Deposition Of Diamond-like Carbon Films Research Articles

Effect of substrate bias voltage on tensile properties of single crystal silicon microstructure fully coated with plasma CVD diamond-like carbon film

Tensile strength and strength distribution in a microstructure of single crystal silicon (SCS) were improved significantly by coating the surface with a diamond-like carbon (DLC) film. To explore the influence of coating parameters and the mechanism of film fracture, SCS microstructure surfaces (120 × 4 × 5 μm3) were fully coated by plasma enhanced chemical vapor deposition (PECVD) of a DLC at five different bias voltages. After the depositions, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal desorption spectrometry (TDS), surface profilometry, atomic force microscope (AFM) measurement, and nanoindentation methods were used to study the chemical and mechanical properties of the deposited DLC films. Tensile test indicated that the average strength of coated samples was 13.2–29.6% higher than that of the SCS sample, and samples fabricated with a −400 V bias voltage were strongest. The fracture toughness of the DLC film was the dominant factor in the observed tensile strength. Deviations in strength were reduced with increasingly negative bias voltage. The effect of residual stress on the tensile properties is discussed in detail.

Application of radio frequency inductively coupled plasma in chemical vapor deposition process of diamond-like carbon films for modification of properties of deposited films

Abstract The authors have deposited the diamond-like carbon (DLC) films by radio frequency inductively coupled plasma enhanced chemical vapor deposition (RF ICP PECVD) method. The investigated DLC films with different sp3 fraction content were deposited on polished and textured silicon substrates. The sp3 fraction content of the deposited DLC films was ranging from 35 % to 70 % and was estimated from acquired Raman scattering spectra (excitation wavelength: 325 nm and 514.5 nm). The measurements of field emission characteristics were carried out in diode configuration. Emission properties of the DLC films were calculated from Fowler-Nordheim plots. The calculated electric field enhancement factor β was ranging from 56 to 198 for the DLC films deposited on polished substrates and from 115 to 445 for films deposited on textured substrates. The surface of the DLC films was observed by scanning electron microscope (SEM) after field emission measurements. The acquired SEM images reveled that the activation of field emission from the DLC films is connected with generation of structural damage to the DLC films.

Pulsed DC plasma CVD system for the deposition of DLC films

Pulsed DC plasma chemical vapour deposition (CVD) system with a compact vacuum chamber has been developed using a simple configured pulsed DC power supply. Pulsed DC discharge was examined with variation of operation parameters as well as source gas materials. Diamond like carbon (DLC) films were deposited on silicon (Si) substrates from acetylene (C2H2) or carbon-monoxide (CO) at two distinct temperatures. The fabricated films were characterized by Raman spectroscopy, FTIR spectroscopy, and scanning electron microscopy (SEM). The results reveal that the films prepared from CO gas exhibited soft conductive DLCs with a large number of graphite like structures whereas mostly insulating hydrogenated amorphous carbon DLCs were obtained from C2H2 gas. The deposition rate from CO was lower than from C2H2 due to etching by oxygen produced from the source gas. As the substrate temperature increased, progressive graphitization was incorporated to the films deposited from both gases. By using the pulsed DC plasma CVD system, the energy efficiency for CVD as the ratio of growth volume to energy consumption was dramatically improved with some distinctive differences in film properties as compared to our previous RF plasma CVD. The results showed many advantageous features of pulsed DC plasma CVD for replacing conventional RF plasma CVD.

Synthesis and electrochemical properties of Ti-doped DLC films by a hybrid PVD/PECVD process

Low electrical conductivity and poor adhesion to metallic substrates are the main drawbacks of diamond-like carbon (DLC) films when used in electrode applications. In this study, Ti-doped DLC films with various Ti contents were synthesized on metal Ti substrates by a hybrid PVD/PECVD process, where PECVD was used for deposition of DLC films and PVD was used for Ti doping. The effects of the Ti doping ratio on the microstructure, adhesion strength, and electrical and electrochemical properties of the DLC films were systematically investigated. An increase in the Ti content led to increased surface roughness and a higher sp2/sp3 ratio of the Ti-DLC films. Ti atoms existed as amorphous-phase Ti carbide when the Ti doping ratio was less than 2.8 at.%, while the nanocrystalline TiC phase was formed in DLC films when the Ti doping ratio was exceeded 4.0 at.%. The adhesion strength, electrical resistivity, electrochemical activity and reversibility of the DLC films were greatly improved by Ti doping. The influence of Ti doping ratio on the electrical and electrochemical properties of the DLC films were also investigated and the best performance was obtained at a Ti content of 2.8 at.%.

