Plasma-assisted Chemical Vapor Deposition Research Articles

Carbon-Nanowall Microporous Layers for Proton Exchange Membrane Fuel Cell.

The cathode microporous layer (MPL), as one of the key components of the proton exchange membrane fuel cell (PEM-FC), requires specialized carbon materials to ensure the two-phase flow and interfacial effects. In this respect, we designed a novel MPL based on highly hydrophobic carbon nanowalls (CNW). Employing plasma-assisted chemical vapor deposition techniques directly on carbon paper, we produced high-quality microporous layers at a competitive yield-to-cost ratio with distinctive MPL properties: high porosity, good stability, considerable durability, high hydrophobicity, and substantial conductivity. The specific morphological and structural properties were determined by scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Thermo-gravimetric analysis was employed to study the nanostructures' thermal stability and contact angle measurements were performed on the CNW substrate to study the hydrophobic character. Platinum ink, serving as a fuel cell catalyst, was sprayed directly onto the MPLs and incorporated in the FC assembly by hot-pressing against a polymeric membrane to form the membrane-electrode assembly and gas diffusion layers. Single-fuel-cell testing, at moderate temperature and humidity, revealed improved power performance comparable to industrial quality membrane assemblies (500 mW cm-2 mg-1 of cathodic Pt load at 80 °C and 80% RH), with elevated working potential (0.99 V) and impeccable fuel crossover for a low-cost system.

Surface Morphology and Spectroscopic Features of Homoepitaxial Diamond Films Prepared by MWPACVD at High CH4 Concentrations.

Single crystal diamond (SCD) is a promising material to satisfy emerging requirements of high-demand fields, such as microelectronics, beta batteries and wide-spectrum optical communication systems, due to its excellent optical characteristics, elevated breakdown voltage, high hardness and superior thermal conductivity. For such applications, it is essential to study the optically active defects in as-grown diamonds, namely three-dimensional defects (such as stacking faults and dislocations) and the inherent defects arising from the cultivation method. This paper reports the growth of SCD films on a commercial HPHT single-crystal diamond seed substrate using a 2.45 GHz microwave plasma-assisted chemical vapor deposition (MWPACVD) technique by varying the methane (CH4) gas concentration from 6 to 12%, keeping the other parameters constant. The influence of the CH4 concentration on the properties, such as structural quality, morphology and thickness, of the highly oriented SCD films in the crystalline plane (004) was investigated and compared with those on the diamond substrate surface. The SCD film thickness is dependent on the CH4 concentration, and a high growth rate of up to 27 µm/h can be reached. Raman spectroscopy, high-resolution X-ray diffractometry (HRXRD), scanning electron microscopy (SEM), surface profilometry and optical microscopic analyses showed that the produced homoepitaxial SCD films are of good quality with few macroscopic defects.

Bottom-up evolution of consolidated porous diamond layer by hot-filament-CVD

Synthesis of the porous chemical vapor deposition (CVD) diamond layer, which might enable many noble applications, usually employed the template growth or post-processing, which accompanied the undesirable complexity and cost issues. In a small number of the porous diamond layer synthesis efforts, majority of them employed the plasma-assisted CVD (PA-CVD), while the hot-filament CVD (HF-CVD) was well known for its outstanding scalability and cost-effectiveness. Here we demonstrate a post-processing/template-free approach for the porous diamond layer synthesis by HF-CVD. Intriguingly, we found that the seeding the substrate by detonation nanodiamond (DND) and the relatively low substrate temperature were key enabling factors. The consolidated layer was consisted of quasi-spherical nanodiamond particles. Such observations suggested a precipitation-relevant growth mechanism, which we disproved here, and we clarified an alternative bottom-up growth mechanism. We also demonstrated a preliminary result of applying the porous diamond layer as a waveguide in the attenuated-total-reflection (ATR)-type waveguide mode resonance sensor.

