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.     

The mechanical and biocompatibility properties of DLC-Si films prepared by pulsed DC plasma activated chemical vapor deposition

Films of diamond-like carbon containing up to 22 at.% silicon (DLC-Si) were deposited on to silicon substrates by low-frequency pulsed DC plasma activated chemical vapor deposition (PACVD). The influence of silicon doping on deposition rate, composition, bonding structure, hardness, stress, surface roughness and biocompatibility was investigated and correlated with silicon content. A mixture of methane and tetramethylsilane (TMS) was used for the deposition of DLC-Si films at a pressure of 200 Pa. The deposition rate increased with increasing TMS flow. The addition of silicon into the DLC film leads to an increase of sp³ bonding, as measured by Raman spectroscopy, and also resulted in lower stress and hardness values. The RMS surface roughness of the films was measured by atomic force microscopy and increased from 0.35 nm for DLC to 6.7 nm for DLC-Si (14 at.% Si) due to the surface etching by the H atoms. Biocompatibility tests were performed using MG-63 osteoblast-like cell cultures that were left to grow for 3 days and their proliferations were assessed by scanning electron microscopy. The results indicated a homogeneous and optimal tissue integration for both the DLC and the DLC-Si surfaces. This pulsed PACVD technique has been shown to produce biocompatible DLC and DLC-Si coating with potential for large area applications.     

Hydrogen plasma etching of diamond films deposited on graphite

Poly- and nanocrystalline diamond films have been deposited using microwave plasma enhanced CVD with gas mixtures of x%CH₄/15%H₂/Ar (x = 0.5, 1, 3, and 5). After deposition the resulting films were exposed to a hydrogen plasma etching for 30 min. The hydrogen plasma produced preferential etching of non-diamond carbon on the surface of the samples and the development of steps and pits. Raman spectroscopy and X-ray photoelectron spectroscopy analyses on the etched films showed increased sp³/sp² ratio and decreased surface oxygen. The etch mechanism proposed is regression of pre-existing steps and step flow.     

Application of diamond-like carbon films to the integrated circuit fabrication process

On account of their attractive properties, amorphous diamond-like carbon (DLC) films have been developed as resist materials for lithography and as hard coatings. In this paper, we investigate the etching properties of DLC films and the electrical properties of a pn junction fabricated using DLC films.Using a parallel-plate radio frequency plasma glow discharge, methane gas was decomposed for the deposition of the DLC films on a silicon substrate. Then oxygen was used to etch the films. Properties, such as the etching rate and the cross-sectional profile, were evaluated by atomic force microscopy (AFM). In order to produce the diode, DLC films were applied to resist materials as a part of the fabrication process.The etching rate of DLC films increases with decreasing oxygen pressure. We suspect that the high etching rate at low pressure from the negative bias voltage originates from the sputtering of accelerated ionic species. The bias voltage also increases with decreasing oxygen pressure. In order to estimate the shape of the etched edge, AFM images and cross-sectional profiles of etched DLC films were investigated as a function of oxygen pressure. At high pressure, isotropic etching by neutral radicals occurred, as the shape of the etched edge was not vertical. The top and bottom edges coincided vertically at low pressure because of the high bias voltage. The yield of excellent pn junctions fabricated using DLC films as resist materials was investigated as a function of deposition and etching pressure. From the results of the characteristics of the pn junction and the yield, for the integrated circuit fabrication process the optimum condition for both deposition and etching is at low pressure.     

Investigation of nanocrystalline diamond films grown on silicon and glass at substrate temperature below 400 °C

We present investigation of nanocrystalline diamond films deposited in a wide temperature range. The nanocrystalline diamond films were grown on silicon and glass substrates from hydrogen based gas mixture (methane and hydrogen) by microwave plasma CVD process. Film composition, nano-grain size and surface morphology were investigated by Raman spectroscopy and scanning electron microscopy. All samples showed diamond characteristic line centred at 1332 cm^− 1 in the Raman spectrum. Nanocrystalline diamond layers revealed high surface flatness (under 10 nm) with crystal size below 60 nm. Surface morphology of grown films was well homogeneous over glass substrates due to used mechanical seeding procedure. Very thin films (40 nm) were successfully grown on glass slides (i.e. standard size 1 × 3″). An increase in delay time was observed when the substrate temperature was decreased. A possible origin for this behaviour was discussed.     

