Amorphous Diamond-like Carbon Research Articles

Effect of Nanoscale Confinement on Freezing of Modified Water at Room Temperature and Ambient Pressure

Understanding the phase behavior of confined water is central to fields as diverse as heterogeneous catalysis, corrosion, nanofluidics, and to emerging energy technologies. Altering the state points (temperature, pressure, etc.) or introduction of a foreign surface can result in the phase transformation of water. At room temperature, ice nucleation is a very rare event and extremely high pressures in the GPa-TPa range are required to freeze water. Here, we perform computer experiments to artificially alter the balance between electrostatic and dispersion interactions between water molecules, and demonstrate nucleation and growth of ice at room temperature in a nanoconfined environment. Local perturbations in dispersive and electrostatic interactions near the surface are shown to provide the seed for nucleation (nucleation sites), which lead to room temperature liquid-solid phase transition of confined water. Crystallization of water occurs over several tens of nanometers and is shown to be independent of the nature of the substrate (hydrophilic oxide vs. hydrophobic graphene and crystalline oxide vs. amorphous diamond-like carbon). Our results lead us to hypothesize that the freezing transition of confined water can be controlled by tuning the relative dispersive and electrostatic interaction.

Influence of Silicon on the Wear Properties of Amorphous Carbon Under Dry and Lubricated Conditions

Diamond-like carbon (DLC) coatings have drawn much attention as potential surface coatings for engineering contacts because of their excellent friction and wear resistance properties. However, much less is known about their friction and wear mechanisms, especially at higher contact pressures. In this study, two amorphous carbon DLCs, with (a-C:Si) and without Si (a-C), have been investigated to understand the influence of Si on friction and wear under dry, base oil- and fully formulated oil-lubricated conditions. Si does not affect friction but significantly affects wear. a-C:Si shows lower wear than a-C but imparts higher wear on the steel counterpart. The steel counterpart that forms a hybrid tribolayer (transferred carbon from DLC + additive-derived tribofilm products) exhibits superior wear resistance properties.

S1140103 無灰系摩擦調整剤及びZnDTP複合添加油下におけるta-C膜のトライボ特性に関する研究([S114-01]トライボロジーの基礎と応用(1),機素潤滑設計部門)

S1140103 無灰系摩擦調整剤及びZnDTP複合添加油下におけるta-C膜のトライボ特性に関する研究([S114-01]トライボロジーの基礎と応用(1),機素潤滑設計部門)

Synthesis and some aspects of the formation mechanism of carbon structures under hydrothermal conditions

The formation of carbon structures upon the reactions of organic compounds with strong mineral acids under hydrothermal conditions was studied. The reactions were found to give amorphous carbon, microcrystalline graphite, nanodiamonds, diamond-like carbon, diamonds, C60 and C70 fullerenes, and carbolite. Hydrocarbons of various compositions including aromatics and naphthenes were detected among the reaction products. A possible mechanism of the formation of carbon structures with sp2 bond hybridization under hydrothermal conditions was proposed.

Atomistic Simulations of Ultrashort Pulsed Laser Ablation of Polycrystalline Diamond

The mechanisms of ultrashort pulsed laser ablation of polycrystalline diamond (PCD) are investigated by means of molecular dynamics simulations. The simulation model provides a detailed atomistic description of the laser energy deposition to the PCD specimen, which is verified by an experiment using 300 fs laser irradiation of a typical PCD sample. It is found that non-homogeneous melting initiates from grain boundaries composed by sp2 hybridized denser diamond-like amorphous carbon atoms of higher potential energies. Furthermore, the interplay of the photomechanical spallation and evaporation is found to be accounted for the material removal in the laser ablation. The laser ablation-induced microstructure changes of the sample are characterized in detail. Simulation results suggest that the sample after laser ablation consists of four zones of different structural lattices. It is found that the top layer of the ablated surface composed by amorphous carbon with abundant vacancies can be wiped off from the surface easily, which agrees well with experimental results. Keywords: Polycrystalline diamond, laser ablation, molecular dynamics, grain boundary.