Synthesis and thermal properties of two novel cobalt (II) Schiff's base complexes as precursors for coating cobalt oxide (Co3O4) thin film by a Plasma Enhanced Metallo-Organic Chemical Vapour Deposition

Two Schiff's base complexes namely, Co(3,5-di-tertbutyl-salicylaldehydatoethylimine)2 (1) and Co(3,5-di-tertbutyl-salicylaldehydatobutylimine)2 (2) were synthesized by template method and characterized by elemental (C, H & N), FT-IR, DART-MS, TG/DTA and single crystal XRD analysis. Both 1 and 2 were found to crystallize in Orthorhombic crystal system. The complexes 1 and 2 undergoes single step volatilization in an inert N2 atmosphere giving a negligible percentage of residues at 331 °C (1) and 362 °C (2) as observed from thermogravimetry (TG) analysis. The molecular mass (M) of Co-bearing species were found to be 580 and 636 Da for 1 and 2 respectively. The equilibrium vapour pressures (pe) measurement by a TG - based transpiration technique over the temperature range of 489–550 K for 1 and 459–561 K for 2 yielded values of 107.0 (±1.8) and 105.2 (±2.1) kJ mol−1 for 1 and 2 respectively for their standard enthalpies of vapourisation (ΔHovap). Complex 2 was used as precursor for demonstrating the formation of Co3O4 thin film at a substrate temperature of 350 °C in an Ar plasma by using a home-built plasma assisted Chemical Vapour Deposition (CVD) method with a deposition pressure of 0.6–1.0 mbar. The phase identification by XRD showed the preferential growth of cubic Co3O4 in (311) plane. The morphology by SEM confirmed densely agglomerated cauliflower like structure. The particle size (D = 15.6 nm) was calculated using Debye-Scherrer's equation. A band gap value of 2.23 eV was obtained using Kubelka-Munk function.

A review of tribological properties and deposition methods for selected hard protective coatings

Surface modification is widely adopted as a viable solution for surface damage under sliding or impacting conditions. Various coatings can be manufactured using different techniques and it has been applied on various substrates in previous studies which results in different characteristics. This review presents the anti-wear techniques with a focus on the most recent coatings of superior properties. Hard protective coatings may consist of various compositions; however, based on the hardness and the resistance to wear, some of the frequently used elements are Titanium (Ti), Nickel (Ni), carbides, Zirconium (Zr), Boron (B) and the Diamond Like Carbon (DLC). The deposition methods such as Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD) as well as the cutting-edge coating hybrid-deposition methods such as Pulsed DC Magnetron Sputtering (PDCMS), High Power impulse (HiPIMS) and Arc Ion Plating (AIP) are reviewed and the resulted significant differences in the coating properties are discussed. In this review, listing the most important findings from previous studies in a table for each group of coatings make it easy to compare between various techniques and coatings. Some of the listed factors affecting the coating properties, such as the substrate, and others affecting the coefficient of friction, such as the counter body, were not been sufficiently highlighted before despite their importance in analyzing the tribological behavior for the coatings investigated. Although the focus was on the most recent studies, a wide range of studies was covered in order to accumulate and integrate the knowledge toward a complete analysis and discussion. Coating hardness is essential for better wear resistance; however, coating bonding, thickness and roughness may be equally important. Various techniques are used to improve the bonding. For some coatings, the Coefficient of Friction (CoF) increases with increasing the wear resistance where the counter body plays a major role. For most of the deposition techniques, the controlling parameters are the cleaning treatment, arc current, pressure, time, and gas supply. It was found that diamond-like carbon coatings are among the hardest coatings and the Plasma-Assisted Chemical Vapor Deposition (PACVD) is frequently reported as one of the most promising deposition techniques. Many coatings including the diamond-like carbon coating were not been investigated for their erosion wear resistance by solid particles despite the importance of such investigations for many applications.

CVD Nanocrystalline Diamond Film Doped with Eu.

