Characterization Of Diamond-like Carbon Films Research Articles

Characterization of Diamond-like carbon films produced by electron- beam physical vapor deposition

Diamond-like carbon (DLC) films were deposited at 300 °C, 400 °C and 500 °C on 304 L stainless steel substrates by electron-beam physical vapor deposition. The obtained coatings were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy and X-ray photo electron spectroscopy (XPS). The FTIR results demonstrate the presence of sp3 and sp2 vibrations corresponding to a diamond-like carbon phase and graphite, respectively. Raman and XPS analysis confirm a presence of high quantity of CC bonds in sp3 state in the deposited DLC films. Increasing the substrate temperature from 300 °C to 500 °C led to a decreasing of the hardness from 4.5 GPa to 3.2 GPa.

Evaluation of Anti-Adhesion Characteristics of Diamond-Like Carbon Film by Combining Friction and Wear Test with Step Loading and Weibull Analysis.

Anti-adhesion characteristics are important requirements for diamond-like carbon (DLC) films. The failure load corresponding to the anti-adhesion capacity varies greatly on three types of DLC film (hydrogen-free amorphous carbon film (a-C), hydrogenated amorphous carbon film (a-C:H), and tetrahedral hydrogen-free amorphous carbon film (ta-C)) in the friction and wear test with step loading using a high-frequency, linear-oscillation tribometer. Therefore, a new method that estimates a representative value of the failure load was developed in this study by performing a statistical analysis based on the Weibull distribution based on the assumption that the mechanism of delamination of a DLC film obeys the weakest link model. The failure load at the cumulative failure probabilities of 10% and 50% increased in the order ta-C < a-C:H < a-C and ta-C < a-C < a-C:H, respectively. The variation of the failure load, represented by the Weibull slope, was minimum on ta-C and maximum on a-C:H. The rank of the anti-adhesion capacity of each DLC film with respect to the load obtained by a constant load test agreed with the rank of the failure load on each DLC film at the cumulative failure probability of 10% obtained by Weibull analysis. It was found to be possible to evaluate the anti-adhesion capacity of a DLC film under more practical conditions by combining the step loading test and Weibull analysis.

Characteristics of Diamond-Like Carbon Films Fabricated by Using a Filtered Vacuum Arc System for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) based on diamond-like carbon (DLC) anti-reflection coating (ARC) thin films are investigated. The DLC film was proposed to improve the cell performance of DSSC devices. In this work, the DLC films were fabricated by using the FVA (filtered vacuum arc) method, the structural, optical, and physical properties of the fabricated DLC films with various film thicknesses were experimentally investigated. All DLC films showed smoother and more uniform surfaces with increasing film thickness. Furthermore, the values of rms surface roughness, friction coefficient, the refractive index, and the absorption coefficient increased with increasing film thickness, the hardness and the elastic modulus of the DLC films were improved. These results are associated with the increased sp3 contents in the amorphous carbon film due to the effects of the energetic ion bombardment during film deposition.

Deposition and characterization of diamond-like carbon films by electron cyclotron resonance microwave plasma enhanced unbalanced magnetron sputtering

We introduce the structure and operational principles of an electron cyclotron resonance microwave enhanced plasma source ion implantation/deposition system for the creation of diamond-like carbon (DLC) film. Using an unbalanced magnetron sputtering process, DLC film was deposited on the silicon substrate using high-purity graphite as the carbon source and argon as the sputtering gas. We used Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy characterization methods to study the structure and chemical ratio of the film under different deposition parameters. The results show that the optimal substrate bias and target-substrate distance are 50 V and 150 mm, respectively; when the deposition bias is increased, the film can be made denser and smoother. We also discuss the formation mechanism of DLC film based on the results of structural characterization.

