Radio-frequency Plasma-enhanced Chemical Vapor Deposition Research Articles

Three elements for the preparation of vertical graphene by RF-PECVD method

Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) is one of the high-efficiency technologies for controlling the preparation of regular vertical graphene and has gained increased attention in recent years. Combined with the current development, the three elements of carbon source/carrier gas/substrate are reviewed for the preparation of vertical graphene by RF-PECVD. The selection and control of carbon source/carrier gas (reactive gas/protective gas/doping gas), the conditions required for preparation, and different growth substrates used by RF-PECVD technology are summarized to provide guidance for further screening of preparation elements. Results reveal the effects of preparation elements on the final application direction of vertical graphene and the important influence of control parameters in various application fields on the final performance of the vertical graphene material. In addition, the growth mechanism of vertical graphene is discussed under the premise of the existing RF-PECVD technology. The challenges and future perspectives are also highlighted to promote the preparation of vertical graphene by radio frequency method.

Characterising a Custom-Built Radio Frequency PECVD Reactor to Vary the Mechanical Properties of TMDSO Films.

Plasma-polymerised tetramethyldisiloxane (TMDSO) films are frequently applied as coatings for their abrasion resistance and barrier properties. By manipulating the deposition parameters, the chemical structure and thus mechanical properties of the films can also be controlled. These mechanical properties make them attractive as energy adsorbing layers for a range of applications, including carbon fibre composites. In this study, a new radio frequency (RF) plasma-enhanced chemical vapour deposition (PECVD) plasma reactor was designed with the capability to coat fibres with an energy adsorbing film. A key characterisation step for the system was establishing how the properties of the TMDSO films could be modified and compared with those deposited using a well-characterized microwave (MW) PECVD reactor. Film thickness and chemistry were determined with ellipsometry and X-ray photoelectron spectroscopy, respectively. The mechanical properties were investigated by nanoindentation and atomic force microscopy with peak-force quantitative nanomechanical mapping. The RF PECVD films had a greater range of Young’s modulus and hardness values than the MW PECVD films, with values as high as 56.4 GPa and 7.5 GPa, respectively. These results demonstrated the varied properties of TMDSO films that could in turn be deposited onto carbon fibres using a custom-built RF PECVD reactor.

Influence of different Ni nanolayers thicknesses on single oscillator model parameters, optical band gap, and disordering energy in CNTs synthesized by Cu‐Ni @ a‐CH catalyst

In this paper, Cu‐Ni NPs @ a‐C:H thin films with different Ni layers thickness by co‐deposition of RF‐sputtering and RF‐plasma enhanced chemical vapor deposition (RF‐PECVD) were prepared using acetylene gas and Ni and Cu targets. The absorption edge and the optical dispersion parameters in CNTs synthesized by Cu‐Ni @ a‐C:H catalyst were studied. RBS measurements were performed, which confirmed the presence of Ni and Cu atoms in these films. Using Atomic Force Microscopy (AFM) system, the morphology of the films surface was investigated. The average diameter of the grown CNTs on Ni‐Cu NPs @ a‐C:H substrates were increased by increasing of Ni layers thickness. The values of dT/dλ and dR/dλ for grown CNTs without Ni show that the minimum value of the optical band gap corresponds to values of 2.55 and 2.56 eV, respectively. The absorption spectra peaks of films are about 400‐600 nm. These peaks are quite sharp for carriers band to band transitions and with increasing Ni layers thickness, there is a small shift. It can be seen that the dispersion energy Ed and the oscillator strength 𝑓 of CNTs synthesized by Cu‐Ni @ a‐C:H catalyst had the lowest values of 2.21 eV and 9.39 eV2, respectively, compared to the other films.

