Radio-frequency Chemical Vapor Deposition Research Articles

Electrostatic self-assembly approach in the deposition of bio-functional chitosan-based layers enriched with caffeic acid on Ti-6Al-7Nb alloys by alternate immersion.

Tailoring surface properties by layer-by-layer (LBL) deposition directed on the construction of complex multilayer coatings with nanoscale precision enables the development of novel structures and devices with desired functional properties (i.e., osseointegration, bactericidal activity, biocorrosion protection). Herein, electrostatic self-assembly was applied to fabricate biopolymer-based coatings involving chitosan (CSM) and alginate (AL) enriched with caffeic acid (CA) on Ti-6Al-7Nb alloyed surfaces. The method of CA grafting onto the chitosan backbone (CA-g-CSM) as well as all used reagents for implant functionalization were chosen as green and sustainable approach. The final procedure of surface modification of the Ti-6Al-7Nb alloy consists of three steps: (i) chemical treatment in Piranha solution, (ii) plasma chemical-activation of the Ti alloy surface in a RF CVD (Radio Frequency Chemical Vapour Deposition) reactor using Ar, O2 and NH3 gaseous precursors, and (iii) a multi-step deposition of bio-functional coatings via dip-coating method. Corrosion tests have revealed that the resulting chitosan-based coatings, also these involving CA, block the specimen surface and hinder corrosion of titanium alloy. Furthermore, the antioxidant layers are characterized by beneficial level of roughness (Ra up ca. 350nm) and moderate hydrophilicity (59°) with the dispersion part of conducive surface energy ca. 30mJ/m2. Noteworthy, all coatings are biocompatible as the intact morphology of cultured eukaryotic cells ensured proper growth and proliferation, while exhibit bacteriostatic character, particularly in contact with Gram-(-) bacteria (E. coli). The study indicates that the applied simple sustainable strategy has contributed significantly to obtaining homogeneous, stable, and biocompatible while antibacterial biopolymer-based coatings.

Plasma Modification of Carbon Coating Produced by RF CVD on Oxidized NiTi Shape Memory Alloy under Glow-Discharge Conditions.

Our previous work has shown that for cardiac applications, combining low-temperature plasma oxidation with an amorphous carbon coating (a-C:N:H type) constitutes a prospective solution. In this study, a short-term modification by low-temperature oxygen plasma is proposed as an example and a method for shaping the topography and surface energy of the outer amorphous carbon coating, produced via the Radio-Frequency Chemical Vapour Deposition (RFCVD) method on NiTi alloy oxidized under glow-discharge conditions. This treatment alters the chemical composition of the outer zone of the surface layer. A slight increase is also noted in the surface roughness at the nanoscale. The contact angles were shown to increase by about 20% for water and 30% for diiodomethane, while the surface free energy decreased by ca. 11%. The obtained results indicate that even short-term contact with low-temperature plasma can shape the surface properties of the carbon coating, an outcome which shows potential in terms of its use in medical applications.

Dual-purpose surface functionalization of Ti-6Al-7Nb involving oxygen plasma treatment and Si-DLC or chitosan-based coatings

The work presents a detailed study on the diamond-like structures doped with Si atoms and biopolymers-based coatings (chitosan, alginate) enriched with Ag nanoparticles (Ag NPs) deposited on the Ti-6Al-7Nb substrate. Multilayers were obtained by Plasma Enhanced Radio Frequency Chemical Vapour Deposition (PE RF CVD) technique and subsequent deposition of biopolymers by immersion method. The impact of Si atoms and Ag NPs on chemical structure, microstructure, topography, cytotoxicity as well as the hardness and Young modulus of the resulting layers was precisely investigated. The most advantageous conditions of plasma functionalization in RF reactor were the mixture of O2-Ar-NH3 in volume ratio of 10/1/9 in the first stage of functionalization (pre-activation). In the case of Si-DLC coatings (up to ca. 19 at.%) the lower silane flow (4 cm3/min) resulted in significant decrease of surface roughness (up to ca. Ra = 0.71 nm) of modified surfaces and increase of hardness reaching ca. 900 nm depth into surface (up to ca. 16 GPa). The most attractive among biopolymer-based coating on Ti-6Al-7Nb in terms of biological activity was chitosan with Ag NPs (diameter of ca. 25 nm) with additional alginate layer. AFM analysis revealed a uniform distribution of Ag NPs in the chitosan matrix. This contributed to advantageous physicochemical and biological properties assuring proper cell adhesion and proliferation. Noteworthy, the resulting surface functionalization of Ti-6Al-7Nb alloy did not cause significant cytotoxicity in vitro, giving a strong hope for perspective applications in implantology.