Magnetron sputter deposited tantalum and tantalum nitride thin films: An analysis of phase, hardness and composition

Tantalum (Ta) and tantalum nitride thin films are highly important as diffusion barriers and adhesion layers in microelectronics and hard coatings for cutting tools. In this study, the effect of the underlying substrate on the phase formation of Ta and the influence of a changing N2/Ar flow ratio on hardness, phase and composition of reactively formed tantalum nitride have been investigated. Ta is DC sputter deposited and forms β-Ta on amorphous diamond-like carbon and on the amorphous natural oxide layers of Ti and Si(100) while a 15nm TaN seed layer results in the formation of α-Ta. The chemical composition of the topmost layers of a substrate influences the formation of α- and β-Ta. With increasing N2/Ar flow ratios a transition from amorphous Ta-rich tantalum nitride over face-centered cubic tantalum nitride (fcc-TaN) to (100) textured fcc-TaN at flow ratios above 45% is observed. The hardness of the tantalum nitride thin film reaches a maximum at a flow ratio of 45%, followed by a decrease in hardness for higher N2/Ar flow ratios. The increase in hardness is associated with a decrease in grain size and shows a stronger correlation for a Meyers and Ashworth relationship than for a Hall–Petch relationship.

Wear behaviour of tetrahedral amorphous diamond-like carbon (ta-C DLC) in additive containing lubricants

Diamond-like carbon (DLC) coatings offer excellent mechanical and tribological properties. They provide ultra-low friction and superior wear resistance. In recent years, the research of DLC coating focuses on the application of these coating in mechanical components which work under boundary lubricated conditions. Since conventional lubricants and lubricant additives were formulated for metal surfaces, the effects of these lubricants on DLC contact and interaction between lubricant additives and DLC surfaces are still unclear. In this work, we present the influence of lubricant additives and counterbody materials on the wear behavior of ta-C DLC coating under boundary lubrication conditions. Tribological tests were performed in a home-build pin-on-disc tribometer. Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), Nano-indenter, X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy and scanning white light interferometry were used for characterization of ta-C DLC and worn surface analysis. The results show that ta-C DLC were totally wear out in DLC/steel contact tested in base oil. Addition of lubricant additives into the base oil significantly reduced the wear in the DLC/steel contact. ta-C DLC exhibited totally different wear behavior in DLC/steel and DLC/DLC contact depending on lubricant formulation. It is concluded that combination of lubricant formulation and counterbody material is a crucial factor for the use of DLC in lubricated conditions.

Graphite of the Turgenevskoe and Tamginskoe deposits of the Lesozavodsk area in the Primor’e region

The regional carbonization of the Riphean metamorphic complexes is discussed using as an example the Tamginskoe and Turgenevskoe graphite deposits located in the northern part of the Khanka terrane. It is shown that the noble metal mineralization associates closely with the graphitization. Isotopic, X-ray, and thermal analyses and Raman spectroscopy were first used for investigating the structural state of the graphite with defining its two varieties. The first of them is represented by nanocrystalline fluidogenic graphite that was formed during gas condensate crystallization from deep-seated reduced ore-bearing fluid. The second variety (large-flake graphite) represents a product of metamorphic recrystallization of carbonaceous terrigenous protoliths. The recrystallization was accompanied by the granitization of the sedimentary protolith, mobilization, and the transfer of the carbonaceous and ore matter of the host rocks. It is inferred that the graphitization associated with noble metal mineralization is a polygenic process. The graphite of the first generation associates closely with amorphous diamond-like carbon. This unexpected find may bear genetic information useful for geological and geochemical reconstructions.

Synthesis and Characterization of Doped and Undoped Nano-Columnar DLC Coating

Amorphous carbon (a-C:H/a-C) or Diamond-like carbon (DLC), has a very high potential diverse engineering and medical application for high wear resistance and tribological performance. Naturally grown columnar DLC films is chemically modified by post-treatment via electron beam irradiation (EB-irradiation), through precise observation and characterization by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and Raman spectroscopy. This nano-columnar a-C:H film has a unique nano-structure and mechanical properties. This nano-columnar structure is composed of graphitic inter-columnar network with amorphous carbon columns. Metallic doping into the inter-columns reflects positively on mechanical response by chemical modification with physical hardening.

Selection and characterization of peptides binding to diamond-like carbon

Phage display was used to find peptides specific for amorphous diamond-like carbon (DLC). A set of putative binders was analyzed in detail and one sequence was found that functioned both as a peptide fused to the pIII protein in M13 phage and as a peptide fused to the enzyme alkaline phosphatase (AP). The dissociation constant of the peptide–AP fusion on DLC was 63nM and the maximum binding capacity was 6.8pmol/cm2. Multiple ways of analysis, including phage titer, enzyme-linked immunosorbent assay, and ellipsometry were used to analyze binding and to exclude possible false positive results. DLC binding peptides can be useful for self-assembling coatings for modifying DLC in specific ways.

