Diamond-like Carbon Thin Films Research Articles

Improvement of the Harmonic Technique of Probe for Measurements of Electron Temperature and Ion Density

Conventional Langmuir probe techniques usually face the difficulty of being used in processing plasmas where dielectric compounds form, due to rapid failure by surface insulation. A solution to the problem, the so-called harmonic probe technique, had been proposed and shown effectiveness. In this study, the technique was investigated in detail by changing bias signal amplitudes V0, and evaluated its accuracy by comparing with the conventional Langmuir probe. It was found that the measured electron temperature Te increased with V0, but showing a relatively stable region when V0 > Te/e in which it was close to the true Te value. This is contrary to the general consideration that V0 should be smaller than Te/e for accurate measurement of Te. The phenomenon is interpreted by the non-negligible change of the ion current with V0 at low V0 values. On the other hand, the measured ni also increased with V0 due to the sheath expansion, and to improve the accuracy of ni it needs to linearly extrapolate the ni-V0 trend to V0=0. The results were applied to a diagnosis of the plasmas for chemical vapor deposition of diamond-like carbon thin films and the relationship between plasma parameters and films deposition rates was obtained.

Networking of human mesenchymal stem cells by diamond-like carbon thin film partially deposited PDMS substrates

Networking of human mesenchymal stem cells by diamond-like carbon thin film partially deposited PDMS substrates

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.

Prediction Surface Morphology of Nanostructure Fabricated by Nano-Oxidation Technology.

Atomic force microscopy (AFM) was used for visualization of a nano-oxidation technique performed on diamond-like carbon (DLC) thin film. Experiments of the nano-oxidation technique of the DLC thin film include those on nano-oxidation points and nano-oxidation lines. The feature sizes of the DLC thin film, including surface morphology, depth, and width, were explored after application of a nano-oxidation technique to the DLC thin film under different process parameters. A databank for process parameters and feature sizes of thin films was then established, and multiple regression analysis (MRA) and a back-propagation neural network (BPN) were used to carry out the algorithm. The algorithmic results are compared with the feature sizes acquired from experiments, thus obtaining a prediction model of the nano-oxidation technique of the DLC thin film. The comparative results show that the prediction accuracy of BPN is superior to that of MRA. When the BPN algorithm is used to predict nano-point machining, the mean absolute percentage errors (MAPE) of depth, left side, and right side are 8.02%, 9.68%, and 7.34%, respectively. When nano-line machining is being predicted, the MAPEs of depth, left side, and right side are 4.96%, 8.09%, and 6.77%, respectively. The obtained data can also be used to predict cross-sectional morphology in the DLC thin film treated with a nano-oxidation process.

Characterization of diamond-like carbon thin film synthesized by RF atmospheric pressure plasma Ar/CH4 jet

The growth of diamond like carbon (DLC) on a Pyrex glass was investigated by a radio frequency (RF) atmospheric pressure plasma jet (APPJ). The plasma jet with capacitive configuration ran by a radio frequency power supply at 13.56 MHz. Alumina ceramic was used as dielectric barrier. Ar and CH4 were used in atmospheric pressure as carrier and precursor gases, respectively. Diamond like carbon thin films were deposited on Pyrex glass at substrate temperature and applied power of 130 °C and 250 Watts, respectively. Performing field emission scanning electron microscope (FE-SEM) and laser Raman spectroscopy analysis resulted in deposition rate and the ID/IG ratio of 21.31 nm/min and 0.47, respectively. The ID/IG ratio indicated that the coating possesses relative high sp3 content The optical emission spectroscopy (OES) diagnostic was applied to diagnose plasma jet species. Estimating electron temperature and density of the RF-APPJ resulted in 1.36 eV and 2.75 × 1014 cm−3 at the jet exit, respectively.

Thickness Effects of TiC Interlayer on Tribological Properties of Diamond-Like Carbon Prepared by Unbalanced Magnetron Sputtering Method.

