Diamond-like Carbon Thin Films Research Articles

Functional diamond like carbon (DLC) coatings on polymer for improved gas barrier performance

We have studied the optimum deposition conditions for the improvement of oxygen and carbon dioxide gas barrier performance of functional diamond-like carbon (DLC) thin films. The a-C:H: a-C:H:Si, a-C:H:N and ta-C:N thin films with 10–400nm thickness were deposited on polyethylene terephthalate (PET) substrates by the radio frequency plasma-enhanced chemical vapour deposition method. To study the microstructure of the PET coated films, we have used the Raman spectroscopy, X-ray photoelectron spectroscopy, nano-indentation and surface profilometry. The gas barrier property were analysed and found that the a-C:H:N's are 5–10 times better gas barrier properties than that of uncoated PET substrates. These thin layer PET coated thin films could be use in food packaging and biomedical applications.

High performance diamond-like carbon layers obtained by pulsed laser deposition for conductive electrode applications

For the future, one of the biggest challenge faced to the technologies of flat panel display and various optoelectronic and photovoltaic devices is to find an alternative to the use of transparent conducting oxides like ITO. In this new approach, the objective is to grow high conductive thin-layer graphene (TLG) on the top of diamond-like carbon (DLC) layers presenting high performance. DLC prepared by pulsed laser deposition (PLD) have attracted special interest due to a unique combination of their properties, close to those of monocrystalline diamond, like its transparency, hardness and chemical inertia, very low roughness, hydrogen-free and thus high thermal stability up to 1000 K. In our future work, we plane to explore the synthesis of conductive TLG on top of insulating DLC thin films. The feasibility and obtained performances of the multi-layered structure will be explored in great details in the short future to develop an alternative to ITO with comparable performance (conductivity of transparency). To select the best DLC candidate for this purpose, we focus this work on the physicochemical properties of the DLC thin films deposited by PLD from a pure graphite target at two wavelengths (193 and 248 nm) at various laser fluences. A surface graphenization process, as well as the required efficiency of the complete structure (TLG/DLC) will clearly be related to the DLC properties, especially to the initial sp3/sp2 hybridization ratio. Thus, an exhaustive description of the physicochemical properties of the DLC layers is a fundamental step in the research of comparable performance to ITO.

Ion induced stress relaxation in dense sputter-deposited DLC thin films

Deposition of high-density and low-stress hydrogen-free diamond like carbon (DLC) thin films is demonstrated using a pulsed ionized sputtering process. This process is based on high power impulse magnetron sputtering, and high C ionization is achieved using Ne as the sputtering gas. The intrinsic compressive stress and its evolution with respect to ion energy and ion flux are explained in terms of the compressive stress based subplantation model for DLC growth by Davis. The highest mass density was ∼2.7 g/cm3, and the compressive stresses did not exceed ∼2.5 GPa. The resulting film stresses are substantially lower than those achieved for the films exhibiting similar mass densities grown by filtered cathodic vacuum arc and pulsed laser deposition methods. This unique combination of high mass density and low compressive stress is attributed to the ion induced stress relaxation during the pulse-off time which corresponds to the post thermal spike relaxation timescales. We therefore propose that the temporal ion flux variations determine the magnitude of the compressive stress observed in our films.

Improved electrochemical performance of nitrocarburised stainless steel by hydrogenated amorphous carbon thin films for bone tissue engineering

In this study, hydrogenated amorphous carbon thin films, structurally similar to diamond-like carbon (DLC), were deposited on the surface of untreated and plasma nitrocarburised (Nitrocarburizing-treated) stainless steel medical implants using a plasma-enhanced chemical vapour deposition method. The deposited DLC thin films on the nitrocarburising-treated implants (CN+DLC) exhibited an appropriate adhesion to the substrates. The results clearly indicated that the applied DLC thin films showed excellent pitting and corrosion resistance with no considerable damage on the surface in comparison with the other samples. The CN+DLC thin films could be considered as an efficient approach for improving the biocompatibility and chemical inertness of metallic implants.