Ultra-low friction of tetrahedral amorphous diamond-like carbon (ta-C DLC) under boundary lubrication in poly alpha-olefin (PAO) with additives

Diamond-like carbon (DLC) coatings have increased demand as protective hard coating for mechanical components due to their exceptional mechanical and tribological performance. They provide ultra-low friction, excellent anti-wear properties and adhesive protection. In recent years, researches focus on the use of DLC coatings under boundary lubricated contacts to increase fuel efficiency of automotive by controlling the friction and to reduce the emission of harmful elements. Commercially available fully formulated oils are designed for ferrous surfaces and contain various additives to enhance the base oils, but interaction between DLC surfaces and those formulated oils is not yet fully understood. In this study we investigated frictional properties of ta-C DLC coating when lubricated with a base oil poly alpha-olefin (PAO) and PAO containing friction modifier glycerol mono-oleate (GMO), anti-wear additives ZnDTP and mixture of GMO+ZnDTP to understand the mechanism of ultra-low friction. The results exhibit that ta-C give ultra-low friction in pure PAO for DLC/steel and DLC/DLC tribopair. GMO additivated PAO provide smooth run-in period for transition to ultra-low friction regime and also enhance the durability of coating. ZnDTP behave differently depending on the presence of ferrous surfaces on the contact. It forms pad-like wear protective tribofilm both on ta-C and steel surfaces for DLC/steel contact, while it form thin white layer on ta-C surfaces for DLC/DLC contact. Using GMO and ZnDTP together does not show any synergistic correlation for steel/steel, DLC/steel and DLC/DLC combinations.

Influence of thermal heating on diamond-like carbon film properties prepared by filtered cathodic arc

Tetrahedral amorphous diamond-like carbon (ta-DLC) films were deposited on magnetic recording heads using the filtered cathodic arc method. The deposited film thickness was on the order of several nanometers. The DLC films were then annealed to 100°C–300°C for 30 and 60min, and the structure of the ta-DLC films was investigated using Raman spectroscopy, where the gross changes were observed in the Raman D and G peaks. Detailed interpretation concluded that there was sp2 clustering as a function of temperature, and there was no sp3-to-sp2 conversion after heating up to 300°C. Furthermore, X-ray photoelectron spectroscopy suggested that oxidation of both the ta-DLC film and the adhesion layer occurs at 300°C. Additionally, more film wear was observed with heating as measured by a nanoindenter.

DLC Coated Textile Vascular Prostheses Tested in Sheep

Textile vascular prostheses ARTECOR were coated by laser with amorphous diamond-like carbon layers (DLC) with thickness up to 200 nm. Layers were created in 0.25 Pa of Argon at laser energy density of 8 or 22 Jcm-2. Depending on the deposition conditions, DLC properties moved from soft „graphitic“ to more „diamond“ (53 % of sp3 bonds). Coated prostheses of various DLC thickness and sp3 content were implanted into carotid artery of Merino sheep. The prostheses were extirpated after 100 days (~180 days). From preliminary results follows that prostheses coated with DLC layer thickness of 20 nm and higher sp3 content showed the best results.

Thermal Stability Evaluation of Diamond-Like Carbon Coated by Filtered Cathodic Arc on Magnetic Recording Head Application

Tetrahedral amorphous diamond-like carbon films were deposited on magnetic recording head by Filtered Cathodic Arc and subsequently thermally heated to various conditions. Raman spectroscopy was then performed to understand film structure; and mechanical property in terms of wear resistance was investigated by nanoindenter. The Raman spectra revealed that G position, FWHM of G peak and Id/Ig changed as a function of heating temperature and time which also agree well with wear depth measured.

Mechanical properties of fluorinated DLC and Si interlayer on a Ti biomedical alloy

Fluorinated amorphous diamond-like carbon (F-DLC) films were deposited on Ti6Al4V substrates by radio frequency plasma enhanced chemical vapor deposition (rf PECVD) technique using a mixture of methane (CH4) and tetrafluoromethane (CF4) gasses. A 100nm Si interlayer was coated in advance by physical vapor deposition (PVD) process to improve the adhesion between F-DLC and Ti alloy. The structure and surface properties of F-DLC coatings, prepared by various fluorine flow ratios, were investigated by using X-ray diffraction spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The mechanical properties were evaluated by nano-indentation, and the adhesion, by micro-scratch. The results showed that a moderate incorporation of the fluorine content in the DLC films can still maintain acceptable mechanical properties, which, on the other hand, obtains remarkable benefits of blood compatibility and anti-corrosion.