Effect of thermodynamic parameters on properties of silicon-carbon films prepared by radio-frequency plasma-enhanced chemical vapor deposition for anti-reflective and photo-luminescent coatings

This work reports an experimental study on the synthesis of hydrogenated amorphous silicon-carbon (a-SiC:H) films with improved antireflective and photo-luminescent characteristics. These films were prepared by plasma-enhanced chemical vapor deposition at a radio frequency of 13.56 MHz, varying the thermodynamic parameters of pressure, gas flows, and temperature. Silane (SiH4), methane (CH4), and hydrogen (H2) were the precursor gases. In a first experiment, composition in gas phase was varied and correlated to the composition in solid phase. Absorption spectra, conductivity, refractive index, optical gap, and photoluminescence (PL) were analyzed. Optical gap and fraction of carbon in gas phase showed a linear dependence with the atomic fraction of carbon in solid phase. Results indicated that the Si0.4C0.6 alloy exhibited a high PL as well as an optimal combination of optical gap and refractive index to be applied as antireflective coating. The subsequent optimization of PL was carried out by a fractional experiment, by varying pressure, H2 flow, and temperature. Results revealed that PL can be improved at high pressure, without H2 flow, and low temperature during glow discharge. Enhancement of PL was correlated to the proper concentration of silicon and carbon in the films, low dark conductivity, negative AM 1.5 conductivity, fluctuating current at low voltage, the increment of Si−H2, C−H2, and C=C bonds, along with vibrational energies in the range of 3190–3585 cm−1.

Duplex treatment of active screen plasma nitriding and amorphous hydrogenated carbon coating

Active screen plasma nitriding (ASPN) has recently emerged as an alternative nitriding technology with the potential to eliminate problems such as edge effect, arcing, and hollow cathode effects, associated with conventional direct current plasma nitriding technology. Amorphous hydrogenated carbon (a-C:H) is a thin film characterized by high hardness, a low friction coefficient, and superior wear resistance. However, the high residual stress of the a-C:H leads to poor adhesion between the a-C:H film and substrate. This study's objective was to investigate the properties of samples obtained by a duplex treatment (i.e., ASPN and a-C:H coating) of SUS304 austenitic stainless steel. The ASPN treatment was performed in 25% N2 + 75% H2 atmosphere for 5 h at 673 K under 600 Pa. An a-C:H film was coated using RF plasma-enhanced chemical vapor deposition in the presence of methane for 90 min. The results indicated that an a-C:H film with an S-phase interlayer formed after the duplex treatment of ASPN and a-C:H coating. Moreover, this treatment improved the adhesion and wear properties of the resulting sample.

Nucleation and growth dynamics of graphene grown by radio frequency plasma-enhanced chemical vapor deposition

We investigated the nucleation and grain growth of graphene grown on Cu through radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at different temperatures. A reasonable shielding method for the placement of copper was employed to achieve graphene by RF-PECVD. The nucleation and growth of graphene grains during PECVD were strongly temperature dependent. A high growth temperature facilitated the growth of polycrystalline graphene grains with a large size (~ 2 μm), whereas low temperature induced the formation of nanocrystalline grains. At a moderate temperature (790 to 850 °C), both nanocrystalline and micron-scale polycrystalline graphene grew simultaneously on Cu within 60 s with 50 W RF plasma power. As the growth time increased, the large graphene grains preferentially nucleated and grew rapidly, followed by the nucleation and growth of nanograins. There was competition between the growth of the two grain sizes. In addition, a model of graphene nucleation and grain growth during PECVD at different temperatures was established.

