Structure Of Diamond-like Carbon Films Research Articles

Raman spectroscopy analysis of the chemical structure of diamond-like carbon films deposited via high-frequency inclusion high-power impulse magnetron sputtering

Aiming to develop a new high-power impulse magnetron sputtering (HiPIMS) method to further improve the functionality of thin films, we previously designed a high-frequency inclusion HiPIMS (HF-HiPIMS) power supply for obtaining high-performance diamond-like carbon (DLC) films. Herein, the chemical structure of DLC films deposited via HF-HiPIMS was analyzed using Raman spectroscopy. First, the peak positions were fixed, and the number of fitting parameters was reduced by conducting a waveform separation of the initial Raman spectrum using a differential spectrum method. Next, the Raman spectra of the DLC films subjected to five-peak separation and two-peak separation analyses were compared, and the limitations of the two-peak separation analysis are discussed. Furthermore, the relation between the Raman parameters of the five-peak separation analysis and film properties suggested that Raman spectroscopy could be used to estimate the sp3 C–C/(sp3 C–C + sp2 C=C) ratio.

Design of an Ultra-Thick Film and Its Friction and Wear Performance under Different Working Conditions

Tantalum (Ta)/Ti/TiN/Ti/diamond-like carbon (DLC) (referred to as TTTD film) and Ta/Ti/TiN/TiCuN/Ti/DLC (referred to as ultra-thick film) films were designed in this study, and the factors affecting the friction and wear properties of DLC films in sodium bicarbonate and lactic acid solutions were analyzed. Moreover, a thin film with a thickness exceeding 50 microns was prepared. Morphology and tribological and mechanical properties were analyzed by scanning electron microscopy, friction and wear testing machine, and nanoindentation instrument, respectively. The results show that the presence of a TiCuN interlayer increases the defects in the DLC film and the roughness of surface, reaching a roughness of 0.19 µm. Compared with the TTTD film, the TiCuN interlayer reduces the hardness and increases the residual stress, which is 0.52 Gpa and −6.08 GPa, respectively. The TTTD film has a smooth and dense surface structure and high hardness, causing it to more easily form boundary lubrication. However, the ultra-thick film has lower hardness and rough surface, which cannot effectively form boundary lubrication. Therefore, the friction coefficient of the ultra-thick film is higher than that of the TTTD film under different working conditions. In sodium bicarbonate solution, a double-hydrolysis reaction is more likely to occur, resulting in a higher friction coefficient than in lactic acid solution. The friction coefficient of the TTTD film has a longer running-in period, which is attributed to the oxides generated by the double-hydrolysis reaction and the precipitated sodium bicarbonate crystals. Finally, it was concluded that the surface quality and the internal bond structure of DLC film have a significant impact on the friction and wear properties. This provides a theoretical basis for the design of multilayer structures.

Effects of Different Silicon Substrates on the Structure and Properties of Deposited Diamond‐like Carbon Films

Diamond‐like carbon (DLC) has attracted much attention due to its unique properties such as excellent physicochemical and biological properties. Herein, DLC coatings are deposited on four different silicon substrates using a radio frequency plasma‐assisted chemical vapor deposition (RF‐PECVD) technique. The structure and mechanical properties of DLC coatings deposited on different types of silicon substrates under different powers are compared. The surface morphology of the samples is characterized by scanning electron microscopy. The surface roughness of DLC films deposited on different silicon substrates is measured by scanning probe microscopy (SPM). The structural changes of the coatings are investigated by visible Raman spectroscopy. The analysis of DLC films deposited on different silicon substrates reveals that the structure of DLC films deposited on silicon is affected by different crystal directions of silicon substrates (different atomic densities in different crystal directions) and different conduction modes (electronic conduction and hole conduction). Regarding the DLC films deposited on the same substrate, the overall performance of P‐type silicon is better at 150 W, and the overall performance of N‐type silicon is better when the deposition power is 100 W.

The Effects of Hemisphere Dome Orientation on the Structure of Diamond-like Carbon Film Prepared Using Ion Beam Assisted Deposition

Diamond-like carbon (DLC) has attracted significant attention in the recent decades because of its unique properties and applications. Ion beam assisted deposition (IBAD) has been widely established in industry due to the advantages of easy handling and scalability. In this work, a hemisphere dome model is specially designed as a substrate. The influence of the surface orientation on the coating thickness, Raman ID/IG ratio, surface roughness and the stress of the DLC films are examined. The reduction in the stress in the DLC films reflects the lower energy-dependence in diamond due to the varied sp3/sp2 fraction and columnar growth pattern. The variation of the surface orientation provides an efficient means of tailoring the properties and microstructure of the DLC films.