We investigated the tribological properties of diamond-like carbon (DLC) films prepared with TiC interlayer of various thicknesses as the adhesive layer. DLC and TiC thin films were prepared using unbalanced magnetron (UBM) sputtering method using graphite and titanium as targets. TiC films as the interlayer were deposited under DLC films and various physical, tribological, and structural properties of the films fabricated with various TiC interlayer thicknesses were investigated. With various TiC interlayer thicknesses under DLC films, the tribological properties of films were improved with increasing thickness and the DLC/TiC layer fabricated by unbalanced magnetron sputtering method are exhibited maximum high hardness over 27 GPa and high elastic modulus over 242 GPa, and a smooth surface below 0.09 nm.

The influence of different silicon adhesion interlayers on the tribological behavior of DLC thin films deposited on steel by EC-PECVD

Diamond-like carbon (DLC) is a hydrogenated amorphous carbon (a-C:H) thin film material owing to its unique tribological properties that may open great opportunities for new applications. However, DLC presents low chemical affinity with metallic alloys and high intrinsic stress, prompting film delamination and poor adherence on the substrate. In the present work, we performed a systematic study about structural and tribological properties of a-C:H thin films grown on steel by introducing adhesive silicon-containing interlayers deposited at different processing temperatures and times. The studied bi-layers were deposited by electrostatic confinement plasma enhanced chemical vapor deposition (EC-PECVD) and were characterized by several techniques. The results showed that the adhesive interlayers produced from tetramethylsilane are chemically structured as a non-stoichiometry hydrogenated amorphous silicon carbide alloy (a-SiCx:H). Its structure, chemical composition and thickness are very dependent on deposition conditions. The thickness of the interlayers increases with deposition time and decreases with deposition temperature. The interlayer contains less hydrogen and silicon atoms at higher deposition temperatures, with enhanced formation of Si–C bonds in its structure. This last chemical event is correlated with the rise in the critical load values found for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 573K to 823K. On the other hand, the interlayer contains less carbon atoms at higher deposition times, decreasing the critical load values for a-C:H film delamination when the a-SiCx:H interlayers are deposited from 5min to 10min.

Enhancement of adhesion and corrosion resistance of diamond-like carbon thin films on Ti–6Al–4V alloy by nitrogen doping and incorporation of nanodiamond particles

Abstract Pure diamond-like-carbon (DLC) and nitrogenated diamond-like-carbon (N-DLC) were deposited by Ion Beam Deposition using a low energy End-Hall Source on titanium and silicon substrates. The beam energy used during the deposition had a mean value of 65 eV. The structure and composition of the films were investigated by visible Raman Spectroscopy and X-ray Absorption Spectroscopy (XAS). Hardness and Young's modulus of the coatings were measured by nanoindentation. Adhesion of the coatings to the substrates was measured by Rockwell C indentation tests. To investigate the corrosion property of the coatings, Tafel polarization tests were performed from − 1.5 V to 1.5 V in 0.89% NaCl solution using the Standard Calomel Electrode as a reference. In our studies, DLC deposited directly on bare titanium alloy (Ti–6Al–4 V) shows poor adhesion and premature delamination. Pre-deposited nanodiamonds on titanium substrate greatly enhance the adhesion. The films produced on nano-diamond pretreated substrates are dense, smooth, and uniform, and DLC films show an average hardness value of 11 GPa, slightly higher than N-DLC (with an average hardness of 9 GPa). Despite its relatively lower hardness, nitrogen doping increases both adhesion and corrosion resistance of DLC coating.

Friction and wear of diamond-like carbon thin films deposited via magnetron sputtering under different bias voltages

This paper presents studies on the friction and wear of diamond-like carbon thin films deposited on steel substrates via magnetron sputtering. The testing mode is ball-on-disc. The graphitization of diamondlike carbon during the tribotest explains the low coefficients of friction (0,09-0,15) observed. The bias voltage plays an important role on the film’s microstructure thus the friction and wear of the films in tribotests. The results showed great potential for applications of diamond-like carbon thin films in engineering.

