Amorphous Diamond-like Carbon Matrix Research Articles

Formation of wear-resistant graphite/diamond-like carbon nanocomposite coatings on Ti using accelerated C60-ions

The nanostructural and tribological characteristics of carbon nanocomposite coatings (CNCs), deposited by accelerated C 60 ions at high temperatures, were studied. The CNCs were successfully fabricated on Ti-alloy using a flux that contained C 60 ions with 5 and 10 keV energies. Unlike the previous studies, ion mass-separator was not implemented to the deposition process. This enabled deposition of sp 2 -rich CNCs with a lower coefficient of friction (COF) at a higher deposition rate. Laser confocal microscopy , atomic force microscopy transmission electron microscopy , Raman spectroscopy , X-ray photoelectron spectroscopy, and X-ray Auger Electron Spectroscopy were used to investigate the structure of the coatings and friction test results. A carbon nanocomposite film consisting of graphite nanocrystals enclosed in an amorphous diamond-like matrix was formed at a deposition temperature of 300–400 °C. Upon deposition of the CNC, a COF of ~0.06 was achieved, which was almost one order of magnitude lower than that of bare Ti-alloy substrate. The surface wear was reduced by 360 times. The wear mechanism was changed from abrasive wear (on bare Ti-alloy) to a burnishing smoothening of the surface roughness (on CNCs). The transfer of graphite nanocrystals from the coating to the counter surface was identified and observed to act as a solid lubricant . • Carbon nanocomposite coatings were deposited on Ti using accelerated C 60 -ions. • Graphite nanocrystals embedded in amorphous diamond-like carbon matrix were formed. • The coatings were deposited without the implementation of ion mass-separator. • Deposition temperature significantly affected the size of graphite nanocrystals. • The coatings reduced the COF and wear rate of Ti by 8 and 360 folds, respectively.

Silver-doped nanocomposite carbon coatings (Ag-DLC) for biomedical applications – Physiochemical and biological evaluation

The formation of bacteria biofilm on the surface of medical products is a major clinical issue nowadays. Highly adaptive ability of bacteria to colonize the surface of biomaterials causes a lot of infections. This study evaluates samples of the AISI 316 LVM with special nanocomposite silver-doped (by means of ion implantation) diamond-like carbon (DLC) coating prepared by hybrid RF/MS PACVD (radio frequency/magnetron sputtering plasma assisted chemical vapour deposition) deposition technique in order to improve the physicochemical and biological properties of biomaterials and add new features such as antibacterial properties. The aim of the following work was to evaluate antimicrobial efficacy and biocompatibility of gradient a-C:H/Ti+Ag coatings in relation to the physiochemical properties of the surface and chemical composition of coating. For this purpose, samples were tested in live/dead test using two cell strains: human endothelial cells (Ea.hy926) and osteoblasts-like cells (Saos-2). For testing bactericidal activity of the coatings, an exponential growth phase of Escherichia coli strain DH5α was used as a model microorganism. Surface condition and its physicochemical properties were investigated using SEM, AFM and XPS. Examined coatings showed a uniformity of silver ions distribution in the amorphous DLC matrix, good biocompatibility in contact with mammalian cells and an increased level of bactericidal properties. What is more, considering very good mechanical parameters of these Ag including gradient a-C:H/Ti coatings, they constitute an excellent material for biomedical application in e.g. orthopedics or dentistry.

Synthesis of Ag-doped hydrogenated carbon thin films by a hybrid PVD–PECVD deposition process

Silver-doped hydrogenated amorphous carbon (Ag-DLC) films were deposited on Si substrates using a hybrid plasma vapour deposition–plasma enhanced chemical vapour deposition (PVD–PECVD) process combining Ag target magnetron sputtering and PECVD in an Ar–CH4 plasma. Processing parameters (working pressure, CH4/Ar ratio and magnetron current) were varied to obtain good deposition rate and a wide variety of Ag films. Structure and bonding environment of the films were obtained from transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy studies. Variation of processing parameters was found to produce Ag-doped amorphous carbon or diamond-like carbon (DLC) films with a range of characteristics with CH4/Ar ratio exercising a dominant effect. It was pointed out that Ag concentration and deposition rate of the film increased with the increase in d.c. magnetron current. At higher Ar concentration in plasma, Ag content increased whereas deposition rate of the film decreased. FTIR study showed that the films contained a significant amount of hydrogen and, as a result of an increase in the Ag content in the hydrogenated DLC film, sp 2 bond content also increased. The TEM cross sectional studies revealed that crystalline Ag particles were formed with a size in the range of 2–4 nm throughout an amorphous DLC matrix.

Microstructure and properties of (Cr:N)-DLC films deposited by a hybrid beam technique

In this paper, diamond-like carbon (DLC) films doped with CrN nano-crystalline were prepared on 316L stainless steel using a hybrid beam deposition system (including a linear ion source (LIS) and a DC magnetron sputtering of Cr target). The microstructure and composition of the films were studied using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Mechanical and tribological properties were investigated using nano-indentation and tribological tester. The results showed that an N doping could significantly influence the microstructure and properties of the as-deposited films. On one hand, the N atoms doped in the film tended to form Cr–N, –CN–H and C–N bonding, which would enhance the binding strength. On the other hand, the formation of CrN/CrC nano-crystalline due to N doping dispersed in the amorphous DLC matrix could play an important role and increase its hardness. In addition, the (Cr:N)-DLC showed low friction coefficient and wear rate compared with the Cr-DLC film.