Characterization of physical and biomedical properties of nitrogenated diamond-like carbon films coated on polytetrafluoroethylene substrates

A technique to coat hydrogen-free diamond-like carbon (DLC) films on polytetrafluoroethylene (PTFE) substrates has been developed by sputtering of a negatively biased graphite target in a mixture of argon and nitrogen plasma. The coated films were characterized by various methods to investigate their chemical, electronic features, and particularly their biomedical properties. DLC films produced by this method have up to 20% sp³ carbon bonds depending on the nitrogen concentration in the plasma. Raman spectroscopy revealed that, bond-disorder increases with nitrogen doping. The average grain size of DLC decreases in the nitrogen doped samples by almost 30%. The roughness of the uncoated PTFE substrate surfaces decreased dramatically from 660 nm to 170 nm after DLC coating. However, the nitrogen contents in the plasma have little effects on the roughness, the cluster size, and shapes. Electronic band gap of the samples decreases with adding nitrogen from ~ 2 eV in nitrogen-free samples to ~ 1 eV in nitrogenated samples. Lower adhesion and aggregation of platelets on PTFE surfaces coated with DLC-10% nitrogen and DLC-20% nitrogen have been observed while there is greater adhesion of platelets on DLC-30% nitrogen and DLC-40% nitrogen.     

Localized DLC etching by a non-thermal atmospheric-pressure helium plasma jet in ambient air

Using a versatile atmospheric-pressure helium plasma jet, diamond-like carbon (DLC) films were etched in ambient air. We observed that the DLC films are etched at a nominal rate of around 60 nm/min in the treated area (230 μm in diameter) during a 20-min exposure. The etching rate increased after the initial 10-min exposure. During this period, the flat DLC surface was structurally modified to produce carbon nanostructures with a density of ~ 2.4 × 10¹¹ cm^− 2. With this increase in surface area, the etching rate increased. After 20 min, the DLC film had a circular pattern etched into it down to the substrate where silicon nanostructures were observed with sizes varying from 10 nm to 1 μm. The initial carbon nanostructure formation is believed to involve selective removal of the sp²-bonded carbon domains. The carbon etching results from the formation of reactive oxygen species in the plasma.     

Investigation on the etching of thick diamond film and etching as a pretreatment for mechanical polishing

Etching with oxygen plasma produced by DC glow discharge was investigated as a potential technique for etching of diamond films and as a pretreatment technique for mechanical polishing of thick diamond films. The influence of DC power and gas pressure to etched morphology and etching rate were studied using scanning electron microscopy and electronic micro-balance, respectively. The electron temperature and plasma density were measured by Langmuir single probe to explicate the influence mechanism of etching parameters according to an etching model. The effect of etching on mechanical polishing was studied through surface roughness measuring instrument and Raman spectrometer.It was found that at a constant gas pressure the rise of DC power would result in the increase of deepening etch pits overspreading from the protuberant facet to the boundary of diamond crystallites with rising etching rate. And the same tendency was engendered by reducing gas pressure when the DC power remained. The numerous etch pits can be ascribed to etching with a higher rate of dislocations whose edges exist at the film surface. In accordance with an etching model, the measured results of Langmuir probe suggest that the main influence mechanism of etching are the plasma density and electron temperature, and the increase of etching rate and deepening etch pits can be mainly attributed to the enhanced directional etching with rising ion flux and sheath voltage. Appropriate etching with oxygen plasma is an effective pretreatment method for enhancing the efficiency of rough polishing process in mechanical polishing of thick diamond film.     