Preparation and characterisation of diamond-like carbon films prepared by MW ECR/PACVD process deposited on 41Cr–Al–Mo7 nitrided steel

ABSTRACTIn the present work, Diamond-Like Carbon (DLC) films were deposited by the Microwave Electron Cyclotron Resonance/Plasma-Assisted Chemical Vapour Deposition process on 41Cr–Al–Mo7 nitrided steel using a benzene–argon gas mixture. The quality of DLC films grown on nitrided steel using different deposit conditions such as benzene flow rate, temperature and time was investigated. Microstructural analysis by Raman spectroscopy showed main G-band peaks are localised between 1564 and 1595 cm−1, while the D-band peaks are centred at 1297 cm−1. Fourier Transform Infrared Spectroscopy showed the peaks attributed to C–H bending and stretching vibration modes are in the range of 2600–3100 cm−1. The microstructure, surface morphology and mechanical properties of the films were examined by X-ray diffraction, atomic force microscopy and use of a Vickers indenter (Zwick). The deposition parameters of the coatings have been studied and optimised to improve mechanical properties. The observed increase in adhesion is related to the formation of (Fe,Cr)3C, Cr3C2 and Cr23C6 interlayer phases. DLC films showed a better wear resistance, higher hardness and low friction coefficient compared to nitrided layers tested for comparison.

Characterization of diamond-like carbon films prepared using various source gases by plasma-based ion implantation and deposition

Diamond-like carbon (DLC) films are prepared by bipolar-type plasma-based ion implantation and deposition (PBIID) using the combination of toluene (C7H8), tetramethylsilane (TMS: Si(CH3)4) and nitrogen (N2) as a source gas. The characteristics and mechanical properties of the films are examined by Raman spectroscopy and nanoindentation measurement, respectively. The film composition is evaluated by X-ray photoelectron spectroscopy (XPS). Raman analysis reveals that polymer-like structure is formed and increases with increasing Si content. The hardness and Young's modulus decrease with increasing Si content. The ratio of Si to C (Si:C) in the films is almost equal to that in the source gases. The addition of N2 together with TMS causes a slight increase of sp2 ring clusters and improvement of the mechanical properties probably due to the formation of SiN bonds. Moreover, the Si:C ratio in the films is enhanced by the N2 addition.

Evaluation of anti-adhesion characteristics of diamond-like carbon film using high-frequency, linear-oscillation tribometer

Abstract The basic significance of a method of evaluating the anti-adhesion characteristics of diamond-like carbon (DLC) films by a reciprocating wear test using a high-frequency, linear-oscillation tribometer under a step loading condition was verified with a single test condition, and processes up to the occurrence of delamination were investigated in this study. The failure load, corresponding to the anti-adhesion capacity of the DLC film, varied greatly. When delamination of the DLC film occurred, the friction coefficient increased and the oscillation stroke decreased. However, these trends up to the occurrence of delamination were not uniform. Even when a delamination did not occur, the friction coefficient may have increased and the oscillation stroke may have decreased owing to the embedment of wear debris. It was revealed that the process from running-in to the occurrence of delamination exhibited two patterns depending on whether or not the embedment of wear debris occurred. A model representing the relationship between the phenomena occurring at sliding surfaces, the friction coefficient and the oscillation stroke was proposed.

Chemical structure and electrical characteristics of diamondlike carbon films

The relationship between the chemical structure and electrical characteristics of diamondlike carbon (DLC) films has been clarified. The DLC films were formed in atmospheres with different ratios of methane to argon under the photoemission-assisted Townsend discharge. The dependence of the dielectric constant of the films on methane concentration in the synthesis was arch-like with a maximum. The breakdown strength was constant irrespective of the synthesis atmosphere and was approximately the same for both electrical polarizations. Raman spectra of the films were deconvoluted into five active bands. Raman analysis in conjunction with the sp2 cluster model elucidated the DLC structure. The sp2 cluster model comprises sp2 clusters floating in a dielectric matrix sea. The sp2 clusters were rather aliphatic for films formed in low methane concentration. The clusters grew to become aromatic with increasing methane concentration. Defects or dangling bonds increased similarly, but they were terminated with hydrogen for films formed in high methane concentration. The hydrogen-terminated bonds occupied large amounts of space in the DLC films, causing internal strain. The dielectric constant of the whole DLC film was determined by the size of sp2 clusters, dielectric constant of the matrix sea material, and space volume induced by the hydrogen–carbon bonds. The breakdown strength was determined by the balance between the size of sp2 clusters and density of dangling bonds in the matrix sea. However, because the dependences of these factors on methane concentration were opposing, the breakdown strength was approximately constant irrespective of methane concentration.

