Formation Of Diamond-like Carbon Research Articles

Physical vapor deposition using a coaxial ion acceleration method.

A novel physical vapor deposition method involving electromagnetic acceleration using a set of coaxial electrodes has been developed. In this study, the coaxial ion acceleration method is applied for a diamond-like carbon (DLC) thin film formation. In the developed method, the central electrode made of the deposition material is sputtered by the noble gas plasma current and accelerated toward the deposition chamber. Because the sputtered ions are accelerated by the Lorentz self-force, the ion injection energy can be controlled separately from the plasma temperature. In addition, the gaseous hydrocarbon, which is commonly used for DLC formation, is not required since a noble gas is used as the discharge gas.

A new DBD apparatus for super-hydrophobic coating deposition on cotton fabric

In this study, we developed a new cold dielectric barrier discharge (DBD) apparatus comprising two covered flat electrodes and an array of bared spinal needles aiming for large scale treatment processes. The favored cold atmospheric pressure plasma was produced using Ar gas and n-hexane vapor for hydrophobic deposition on cotton fabric. It was shown that installing the third electrode is crucial in this configuration for producing hydrophobic deposition on cotton fabric. Formation of diamond-like carbon (DLC) deposition was confirmed by experimental analysis. Our samples were analyzed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The presence of sp3 CH bonds was observed from ATR-FTIR analysis. Diesel oil/water separation experiments were performed to show the effectiveness of the treated cotton in the filtering of oil from water. The static water contact angle (WCA) measurements showed an excellent super-hydrophobicity of cotton fabric with WCA higher than 1500 (Ө = 159.590) and sliding angle of ~40. Additionally, aging experiments proved that the treated samples maintained superhydrophobic properties even after multiple washing.

Kinetically driven graphite-like to diamond-like carbon transformation in low temperature laminar diffusion flames

Historically, the synthesis of diamond and graphite via combustion flames stands out as a simplified, scalable and inexpensive approach. Unfortunately, this method is not beneficial for industrial applications in coatings due to limitations related with the high flame and substrate temperatures. Here, we report novel findings about the formation mechanism of graphite-like and diamond-like supported nanostructures in low temperature laminar diffusion flames. Both materials are formed upon controllable combustion at atmospheric pressure of a cylindrical paper wick immersed in rapeseed oil. An accurate adjustment of the incident air flow and the amount of available fuel allow deposition of carbon soot or diamond-like carbon (DLC). The DLC formation is favorable in a narrow stoichiometric range at flame temperatures within ~210–260°C and beyond this range the particles precipitate as soot. The comparative structural analysis using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy, along with the full thermal and stoichiometric profiles for the chosen combustion conditions, suggest a kinetically driven graphite-to-diamond transformation rather than a thermodynamically induced phase transition. Our results reveal a new direction in the principles of graphite and diamond formation in flames that could be applied to surmount the existing shortcomings in flame synthesis.

Argon and hydrogen plasma influence on the protective properties of diamond-like carbon films as barrier coating

Diamond like carbon (DLC) films are becoming materials of choice for mechanical and corrosion protection barrier films due to their excellent properties of low-friction and chemical inertness. As DLC functional properties are strictly dependent on process parameters, different DLC coatings have been deposited onto silicon substrates by Plasma Enhanced Chemical Vapour Deposition (PECVD) evaluating the effect of the variation of argon and hydrogen gas flows on the coating resistance properties. It has been observed that the hydrogen variation is the main factor affecting the DLC films resistance in aggressive environments, while DLC samples deposited by varying Ar showed significant delamination phenomena. These differences have been related to the morphological and microstructural characteristics of DLC films taking into account for the specific role of both Ar and H2 in the mechanism of DLC formation. In particular, it has been observed that the resistance against corrosive environment for DLC coatings may be related to the compressive residual stress values in conjunction with surface and structural properties of the film. This can be considered an understanding at the atomic scale providing the key for the optimization of the protective coating performance.

Conditions for forming composite carbon nanotube-diamond like carbon material that retain the good properties of both materials

Carbon nanotubes are of wide interest due to their excellent properties such as tensile strength and electrical and thermal conductivity, but are not, when placed alone on a substrate, well resistant to mechanical wear. Diamond-like carbon (DLC), on the other hand, is widely used in applications due to its very good wear resistance. Combining the two materials could provide a very durable pure carbon nanomaterial enabling to benefit from the best properties of both carbon allotropes. However, the synthesis of high-quality diamond-like carbon uses energetic plasmas, which can damage the nanotubes. From previous works it is neither clear whether the quality of the tubes remains good after DLC deposition, nor whether the DLC above the tubes retains the high sp3 bonding fraction. In this work, we use experiments and classical molecular dynamics simulations to study the mechanisms of DLC formation on various carbon nanotube compositions. The results show that high-sp3-content DLC can be formed provided the deposition conditions allow for sidewards pressure to form from a substrate close beneath the tubes. Under optimal DLC formation energies of around 40–70 eV, the top two nanotube atom layers are fully destroyed by the plasma deposition, but layers below this can retain their structural integrity.