Effect of substrate bias voltage on the properties of diamond-like carbon thin films deposited by microwave surface wave plasma CVD

Diamond-like carbon (DLC) thin films were deposited on silicon and ITO substrates with applying different negative bias voltage by microwave surface wave plasma chemical vapor deposition (MW SWP-CVD) system. The influence of negative bias voltage on optical and structural properties of the DLC film were investigated using X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. Optical band gap of the films decreased from 2.4 to 1.7 with increasing negative bias voltage (0 to − 200 V). The absorption peaks of sp³ CH and sp² CH bonding structure were observed in FT-IR spectra, showing that the sp²/sp³ ration increases with increasing negative bias voltage. The analysis of Raman spectra corresponds that the films were DLC in nature.     

Structural and mechanical properties of DLC films prepared by bipolar PBII&D

In the present study, diamond-like carbon (DLC) films were prepared by bipolar plasma based ion implantation and deposition (PBII&D), and the structural and mechanical properties of the DLC films deposited on Si substrates were evaluated by Raman spectroscopy. In the PBII&D processing, the positive and negative pulse voltages were varied from 1 to 3 kV and from ? 1 to ? 15 kV, respectively. With an increase in the pulse voltages, the Raman G-peak position and I(D) / I(G) ratio increased, and the G-peak full width at half maximum (FWHM(G)) decreased, indicating graphitization of the DLC films. In the low wavenumber regime, the FWHM(G) increases when the G-peak shifts to higher wavenumbers, reaching a maximum value at around 1540 cm^? 1, and then decreases. This behavior was due to the structural changes occurring in the DLC films with an increase in the wavenumber. DLC to polymer-like carbon (PLC) transition occurred in the low wavenumber regime, and DLC to graphite-like carbon (GLC) transition occurred in the high wavenumber regime. Further, two different trends were observed in the relationship between the mechanical properties (hardness, elastic modulus, and internal stress) of the DLC films and the FWHM(G), originating from the structural change from DLC to GLC and PLC.     

Antibacterial property of DLC film coated on textile material

To evaluate the antibacterial property for diamond-like carbon films (DLC), DLC films were coated on textile material (cotton fibres) using a plasma-based ion implantation (PBII). Raman spectra show the DLC films were successfully coated on the cotton fibres. An antibacterial property of DLC film against two types of bacteria (Staphylococcus aureus, and Klebsiella pneumoniae) was investigated by the standard evaluation technique International Organization for Standardization (ISO) 20743. After incubation for 18 h, the number of cell colonies of the normal cotton fibres increased 100 times more than that of the initial condition. In contrast with the cotton fibres with DLC coating, no active bacteria could be observed after incubation for 18 h. X-ray photoelectron spectroscopy confirms that DLC coating formed C–H bond on cotton surface. Consequently, DLC film coating is a promising method to inhibit the increase of active bacteria. The DLC coatings are expected for biomedical applications with antibacterial property for coating of the commercial items.     

Diamond-like carbon films: electron spin resonance (ESR) and Raman spectroscopy

Tetrahedral diamond-like carbon (ta-C) films and hydrogenated a-C:H films were deposited onto Si substrates using filtered cathodic vacuum arc (FCVA) process and direct ion beam deposition from CH₄/C₂H₄ plasma, respectively. Stress of deposited films was varied in the range 2.8–8.5 GPa depending on deposition conditions. Stationary and pulse electron spin resonance (ESR), and Raman spectroscopy techniques were used to analyze sp² related defects in pseudo-gap of undoped as deposited and annealed 20–100 nm thick films.¹ High density of ESR active paramagnetic centers (PC) N_s=(1.0–4.5)×10²¹ cm⁻³ at g=2.0025 was observed in the films. The dependence of ESR line width and line shape vs. deposition conditions and internal film stress were investigated. The several actual mechanisms for ESR line width broadening were considered: spin–spin dipole–dipole and exchange interactions, super-hyperfine interaction (SHFI) with ¹H (for a-C:H), averaging of SHFI due to electron jumps between PC positions with different SHFI values, and broadening due to Mott's electron hopping process. Three types of samples were revealed depending on relative contribution of these mechanisms. Effects of annealing on mechanical and paramagnetic properties of films were studied. An electrical resistance anisotropy at room temperature for ta-C films and g-value anisotropy at low temperature (T<77 K) for both ta-C and a-C:H films were found for the first time. Nature and distribution details of paramagnetic defects in DLC films, anisotropy effects and Raman spectroscopy data are discussed.     