Oxygen doping effect on the wettability of diamond-like carbon thin films

Diamond like carbon (DLC) thin films as a great coating to protect biomedical tools and optical devices are being developed. Modifying the surface properties, such as wettability, is necessary in some application. In this research, oxygen doping effect on the DLC films wettability was investigated. Oxygen doped diamond-like carbon (DLC) thin films were deposited by the RF-PECVD method with different oxygen concentrations in feeding gas (0.0, 1.9, 3.8, 5.6, 7.4 and 9.1vol%). The film's structure was studied by Raman spectroscopy (RS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The chemical composition was determined by a combination of elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS). Surface roughness and morphology of the films were analyzed by an atomic force microscopy (AFM). Wettability of the films was characterized by measuring the contact angles of the films with water. The results showed that by increasing the incorporation of oxygen into the films' structure, the contact angles of water with films were reduced. The increase in the oxygen content of the films, from zero to 11at%, caused to reduce water contact angles from 78.4° to 66.0°. By adding the oxygen into the film's structure, CO and CC bonds content increased in the films. Due to the more polarizability of CO and CC bonds in comparing with CC and CH bonds, a polar component of films' surface energy was increased by adding the oxygen to the films' structure. The surface roughness of the un-doped and doped DLC films were so low (less than 1nm) that they had no roles in the films' surface energy. Doping the DLC films with oxygen caused to increase wettability, without no significant change in the morphology and surface roughness.

Structural and optical properties of gold-incorporated diamond-like carbon thin films deposited by RF magnetron sputtering

Pure and gold-doped diamond-like carbon (Au-DLC) thin films are deposited at room temperature by using RF magnetron sputtering in an argon gas-filled chamber with a constant flow rate of 100 sccm and sputtering time of 30 min for all DLC thin films. Single-crystal silicon (1 0 0) substrates are used for the deposition of pristine and Au-DLC thin films. Graphite (99.99%) and gold (99.99%) are used as co-sputtering targets in the sputtering chamber. The optical properties and structure of Au-DLC thin films are studied with the variation of gold concentration from 1%–5%. Raman spectroscopy, atomic force microscopy (AFM), Vickers hardness measurement (VHM), and spectroscopic ellipsometry are used to analyze these thin films. Raman spectroscopy indicates increased graphitic behavior and reduction in the internal stresses of Au-DLC thin films as the function of increasing gold doping. AFM is used for surface topography, which shows that spherical-like particles are formed on the surface, which agglomerate and form larger clusters on the surface by increasing the gold content. Spectroscopy ellipsometry analysis elucidates that the refractive index and extinction coefficient are inversely related and the optical bandgap energy is decreased with increasing gold content. VHM shows that gold doping reduces the hardness of thin films, which is attributed to the increase in sp2-hybridization.

Grey fuzzy logic approach for the optimization of DLC thin film coating process parameters using PACVD technique

Diamond-like carbon (DLC) coatings are widely used in medical, manufacturing and aerospace industries due to their excellent mechanical, biological, optical and tribological properties. The selection of optimal process parameters for efficient characteristics of DLC film is always a challenging issue for the materials science researchers. The optimal combination of the process parameters involved in the deposition of DLC films provide a better result, which subsequently help other researchers to choose the process parameters. In the present work Grey Relation Analysis (GRA) and Fuzzy-logic are being used for the optimization of process parameters in DLC film coating by using plasma assist chemical vapour deposition (PACVD) technique. The bias voltage, bias frequency, deposition pressure, gas composition are considered as input process parameters and hardness (GPa), Young's modulus (GPa), ratio between diamond to graphic fraction, (Id/Ig) ratio are considered as response parameters. The input parameters are optimized by grey fuzzy analysis. The contribution of individual input parameter is done by ANOVA. In this analysis found that bias voltage having the least influence and gas composition has highest influence in the PACVD deposited DLC films. The grey fuzzy analysis results indicated that optimum results for bias voltage, bias frequency, deposition pressure, gas composition for the DLC thin films are -50 V, 6 kHz, 4 μbar and 60:40 % respectively.