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.

Negative magnetoresistance in Cr-containing diamond-like carbon-based heterostructures

We have characterized the local structure around the Cr atom, as a function of Cr content, in films of chromium-doped hydrogenated amorphous diamond-like carbon (Cr-DLC) synthesized by plasma-enhanced chemical vapor deposition (PECVD). The composition appears to be related to the structure and forward bias magnetoresistance in heterojunction devices. Chromium in diamond-like carbon (DLC) has a chemical state much like chromium carbide and, at low Cr content, the Cr is dissolved in an amorphous DLC matrix forming an atomic-scale composite. At higher Cr content, Cr is present as nano-composite and chromium carbide precipitates preferentially form at the surface of the film. In these films of higher chromium concentration, a large coefficient of negative magnetoresistance is observed in heterojunction devices with n-type silicon.

Modified DLC coatings prepared in a large-scale reactor by dual microwave/pulsed-DC plasma-activated chemical vapour deposition

Diamond-Like Carbon (DLC) films find abundant applications as hard and protective coatings due to their excellent mechanical and tribological performances. The addition of new elements to the amorphous DLC matrix tunes the properties of this material, leading to an extension of its scope of applications. In order to scale up their production to a large plasma reactor, DLC films modified by silicon and oxygen additions have been grown in an industrial plant of 1m 3 by means of pulsed-DC plasma-activated chemical vapour deposition (PACVD). The use of an additional microwave (MW) source has intensified the glow discharge, partly by electron cyclotron resonance (ECR), accelerating therefore the deposition process. Hence, acetylene, tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO) constituted the respective gas precursors for the deposition of a-C:H (DLC), a-C:H:Si and a-C:H:Si:O films by dual MW/pulsed-DC PACVD. This work presents systematic studies of the deposition rate, hardness, adhesion, abrasive wear and water contact angle aimed to optimize the technological parameters of deposition: gas pressure, relative gas flow of the monomers and input power. This study has been completed with measures of the atomic composition of the samples. Deposition rates around 1 μm/h, typical for standard processes held in the large reactor, were increased about by a factor 10 when the ionization source has been operated in ECR mode.

Synthesis of tin-incorporated nanocomposite diamond like carbon films by plasma enhanced chemical vapor deposition and their characterization

Sn-incorporated nanocomposite diamond like carbon (DLC) films were synthesized using direct current plasma enhanced chemical vapor deposition method. The precursor gas used was acetylene. For Sn incorporation, SnCl2∙2H2O dissolved in methanol was used. Fourier-transform infrared spectroscopy measurements showed different vibrational modes of tetrahedrally bonded carbon and also some small peaks due to SnC bonding vibrations. Transmission electron microscopy image and electron diffraction patterns also confirmed the incorporation of nanocrystalline Sn particles into the amorphous DLC matrix. Due to the presence of Sn clusters, the Tauc gap of the films decreased sharply, compared to the intrinsic material. It was found that the resistivity of Sn-incorporated DLC films decreased drastically (by eight orders of magnitude) compared to the undoped DLC film. Also, the films exhibited good field emission properties at a lower turn-on field.

Self-assembled Co nanorods in diamond-like carbon thin films synthesized by plasma-assisted magnetron sputtering

We report on self-assembled, high-aspect-ratio nanostructures of Co rods in diamond-like carbon (DLC) thin films synthesized by plasma-assisted magnetron sputtering. Cross-sectional and plan-view transmission electron microscopy investigations show that the nanorods continuously grow vertically to the substrate and have a relatively narrow distributed lateral size. The nanorods in the as-deposited thin films are found to have an ε-Co structure with a high density of defects and are encapsulated by 1–2 nm of an amorphous DLC matrix.

Nanocomposite tribological coatings for aerospace applications

Challenges in aerospace tribology and composite coatings for aerospace applications are briefly reviewed. Attention is given to nanocomposite coatings made of carbide, diamond-like carbon (DLC) and transition-metal dichalcogenide phases. The preparation of such coatings within the W–C–S material system using a hybrid of magnetron sputtering and pulsed laser deposition is described. Coatings consist of 1–2 nm WC and 5–10 nm WS2 grains embedded in an amorphous DLC matrix. These WC/DLC/WS2 nanocomposites demonstrate low friction and wear in tests performed in high vacuum, dry nitrogen and humid air. Coatings are found to adapt to the test conditions, which results in: (1) crystallization and reorientation of initially nanocrystalline and randomly oriented WS2 grains; (2) graphitization of the initially amorphous DLC matrix; (3) reversible regulation of the composition of the transfer film between WS2 and graphite with environmental cycling from dry to humid; and (4) possible DLC/WS2 synergistic effects, providing friction reduction in oxidizing environments. These adaptive mechanisms achieve low friction coefficients of 0.02–0.05 and an endurance above two million cycles in space simulation tests. This also provides stable coating performance and recovery of low friction in tests simulating ambient/space environmental cycling. Correlations among WC/DLC/WS2 chemistry, structure, hardness, friction and wear are discussed. The tremendous potential of such composites for aerospace tribology is demonstrated.