Plasma-activated Chemical Vapor Deposition Research Articles

Comparative Study of Multilayer Hard Coatings Deposited on WC-Co Hardmetals

This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing (HIP) process using nanoparticle powders and coated with two distinct multilayer coatings: titanium nitride (TiN) and titanium carbonitride (TiCN). Nanosized grain formation without microstructural defects of the substrates, prior to coating, was confirmed by magnetic saturation and coercivity testing, microstructural analysis, and field emission scanning electron microscope (FESEM). Nanoindentation, fracture toughness and hardness testing were conducted for uncoated samples. After coatings deposition, characterizations including microscopy, surface roughness determination, adhesion testing, coating thickness measurement, and microhardness examination were conducted. The impact of deposited coatings on wear resistance of produced hardmetals was analyzed via scratch test and dry sliding wear test. Samples with higher Co content exhibited improved adhesion, facilitating surface cleaning and activation before coating. TiN and TiCN coatings demonstrated similar roughness on substrates of identical composition, suggesting Co content’s minimal influence on layer growth. Results of the mechanical tests showed higher microhardness, higher elastic modulus, better adhesion, and overall superior tribological properties of the TiCN coating.

Plasmochemical Modification of Crofer 22APU for Intermediate-Temperature Solid Oxide Fuel Cell Interconnects Using RF PA CVD Method.

The results of plasmochemical modification on Crofer 22APU ferritic stainless steel with a SiCxNy:H layer, as well as the impact of these processes on the increase in usability of the steel as intermediate-temperature solid oxide fuel cell (IT-SOFC), interconnects, are presented in this work. The layer was obtained using Radio-Frequency Plasma-Activated Chemical Vapor Deposition (RF PA CVD, 13.56 MHz) with or without the N+ ion modification process of the steel surface. To determine the impact of the surface modification on the steel’s resistance to high-temperature corrosion and on its mechanical properties, the chemical composition, atomic structure, and microstructure were investigated by means of IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Microhardness, Young’s modulus, wear rate, as well as electrical resistance, were also determined. Micromechanical experiments showed that the plasmochemical modification has a positive influence on the surface hardness and Young’s modulus of the investigated samples. High-temperature oxidation studies performed for the samples indicate that N+ ion modification prior to the deposition of the SiCxNy:H layer improves the corrosion resistance of Crofer 22APU steel modified via CVD. The area-specific resistance of the studied samples was 0.01 Ω·cm2, which is lower than that of bare steel after 500 h of oxidation at 1073 K. It was demonstrated that the deposition of the SiCxNy:H layer preceded by N+ ion modification yields the best properties.

High-Temperature Tribological Performance of Al2O3/a-C:H:Si Coating in Ambient Air

The study investigates thermal stability and high temperature tribological performance of a-C:H:Si diamond-like carbon (DLC) coating. A thin alumina layer was deposited on top of the a-C:H:Si coating to improve the tribological performance at high temperatures. The a-C:H:Si coating and alumina layer were prepared using plasma-activated chemical vapour deposition and atomic layer deposition, respectively. Raman and X-ray photoelectron spectroscopy were used to investigate the structures and chemical compositions of the specimens. The D and G Raman peaks due to sp2 bonding and the peaks corresponding to the trans-polyacetylene (t-Pa) and sp bonded chains were identified in the Raman spectra of the a-C:H:Si coating. Ball-on-disc sliding tests were carried out at room temperature and 400 °C using Si3N4 balls as counter bodies. The a-C:H:Si coating failed catastrophically in sliding tests at 400 °C; however, a repeatable and reproducible regime of sliding with a low coefficient of friction was observed for the Al2O3/a-C:H:Si coating at the same temperature. The presence of the alumina layer and high stress and temperature caused structural changes in the bulk a-C:H:Si and top layers located near the contact area, leading to the modification of the contact conditions, delivering of extra oxygen into the contact area, reduction of hydrogen effusion, and suppression of the atmospheric oxidation.