Structural Characteristics of Diamond-Like Carbon Films Synthesized by Different Methods

In the present study, the Raman spectra of diamond-like amorphous (a-C) and hydrogenated amorphous (a-C:H) carbon films on silicon obtained using the ion-beam methods and the pulse cathodic arc deposition technique were investigated with the aim of elucidating the relation between the hardness and structure of the films. The hardness of the samples used in the present study was 19 – 45 GPa. Hydrogenated carbon films were synthesized using END–Hall ion sources and a linear anode layer ion source (LIS) on single-crystal silicon substrates. The gas precursors were CH4 and C3H8, and the rate of the gas flow fed into the ion source was 4.4 to 10 sccm. The ion energies ranged from 150 to 600 eV. a-C films were deposited onto Si substrates using the pulse cathodic arc deposition technique. The films obtained by the pulse arc technique contained elements with an ordered structure. In the films synthesized using low- (150 eV) and high-energy (600 eV) ions beams, an amorphous phase was the major phase. The significant blurriness of the diffraction rings in the electron diffraction patterns due to a large film thickness (180 – 250 nm) did not allow distinctly observing the signals from the elements with an ordered structure against the background of an amorphous phase.

Evaluation of anti-adhesion characteristics of diamond-like carbon film using high-frequency, linear-oscillation tribometer

The basic significance of a method of evaluating the anti-adhesion characteristics of diamond-like carbon (DLC) films by a reciprocating wear test using a high-frequency, linear-oscillation tribometer under a step loading condition was verified with a single test condition, and processes up to the occurrence of delamination were investigated in this study. The failure load, corresponding to the anti-adhesion capacity of the DLC film, varied greatly. When delamination of the DLC film occurred, the friction coefficient increased and the oscillation stroke decreased. However, these trends up to the occurrence of delamination were not uniform. Even when a delamination did not occur, the friction coefficient may have increased and the oscillation stroke may have decreased owing to the embedment of wear debris. It was revealed that the process from running-in to the occurrence of delamination exhibited two patterns depending on whether or not the embedment of wear debris occurred. A model representing the relationship between the phenomena occurring at sliding surfaces, the friction coefficient and the oscillation stroke was proposed.

The Relationship Between Characteristics of DLC Film and Electron Temperature Measured by Optical Emission Spectroscopy

Electron temperatures in Ne or Ar plasma produced by a dc magnetron sputtering source were measured by 2-D optical emission spectroscopy using a charge-coupled device camera. In addition, diamond-like carbon (DLC) films were prepared on glass plates using the same sputtering equipment. When increasing dc target current between 0.5 and 2.5 A, we observed a change in Raman spectra accompanied by increases in electron density and electron temperature. In Ar plasmas with a lower pressure and a higher target current, we obtained relatively hard DLC films, which is consistent with the change in the electron temperature.

Pulse widths dependence of programming and erasing behaviors for diamond like carbon based resistive switching memories

We report the influences of pulse widths on the programming and erasing characteristics of diamond-like carbon films based resistive random access memory. The device can be only programmed with pulses wider than 50 ns for SET operations when the pulse voltage is 1.2 V and erased with pulses narrower than 25 ns for RESET operations when the pulse voltage is 0.4 V. The formation, rupture, and re-growth of the conductive sp2-like graphitic filaments are proposed to be responsible for the resistive switching behaviors, based on which the pulse widths dependences on its programming and erasing properties can be further explained.