Morphology and structure of diamond-like carbon film induced by picosecond laser ablation

Morphology and structure of diamond-like carbon film induced by picosecond laser ablation

Spectroscopic analyses of structural alterations in diamond-like carbon films deposited on zirconia substrates

Diamond-like carbon (DLC) films represent promising surface treatments for biomedical implants. In this paper, using Raman and X-ray photoelectron spectroscopies, we analyzed the effects of secondary phases present in ZrO2 substrates on the structure of DLC films fabricated by plasma-based ion implantation and deposition method, and the structural stability of the films in response to applied indentation prints. The results revealed oxygen incorporation in DLC films from the oxide substrates during deposition, and a clear dependence of sp3 carbon content on the oxygen fraction of the substrate and on gas pressure. Moreover, a pronounced structural distortion of the DLC films at the film/substrate interface was observed, which resulted from polymorphic transformation on the zirconia surface during deposition, while a pronounced change in Raman spectral morphology of carbon induced by structural alterations could also be observed around the indentation prints. The findings clearly pointed at the need to take into considerations the structural alterations of the DLC film structure at the interface associated with interfacial defects and film adhesion, especially for biomedical applications that involve surface loading.

Understanding the DLC film – Polyamide 12 substrate interrelation during pulsed laser deposition

High-quality hydrogen-free diamond-like carbon (DLC) films that are free of any detectable signs of cracks and delamination are produced on polyamide 12 (PA) substrates using the Pulsed Laser Deposition (PLD) technique, resulting in subplantation of the polymeric substrate by carbon species and the formation of an interphase between the DLC film and the substrate. The interrelation between the DLC films and PA substrates of different crystallinity degree is investigated using spectroscopic (NMR, IR, XPS, and Raman) techniques and the morphology and topography of the films are evaluated using SEM and AFM. It is demonstrated that the laser fluence (16 and 20 J cm−2) directly affects the subplantation intensity and the DLC film structure. Additionally, it is shown that by changing the physical characteristics of the polymer substrate, such as the degree of crystallinity, the characteristics of the DLC layer and the response of the substrate to the energetic carbon species can be influenced. The studies open up new avenues for research aimed at understanding the interaction of energetic species with polymer substrates and enable the identification of parameters that are important in obtaining hard thin films of high quality on such substrates.

High-temperature tribological properties of diamond-like carbon films: A review

Abstract The rapid development of aerospace industry has made more and more machinery parts of equipment working at high temperature. Due to the lubrication failure of lubricating oil and grease at high temperature, solid lubricant coatings are almost the only effective method to achieve super low friction at high temperature. In recent years, the tribological properties of diamond-like carbon (DLC) films have been extensively studied at high temperature. The present study reviews the microstructure of DLC films and the influence of doping different elements on the structure of DLC films. Second, the mechanical properties and thermal stability of pure DLC films and DLC doped with different elements are also described. DLC films have different microstructures and tribological properties by different preparation methods. Finally, the high-temperature lubrication failure mechanism of DLC films and the tribological properties of DLC films when doped with different elements are discussed from the macro and micro perspectives.

Atomic structure of carbon clusters laser-produced diamond-like carbon films

Structural state of thin diamond-like carbon films has been studied by high-resolution transmission microscopy. Diamond-like carbon films have been obtained by vapor-gas phase carbon concentration on glass substrates, using defocused NTS 300 laser beam for graphite targets evaporation in vacuum. Defocused laser beam provided an area of 3 mm in diameter on the target for carbon direct evaporation. It has been established that diffraction of electrons identifies diamond reflections (111) and (220), and this corresponds to interplane spacing d111 = 0.207 nm, d220 = 0.119 nm of the diamond lattice. The obtained values of interplanar distances are close to the values of interplanar distances of carbon macroscopic crystals with d111 = 0.205 nm and d220 = 0.125 nm. The research of the film atomic structure shows that sp3-bonding generally participate in assembling carbon atoms into diamond clusters having the size less than 1 nm. The ratio of graphite clusters formed by sp2-bonds within the structure of diamond-like carbon films is negligible. In spite of the pronounced cluster pattern of the structure, the film is not an analogue of the polycrystalline one with graded junction from one crystalline domain to another observed. As distinguished from polycrystals, there is no structure stepwise changing on the mating clusters boundaries. It is shown that clusters are linked with each other into homogeneous cluster structure by sp3- and sp2-bonds. These bonds are well-identified in the diamond-like carbon film structure, as the length of sp2-bonds exceeds considerably the length of sp3- bonds. Carbon film properties are determined by diamond clusters due to domination of clusters with tetragonal diamond lattice, for instance, the film is a good dielectric.

