Diamond-like Carbon Matrix Research Articles

Structural and electrical characterization of boron-containing diamond-like carbon films deposited by femtosecond pulsed laser ablation

The present study investigates the influence of the incorporation of boron in Diamond-Like Carbon (DLC) films deposited by femtosecond laser ablation, on the structure and electrical properties of the coatings within the temperature range 70–300 K. Doping with boron has been performed by ablating alternatively graphite and boron targets. The film structure and composition have been highlighted by coupling Atomic Force Microscopy (AFM), Scanning Electron Microscopy equipped with a field emission gun (SEM-FEG) and High Resolution Transmission Electron Microscopy (HRTEM). Boron dilution ranges between 2 and 8% and appears as nanometer size clusters embedded in the DLC matrix. Typical resistivity values are 100 W cm for pure a-C films, down to few W cm for a-C:B films at room temperature. The resistance decreases exponentially when the temperature increases in the range 70–300 K. The results are discussed considering the classical model of hopping conduction in thin films. Some coatings show temperature coefficients of resistance (TCR) as high as 3.85%. TCRs decrease when the doping increases. Such high values of TCR may have interests in the use of these films as thermometer elements in micro and nanodevices.

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.

Enhancement of electron field emission property with silver incorporation into diamondlike carbon matrix

Effects of silver doping on the electron field emission properties of diamondlike carbon films deposited on silicon substrates by the rf reactive sputtering technique were studied in detail. It was found that the threshold field and effective emission barrier were reduced by Ag doping and the emission current strongly depends on the Ag doping percentage. The threshold field was found to decrease from 6.8to2.6V∕μm with a variation of Ag at. % from 0 to 12.5. The field enhancement factor was calculated and we have explained the emission mechanism.

Silver nanocluster containing diamond like carbon

AbstractApplying Diamond Like Carbon (DLC) as medical coating has become well established since large scale plasma processes like Plasma Immersion Ion Implantation and Deposition (PIII&D) are available. Now the focus of research lies on systematic modification of certain biological relevant properties and the most recent field of interest turned to generating antimicrobial behaviour. This is desirable for medical tools as well as for different types of medical implants. Since silver and copper are known to provide a bactericidal effect, one tries to introduce clusters of these noble metals into the carbon matrix.The basic principle of the method presented is to convert a metal containing polymer film into DLC by ion bombardment. In this paper the hydrogenated DLC matrix is characterized and the evolution of the metal particles is studied. By means of film composition (RBS/ERD), bonding structure (Raman spectroscopy) and hardness (nanoindentation), the dependency of these material properties on ion species, energy and fluence is investigated. TEM imaging is used to visualize the film structure.Upon ion irradiation of the polymer films, increased density and considerable loss of hydrogen can be observed, which both are controlled by ion fluence and mass. The crosslinking of the carbon network, caused by hydrogen drive out as well as atomic displacements in collision cascades, results in the formation of a‐C:H. The silver particles in the film some ion induced growth, but still remain as nanoclusters in the a‐C:H matrix. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Monochromatic photoluminescence obtained from embedded ZnO nanodots in an ultrahard diamond-like carbon matrix

At room temperature, we observe the self assembly of nanoclusters in an amorphous matrix using a vacuum deposition technique. Self-assembled ZnO nanoclusters embedded in hard diamond-like amorphous carbon thin films, deposited by high vacuum Filtered Cathodic Vacuum Arc (FCVA) technique at room temperature without post-processing, have been observed. A selective self assembly of metal and oxygen ions in a 3-element plasma was observed. XPS distinctly showed presence of ZnO and DLC-mixture in 5, 7 and 10 at.% Zn (in target) films while maintaining high sp 3 content. This in turn improved the Young's modulus value of the ZnO nanoclusters embedded in DLC film (~ 220 GPa) compared to bulk ZnO (~ 110 GPa). Films with ZnO detected were observed to exhibit absorption edge at 377 nm monochromatic UV light emissions. This corresponded to a band gap value of about 3.30 eV. The emission with greatest intensity (after normalization) was detected from 10 at.% Zn (in target) film where presence of ZnO nanoclusters (~ 40 nm) in DLC matrix were confirmed by TEM. This showed that well-defined crystalline ZnO nanoclusters contributed to strong PL signal. Strong monochromatic emissions detected hinted that no defect states were present.