Carbon matter in kimberlite-like rocks of the Charteskii Complex (Subpolar Urals)

Results of the study of carbon material (CM) discovered in kimberlite-like rocks of the Charteskii Complex (Subpolar Urals) are considered. It is shown that CM is represented by partially oxidized graphite and optically transparent amorphous CM (presumably diamond-like carbon). The data obtained are important for estimation of the diamond potential of this object, as well as for understanding of the new mechanism of the formation of diamond-like carbon and diamond.

Nanostructured Diamond-Like Carbon Films Grown by Off-Axis Pulsed Laser Deposition

Nanostructured diamond-like carbon (DLC) films instead of the ultrasmooth film were obtained by pulsed laser ablation of pyrolytic graphite. Deposition was performed at room temperature in vacuum with substrates placed at off-axis position. The configuration utilized high density plasma plume arriving at low effective angle for the formation of nanostructured DLC. Nanostructures with maximum size of 50 nm were deposited as compared to the ultrasmooth DLC films obtained in a conventional deposition. The Raman spectra of the films confirmed that the films were diamond-like/amorphous in nature. Although grown at an angle, ion energy of >35 eV was obtained at the off-axis position. This was proposed to be responsible for subplantation growth of sp3hybridized carbon. The condensation of energetic clusters and oblique angle deposition correspondingly gave rise to the formation of nanostructured DLC in this study.

Phase transformations during high-pressure torsion (HPT) in titanium, cobalt and graphite

Several elements were processed by high-pressure torsion and phase transformations were investigated. Titanium exhibited a transition from hcp to an ω phase at pressures higher than 4 GPa, while the transition was facilitated with increasing the shear strain. The stability of ω phase appeared to decrease with decreasing the grain size to the nanometer level (e.g., by processing at cryogenic temperatures and/or by consolidation of powders). Cobalt exhibited a transition from metastable fcc to hcp until the grain size reached the submicrometer level, but the fcc phase appeared to be more stable with decreasing the grain size to the nanometer level. Graphite exhibited a transition to diamond-like carbon (DLC), while the formation of DLC was facilitated with increasing the pressure, temperature and strain.

DLC coating on stainless steel by pulsed methane discharge in repetitive plasma focus

Amorphous hydrogenated carbon (a-C:H)/diamond-like carbon (DLC) coatings have been achieved on AISI 304 stainless steel (SS) substrates by employing energetic ions emitted from a repetitive plasma focus operated in CH4 discharge. The Raman spectroscopy of the coatings exhibits the evolution of a-C:H/DLC coatings with clearly observed D and G peaks centered about 1320–1360 and 1560–1620cm−1 respectively. The diamond character of the coatings is influenced by the ion flux and repetition rate of the focus device. The repetitive discharge mode of plasma focus has led to the formation of a-C:H/DLC coatings in short duration of time. The coatings transform from a-C to a-C:H depending upon substrate angular position. X-ray diffraction (XRD) analysis confirms the formation of DLC coating owing to stress-induced restructuring in SS. The estimated crystallite size is found to be ∼40–50nm. Field emission scanning electron micrographs exhibit a layered granular surface morphology of the coatings. The Vickers surface hardness of the DLC coated SS samples has been significantly improved.

Graphite to diamond-like carbon phase transformation by high-pressure torsion

Diamond-like carbon (DLC) with significant fraction of tetrahedral sp3 bonds and amorphous structure is generally produced in the form of thin films by rapid cooling of high-energy carbon atoms in vacuum. This study shows that DLC can be directly formed from bulk samples of graphite by application of severe plastic deformation under high pressures. The formation of DLC is enhanced with increasing the shear strain, pressure, and temperature. It is suggested that the high pressure thermodynamically stabilize DLC and formation of high density of lattice defects by straining reduces the energy barrier for DLC formation.

Sputtering yields and surface modification of poly(methyl methacrylate) (PMMA) by low-energy Ar+/ ion bombardment with vacuum ultraviolet (VUV) photon irradiation

Sputtering yields and surface modification of poly(methyl methacrylate) (PMMA) by mono-energetic ion beams and/or vacuum ultraviolet (VUV) light are studied with the use of a low-energy mass-selected ion beam system. Sputtering yields of PMMA by Ar+ or ion beams are obtained as functions of ion incident energy below 500 eV. It is found that surface modification of PMMA due to ion incidence is limited to the region near the film surface, whereas that due to Ar+ ion incidence is seen in a relatively deeper region of the film, where PMMA is partially carbonized and diamond-like carbon (DLC) is formed. Under the conditions of incident energies and fluxes of ion and VUV light used in the experiments, the sputtering yield of PMMA by simultaneous incidence of VUV light and ions is found to be nearly equal to the sum of the yields by separate incidences of VUV light and ions. Some of the etching characteristics observed in this study (such as DLC formation by ion sputtering) may be shared by a wide range of organic polymers that have main chain structures similar to those of PMMA.

