Radio-frequency Plasma-enhanced Chemical Vapor Research Articles

Structural, mechanical and tribological characterizations of a-C : H : Si films prepared by a hybrid PECVD and sputtering technique

a-C : H : Si films were prepared under different CH4/Ar ratios by a hybrid radio frequency plasma-enhanced chemical vapour deposition (RFPECVD) and unbalanced magnetron sputtering technique. Characterizations showed that the CH4/Ar ratio affected not only the content but also the chemical state of the doped Si, thus further affecting the microstructures, mechanical and tribological performances of the a-C : H : Si films. Generally, when the CH4/Ar ratio was low (⩽4/2), the Si-doping content dropped with increased CH4 percentage, accompanied by a decreased sp3(C–Si+C–C)/sp2(C=C), increased ID/IG ratio and up-shift of the G peak position, as can be seen from the Raman spectra, while at a higher CH4 percentage (e.g. CH4/Ar = 5/2), the prepared a-C : H : Si films exhibited a series of aberrant properties due to the incorporation of abundant H and the high oxidization of the doped Si. Another unique characteristic of our films was the presence of numerous Si–Si bonds at high Si content, which was not observed in the a-C : H : Si films produced by the decomposition of Si-containing gaseous precursors. Moreover, although Si incorporation improved such properties of the DLC films as adhesion strength, internal stress and tribological moisture sensitivity, its effectiveness in enhancing the mechanical and tribological performances were governed not by the Si-doping content or sp3-C fraction but by the film continuity or adhesion (minimized interlinking destruction by the Si–H, C–H, Si–O–Si bonds) and sp2(C=C) fraction (based on the film continuity).

Large-grained and Highly-ordered Graphene Synthesized by Radio Frequency Plasma-enhanced Chemical Vapor Deposition

We have synthesized a very thin graphite film on polycrystalline Ni foil using radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at relatively low temperature. Structural analysis through electron diffraction and Raman spectroscopy demonstrated that the PECVD grown graphite film consists of large grains sized over tens of microns and is highly ordered structure exhibiting Bernal stacking despite of low synthetic temperature of 850oC. Accordingly, the high carrier mobility of 4,500 cm2/Vsec was obtained at room temperature from a monolayer of PECVD grown graphene, which is higher than any reported value of CVD-grown graphene.

Large-grained and Highly-ordered Graphene Synthesized by Radio Frequency Plasma-enhanced Chemical Vapor Deposition

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Gas barrier properties of diamond-like carbon films coated on PTFE

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapour deposition (PE-CVD). Before the DLC coating, the PTFE substrate was modified with a N 2 plasma pre-treatment to enhance the adhesive strength of the DLC to the substrate. The influences of the N 2 plasma pre-treatment and process pressure on the gas permeation properties of these DLC-coated PTFE samples were investigated. In the Raman spectra, the G peak position shifted to a lower wave number with increasing process pressure. With scanning electron microscopy (SEM), a network of microcracks was observed on the surface of the DLC film without N 2 plasma pre-treatment. The density of these cracks decreased with increasing process pressure. In the film subjected to a N 2 plasma pre-treatment, no cracks were observed at any process pressure. In the gas barrier test, the gas permeation decreased drastically with increasing film thickness and saturated at a thickness of 0.2 μm. The DLC-coated PTFE with the N 2 plasma pre-treatment exhibited a greater reduction in gas permeation than did the samples without pre-treatment. For both sample types, gas permeation decreased with increasing process pressure.