Hybrid carbon nanomaterials for electrochemical detection of biomolecules

Electrochemical detection of different biomolecules in vivo is a promising path towards in situ monitoring of human body and its functions. However, there are several major obstacles, such as sensitivity, selectivity and biocompatiblity, which must be tackled in order to achieve reliably and safely operating sensor devices. Here we show that by utilizing hybrid carbon materials as electrodes to detect two types of neurotransmitters, dopamine and glutamate, several advantages over commonly used electrode materials can be achieved. In particular, we will demonstrate here that it is possible to combine the properties of different carbon allotropes to obtain hybrid materials with greatly improved electrochemical performance. Three following examples of the approach are given: (i) diamond-like carbon (DLC) thin film electrodes with different layer thicknesses, (ii) multi-walled carbon nanotubes grown directly on top of DLC and (iii) carbon nanofibres synthesized on top of DLC thin films. Detailed structural and electrochemical characterization is carried out to rationalize the reasons behind the observed behvior. In addition, results from the atomistic simulations are utilized to obtain more information about the properties of the amorphous carbon thin films.

Free standing diamond-like carbon thin films by PLD for laser based electrons/protons acceleration

This study we reports for the first time on the synthesis and optical characteristics of free standing diamond-like carbon (DLC) deposited by pulsed laser deposition (PLD) onto graphene buffer layers for ultrahigh intensity laser based electron/proton acceleration applications. The fingerprint techniques of micro-Raman, UV–VIS–NIR and the IR spectroscopic investigations indicate that the suitability of such free standing DLC thin-films within the laser window and long wave infrared (LWIR) spectral range and hence their appropriateness for the targeted applications.

Fabrication of DLC thin films with improved diamond-like carbon character by the application of external magnetic field

Diamond-like carbon (DLC) thin films were grown on Si-(100) substrates by a magnetically-assisted pulsed laser deposition (PLD) technique. The role of magnetic field on the structural, morphological, mechanical properties and deposition rate of DLC thin films has been studied. The obtained films were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and nanoindentation techniques. It was found that the diamond-like character, thickness and deposition rate of the DLC films increase in the presence of magnetic field. The films deposited under magnetic field exhibit a denser microstructure and smoother surface with lower surface roughness. Meanwhile, the mechanical properties of the magnetically processed DLC thin films experience an improvement, relative to the conventionally processed ones. It seems that the DLC films deposited under magnetic field can be better candidate for hard and wear resistance coating applications.

Synthesis and characterization of boron incorporated diamond-like carbon thin films

Boron incorporated diamond-like carbon (B-DLC) (up to 8wt.% boron) thin films were synthesized on silicon wafers using biased target ion beam deposition technique, where diamond-like carbon (DLC) was deposited by ion beam deposition and boron (B) was simultaneously incorporated by biased target sputtering of a boron carbide (B4C) target under different conditions. Pure DLC films and B–C films were also synthesized by ion beam deposition and biased target sputtering of B4C under similar conditions, respectively, as reference samples. The microstructure and mechanical properties of the synthesized films have been characterized by various technologies. It has been found that B exists in different states in B-DLC, including carbon-rich and B-rich boron carbides, boron suboxide and boron oxide, and the oxidation of B probably occurs during the film deposition. The incorporation of B into DLC leads to the increase of sp3 bonded carbon in the films, the increase of both film hardness and elastic modulus, and the decrease of both surface roughness and friction coefficient. Furthermore, the content of sp3 bonded carbon, film hardness and elastic modulus increase, and the film surface roughness and friction coefficient decrease with the increase of B-rich carbide in the B-DLC films.