Anomalous characteristics of nanostructured hydrogenated carbon thin films

Hydrogenated diamond-like carbon (DLC) films are sought for several technological applications including electronics, optics, mechanics, and tribology. However, conventional hydrogenated DLC films, that commonly deposit at low base pressure (~10−5 to 10−8 Torr), have many intrinsic limitations in terms of moderate hardness (15–25 GPa), low electrical conductivity (in insulating regime), and they display amorphous morphology. Here we develop high-performance hydrogenated carbon-based films using a cost-effective and fast deposition approach. We report the room temperature synthesis of nitrogen incorporated nanostructured hydrogenated carbon films (n-C:N:H) at a high base pressure of ~5 × 10−3 Torr, employing a non-conventional radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) system equipped with only a primary pump. The n-C:N:H films show appealing properties such as wide band gap (2.35–2.9 eV), high optical transparency, high hardness (up to ~ 40 GPa), ultrahigh elasticity (elastic recovery ~95%), reasonably good electrical conductivity, and diode-like behavior when examined in n-C:N:H/Si heterojunction device configuration. Interestingly, some of n-C:N:H films revealed the multifunctional activities with properties surpassing to those of many low base pressure grown traditional amorphous DLC films. This discovery solves many fundamental concerns of hydrogenated DLC films and opens new paths for their enhanced commercial applications.

Multifractal investigation of Ag/DLC nanocomposite thin films

The objective of this study is the experimental investigation of the silver in diamond-like carbon (Ag/DLC) nanocomposite prepared by the co-deposition of radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) and RF-sputtering. Atomic force microscopy (AFM), X-ray diffraction analyses, ultraviolet–visible (UV–visible) spectroscopy measurements were applied to describe the three-dimensional surface texture data in connection with the statistical, and multifractal analyses. Additional information about structure–property relationships in prepared Ag/DLC nanocomposite was studied in detail to allow a better understanding of the surface micromorphology. The performed analysis revealed the studied samples have multifractal properties and can be included in novel algorithms for graphical representation of complex geometrical shapes and implemented in computer simulation algorithms.

Research on the fabrication and anti-reflection performance of diamond-like carbon films

In this work, a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system has been employed to fabricate diamond-like carbon (DLC) films for the application in crystalline silicon solar cells. The morphological, structural and optical properties of the synthesised DLC films were investigated under different deposition times, different plasma discharge powers, different CH4 flow rates, and different substrate temperatures, respectively. It is shown that, when the plasma discharge power was 100 W, the CH4 flow rate was 60 sccm, and the substrate temperature was 100 °C, the synthesised DLC film features a high transmittance of 95%, a low surface reflectivity of approximately 14%, a wide optical band gap of 2.6 eV, as well as a uniform and dense texture. Subsequently, the DLC films with different thicknesses were grown on the surface of crystalline silicon solar cells as anti-reflection coatings. The solar cell current-voltage characteristic testing system was used to investigate the change of solar cell performance parameters, i.e., Jsc, Voc, FF and η. After the growth of a DLC film with a deposition time of 20 min on the surface of a crystalline silicon solar cell, the photovoltaic conversion efficiency of the solar cell increases from 4.12% to 5.2%. This work demonstrates that the DLC film has a promising application potential as an anti-reflection layer in crystalline silicon solar cells.

Highly Conductive Nitrogen-Doped Vertically Oriented Graphene toward Versatile Electrode-Related Applications.

The direct growth of vertically oriented graphene (VG) on low-priced, easily accessible soda-lime glass can propel its applications in transparent electrodes and energy-relevant areas. However, graphene deposited at low temperature (∼600 °C) on the catalysis-free insulating substrates usually presents high defect density, poor crystalline quality, and unsatisfactory electrical conductivity. To tackle this issue, we select high borosilicate glass as the growth substrate (softening point ∼850 °C), which can resist higher growth temperature and thus afford higher graphene crystalline quality, by using a radio-frequency plasma-enhanced chemical vapor deposition (rf-PECVD) route. A nitrogen doping strategy is also combined to tailor the carrier concentration through a methane/acetonitrile-precursor-based synthetic strategy. The sheet resistance of as-grown nitrogen-doped (N-doped) VG films on high borosilicate glass can thus be lowered down to ∼2.3 kΩ·sq-1 at a transmittance of 88%, less than half of the methane-precursor-based PECVD product. Significantly, this synthetic route allows the achievement of 30-inch-scale uniform N-doped graphene glass, thus promoting its applications as excellent electrodes in high-performance switchable windows. Additionally, such N-doped VG films were also employed as efficient electrocatalysts for electrocatalytic hydrogen evolution reaction.

