Radio Frequency Plasma Assisted Chemical Vapor Deposition Research Articles

Tailoring Black TiO2 Thin Films: Insights from Hollow Cathode Hydrogen Plasma Treatment Duration

In this study, we report the use of a radiofrequency plasma-assisted chemical vapor deposition (RF-CVD) system with a hollow cathode geometry to hydrogenate anatase TiO2 thin films. The goal was to create black TiO2 films with improved light absorption capabilities. The initial TiO2 was developed through magnetron sputtering, and this study specifically investigated the impact of hollow cathode hydrogen plasma (HCHP) treatment duration on the crucial characteristics of the resulting black TiO2 films. The HCHP treatment effectively created in-bandgap states in the TiO2 structure, leading to enhanced light absorption and improved conductivity. Morphological analysis showed a 24% surface area increase after 15 min of treatment. Wettability and surface energy results displayed nonlinear behavior, highlighting the influence of morphology on hydrophilicity improvement. The anatase TiO2 phase remained consistent, as confirmed by diffractograms. Raman analysis revealed structural alterations and induced lattice defects. Treated samples exhibited outstanding photodegradation performance, removing over 45% of methylene blue dye compared to ~25% by the pristine TiO2 film. The study emphasized the significant impact of 15-min hydrogenation on the HCHP treatment. The research provided valuable insights into the role of hydrogenation time using the HCHP treatment route on anatase TiO2 thin films and demonstrated the potential of the produced black TiO2 thin films for photocatalytic applications.

Effects of Different Silicon Substrates on the Structure and Properties of Deposited Diamond‐like Carbon Films

Diamond‐like carbon (DLC) has attracted much attention due to its unique properties such as excellent physicochemical and biological properties. Herein, DLC coatings are deposited on four different silicon substrates using a radio frequency plasma‐assisted chemical vapor deposition (RF‐PECVD) technique. The structure and mechanical properties of DLC coatings deposited on different types of silicon substrates under different powers are compared. The surface morphology of the samples is characterized by scanning electron microscopy. The surface roughness of DLC films deposited on different silicon substrates is measured by scanning probe microscopy (SPM). The structural changes of the coatings are investigated by visible Raman spectroscopy. The analysis of DLC films deposited on different silicon substrates reveals that the structure of DLC films deposited on silicon is affected by different crystal directions of silicon substrates (different atomic densities in different crystal directions) and different conduction modes (electronic conduction and hole conduction). Regarding the DLC films deposited on the same substrate, the overall performance of P‐type silicon is better at 150 W, and the overall performance of N‐type silicon is better when the deposition power is 100 W.

In-situ growth mechanism and structural evolution of silicon quantum dots embedded in Si-rich silicon carbide matrix prepared by RF-PECVD

Amorphous silicon-rich silicon carbide (a-SixC1-x) thin films that contain Si quantum dots (QDs) were prepared using radio-frequency plasma-assisted chemical vapor deposition (RF-PECVD) from reactive silane and methane precursor gases at a substrate temperature of 300 °C. The effect of the silane-to-methane flow ratio on the structural properties of the Si QDs/a-SixC1-x nanocomposite films, is systematically studied by means of high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The obtained results confirm the in-situ formation of Si QDs within the amorphous SiC matrix. Moreover, it is found that the Si crystalline fraction increases from 60.7 to 78.5% with increasing the gas flow ratio. Photoluminescence analyses reveal broader emission spectra which are explained in terms of quantum confinement-related emission corresponding to different QD sizes. Based on the obtained results, the growth mechanisms of Si QDs during the deposition of the a-SixC1-x film and the amorphous-to-crystalline transition are discussed.

Impact of Plasma Pre-Treatment on the Tribological Properties of DLC Coatings on PDMS Substrates.

The processes of the deposition of carbon coatings on PDMS (polydimethylsiloxane) substrates using plasma techniques are widely used in a large number of studies, in applications ranging from electronic to biological. That is why the potential improvement of their functional properties, including tribological properties, seems very interesting. This paper presents an analysis of the impact of plasma pre-treatment on the properties of the produced diamond-like carbon (DLC) coatings, including changes in the coefficients of friction and wear rates. The initial modification processes were performed using two different techniques based on low-pressure plasma (RF PACVD, radio-frequency plasma-assisted chemical vapour deposition) and dielectric barrier discharge (DBD) plasma. The effects of the above-mentioned treatments on the geometric structure of the PDMS surface and its water contact angles and stability over time were determined. The basic properties of the DLC coatings produced on unmodified substrates were compared to those of the coatings subjected to plasma pre-treatment. The most interesting effects in terms of tribological properties were achieved after the DBD process and production of DLC coatings, achieving a decrease in wear rates to 2.45 × 10−8 mm3/Nm. The tests demonstrate that the cross-linking of the polymer substrate occurs during plasma pre-treatment.