Relationship between the structure and electrical characteristics of diamond-like carbon films

To elucidate the relationship between the structure and the electrical characteristics of diamond-like carbon (DLC) films, DLC films were synthesized in a well-controlled glow discharge with the aid of photoelectrons in an argon/methane atmosphere. The dielectric constant and breakdown strength of the films exhibited opposite behaviors, depending on the total pressure during the synthesis. The product of these two values decreased monotonically as the pressure increased. The Raman spectra were analyzed with a Voigt-type formula. Based on the results, the authors propose the “sp2 cluster model” for the DLC structure. This model consists of conductive clusters of sp2 carbons surrounded by a dielectric matrix sea of sp2 carbon, sp3 carbon, and hydrogen, and indicates that the dielectric constant of the whole DLC film is determined by the balance between the dielectric constant of the matrix and the total size of the clusters, while the breakdown strength is determined by the reciprocal of the cluster size. The model suggests that a high-κ DLC film can be synthesized at a middle pressure and consists of well-grown sp2 clusters and a dense matrix. A low-κ DLC film can be synthesized both at low and high pressures. The sp2 cluster model explains that a low-κ DLC film synthesized at low pressure consists of a dense matrix and a low density of sp2 clusters, and exhibits a high breakdown strength. On the other hand, a low-κ film synthesized at high pressure consists of a coarse matrix and a high density of clusters and exhibits a low breakdown strength.

Synthesis and characterization of diamond-like carbon film on silicon by electrodeposition from solution of ethanol and methanol

Diamond-like carbon (DLC) films were prepared by electrodeposition technique on single crystalline n-type Si (100) substrates. Electrolysis of ethanol and methanol solution with different volume ratios at 60°C under constant voltage of 1200V is presented. The DLC films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), Raman spectroscopy, and atomic force microscopy (AFM). The deposited DLC films composed of small and compact grains and seem to be uniform, smooth and homogeneous with a structure influenced by the amount of methanol. The EDX spectra of the prepared films indicated that carbon and oxygen are their main composition. The root mean square (RMS) roughness of the DLC films, synthesized from electrolytes containing 20 by volume of methanol, was 1.17nm. Raman spectra of films showed the presence of a peak located at 1450cm−1 in addition to G and D peaks which confirmed the formation of DLC film. These spectra confirmed the amorphous nature of all deposited DLC films.

Deposition and characterization of diamond-like carbon films by microwave resonator microplasma at one atmosphere

Diamond-like carbon (DLC) films have been deposited at atmospheric pressure by microwave-induced microplasma for the first time. Typical precursor gas mixtures are 250ppm of C2H2 in atmospheric pressure He. Chemically resistant DLC films result if the Si (100) or glass substrate is in close contact with the microplasma, typically at a standoff distance of 0.26mm. The films deposited under this condition have been characterized by various spectroscopic techniques. The presence of sp3 CH bonds and ‘D’ and ‘G’ bands were observed from FTIR and Raman spectroscopy, respectively. The surface morphology has been derived from SEM and AFM and shows columnar growth with column diameters of approximately 100nm. Likely due to the low energy of ions striking the surface, the hardness and Young's modulus for the films were found to be 1.5±0.3GPa and 60±15GPa respectively with a film thickness of 2μm. The hypothesis that a high flux of low energy ions can replace energetic ion bombardment is examined by probing the plasma. Rapid deposition rates of 4–7μm per minute suggest that the method may be scalable to continuous coating systems.

Growth and characteristics of diamond-like carbon films with titanium and titanium nitride functional layers by cathode arc plasma

Diamond-like carbon (DLC) bilayer films were prepared on silicon substrate by direct-current and pulse cathode arc method, using nano-scaled Ti and TiN interlayer and surface layer as functional layer. All films were annealed at 500°C in vacuum. The structural, morphological and mechanical properties of DLC bilayers were investigated in dependence of functional layer and annealing by Raman spectroscopy, Auger electron spectroscopy, scanning electron microscopy and atomic force microscopy, Knoop sclerometer and surface profilometer. The results showed that adding interlayer or surface layer on carbon layer could change the microstructure of the bilayer, including the atom diffusion at interface, the ordering and size of sp2 carbon clusters, and atomic rearrangement of carbon bonds. The interlayer introduced in the bilayer determined the growth mode of carbon layer, while the surface layer was characterized by the injection effect of Ti and N atoms/ions to the carbon layer. Moreover TiN surface layer facilitated the formation of graphitic microcrystal in the carbon layer. Some significant differences of Ti and TiN functional layers in the bilayer depended on themselves structure feature and reaction ability with carbon. The hardness and internal stress of the bilayer were affected accordingly. All bilayers after annealing showed an improved hardness especially for the case of Ti and TiN surface layers.