3D-graphene-laser patterned p-type silicon Schottky diode

The influence of the laser patterning (LP) process on the quality of graphene (Gr) film and Schottky diode characteristics was researched in this study. First of all, p-type silicon (Si) was patterned by homemade femtosecond laser source. To compare the resulting effect, non-patterned n-Si and p-Si were used as substrates. To achieve vertically oriented three-dimensional (3D) Gr nanosheets (VGNs) onto the laser patterned p-type Si, non-patterned n-Si, and p-Si substrates, we used Radio-Frequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) technique. Then, Raman analyses for VGNs obtained on patterned and non-patterned p-Si and n-Si substrates were conducted. All results indicate that the Gr obtained on all substrates is vertically oriented. Scanning electron microscopy (SEM) analyses were also performed to obtain information about the morphological properties of the 3D Gr structure. In addition, the influence of the laser patterning at the Gr-Si interface was evaluated by comparing two sets of devices which are junctions of Gr-Laser Patterned Si (Gr-LPSi) and Gr-Insulator-Silicon (Gr-I-Si) at 300 K in the dark medium. D1 device consists of a Gr-LPSi junction that involves RF-PECVD grown Gr on the silicon, whose surface exposed the laser beam for patterning. D2 device consists of a Gr-I-Si junction that involves RF-PECVD grown Gr onto the silicon, whose surface involves a thin native oxide layer (~2 nm). The results show that the laser treatment causes an increment in Schottky barrier height (SBH) and decreases leakage currents under a reverse bias voltage of the diode. Notably, we have seen the influence of the laser patterning process on 3D Gr nano-sheets which is that the entire surface of the substrate has now reformed new structures in the nano-sphere and nano-rose morphology, so we believe that this is the first work that shows these structures in this form.

Boron carbide thin films deposited by RF-PECVD and PLD technique: A comparative study based on structure, optical properties, and residual stress

Radio-Frequency Plasma Enhanced Chemical Vapour Deposition (RF-PECVD), and Pulsed Laser Deposition (PLD) techniques were used to deposit boron carbide (BxC) thin films. Films were investigated to compare crystallinity, chemical composition, optical properties, and residual stress. X-ray diffraction analysis revealed that the film deposited by PLD was amorphous, while PECVD technique yielded crystalline BxC film. PLD technique provided films with better stoichiometric purity with B4C being the most dominant phase, as observed in XPS spectra. However, super-stoichiometric phase (BxC (x > 4)) was dominant in PECVD film. Moreover, the PECVD film had greater adhesion (Lc3 ~29.5 N), hardness (~2798 HK), and lubricity (COF~ 0.03) compared to PLD deposited film. Optically, PECVD deposited film have higher value of refractive indices (1.82 at 600 nm) and lower extinction coefficient. Finally, residual stress measured via substrate curvature method revealed that for PLD 400 C film, the stress was compressive in nature while the same for PECVD -100 V film was tensile, with 10 times less in magnitude. Ultimately, this study provides the user with opportunity to weigh the advantages and disadvantages of PECVD and PLD techniques for deposition of functional BxC films.

The effect of Cu content in MWCNTs synthesized by Ni - Cu @ a-C:H catalyst on the optical constants and the optical loss

In this paper, Ni-Cu NPs @ a-C:H films with different Cu content, by co-deposition of RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) were prepared using acetylene gas and Ni and Cu targets. We studied optical constants of MWCNTs synthesized, with constant Ni content and different percentages of 5, 40 and 75 % from Cu atoms. With increase of Cu content, the average diameter of MWCNTs were increased however the RMS roughness of films were decreased. It is found that the absorption coefficients of films deposited with 5% Cu have maximum value. Also it can be seen that the minimum values of the optical band gaps of films happen in films deposited with 5% Cu. With increase of Cu content, the values of energy loss by the free charge carriers were increased however the plasma frequency ωp and free charge carriers concentration N/m* of films were decreased. The free carriers electric susceptibility χc at in films deposited with 75 % Cu has maximum value. The values of the ratio of free charge carriers concentration to effective mass, N/m*, in films deposited with 5% Cu has maximum value about of 423.731048 m−3 kg−1.