Alterations to the adhesion, growth and osteogenic differentiation of human osteoblast-like cells on nanofibrous polylactide scaffolds with diamond nanoparticles

Nanofibrous scaffolds are promising materials for engineering various types of tissues, including bone tissue. The properties of nanofibers for bone tissue engineering can be improved by adding ceramic or carbon nanoparticles, including diamond nanoparticles (DNPs). In this study, poly(l-lactide) (PLLA) nanofibrous membranes reinforced with detonation DNPs (concentration from 0 to 12.28 wt%), provided by the NanoCarbon Research Institute (Japan) under the name NanoAmando®, were prepared by a needle-less electrospinning process. The biocompatibility of these DNP-reinforced PLLA membranes was tested in vitro using two human lines of osteoblast-like cells, MG-63 and Saos-2. Microscopic and biochemical methods were used. In addition, the expression of cell survival markers, focal adhesion proteins and osteogenic markers were studied in both cell types at mRNA level and at protein level. The mitochondrial activity of both cells types decreased with increasing DNP concentration in the PLLA matrix. At the same time, the expression of cyclin D and survivin, i.e. factors supporting cell growth and survival were downregulated on the DNP-loaded PLLA scaffolds, while KLF6, an antiproliferative factor, was often upregulated, at least in MG-63 cells. Thus, loading the nanofibrous polymeric scaffolds with detonation DNPs had rather adverse effects on the behavior of human bone-derived cell lines. These results are mostly in conflict with our earlier studies on poly(lactide-co-glycolide) (PLGA) scaffolds, loaded with DNPs prepared by etching the diamond layer fabricated by radiofrequency plasma-assisted chemical vapour deposition. The cell behavior on DNP-loaded scaffolds is therefore markedly influenced by the origin and the properties of the DNPs.

Morphology, mechanical and tribological properties of hybrid carbon layer fabricated by Radio Frequency Plasma Assisted Chemical Vapor Deposition

Improvement of mechanical properties and simultaneous preservation of corrosion resistance of austenitic steels applied as medical implants is the subject of numerous papers published in the last years.Conventional thermal treatments are eliminated due to susceptibility of this group of materials to elevated temperatures.Commercial solutions allowing modification of austenitic steels implants are based on carbon coatings deposition on theirs surfaces.The authors of publication present results of researches on an innovative solution - hybrid carbon layer created in a single stage process carried out inside a RFPACVD (Radio Frequency Plasma Assisted Chemical Vapour Deposition) reactor. The developed hybrid process allows to create simultaneously a diffusive carbon layer and adhesive carbon coating. Mechanical and tribological tests proved that modified austenitic steels are characterised by increased hardness and wear resistance in comparison to currently applied carbon coatings.

Studies of thermal stability of a-C:H:Si coatings produced by radio-frequency plasma assisted chemical vapour deposition (RF-PACVD) method

Studies of thermal stability of a-C:H:Si coatings produced by radio-frequency plasma assisted chemical vapour deposition (RF-PACVD) method

RF-PACVD of water repellent and protective HMDSO coatings on bell metal surfaces: Correlation between discharge parameters and film properties

Hexamethyldisiloxane (HMDSO) films have been deposited on bell metal using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) technique. The protective performances of the HMDSO films and their water repellency have been investigated as a function of DC self-bias voltage on the substrates during deposition. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. Optical emission spectroscopy (OES) analyses of the plasma during deposition reveal no significant change in the plasma composition within the DC self-bias voltage range of −40 V to −160 V that is used. Raman and X-ray photoelectron spectroscopy (XPS) studies are carried out for film chemistry analysis and indicate that the impinging ion energy on the substrates influences the physio-chemical properties of the HMDSO films. At critical ion energy of 113 qV (corresponding to DC self-bias voltage of −100 V), the deposited HMDSO film exhibits least defective Si–O–Si chemical structure and highest inorganic character and this contributes to its best corrosion resistance behavior. The hardness and elastic modulus of the films are found to be bias dependent and are 1.27 GPa and 5.36 GPa for films deposited at −100 V. The critical load for delamination is also bias dependent and is 11 mN for this film. The water repellency of the HMDSO films is observed to be dependent on the variation in surface roughness. The results of the investigations suggest that HMDSO films deposited by RF-PACVD can be used as protective coatings on bell metal surfaces.