This paper submits experimental results of a study directed towards the formation of Eu ions’ luminescent centers in CVD diamond films. A new approach is based on use of diamond nanoparticles with a surface modified with Eu ions for seeding at CVD growth. Nanocrystalline diamond films (NCD) doped with Eu have been grown from the gas phase on silicon substrates by microwave plasma-assisted CVD at a frequency of 2.45 GHz. The photoluminescence spectra clearly show several electronic transitions of the Eu3+ ions, which confirm the incorporation of Eu ions into the NCD film.

Diamondized carbon nanoarchitectures as electrocatalytic material for sulfate-based oxidizing species electrogeneration

The introduction of nanotechnology seems to be an imperative factor to intensify the synergic effects of electrocatalytic materials to produce strong oxidant species or to increase the active sites on their surfaces as well as to enhance the conversion yield in a fuel cell, high-added value products, electrolytic treatment for environmental protection or the detection limit in electroanalysis. Recently, a new type of 3D-diamond electrodes was developed with boron-doped carbon nanowalls (B:CNW), which was manufactured using the microwave plasma-assisted chemical vapor deposition (CVD) process, improving the charge transfer and enhancing the electrochemical performance. The applicability of a BDD/boron-doped carbon nanowalls (BDD/B:CNW) anodes to degrade organic pollutants has been already investigated; however, no attempts at the electrosynthesis of oxidizing species using these diamond-carbon nanostructures have been reported yet. Therefore, the electrosynthesis of sulfate-based oxidizing species was studied here to answer relevant questions from both fundamental and practical point-of-view. The results demonstrated that persulfate was efficiently produced at the BBD electrode, while that the ion-radical sulfate could be the most important oxidant at BDD/B:CNW anode when compared to other electrocatalytic materials, including BDD surfaces. Persulfate concentrations ranged from 3 to 6 µM, depending on the applied current density (2.5, 5.0, and 15 mA cm−2), at diamond electrodes. A dye-model pollutant - methyl orange (MO) was degraded below the limit of detection within 45 min using BDD/B:CNW when in-situ sulfate-based oxidizing species were electrogenerated. These kinds of 3D-diamond-carbon nanostructures are thus promising as novel electrocatalyst for various catalytic applications in the environmental and energy fields.

AISI 316L stainless steel modification by surface alloy and a-C:H:SiOx coating synthesis

AISI 316L austenite stainless steel is often used in orthopedics, although metal particles and metal ions are the major weakness of metallic prostheses associated with the tissue inflammation and proliferation. This paper presents the surface modification of the AISI 316L steel substrate to reduce its wear and corrosion rate using a combination of two methods. For that, the titanium alloy is synthesized on the substrate surface using the magnetron sputtering and electron-beam treatment. The elemental and phase compositions of the surface are investigated by energy dispersive X-ray spectrometry and X-ray diffraction. The a-C:H:SiOx coating is deposited onto substrates with the surface alloy by plasma assisted chemical vapor deposition to significantly improve the mechanical, anti-corrosion and wear-resistant properties of AISI 316L austenite stainless steel. The mechanical properties and the surface of the obtained coating are examined by nanoindentation and optical microscopy, respectively. It is shown that substrates with the surface alloy and a-C:H:SiOx coating manifest stability to autoclave sterilization proven by the results of optical microscopy.

Cleaning of nitrogen-containing carbon contamination by atmospheric pressure plasma jet