Microstructural and corrosion resistance characterisation of NiTi shape memory alloy modified at low-temperature plasma with carbon coatings produced via RFCVD and IBAD methods

ABSTRACTNiTi shape memory alloy, both before and after low-temperature oxynitriding under glow discharge conditions combined with the production of a nano-sized outer carbon coating, was investigated. The study compares two types of carbon coatings: produced via the RFCVD (radio frequency chemical vapour deposition) and IBAD (ion beam-assisted deposition) methods. The latter was also enriched by randomly distributed silver nanoparticles. The study showed slight changes in roughness parameters and increased corrosion resistance after surface treatment processes. The largest impedance module and corrosion potential and the smallest density of corrosion current were achieved for samples with a carbon coating produced via the RFCVD process. The presented surface modifications using hybrid processes can extend the use of NiTi alloy in medicine due to the increased biocompatibility.

Physicochemical and Biological Activity Analysis of Low-Density Polyethylene Substrate Modified by Multi-Layer Coatings Based on DLC Structures, Obtained Using RF CVD Method

In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the RF CVD (radio frequency chemical vapor deposition) method. In particular, polyethylene with deposited N-DLC and DLC layers in one process was characterized by a surface hardness ca. seven times (up to ca. 2.3 GPa) higher than the unmodified substrate. Additionally, its surface roughness was determined to be almost two times higher than the respective plasma-untreated polymer. It is noteworthy that plasma-modified LDPE showed no significant cytotoxicity in vitro. Thus, based on the current research results, it is concluded that a multilayer system (based on DLC coatings) obtained using plasma treatment of the LDPE surface can be proposed as a prospective solution for improving mechanical properties while maintaining biocompatibility.

One-Step RF-CVD Method for the Synthesis of Graphene Decorated with Metal and Metal Oxide Nanoparticles.

Bilayer and few layer-graphene (Gr) with noble metal (Ag and Au) and TiO2 nanoparticles were synthesized using atmospheric pressure radio frequency chemical vapor deposition (APRF-CVD). The precursors for the formation of the respective nanoparticles were dissolved in ethanol and injected into the APRF-CVD containing a Cu foil catalyst at 1000 °C. The graphene obtained had a blistered morphology similar to bubble-wrap. The bubble-like protrusions on the graphene sheet were caused by large nanoparticle clusters (~220 nm) formed below the graphene sheets. Smaller nanoparticles (10-80 nm) were also observed on top of the graphene sheets. Encapsulation of the nanoparticles with graphene, to yield core-shell particles was observed. Similarly, secondary growth of carbon nanotubes (CNTs) from the Au nanoparticles was observed. The average full width half maxima (FWHM) of 2D bands in the Raman spectra indicate that the graphene formed was predominantly bilayer graphene for Gr-TiO2 (55 ± 1.72 cm-1), and few-layer graphene for Gr-Ag (76 ± 22 cm-1) and Gr-Au (88 ± 4.7 cm-1). Raman spectroscopy also showed evidence for the doping of graphene and surface-enhanced Raman sensitivity (SERS) in the materials. These electronic properties of graphene with nanoparticles are relevant to various applications such as optoelectronics, catalysis, chemical and biological sensing.

Hybrid a-CNH+TiO2+TiN-type surface layers produced on NiTi shape memory alloy for cardiovascular applications.

The goal was to improve the properties of NiTi shape memory alloy to make it suitable for cardiac applications. For this purpose, a hybrid a-CNH+TiO2+TiN-type surface layer was produced on NiTi alloy and characterized. The NiTi alloy subjected to hybrid process combining low-temperature oxynitriding under glow discharge conditions and radio frequency chemical vapor deposition process was examined for microstructure, surface topography, corrosion resistance, wettability and surface-free energy, Ni ion release and platelets adhesion, aggregation and activation. The hybrid surface layers showed slightly increased surface roughness, better corrosion resistance, a more hydrophobic nature, decreased surface free energy, smaller release of nickel ions and reduced platelets activation. The produced layers could expand the range of NiTi medical applications.