Combination of laser surface texturing and DLC coating on PEEK for enhanced tribological properties

Poly-ether-ether-ketone (PEEK) is a thermoplastic polymer marked by high mechanical properties and chemical inertia. PEEK is also a well-known biomaterial which has been subjected to intensive research over the last decades. In particular, it has recently been shown that laser surface texturing as well as diamond-like carbon (DLC) film deposition was able to reduce PEEK wear in tribological testing.This study focuses on evaluating the mechanical and tribological performance of PEEK surfaces modified via laser surface texturing (LST) combined with DLC coating. An ultrashort-pulse laser was used in order to pattern a hexagonal array of 33μm in diameter dimples onto the PEEK surface. The depth of dimples was varying (2, 12 and 21μm) as well as the dimple density (10, 30 and 48%). Subsequently, a 2-μm thick DLC film was deposited on the textured PEEK surface.It was shown that LST did not significantly affect the DLC/PEEK adhesion in pull-off testing, however, deep dimples and high dimple densities led to a large deformation of the substrate and caused the film to be more susceptible to cracking in scratch testing. The DLC-coated LST PEEK surfaces were rubbed against an alumina ball in dry conditions, water and bovine calf serum solutions. DLC-coated PEEK with shallow dimples and a low dimple density enabled to significantly, reduce wear and friction in distilled water and reduce wear in bovine calf serum compared with smooth DLC-coated PEEK. Smooth and LST DLC films exhibited a great stability in terms of microstructure and chemistry in all tested media.

Fast deposition of thick diamond-like carbon films by ion-beam technique

A diamond-like carbon film doped with TiC nanocrystallites (TiC–DLC) with a thickness of 35.8 μm was successfully prepared on a stainless steel substrate by employing a combination of metal vapor vacuum arc and filtered cathode vacuum arc techniques. A maximum deposition rate of 0.25 μm/min was achieved for TiC–DLC films. The structure and properties of the TiC–DLC films were systematically analyzed using different methods such as transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, X-ray diffraction, and friction and wear tests. The results indicated that typical a-C:H films containing nano-sized TiC grains were deposited which exhibit improved mechanical properties such as high cohesive strength, Vickers hardness, and capacity against high temperature. Parameter windows for C2H2 flow rate and solenoid current were also provided for the deposition of TiC–DLC films to meet the requirements for using the material for specific commercial applications.

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.

Influence of Ne sputtering gas on structure and properties of diamond-like carbon films deposited by pulsed-magnetron sputtering

The key process in diamond-like carbon (DLC) film deposition is the formation of sp3-C hybridized bond, which is believed to significantly link to the ionization degrees of the carbon atoms. Ne has a high ionization energy and can facilitate the ionization degree of sputtered carbon. In this paper, Ne and Ar gas mixture was used as the sputtering gas to prepare DLC film by using a pulsed-magnetron sputter. The influences of the Ne fraction in the sputtering gas mixture on the growth character, carbon bond structure, residual stress and mechanical properties of the as-deposited DLC films were studied carefully by using scanning electron microscope, Raman spectroscopy, stress tester and nano-indentation, respectively. The results reveal that the introduction of Ne in sputtering gas mixture can induce the structure densification of the coatings, and significantly increase the sp3 fraction of the DLC films. However, it was found that the sp3 fraction of the films increased little as the Ne fraction exceeded 25%. This phenomenon might be attributed to the reduction of the electron density of the plasma due to the increase of the Ne fraction in the sputtering gas mixture. The residual stress of the DLC films was believed to depend on the sp3 fraction of the films, and thus exhibited a similar changing trend to sp3 fraction as a function of Ne fraction. However, the hardness and elastic modulus of the films increased continuously as the Ne fraction increased. The structure densification and the increase of the sp3 fraction caused by the addition of Ne may be the main factors contributed to the increase of the hardness and elastic modulus of the films.