The effect of nitrogen addition on field emission of diamond-like carbon films

Diamond-like carbon (DLC) films and nitrogen-doped DLC (N-DLC) films were deposited on a molybdenum-coated ceramic substrate using the pulsed laser deposition technique. The structure and surface morphology of the films were examined using X-ray diffraction, Raman spectroscopy, Auger electron spectroscopy and scanning electron microscopy. Field emission measurements were carried out, with the DLC or the N-DLC films as the cathode and ITO-coated glass as the anode. The field emission measurements indicated that the nitrogen doping could lower the turn-on field and increase the current density. It was believed that the interface at the molybdenum–N-DLC film plays an important role in improving the field emission performance of the N-DLC film.     

Effect of carbonitriding temperature process on the adhesion properties of diamond like-carbon coatings deposited by PECVD on austenitic stainless steel

The deposition of adherent coatings such as diamond-like carbon (DLC) on substrates of iron-based materials is difficult to obtain for two reasons: high residual compressive stress occurs in the inner film formation, and the mismatch of thermal expansion coefficient between steel and DLC film generates delamination effects. In order to determine the carbonitriding temperature prior to film deposition, the steel substrate and the DLC films were analyzed for their microstructure and mechanical properties of adhesion as a function of temperature. The technique used to deposit the coating was DC-pulsed plasma enhanced chemical vapor deposition. The delamination distances and the critical load of the film were obtained by scratch testing. The surface analysis by X-ray diffraction indicated the formation of nitride phases on the steel. Raman spectroscopy showed the fraction of sp³ carbon bonds in DLC films. Hardness profiling was used to verify the extent of the interface modified by carbonitriding along the cross section. For this, the steel sample with the appropriate surface modification to have high adhesion of the DLC film was used.     

Influence of bias voltage on diamond like carbon (DLC) film deposited on polyethylene terephthalate (PET) film surfaces using PECVD and its blood compatibility

In this paper, diamond like carbon (DLC) films were coated on polyethylene terephthalate (PET) film substrate as a function of biasing voltage using plasma enhanced chemical vapour deposition. The surface morphology of the DLC films was analyzed by scanning electron microscopy and atomic force microscopy. The chemical state and structure of the films were analyzed by X-ray photoelectrons spectroscopy and Raman spectroscopy. The micro hardness of the DLC films was also studied. The surface energy of interfacial tension between the DLC and blood protein was investigated using contact angle measurements. In addition, the blood compatibility of the films was examined by in vitro tests. For a higher fraction of sp³ content, maximum hardness and surface smoothness of the DLC films were obtained at an optimized biasing potential of ? 300 V. The in vitro results showed that the blood compatibility of the DLC coated PET film surfaces got enhanced significantly.     

Effect of oxygen plasma treatment on non-thrombogenicity of diamond-like carbon films

The non-thrombogenicity of oxygen-plasma-treated DLC films was investigated as surface coatings for medical devices. DLC films were deposited on polycarbonate substrates by a radio frequency plasma enhanced chemical vapor deposition method using acetylene gas. The deposited DLC films were then treated with plasma of oxygen gas at powers of 15 W, 50 W, and 200 W. Wettability was evaluated by water contact angle measurements and the changes in surface chemistry and roughness were examined by X-ray photoelectron spectroscopy and atomic force microscope analysis, respectively. Each oxygen-plasma-treated DLC film exhibited a hydrophilic nature with water contact angles of 11.1°, 17.7° and 36.8°. The non-thrombogenicity of the samples was evaluated through the incubation with platelet-rich plasma isolated from human whole blood. Non-thrombogenic properties dramatically improved for both 15 W- and 50 W-oxygen-plasma-treated DLC films. These results demonstrate that the oxygen plasma treatment at lower powers promotes the non-thrombogenicity of DLC films with highly hydrophilic surfaces.     