Characterizations of nano-crystalline diamond coating cutting tools

Diamond coatings made by processes such as chemical vapor deposition (CVD) have been increasingly explored for cutting tools applications, in particular, for machining lightweight high-strength materials. However, most literature to date reported that the wear resistance of CVD diamond tools is still distant to the polycrystalline diamond (PCD) counterparts. Recently, a microwave plasma-assisted CVD technology was developed to increase the diamond growth rate, and by adding nitrogen gas, this process can produce nano-structured coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix and have high hardness and low surface roughness. In this study, the nano-crystalline diamond (NCD) coating tools were characterized, compared to the conventional microcrystalline diamond coating (MCD) and PCD tools, in surface topography, grain sizes, carbon bonds, and mechanical properties. Moreover, the diamond tools were evaluated in machining Al-matrix composite and high-strength Al alloy. The results show that the NCD tools have smoother surfaces than the MCD tools, but rougher than the polished PCD tools. As to the diamond crystals, the NCD tools have ultrafine grains and the PCD tools have the largest grains. For the cutting edges, the PCD tools have the sharpest edge resulted from polishing and the NCD tools have larger edge rounding than the MCD counterparts. In addition to the nature-diamond peak identified in the Raman spectra, the NCD and MCD tools have additional Raman shifts associated with graphite and other disordered carbon bonds. The NCD tools have a much higher hardness, but a lower elasticity, than both the MCD and PCD tools. In machining testing, the NCD tools substantially outperform the MCD tools and are comparable to the PCD tools. For both the NCD and MCD tools, coating delamination is the major tool wear mechanism that leads to catastrophic tool failures.

Nanocrystalline diamond coating tools for machining high-strength Al alloys

Abstract Diamond coating tools have been increasingly used for machining advanced materials. Recently, a microwave plasma-assisted chemical vapor deposition (CVD) technology was developed to produce diamond coatings which consist of nano-diamond crystals embedded into a hard amorphous diamond-like carbon matrix. In this study, the nanocrystalline diamond (NCD) coating tools were evaluated in machining high-strength aluminum (Al) alloy. The conventional CVD microcrystalline diamond coating (MCD) tools and PCD tools were also tested for performance comparisons. In addition, stress distributions in diamond coating tools, after deposition and during machining, were analyzed using a 2D finite element (FE) thermomechanical model. The results show that catastrophic failures, reached in all except one machining conditions, limit the NCD tool life, which is primarily affected by the cutting speed. In addition, coating delamination in the worn NCD tools is clearly evident from scanning electron microscopy (SEM) and force monitoring in machining can capture the delamination incident. At a high feed, coating delamination may extend to the rake face. Furthermore, SEM observations of coating failure boundaries show intimate coating-substrate contact. Though the NCD tools are inferior to the PCD tools, they substantially outperform the MCD tools, which failed by premature delamination. The diamond coating tools can have high residual stresses from the deposition and stresses at the cutting edge are highly augmented. Further machining loading causes the stress reversal pattern which seems to correlate with the tool wear severity.

Self-assembled Ni nanoclusters in a diamond-like carbon matrix

Trace amounts (∼5 at%) of metal-containing diamond-like carbon films (DLC) have been deposited using a Off Plane Double Bend Filtered Cathodic Vacuum Arc (OPDB-FCVA) system. The films prepared this way resulted in amorphous thin films where the metal atoms are randomly mixed in a DLC matrix. These films are sometimes called carbon composites. In this paper, the observation of self-assembled Ni nanoclusters by high resolution TEM in a DLC matrix is reported. This phenomenon has only been observed in Ni and not in other metals such as Al, W etc. These Ni nanoclusters have a diameter of ∼2 nm and XRD measurements confirms a (111) orientation while XPS shows that no carbide formation occurs between Ni and DLC.

Deposition of Ti-containing diamond-like carbon (DLC) films by PECVD technique

Diamond-like carbon (DLC) films have been largely studied for their excellent mechanical properties and their high potential in many industrial applications. Although DLC films have poorer physical properties than diamond films, their lower thermal stability and high internal residual stress can be avoided with the incorporation of other elements, such as silicon, nitrogen and some metals.Nanostructured DLC coatings are usually deposited by a combined plasma assisted PVD/CVD technique and sputtering system. We have prepared Ti-containing DLC films deposited by plasma decomposition of CH4/H2/Ar gas mixture with titanium isopropoxide (Ti[OCH2CH3]4), as a metal precursor. The deposited films were found to be composed of amorphous titanium oxide and nanocrystalline titanium carbide, embedded in an amorphous hydrogenated (a-C:H) matrix (DLC). The TiC/TiO2 ratio in the DLC matrix was dependent on the process parameters. The films' composition was monitored as a function of gaseous fluxes. The structural and chemical–physical characterization has been performed by means of XRD and XPS techniques.