Optical properties of plasma-enhanced chemical vapor deposited SiCxNy films by using silazane precursors

In this study, amorphous silicon carbonitride (SiCxNy) films were fabricated by radio frequency (RF) chemical vapor deposition (PECVD) using a single silazane precursor and a low power density (0.15W/cm3) for better compositional control. The effects of the precursor chemical structure (C/Si ratio, CSiN structure, and vinyl groups) and deposition temperature (Ts) on the chemical structure and optical properties of SiCxNy films were examined using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Specifically, two new single precursors; namely, n-methyl-aza-2,2,4-trimethylsilacyclopentane (MTSCP) and 1,3-divinyl-1,1,3,3-tetramethyl-disilazane (DVTMDS) were studied and compared.SiCxNy films deposited using MTSCP involving SiC3N rings formed SiN and Si(CH2)3 crosslinked structures at Ts≤100°C, and were then changed to predominantly SiCH2NSi crosslinked structures at Ts>300°C, leading to a wide range of optical band gap from 5.2 to 3.7eV. Compared to DVTMDS-deposited SiCxNy films, their relatively higher percentage of SiCN structure accounted for the lower optical band gap and reduced transmission. DVTMDS with di-vinyl groups readily formed a Si(CH2)2 bridge in SiCxNy films Ts≤200°C, resulting in excellent optical transmittance. The transmittance in the visible wavelengths of 400°C-deposited SiCxNy film using DVTMDS still showed 85%. Also, tunable refractive index between 1.44 and 2.10 were obtained for SiCxNy films deposited at Ts≤400°C.

NiTi shape-memory alloy oxidized in low-temperature plasma with carbon coating: Characteristic and a potential for cardiovascular applications

Surface layers currently produced on NiTi alloys do not meet all the requirements for materials intended for use in cardiology. Plasma surface treatments of titanium and its alloys under glow discharge conditions make it possible to produce surface layers, such as TiN or TiO2, which increases corrosion resistance and biocompatibility. The production of layers on NiTi alloys with the same properties, and maintaining their shape memory and superelasticity features, requires the use of low-temperature processes. At the same time, since it is known that the carbon-based layers could prevent excessive adhesion and aggregation of platelets, we examined the composite a-CNH+TiO2 type surface layer produced by means of a hybrid method combining oxidation in low-temperature plasma and Radio Frequency Chemical Vapor Deposition (RFCVD) processes. Investigations have shown that this composite layer increases the corrosion resistance of the material, and both the low degree of roughness and the chemical composition of the surface produced lead to decreased platelet adhesion and aggregation and proper endothelialization, which could extend the range of applications of NiTi shape memory alloys.

Plasmochemical modification of aluminum-zinc alloys using NH3-Ar atmosphere with anti-wear coatings deposition

This paper constitutes a continuation of studies on modification technologies for 7075 series aluminum alloys (Al-Zn) in plasmochemical conditions using the RF CVD (Radio-Frequency Chemical Vapor Deposition) method. This technique is simultaneously the second stage of alloy ageing. The presented results concern optimization of alloy surface modification using N+ ions (in NH3 or NH3/Ar atmosphere) before obtaining a DLC (Diamond-Like Carbon) layer doped with Si and N.From the results it can be concluded that the most profitable mechanical properties (H, ca. 12 GPa and E, ca. 115 GPa) are obtained when the SiCNH coating process is preceded by Al-Zn alloy surface modification with nitrogen ions. These ions are provided by a flowing NH3 and Ar gas mixture (1:1 ratio). In these process conditions, the lowest tribological wear of the surface is also observed. Furthermore, the obtained coating exhibits a fine-grained structure.