Studying the effects of plasma produced species on the optical characteristics and bonding structure of diamond-like carbon films deposited by direct current unbalanced magnetron sputtering

Abstract In the present study, the influence of target power and plasma produced species on optical, structural and morphological properties of diamond-like carbon thin films deposited by direct current unbalanced magnetron sputtering is investigated. Raman spectroscopy and spectroscopic ellipsometry are used to study the structural properties and optical characteristics, respectively. Additionally, optical spectroscopy is used to measure the optical band gap of the films and investigate the produced active species in the plasma. Optical emission spectroscopy of the plasma shows that increasing the target power from 60 W to 120 W, increases the hydrogen containing species in the plasma which was due to the water vapor remained in the vacuum chamber. Surface topography of the films illustrates that the surface roughness of the films decreases slightly which leads to the smoother surfaces. Raman spectroscopy shows that ID/IG ratio decreases and the G peak position shifts toward lower wavenumber. Indirect optical band gap also increases from 1.77 eV to 2.18 eV. Results of spectroscopic ellipsometry measurements illustrate that the refractive index decreases from 2.01 to 1.67 at 550 nm and the spectrum of the extinction coefficient decreases as well. These results indicate that increasing the sputtering power, increases the sp3 C H bonding more than C C bonding in the matrix of the film.

Corrosion resistance and cytotoxicity studies of DLC, TiN and TiCN films coated on 316L stainless steel

Corrosion resistance and cytotoxicity of diamond-like carbon (DLC), titanium nitride (TiN) and titanium carbo-nitride (TiCN) films coated on AISI 316L grade stainless steel were investigated. All films were deposited on the stainless steel substrates using a cathodic arc plasma deposition-physical vapor deposition (PVD) technique. Film compositions were measured using energy dispersive X-ray spectroscopy (EDS). Contact angle was measured using contact angle measurement. Corrosion resistance was determined using potentiodynamic polarization. Cell viability was analysed using cytotoxicity test. The results show that all films are more hydrophilic (80.75° to 87.79°) than uncoated stainless steel sample (96.63°). Moreover, TiCN, DLC and TiN films have good potential corrosion resistance values of -0.353 V, -0.58 V and -0.68 V, respectively. This is due to the formation of titanium carbides and the sp3 sites structure of DLC film. Meanwhile, DLC film appears to be the most biocompatible with the highest cell viability of 104%.

Regulating the uniformity of DLC films in ECR plasma with negative substrate biasing

Diamond-like carbon (DLC) films were deposited by electron cyclotron resonance plasma-chemical vapor deposition (ECR-CVD) at different substrate bias potential (Us = −200 and −800 V). The mechanical properties and microstructure uniformity of the DLC films deposited at different positions (the distance between substrate and ECR plasma source, Decr-s) were studied. The results showed that the ionization of acetylene (C2H2) at different positions decreased with the increase of Decr-s at substrate bias potential Us = −200 V. The plasma distribution was non-uniform, so the mechanical properties and structure of the DLC films varied a lot with the change of deposition position. At substrate bias potential Us = −800 V, an additional self-sustained discharge around the substrate could be generated during ECR plasma discharge, then the ionization of C2H2 and the plasma distribution uniformity at different positions were found to be improved. The uniformity of mechanical properties and structure of DLC films could be improved due to enhanced ionization of C2H2 in front of the substrate at high values of the negative substrate bias (Us = −800 V).