Silicon solar cell performance deposited by diamond like carbon thin film “Atomic oxygen effects”

In this research, a diamond-like carbon thin film was deposited on p-type polycrystalline silicon solar cell via plasma-enhanced chemical vapor deposition method by using methane and hydrogen gases. The effect of atomic oxygen on the functioning of silicon coated DLC thin film and silicon was investigated. Raman spectroscopy, field emission scanning electron microscopy, atomic force microscopy and attenuated total reflection–Fourier transform infrared spectroscopy were used to characterize the structure and morphology of the DLC thin film. Photocurrent–voltage characteristics of the silicon solar cell were carried out using a solar simulator. The results showed that atomic oxygen exposure induced the including oxidation, structural changes, cross-linking reactions and bond breaking of the DLC film; thus reducing the optical properties. The photocurrent–voltage characteristics showed that although the properties of the fabricated thin film were decreased after being exposed to destructive rays, when compared with solar cell without any coating, it could protect it in atomic oxygen condition enhancing solar cell efficiency up to 12%. Thus, it can be said that diamond-like carbon thin layer protect the solar cell against atomic oxygen exposure.

Antimicrobial and anti-biofilm properties of polypropylene meshes coated with metal-containing DLC thin films.

A promising strategy to reduce nosocomial infections related to prosthetic meshes is the prevention of microbial colonization. To this aim, prosthetic meshes coated with antimicrobial thin films are proposed. Commercial polypropylene meshes were coated with metal-containing diamond-like carbon (Me-DLC) thin films by the magnetron sputtering technique. Several dissimilar metals (silver, cobalt, indium, tungsten, tin, aluminum, chromium, zinc, manganese, tantalum, and titanium) were tested and compositional analyses of each Me-DLC were performed by Rutherford backscattering spectrometry. Antimicrobial activities of the films against five microbial species (Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis) were also investigated by a modified Kirby-Bauer test. Results showed that films containing silver and cobalt have inhibited the growth of all microbial species. Tungsten-DLC, tin-DLC, aluminum-DLC, zinc-DLC, manganese-DLC, and tantalum-DLC inhibited the growth of some strains, while chromium- and titanium-DLC weakly inhibited the growth of only one tested strain. In-DLC film showed no antimicrobial activity. The effects of tungsten-DLC and cobalt-DLC on Pseudomonas aeruginosa biofilm formation were also assessed. Tungsten-DLC was able to significantly reduce biofilm formation. Overall, the experimental results in the present study have shown new approaches to coating polymeric biomaterials aiming antimicrobial effect.

Partial formation of linear concavo-convex microstructure onto microwells by diamond-like carbon thin film deposition

By a procedure to partially deposit rigid diamond-like carbon (DLC) thin films using a mask on a soft elastomer, poly(dimethylsiloxane) (PDMS), substrate directionally stretched, areas with the regular linear pattern consisting of a periodical concavo-convex shape with several μm size were successfully formed onto microwells fabricated on the substrate. The DLC thin film depositions were performed by an inductively-coupled plasma (ICP) CVD method, and the optimal deposition conditions, mainly the substrate bias voltage of −650V, to form the linear pattern of the periodical concavo-convex shape were revealed. When an elongation strain applied on the PDMS substrate increased, the height of the concavo-convex shape increased. In addition, by an increase in the deposition time both height and width of the concavo-convex shape showed the tendency to increase. A model that the compressive stress arisen from the large mismatch of the elastic moduli between the DLC thin film and the PDMS substrate induces buckling of the film to produce the wrinkled microstructure was in close agreement with the obtained results.

Friction Durability of Extremely Thin Diamond-Like Carbon Films at High Temperature.