Atmospheric pressure plasma jet (APPJ) was used to clean nitrogen-containing carbon films (C–N) fabricated by plasma-assisted chemical vapor deposition method employing the plasma surface interaction linear device at Sichuan University (SCU-PSI). The properties of the contaminated films on the surface of pristine and He-plasma pre-irradiated tungsten matrix, such as morphology, crystalline structure, element composition and chemical structure were characterized by scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. The experimental results revealed that the removal of C–N film with a thickness of tens of microns can be realized through APPJ cleaning regardless of the morphology of the substrates. Similar removal rates of 16.82 and 13.78 μm min−1 were obtained for C–N films deposited on a smooth pristine W surface and rough fuzz-covered W surface, respectively. This is a remarkable improvement in comparison to the traditional cleaning method. However, slight surface oxidation was found after APPJ cleaning, but the degree of oxidation was acceptable with an oxidation depth increase of only 3.15 nm. Optical emission spectroscopy analysis and mass spectrometry analysis showed that C–N contamination was mainly removed through chemical reaction with reactive oxygen species during APPJ treatment using air as the working gas. These results make APPJ cleaning a potentially effective method for the rapid removal of C–N films from the wall surfaces of fusion devices.

The effect of boron concentration on the electrical, morphological and optical properties of boron-doped nanocrystalline diamond sheets: Tuning the diamond-on-graphene vertical junction

In this paper, the effect of boron doping on the electrical, morphological and structural properties of free-standing nanocrystalline diamond sheets (thickness ~ 1 μm) was investigated. For this purpose, we used diamond films delaminated from a mirror-polished tantalum substrate following a microwave plasma-assisted chemical vapor deposition process, each grown with a different [B]/[C] ratio (up to 20,000 ppm) in the gas phase. The developed boron-doped diamond (BDD) films are a promising semiconducting material for sensing and high-power electronic devices due to band gap engineering and thermal management feasibility. The increased boron concentration in the gas phase induces a decrease in the average grain size, consequently resulting in lower surface roughness. The BDD sheets grown with [B]/[C] of 20,000 ppm reveal the metallic conductivity while the lower doped samples show p-type semiconductor character. The charge transport at room temperature is dominated by the thermally activated nearest-neighbor hopping between boron acceptors through impurity band conduction. At low temperatures (<300 K), the Arrhenius plot shows a non-linear temperature dependence of the logarithmic conductance pointing towards a crossover towards variable range hopping. The activation energy at high temperatures obtained for lowly-doped sheets is smaller than for nanocrystalline diamond bonded to silicon, while for highly-doped material it is similar. Developed sheets were utilized to fabricate two types of diamond-on-graphene heterojunctions, where boron doping is the key factor for tuning the shape of the current-voltage characteristics. The graphene heterojunction with the low boron concentration diamond sheet resembles a Schottky junction behavior, while an almost Ohmic contact response is recorded with the highly doped BDD sheet of metallic conductivity. The free-standing diamond sheets allow for integration with temperature-sensitive interfaces (i.e. 2D materials or polymers) and pave the way towards flexible electronics devices.

In Vitro Biodegradation of a-C:H:SiOx Films on Ti-6Al-4V Alloy.

This paper focuses mainly on the in vitro study of a five-week biodegradation of a-C:H:SiOx films of different thickness, obtained by plasma-assisted chemical vapor deposition onto Ti-6Al-4V alloy substrate using its pulsed bipolar biasing. In vitro immersion of a-C:H:SiOx films in a solution of 0.9% NaCl was used. It is shown how the a-C:H:SiOx film thickness (0.5–3 µm) affects the surface morphology, adhesive strength, and Na+ and Cl− precipitation on the film surface from the NaCl solution. With increasing film thickness, the roughness indices are reducing a little. The adhesive strength of the a-C:H:SiOx films to metal substrate corresponds to quality HF1 (0.5 µm in thickness) and HF2-HF3 (1.5–3 µm in thickness) of the Rockwell hardness test (VDI 3198) that defines strong interfacial adhesion and is usually applied in practice. The morphometric analysis of the film surface shows that on a-C:H:SiOx-coated Ti-6Al-4V alloy surface, the area occupied by the grains of sodium chloride is lower than on the uncoated surface. The reduction in the ion precipitation from 0.9% NaCl onto the film surface depended on the elemental composition of the surface layer conditioned by the thickness growth of the a-C:H:SiOx film. Based on the results of energy dispersive X-ray spectroscopy, the multiple regression equations are suggested to explain the effect of the elemental composition of the a-C:H:SiOx film on the decreased Na+ and Cl− precipitation. As a result, the a-C:H:SiOx films successfully combine good adhesion strength and rare ion precipitation and thus are rather promising for medical applications on cardiovascular stents and/or friction parts of heart pumps.