Synthesis of carbon nanotubes on diamond-like carbon by the hot filament plasma-enhanced chemical vapor deposition method

Carbon nanotubes (CNTs) have attracted considerable attention as possible routes to device miniaturization due to their excellent mechanical, thermal, and electronic properties. These properties show great potential for devices such as field emission displays, transistors, and sensors. The growth of CNTs can be explained by interaction between small carbon patches and the metal catalyst. The metals such as nickel, cobalt, gold, iron, platinum, and palladium are used as the catalysts for the CNT growth. In this study, diamond-like carbon (DLC) was used for CNT growth as a nonmetallic catalyst layer. DLC films were deposited by a radio frequency (RF) plasma-enhanced chemical vapor deposition (RF-PECVD) method with a mixture of methane and hydrogen gases. CNTs were synthesized by a hot filament plasma-enhanced chemical vapor deposition (HF-PECVD) method with ammonia (NH 3) as a pretreatment gas and acetylene (C 2H 2) as a carbon source gas. The grown CNTs and the pretreated DLC films were observed using field emission scanning electron microscopy (FE-SEM) measurement, and the structure of the grown CNTs was analyzed by high resolution transmission scanning electron microscopy (HR-TEM). Also, using energy dispersive spectroscopy (EDS) measurement, we confirmed that only the carbon component remained on the substrate.

Infrared analysis on hydrogen content and Si—H bonding configuration of hydrogenated nanocrystalline silicon thin films

Hydrogenated silicon films were prepared by conventional radio frequency plasma-enhanced chemical vapor phase deposition technique at a high deposition rate at temperatures from 100 to 350℃, which were studied by Fourier transform infrared spectrum and Raman scattering spectrum. The results showed that the hydrogen content and the silicon-hydrogen bonding configurations of the films were closely related to their crystallization properties. When the films changed from amorphous to nanocrystalline phase, the hydrogen content decreased by over a half, and the Si—H bonding configuration was mainly SiH2. With the increase of substrate temperature and crystallinity, the hydrogen content and the structural factor of the nanocrystalline silicon films was reduced gradually.

20310 CVD法により作製されたフッ素添加DLC膜のタンパク質吸着特性評価(人工臓器と医用工学(3),OS.8 人工臓器と医用工学)

Fluorinated diamond-like carbon (F-DLC) films were deposited on polytetrafluoroethylene (PTFE) using radio frequency (RF) plasma-enhanced chemical vapor deposition (CVD) by changing the ratio of tetrafluoromethane (CF4) and methane (CH4). To enhance the adhesion strength of the F-DLC to the PTFE substrate, the PTFE surface was modified with a N2 plasma pre-treatment. In the pull-out test, the strength of the F-DLC film without the N2 plasma pre-treatment increased with the CF4 ratio. In contrast, in the case with the N2 plasma pre-treatment, the adhesion strength of the F-DLC film decreased with an increasing CF4 ratio. Regarding the adsorption of albumin and γ-globulin, the amount of adsorbed albumin on the film decreased with an increasing CF4 ratio, and the amount of adsorbed γ-globulin increased with the CF4 ratio. The CF4-0% DLC film showed the most adsorbed albumin and the least adsorbed γ-globulin. This result suggests that the DLC film without fluorine had better antithrombogenecity than the F-DLC film.

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

Films of diamond-like carbon containing up to 39.2 at.% fluorine (F-DLC) were deposited on silicon substrates by radio frequency plasma-enhanced chemical vapour deposition (rf PECVD). A mixture of acetylene (C 2H 2) and carbon tetrafluoride (CF 4) was used for the deposition of F-DLC films. The influence of fluorine content on self-bias voltage, deposition rate, and composition, bonding structure, surface energy, hardness, stress and surface roughness were investigated and correlated with fluorine content. The deposition rate was found to decrease linearly with increasing CF 4 in the plasma due to the higher density of F +. X-ray photoelectron spectroscopy (XPS) analysis revealed the presence C–C, C–CF and C–F for F-DLC films with low fluorine concentration (6.5 at.%), however for films with higher fluorine content (20.7 at.% and 39.2 at.%) an additional peak due to CF 2 bonding was detected. The Raman G-band peak position shifted to higher frequency and can be attributed to the increased amount of sp 2 bonds. Ion scattering spectrometry (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 surface energy was found to reduce 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. The addition of fluorine into the DLC film resulted in lower stress and hardness values. The work of adhesion of the surface of the films for Pseudomonas aeruginosa bacteria was estimated to increase with fluorine content, which is indicative of an improved antibacterial activity for F-DLC films.

