Diamond-like Carbon Thin Films Research Articles

Electrical and magnetic properties of electrodeposited nickel incorporated diamond-like carbon thin films

Abstract Nanocomposite diamond-like carbon (DLC) thin films have been synthesized by incorporating nickel (Ni) nanoparticles in DLC matrix with varying concentration of nickel. DLC and Ni-DLC thin films have been deposited on ITO coated glass substrates employing low voltage electrodeposition method. Electrical properties of the samples were studied by measuring current–voltage characteristics and dielectric properties. The current approaches toward an ohmic behavior with metal addition. This tendency of increasing ohmicity is enhanced with increase in dilution of the electrolyte. The conductivity increases with Ni addition and interestingly it continues to increase with dilution of Ni concentration in the electrolyte in the range of our study. Magnetic properties for DLC and Ni-DLC thin film samples were examined by electron paramagnetic resonance (EPR) measurements and Super Conducting Quantum Interference Device (SQUID) measurements. g -Value for DLC is 2.074, whereas it decreases to 2.055 with Ni addition in the electrolyte. This decrement arises from the increased sp 2 content in DLC matrix. The magnetic moment vs. magnetic field ( m – H ) curves of Ni-DLC indicate superparamagnetic behavior which may be due to ferromagnetic contribution from the incorporated nickel nanoparticles in the DLC matrix. The ZFC curve of Ni-DLC after the blocking temperature shows a combined contribution of ferromagnetic, superparamagnetic and paramagnetic nature of the materials persisting up to 300 K.

Correlations between microstructure and hydrophobicity properties of pulsed laser deposited diamond-like carbon films

Diamond-like carbon (DLC) thin films were deposited by pulsed laser deposition (PLD) on Si-(100) substrates in the substrate temperature range of room temperature (RT) to 300°C. The structural, hydrophobicity, mechanical, and morphological properties of the DLC films were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, water contact angle (CA) measurement, atomic force microscopy (AFM). It was found that the DLC films deposited at RT were purely amorphous in structure with high sp3 bonding and had very smooth surfaces. Raman and XPS results indicated a structural transition from amorphous to nano-crystalline graphitic nature, structural ordering of DLC films, and decrease of the sp3 content with increasing substrate temperature. Degradation of the surface morphology and enhancement of the surface roughness with the substrate temperature were observed by AFM. It was also found that the mechanical properties such as nanohardness, elastic modulus, plastic index parameter, and elastic recovery decreased with the increasing substrate temperature. The CA measurements indicated that the hydrophobicity of DLC films increased with the substrate temperature and was sensitive not only to sp2/sp3 ratio, but also to the ordering of sp2 clusters. The observed hydrophobicity, mechanical and morphological properties were attributed to structural changes during deposition based on the sub-plantation model and stress induced mechanism.

Comparison of Black Oxide and Tungsten Carbide–Reinforced Diamond-Like Carbon (WC/a-C:H) Surface Treatments for Rolling Element Bearings

Surface-initiated damage increasingly limits the service life of rolling element bearings in challenging environments. In particular, operation in the boundary lubrication regime and/or conditions that produce excessive rolling element–raceway slip require the use of surface treatments on roller bodies and raceways to extend surface durability and component life. The tribological performance of two approaches is compared and contrasted: black oxide chemical conversion treatment and tungsten carbide–reinforced diamond-like carbon (WC/a-C:H) thin film hard coating. Black oxide treatment is performed on both rollers and raceways, whereas WC/a-C:H coatings are deposited on rollers only. The cross-sectional layer structure is compared using transmission electron microscopy, and mechanical properties are measured using nanoindentation. Ring-on-ring friction and wear testing is conducted to obtain Stribeck curves and evaluate adhesive wear resistance and cyclic acceleration performance. Tapered roller bearing fatigue test results are reported for treated bearings. Results from both bench-scale tribological tests and bearing fatigue tests indicate the superiority of WC/a-C:H coatings in protecting against severe adhesive wear damage and extending bearing fatigue life in boundary-lubricated conditions.

Research of electrosurgical unit with novel antiadhesion composite thin film for tumor ablation: Microstructural characteristics, thermal conduction properties, and biological behaviors.