Ferromagnetism in a diamond-like carbon film after nickel implantation

Mass selective ion beam deposited diamond-like carbon (DLC) films were implanted with Ni+ ions at 30 keV with a fluence of 3.6 × 1016 atoms cm−2. The peak concentration of nickel in the implanted film was calculated to be 12.5% at an implantation depth of ∼30 nm into the DLC film. Raman measurements showed that the integrated intensity of the D peak at ∼1370 cm−1 divided by the G peak at ∼1560 cm−1 increases after ion implantation, which indicates that the implanted films are more graphitic. The implanted film shows ferromagnetic order at room temperature. However the saturation moment of the implanted film increased significantly when the measurement temperature was lowered. This may suggest that implantation leads to a dilute ferromagnetic semiconductor although more research is required.

Improvement of radiation stability of semi-insulating gallium arsenide crystals by deposition of diamond-like carbon films

We studied the properties of optical elements for the IR spectral range based on semi-insulating gallium arsenide (SI-GaAs) and antireflecting diamond-like carbon films (DLCF). Particular attention has been paid to the effect of penetrating γ-radiation on transmission of the developed optical elements. A Co60 source and step-by-step gaining of γ-irradiation dose were used for treatment of both an initial SI-GaAs crystal and DLCF/SI-GaAs structures. It was shown that DLCF deposition essentially increases degradation resistance of the SI-GaAs-based optical elements to γ-radiation. Particularly, the transmittance of the DLCF/SI-GaAs structure after γ-irradiation with a dose 9⋅104 Gy even exceeds that of initial structures. The possible mechanism that explains the effect of γ-radiation on the SI-GaAs crystals and the DLCF/SI-GaAs structures at different irradiation doses was proposed. The effect of small doses is responsible for non-monotonic transmission changes in both SI-GaAs crystals and DLCF/SI-GaAs structures. At further increasing the γ-irradiation dose, the variation of properties of both DLCF and SI-GaAs crystal influences on the transmission of DLCF/SI-GaAs system. At high γ-irradiation dose 1.4⋅105 Gy, passivation of radiation defects in the SI-GaAs bulk by hydrogen diffused from DLCF leads to increasing the degradation resistance of the SI-GaAs crystals coated with DLCF as compared with the crystals without DLCF.

Self-enhanced plasma discharge effect in the deposition of diamond-like carbon films on the inner surface of slender tube

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) have been proved to be highly effective for depositing diamond-like carbon (DLC) films on the inner surface of the slender quartz tube with a deposition rate of 1.3μm/min. Such a high-efficiency DLC films deposition was explained previously as the short electrons mean free path to cause large collision frequency between electrons and neutral particles. However, in this paper, we found that the inner surface material of the tube itself play a vital role on the films deposition. To disclose the mechanism of this phenomenon, the effect of different inner surface materials on plasma discharge was experimentally and theoretically investigated. Then a self-enhancing plasma discharge is discovered. It is found that secondary electrons emitted from the inner surface material, whatever it is the tube inner surface or deposited DLC films, can dramatically enhance the plasma discharge to improve the DLC films deposition rate.

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.

Tribological behavior of diamond-like carbon thin films deposited by the pulse laser technique at different substrate temperatures

Diamond-like carbon (DLC) thin films were deposited by the pulse laser deposition at different substrate temperatures. They were deposited at the temperature range 100–500°C and evaluated for their tribological behavior. The as-synthesized DLC films were characterized by different techniques. Ultrafine nanoparticles were observed in the deposited DLC films. The morphology of the deposited DLC films was significantly modified by increasing the substrate temperature. The particle size was increased from around 10nm to approximately 30nm by increasing the substrate temperature from 100 to 500°C. The surface roughness was also increased, beside a formation of DLC clusters mainly at 500°C. Raman and XPS spectra showed a significant improvement in the graphitization along with pronounced defects in the amorphous carbon structures in these DLC films. These modifications, induced by increasing the DLC substrate temperature have increased values of the friction coefficient and specific wear rate. These results showed that the DLC films with ultrafine nanoparticles have good prospect to be used as protective layers for metallic surfaces as they show low friction property and high wear ability.