To clarify the friction durability, both during and after the high-temperature heating of nanometer-thick diamond-like carbon (DLC) films, deposited using filtered cathodic vacuum arc (FCVA) and plasma chemical vapor deposition (P-CVD) methods, the dependence of the friction coefficient on the load and sliding cycles of the DLC films, were evaluated. Cluster-I consisted of a low friction area in which the DLC film was effective, while cluster-II consisted of a high friction area in which the lubricating effect of the DLC film was lost. The friction durability of the films was evaluated by statistical cluster analysis. Extremely thin FCVA-DLC films exhibited an excellent wear resistance at room temperature, but their friction durability was decreased at high temperatures. In contrast, the durability of the P-CVD-DLC films was increased at high temperatures when compared with that observed at room temperature. This inverse dependence on temperature corresponded to the nano-friction results obtained by atomic force microscopy. The decrease in the friction durability of the FCVA-DLC films at high temperatures, was caused by a complex effect of temperature and friction. The tribochemical reaction produced by the P-CVD-DLC films reduced their friction coefficient, increasing their durability at high temperatures.

Deposition of diamond-like carbon thin films by the high power impulse magnetron sputtering method

The goal of the conducted experiments was to evaluate if the increased density of the plasma in High Power Impulse Magnetron Sputtering (HiPIMS) argon discharge would give the possibility of obtaining diamond-like films with high sp3 fraction content at room temperature. The magnetron cathode was driven by the self-designed supply. It consisted of high voltage supply, tank capacitors and a set of switches. The tank capacitors and the inductances of connecting wires formed an LC resonant circuit. As a result, each sputtering pulse (duration of 20μs, peak current of 1500–2200A) was followed by the inverse pulse (duration of 25μs, peak current of 400–700A), both having a sinusoidal shape. The repetition time was 3s. The silicon substrates were placed 8cm above the target surface. The sputtering processes of 99.99% pure graphite target were conducted in argon atmosphere at a pressure of 6–8×10−3hPa. The carbon films obtained after 400 deposition pulses had a thickness of 35nm. The surface RMS roughness, measured using an optical profiler, was about 2nm. The refractive index was estimated by means of ellipsometric studies to be 2.45 and 2.3 at 400 and 800nm, respectively. The sp3 hybridization fraction content of about 70–80% was calculated based on the analysis of Raman Scattering spectra.

Numerical study of temperature profile on diamond-like carbon thin films under different laser pulses

In this work, a numerical analysis of the coupled thermal-optical problem for a diamond-like carbon (DLC) thin films deposited on Si-wafer substrate under different laser pulses were investigated. Four different shapes of pulse laser (ruby laser; λ=694 nm, power 0.60 J/cm2), consisting of rectangular, symmetric triangular, Gaussian and Weibull were employed in the numerical simulation using Maxwell’s equations and heat conduction equation in one dimensional. The thermal and optical properties of material are temperature dependent. The energy absorption and temperature profile of DLC films is solved by an explicit finite difference method. The results show that energy absorption within DLC films exhibits gradually decreasing from its surface to Si-substrate at all different pulsed shapes. The energy absorption is in the order of 1017-1018 W/m3 and characteristic as a function of time is similar the pulse shapes pattern. The corresponding temperature depth profiles show the increasing temperature from surface and then gradually decreased near the substrate in the range of 1000-1800 K. In addition, the different laser pulses affect the temperature rising speed and the temperature profile distribution. In the conclusion, Weibull pulse is the most appropriate in order to obtain high speed heating, and the uniformity profile within DLC films.

Optimization of Diamond-Like Carbon Thin Film on Copper Substrate for Carbon Nanotubes Synthesis by ACVD Technique

In this research, demonstrate plasma treatment on copper substrate by Radio Frequency Plasma (RF) using a mixture of 70%C2H2 + 30%H2 as the working gases. The plasma exposure time were varied from 10, 20 and 30 min under the electrical power of 50 Watts for synthesizing the diamond-like carbon (DLC) thin film on copper substrate. Thereafter, the substrates were used for synthesizing the carbon nanotubes (CNTs) via alcohol chemical vapor deposition technique (ACVD). It could be found that the plasma treatment for 10 min exhibited the small contact angle less than those of substrates treated with 20, 30 min and untreated sample which relate to the hydrophilic and affect to improve the adhesion and distribution of catalyst on substrate. The roughness of DLC film showed the different high and low level like hillock. After that, the 10 min treatment time sample was used for synthesizing the CNTs and the results found that the obtained CNTs showed good distribution on substrate.