Hemocompatibility of diamondlike carbon–metal composite thin films

We have investigated the hemocompatibility of diamondlike carbon–silver composite and diamondlike carbon–titanium composite thin films prepared using a multicomponent target pulsed laser deposition process. These materials were examined using transmission electron microscopy, Raman spectroscopy, nanoindentation, electrochemical charge transfer testing, and platelet adhesion testing. Cross-sectional transmission electron microscopy revealed that silver self-assembles into nanoparticle arrays within the diamondlike carbon matrix in the diamondlike carbon–silver composite film. On the other hand, titanium self-assembles into alternating nanometer-thick titanium carbide layers within the diamondlike carbon matrix in the diamondlike carbon–titanium composite film. The hemocompatibility of these materials was examined using electrochemical charge transfer testing and platelet adhesion testing. A few small, widely scattered crystals were observed on the surface of the unalloyed diamondlike carbon film exposed to platelet rich plasma. On the other hand, dense fibrin networks with densely aggregated platelets were observed on the surfaces of diamondlike carbon–silver and diamondlike carbon–titanium composite thin films exposed to platelet rich plasma. Electrochemical testing revealed that the time constant for the diamondlike carbon thin film ( λ = 1) was significantly higher than those for the diamondlike carbon–silver and diamondlike carbon–titanium composite thin films. These results suggest possible uses for diamondlike carbon thin films and diamondlike carbon–metal composite thin films as coatings in next generation cardiovascular implants.

Incorporation of silver nanoparticles in DLC matrix and surface plasmon resonance effect

Silver nanoparticles were embedded in diamond-like carbon (DLC) matrix by using electrochemical technique on SnO 2-coated glass substrates. Particle size and metal volume fraction were tailored by varying the amount of silver containing salt (silver acetate) in the electrolyte. Reduction in size of the metal particles culminated in red-shift of the surface plasmon resonance peak in the optical absorbance spectra of the films. Experimental absorbance spectra were theoretically simulated by Mie scattering theory and Maxwell-Garnett (M-G) effective medium theory. It was observed that Mie theory described the experimental observation more faithfully than the MG model.

Electrochemical and antimicrobial properties of diamondlike carbon-metal composite films

Implants containing antimicrobial metals may reduce morbidity, mortality, and healthcare costs associated with medical device-related infections. We have deposited diamondlike carbon–silver (DLC–Ag), diamondlike carbon–platinum (DLC–Pt), and diamondlike carbon–silver–platinum (DLC–AgPt) thin films using a multicomponent target pulsed laser deposition process. Transmission electron microscopy of the DLC–silver and DLC–platinum composite films revealed that the silver and platinum self-assemble into nanoparticle arrays within the diamondlike carbon matrix. The diamondlike carbon–silver film possessed hardness and Young’s modulus values of 37 GPa and 331 GPa, respectively. The diamondlike carbon-metal composite films exhibited passive behavior at open-circuit potentials. Low corrosion rates were observed during testing in a phosphate-buffered saline (PBS) electrolyte. In addition, the diamondlike carbon–metal composite films were found to be immune to localized corrosion below 1000 mV (SCE). DLC–silver–platinum films demonstrated exceptional antimicrobial properties against Staphylococcus bacteria. It is believed that a galvanic couple forms between platinum and silver, which accelerates silver ion release and provides more robust antimicrobial activity. Diamondlike carbon–silver–platinum films may provide unique biological functionalities and improved lifetimes for cardiovascular, orthopaedic, biosensor, and implantable microelectromechanical systems.

Cr-diamondlike carbon nanocomposite films: Synthesis, characterization and properties

Diamondlike carbon (DLC) films, known for exhibiting attractive combination of properties, have been extensively studied in the recent past. The inherent, internal compressive stresses affecting their adhesion and their relatively low thermal stability above 400 °C are two major drawbacks preventing wide usage of these films. Carbide formers incorporated into the carbon network have the potential to stabilize the film structure, relax internal stresses and improve their performance. The present work focuses on the synthesis, structure and mechanical and tribological property characterization of Cr-containing nanocomposite DLC films. The films were synthesized using a plasma-enhanced hybrid chemical vapor and physical vapor deposition process in a discharge composed of a mixture of CH 4 and Ar gases. The Cr content in the films varied up to 18 at.%. The film morphology and composition were characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and nuclear reaction analysis. The mechanical and tribological behavior of the films was studied as a function of Cr concentration by conducting nanoindentation and pin-on-disc experiments, respectively. The results showed that the films can be either amorphous with dispersed metallic-like Cr (at low Cr content) or nanocomposite consisting of face-centered cubic metastable CrC nanoparticles dispersed in the DLC matrix. Films with low Cr content (< 5 at.%) were found to possess similar tribological characteristics with those of pure DLC films. Incorporation of more Cr (> 12 at.%) results in larger chromium carbide particles that have an adverse effect on wear resistance. The films with the low Cr content offer the opportunity to combine the excellent tribological behavior with other desirable properties deriving from the presence of the second phase.

