Diamond-like Carbon Samples Research Articles

Study on properties of diamond-like carbon films deposited by RF ICP PECVD method for micro- and optoelectronic applications

In this paper, a comparison of Diamond-like Carbon (DLC) films with different sp3 fraction content prepared by Radio Frequency Inductively Coupled Plasma Enhanced Chemical Vapour Deposition (RF ICP PECVD) was presented. Structural, surface, optical, and mechanical properties of deposited DLC films were analyzed with the use of awide range of measurement techniques. The investigated films were deposited on silicon (Si), amorphous silica (SiO2), and metallic (Ti6Al4V) substrates at room temperature. The deposited DLC films have sp3 fraction content ranging from 35 % to 70 %, uniform, compact and dense microstructure. The investigation indicates that the properties of DLC films required for micro- and optoelectronic applications improve with the sp3 fraction content. The refractive index (n) increased from 1.976 to2.086, packaging density (PD) from 0.964 to 0.744, electrical resistivity (ρ) from 2.1 ∙ 1010 to 4.4 ∙ 1011 Ωcm, hardness (H) from 16.4 19.1 to GPa and elastic modulus (E) from 109 to 129 GPa. However, the 50 % sp3 DLC thin film exhibited the highest resistance to cracking (H3/E2 = 0.44). The decrease of Urbach energy (EU) from 0.75 to 0.46 eV was observed for the DLC film with the highest sp3 fraction content, while all investigated DLC samples had similar optical bandgap energy (Egopt ≈ 1.3 eV). The research has shown that it is possible to obtain DLC coatings using the RF ICP PECVD technique that has better properties than films deposited by the classic PECVD technique.

Thermomechanical properties and frictional contact behavior of oxygen doped DLC film through molecular dynamics simulation

Using the MD simulation techniques, we investigated the effects of doped oxygen atoms on the thermomechanical properties and tribological performance of diamond like carbon (DLC). The atomic percentage of oxygen (at.% O) in DLC was varied from 0 to 20.0%. The mechanical stiffness of oxidized DLC samples was evaluated using the nanoindentation simulation, while the coefficient of friction (COF) and the frictional temperature rise were obtained from the sliding contact simulation. From the simulation results, it could be found that the mechanical stiffness and the COF decreased with the at.% O in DLC. The lower COF for the oxidized DLC could be explained by the less covalent interactions with the diamond tip surface. Due to the lower stiffness, the oxidized DLC showed larger surface displacement and wear during the sliding contact. Also, the frictional temperature rise was evaluated with respect to the at.% O in DLC. The higher at.% O in DLC, the lower surface temperature rise. This could be attributed to the lower frictional heat flux and the higher specific heat of the oxidized DLC samples.

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.

Effect of diamond-like carbon doped with chromium on cell differentiation, immune activation and apoptosis.

Diamond-like carbon (DLC) is a biocompatible material that has many potential biomedical applications, including in orthopaedics. DLC layers doped with Cr at atomic percent (at.%) of 0, 0.9, 1.8, 7.3, and 7.7 at.% were evaluated with reference to their osteoinductivity with human bone marrow mesenchymal stromal cells (hMSCs), immune activation potential with RAW 264.7 macrophage-like cells, and their effect on apoptosis in Saos-2 human osteoblast-like cells and neonatal human dermal fibroblasts (NHDFs). At mRNA level, hMSCs on DLC doped with 0.9 and 7.7 at.% of Cr reached higher maximum values of both RUNX2 and alkaline phosphatase. An earlier onset of mRNA production of type I collagen and osteocalcin was also observed on these samples; they also supported the production of both type I collagen and osteocalcin. RAW 264.7 macrophages were screened using a RayBio™ Human Cytokine Array for cytokine production. 10 cytokines were at a concentration more than 2 × as high as the concentration of a positive control, but the values for the DLC samples were only moderately higher than the values on glass. NHDF cells, but not Saos-2 cells, had a higher expression of pro-apoptotic markers Bax and Bim and a lower expression of anti-apoptotic factor BCL-XL in proportion to the Cr content. Increased apoptosis was also proven by annexin V staining. These results show that a Cr-doped DLC layer with a lower Cr content can act as an osteoinductive material with relatively low immunogenicity, but that a higher Cr content can induce cell apoptosis.