Polyethylene Oxide Films Polymerized by Radio Frequency Plasma-Enhanced Chemical Vapour Phase Deposition and Its Adsorption Behaviour of Platelet-Rich Plasma

We present polyethylene oxide (PEO) functional films polymerized by rf plasma-enhanced vapour chemical deposition (rf-PECVD) on p-Si (100) surface with precursor ethylene glycol dimethyl ether (EGDME) and diluted Ar in pulsed plasma mode. The influences of discharge parameters on the film properties and compounds are investigated. The film structure is analysed by Fourier transform infrared (FTIR) spectroscopy. The water contact angle measurement and atomic force microscope (AFM) are employed to examine the surface polarity and to detect surface morphology, respectively. It is concluded that the smaller duty cycle in pulsed plasma mode contributes to the rich C-O-C (EO) group on the surfaces. As an application, the adsorption behaviour of platelet-rich plasma on plasma polymerization films performed in-vitro is explored. The shapes of attached cells are studied in detail by an optic invert microscope, which clarifies that high-density C-O-C groups on surfaces are responsible for non-fouling adsorption behaviour of the PEO films.

Superlow friction behavior of Si-doped hydrogenated amorphous carbon film in water environment

Si-doped hydrogenated amorphous carbon (a-C:H:Si) film was prepared using hybrid radio frequency plasma-enhanced chemical vapor deposition (R.F. PECVD) and non-balanced magnetron sputtering deposition technique. The microstructure of the film was characterized by means of Raman spectrometry, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), while its friction behavior in water environment was investigated using a ball-on-disc tribometer. Results show that the a-C:H:Si film has typical diamond-like characteristics, and Si doped with a relative atomic concentration of about 3.9% in the film mainly exists in the form of Si, SiC, and SiO 2, while it shows a superlow friction coefficient of about 0.005 in water environment when sliding against Si 3N 4 ball. The superlow friction behavior of the hybrid diamond-like-carbon (DLC) film could be attributed to the formation of a tribochemical reaction film and boundary lubrication layer mainly consisting of colloidal silica generated from tribochemical reactions between silicides and water molecules.

Amorphous hollow carbon spheres synthesized using radio frequency plasma-enhanced chemical vapour deposition

We report a method to synthesize amorphous hollow carbon spheres, with diameters ranging from 100 to 800 nm, which are dispersed among bent graphitized carbon nanotubes using radio frequency plasma-enhanced chemical vapour deposition in mixed CH4/H2 gases. The products are characterized by techniques including scanning electron microscopy, energy-dispersive x-ray spectroscopy, Raman spectroscopy and transmission electron microscopy. It is found that MgO and Ni nanoparticles together with hydrogen play important roles in the formation of the spheres. A possible formation mechanism for the carbon composites has been proposed.

Horizontally directed growth of carbon nanotubes utilizing self-generated electric field from plasma induced surface charging

Plasma induced surface charging during carbon nanotube (CNT) growth via radio frequency plasma-enhanced chemical vapor deposition is exploited to direct the growth in a horizontal direction on a device substrate without the need for external biasing arrangements. Using a silicon-on-insulator substrate, a pair of electrodes is fabricated in which one electrode is shorted to the handle layer and the other is left floating. A potential difference results from the plasma, and creates a lateral electric field between the electrodes that is used to direct the growth of CNTs. The approach allows for wafer-scale growth of laterally aligned CNTs.

Radio Frequency Power Dependence in Formation of SiO:CH Thin Films by Plasma-Enhanced Chemical Vapor Deposition

SiO:CH films were prepared by capacitively coupled radio frequency (RF) plasma-enhanced chemical vapor deposition to investigate the dependence on RF power on the basis of plasma reactions and film properties. The RF power dependence can be divided into two broad categories, the reaction-controlled regime (regime R) and the flow rate-controlled regime (regime F). In the regime R, the introduced RF power initially dissociates and recombines the trimethylmethoxysilane reactant, and leads to drastic increase in deposition rate. In the regime F, the insufficient flow of reactants saturates the deposition rate. Moreover, the extra energy dissociates and recombines the reactant drastically and heats electrons in the plasma.

