prepared by filtered arc deposition (FAD) technique. In contrast to most reported SE studies, the DLC film was simulated by a mixture of sp 3 C, sp 2 C and void constituents instead of treating it as a whole. From the interpretation of SE spectra, the film thickness and the volume fractions of sp 3 C, sp 2 C and void have been derived, respectively. In addition, comparison between SE results and Rutherford backscattering spectroscopy (RBS) and electron energy loss spectroscopy (EELS) results will be given. This work shows that SE using multiple sample analysis method is a very useful optical method to determine sp 3 C fractions in DLC films.

Characterization of diamond-like carbon films before and after pulsed laser irradiation

In this work, we correlate the structural properties of DLC films with their photoelectric properties. DLC layers are deposited on silicon wafers by RF plasma-assisted chemical vapor deposition (RF PACVD). The films are irradiated with picosecond Nd 3+-YAG laser pulses at different wavelengths (213 and 266 nm) and energies (few μJ to mJ). Photoelectric sensitivity values are reported and compared with those of metals. The DLC coatings are characterized before and after irradiation by IR spectroscopy, micro-Raman spectroscopy and ellipsometry in order to observe laser-induced structural modifications of the layers. In situ measurements of work function variations at the surface induced by laser pulses are also reported.

巻取方式マグネトロンプラズマ化学蒸着によるダイヤモンド状炭素膜の形成とその特性

巻取方式マグネトロンプラズマ化学蒸着によるダイヤモンド状炭素膜の形成とその特性

The tribological characteristics of diamond-like carbon films at elevated temperatures

To determine whether diamond-like carbon (DLC) films could be applied as a kind of solid lubricant coating at high temperatures, the friction properties and wear ability of DLC films in sliding against alumina at elevated temperatures up to 400°C were investigated. We used Raman spectroscopy to determine the chemical and structural changes of DLC films, a scratch tester to investigate the variation of the adherence between DLC films and the silicon wafer substrate, and scanning electron microscopy (SEM) to observe the wear tracks at different test temperatures. We confirmed that chemical-vapor-deposited DLC films are good lubricant and wear resistant films within a suitable temperature range. Increasing the temperature decreased the friction coefficient and increased the wear rate of DLC films. These phenomena are due to film graphitization as revealed by Raman spectroscopy. Above the critical temperature of 300°C, films peeled off quickly, i.e. their wear lives are shortened, since the adherence between film and substrates abruptly decreased at high temperatures. Below 200°C, the dominant film wear mechanism is plastic deformation. At 300 and 400°C, the dominant wear mechanisms of DLC films are fracture and delamination.

Ultraviolet Raman characterisation of diamond-like carbon films

Diamond-like carbon (DLC) films with a range of sp(3) fractions have been examined by ultraviolet (UV) spectroscopy with 244 nm excitation. The UV Raman spectra of both hydrogenated and unhydrogenated films show the G peak near 1600 cm(-1) and a broad peak around 1200 cm(-1), which is attributed to C-C stretching vibrations of sp(3) sites. It is found that the ratio of the intensities of the C peak and the 1200 cm(-1) peak follows a universal dependence with the sp(3) content in both hydrogenated and unhydrogenated DLCs. This can be used for non-destructive evaluation of the sp(3) content of any DLC film.

Growth and characterization of diamond-like carbon films by pulsed laser deposition and hydrogen beam treatment

Amorphous diamond-like carbon films have been grown by pulsed laser deposition using a graphite target both with and without an atomic hydrogen beam incident on the growing film. Films grown with the hydrogen beam showed resistivity nearly two orders of magnitude higher than the films grown without hydrogen. Raman scattering confirmed a higher degree of sp 3 bonding in films exposed to hydrogen atoms during growth. Films grown without hydrogen but exposed to the hydrogen beam after growth showed a significant increase in resistivity after exposure.

Spectroscopic ellipsometric characterization of diamondlike carbon films

Amorphous diamondlike carbon films have been investigated by means of spectroscopic ellipsometery (SE). The films were measured by a null ellipsometer in the 230–750 nm range and the measured spectra were analyzed using an empirical dielectric function suitable for amorphous materials. The fitting of SE data with empirical dielectric function shows that the measured spectra can be well explained using the empirical dielectric function. The optical constants calculated from the fitting of SE data were used to calculate the optical reflectance spectra of these films. It was found that the calculated reflectance spectra coincide with the measured spectra suggesting that the optical properties obtained from the fitting of SE data are accurate.