Multi-Peak Fitting Analysis of Visible Raman Spectra on DLC Coatings Deposited by Vacuum Arc

The typical two-Gaussian fitting of Raman spectra is widely used in disordered and amorphous carbon. However, two-peak fitting method was not always suitable for all amorphous carbons, which made it important to choose appropriate fitting method for different carbon coatings. In this study the diamond-like carbon (DLC) coatings were deposited on steel (P2000) by a vacuum arc adjustable from anodic to cathodic operation mode. The ID/IG ratios of DLC coatings were investigated by visible Raman spectroscopy with multi-peak fitting analysis. It is found that for Raman spectra of DLC coatings deposited by vacuum arc four-peak Gaussian fitting is the most suitable method which is conducive to revealing fine structure of DLC films. Furthermore, by comparing with two-peak and three-peak fitting methods, the four-peak fitting method have lower ID/IG ratio. It is shown that the values of ID1/IG1 and I(D1+D2)/I(G1+G2) of four-peak Gaussian function are consistent nearly.

Effect of applied electric field on the chemical structure and thermal diffusion of DLC film irradiated by laser

Diamond-like carbon (DLC) films have attracted much attention because of their excellent performance; however, the low anti-laser damage ability of such films seriously restricts their applicability to high-power infrared optical windows or laser system, etc. To overcome this problem, in this study, Titanium (Ti) electrodes were deposited on DLC films directly, forming a transverse bias field on films' surfaces. The damage morphology under laser irradiation was observed both before and after the bias field was applied, and Raman spectroscopy was used to analyse chemical structure of DLC films. It was shown that as the I(D)/I(G) ratio increased, the sp3 content decreased in laser-irradiated regions of DLC films when a bias electric field was not applied. When the bias electric field was applied to DLC films, it could effectively stop the content changing from sp3-bonding carbon to sp2-bonding carbon, prevent the formation of sp2 clusters, and slow down the films graphitisation process. The fast thermal diffusion improves the DLC films' anti-laser damage ability ultimately.

Effect of applied electric field on the chemical structure and thermal diffusion of DLC film irradiated by laser

Diamond-like carbon (DLC) films have attracted much attention because of their excellent performance; however, the low anti-laser damage ability of such films seriously restricts their applicability to high-power infrared optical windows or laser system, etc. To overcome this problem, in this study, Titanium (Ti) electrodes were deposited on DLC films directly, forming a transverse bias field on films' surfaces. The damage morphology under laser irradiation was observed both before and after the bias field was applied, and Raman spectroscopy was used to analyse chemical structure of DLC films. It was shown that as the I(D)/I(G) ratio increased, the sp3 content decreased in laser-irradiated regions of DLC films when a bias electric field was not applied. When the bias electric field was applied to DLC films, it could effectively stop the content changing from sp3-bonding carbon to sp2-bonding carbon, prevent the formation of sp2 clusters, and slow down the films graphitisation process. The fast thermal diffusion improves the DLC films' anti-laser damage ability ultimately.

大電力パルスマグネトロンスパッタを用いた炭素系薄膜の特性

The characteristics of diamond-like carbon (DLC) films deposited by high power impulse magnetron sputtering (HiPIMS) with multipolar magnetic plasma confinement (MMPC) were investigated. DLC films were prepared on silicon (Si) by HiPIMS and HiPIMS-MMPC over varying substrate bias voltage. Depositions were performed from a graphite target (210 mm in diameter) under argon (Ar) gas atmosphere at chamber pressure of 0.5 Pa. The DLC films were analyzed by several methods. In HiPIMS-MMPC, the peak power density was approximately 690 W/cm2 at a duty cycle of 1% (frequency: 200 Hz). According to Raman spectroscopy, the structure of DLC film deposited by HiPIMS-MMPC could be changed from amorphous carbon (a-C) to tetrahedral amorphous carbon (ta-C). The deposition rate in HiPIMS-MMPC was approximately 50% (10 nm/min) lower than that in HiPIMS. However, HiPIMS-MMPC is considered as one of the effective methods to prepare hard and dense DLC films (20 GPa and 2.00 g/cm3 at the maximum).