Plasma-Assisted Functionalization of the Carbon Black Surface: Enhancement of Mechanical Properties of Carbon Black/Poly(vinylidene fluoride-co-hexafluoropropene) Nanofibers.

Dispersion of carbon black (CB) powder in CB/polymer composites considerably influences their mechanical properties, electrical conductivity, and thermal conductance. In this study, with the aim to improve the dispersion of CB powder in the CB/polymer composites, CB was treated with oxygen and nitrogen plasma generated by radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD), and then, dispersed in a poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) solution. The solution was then subjected to electrospinning, leading to the formation of a nanofiber mat. The dispersion states of plasma treated CBs have been characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. A stress-strain curve was used to investigate the influence of dispersion on the mechanical properties of CB/polymer composites.

Influence of cellulose microfiber reinforcement for polyvinyl alcohol on the layer growth of plasma-deposited a-C:H

Pure polyvinyl alcohol (PVA) and PVA reinforced with cellulose microfibers (PVA/CMF) composite films were coated with amorphous carbon layers (a-C:H, 50 and 100 nm thick) using radio frequency plasma enhanced chemical vapour deposition (RF-PECVD). The effects of cellulose microfibers on the polymer coatability were investigated. The reinforcement of PVA with CMF fibres leads only to a small variation for the resulting coatings. The measurements for the 50 nm samples differ chemically due to the different interlayer phase through the different base materials. Increasing of the layer thickness leads to an equalization of the layer for both materials. Deposited carbon layers were characterized surface morphologically by ex-situ atomic force microscopy (AFM), surface wettability by contact angle (CA) measurements. The chemical composition was analysed by surface sensitive synchrotron X-ray based techniques (near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS)) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). Novelty-statementAmorphous carbon layers (a-C:H) were successfully deposited on polyvinyl alcohol (PVA) and cellulose microfiber (CMF) reinforced PVA. Differences in the chemical composition of deposited carbon layers (sp2/sp3) were detected with synchrotron based techniques in combination with changes in their morphology and wettability showing clear substrate effects when used with microfiber reinforcement.

A disposable and sensitive non-enzymatic glucose sensor based on 3D graphene/Cu2O modified carbon paper electrode

Herein, a three-dimensional graphene wall (GWs) and nano-Cu2O modified carbon fiber paper (CFP) electrode were used to develop a disposable and sensitive non-enzymatic glucose sensor. This sensing interface of GWs/Cu2O consists of an interlaced CFP on which intercrossed graphene walls (GWs) were vertically tethered in situ by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD), and Cu2O nanoparticles (NPs) were evenly grew on the 3D GWs layer and skeleton through the complete thermal decomposition of copper acetate (Cu (CH3COO)2) at high temperature. The CFP/GWs/Cu2O shows a large specific surface area and rich solution diffusion channels, which can expose more catalytic active sites without Nafion fixation film, thus greatly improving the electrocatalytic performance of this glucose sensor. The CFP/GWs/Cu2O sensor shows excellent catalytic performance to glucose with a linear detection range of 0.5 μM–5166 μM, LOD of 0.21 μM, and response time <4 s. This kind of disposable and sensitive electrode can capable of controlling uniform growth and accurate quantification, and has great development potential in the field of medical detection and the commercialization of wearable sensors.