Flame retardant properties of plasma pre-treated/diamond-like carbon (DLC) coated cotton fabrics

Textiles with superior anti-flammability properties combined with minimal environmental impact are extremely necessary to reduce fire-related issues. In this regard, diamond-like carbon (DLC) coatings on cotton fabrics may represent promising candidates as potential flame-retardant (FR) materials. Herein, superhydrophobic and fire-resistant cotton fabrics were fabricated through a two-step plasma strategy by alternately exposing substrates to H2 and O2 plasma pre-treatments and subsequent DLC deposition. Fourier transform-infrared spectroscopy analysis has revealed that different plasma pre-treatments can impose surface modifications on the chemical structure of cotton, especially in carboxylic and hydroxyl groups, leading to a radical alteration of surface roughness and of the crystalline cellulosic external structure. These changes deeply influenced the growth of DLC thin films and the surface properties of cotton fabric because of the combination of a hierarchical structure and surface chemistry as verified using field emission gun-scanning electron microscopy and water contact angle measurements. The effects of both specific gases used in the pre-treatment step and duration of pre-treatment were analysed and compared using thermogravimetric analyses. The H2-pre-treated DLC cottons exhibited good potential as an FR material, showing improved thermal stability in respect to untreated cotton, as evidenced by increased ignition times. Moreover, vertical burning tests have demonstrated that DLC-cotton systems exhibit enhanced flammability resistance.

Cell proliferation on modified DLC thin films prepared by plasma enhanced chemical vapor deposition.

Recently, diamondlike carbon (DLC) thin films have gained interest for biological applications, such as hip and dental prostheses or heart valves and coronary stents, thanks to their high strength and stability. However, the biocompatibility of the DLC is still questionable due to its low wettability and possible mechanical failure (delamination). In this work, DLC:N:O and DLC: SiOx thin films were comparatively investigated with respect to cell proliferation. Thin DLC films with an addition of N, O, and Si were prepared by plasma enhanced CVD from mixtures of methane, hydrogen, and hexamethyldisiloxane. The films were optically characterized by infrared spectroscopy and ellipsometry in UV-visible spectrum. The thickness and the optical properties were obtained from the ellipsometric measurements. Atomic composition of the films was determined by Rutherford backscattering spectroscopy combined with elastic recoil detection analysis and by x-ray photoelectron spectroscopy. The mechanical properties of the films were studied by depth sensing indentation technique. The number of cells that proliferate on the surface of the prepared DLC films and on control culture dishes were compared and correlated with the properties of as-deposited and aged films. The authors found that the level of cell proliferation on the coated dishes was high, comparable to the untreated (control) samples. The prepared DLC films were stable and no decrease of the biocompatibility was observed for the samples aged at ambient conditions.

Effects of TiCN interlayer on bonding characteristics and mechanical properties of DLC-coated Ti-6Al-4V ELI alloy

The delamination of diamond-like carbon (DLC) films on titanium alloys can be prevented by using an interlayer coating. In this study, a DLC film was deposited using a filtered vacuum arc (FVA), and a TiCN interlayer was applied between the Ti-6Al-4V ELI alloy and the DLC film. The interface boundary, carbon bonding, and mechanical properties of the DLC-coated Ti-6Al-4V were investigated, and the results indicate that DLC thin films with a TiCN interlayer are suitable coating materials for Ti-6Al-4V. The coated DLC films had a crystal structure that consisted of an amorphous phase while the TiCN interlayer exhibited a crystalline structure. The TiCN interlayer was necessary in order to improve the hardness, elastic modulus, and interface bonding. The TiCN interlayer on the DLC film was observed to increase the ID/IG ratio as a result of the sp3 bonding of the carbon atoms. The resulting friction coefficient of the DLC-coated Ti-6Al-4V with the TiCN interlayer had an extremely low value of 0.03.