DLC coating on a micro-trench by bipolar PBII&D and analysis of plasma behaviour

Bipolar plasma-based ion implantation and deposition (bipolar PBII&D) has been recognized as a promising technique for coating deposition on complex three-dimensional targets. As the target is fully immersed in the plasma throughout the process, the plasma sheath can be formed with quite high conformability around the target. In this study, diamond-like carbon (DLC) coating was deposited on a micro-trench pattern by using bipolar PBII&D, and the structure of the DLC film across the overall surface region of the trench was examined by making use of their corresponding Raman spectra. The two types of negative high voltage pulses were applied to the targets for comparison: −0.5 and −15 kV. The scale of the micro-trench used in the study is much smaller than that of the plasma sheath produced under these negative voltages (about 1 cm and 14 cm for −0.5 kV and −15 kV, respectively). The plasma behaviour (i.e., ion flux, impact angle and energy) in the surrounding of the micro-trench was calculated with the particle-in-cell Monte Carlo collision method (PIC-MCCM). As a result, DLC film was successfully coated on the overall surface of the trench. When the applied negative voltage was −0.5 kV, the structure of DLC film coated on the sidewall of the trench became a more polymer-like carbon (PLC) than those of the top and bottom surfaces. This, as indicated by the simulation results, is because the ions, which strike the sidewall, tend to have less incident energy. Whereas in the case of −15 kV, the DLC film on the sidewall was a more graphite-like carbon (GLC) film, despite its smaller incident ion energy in comparison to those of the top and bottom surfaces. This phenomenon is attributed to the sputtering effect from the bottom surface of the trench, as evidenced by the plasma simulation.

The stability of DLC film on nitrided CoCrMo alloy in phosphate buffer solution

Abstract CoCrMo alloy is often used as the material for metal artificial joint, but metal debris and metal ions are the main concern on tissue inflammation or tissue proliferation for metal prosthesis. In this paper, nitrogen ion implantation and diamond like carbon (DLC) film composite treatment was used to reduce the wear and ion release of biomedical CoCrMo substrate. The mechanical properties and stability of N-implanted/DLC composite layer in phosphate buffer solution (PBS) was evaluated to explore the full potential of N-implanted/DLC composite layer as an artificial joint surface modification material. The results showed that the DLC film on N implanted CoCrMo (N-implanted/DLC composite layer) had the higher surface hardness and wear resistance than the DLC film on virgin CoCrMo alloy, which was resulted from the strengthen effect of the N implanted layer on CoCrMo alloy. After 30 days immersion in PBS, the structure of DLC film on virgin CoCrMo or on N implanted CoCrMo had no visible change. But the adhesion and corrosion resistance of DLC on N implanted CoCrMo (N-implanted/DLC composite layer) was weakened due to the dissolution of the N implanted layer after 30 days immersion in PBS. The adhesion reduction of N-implanted/DLC composite layer was adverse for in vivo application in long term. So researcher should be cautious to use N implanted layer as an inter-layer for increasing CoCrMo alloy load carrying capacity in vivo environment.

Investigation of superfast deposition of metal oxide and Diamond-Like Carbon thin films by nanosecond Ytterbium (Yb+) fiber laser

Metal oxide (MOx, M: titanium, magnesium) and Diamond-Like Carbon (DLC) thin films were synthesized by Pulsed Laser Deposition (PLD) at room temperature and low vacuum of 2Pa for MOx and vacuum of 4×10−3Pa for DLC films. A fiber based Ytterbium (Yb+) laser operating in the nanosecond regime at a repetition rate of 20kHz was used as an ablation source. Dense and smooth thin films with a thickness from 120 to 360nm and an area of up to 10cm2 were deposited on glass and stainless steel substrates at high growth rates up to 2nm/s for a laser intensity of 10–12J/cm2. The thin films synthesis was compared for two fiber laser modes of operation, at a repetition rate of 20kHz and with an additional modulation at 1kHz. The morphology, chemical composition and structure of the obtained thin films were evaluated using optical microscopy, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and Raman spectroscopy. The morphology of the MOx thin films and the deposition rate strongly depend on the fiber laser mode of operation. Very smooth surfaces were obtained for the metal oxide thin films deposited at lower deposition rates in the modulation mode at 1kHz. The effect of the substrate on the DLC film structure was studied. The films deposited on dielectric substrates were identified as typical tetrahedral (ta-C) DLC with high sp3 content. DLC films on metal substrates were found typical a-C amorphous carbon films with mixing sp2/sp3 bonds.

Modeling of the effects of substrate temperature and C2-containing plasma pressure on the structure of carbon films

This paper examines the role of carbon (C2) molecules in structure formation of crystalline and amorphous diamond films. Analysis of the potential energy of chemisorbed particles and possible interactions between them is used to model the layer assembly process. The modeling results demonstrate how the substrate temperature and C2 partial pressure (the most important process parameters) influence the structure of diamond-like carbon films.