Tribological properties of hydrogenated boron carbide (BxC:Hy) thin films on stainless steel deposited by RF-PECVD technique

This study narrates the findings regarding investigation of tribological properties of BxC:Hy thin films deposited by Radio Frequency Plasma Enhanced Chemical Vapour Deposition (RF-PECVD) technique. To study tribological properties, two sets of films were prepared with variation in composition and thickness by tuning deposition parameters. Tribological properties were studied in ambience for three different applied vertical load values (5, 10 and 15 N). Lower self-bias (−75 V) seems advantageous for synthesis of BxC:Hy films offering superior hardness, lubricity and wear resistance in tribologically stressed conditions. For a given composition, the film with the highest thickness (∼3 μm) exhibited better friction and wear resistance, offering lowest co-efficient of friction (COF) ∼0.23 for 5 N load and specific wear rate of 2.56 × 10−5 mm3/Nm for 10 N load. Lower self-bias during deposition (−75 V) seems advantageous for synthesis of BxC:Hy films having high hardness (∼2800 HK) and excellent Co-efficient of friction (COF).

Effect of Cellulose Nanocrystals on the Coating of Chitosan Nanocomposite Film Using Plasma-Mediated Deposition of Amorphous Hydrogenated Carbon (a–C:H) Layers

The substitution of petroleum-based polymers with naturally derived biopolymers may be a good alternative for the conservation of natural fossil resources and the alleviation of pollution and waste disposal problems. However, in order to be used in a wide range of applications, some biopolymers’ properties should be enhanced. In this study, biocompatible, non-toxic, and biodegradable chitosan (CS) film and CS reinforced with 10 wt% of cellulose nanocrystals (CN–CS) were coated with amorphous hydrogenated carbon layers (a–C:H) of different thickness. To investigate the effect of the nano-reinforcement on the a–C:H layer applied, mild radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) was used to coat the CS and its CN–CS bio-nanocomposite film. Both the surface characteristics and the chemical composition were analyzed. The surface morphology and wettability were examined by ex-situ atomic force microscopy (AFM) and contact angle measurements (CA), respectively. Hereby, the relationship between sp2/sp3 ratios on a macroscopic scale was also evaluated. For the investigation of the chemical composition, the surface sensitive synchrotron X-ray radiation techniques near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) as well as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were used.

Surface modification of SiOx film anodes by laser annealing and improvement of cyclability for lithium-ion batteries

SiOx (x = 0.66, 0.76 and 1.04) film anodes with the different oxygen content were prepared by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) through adjusting SiH4/N2O (R) gas flow ration. The introduction of oxygen can alleviate volume expansion in the discharge/charge process at the expense of cyclic specific capacity. To obtain both higher capacity and cyclically stable SiOx film anodes, KrF excimer laser system operated at λ = 248 nm can induce to form nanoparticles on the surface of SiO0.76 film, which is related to the formation of solid electrolyte interphase (SEI) area during charge/discharge process. The SEI area becomes larger and mechanically robust with increase of laser energy density, which suppresses structural degeneration for giving lithium-ion battery longer cycle life. At the laser energy density of 266 mJ/cm2, SiO0.76 annealed film anode delivers capacity of 1731 mAh/g and capacity retention of 94.8% after 300 cycles, which are much higher than that of as-deposited anode. Increasing laser energy density to 433 mJ/cm2, SiO0.76 film anode shows higher capacity retention of 97.4% after 300 cycles.

Formation of anatase and srilankite mixture as a result of the thermally induced transformation of the a-C:H:TiOx coating

The a-C:H:TiOx coating deposited by radio-frequency plasma-enhanced chemical vapor deposition (RF PECVD) method, using methane and titanium (IV) isopropoxide mixture atmosphere, was post-deposition annealed at 400 °C in the atmosphere of air. Phase composition and coating structure were studied in detail by Raman spectroscopy, X-ray diffraction and transmission electron microscopy. Depending on the duration of the annealing process, two stages of transformation were identified. In the first stage, during the first 30 min of annealing, processes related to the degradation of a carbon matrix occurred. Characteristic bands attributed to carbon coatings disappeared in Raman spectra and hardness decreased from 10 GPa measured for the as-deposited coating to 2.7 GPa. In the second stage, after additional 10 min of annealing, the coating transformed into a crystalline TiO2 in which two polymorphs (anatase and srilankite) coexisted.