Integration of silicon-vacancy centers in nanodiamonds with an optical nanofiber

We experimentally demonstrate the integration of silicon-vacancy centers in nanodiamonds (SiV-NDs) with an optical nanofiber (ONF). We grow SiV-NDs on seed NDs dispersed on a quartz substrate using a microwave plasma-assisted chemical vapor deposition method. First, we search and characterize SiV-NDs on a quartz substrate using an inverted confocal microscope and an atomic force microscope (AFM). Subsequently, we pick up SiV-NDs from the quartz substrate and deposit them on the surface of a free-standing ONF using the AFM tip. The fluorescence emission spectrum, photon count rate, and intensity correlations for SiV-NDs are systematically measured.

Simplified CVD route to near-zero thickness silicon nitride films

Silicon nitride (SiNx, x ∼ 1) thin films were deposited by chemical vapor deposition on silicon oxide (SiO2) substrates by combining controlled pulses of the precursor 1,3,5-tri(isopropyl)cyclotrisilazane (TICZ, C9H27N3Si3) with a continuous ammonia (NH3) plasma. This plasma-assisted pulsed CVD (PPCVD) process enables the integration of the nanoscale thickness and uniformity control achieved in atomic layer deposition with the efficiency of plasma-enhanced CVD (PE-CVD). TICZ was selected because it is a nonpyrophoric stable liquid with a high vapor pressure (∼133 Pa at 70 °C) and could act as a single source for SiNx with both high Si and N contents. An optimized PPCVD process window was identified consisting of a substrate temperature of 350 °C, a TICZ pulse of ≤0.2 s, and a TICZ purge pulse ≥10 s in a continuous direct NH3 plasma at a NH3 flow rate and a power of 40 SCCM and 3000 W, respectively. The as-deposited films were analyzed by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS analysis confirmed the absence of any C inclusion and demonstrated the existence of the 1:1 Si:N ratio. In situ, real-time ellipsometry measurements indicated that SiNx growth occurred in a typical PE-CVD regime. They also yielded an as-grown SiNx average refractive index of ∼1.75.

Barrier Diamond-like Carbon Coatings on Polydimethylsiloxane Substrate.

The plasma modification of polydimethylsiloxane (PDMS) substrates is one way to change their surface geometry, which enables the formation of wrinkles. However, these changes are very often accompanied by the process of restoring the hydrophobic properties of the modified material. In this work, the RF PACVD device (radio frequency plasma-assisted chemical vapor deposition) was used, with which the plasma treatment of PDMS substrates was carried out in argon, nitrogen, oxygen, and methane atmospheres at variable negative biases ranging from 100 V to 500 V. The obtained results show the stability of contact angles for deionized water only in the case of surfaces modified by diamond-like carbon (DLC) coatings. The influence of the applied production conditions on the thickness (between 10 and 30 nm) and chemical structure (ID/IG between 0.41 and 0.8) of DLC coatings is discussed. In the case of plasma treatments with other gases introduced into the working chamber, the phenomenon of changing from hydrophilic to hydrophobic properties after the modification processes was observed. The presented results confirm the barrier nature of the DLC coatings produced on the PDMS substrate.

