Tetrahedral Diamond-like Carbon Research Articles

High Pressure Carbon Polymers from Impact Melt Rock of the Giant Popigai Astrobleme (Siberia, Russia)

The Popigai astrobleme is a unique geological object with huge storages of impact diamonds of high hardness quality being perspective as an abrasive material. In spite on very well-known after-graphitic nature of the Popigai diamonds, it was predicted that a part of them might have non-graphitic precursor as the target of the meteorite crater partly consist of sedimentary rocks with coals and bitumens. In this study by use of a complex of modern methods we have analyzed unusual carbon particles from impact melt rocks of the Popigai astrobleme. The studied carbons according to the provided Raman studies belong to high pressure polymers with hydrogenated carbons - hydrogenated amorphous tetrahedral diamond-like carbon (ta-C:H) and rare polymeric a-C:H. A list of typomorphic features of the high pressure non-crystalline carbons are described in the paper on the basis of UV Raman spectroscopy, scanning electron microscopy, microprobe and 813C isotopic composition analysis.

Tribological properties of hydrogen free DLC in self-mated contacts against ZDDP-added oil

PurposeThe purpose of this study is to investigate the tribological properties of tetrahedral diamond-like carbon (DLC) films in self-mated contacts in the presence of additivated and non-additivated vegetable oils. DLC films have high practical value due to low friction and low wear properties. On the other hand, vegetable oils are considered to be lubricants for future due to its resource renewability and biodegradability. Sometimes different chemical agents are added to vegetable oils to further improve its tribological properties. Thus, the tribological study of DLC films against additivated oils becomes important.Design/methodology/approachThe tribology tests were conducted in a four ball tribo-meter under the boundary lubricated conditions.FindingsTa-C DLC exhibited 80 per cent lower wear rate under Zinc dialkyldithiophosphates (ZDDP)-added oil compared to that of base oil. In contrast, the friction coefficient under additivated oil was slightly higher than the base oil lubricated case. Moreover, the carbonyl band area as well as the viscosity change of ZDDP-added oil was much smaller than that of base oil. Therefore, ZDDP reduced the wear of DLC film and prevented the oxidation of base oil during tribotests.Originality/valueThis is the first work on the tribological properties of ta-C DLC lubricated with corn oil with and without anti-wear additives.

Tribological Study of a Tetrahedral Diamond-Like Carbon Coating under Vegetable Oil–Based Lubricated Condition

Maintaining a clean environment is the major concern of industries that produce fuel and lubricants for automotive applications. Thus, vegetable-based oils are being explored for the preparation of biobased lubricants because of their biodegradability and nontoxicity. Despite their low thermal stability, vegetable oils show better tribological characteristics than mineral oils. Nonetheless, the thermal stability of vegetable oils could be improved by transesterification. In this study, three vegetable-based oils (sunflower, palm, and coconut) were used to investigate the tribological properties of ta-C diamond-like carbon (DLC) coating under DLC–steel contact condition. A BICERI ball-on-a plate tribotesting machine was used to conduct experiments. During the experiment, test contacts of tribopairs lubricated with sunflower oil exhibited better tribological characteristics than those using coconut oil as a lubricant.

Tribological Characteristics of Tetrahedral (ta-C) DLC Coating in the Presence of Commercial Lubricating Oil

Currently, the application of diamond-like carbon (DLC) coatings for automotive components is becoming a favorable strategy to cope with the new challenges faced by the automotive industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Commercially available fully formulated lubricating oils enhance the lubrication of ferrous materials. Therefore, the interaction between nonferrous coatings (e.g., DLC) and commercial lubricating oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with tetrahedral DLC (ta-C) sliding against a 440C stainless steel ball. Wear track was investigated by scanning electron microscopy and atomic force microscopy. Energy dispersive spectroscopy was used to analyze the tribofilms inside the wear track. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases but the wear rate increases in the ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization.