The effects of self-generated DC bias on the characteristics of diamond-like carbon films prepared using ECR-CVD

The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron resonance chemical vapour deposition (ECR-CVD) method with radio-frequency (RF) bias is reported. The structural characteristics of the DLC films were characterized using Raman spectroscopy. The effects of the self-generated DC bias resulting from the RF power on the optical gap, Raman spectra, infrared (IR) absorption and film hardness in depositions carried out at 7 and 15 mtorr process pressures were investigated. Under conditions of 100 W microwave power and for a DC bias variation ranging from −10 V to −200 V, there exists evidence from Raman scattering analysis to show an increase in the diamond-like characteristic in films deposited at low DC bias at both process pressures. The variation of the D and G line peak position and integrated intensity ratio (IDID) in the Raman spectra correlates well with the film hardness profile. There does not seem to be a relationship between the variation of the CH absorption peak intensity in the IR spectra (bonded hydrogen content) and the optical gap, although films with the highest optical gap tend to show a relatively higher CH absorption peak intensity in the IR spectra. Films deposited at high DC bias showed a reduction in the CH infrared absorption, suggesting a reduction in the bonded hydrogen content.

Field emission characteristics of diamondlike carbon films synthesized by pulsed laser deposition process using a Au-intermediate layer

The characteristics of the diamondlike carbon (DLC) films deposited on Au-coated silicon substrate are observed to vary markedly with the substrate temperature. Large relative proportion of sp3-bonds had pronouncedly improved the electron emission properties of the DLC films. A low turn on field as 7 V/μm and a large emission current density as 2000 μA/cm2, at 20 V/μm, were achieved for DLC/Au/Si films deposited at 200 °C. Too high a substrate temperature (i.e., 600 °C) induced graphitization that degraded the field emission behavior. The DLC/Au/Si films grow in a similar behavior as DLC/Mo/Si films, but possess substantially better field emission characteristics. The scanning electron microscopic and secondary ion mass spectroscopics analyses implied that the main factor is the improvement on the interfacial structure through the interdiffusion between DLC, Au, and Si layers.

Characterization of diamond-like carbon films deposited on Zr-2.5Nb pressure tube material by excimer laser

Diamond-like carbon films were deposited by excimer laser ablation of graphite on Zr-2.5Nb pressure tube material at substrate temperatures of 25 and 200 °C. Characterizations of the films by nanoindentation, Raman spectroscopy, and Fourier transform infrared reflection spectroscopy show that the films have a very high hardness, are transparent to infrared light, and exhibit Raman spectra typical of diamond-like carbon films. The films also exhibit a high refractive index in the infrared spectrum. Increasing the substrate temperature from 25 to 200 °C results in a 25% increase in the deposition rate, but produces lower mechanical properties for the DLC films. The high refractive index was attributed to a lack of incorporation of hydrogen into the films and the lower mechanical properties of the films deposited on the heated substrate were explained by an increase in the sp 2 sp 3 bonds ratio.

Thin film characterization of diamond-like carbon films prepared by r.f. plasma chemical vapor deposition

Using atomic force microscopy and infrared spectroscopy, diamond-like carbon films deposited by r.f. plasma discharge were investigated. Hardness and roughness of the films strongly depend on the bias voltage of the substrates and thus the pressure in the deposition chamber. At higher pressures, the surface roughness of the films increases with their thickness. For films deposited at medium pressures, the roughness is almost constant regardless of the film thickness. At pressure below 53 Pa decreasing roughness is observed and hard films are obtained. These findings can be explained by the predominance of different species in the plasma. At low pressure, ionic species are accelerated towards sharp tips on the film surface leading to sputter removal of weakly bond material in these regions. At higher pressure neutral species in the plasma dominate. Thus, the balancing effect of sputtering is not observed. Hydrogen content and sp 3/sp 2 ratios obtained from IR spectra revealed that the lower hardness of the rough surfaces can be explained by a higher content of sp 2 species in the films deposited at high pressure. Whereas the intensity ratio of sp 3/sp 2 is almost constant for the films at higher pressure preferred sputter removal of sp 2 species leads to a significant increase of that ratio at low pressure.