Investigations of the hydrophobic and scratch resistance behavior of polystyrene films deposited on bell metal using RF-PACVD process

Polystyrene films are deposited on bell metal substrates using radiofrequency plasma assisted chemical vapor deposition (RF-PACVD) process. The deposition of polystyrene film is carried out at working pressure of 1.6×10−1mbar and in the RF power range of 20–110W. The hydrophobic and mechanical behaviors of the polystyrene films are studied as a function of RF power. The chemical compositions and surface chemistry of the polystyrene films are investigated using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It is revealed that enhanced cross-linked chemical structure and higher loss of oxygen by peroxy polystyryl radical with increasing RF power results in the formation of polystyrene films with more hydrophobic and scratch resistance behavior. However, extensive destruction of cross-linked chemical structure due to high energetic ion bombardment tends to decrease the hydrophobic and scratch resistance behavior of the polystyrene film deposited at RF power of 110W. Atomic force microscopy (AFM) images show quite uniform and crack free surfaces of the polystyrene films having rms roughness in the range of 0.35–0.87nm. Attempts are made to correlate the characterization results with the parameters that are used for thin film depositions.

Characterization and degradation comparison of DLC film on different magnesium alloys

Recently, magnesium (Mg) alloys have been attracted as biodegradable implants. However, high degradation rate in human body limits its application. Modifying material surfaces with a coating layer is an effective means to control degradation, and biocompatibility. In this study, thin diamond-like carbon (DLC) films were synthesized on different magnesium alloy substrates by radio frequency plasma assisted chemical vapor deposition (RFPACVD). The morphology, composition and structure of the coating layers were investigated with scanning electron microscopy (SEM) with an energy dispersive spectroscopy (EDS), micro-raman spectra (RAMAN), and Atomic force microscopy (AFM). Static contact angle measurement and nanoindentation test were also used to analyze surface properties. The degradation behavior of naked and coated Mg alloy were evaluated in stimulated body fluid (SBF), and DLC layers on different Mg alloy substrates significantly decreased the degradation rate of substrate, which is useful for the biological applications especially in bone tissue and cardiovascular stent.

Studies of radiofrequency plasma deposition of hexamethyldisiloxane films and their thermal stability and corrosion resistance behavior

Hexamethyldisiloxane (HMDSO) films (thickness: 282–929 nm) are prepared by the radiofrequency plasma assisted chemical vapour deposition (RF-PACVD) method using an Ar/HMDSO/O 2 gas mixture. The deposition process is carried out in an RF reactor at a working pressure of 1.2 × 10 −1 mbar and an RF power range of 20–100 W. From the studies on Ar/O 2 and Ar/HMDSO/O 2 discharge characteristics using a self-compensated emissive probe, it is revealed that electrons play an important role in the plasma polymerization of HMDSO monomers. Optical emission spectroscopy (OES) and Fourier transform infrared (FT-IR) spectroscopy show that the plasma deposited HMDSO films tend to be more inorganic in nature at higher RF powers. A film prepared at an RF power of 100 W exhibits more thermal stability and corrosion resistance behavior in comparison to films deposited at lower powers (20–80 W). A correlation of the results obtained from OES and FT-IR analyses with the thermal stability and corrosion resistance behavior of the films has been attempted.

Hemocompatibility of surface-modified, silicon-incorporated, diamond-like carbon films

The hemocompatibility of plasma-treated, silicon-incorporated, diamond-like carbon (Si-DLC) films was investigated. Si-DLC films with a Si concentration of 2 at.% were prepared on Si (100) or Nitinol substrates using a capacitively coupled radiofrequency plasma-assisted chemical vapor deposition method using a mixed gas of benzene (C 6H 6) and diluted silane (SiH 4:H 2 = 10:90). The Si-DLC films were then treated with O 2, CF 4 or N 2 glow discharge for surface modification. The plasma treatment revealed an intimate relationship between the polar component of the surface energy and its hemocompatibility. All in vitro characterizations, i.e. protein absorption behavior, activated partial thromboplastin time measurement and platelet adhesion behavior, showed improved hemocompatibility of the N 2-- or O 2-plasma-treated surfaces where the polar component of the surface energy was significantly increased. Si–O or Si–N surface bonds played an important role in improving hemocompatibility, as observed in a model experiment. These results support the importance of a negatively charged polar component of the surface in inhibiting fibrinogen adsorption and platelet adhesion.