Tribological characteristics of amorphous hydrogenated (a-C:H) and tetrahedral (ta-C) diamond-like carbon coating at different test temperatures in the presence of commercial lubricating oil

Currently, the application of diamond-like carbon (DLC) coatings for automotive components is becoming a favorable strategy to cope with the new challenges faced by the automotive industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, consequently improving the fuel efficiency and durability of these components. Commercially available fully formulated lubricating oils enhance the lubrication of ferrous materials. Therefore, the interaction between nonferrous coatings (e.g., DLC) and commercial lubricating oil must be investigated. A ball-on-plate tribotester was used to run the experiments using stainless steel plates coated with amorphous hydrogenated DLC (a-C:H) and tetrahedral DLC (ta-C) sliding against a 440C stainless steel ball. Wear track was investigated by scanning electron microscopy and atomic force microscopy. Energy dispersive spectroscopy and X-ray photoelectron spectroscopy were used to analyze the tribofilms inside the wear track. Raman analysis was performed to investigate the structural change of the coatings. At high temperatures, the CoF decreases but the wear rate increases in the a-C:H and ta-C DLC-coated plates. CoF and wear rate (coated layer and counter surface) are mostly influenced by coating graphitization. Tribochemical films, such as polyphosphate glass, are formed in ta-C and act as protective layers. Therefore, the wear rate of ta-C DLC is lower than that of a-C:H DLC.

Mechanical and tribological characterization of tetrahedral diamond-like carbon deposited by femtosecond pulsed laser deposition on pre-treated orthopaedic biomaterials

Femtosecond pulsed laser deposition (PLD) has been performed using a mode-locked Ti:sapphire laser including an amplification stage (150 fs, 800 nm, 1 kHz) to deposit tetrahedral-amorphous carbon films (ta-C) on AISI 316L stainless steel and ultra high molecular weight polyethylene, in perspective to extend the wear resistance of materials used in hip joints. Ta-C films have been elaborated in high vacuum conditions at room temperature. The diamond-like coated silicon substrates exhibit high wear resistance (in the 10 −8–10 −9 mm 3 (N m) −1 range) with moderate hardness (in the 20–30 GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. In situ sputter cleaning of the orthopaedic substrates in argon plasma prior to carbon deposition has been investigated, leading to the enhancement of the adhesion of the films onto the stainless steel substrates. The adhesion properties of films deposited in various conditions on metallic substrates have been studied by tensile tests. The tribological behavior of the coatings deposited on cleaned substrates have been widely investigated in a pin-on-flat configuration in ambient air and Ringer solution. Finally, a DLC thin film with an homogeneous thickness has been deposited on hemispherical surface of 22.2 mm in diameter of a stainless steel femoral head of a hip prosthesis, whose wear behavior will be quantified using a hip joint simulator during one million of cycles (corresponding to the human activity during one year).

Towards the deposition of tetrahedral diamond-like carbon films on hip joints by femtosecond pulsed laser ablation

Compared to conventional nanosecond laser ablation, femtosecond pulsed laser deposition (PLD) allows the production of higher energy ions (up to a few keV) in the plasma plume, which strongly affect the structure and properties of the deposited films. In this work, tetrahedral diamond-like carbon (ta-C) films have been deposited by femtosecond PLD on various substrates, including 316L stainless steel, in order to extend the wear resistance of materials used for hip joint replacement. The deposition process has been optimized to obtain smooth and wear-resistant carbon films by ablating a graphite target in ultra-high vacuum conditions at room temperature, with a laser fluence (energy density) ranging from 1 to 6 J cm −2. In situ sputter cleaning of the substrates in an argon atmosphere prior to carbon deposition has been widely investigated: tensile tests show that the adhesion of the films on stainless steel substrates is remarkably enhanced by removing the contamination and oxidized top-coats. The films exhibit high wear resistance (in the 10 −8 to 10 −9 mm 3 N −1 m −1 range) with moderate hardness (in the 20–30 GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. The ability of these films to satisfy the biomedical requirements is discussed and the possibility to deposit homogeneous ta-C films on a 22.2-mm diameter hemispherical surface is examined. Finally, homogeneous films have been deposited on a 316L stainless steel femoral head, whose wear behavior will be quantified using a walking simulator during several millions of cycles (corresponding to the human activity during several years).

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 CH 4/C 2H 4 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 sp 2 related defects in pseudo-gap of undoped as deposited and annealed 20–100 nm thick films. 1 1 The preliminary results of this study were reported on the MRS 1999 Fall Meeting. Symposium U: Amorphous and Nanostructures Carbon. Boston, USA, November 1999. Mat. Res. Soc. Symp. Proc., Vol. 593, p. 249 (2000). High density of ESR active paramagnetic centers (PC) N s=(1.0–4.5)×10 21 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.