Corrosion resistance of NiTi shape memory alloy after hybrid surface treatment using low-temperature plasma

This article presents a study of the structure, surface roughness and corrosion resistance of composite layers consisting of a layer of Ti(ON) titanium oxynitride with a surface zone of amorphous carbon modified with nitrogen and hydrogen. They were produced on NiTi alloy in a hybrid process combining oxidation in low-temperature plasma and Radio Frequency Chemical Vapor Deposition process (RFCVD). Ti(ON)+a-CNH type composite layers can be produced in temperatures below 300 °C, i.e. in conditions ensuring that the specific properties of NiTi alloys, namely shape memory and superelasticity, are maintained. They provide a significant increase in corrosion resistance and may be produced on specimens having complex shapes, which is of great importance in the case of possible application as medical implants.

Influence of gas mixture during N+ ion modification under plasma conditions on surface structure and mechanical properties of Al–Zn alloys

Aluminum, and particularly its alloys, are the materials of an increasing significance in construction and automotive industry due to the combination of their strength properties. However, their functionality is limited mainly because of the susceptibility on tribological wear. This paper presents the results of the study aimed at determining the optimum conditions of the process of alloy surface modification with N+ ions in the atmosphere of N2–H2, using the method of chemical precipitation from gaseous phase, combined with a discharge of a frequency of 13.56MHz (radio frequency chemical vapor deposition). It was demonstrated that the process of Al–Zn alloy surface modification with nitrogen ions is a necessary prerequisite to obtain low-friction coatings (SiCNH in this case) characterized by a good and stable adhesion to the aluminum alloy substrate. The highest hardness is obtained in the case of SiCNH coating deposition process, preceded by the process of surface modification in plasma conditions, provided for N2 only (hardness 10.0GPa) of the N2/H2 mixture (flow ratio 3/1, hardness 10.5GPa). The surface of alloy combined with the obtained DLC (diamond-like carbon) layers, doped with N and Si atoms is characterized by ca. 30% decrease in the friction coefficient value (up to the 0.2 value) and ca. 25% decrease in the value of surface roughness (Ra, 6.5nm), compared to unmodified substrates.

Chemical composition and selected mechanical properties of Al–Zn alloy modified in plasma conditions by RF CVD

The paper reports results of the study of surface composition and selected functional properties of 7075 (Al–Zn) alloys modified in Ar, N2, SiH4 and CH4 atmosphere at reduced pressure. RF CVD (Radio Frequency Chemical Vapour Deposition) technique was used in the study. The type or weight percentage of carbon in each modification varied in the resultant SiN:H and SiCN:H coatings. Alloy samples were treated with Ar+ plasma etching and N+ ion implantation at reduced pressure.

Influence of plasmochemical modification of Al–Cu–Mg alloys on surface structure and functional properties

The article presents the results of the study of the composition and selected functional properties of Al–Cu–Mg alloys modified by RF CVD technique (Radio-Frequency Chemical Vapor Deposition). The type and composition of the deposited SiNH and carbon doped SiNH layers was altered in the experiments. The samples were pre-treated with argon plasma etching and N+ ion implantation.On the basis of the experimental evidence it is concluded that the deposition of an anti-wear SiCNH coating (using SiH4:CH4:N2 = 1:1:2 gas mixture) improves both the investigated mechanical properties (hardness ca. 10 GPa, Young modulus ca. 95 GPa) and tribological performance of the control (unmodified) alloy sample as well as those of the modified alloy samples whose outer layer is SiNH.

Graphene nanosheets by low-temperature thermal reduction of graphene oxide using RF-CVD

A novel technique for synthesis of thin-layered graphene sheets (GNS) were established by hydrogen-induced reduction of graphene oxide at low temperature of 200°C, using radio frequency chemical vapour deposition. The functional group and microstructures of the prepared GNS were characterised by various techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, Raman spectroscopy and particle-size analyser. Further the as-prepared GNS with an average diameter of 528.8 nm was confirmed by particle-size analyser. This GNS-generation process is rapid with high efficiency of exfoliation process, non-toxic, environmental friendly and ideal for large-scale production for industrial applications.

Synthesis of Ag-decorated, few-layer graphene structures over a novel Ag/MgO catalytic system by radio-frequency chemical vapor deposition

We report the synthesis, by radio-frequency chemical vapor deposition with methane as the carbon source, of multicomponent nanostructural materials based on Ag nanoparticles embedded into graphene layers and discuss their properties. We found that the Ag concentration plays an important role in controlling the morphology and the structure of the resulting graphene sheets. Raman analysis was used to calculate the in-plane crystallites (La) from the (IG/ID) ratio, which were found to range between 12.1 and 13.1 nm. Such composites could find applications in a number of areas ranging from energy harvesting and plasmonics to sensing and nanomedicine.