The objective of this study was to use surface functionalization to evaluate the antiadhesion property and thermal injury effects on the liver when using a novel electrosurgical unit with nanostructured-doped diamond-like carbon (DLC-Cu) thin films for tumor ablations. The physical and chemical properties of DLC-Cu thin films were characterized by contact angle goniometer, scanning electron microscope, and transmission electron microscope. Three-dimensional (3D) hepatic models were reconstructed using magnetic resonance imaging to simulate a clinical electrosurgical operation. The results indicated a significant increase of the contact angle on the nanostructured DLC-Cu thin films, and the antiadhesion properties were also observed in an animal model. Furthermore, the surgical temperature in the DLC-Cu electrosurgical unit was found to be significantly lower than the untreated unit when analyzed using 3D models and thermal images. In addition, DLC-Cu electrodes caused a relatively small injury area and lateral thermal effect. The results indicated that the nanostructured DLC-Cu thin film coating reduced excessive thermal injury and tissue adherence effect in the liver.

Carbon nanotube (CNT) forest grown on diamond-like carbon (DLC) thin films significantly improves electrochemical sensitivity and selectivity towards dopamine

In this study we demonstrate a scalable and CMOS compatible synthesis of robust diamond-like carbon (DLC)–multi-walled carbon nanotube (MWCNT) hybrid electrodes. MWCNTs were grown directly on top of DLC thin film electrodes by utilizing Al/Co/Fe tri-layer catalyst structure at 550°C. The structure of the hybrid material was characterized in detail by utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman investigations and X-ray photoelectron spectroscopy (XPS). After a very simple activation step with nitric acid the material was shown to exhibit a wide stable water window, almost reversible electron transfer kinetics and high sensitivity as well as selectivity towards dopamine (DA) in the presence of ascorbic acid (AA). Thus, it can be argued that the electrochemical properties of DLC and MWCNT were combined in a unique way in this new hybrid nanomaterial. The possible reasons behind the observed behavior are discussed in considerable detail. Despite the fact that present results are valid only for this particular hybrid material synthesized under conditions described in this paper, we anticipate that by utilizing the concept of DLC–MWCNT hybrids, several other novel carbon based electrode materials may be introduced for a wide variety of electrochemical and other applications.

Contact damage of hard and brittle thin films on ductile metallic substrates: an analysis of diamond-like carbon on titanium substrates

Friction and wear minimizing coatings are crucial for applications in combustion engines and medical implants. Their performance is typically limited by mechanical failure especially due to local overload. In this work, the contact damage creation, evolution, and final morphology of hydrogenated diamond-like carbon (DLC)-coated titanium (Ti) substrates are investigated. The influence of the DLC film thickness and the elastic–plastic deformation of the Ti on the contact damage are studied by microindentation and static finite-element analysis. Film thickness, indenter radius, and applied load as well as the elastic–plastic deformation of the Ti are shown to significantly affect contact damage. A failure plot is presented with the location of first failure in the DLC and compared to the experimental observation. In addition, a case study with variable fracture toughness of the DLC and its influence on the failure plot is shown. The stress distribution in the DLC follows a transition from a membrane-like to a plate-like deformation behavior upon increasing the DLC film thickness. Thin DLC films reveal increased cracking in the inner zone of the indent, while thicker DLC films reveal pronounced edge cracking. These edge cracks were correlated to pop-ins in force–displacement curves upon microindentation. Finally, a film thickness optimization process is presented for hard and brittle films on soft and ductile metallic substrates.

Deposition and characterization of multilayer DLC:Mo thin films grown on silicon substrate by off-axis pulsed laser deposition technique

Off-axis pulsed laser deposition technique was used to deposit a diamond-like carbon (DLC) thin film and three multilayer DLC:Mo thin films of various compositions on p-type Si (111) substrate at room temperature keeping the DLC content constant. Excimer laser was used to ablate graphite and Mo targets in a vacuum of ∼10−5mbar, whereas the p-type Si (111) substrate was placed downside the target at a distance of 1cm in off-axis PLD geometry. Morphological, structural, optical, and electrical characteristics of the deposited thin films were then investigated. SEM images of the thin films show that surface roughness increases as Mo content in the film increases. XRD patterns of DLC:Mo thin films rule out any carbide formation. Both crystallite size of Mo particles and film thickness increase whereas microstrain decreases with the increase in Mo content. Moreover, both refractive index and indirect optical band gap decrease exponentially while Urbach energy increases linearly with the increase in Mo content. Electrical resistivity of the thin films has been found to follow an exponential decay with the increase in Mo content in multilayer DLC:Mo thin films.