In-depth distribution of elements and chemical bonds in the surface region of calcium-doped diamond-like carbon films

In the present work we determined surface composition and chemical bonds at the top surface and in a shallow sub-surface region of the calcium-doped diamond-like carbon (DLC) layers using angular-resolved photoelectron spectroscopy (ARXPS) aided by the Maximum Entropy Method (MEM). The resulting non-destructive depth profiles showed that the composition and the chemical bonding vary significantly on the way from the top surface to the shallow sub-surface region. We demonstrate, for the first time, that Ca doping induced (i) the accumulation of the calcium carbonate, CaCO3, at the surface, while the calcium oxide, CaO, is locatedin a deeper sub-surface region, (ii) structural conversion from the C sp2-rich top surface observed in the undoped DLC layer to the C sp3-rich top surface of the Ca-doped DLC samples, and (iii) conversion in the opposite direction which occurred in a sub-surface region. Our conclusions are consistent with Raman and Ion Surface Scattering spectra. Obtained results can be useful for deeper understanding the interaction between doped DLC layer surfaces with surroundings and particularly with living tissue.

An Exploding Wire-Compression Method for Evaluating the Electrical Conductivity of Diamond-Like Carbon in a Warm Dense State

We have employed an exploding-wire compression method to measure the electrical conductivity of diamond-like carbon (DLC) in a warm dense matter (WDM) state. We generated a DLC in the WDM state using shock compression driven by an exploding-wire discharge within a rigid capillary. To elucidate the generation of DLC in WDM, we performed a 1-D magnetohydrodynamic simulation. Using the numerical results, we estimated the electrical conductivity of the DLC plasma. By comparing the time-evolutions of the voltage and current for gold and gold + DLC samples, we demonstrated that the voltage–current evolution is different in the two cases. From the absorption spectroscopy, we estimated the DLC temperature to be 8000–9000 K. By comparing the results of the experiment with those of the numerical simulation, we determined the electrical conductivity of the DLC plasma to be 106 S/m. This is relatively high compared with the electrical conductivity of the conventional carbon plasma, but the experimental results are similar to the theoretical values for diamond at solid density.

XPS and XAS preliminary studies of diamond-like carbon films prepared by HiPIMS technique

X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) were employed for the investigations of diamond-like carbon (DLC) films prepared by highpower impulse magnetron sputtering technique (HiPIMS). The measurements were done ex-situ, i.e. the prepared DLC samples were exposed to air during transferring from the deposition to analysis chambers. It is inevitable that the surface of the samples was contaminated by absorbed air molecules. XPS analyses revealed that the main surface contaminants are carbon and oxygen, which introduce the difficulties for the determination of carbon species in the DLC films. In this work, a complementary XAS technique was used for analyzing carbon species in the DLC films. It was found that the DLC film contain more sp2 than sp3 carbon. The discrepancy in the sp2/sp3 ratio from the two techniques is different as a result of the difference in depth/surface sensitivity.

Adhesion and differentiation of Saos-2 osteoblast-like cells on chromium-doped diamond-like carbon coatings.

Diamond-like carbon (DLC) thin films are promising for use in coating orthopaedic, dental and cardiovascular implants. The problem of DLC layers lies in their weak layer adhesion to metal implants. Chromium is used as a dopant for improving the adhesion of DLC films. Cr-DLC layers were prepared by a hybrid technology, using a combination of pulsed laser deposition (PLD) from a graphite target and magnetron sputtering. Depending on the deposition conditions, the concentration of Cr in the DLC layers moved from zero to 10.0 at.%. The effect of DLC layers with 0.0, 0.9, 1.8, 7.3, 7.7 and 10.0 at.% Cr content on the adhesion and osteogenic differentiation of human osteoblast-like Saos-2 cells was assessed in vitro. The DLC samples that contained 7.7 and 10.0 at.% of Cr supported cell spreading on day 1 after seeding. On day three after seeding, the most apparent vinculin-containing focal adhesion plaques were also found on samples with higher concentrations of chromium. On the other hand, the expression of type I collagen and alkaline phosphatase at the mRNA and protein level was the highest on Cr-DLC samples with a lower concentration of Cr (0-1.8 at.%). We can conclude that higher concentrations of chromium supported cell adhesion; however DLC and DLC doped with a lower concentration of chromium supported osteogenic cell differentiation.

Argon and hydrogen plasma influence on the protective properties of diamond-like carbon films as barrier coating

Diamond like carbon (DLC) films are becoming materials of choice for mechanical and corrosion protection barrier films due to their excellent properties of low-friction and chemical inertness. As DLC functional properties are strictly dependent on process parameters, different DLC coatings have been deposited onto silicon substrates by Plasma Enhanced Chemical Vapour Deposition (PECVD) evaluating the effect of the variation of argon and hydrogen gas flows on the coating resistance properties. It has been observed that the hydrogen variation is the main factor affecting the DLC films resistance in aggressive environments, while DLC samples deposited by varying Ar showed significant delamination phenomena. These differences have been related to the morphological and microstructural characteristics of DLC films taking into account for the specific role of both Ar and H2 in the mechanism of DLC formation. In particular, it has been observed that the resistance against corrosive environment for DLC coatings may be related to the compressive residual stress values in conjunction with surface and structural properties of the film. This can be considered an understanding at the atomic scale providing the key for the optimization of the protective coating performance.