Anti‐wear properties of amorphous a‐C:H and a‐C:N:H carbon coatings deposited on polycarbonate

In this study, we investigate the tribological properties of amorphous hydrogenated (a‐C:H) and nitrogenated (a‐C:N:H) carbon coatings deposited on polycarbonate substrates (PC). The a‐C:H and a‐C:N:H coatings of 700‐nm thickness were deposited by radio frequency chemical vapour deposition method (13.56 MHz, 300 W). The chemical composition of the coatings was determined by X‐ray photoelectron spectroscopy and their structure with the use of Fourier transform infrared spectroscopy spectroscopy. A surface roughness was measured by contact method. It was found that the nitrogenated a‐C:N:H coatings have much lower surface roughness in comparison with hydrogenated a‐C:H one. All examined coatings showed very good adhesion to PC substrate in the scratch test. Tribological properties were investigated with the use of ball‐on‐disc tribometer in the contact with 100Cr6 steel ball. The pure PC exhibited higher coefficient of friction (0.38) as compared to those with the coatings. The lowest value of friction coefficient (around 0.17) was found for a‐C:H coating. The wear resistance of the amorphous carbon/substrate system is about 10 times higher than that of PC substrate. Copyright © 2012 John Wiley & Sons, Ltd.

Novel Multicomponent and Biocompatible Nanocomposite Materials Based on Few-Layer Graphenes Synthesized on a Gold/Hydroxyapatite Catalytic System with Applications in Bone Regeneration

We present the synthesis of few-layer graphenes over a novel Au/hydroxyapatite catalytic system by radio-frequency chemical vapor deposition, with acetylene and methane as the carbon sources. The synthesis time was found to influence linearly the dimensions of the graphitic layers and asymptotically their corresponding thermal decomposition temperature. The resulting multicomponent nanocomposite material formed out of graphene layers, Au nanoparticles (AuNPs) supported on the surface of hydroxyapatite nanoparticles, was found to have good biocompatibility and induce excellent bone cellular proliferation. Such multicomponent composites could find numerous applications in the area of bone regeneration given the excellent biocompatibility, 3D structure, and unique composition.

Silicon nitride layers of various n-content: Technology, properties and structure

Two series of amorphous silicon nitride layers (a-SiN x:H) were formed with Radio Frequency Chemical Vapor Deposition method (13.56 MHz) from a NH 3/SiH 4 gas mixture: the first one on Si (001) and the second on glass. The deposition process was repeated at various [NH 3]/[SiH 4] ratios, while the other parameters (pressure, plasma generator power, substrate temperature, total gas flow, and time) were kept constant. It has been confirmed in optical measurements that the refractive indexes decrease for the layers obtained at increasing [NH 3]/[SiH 4] ratios. Simultaneously, the position of the band assigned to Si–H stretching vibrations (at about 2100 cm − 1 ) shifts towards higher frequencies. The observed dependencies were applied in evaluation of nitrogen and hydrogen contents in the respective layers. It has been shown that when [NH 3]/[SiH 4] increases from 0 (no silane flow) to 0.2 then the a-SiN x:H layers of x = [N]/[Si] increasing between 0 and nearly 1.4 may be obtained. The obtained layers have the refractive indexes higher than 2.1 and lower than 2.7 which make them good materials for antireflective coatings on crystalline and multicrystalline silicon solar cells.

The role of hydrocarbon concentration on the synthesis of large area few to multi-layer graphene structures

Large area and few to multi-layer graphene sheets were synthesized on a bimetallic catalyst system via radio-frequency chemical vapor deposition (RF-CVD). Synthesis conditions were varied and their effects on the morphological properties of the graphene structures were observed. As the flow rate of the hydrocarbon was varied, the diameter of the graphene structures increased from a few hundred nanometers to a few micrometers. The number of graphene layers was also found to be dependent on the hydrocarbon concentration. This method shows great potential for the synthesis of large area few-layer graphene sheets, which can be used in various electronic applications.