Electrochemical deposition and characterization of diamond-like carbon films doped with surface-capped silica nanoparticles

Diamond-like carbon films doped with surface-capped nanosilica (nano-SiO2/DLC) were prepared on Si substrate via electrochemical deposition of dimethyl sulfoxide (DMSO) as the carbon source and nanosilica as the dopant. Undoped DLC films were also prepared at various deposition durations for comparative studies. It has been found that silica nanoparticles are well embedded in amorphous carbon matrix forming nanosilica-doped DLC composite films, confirmed by transmission electron microscopy (TEM). In particular, Raman and AFM analysis revealed the as-obtained composite films consist of both tetrahedral (sp3) and trigonal (sp2) bonded C species, and silica incorporation results in variation of surface roughness, decrease of sp3-hybridized carbon concentration and enhancement of graphitization. Furthermore, nanosilica surface-capped with organic compound containing hydroxyl group is doped in amorphous carbon film by forming SiO bond, which helps to lower the surface energy and induce hydrophilic to hydrophobic transformation of the carbon films. Tribology tests also showed that composite films have better friction and wear behaviors, compared with pure carbon film.

Monitoring Technological Conditions for Preparing DLC Films in Supersonic Flow of Hydrocarbon Plasma

Properties of diamond-like carbon films deposited by a new method in a supersonic flow of hydrocarbon plasma generated by a disk-type magneto-hydro-dynamic accelerator were studied. Two methods are used for optical and structural characterization of diamond-like carbon films: nondestructive spectroscopic ellipsometry and Raman spectroscopy.

Characteristics of Diamond-Like Carbon Films Deposited on Polymer Dental Materials

Characterizations of diamond-like carbon (DLC) deposited on a polymer artificial tooth were performed. DLC films were deposited on dental parts made of poly(methyl methacrylate) (PMMA) resin by dc-pulse plasma chemical vapor deposition (CVD) from methane. Wear resistance test results revealed that a DLC-coated resin tooth has a very high wear resistance against tooth brushing, and endures 24 h brushing without a marked weight decrease. Cell cultivation test results show that DLC plays an important role in preventing cell death. Moreover, a biocompatibility test using a rabbit revealed that a connective tissue in the vicinity of DLC-coated PMMA is significantly thinner than that of noncoated PMMA. The numbers of inflammatory cells in the vicinity of DLC-coated and noncoated surfaces are 0 and 508 cells/mm2, respectively. These results led us to conclude that DLC films are an excellent material for use as the coating of a polymer artificial tooth in terms of not only high wear resistance but also biocompatibility.

Characteristics of Diamond-Like Carbon Films Deposited on Polymer Dental Materials

Characterizations of diamond-like carbon (DLC) deposited on a polymer artificial tooth were performed. DLC films were deposited on dental parts made of poly(methyl methacrylate) (PMMA) resin by dc-pulse plasma chemical vapor deposition (CVD) from methane. Wear resistance test results revealed that a DLC-coated resin tooth has a very high wear resistance against tooth brushing, and endures 24 h brushing without a marked weight decrease. Cell cultivation test results show that DLC plays an important role in preventing cell death. Moreover, a biocompatibility test using a rabbit revealed that a connective tissue in the vicinity of DLC-coated PMMA is significantly thinner than that of noncoated PMMA. The numbers of inflammatory cells in the vicinity of DLC-coated and noncoated surfaces are 0 and 508 cells/mm2, respectively. These results led us to conclude that DLC films are an excellent material for use as the coating of a polymer artificial tooth in terms of not only high wear resistance but also biocompatibility.