Magnetic-field enhanced plasma immersion ion implantation and deposition (PIII&D) of diamond-like carbon films inside tubes

The present work deals with Diamond-like Carbon (DLC) films deposition inside metallic tubes using magnetic field generated in a PIII&D system. Firstly, the features of plasma discharges with the magnetic field application were studied using different feeding gases as nitrogen, methane and acetylene. The experimental results demonstrate that a stable hollow cathode discharge can be established inside the tubes as the magnetic field is applied. The discharge breakdown is strongly affected by the presence of the magnetic field during the treatment. Secondly, PIII&D experiments regarding DLC films deposition inside the inner surface of the tubes are also described and those ones enhanced by the applied magnetic field are emphasized. The sample tubes used in both experimental stages are of austenitic stainless steel with 150mm in length and different diameters: 110mm, 40mm and 20mm. For the case of DLC deposition, polished steel samples were fixed in the bottom of the inner tube wall for subsequent analysis of the coatings. The as-coated DLC samples surface were analyzed by Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), optical profilometry and also pin-on-disk tests. The properties of the obtained DLC films are correlated to the magnetic field used during the PIII&D process. In this work, the optimal range of magnetic field intensity is shown for depositing DLC films with acceptable adhesion strength on the inner surface of steel tubes.

A facile method for the deposition of thermally stable diamond like carbon thin films via carbon dioxide precursor gas

The thermal stability and tribological performance of silicon- and oxygen-incorporated diamond-like carbon (DLC) and silicon doped-DLC films were investigated. The DLC and DLC:Si are deposited on various (silicon, stainless steel and aluminium) substrates within the thickness range 200–400nm by radio frequency plasma-enhanced chemical vapour deposition (PECVD) method. Carbon dioxide (CO2) precursor gas is used to reduce the hydrogen content and to increase the adhesion of the films to the substrate. The X-ray photoelectron spectroscopy, Raman spectroscopy, surface profilometry and nano-indentation are used to study the chemical composition, microstructure, thermal stability and mechanical properties of the films. For CO2 precursor made DLC samples, Raman parameters did not show any significant change up to temperature 500°C. The lowest coefficient of friction was found to be 0.298 for the DLC:Si film prepared with CO2 at room temperature and corresponded lowest wear rate of 1.77×10−10mm3/Nm. The micro-structural properties at various annealing temperature were critically analysed by monitoring graphitization behaviour and oxidation of the film surface.

Optimization of pulsed DC PACVD parameters: Toward reducing wear rate of the DLC films

The effect of pulsed direct current (DC) plasma-assisted chemical vapor deposition (PACVD) parameters such as temperature, duty cycle, hydrogen flow, and argon/CH4 flow ratio on the wear behavior and wear durability of the diamond-like carbon (DLC) films was studied by using response surface methodology (RSM). DLC films were deposited on nitrocarburized AISI 4140 steel. Wear rate and wear durability of the DLC films were examined with the pin-on-disk method. Field emission scanning electron microscopy, Raman spectroscopy, and nanoindentation techniques were used for studying wear mechanisms, chemical structure, and hardness of the DLC films. RSM results show that duty cycle is one of the important parameters that affect the wear rate of the DLC samples. The wear rate of the samples deposited with a duty cycle of >75% decreases with an increase in the argon/CH4 ratio. In contrast, for a duty cycle of <65%, the wear rate increases with an increase in the argon/CH4 ratio. The wear durability of the DLC samples increases with an increase in the duty cycle, hydrogen flow, and argon/CH4 flow ratio at the deposition temperature between 85°C and 110°C. Oxidation, fatigue, abrasive wear, and graphitization are the wear mechanisms observed on the wear scar of the DLC samples deposited with the optimum deposition conditions.