Physical and electrical properties of nitrogen-doped hydrogenated amorphous carbon films

Nitrogen-doped hydrogenated amorphous carbon films (a-C:H:N) have been prepared by a plasma-activated chemical vapor deposition technique (PACVD) by using a plasma beam source (PBS). The properties of the a-C:H:N films were changed by varying the total pressure, the substrate temperature (100 °C, 300 °C) and nitrogen partial pressure p(N2) by adding nitrogen to the precursor acetylene (C2H2). For the investigations, a-C:H:N films have been deposited onto glass slides and doped silicon wafers. The deposition rate decreased with increasing nitrogen content in the N2/C2H2 gas mixture and with decreasing total pressure. The elemental composition of two sample series (300 °C) has been analyzed with Elastic Recoil Detection Analysis (ERDA). The highest N content and N/C ratio was estimated to be 16 at.% and 0.25 at the highest p(N2), respectively. Microhardness measurements showed that the hardness decreased with increasing p(N2). Electrical resistance of the a-C:H:N films was measured by 4-point probe. Electrically conductive coatings have been obtained by nitrogen-doped a-C:H films at higher substrate temperature (300 °C). The electrical resistance of the a-C:H:N films also decreases with decreasing total pressure, with the lowest value being about 1 Ohm cm. The film density was determined by means of X-ray reflectometry (XRR).

Electron-beam modification of DLC coatings for biomedical applications

The interest in diamond like carbon (DLC) coatings and their modification for biomedical applications is strongly increasing during the last years. Improvement of surface resistance to scratching and biocompatibility are the main goals of recent developments. Moreover, different capabilities of adjacent areas on surfaces are often required by complex applications.In this study, different deposition methods for diamond-like carbon (DLC) coatings were compared for their suitability in biomedical applications. In addition, DLC coatings modified by non-thermal electron-beams were investigated with regard to their biological interactions. The DLC coatings were deposited using four different methods (plasma-activated chemical vapor deposition, physical vapor deposition by magnetron sputtering, and physical vapor deposition via cathodic arc – both unfiltered and filtered). The different DLC coatings were characterized with regard to their wettability, morphology, roughness, and coating adhesion. The ability of coatings to withstand repeated sterilization cycles was investigated using a specialized test protocol parallel to standard sterilization procedures for medical devices. Biological evaluation was performed using human fibroblasts by assessing metabolic activity and cell counts. Electron-beam modification of the coatings was performed under ambient conditions using a low-energy electron-beam facility (150kV acceleration voltage).All DLC coatings investigated were found to be biocompatible, with the coating deposited by magnetron sputtering showing the best results. In general, electron-beam modification resulted in the hydrophilicity of the different DLC coatings increasing, but no changes in surface morphology or roughness were observed. The cell adhesion to electron-beam-modified DLC coatings was reduced to 30% of the untreated DLC coatings, what can be attributed to changes in the surface chemistry. The long-term stability of the modified DLC coatings was also confirmed. Therefore, electron-beam treatment represents a promising tool for modifying and functionalizing DLC coatings, especially if varying requirements concerning biomedical functionality and cell adhesion are involved.

Study of Gas Permeation Through Thin ta-C:H Films

Protective ultra-thin barrier lms gather increasing economic interest for controlling permeation and di usion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was the investigation of the lm thickness in uence on the gas permeation barrier of ultra-thin, cytocompatible tetrahedral amorphous carbon (ta-C:H) lms on polyimide (PI) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit these diamond-like carbon lms. The results indicate high barrier to hydrogen gas permeation by all lm thicknesses (<0.2% H2 permeation compared to uncoated PI). While the thickness of the ta-C:H layers has minor in uence, the number of layers, realized by oneor double-side deposition strongly impacts the barrier e ect. Finally, tests under tensile stresses showed minor impact in the elasto-plastic deformation regime, but the expected strong increase of gas permeation after exceeding the tensile strength and lm fracture.