Development of silver-containing diamond-like carbon for biomedical applications. Part I: Microstructure characteristics, mechanical properties and antibacterial mechanisms

Nanosilver containing diamond-like carbon films with different silver fractions were synthesized by the radio frequency magnetron sputtering using a single silver target in an atmosphere of Ar/CH4 mixture. The nanocrystalline silver clusters spontaneously segregated within an amorphous diamond-like carbon matrix. The amorphous-to-crystalline phase transformation resulted in both the surface hardness and electrical resistivity of the composite films decreasing with increasing the silver cluster size. The enlarged cluster size also increased the film surface roughness and water contact angle. All the films exhibited an anti-bacterium rate of over 93%, which evidenced that applying these composite films to anti-bacterium surface treatment is effective.

Phase transformation of diamond-like carbon/silver composite films by sputtering deposition

This study fabricated hydrogenated diamond-like carbon/silver bioceramic films on glass substrates using radio frequency magnetron sputtering with a single silver target in an atmosphere of Ar/CH4 mixture. The effects of applied power on the composition and microstructure of bioceramic film were evaluated. A phase transformation, amorphous diamond-like carbon → nano-silver precipitation → nano-silver growth in the amorphous diamond-like carbon matrix was observed during sputtering. The film growth rate, surface roughness, silver content and size of silver nanoclusters in the films all increased with the silver target power due to the higher flux of sputtered silver species toward the substrate.

Growth of nanocomposite films from accelerated C60 ions

A beam of accelerated C60 ions is used to deposit superhard (∼50 GPa) carbon films that exhibit high index plasticity (∼0.13–0.14) and high conductivity (up to 3000 S m−1). Transmission electron microscopy, Raman spectroscopy and x-ray photoelectron spectroscopy are subsequently used to study the microstructure and bond character of the deposited films. The films consist of textured graphite nanocrystals and diamond-like amorphous carbon (DLC). The graphene plane of the nanocrystals is aligned perpendicular to the film surface. It is shown that sp2 bonds dominate in the films. The percentage of sp3 bonds depends on the ion energy and the substrate temperature, and does not exceed 40%. The obtained results suggest that a new nanocomposite material consisting of oriented graphite nanocrystals reinforced by a DLC matrix is synthesized. A simple model is proposed to correlate the excellent mechanical properties with the observed structure.

Wettability of Amorphous Diamond-Like Carbons Deposited on Si and PMMA in Pulse-Modulated Plasmas

Pulse-modulated direct-current methane plasmas are used to deposit amorphous diamond-like carbon films on Si and dentistry-use polymethyl methacrylate (PMMA) substrates as a function of the negative pulse voltage applied to the substrate (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ). The films on PMMA show a transition from diamond-like to more graphitic carbon in the Raman spectra with increasing V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> , dissimilar to those on Si. This is attributed to easy deformation of PMMA, leading to the low compressive stress of the films (1 to 2 GPa). The contact angle of water for the films on both Si and PMMA is large, ranging from 79° to 94° almost independent of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> , confirming that the films are hydrophobic despite the difference in carbon bonding state. The large dispersion component (41-43 mJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of the surface free energy of the films measured from the contact angle of water and 1-bromonaphthalene indicates the high mass density of the films. The small polar component (0.2-3.5 mJ/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) is attributed to hydrogen saturation of the surface sites forming nonpolar C-H bonds and, thus, responsible for the hydrophobic behavior.

INFLUENCE OF THE SILICON INTERLAYER ON DIAMOND-LIKE CARBON FILMS DEPOSITED ON GLASS SUBSTRATES

Diamond-like carbon (DLC) films as a hard protective coating have achieved great success in a diversity of technological applications. However, adhesion of DLC films to substrates can restrict their applications. The influence of a silicon interlayer in order to improve DLC adhesion on glass substrates was investigated. Amorphous silicon interlayer and DLC films were deposited using plasma enhanced chemical vapor deposition from silane and methane, respectively. The bonding structure, transmittance, refraction index, and adherence of the films were also evaluated regarding the thickness of the silicon interlayer. Raman scattering spectroscopy did not show any substantial difference in DLC structure due to the interlayer thickness of the silicon. Optical measurements showed a sharp decrease of transmittance in the ultra-violet region caused by the fundamental absorption of the light. In addition, the absorption edge of transmittance shifted toward longer wavelength side in the ultra-violet region as the thickness of the silicon interlayer increased. The tribological results showed an increase of DLC adherence as the silicon interlayer increased, which was characterized by less cracks around the grooves.