Electrochemical Detection of Plant Pathogens Using Boron-Doped Carbon Nanowalls Immunosensor

This study reports the electrochemical immunosensor development for the detection of bacteria from the <i>Pseudomonas</i> genus &#x2013; the causative of many plant infections, inclusive of canker. This firstly reported assay on carbon-based material included: boron-doped carbon nanowalls (B:CNW) electrodes fabrication, sensor manufacturing, antigen detection, and specificity tests. B:CNW was fabricated by microwave plasma-assisted chemical vapor deposition (CVD) method. Cyclic voltammetry (CV) was applied during the modification step &#x2013; the electrochemical reduction of the diazonium salt. Electrochemical impedance spectroscopy (EIS) measurements confirmed the accurate sensor preparation and were used for the quantitative detection of antigen. The antibodies were utilized as the biological recognition system and immobilized on the sensor surface by covalent linkage. The optimized assay showed high sensitivity towards seven strains of <i>Pseudomonas syringae</i> pv. <i>lachrymans</i> (Psl) in the concentration range of <inline-formula> <tex-math notation="LaTeX">$3.25\times 10^{-3}$ </tex-math></inline-formula>&#x2013; <inline-formula> <tex-math notation="LaTeX">$3.25\times 10^{5}$ </tex-math></inline-formula> CFU/<inline-formula> <tex-math notation="LaTeX">$\mu \text{l}$ </tex-math></inline-formula> (limit of detection, LOD of 0.119 CFU/<inline-formula> <tex-math notation="LaTeX">$\mu \text{l}$ </tex-math></inline-formula>). The specificity of the assay was confirmed on four non-target bacteria: <i>Streptococcus pneumoniae</i>, <i>Streptococcus pyogenes</i>, <i>Bordetella parapertussis</i>, and <i>Haemophilus influenzae</i>. These results indicate the importance of the sensing material choice and its modification procedure as they affect successive analytical performance.

Design of New Concept of Knitted Hernia Implant.

A knitted implant, unilaterally modified with plasma-assisted chemical-vapor deposition (PACVD), and with a nano-layer of fluorine derivative supplementation, for reducing the risk of complications related to adhesions, and the formation of a thick postoperative scar was prepared. The biological evaluation of designed or modified medical devices is the main aspect of preclinical research. If such studies use a medical device with prolonged contact with connective tissue (more than 30 days), biocompatibility studies require a safety assessment in terms of toxicity in vitro and in vivo, allergenicity, irritation, and cancerogenicity, reproductive and developmental toxicity. The ultimate aspect of biological evaluation is biofunctionality, and evaluation of the local tissue response after implantation, resulting in the determination of all aspects of local biocompatibility with the implemented synthetic material. The implantation of PACVD-modified materials in muscle allows us to estimate the local irritation effect on the connective tissue, determining the risk of scar formation, whereas implantation of the above-mentioned knitted fabric into the abdominal wall, assists with evaluating the risk of fistula formation—the main post-surgical complications. The research aimed to evaluate the local reaction of the soft tissues after the implantation of the knitted implants modified with PACVD of the fluoropolymer in the nanostuctural form. The local effect that occurred during the implantation of the designed implants was quantitatively and qualitatively evaluated when PACVD unmodified (reference), and modified medical devices were implanted in the abdominal cavity (intra-abdominal position) for 12 or into the muscles for 56 weeks. The comparative semi-quantitative histological assessment included the severity of inflammatory cells (multinucleated cells, lymphocytes, plasma cells, macrophages, giant cells) and the tissue response (necrosis, neovascularization, fibrosis, and fat infiltration) on a five-point scale. The knitted implants modified by PACVD did not indicate cumulative tissue response when they were implanted in the muscle and intra-abdominally with direct contact with the viscera. They reduced local tissue reaction (score −2.71 after 56 weeks of the implantation) and internal organ adhesion (irritation score −2.01 and adhesion susceptibility −0.3 after 12 weeks of the implantation) compared with the reference (unmodified by PACVD) knitted implant, which had an identical structure and was made of the same source.

Diamond Structures for Tuning of the Finesse Coefficient of Photonic Devices.

Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry–Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry–Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented.

Investigation of a Highly Sensitive Surface-Enhanced Raman Scattering Substrate Formed by a Three-Dimensional/Two-Dimensional Graphene/Germanium Heterostructure.