Buckled diamond-like carbon nanomechanical resonators.

We have developed capacitively-transduced nanomechanical resonators using sp(2)-rich diamond-like carbon (DLC) thin films as conducting membranes. The electrically conducting DLC films were grown by physical vapor deposition at a temperature of 500 °C. Characterizing the resonant response, we find a larger than expected frequency tuning that we attribute to the membrane being buckled upwards, away from the bottom electrode. The possibility of using buckled resonators to increase frequency tuning can be of advantage in rf applications such as tunable GHz filters and voltage-controlled oscillators.

Friction at single-asperity contacts between hydrogen-free diamond-like carbon thin film surfaces

This work investigates the friction and adhesive forces at the single-asperity contact between hydrogen-free diamond-like carbon (DLC) coated surfaces in humid air and in argon. High power impulse magnetron sputtering deposition has been used to produce hydrogen-free DLC thin films on commercial silicon AFM tips and silicon wafers. The structure and surface morphology of the deposited DLC films has been investigated by X-ray photoelectron spectroscopy and tapping AFM, investigations that showed very smooth DLC films with about 29% of sp3 C−C bonds. The as-deposited hydrogen-free DLC thin films were hydrophilic (water contact angle about 65°) due to incorporation of a small amount of oxygen (about 9% of C=O bonds) at the film surfaces. The friction force measurements show that at low normal loading force the contact friction is much lower in the humid air than in the argon, while at large values of the loading force the contact friction does not depend on the measurement medium. A qualitative friction model based on the concept of dry and wet friction regimes, when the layer of water adsorbed on DLC film surfaces plays the role of lubricator, is proposed to explain these findings.

Microstructure and properties of silicon-incorporated DLC film fabricated using HMDS gas and RF-PECVD process.

The microstructure and characteristics of silicon-incorporated diamond-like carbon film, fabricated using a radio-frequency plasma-enhanced chemical vapor deposition process with hexamethyldisilane [(CH3)3,Si x Si(CH3)3:HMDS] gas as a silicon source, were investigated. Diamond-like carbon films with silicon compositions from 0 to 5 atomic percent were deposited onto ultra-fine grained AZ31 magnesium alloy substrate as buffer layers or multilayers. Si doping led not only to an increase in the bonding ratio (sp3/sp2), but improvements in hardness, critical adhesion, and corrosion resistance. Out of the investigated samples, the multi-deposited silicon diamond-like carbon thin film on magnesium substrate showed the best combination of adhesive, wear resistance, and corrosion resistance properties.

Electrochemical performance of porous diamond-like carbon electrodes for sensing hormones, neurotransmitters, and endocrine disruptors.

Porous diamond-like carbon (DLC) electrodes have been prepared, and their electrochemical performance was explored. For electrode preparation, a thin DLC film was deposited onto a densely packed forest of highly porous, vertically aligned multiwalled carbon nanotubes (VACNT). DLC deposition caused the tips of the carbon nanotubes to clump together to form a microstructured surface with an enlarged surface area. DLC:VACNT electrodes show fast charge transfer, which is promising for several electrochemical applications, including electroanalysis. DLC:VACNT electrodes were applied to the determination of targeted molecules such as dopamine (DA) and epinephrine (EP), which are neurotransmitters/hormones, and acetaminophen (AC), an endocrine disruptor. Using simple and low-cost techniques, such as cyclic voltammetry, analytical curves in the concentration range from 10 to 100 μmol L(-1) were obtained and excellent analytical parameters achieved, including high analytical sensitivity, good response stability, and low limits of detection of 2.9, 4.5, and 2.3 μmol L(-1) for DA, EP, and AC, respectively.

Chromium-doped DLC for implants prepared by laser-magnetron deposition.