On interlayer stability and high-cycle simulator performance of diamond-like carbon layers for articulating joint replacements.

Diamond like carbon (DLC) coatings have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the orthopaedic field, layer performance, stability and adhesion in physiologically relevant setups are crucial and not consistently investigated. In vitro wear testing as well as adequate corrosion tests of interfaces and interlayers are of great importance to verify the long term stability of DLC coated load bearing implants in the human body. DLC coatings were deposited on articulating lumbar spinal disks made of CoCr28Mo6 biomedical implant alloy using a plasma-activated chemical vapor deposition (PACVD) process. As an adhesion promoting interlayer, tantalum films were deposited by magnetron sputtering. Wear tests of coated and uncoated implants were performed in physiological solution up to a maximum of 101 million articulation cycles with an amplitude of ±2° and −3/+6° in successive intervals at a preload of 1200 N. The implants were characterized by gravimetry, inductively coupled plasma optical emission spectrometry (ICP-OES) and cross section scanning electron microscopy (SEM) analysis. It is shown that DLC coated surfaces with uncontaminated tantalum interlayers perform very well and no corrosive or mechanical failure could be observed. This also holds true in tests featuring overload and third-body wear by cortical bone chips present in the bearing pairs. Regarding the interlayer tolerance towards interlayer contamination (oxygen), limits for initiation of potential failure modes were established. It was found that mechanical failure is the most critical aspect and this mode is hypothetically linked to the α-β tantalum phase switch induced by increasing oxygen levels as observed by X-ray diffraction (XRD). It is concluded that DLC coatings are a feasible candidate for near zero wear articulations on implants, potentially even surpassing the performance of ceramic vs. ceramic.

Gas Permeation, Mechanical Behavior and Cytocompatibility of Ultrathin Pure and Doped Diamond-Like Carbon and Silicon Oxide Films

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth.

Titaniumcarboxonitride layer increased biocompatibility of medical polyetherurethanes

Polyetherurethane (PEU) is in use for blood-contacted devices because of its excellent mechanical properties. However, poor hemocompatibility of the hydrophobic material required surface modification or endothelialization. To increase the biocompatibility of PEU, the polymer was coated with a titaniumcarboxonitride [Ti(C,N,O)] layer by a plasma-activated chemical vapor deposition (PACVD) process. Biocompatibility of titaniferously coated PEU was verified using static and dynamic cell culture techniques. Titaniferous coating significantly improved proliferation and mitochondrial activity of human endothelial cells on PEU. These cells captured significantly less mononuclear cells and platelets. Under shear stress for up to 72 hours, titaniferous coating increased endothelial cell adhesion, spreading, and cell density to form an organized monolayer covering the whole luminal surface of vascular PEU grafts. In summary, coating of PEU surfaces with Ti(C,N,O) might be a promising strategy to improve the biocompatibility of biomedical biomaterials.

A New Ge/F-Co-doped SMF with Enhanced SBS Threshold Fabricated by PCVD

A new single-mode fibre (SMF) with high stimulated Brillouin scattering (SBS) threshold which is co-doped with GeO2 and F2 in the core is reported. To increase the SBS threshold, the acousto-optic effective area is increased by designing a transverse acoustic waveguide and adjusting the doping level of GeO2 and F2 while the designed fiber retains a step optical refractive index profile. The optimal design is found by numerical simulation and the optimal fiber is fabricated by a plasma-activated chemical vapor deposition (PCVD) process. It yields the threshold 6.79 dB, which is higher than the conventional single-mode fiber G.652 and 3dB higher than the Corning® SMF-28e+™ optical fiber with NexCor® technology.