Effect of deposition pressure on the adhesion and tribological properties of a-CN x H films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CNxH films) was deposited on n-type single-crystal Si (100) by direct current radio frequency plasma-enhanced chemical vapor deposition (DC-RF-PECVD), under the working pressure of 5.0–17.0 Pa, using the CH4 and N2 as feedstock. The composition and surface morphology of the a-CNxH films were characterized by means of Raman spectroscopy and atomic force microscopy, while the Young’s modulus, elastic recovery, adhesion strength, and tribological properties were evaluated using nano-indentation, scratch test and friction test system. It was found that the surface roughness and Raman spectra peak intensity ratio ID/IG of the films increased with the increase of working pressure, while the Young’s modulus, elastic recovery and adhesion strength of the films significantly decreased. Moreover, the tribological properties of the films also varied with the working pressure. The wear life sharply increased with the increase of working pressure from 5.0 Pa to 7.5 Pa, further, an increase in the deposition pressure led to a gradual decrease in the wear life, consequently, the a-CNxH film deposited at 7.5 Pa exhibited the longest wear life. The deposition pressure seemed to have slight effect on the average friction coefficients, whereas the surface roughness and adhesion strength have deteriorated with increasing deposition pressure.

Synthesis and mechanical properties of carbon nanotube/diamond-like carbon composite films

Diamond-like carbon (DLC) coatings were successfully deposited on carbon nanotube (CNT) films with CNT densities of 1 × 10 9/cm 2, 3 × 10 9/cm 2, and 7 × 10 9/cm 2 by a radio frequency plasma-enhanced chemical vapor deposition (CVD). The new composite films consisting of CNT/DLC were synthesized to improve the mechanical properties of DLC coatings especially for toughness. To compare those of the CNT/DLC composite films, the deposition of a DLC coating on a silicon oxide substrate was also carried out. A dynamic ultra micro hardness tester and a ball-on-disk type friction tester were used to investigate the mechanical properties of the CNT/DLC composite films. A scanning electron microscopic (SEM) image of the indentation region of the CNT/DLC composite film showed a triangle shape of the indenter, however, chippings of the DLC coating were observed in the indentation region. This result suggests the improvement of the toughness of the CNT/DLC composite films. The elastic modulus and dynamic hardness of the CNT/DLC composite films decreased linearly with the increase of their CNT density. Friction coefficients of all the CNT/DLC composite films were close to that of the DLC coating.

Microstructure and mechanical properties of Ti-Si-C-N films synthesized by plasma-enhanced chemical vapor deposition

A systematic investigation of the microstructure and mechanical properties of Ti-Si-C-N films was conducted as a function of Si contents. The Quaternary Ti-Si-C-N films were synthesized on AISI 304 stainless steel and Si wafer by Radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using a gaseous mixture of TiCl 4, SiH 4, CH 4, Ar, N 2, and H 2. The substrate temperature during film growth was maintained constant at 600 °C. The Si addition into Ti-C(0.6)-N(0.4) film resulted in microstructure and mechanical modification, i.e., a crystal phase of Ti(C,N) diminished and an amorphous phase of Si 3N 4/SiC appeared. The quaternary Ti-Si(9.2 at.%)-C-N film had a fine composite microstructure consisting of nano-sized Ti(C,N) crystallites surrounded by the amorphous phase of Si 3N 4/SiC. The microhardness of the film increased from ∼ 24 GPa for Ti-C-N film and reached to a maximum hardness of ∼ 46 GPa for Ti-Si(9.2at.%)-C-N film. In addition, the average friction coefficient of the Ti-Si-C-N films largely decreased with increasing Si content.