Diamond-like carbon (DLC) thin films are frequently used for coating of implants. The problem of DLC layers lies in bad layer adhesion to metal implants. Chromium is used as a dopant for improvement of adhesion of DLC films. DLC and Cr-DLC layers were deposited on silicon, Ti6Al4V and CoCrMo substrates by a hybrid technology using combination of pulsed laser deposition (PLD) and magnetron sputtering. The topology of layers was studied using SEM, AFM and mechanical profilometer. Carbon and chromium content and concentration of trivalent and toxic hexavalent chromium bonds were determined by XPS and WDS. It follows from the scratch tests that Cr doping improved adhesion of DLC layers. Ethylene glycol, diiodomethane and deionized water were used to measure the contact angles. The surface free energy (SFE) was calculated. The antibacterial properties were studied using Pseudomonas aeruginosa and Staphylococcus aureus bacteria. The influence of SFE, hydrophobicity and surface roughness on antibacterial ability of doped layers is discussed.

Nickel Nanoparticles on Nitrogen-Doped Diamond-Like Carbon Thin Films: Variation in Nucleation Density with Deposition Potential

Nickel Nanoparticles on Nitrogen-Doped Diamond-Like Carbon Thin Films: Variation in Nucleation Density with Deposition Potential

New electrochemically improved tetrahedral amorphous carbon films for biological applications

Carbon based materials have been frequently used to detect different biomolecules. For example high sp3 containing hydrogen free diamond-like carbon (DLC) possesses many properties that are beneficial for biosensor applications. Unfortunately, the sensitivities of the DLC electrodes are typically low. Here we demonstrate that by introducing topography on the DLC surface and by varying its layer thickness, it is possible to significantly increase the sensitivity of DLC thin film electrodes towards dopamine. The electrode structures are characterized in detail by atomic force microscopy (AFM) and conductive atomic force microscopy (C-AFM) as well as by transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS). With cyclic voltammetry (CV) measurements we demonstrate that the new improved DLC electrode has a very wide water window, but at the same time it also exhibits fast electron transfer rate at the electrode/solution interface. In addition, it is shown that the sensitivity towards dopamine is increased up to two orders of magnitude in comparison to the previously fabricated DLC films, which are used as benchmarks in this investigation. Finally, it is shown, based on the cyclic voltammetry measurements that dopamine exhibits highly complex behavior on top of these carbon electrodes.

Tribological properties of platinum/ruthenium/nitrogen doped diamond-like carbon thin films deposited with different negative substrate biases

Abstract The platinum/ruthenium/nitrogen doped diamond-like carbon (PtRuN-DLC) thin films were deposited on Si substrates via DC magnetron sputtering by varying negative substrate bias. The tribological performance of the PtRuN-DLC films was systematically investigated using ball-on-disc microtribological test. The Raman results showed that the increased negative substrate bias significantly increased the number of sp3 bonds in the PtRuN-DLC films as a result of the increased kinetic energies of impinging ions. The adhesion strength of the PtRuN-DLC films apparently decreased with increased negative substrate bias due to the promoted residual stress in the films. The tribological results clearly revealed that the increased negative substrate bias decreased the friction and wear of the PtRuN-DLC films by improving the sp3 bonded cross-linking structures of the films. It can be concluded that the PtRuN-DLC films could effectively prevent their underlying Si substrates from wear as the negative substrate bias had a significant influence on the tribological properties of the PtRuN-DLC films.

Optical properties of diamond-like carbon thin films deposited by DC-PECVD

Diamond-like carbon (DLC) thin films were deposited at different substrate temperatures using methane gas in DC-PECVD at 1x10-1 Torr. From the lighttransmission using UV-VIS spectroscopy it was found that the optical transition had changed from allowed indirect transition to forbidden directtransition as the substrate temperature increased. The photoluminescence study has shown that the recombination centre occurred at 1.738 eV. Theobservation in the present work shows that the Urbach energy decreases with increasing substrate temperature provides evidence that such films have anarrowed band tail. This decrease in Urbach energy is due to a more ordered structure with lower hydrogen concentration and larger cluster by theincrease in the degree of cross-linking of the C-C network. Distorted cluster which contribute to the broadening of the band tail may also contribute to thePL peak width. As the substrate temperature increases, the cluster size in the tetrahedral hydrogenated amorphous carbon (ta-C:H) increases, resulting insmaller band gap and the structure is more ordered as the decrease in Urbach energy, give the decrease in PL peak energy.