Long-term surface restoration effect introduced by advanced silicate based lubricant additive

Long-term effect (up to 300h) of an advanced silicate based lubricant additive on the tribological properties is studied using a newly designed pin-on-disk tester. With the additive, the coefficient of friction was reduced by ∼40%. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) examinations showed that a smooth and high C-content outer layer was formed on the specimen surfaces, suggesting possible formation of diamond-like carbon (DLC) films. Using nano-hardness measurements, the hardness of the layer on the disk and the pin were 10.2GPa and 16.7GPa respectively. Wear loss and ferrographic analyses indicated that a “negative wear” occurred when the additive was applied, suggesting the debris particles were captured by the specimen to form a self-repairing layer.

Diamond-Like Carbon produced by highly charged ions impact on highly oriented pyrolytic graphite

The formation of Diamond-Like Carbon (DLC) structure on the surface of Highly Oriented Pyrolytic Graphite (HOPG) following Xe q+ (q = 5 ∼ 26) ions irradiation with different fluence is studied with Raman and X-ray photoelectron spectroscopy (XPS) analyses in this work. The DLC structure formed on HOPG is shown by the electronic structure transition from sp 2 to sp 3 hybridization. An obvious evolution of the transition depending on the charge state and the fluence of the impact ions were found. The DLC production is considered to be caused by both kinetic energy and potential energy deposition, the surface structure could be strongly changed due to high-density energy deposition and the intense inelastic electronic energy exchange process.

Parametric studies of diamond-like carbon by pulsed Nd:YAG laser deposition

This paper presents the results, analysis and discussions of parametric studies of diamond-like carbon (DLC) thin films by pulsed Nd:YAG laser deposition. Effects on the DLC properties and growth rate were investigated by varying the deposition parameters, namely the laser wavelength and fluence, substrate and temperature. For characterization, visible Raman spectroscopy, current-voltage measurement, optical interferometry, and optical absorption technique were employed. Comparisons were made with previous work by other workers who had also employed pulsed Nd:YAG lasers. The results also supported the subplantation mechanism for DLC formation.

Synthesis and field emission of diamond-like carbon nanorods on TiO 2/Ti nanotube arrays

Highly ordered TiO 2/Ti nanotube arrays were fabricated by anodic oxidation method in 0.5 wt% HF. Using prepared TiO 2/Ti nanotube arrays deposited Ni nanoparticles as substrate, high quality diamond-like carbon nanorods (DLCNRs) were synthesized by a conventional method of chemical vapor deposition at 750 °C in nitrogen atmosphere. DLCNRs were analyzed by filed emission scanning electron microscopy and Raman spectrometer. It is very interesting that DLCNRs possess pagoda shape with the length of 3–10 μm. Raman spectra show two strong peaks about 1332 cm −1 and 1598 cm −1, indicating the formation of diamond-like carbon. The field emission measurements suggest that DLCNRs/TiO 2/Ti has excellent field emission properties, a low turn-on field about 3.0 V/μm, no evident decay at 3.4 mA/cm 2 in 480 min.

SURFACE AND QUALITY MODIFICATION OF DIAMOND-LIKE CARBON FILMS BY CO2 LASER HEATING ASSISTED HOT FILAMENT CHEMICAL VAPOR DEPOSITION

An infrared CO 2 laser was used for regional heating to study the heating effect on hot filament chemical vapor deposition of diamond-like carbon formation on Si (100) face substrates. The substrate surface temperature was about 450–500°C. The power of the laser called low, medium, and high raised the temperature of the substrate locally by 25, 45, and 55°C, respectively. At medium laser power, at the central laser beam region, a narrow Raman peak centered at 1438 cm-1 was detected. It can be concluded that this region has good-quality DLC. This moderate high-frequency peak corresponds to a fourfold-rotation-symmetry atom in an amorphous carbon network from the tight-binding molecular dynamics simulation of Wang and Ho.