Investigation of anti-corrosion properties of Ti:C gradient layers manufactured in hybrid deposition system

Excellent properties of hard carbon layers and especially, the unique combination of tribological, chemical and physical properties make them a popular coating material for use on surgical prosthesis, biomedical implants, and machine tools. However, their well-known poor adhesion and high internal stress disqualifies them in many possibilities of industrial applications. These drawbacks were improved by deposition of Ti buffer layer. By a combination of Radio Frequency Plasma Assisted Chemical Vapor Deposition (RFPACVD) and DC magnetron sputtering methods, thick carbon films were manufactured on Rex 734 steel. Structure and chemical composition of deposited layers was determined by scanning electron microscope and energy dispersive spectrometer analysis. The main purpose of this work was to determine the corrosion properties of Rex 734 alloy in a typical 0.5 M NaCl solution and to find the influence of Ti:C gradient layers on these properties. Anti-corrosion behavior was measured by the detection of corrosion potential in open circuit and the registration of potentiodynamic characteristics according to Stern–Geary and Tafel methods. Five different types of samples were studied: for full analysis the investigation was conducted for every structural component of the layer: for pure Ti deposited on Rex 734 as well as for Ti containing carbon layer and carbon layer deposited subsequently, and finally the corrosion resistance of Rex 734 steel was measured for comparison. As a result of the investigation it was noticed that the Ti–C interlayer enables to maximize the thickness of DLC films and Ti:C gradient layers have the good influence on the corrosion features of Rex 734 alloy.

A role of parameters in RF PA CVD technology of a-C:N:H layers

Results concerning influence of radio-frequency plasma-assisted chemical vapor deposition (RF PA CVD; 13.56 MHz) processing parameters on a-C:N:H layer deposition are presented in this work. The following parameters have been taken into consideration: substrate temperature, plasma RF generator power, composition of reactive gas mixture, gas pressure and time of deposition. A special interest has been focused on the deposition rate as well as on the structure and chemical composition of layers. The layer thicknesses have been measured and deposition rates evaluated. Structure analysis has been performed with application of FT-IR spectroscopy. The obtained results may serve as a basis in the design of the technology of a-C:N:H layers for various applications.

Effects of plastic strain of diamond-like carbon coated stainless steel on the corrosion behavior in simulated body fluid environment

We have investigated the effect of plastic deformation of diamond-like carbon (DLC) coated and uncoated stainless steel on the corrosion resistance in a simulated body fluid environment to measure its protective efficiency as a biomedical coating material. We deposited the DLC film on 304 stainless steel specimens by radio frequency plasma assisted chemical vapor deposition(R.F.-PACVD) method, followed by a tensile test to apply plastic strain on the coated specimen. Corrosion behavior in the simulated body fluid environment was studied by a potentiodynamic polarization test. As the tensile deformation progressed, the cracks of the film were observed to be perpendicular to the tensile axis. Further deformation increased both cracking and the spallation. Estimated porosity and corrosion current density increased, and thus the protective efficiency decreased at a strain of 2%. In spite of the degradation, the anti-corrosion properties were significantly improved relative to the uncoated stainless steel. However, a significant increase in porosity and corrosion current density was observed at a strain of 4%. This study showed that increasing the thickness of the Si interlayer of film improved the corrosion resistance with reduction of spallations and cracks.