Friction and wear of diamond-like carbon film deposited on CoCrMo alloy under different lubrication

Abstract CoCrMo alloys are widely used as artificial joint implants due to their excellent mechanical properties, good wear resistance and outstanding corrosion resistance. However, the risks of release of cobalt and chromium ions urge researchers to improve the wear resistance of implants further by using surface modification technology. Diamond-like carbon film with 3.0 μm thickness was deposited on the surface of CoCrMo alloy using ion-source-assisted magnetron sputtering. The friction coefficients of the CoCrMo alloy decreased remarkably under different conditions after the formation of diamond-like carbon film. After the deposition of diamond-like carbon film the wear rates of the CoCrMo alloy decreased by 52.4 %, 47.1 % and 49.4 %, under dry friction, physiological saline, and bovine serum lubrication, respectively.

Effect of additional sample bias in Meshed Plasma Immersion Ion Deposition (MPIID) on microstructural, surface and mechanical properties of Si-DLC films

Meshed Plasma Immersion Ion Deposition (MPIID) using cage-like hollow cathode discharge is a modified process of conventional PIID, but it allows the deposition of thick diamond-like carbon (DLC) films (up to 50μm) at a high deposition rate (up to 6.5μm/h). To further improve the DLC film properties, a new approach to the MPIID process is proposed, in which the energy of ions incident to the sample surface can be independently controlled by an additional voltage applied between the samples and the metal meshed cage. In this study, the meshed cage was biased with a pulsed DC power supply at −1350V peak voltage for the plasma generation, while the samples inside the cage were biased with a DC voltage from 0V to −500V with respect to the cage to study its effect. Si-DLC films were synthesized with a mixture of Ar, C2H2 and tetramethylsilane (TMS). After the depositions, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectrons spectroscopy (XPS), Raman spectroscopy and nanoindentation were used to study the morphology, surface roughness, chemical bonding and structure, and the surface hardness as well as the modulus of elasticity of the Si-DLC films. It was observed that the intense ion bombardment significantly densified the films, reduced the surface roughness, reduced the H and Si contents, and increased the nanohardness (H) and modulus of elasticity (E), whereas the deposition rate decreased slightly. Using the H and E data, high values of H3/E2 and H/E were obtained on the biased films, indicating the potential excellent mechanical and tribological properties of the films. In this paper, the effects of the sample bias voltage on the film properties are discussed in detail and the optimal bias voltage is presented.

Abutment Coating With Diamond-Like Carbon Films to Reduce Implant-Abutment Bacterial Leakage.

The influence of diamond-like carbon (DLC) films on bacterial leakage through the interface between abutments and dental implants of external hexagon (EH) and internal hexagon (IH) designs was evaluated. Film deposition was performed by plasma-enhanced chemical vapor deposition. Sets of implants and abutments (n = 30 per group, sets of 180 implants) were divided according to connection design and treatment of the abutment base: 1) no treatment (control); 2) DLC film deposition; and 3) Ag-DLC film deposition. Under sterile conditions, 1 μL Enterococcus faecalis was inoculated inside the implants, and abutments were tightened. The sets were tested for immediate external contamination, suspended in test tubes containing sterile culture broth, and followed for 5 days. Turbidity of the broth indicated bacterial leakage. At the end of the period, the abutments were removed and the internal content of the implants was collected with paper points and plated in Petri dishes. After 24-hour incubation, they were assessed for bacterial viability and colony-forming unit counting. Bacterial leakage was analyzed by χ(2) and Fisher exact tests (α = 5%). The percentage of bacterial leakage was 16.09% for EH implants and 80.71% for IH implants (P <0.0001). The bacterial load was higher inside IH implants (P = 0.000). The type of implant significantly influenced the results (P = 0.000), whereas the films did not (P = 0.487). IH implants show a higher frequency of bacterial leakage; and DLC and Ag-DLC films do not significantly reduce the frequency of bacterial leakage and bacteria load inside the implants.