Synthesis of diamond-like carbon coatings on aluminum 6061 T-91 substrates by laser sintering of ultra-nanocrystalline diamond powders

Diamond-like carbon (DLC) coatings have been prepared on aluminum 6061 T-91 substrates with the aid of electrostatic spray deposition (ESD) of ultra-nanocrystalline diamond powders (2-8 nm) followed by direct laser sintering technique. A continuous-wave CO 2 laser was utilized, producing a dense, adherent DLC coating with a nominal thickness of 10 μm under optimal laser parameters that included laser power of 200 W, spot size of 1 mm by 0.1 mm and scanning speed of 254 mm/s. The evidence of DLC formation and its purity was obtained by characterizing the samples with Raman spectroscopy, X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy. Functional evaluation of DLC coatings was performed using scratch, micro-hardness, fracture toughness and surface roughness tests. Raman measurements showed the presence of a broader peak at around 1332 cm − 1 (characteristic of pure diamond) for electrostatically deposited samples and the presence of DLC with a broad asymmetric hump in the region of 1000 to 1600 cm − 1 for laser-sintered samples. X-ray diffraction and energy dispersive spectroscopy confirmed the presence of carbon phases in the coatings. Scanning electron microscopy examination showed a fairly uniform and dense coating with a nominal thickness of 10 μm and a heat affected zone of 60–80 μm. These coatings exhibited micro-hardness in the range of 2150 to 2350 kg/mm 2 when measured using a Vickers diamond pyramid indenter at a load of 0.5 N. In some localized regions, hardness of 9000 kg/mm 2 was obtained. Scratch tests revealed a fairly homogenous coating with strong adhesive nature having almost four times the average critical force when compared against the electrostatically deposited sample. Fracture toughness and surface roughness are well within the acceptable ranges of DLC coatings. The capability of laser sintering to produce thick DLC coatings with outstanding mechanical and tribological properties and excellent bonding with aluminum offers the possibility to tailor an extreme lightweight, strong and wear-resistant material.

Target-plane deposition of diamond-like carbon in pulsed laser ablation of graphite

In pulsed Nd:YAG laser ablation of highly oriented pyrolytic graphite (HOPG) at 10 −6 Torr, diamond-like carbon (DLC) are deposited at laser wavelengths of 1064, 532, and 355 nm on substrates placed in the target-plane. These target-plane samples are found to contain varying sp 3 content and composed of nanostructures of 40–200 nm in size depending on the laser wavelength and laser fluence. The material and origin of sp 3 in the target-plane samples is closely correlated to that in the laser-modified HOPG surface layer, and hardly from the backward deposition of ablated carbon plume. The surface morphology of the target-plane samples shows the columnar growth and with a tendency for agglomeration between nanograins, in particular for long laser wavelength at 1064 nm. It is also proposed that DLC formation mechanism at the laser-ablated HOPG is possibly via the laser-induced subsurface melting and resolidification.

Phase transformation of graphite irradiated by high-intensity pulsed ion beams

The microstructure and morphology of graphite irradiated by high-intensity pulsed ion beams (HIPIB) has been studied by varying the ion current density as 200, 350 and 1500 A/cm 2 with one to five shots. Phase transformation from graphite to diamond-like carbon (DLC) on the HIPIB-irradiated graphite was confirmed by Raman spectroscopy where a typical broadened asymmetric peak appeared in the wavenumber range of 1100–1700 cm −1. Formation of DLC on the irradiated graphite strongly depended on the HIPIB parameters and preferably took place at the medium ion current density of 350 A/cm 2 up to five shots. Numerical simulation of ablation process was performed to explore the transformation mechanism of DLC from graphite irradiated by HIPIB. The calculation showed that the temperature profile in irradiated graphite at 350 A/cm 2 is almost identical to that at 200 A/cm 2, showing a deeper heat-affected zone in comparison with that of 1500 A/cm 2. Moreover, the ablation depth per shot is around 0.8 μm at 350 A/cm 2, higher than that of 0.4 μm at 200 A/cm 2 and much lower than that of 8.4 μm at 1500 A/cm 2, respectively. The experimental and numerical results indicate that a proper temperature and pressure repetitively created in the top layer of ablated graphite during HIPIB irradiation facilitates the phase transformation.

Formation of diamond-like carbon (DLC) film on the NiTi alloys via plasma immersion ion implantation and deposition (PIIID) for improving corrosion resistance

NiTi alloys are potentially useful in biomedical application due to their unique superelasticity and shape memory effect. However, the materials are vulnerable to surface corrosion and the most serious issue is out-diffusion of toxic Ni ions from the substrate into body tissues and fluids. In this paper, Diamond-like carbon (DLC) film is fabricated on the NiTi alloys using plasma immersion ion implantation and deposition (PIIID) at room temperature to improve their corrosion resistance and block the out-diffusion of the Ni ions. The results show that the DLC films cannot only improve the corrosion resistance of the NiTi substrate, but also effectively suppress the Ni ions release from the substrate. The reason that the corrosion resistance of the coated samples is markedly improved due to the DLC films formation is systematically investigated.