Three-dimensional graphene (3D-graphene) is used in surface-enhanced Raman spectroscopy (SERS) because of its plasmonic nanoresonator structure and good ability to interact with light. However, a thin (3-5 nm) layer of amorphous carbon (AC) inevitably appears as a template layer between the 3D-graphene and object substrate when the 3D-graphene layer is synthesized, weakening the enhancement factor. Herein, two-dimensional graphene (2D-graphene) is employed as a template layer to directly synthesize 3D-graphene on a germanium (Ge) substrate via plasma-assisted chemical vapor deposition, bypassing the formation of an AC layer. The interaction and photoinduced charge transfer ability of the 3D-graphene/Ge heterojunction with incident light are improved. Moreover, the high density of electronic states close to the Fermi level of the heterojunction induces the adsorbed probe molecules to efficiently couple to the 3D-graphene-based SERS substrate. Our experimental results imply that the lowest concentrations of rhodamine 6G and rhodamine B that can be detected on the 3D/2D-graphene/Ge SERS substrate correspond to 10-10 M; for methylene blue, it is 10-8 M. The detection limits of the 3D/2D-graphene/Ge SERS substrate with respect to 3-hydroxytyramine hydrochloride and melamine (in milk) are both less than 1 ppm. This work may provide a viable and convenient alternative method for preparing 3D-graphene SERS substrates. It also constitutes a new approach to developing SERS substrates with remarkable performance levels.

Kinetics of plasma-assisted chemical vapor deposition combined with inductively excited RF discharge and properties of a-C:H:SiOx coatings

The paper studies the plasma-assisted chemical vapor deposition of a-C:H:SiOx coatings in plasma of non-self-sustained arc discharge with a hot cathode combined with inductively excited radio-frequency (RF) discharge. The a-C:H:SiOx coatings are produced by polyphenyl methylsiloxane (PPMS) dissociation in plasma with and without RF discharge. The optical emission spectroscopy is used to study the PPMS dissociation process. Raman spectroscopy provides the structural investigations of the obtained coatings, while the energy dispersive X-ray spectroscopy is used to analyze the chemical composition. It is shown that the mechanical and tribological properties of a-C:H:SiOx coatings depend on the RF discharge power and the bias voltage amplitude of the substrate. It is demonstrated that substrate bias voltage can be reduced during the coating deposition in combined discharge without significant degradation of its mechanical and tribological properties due to the better dissociation and ionization of PPMS vapor molecules in inductively excited RF discharge.

Investigating the corrosion performance of Ti-6Al-4V biomaterial alloy with hydroxyapatite coating by artificial neural network

As a result of its excellent mechanical characteristics and bio-compatibility, the Ti-6Al-4V alloy offers a wide-ranging applications in the medical industry. However, long-term application of these alloys may lead to a decline in corrosion resistance as well as other serious problems in these alloys. To resolve these problems, it is possible to modify the implant surface to enhance the corrosion and bio-compatibility properties. On the Ti-6Al-4V substrate surface, the TiN coating was applied by the Plasma-Assisted Chemical Vapour Deposition (PACVD) method together with the hydroxyapatite coating (HA) using the sol–gel method. Furthermore, the corrosion performance of bio-active hydroxyapatite layer coating on Ti-6Al-4V implant surface was evaluated through the application of the Artificial Neural Network (ANN) and Gene Expression Programming (GEP) models. The generated models were analysed and compared to a response surface methodology (RSM). The hydroxyapatite sol–gel parameters on Ti-6Al-4V implant materials were used as independent variables (input variables). The Ecorr values computed from potentiodynamic polarization measurements were used as a dependent variable (output variable) in the models. The results of the ANN technique (sigmoid activation function, LM training algorithm and 9 neurons in hidden layer) were in good consistent with the experimental Ecorr values, indicating this model is slightly better than the GEP and RSM models. Finally, the findings demonstrated that the ANN technique is an appropriate and robust tool for quantitative modeling of corrosion resistance, and that it can be applied to a variety of surface engineering applications.