Deposition of tetrahedral diamond-like carbon thin films by femtosecond laser ablation for applications of hip joints

Tetrahedral diamond-like carbon films (ta-C) were deposited by femtosecond pulsed laser deposition (PLD) on various substrates, including 316L stainless steel and ultra high molecular weight polyethylene, in perspective to extend the wear resistance of materials used in hip joints. Usually films are deposited by plasma enhanced chemical vapor deposition or by PLD, principally performed with laser pulse duration in the nanosecond range. In the present study, DLC films were deposited by femtosecond laser ablation in high vacuum conditions at room temperature. The 800 nm, 150 fs laser pulses are generated by a mode-locked Ti:Sapphire laser, including an amplification stage. The fluence ranges from 1 to 6 J/cm2. Sputter cleaning of the substrates in an argon atmosphere prior carbon deposition was widely investigated; the adhesion of the films onto the stainless steel substrates was then considerably enhanced by removing the contamination and oxidized top-coats. The adhesion properties of films deposited in various conditions on 316L stainless steel substrates were studied by tensile tests. The films exhibit high wear resistance (in the 10−8 mm3 N−1 m−1 range) with moderate hardness (in the 20–30 GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. The capacity of these films to satisfy the biomedical demand is discussed.

Atomic structure, electrical properties, and infrared range optical properties of diamondlike carbon films containing foreign atoms prepared by pulsed laser deposition

We investigated the atomic structure, electrical, and infrared range optical properties of diamondlike carbon (DLC) films containing alloy atoms (Cu, Ti, or Si) prepared by pulsed laser deposition. Radial distribution function (RDF) analysis of these films showed that they are largely sp3 bonded. Both pure DLC and DLC + Cu films form a Schottky barrier with the measuring probe, whereas DLC + Ti films behave like a linear resistor. Pure DLC films and those containing Cu exhibit p-type conduction, and those containing Ti and Si have n-type conduction. Photon-induced conduction is observed for pure DLC, and the mechanism is discussed in terms of low-density gap states of highly tetrahedral DLC. Our results are consistent with relative absence of gap states in pure DLC, in accordance with theoretical prediction by Drabold et al.37 Temperature dependence of conductivity of DLC + Cu shows a behavior σ ∞ exp(−B/T1/2), instead of the T−1/4 law (Mott–Davis law). Contributions from band-to-band transitions, free carriers, and phonons to the emissivity spectrum are clearly identified in pure DLC films. The amorphous state introduces a large contribution from localized states. Incorporation of a small amount of Si in the DLC does not change the general feature of emissivity spectrum but enhances the contribution from the localized states. Cu and Ti both enhance the free carrier and the localized state contributions and make the films a black body.

Electron field emission from filtered arc deposited diamond-like carbon films using Au and Ti layers

Abstract In this work, tetrahedral diamond-like carbon (DLC) films are deposited on Si, Ti/Si and Au/Si substrates by a new plasma deposition technique — filtered arc deposition (FAD). Their electron field emission characteristics and fluorescent displays of the films are tested using a diode structure. It is shown that the substrate can markedly influence the emission behavior of DLC films. An emission current of 0.1 μA is detected at electric field E DLC/Si =5.6 V/μm, E DLC/Au/Si =14.3 V/μm, and E DLC/Ti/Si =5.2 V/μm, respectively. At 14.3 V/μm, an emission current density J DLC/Si =15.2 μA/cm 2 , J DLC/Au/Si =0.4 μA/cm 2 , and J DLC/Ti/Si =175 μA/cm 2 is achieved, respectively. It is believed that a thin TiC transition layer exists in the interface between the DLC film and Ti/Si substrate.

Electron emission induced modifications in amorphous tetrahedral diamondlike carbon

The cold-cathode electron emission properties of amorphous tetrahedral diamondlike carbon are promising for flat-panel display and vacuum microelectronics technologies. The onset of electron emission is, typically, preceded by “conditioning” where the material is stressed by an applied electric field. To simulate conditioning and assess its effect, we combined the spatially localized field and current of a scanning tunneling microscope tip with high-spatial-resolution characterization. Scanning force microscopy shows that conditioning alters surface morphology and electronic structure. Spatially resolved electron-energy-loss spectroscopy indicates that the predominant bonding configuration changes from predominantly fourfold to threefold coordination.

Influence of carbon ion energy on properties of highly tetrahedral diamond-like carbon

A tetrahedrally bonded form of non-hydrogenated amorphous carbon is produce by deposition from energy filtered ions emanating from a carbon cathodic vacuum arc. A range of such films was grown and the plasmon energies, compressive stresses, density and resistivities were measured as a function of ion energy (10–500 eV). These properties are found to be strongly correlated to the sp3 fraction and each to pass through a maximum at an ion energy of about 140 eV. The optimal accelerating potential is observed to depend on the type of carbon ions exiting the magnetic filter. The data is found to support deposition models in which the sp3 bonding arises from the subplantation of incident ions, giving rise to a quenched-in increase in density and strain.