Characteristics of nitrogen doped diamond-like carbon thin films grown by microwave surface-wave plasma CVD

Nitrogen doped diamond-like carbon (DLC:N) thin films were deposited on p-type silicon (p-Si) and quartz substrates by microwave (MW) surface-wave plasma (SWP) chemical vapor deposition (CVD) at low temperature (< 100 °C). For films deposition, argon (Ar: 200 sccm), acetylene (C₂H₂:10 sccm) and nitrogen (N: 5 sccm) were used as carrier, source and doping gases respectively. DLC:N thin films were deposited at 1000 W microwave power where as gas composition pressures were ranged from 110 Pa to 50 Pa. Analytical methods such as X-ray photoelectron spectroscopy (XPS), UV-visible spectroscopy, FTIR and Raman spectroscopy were employed to investigate the chemical, optical and structural properties of the DLC:N films respectively. The lowest optical gap of the film was found to be 1.6 eV at 50 Pa gas composition pressure.     

Effect of nitrogen incorporation into diamond-like carbon films by ECR-CVD

Diamond-like carbon (DLC) and nitrogenated DLC (a-C:N) films were prepared on Si and glass substrates using an electron cyclotron resonance-assisted microwave plasma chemical vapour deposition (ECR-MPCVD) system with radio frequency substrate bias. The hardness and optical bandgap of the resulting films were investigated and correlated to the elemental and phase composition. The a-C:N films, deposited under conditions identical to those for the DLC films except for the introduction of a nitrogen flow, contain nitrogen which partly substitutes for hydrogen and forms carbon–nitrogen triple bonds. These bonds obstruct the formation of carbon–carbon cross-linking, resulting in softer films. These changes can be interpreted with reference to various changes of active vibronic states determined by Raman spectroscopy.     

Duplex DLC coatings fabricated on the inner surface of a tube using plasma immersion ion implantation and deposition

A duplex plasma immersion ion implantation and deposition (PIIID) process, involving carbon ion implantation and diamond-like carbon (DLC) deposition, is proposed to modify the inner surface of a tube. In the research, samples of GCr15 bearing steel were placed inside a tube in the vacuum chamber. After the vacuum chamber was evacuated to a base pressure of 6 × 10^− 3 Pa, C₂H₂ gas was introduced into the chamber, and the tube was biased by a negative pulsed bias. Since a pulsed glow discharge (PGD) plasma can be formed by the bias, carbon ion implantation and DLC film deposition process can be obtained by biasing the tube with a high and low bias, respectively. To synthesize different DLC films, single PIIID processes employing a low voltage (several kV) PGD method and duplex PIIID processes combining the high (several tens kV) and low voltage PGD techniques were carried out. The as-synthesized films were characterized by Raman spectrum, nano-indentation, scratch, tribological and electrochemical tests. Raman results show that duplex DLC films were synthesized by this duplex PIIID process. In addition, compared with the single DLC film synthesized by the low voltage PGD process, the duplex DLC films can obtain a high wear and corrosion resistances. Furthermore, using this duplex PIIID method, batch treatment of outer-rings of the bearing was realized.     

Pulsed laser surface modifications of diamond thin films

In view of practical applications requiring diamond films, plates and membranes with very smooth surfaces, ArF excimer laser polishing treatments were applied to thin (30 μm) diamond films grown by CVD on silicon substrates. The as-prepared diamond surfaces and the laser-treated parts of the samples were characterised by SEM analysis, Raman and micro-Raman spectroscopy. The presence on the laser-treated surface of a thin amorphous carbon layer responsible for the higher surface electrical conductivity and for the different optical reflectivity properties was evidenced. Using confocal micro-Raman spectroscopy a comparative depth profile analysis of the phase quality, below the surface in different regions of the films, was carried out. After short (10 min) treatment by H₂ plasma etching in the CVD chamber the graphitic top layer was completely removed from the samples.