Optical, structural and bonding properties of diamond-like amorphous carbon films deposited by DC magnetron sputtering

In the present study effects of working pressure on the optical, structural and bonding properties of diamond-like amorphous carbon (DLC) thin films prepared by direct current (DC) magnetron sputtering technique were investigated. XPS analysis is used to determine the bonding properties and optical spectroscopy to determine optical constants. Increasing the working pressure from 2 to 50mTorr is shown to strongly influence the optical and structural properties due to a large increase in the sp3/sp2 ratio from 0.51 to 2.81. With increasing pressure, the real part of the refractive index decreases from 2.4 to 1.6 at 550nm, while the imaginary part also decreases from 0.38 to 0.02 at 550nm, leading to a large increase in optical transmission in the visible region from 10% to 80% for films of approximately equal thickness, while the Tauc gap of the films increases from 0.80eV to 2.06eV. RMS surface roughnesses of the films increased from 0.95nm to 4.69nm with increasing working pressure. These results indicate that the sp3 sites mainly consist of C–H bonds at higher working pressures and the optical and structural properties are consistent with a change from graphitic to a more polymer-like DLC. The resulting strong increase of transparency in the visible range extends the optically useful range for DLC films into the visible part of the spectrum, for applications such as low-e coatings for windows.

Effects of the ion-beam voltage on the properties of the diamond-like carbon thin film prepared by ion-beam sputtering deposition**Project supported by the National Natural Science Foundation of China (Grant No. 61235011) and the Science Foundation of the Science and Technology Commission of Tianjin Municipality, China (Grant Nos. 13JCYBJC17300 and 12JCQNIC01200).

Diamond-like carbon (DLC) thin film is one of the most widely used optical thin films. The fraction of chemical bondings has a great influence on the properties of the DLC film. In this work, DLC thin films are prepared by ion-beam sputtering deposition in Ar and CH4 mixtures with graphite as the target. The influences of the ion-beam voltage on the surface morphology, chemical structure, mechanical and infrared optical properties of the DLC films are investigated by atomic force microscopy (AFM), Raman spectroscopy, nanoindentation, and Fourier transform infrared (FTIR) spectroscopy, respectively. The results show that the surface of the film is uniform and smooth. The film contains sp2 and sp3 hybridized carbon bondings. The film prepared by lower ion beam voltage has a higher sp3 bonding content. It is found that the hardness of DLC films increases with reducing ion-beam voltage, which can be attributed to an increase in the fraction of sp3 carbon bondings in the DLC film. The optical constants can be obtained by the whole infrared optical spectrum fitting with the transmittance spectrum. The refractive index increases with the decrease of the ion-beam voltage, while the extinction coefficient decreases.

Degradation of Lubricant Film and Carbon Overcoat Subjected to Laser Heating in an Inert Gas Environment in Thermally Assisted Magnetic Recording

This paper investigates the depletion of a thin lubricant film subjected to laser heating in an inert gas environment, and we experimentally elucidate the fundamental characteristics and mechanisms related to lubricant depletion in air and inert gas environments. In addition, fundamental experimental studies are conducted to understand the structural stability or degradation, such as through oxidation and graphitization of diamond-like carbon (DLC) thin films subjected to laser heating, in an inert gas environment compared to air environment. The degradation and its mechanisms are investigated using Raman spectroscopy. The results suggest that less degradation would occur by oxidation for a DLC thin film in an inert gas environment than air environment. It is found that, from the view point of the reliability in the head/disk interface, the lubricant depletion issue is more crucial than DLC thin-film degradation for thermally assisted magnetic recording in an inert gas environment.

Influence of diamond and graphite bonds on mechanical properties of DLC thin films

Mechanical properties of diamond-like carbon thin films with various ratios of sp3/sp2 bonds were studied. The films were prepared in argon atmosphere (0.25 Pa) by laser deposition method for laser energy densities from 4 J·cm−2 to 14 J·cm−2. The sp2 and sp3 bonds were calculated by X-ray photoelectron spectroscopy. Films contained sp3 bonds up to 70 %. Surface properties as roughness and atomic force microscopy topology were measured. Hardness (and reduced Young's modulus) were determined by nanoindentation and reached of 30 GPa (203 GPa). Films adhesion was studied using scratch test and was up to 12 N for biomedical alloy (titanium substrates – Ti-6Al-4V). Relations among deposition conditions and measured properties are presented.