Deposition and thermal conductivity of diamond-like carbon film on a silicon substrate

Diamond-Like Carbon (DLC) is thought to be a potential material in solving heat dissipation problems in light emitting diode module packages. It is of vital importance in evaluating the thermal conductivity of DLC film deposited on a silicon substrate. In this paper, the molecular dynamics method is used to simulate the formation of a DLC film by the deposition of carbon atoms on a isilicon substrate. Tersoff potential is adopted to reproduce the structures and densities of silicon, carbon, and SiC. A silicon substrate consisting of 544 atoms is located at the bottom of the simulation domain. The substrate is kept at a temperature of 600 K through a Noose-Hover thermostat. Carbon atoms are injected into the substrate individually every 0.5 ps at an energy of 1 eV. After a 7.5 ns deposition process, a 4 nm amorphous film containing 15000 carbon atoms is formed. Injected carbon atoms and substrate silicon atoms are intermixed at the bottom layer of the deposited film while the rest of the film contains only carbon atoms. The density of the film decreases slightly with the increase of the height of the deposited film and the average density is 2.8 g/cm3. Analysis of the coordination number shows that the sp3 fraction of carbon atoms in the film also decreases with the increase of the height of the deposited film, with a maximum value of 22%. It might be caused by the continuous impacts of the subsequently injected carbon atoms on the previously formed DLC film. The thermal conductivities of the DLC film in the planar and normal directions are calculated by the Green-Kubo method. The thermal conductivity of pure diamond film is also calculated for comparison. The results show that the planar thermal conductivity of the deposited DLC film is approximately half of that of the pure diamond film with the same size. It is higher than the normal thermal conductivity of the deposited film. The thermal conductivities of the DLC film in both planar and normal directions increase with the increase of film density and sp3 fraction in the DLC film. The results indicate that the local tetrahedral structure of sp3 carbon atoms contributes to the improvement of thermal conductivity in the DLC film.

Formation of diamond-like carbon thin films using barrier-type surface discharge plasma under atmospheric pressure

We studied the deposition of diamond-like carbon (DLC) thin films using barrier-type surface discharge plasma under atmospheric pressure. The main radicals generated by the barrier-type surface discharge using H2, CH4, and He as the plasma gases were Hα, Hβ, and CH. The emission intensities increased as the ratio of CH4 in the mixed gas decreased, and the mixed gas ratios of 2% CH4, 18% H2, 80% He were appropriate for the generation of the barrier-type surface discharge. The gas flow rate and applied voltage required to achieve a suitable plasma state for deposition of the DLC films varied depending on the polarity of the applied pulse. When a negative pulse is used, homogenous films can be obtained on the silicon wafer under the entire hole of the electrode; however, the deposition rate becomes very low in the range of 1.8–5.8 nm/min because the surface streamer plasma is very weak. On the other hand, using a bipolar and a positive pulse, a relatively high deposition rate in the range of 10–30 nm/min can be achieved on the silicon wafer under the central part of the electrode, although the thickness of the DLC films becomes nonuniform at the edge part of the electrode. The appropriate conditions of the DLC film deposition in this study were the pulse voltages of 6–8 kV and a gas flow rate of 1500 mL/min when using bipolar- and positive-pulse voltages. The relatively hard DLC films (6–8 GPa) were obtained under these conditions.

Researches on uniformity of diamond-like carbon films deposited on inner surface of long and slender quartz glass tube by enhanced glow discharge plasma immersion ion implantation and deposition

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PIII&D) has been successfully used for depositing diamond-like carbon (DLC) on the inner surface of the quartz glass tube with an inner diameter as small as 0.9mm and aspect ratios of over 100. And the uniformity is a key problem for the DLC films deposited on the inner surface. By changing the C2H2 flow rate and negative voltage, the effects of the gas flow rate and voltage on the uniformity of the DLC films deposited on the inner surface of the quartz glass tube are experimentally examined. The electron-neutral collision frequency, νe, is used to qualitatively analyze the mechanism of uniformizing DLC films. The results reveal that uniform DLC films may be obtained by balancing both the gas flow rate and the negative voltage.

Improvement in the degradation resistance of silicon nanostructures by the deposition of diamond-like carbon films

It is established that the deposition of a diamond-like film onto a structure with silicon nanoclusters in a silicon dioxide matrix yields an increase in the long-wavelength photoluminescence intensity of silicon nanoclusters due to the passivation of active-recombination centers with hydrogen and a shift of the photoluminescence peak to the region of higher photosensitivity of silicon-based solar cells. It is also shown that, due to the deposited diamond-like film, the resistance of such a structure to degradation upon exposure to γ radiation is improved, which is also defined by the effect of the passivation of radiation-induced activerecombination centers by hydrogen that is released from the films during treatment.