Pulsed laser deposition of functionally gradient diamondlike carbon–metal nanocomposites

Diamondlike carbon thin films possess atomic smoothness, chemical inertness, and hardness properties close to those of diamond. Unfortunately, these films exhibit poor adhesion to metals and polymers used in medical prostheses. This paper presents the processing and characterization of diamondlike carbon–copper, diamondlike carbon–silver, diamondlike carbon–silicon, and diamondlike carbon–titanium nanocomposite films with enhanced adhesion to Ti–6Al–4V alloy substrates. Silver forms nanoparticle arrays within the diamondlike carbon matrix in diamondlike carbon–silver nanocomposite films. On the other hand, titanium forms layers of titanium carbide within the diamondlike carbon matrix in diamondlike carbon–titanium nanocomposite films. These films were characterized using electron energy loss spectroscopy, transmission electron microscopy, Raman spectroscopy, Rutherford backscattering spectrometry, nanoindentation, wear testing, and scratch adhesion testing. Diamondlike carbon–metal nanocomposite films have numerous potential medical applications, including use on the surfaces of medical prostheses.

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.

Structure and properties of diamond-like carbon nanocomposite films containing copper nanoparticles

Diamond-like carbon (DLC) nanocomposite films, containing copper (Cu) nanocrystallites, were synthesized and studied. Cu bonds very weakly with carbon, and does not form a carbide phase. Therefore, Cu nanoparticles can be easily formed in a DLC matrix by depositing Cu and carbon together. The mechanical properties of DLC films that contain Cu nanoparticles are interesting since the film toughness may be increased by grain–matrix interface sliding. Hard, tough and stress-free DLC/Cu films were prepared by a sputtering Cu target in an argon/acetylene atmosphere while biasing the substrate with a radio frequency power supply. The residual stress of the film, calculated by Stoney's equation, was as low as 0.7 GPa. The reduced stress and the increased film toughness increased the critical load from 66 N for a conventional DLC film to 80 N for the DLC/Cu film, as measured in a scratch test. However, the DLC/Cu films were slightly less hard than the DLC films.

Deposition and microstructure of Ti-containing diamond-like carbon nanocomposite films

Ti-containing diamond-like carbon (DLC) films were deposited by plasma decomposition of CH 4/Ar gas mixtures with an introduction of tetrakis(dimethylamino)titanium (TDMAT, Ti[(CH 3) 2N] 4), which was used as a precursor of titanium. The films deposited were found to be nanocomposite coatings consisting of TiN nanocrystalline clusters and amorphous hydrocarbon (a-C:H), indicating that the nanocrystalline clusters were embedded in the DLC matrix. The crystallinity of TiN clusters, as well as the Ti atomic concentrations in the films, increased with an increase of substrate temperature. The substrate temperature applied to form a crystalline phase in the DLC matrix induced a graphitization of amorphous hydrocarbon matrix. The increase of volume fraction of TiN nanocrystalline clusters in the DLC matrix enhanced the mechanical properties of nanostructured coatings, although the graphite-like structural transition of DLC matrix happened due to the applied heating.

Electron field emission from nitrogen and sulfur-doped diamond-like carbon films deposited by simple electrochemical route

Nitrogen and sulfur-doped diamond-like carbon (DLC) films were deposited on Si (400) substrates by electrolysis of organic liquid under high voltage, at atmospheric pressure and at temperature below 350 K. Fourier transform infrared spectroscopy (FTIR) measurements showed different vibrational modes of tetrahedrally bonded carbon. In addition, appearance of C–N and C–S vibrational modes in the FTIR spectra confirmed the incorporation of N and S into the DLC matrix. Electron field emission properties of the films were studied. It was found that turn-on field and effective emission barrier were reduced by N and S doping.

Microstructural evolution of Co nanostructures in diamond-like carbon by plasma-assisted processing

Nanocomposite thin films consisting of Co nanoparticles in a diamond-like carbon (DLC) matrix were synthesized by plasma-assisted magnetron sputtering using a discharge with different Ar/CH4 gas flow ratio and chamber pressure. The evolution of the Co nanostructures was studied by x-ray photoelectron spectroscopy and transmission electron microscopy. It was found that depending on processing parameters, the Co nanostructures develop from slightly elongated nanoparticles to self-assembled nanorods of high aspect ratio. Flow rate and pressure were also found not only to influence the degree of crystallinity of the Co nanostructures, but also the chemical state of C in the DLC matrix. It is suggested that under the prevailing processing conditions the evolution of the Co nanorods is under kinetic control.

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.