Mechanisms of interfacial adhesion in metal–polymer composites – Effect of chemical treatment

Hybrid materials featuring thermoplastic polymer composites in conjunction with metals are being increasingly used as structural materials in military and commercial transport vehicles, and for protection of buildings and infrastructure. Hybrid materials offer improved options compared to its constituents; however the compatibility of the interface between a metal and polymer/composite strongly influences the structural response. This study focuses on the effect of surface treatment to improve adhesion between organic polymer(s) with steel reinforcement. The primary approaches to provide maximize interfacial adhesion are via surface modification to create greater surface area, and to impart free radical surfaces to create new surface bonds with the introduced chemical functionalities. Plasma activated chemical vapor deposition (PACVD) was used to impart silicon, carbon and hydrogen radicals to the metal surface. Thermoplastic polymers namely polypropylene (PP), polypropylene maleic anhydride (PP-MA), and thermoplastic polyurethane (TPU) were used to investigate the effect of polar groups ( NH, C O and OH) on the surface energy and adhesion. In addition, a thermoset resin embedded with fullerene was also considered to evaluate the interfacial adhesion. The degree of modification of the polymers was determined by Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR) for the absorption of polar groups. Plasma coating was analyzed by energy dispersive spectrometry and scanning electron microscopy (EDS/SEM). The increment in surface energy was determined by contact angle measurements. This work establishes the basis that polar groups and free radicals improve adhesion between a thermoplastic polymer and a metal surface.

Influence of Surface Defects and Aging of Coated Surfaces on Fouling Behavior

To avoid the negative effects caused by fouling in heat exchanger equipment, the heat exchanger surface can be modified energetically or mechanically. Thus, mechanical, chemical, and thermal stability of the coatings with respect to the fouling and cleaning conditions is crucial. The surface is typically characterized by the measurement of the contact angles of different wetting fluids to calculate surface energy and tactile roughness measurements. The influence of several cleaning and fouling cycles on surface energy and the composition of the coatings has been investigated. The experimental investigation of different cleaning methods from acid to base solution displays the influence of the interface reactions on the surface energy. Structural analysis of the plasma-activated chemical vapor deposition (PACVD) coatings show a build-in of oxygen inside the a-C:H matrix with time, resulting in higher surface energies and an increase of polar interactions. Also, structural defects of the coatings have been analyzed by a defined disturbance of the coating process or mechanical treatment of the already coated material. These defects act as a starting point for crystallization fouling due to reduced activation energy of nucleation. Depending on the interface and process conditions, defects can enhance fouling if the crystals are able to adhere on the coated surface. The results should lead to a better understanding of interface reactions, stability of coatings, and the aging of surfaces.

Effects of doping concentrations on the regeneration of Bragg gratings in hydrogen loaded optical fibers

The fabrication and optimization of regenerated Bragg gratings (RBGs) in hydrogen loaded single mode optical fibers (SMF) are presented. In addition to standard Ge-doped SMF, two kinds of B–Ge codoped SMFs with different doping concentrations are prepared using plasma-activated chemical vapor deposition (PCVD) technique to fabricate RBGs. The effects of doping concentrations on the dynamics of grating regeneration and the thermal stability of RBGs are experimentally investigated. The reflectivity of RBGs with length of 10 mm was enhanced from 20% to 40% through the optimization of doping concentrations. All fabricated RBGs can sustain in high temperature up to 1000 °C.

Dependence of the emission properties of the germanium lone pair center on Ge doping ofsilica

We present an experimental investigation regarding the changes induced by the Gedoping level on the emission profile of the germanium lone pair center (GLPC) inGe doped silica. The investigated samples have been produced by the sol–gelmethod and by plasma-activated chemical vapor deposition and have dopinglevels up to 20% by weight. The recorded photoluminescence spectra show thatthe GLPC emission profile is the same when the Ge content is lower than ∼ 1% by weight, whereas it changes for higher doping levels. We have also performedRaman scattering measurements that show the decrease of the D1 Raman band at490 cm − 1 when the Ge content is higher than 1% by weight. The data suggest that both changes canbe related to matrix modifications. These findings improve our knowledge of the matrixeffects on the physical properties of the point defects and, in particular, for the GLPC theyshow that variations in their emission properties are induced by the presence of asecond Ge atom close to the defect within a sphere with a radius of about 2 nm.