Study of facing target sputtered diamond-like carbon overcoats for hard disk drive media

The demand for higher areal density in the hard disk drive industry has fuelled extensive research efforts and focuses on magnetic spacing reduction. In the head–disk interface arena, one of the key focuses is to reduce the carbon overcoat thickness without compromising the overcoat protection performance. Thus, in the search for alternative methods to reduce the carbon overcoat thickness, the facing target sputtering (FTS) process for diamond-like carbon deposition has been investigated. The resulting properties have been presented in this paper, with comparison to conventional diamond-like carbon (DLC) layers by other processes such as chemical vapor deposition and reactive sputtering with nitrogen. X-ray reflectometry results showed that facing target sputtered DLC samples displayed significantly higher density, at 2.87g/cm3, as compared to hydrogenated and nitrogenated DLC samples. This was attributed to the higher sp3 content, as obtained by X-ray photoelectron spectroscopy measurements. As a result of the high sp3 content, hardness of the FTS deposited samples was higher than that of the hydrogenated and nitrogenated DLC samples. In addition, the surface energy of FTS samples was observed to be comparable, but lower, than that of nitrogenated DLC samples through contact angle measurements. Clearances comparable to that of conventional DLC samples were achieved and the sample disks were flyable. Wear performance tests also revealed more wear resistance for the FTS deposited DLC samples, but also higher head wear.

Electrical and magnetic properties of electrodeposited nickel incorporated diamond-like carbon thin films

Abstract Nanocomposite diamond-like carbon (DLC) thin films have been synthesized by incorporating nickel (Ni) nanoparticles in DLC matrix with varying concentration of nickel. DLC and Ni-DLC thin films have been deposited on ITO coated glass substrates employing low voltage electrodeposition method. Electrical properties of the samples were studied by measuring current–voltage characteristics and dielectric properties. The current approaches toward an ohmic behavior with metal addition. This tendency of increasing ohmicity is enhanced with increase in dilution of the electrolyte. The conductivity increases with Ni addition and interestingly it continues to increase with dilution of Ni concentration in the electrolyte in the range of our study. Magnetic properties for DLC and Ni-DLC thin film samples were examined by electron paramagnetic resonance (EPR) measurements and Super Conducting Quantum Interference Device (SQUID) measurements. g -Value for DLC is 2.074, whereas it decreases to 2.055 with Ni addition in the electrolyte. This decrement arises from the increased sp 2 content in DLC matrix. The magnetic moment vs. magnetic field ( m – H ) curves of Ni-DLC indicate superparamagnetic behavior which may be due to ferromagnetic contribution from the incorporated nickel nanoparticles in the DLC matrix. The ZFC curve of Ni-DLC after the blocking temperature shows a combined contribution of ferromagnetic, superparamagnetic and paramagnetic nature of the materials persisting up to 300 K.

Cell adhesion and growth on ultrananocrystalline diamond and diamond-like carbon films after different surface modifications

Diamond and diamond-like carbon (DLC) films possess a set of excellent physical and chemical properties which together with a high biocompatibility make them attractive candidates for a number of medical and biotechnological applications. In the current work thin ultrananocrystalline diamond (UNCD) and DLC films were comparatively investigated with respect to cell attachment and proliferation after different surface modifications. The UNCD films were prepared by microwave plasma enhanced chemical vapor deposition, the DLC films by pulsed laser deposition (PLD). The films were comprehensively characterized with respect to their basic properties, e.g. crystallinity, morphology, chemical bonding nature, etc. Afterwards the UNCD and DLC films were modified applying O2 or NH3/N2 plasmas and UV/O3 treatments to alter their surface termination. The surface composition of as-grown and modified samples was studied by X-ray photoelectron spectroscopy (XPS). Furthermore the films were characterized by contact angle measurements with water, formamide, 1-decanol and diiodomethane; from the results obtained the surface energy with its dispersive and polar components was calculated. The adhesion and proliferation of MG63 osteosarcoma cells on the different UNCD and DLC samples were assessed by measurement of the cell attachment efficiency and MTT assays. The determined cell densities were compared and correlated with the surface properties of as-deposited and modified UNCD and DLC films.

Tribological behavior of diamond-like carbon produced by rf-PCVD based on energetic evaluation

Two types of diamond-like carbon (DLC) were evaluated for their tribological behavior in terms of the tribometer input energy. The DLC samples were prepared from methane (denoted DLC[CH4]) or benzene (denoted DLC[C6H6]) as a gas source on tungsten-carbide (WC) substrates by radio-frequency plasma chemical vapor deposition (rf-PCVD). The hydrogen contents of the DLCs were measured by Elastic Recoil Detection Analysis (ERDA). The DLC structures were investigated by Raman spectrometry and X-ray photoelectron spectroscopy (XPS). The basic mechanical properties, such as the hardness and the Young's modulus, were obtained by a nano-indenter. The DLC films against alumina were tribo-tested by a ball-on-disk. The input energy was calculated using the applied load, the friction coefficient, and the sliding distance in each tribo-test. The wear behavior of the DLC[CH4] sample was better than that of the DLC[C6H6], even though the hardness of DLC[CH4] was lower than that of DLC[C6H6]. The wear loss of DLC[CH4] and DLC[C6H6] was evaluated by the input energy, and the wear resistance difference of the DLCs was characterized in terms of the input energy.