A Comparison of the Surface Properties of DLC and Nanocrystalline Diamond

Diamond-like carbon (DLC) films have been deposited by radio frequency plasma enhanced chemical vapour deposition (rf-PECVD) with different Ar-CH4 mixtures. Nanocrystalline diamond films have been deposited by microwave plasma-enhanced chemical vapour deposition (MPCVD), using Ar-H2-CH4 mixtures. X-ray photoelectron spectroscopy (XPS) and nanotribological investigation (by scanning force microscopy) have been used to compare the mechanical properties and structures of these films. Highly orientated and non-orientated microcrystalline diamond films and MPCVD-produced amorphous carbon have also been studied by way of comparison. The diamond films exhibit a linear relationship between roughness and the coefficient of friction. The DLC and amorphous carbon have higher friction coefficients than the best performing diamond film, but may more easily be deposited as smooth coating. Possible applications for these various carbon-based films include microelectromechanical components, for which smooth, hard coatings are required.

STRUCTURAL AND OPTICAL CHARACTERIZATION OF BORON–NITROGEN-DOPED AMORPHOUS CARBON FILMS DEPOSITED BY r.f. PECVD

Boron–nitrogen-doped amorphous carbon (a-C:H:B:N) films have been deposited onto glass and n-type Si(100) substrates by radio frequency (r.f.) plasma-enhanced chemical vapor deposition at a frequency of 13.56 MHz at room temperature using CH 4 as precursor of carbon source and H2 as a carrier gas. The film deposition was performed in the presence of crystalline boron source at different flow rates of 0, 6, 8, 10, 12 sccm of nitrogen under constant r.f. power and fixed partial pressure of mixed CH 4, N 2, and H 2 gases. Effects of boron and nitrogen doping on the bonding states, growth kinetics and optical properties of the as-deposited films have been examined by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The experimental results show that the incorporation of boron and nitrogen has a considerable effect on the properties of the deposited films. FTIR spectra show that the nitrogen is bonded to carbon and hydrogen as C=N , N–H and C–H bonding configurations in the as-deposited film. The incorporation of boron and nitrogen shifts the G-peak towards the higher wave number and an increase in the I D /I G ratio demonstrating the graphitic character of the a-C:H:B:N films. Optical band gap is found to be reduced from 1.62 to 1.35 eV with the increase in nitrogen concentration in the presence of boron.

Diamond nanocrystals and amorphous SiO x nanowires formed by rapid thermal annealing of carbon film

Rapid thermal annealing (RTA) has been performed on the carbon films prepared by radio frequency plasma-enhanced chemical vapor deposition on Si substrate. The RTA at 800 °C for 60 s leads to the formation of many diamond nanocrystallites agglomerating on the film surface. Higher temperature RTA at 1100 °C for 60 s induces the high-density amorphous SiO x ( x = 1.2) nanowires on the film surface without diamond nanocrystallites. At both the RTA temperatures, a well-oriented SiC interlayer is also formed simultaneously. The sp 3 sites in the carbon film and the oxygen during the RTA treatment as well as the RTA temperature are considered to play important roles in determining the final reaction products.

An examination of trace surface on diamond-like carbon film after ball-on disk measurement

Hydrogenated diamond-like carbon (DLC) films were prepared by the radio frequency plasma-enhanced chemical vapor deposition method on silicon substrates using methane (CH 4) and hydrogen (H 2) gas. The wear track on DLC films was examined after the ball-on disk (BOD) measurement with a Raman mapping method. The BOD measurement of DLC films was performed for 1 to 3 h with a 1-hour step time. The sliding traces on the hydrogenated DLC film after the BOD measurement were also observed using an optical microscope. The films synthesized in this work had a very low friction coefficient (about 0.06) and were adhered very well without peeling off during the BOD measurement even with very thin thickness. Energy dispersive X-ray spectra show the decrease of C atomic % and the increase of O atomic % according to the sliding time. The novel Raman mapping method effectively showed the graphitization of DLC films according to the sliding time.