The properties of fluorine-containing diamond-like carbon films prepared by pulsed DC plasma-activated chemical vapour deposition

Diamond-like carbon films containing up to 23.1 at. % of fluorine (F-DLC), were deposited onto silicon substrates by low-frequency, pulsed DC, plasma-activated, chemical vapour deposition (PACVD). The influence of fluorine on plasma current density, deposition rate, composition, bonding structure, surface energy, hardness, stress and biocompatibility was investigated and correlated with the fluorine content. X-ray photoelectron spectroscopy (XPS) analysis revealed the presence C–C, C–CF and C–F for F-DLC films with a low fluorine concentration (1.5–12.1 at. %), however for films with a higher fluorine content (23.0 at. %) an additional peak due to CF 2 bonding was detected. The addition of fluorine into the DLC film resulted in lower stress and hardness values. The reduction in these values was attributed to the substitution of strong C=C by weaker C–F bonds which induces a decrease in hardness. Ion scattering spectrometery (ISS) measurements revealed the presence of fluorine atoms in the outmost layer of the F-DLC films and there was no evidence of surface oxygen contamination. The water contact angle was found to increase with increasing fluorine content and has been attributed to the change of the bonding nature in the films, in particularly increasing CF and CF 2 bonds . Biocompatibility tests performed using MG-63 osteoblast-like cell cultures indicated homogeneous and optimal tissue integration for both the DLC and the F-DLC surfaces. This pulsed-PACVD technique has been shown to produce biocompatible DLC and F-DLC coatings with a potential for large area applications.

Biological Properties of Different Type Carbon Particles &lt;I&gt;In Vitro&lt;/I&gt; Study on Primary Culture of Endothelial Cells

Carbon powders have extended surface of carbon layers, which is of significant biomedical importance since the powders are employed to cover implants material. Carbon Powder Particles are produced by different methods: by a detonation method, by RF PACVD (Radio Frequency Plasma Activated Chemical Vapour Deposition) or MW/RF PCVD (Microwave/Radio Frequency Plasma Activated Chemical Vapour Deposition) and others. Our previous data showed that Carbon Powder Particles may act as antioxidant and/or anti-inflammatory factor. However the mechanism of such behavior has been not fully understood. The aim of the work was tested influence carbon powders manufactured by Radio Frequency Plasma Activated Chemical Vapour Deposition RFPACVD method and detonation method on selected parameters of human endothelial cells, which play a crucial role in the regulation of the circulation and vascular wall homeostasis. Graphite powder was used as a control substance. Endothelial cells are actively involved in a wide variety of processes e.g., inflammatory responses to a different type of stimuli (ILs, TNF-alpha) or regulating vasomotor tone via production of vasorelaxants and vasocontrictors. Biological activation is dependent on the type and quantity of chemical bonds on the surface of the powders. The effect of powders on the proliferation of HUVECs (Human Umbilical Vein Endothelial Cells) was determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction assay. We found decreased cell proliferation after 72 h treatment with graphite as well as Carbon Powder Particles.