Evaluation of protuberance and groove formation in extremely thin DLC films on Si substrates due to diamond tip sliding by atomic force microscopy

In order to enable higher density recording, a better understanding of the magnetic disk/head interface is required. Therefore, the nanowear properties of extremely thin diamond-like carbon (DLC) films deposited on a Si(100) surface via filtered cathodic vacuum arc (FCVA) and electron cyclotron resonance-chemical vapor deposition (ECR-CVD) methods were evaluated using atomic force microscopy. It is proposed that tribochemical reactions led to the formation of protuberances on the thin DLC films coated on Si substrates. However, the FCVA-DLC films were more resistant to these tribochemical reactions of Si than the ECR-CVD-DLC films. For both 1.5-nm-thick ECR-CVD-DLC and 0.8-nm-thick FCVA-DLC films, the film was removed even at low loads, and the protuberances increased with the load because of direct contact between the diamond tip and the Si surface. Diamond tip sliding at higher loads also removed thicker ECR-CVD-DLC films, while thicker FCVA-DLC films remained on the Si surface and prevented tribochemical reactions. Furthermore, thicker ECR-CVD-DLC films exhibited deeper wear depths than FCVA-DLC films. These results reveal the differences in the resistance to wear and tribochemical reactions of extremely thin DLC films prepared using different deposition methods and confirm the superior properties of FCVA-DLC films.

Impact of the difference in power frequency on diamond-like carbon thin film coating over 3-dimensional objects

With a type of capacitatively coupled plasma enhanced chemical vapor deposition (PECVD) technique, where two specially designed electrodes face to each other, the inner surface of hollow 3-dimensional objects such as poly(ethylene terephthalate) (PET) bottles can be coated with diamond-like carbon (DLC) thin film. DLC-coated PET bottles obtained with this technique have an enhanced gas barrier property, and therefore are applicable to industrial use such as for the extension of the shelf-life of contents sensitive to gas permeation. In this paper, the impact of power frequency ranging from 2.5 to 13.56MHz was studied in order to research the behavior of plasma inside PET bottles and resultant properties. Different power frequency turned out to be influential on gas barrier property, the overall and distribution of tint, and adhesion between DLC and PET substrate. In addition, positron annihilation turned out to be powerful tool for the comparison of different coating conditions because it clarifies the homogeneity of DLC thin films through providing information on overall structure and thickness of them. These findings can be used for the optimization not only in the beverage PET bottle application, but also in other capacitatively coupled PECVD devices.

Laser-assisted replication of large-area nanostructures

We proposed and demonstrated a high-throughput fabrication method for large-area nanostructured polymers. The mold used consists of a quartz substrate and a nanostructured diamond-like carbon (DLC) thin film. A laser is irradiated from the back of the mold and only the DLC surface is directly heated. Then the surface of a polymethyl methacrylate (PMMA) film pressed by the mold is melted and the nanostructures are replicated. In this method, replication can be achieved with a low amount of heat and a short cycle time compared with conventional thermal replication. The effects of the laser power density, irradiation time, and environmental temperature on the replication area were experimentally investigated via the spot irradiation of a laser. Furthermore, the temperature distribution around the surfaces of the mold and polymer was investigated by performing numerical simulations. By scanning the laser, we successfully demonstrated the replication of a 500-nm-pitch pattern on a PMMA film with an area of 10×10mm2 in about 10s. This technique is expected to lead to the high-throughput and low-energy fabrication of large-area nanostructured optical films.

Maintenir au travail les personnes en situation de handicap : nouveaux modèles, nouvelles méthodes pour l’ergonomie

With a type of capacitatively coupled plasma enhanced chemical vapor deposition (PECVD) technique, where two specially designed electrodes face to each other, the inner surface of hollow 3-dimensional objects such as poly(ethylene terephthalate) (PET) bottles can be coated with diamond-like carbon (DLC) thin film. DLC-coated PET bottles obtained with this technique have an enhanced gas barrier property, and therefore are applicable to industrial use such as for the extension of the shelf-life of contents sensitive to gas permeation. In this paper, the impact of power frequency ranging from 2.5 to 13.56 MHz was studied in order to research the behavior of plasma inside PET bottles and resultant properties. Different power frequency turned out to be influential on gas barrier property, the overall and distribution of tint, and adhesion between DLC and PET substrate. In addition, positron annihilation turned out to be powerful tool for the comparison of different coating conditions because it clarifies the homogeneity of DLC thin films through providing information on overall structure and thickness of them. These findings can be used for the optimization not only in the beverage PET bottle application, but also in other capacitatively coupled PECVD devices.