Deformation behaviour of DLC coatings on (111) silicon substrates

The deformation mechanisms operating in diamond-like carbon (DLC) coatings on (111) silicon substrates have been investigated. A hydrogenated amorphous carbon coating of ∼ 500 nm thickness was deposited by radio-frequency plasma-assisted chemical-vapour deposition onto a (111) oriented silicon substrate. Indentations were performed on the coatings using a spherical indenter with a radius of 5 μm for various loads up to a maximum of 150 mN. The coatings exhibited substantial elastic recovery on unloading. Minor pop-ins appeared for loads above 100 mN and a distinct pop-out was observed following indentation to 150 mN. Focused ion beam microscopy of cross-sections through the indentations revealed localized plastic compression of the coating beneath the indenter and bending at the coating-substrate interface. Although the coating was free from cracking or delamination, the substrate showed evidence of median cracks and lateral cracks for loads above 100 mN. Cross-sectional transmission electron microscopy examination of indentations revealed cracks in the coating, as well as cracks, crystalline defects and a transformation zone in the silicon substrate. These observations have been correlated with the deformation behaviour of the coating-substrate composite.

FRACTURE CHARACTERISTICS OF DLC ON SILICON USING NANO-INDENTATION AND FEA

In this study, using the nano and micro-indentation tests and finite element analysis (FEA), we investigated the fracture behaviors of diamond like carbon (DLC) on silicon in indentation state. Diamond like carbon coating of 3μm and 1.5μm thickness were deposited on polished (100) single crystal silicon substrates by radio frequency plasma assisted chemical vapor deposition (RF-PACVD), respectively. Fracture toughness of DLC films was calculated from the measured lengths of the cracks formed by nano and micro-indentation on each sample. We used various equations such as Lawn's and Liang's equation to calculate the fracture toughness. The effective fracture toughnesses of these DLC films were 1.2 ~1.3 MPam 0.5, calculated by Lawn's and Liang's equations. The true fracture toughness of DLC on silicon, excluding the portion of fracture toughness due to a substrate, was determined to be 4.0~5.1 MPam 0.5. DLC films with crack initiation and propagation were analyzed by finite element method.

Elastic modulus and structural evolution of diamond-like carbon films deposited by RF-PACVD

Dependence of the elastic modulus of diamond-like carbon (DLC) films on film thickness was investigated by the recently suggested free overhang method. The DLC films of thickness ranging from 50 to 1300 nm were deposited on Si (100) wafer by 13.56-MHz radio frequency plasma assisted chemical vapor deposition (RF-PACVD) process. In the free overhang method, the elastic modulus of thin film could be measured without considering the substrate effect since the substrate was completely excluded from the measurement. It was observed that the elastic modulus of the very thin film was smaller than that of the thick film in both cases where the ion energy was higher and lower than the optimum value for dense and hard DLC film deposition. However, at the optimum ion energy, the elastic modulus was independent of film thickness. Raman spectroscopy analysis showed that the change of elastic modulus in very thin DLC films was intimately related to the structural evolution which occurred in the initial stage of the film deposition. When the ion energy was lower than the optimum value, more polymeric component was deposited in the initial stage. On the other hand, a more graphitic component was involved in very thin films at an ion energy higher than the optimum value.

BCN coatings on polymer substrates by plasma CVD at low temperature

An overview is given of the plasma-assisted techniques for coating ceramics on polymer substrates at low temperature. Deposition of boron carbon nitride was carried out on polycarbonate substrates by a radio-frequency plasma-assisted chemical vapor deposition process using different metallo-organics as precursors. The films deposited were found to be stable and adherent under ambient conditions. The chemical composition of the layers varied in a wide range. Nearly stoichiometric BCN layers, as well as films with a high carbon content, were obtained. The chemical bonding of boron, carbon and nitrogen was analyzed by X-ray photoelectron spectroscopy. The deposited films have a high transparency (90%) in the ultraviolet–visible region. The transmission depends on the layer thickness and on the precursor used. The coatings have a hardness of up to 1500 HK0.005.

Surface conditioning of chemical vapor deposited hexagonal boron nitride film for negative electron affinity

The surface conditions favoring a negative electron affinity (NEA) on hexagonal boron nitride (h-BN) grown by radio-frequency plasma-assisted chemical vapor deposition (CVD) have been investigated by ultraviolet photoelectron spectroscopy. The NEA condition on the h-BN film appears to be resistant to oxygen-plasma or in-vacuo atomic oxygen treatment. It is not certain whether the segregation of bulk hydrogen onto the surface helps to promote the NEA; the depth profile of the deposited film reveals about 0.01%–0.1% atomic concentration of hydrogen. High temperature annealing at 1100 °C results in a positive electron affinity surface (PEA). Reexposure of PEA surface to atomic hydrogen at room temperature regenerates the NEA condition. This is evident of the role of superficial hydrogen in promoting NEA on the h-BN film.