Preparation and comparison of a-C:H coatings using reactive sputter techniques

Amorphous hydrogenated carbon (a-C:H) coatings are widely used in several industrial applications. These coatings commonly will be prepared by plasma activated chemical vapor deposition (PACVD). The main method used to prepare a-C:H coating in industrial scale is based on a glow discharge in a hydrocarbon gas like acetylene or methane using a substrate electrode powered with medium frequency (m.f. — some 10 to 300kHz). Some aims of further development are adhesion improvement, increase of hardness and high coating quality on complex geometries. A relatively new and promising technique to fulfil these requirements is the deposition of a-C:H coatings by a reactive d.c. magnetron sputter deposition from a graphite target with acetylene as reactive gas. An advancement of this technique is the deposition in a pulsed magnetron sputter process. Using these three mentioned techniques a-C:H coatings were prepared in the same deposition machine. For adhesion improvement different interlayer systems were applied. The effect of different substrate bias voltages (d.c. and d.c. pulse) was investigated. By applying the magnetron sputter technique in the d.c. pulse mode, plastic hardness values up to 40GPa could be reached. Besides hardness other mechanical properties like resistance against abrasive wear were measured and compared. Cross sectional SEM images showed the growth structure of the coatings.

Understanding the chemical vapor deposition of diamond: recent progress

In this paper we review and provide an overview to the understanding of the chemicalvapor deposition (CVD) of diamond materials with a particular focus on the commonlyused microwave plasma-activated chemical vapor deposition (MPCVD). The major topicscovered are experimental measurements in situ to diamond CVD reactors, and MPCVD inparticular, coupled with models of the gas phase chemical and plasma kinetics to provideinsight into the distribution of critical chemical species throughout the reactor,followed by a discussion of the surface chemical process involved in diamondgrowth.

Incorporation of Si and SiO x into diamond-like carbon films: Impact on surface properties and osteoblast adhesion

The interaction of human osteoblast cells with diamond-like carbon films incorporating silicon and silicon oxide (SiO x , 1 ⩽ x ⩽ 1.5) and synthesized using the direct-current plasma-activated chemical vapour deposition method was investigated. Cell culture studies were performed for films with Si contents ranging from ∼4 at.% to 15 at.%. Substantial differences between Si-incorporated and SiO x -incorporated films were found for the bonding environments of Si atoms and the hybridization of underlying carbon structures. However, osteoblast-attachment studies did not show statistically significant trends in properties of cell growth (count, area and morphology) that can be attributed either to the Si content of the films or to the chemical structure of the films. The surface energy decreased by 40% as the Si content of the SiO x incorporated DLC films increased to 13 at.%. The cell adhesion properties however did not change in response to lowering of the surface energy. The incorporation of both Si and SiO x leads to a beneficial reduction in the residual stress of the films. The average roughness of the films increases and the hardness decreases when Si and SiO x are added to DLC films. The impact of these changes for load-bearing biomedical applications can be determined only by carefully controlled experiments using anatomic simulators.

Up-scaling the production of modified a-C:H coatings in the framework of plasma polymerization processes

Hydrogenated amorphous carbon (a-C:H) films with silicon and oxygen additions, which exhibit mechanical, tribological and wetting properties adequate for protective coating performance, have been synthesized at room temperature in a small- (0.1 m 3) and a large-scale (1 m 3) coaters by low-pressure Plasma-Activated Chemical Vapour Deposition (PACVD). Hence, a-C:H:Si and a-C:H:Si:O coatings were produced in atmospheres of tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO), respectively, excited either by radiofrequency (RF – small scale) or by pulsed-DC power (large scale). Argon was employed as a carrier gas to stabilize the glow discharge. Several series of 2–5 μm thick coatings have been prepared at different mass deposition rates, R m, by varying total gas flow, F, and input power, W. Arrhenius-type plots of R m/ F vs. ( W/ F) −1 show linear behaviours for both plasma reactors, as expected for plasma polymerization processes at moderated energies. The calculation of apparent activation energy, E a, in each series permitted us to define the regimes of energy-deficient and monomer-deficient PACVD processes as a function of the key parameter W/ F. Moreover, surface properties of the modified a-C:H coatings, such as contact angle, abrasive wear rate and hardness, appear also correlated to this parameter. This work shows an efficient methodology to scale up PACVD processes from small, lab-scale plasma machines to industrial plants by the unique evaluation of macroscopic parameters of deposition.