Образование графита в алмазоподобных тонких углеродных пленках

In the present work, particularities of the formation and structure of a graphite phase appearing in a thin amorphous diamond-like carbon (ta-C) film were studied using the method of high resolution electron microscopy. In order to obtain a thin carbon film, a neodymium laser NTS300 with a wavelength of 1064 nm was used. The film was deposited on a glass substrate in the process of a direct evaporation of a graphite target. Study of the graphite phase formation in the film was carried out using the high resolution transmission electron microscopy that allowed for a direct observation of the thin film atomic structure. Electron diffraction analysis shows that in local areas of a thin film a phase transition from amorphous diamond-like ta-C state to graphite occurs. Single crystals of graphite are oriented so that their basic hexagonal planes are parallel to the film surface. This is due to the fact that sp3 bonds are metastable and can be unstable, particularly on the film surface. Therefore, the transition of sp3 bonds to sp2 ones with the formation of planar complexes with a ring structure initially occurs on the film surface. The growth of a graphite crystal nucleus in the ta-C matrix increases the stress and stabilizes the diamond state. Due to this, the graphite phases form dominantly on the film edges. Analysis of electron diffraction patterns has shown that the interplanar spacings depend on the orientation of the planes relative to the film edge. Measurements of interplanar spacings reveals a complicated character of the stress state of the graphite lattice in the thin film. Along with tension-compression stresses, shear stresses are present and they result in a change of the angles between carbon interatomic bonds.

Modification Processes for Highly Hydrogenated Diamond-Like Carbon Thin Films by Soft X-ray Irradiation

Modification Processes for Highly Hydrogenated Diamond-Like Carbon Thin Films by Soft X-ray Irradiation

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.

Thermal Analysis on Monopolar Electrosurgery Device with Novel Electrode for Minimizing Tissue Damage Using Computer-Aided System

The aim of the present study was to investigate the thermal injury in the liver after a minimally invasive electrosurgery with a titanium dioxide (TiO2), a chromium nitride (CrN) and a diamondlike carbon (DLC) surface modifications. Three-dimensional (3-D) liver models were reconstructed using magnetic resonance imaging to simulate the electrosurgical procedure. Several reports have investigated 3D finite element models for electrosurgical devices, but few have examined a model for devices with treated layers. Data indicated that the temperature decreased significantly when minimally electrosurgery with nanostructured TiO2, CrN and DLC thin films were used. Moreover, DLC electrosurgery created a relatively small thermal injury area and decreased 12.93% temperature compared with control groups. The present study reveals that the novel nanostructured thin film on electrode substrates is an effective means of improving the performance of reducing excessive thermal injury and uniformly distributing temperature in the liver.

Amorphous carbon buffer layers for separating free gallium nitride films

The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al2O3) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the “GaN film–Al2O3” substrate interface decreases, which facilitates separation of the GaN layers.

Raman spectroscopy of thin DLC film deposited by plasma electrolysis process

A thin diamond-like carbon film was deposited on Ni substrate by plasma electrolytic deposition in ethanol-water solution. The thickness of the deposited carbon film was measured about 40–60 nm by using glow discharge optical emission spectroscopy and optical profilometer. The characterization of film structure by Raman spectroscopy showed the superposition of Raman features on a photoluminescence background because of low thickness of the deposited film. The surface enhanced Raman scattering technique by coating the carbon film with Au nanoparticles and high power laser in Raman spectroscopy was used as Raman intensity enhancer. Amplified Raman signals by using both techniques showed formation of diamond-like carbon film and various sp2 and sp3-bonded compositions on grain boundaries of nanostructure carbon coating. The Raman spectrum of the Au coated carbon film revealed an additional band at 2150 cm− 1, which is related to the carbyne structure whereas carbyne band could not be detected using high power laser. Comparison of Raman spectra at two wavelengths of 632.8 and 785 nm showed changes in the intensity and position of Raman bands. Likewise, the 785 nm laser wavelength excitation has sufficient energy to enhance the scattering from the grain boundary structures.