Classification of DLC films in terms of biological response

In this study, various kinds of diamond-like carbon (DLC) films were classified in terms of their biological responses (specifically the number of adhering cells). Forty three kinds of DLC samples that had been deposited on Si substrate by various physical vapor deposition (PVD) and chemical vapor deposition (CVD) system equipment were obtained at random from coating companies, universities, and public organizations in Japan. Mouth fibroblasts (NIH-3T3) were used to estimate the cellular responses on the DLC samples. During the cell culture, 12 of the DLC samples were peeled off from the Si substrates. As a result, the remaining 31 DLC samples with a wide range of properties were classified into four groups in terms of their number of adhering cells. Group 1 (high density, low sp2 content, and low hydrogen contents) and Group 2 (low or medium density, high sp2 content, and low hydrogen contents) had a low number of adhering cells. Group 3 (medium density, and medium sp2 content, and relatively high hydrogen contents) and Group 4 (low sp2 content, low density, and a wide range of hydrogen contents) had a wide range of number of adhering cells. Especially, 7 DLC samples in Group 4 had good cell growth. It was shown that this classification is one of the design criteria of DLC film deposition for biomaterials regardless of the various deposition system equipment. It is expected that ordinary DLC users can carefully select a DLC film for specific applications to medical devices using the classification.

Comparative Study on the Tribological Performance of HFCVD Diamond and DLC Films under Water Lubricating Condition

The tribological performance of conventional microcrystalline diamond (MCD) film and diamond-like carbon (DLC) film is investigated comparatively under water lubricating condition. The MCD and DLC film are deposited on cobalt cemented tungsten carbide (WC-Co) substrate using the hot filament chemical vapor deposition (HFCVD) method and the vacuum arc discharge with a graphite cathode respectively. Scanning electron microscopy (SEM), white light interferometer, and Raman spectra are employed to characterize as-deposited MCD and DLC samples. The friction tests are carried out on a ball-on-plate reciprocating friction tester, where the sliding process is conducted under water lubricating condition. Silicon nitride, tungsten carbide, ball-bearing steel and copper are used as counterpart materials. The results indicate that DLC film always exhibits lower friction coefficient than MCD film under water lubricating condition, except the case of sliding against the silicon nitride, in which DLC film is worn out very rapidly and thus leads to the high friction coefficient. The wear resistance of DLC film under water lubricating condition is significantly poorer than that of MCD film. While sliding against silicon nitride, tungsten carbide, ball-bearing steel and copper, its wear rate is calculated as 3.67´10-7mm3N-1m-1, 9.31´10-9mm3N-1m-1, 3.54´10-7mm3N-1m-1, and 4.97´10-8mm3N-1m-1respectively. Comparatively, no measurable wear track can be found on the worn surface of MCD films.

Beneficial silver: antibacterial nanocomposite Ag-DLC coating to reduce osteolysis of orthopaedic implants

Silver-containing diamond-like-carbon (DLC) is a promising material for biomedical implants due to its excellent combination of antibacterial and mechanical properties. In this work, a dual-cathode pulsed filtered cathodic arc source containing silver and graphite rods was employed in order to obtain DLC samples with various silver contents. Chemical composition of the samples was analyzed by acquiring their compositional depth-profiles using radio-frequency Glow Discharge Optical Emission Spectroscopy (rf-GDOES), while the microstructural properties were analyzed by X-ray diffraction and Raman spectroscopy. Tribological studies carried out against UHMWPE balls in fetal bovine serum indicate that the presence of silver in DLC could be beneficial to reduce the wear of the polymeric surfaces.

Quantitative measurements of sp3 content in DLC films with Raman spectroscopy

Hydrogenated and H-free diamond-like carbon (DLC) samples were prepared and 244nm and 514nm Raman spectra were collected and analyzed. Correlations between Raman spectra and sp3 content of DLC samples from this and previous studies have been analyzed. The dispersion rate of the G peak is shown to correlate linearly with the sp3 content of hydrogenated DLC samples, while the full-width-half-maximum of the G peak is shown to correlate nonlinearly with the sp3 content of H-free DLC samples. Quantitative relations are presented for measuring the sp3 content of both hydrogenated and H-free DLC.