202746457
Synthesis of Vertically Oriented Graphene Sheets or Carbon Nanowalls—Review and Challenges
The paper presents a review on the current methods for deposition of vertically oriented multilayer graphene sheets (often called carbon nanowalls—CNWs) on solid substrates. Thin films of CNWs are among the most promising materials for future applications in capacitors, batteries, electrochemical devices, and photovoltaics, but their application is currently limited by slow deposition rates and difficulties in providing materials of a desired structure and morphology. The review paper analyzes results obtained by various groups and draws correlations between the reported experimental conditions and obtained results. Challenges in this scientific field are presented and technological problems stressed. The key scientific challenge is providing the growth rate as well as morphological and structural properties of CNWs thin films versus plasma parameters, in particular versus the fluxes of reactive plasma species onto the substrate surface. The technological challenge is upgrading of deposition techniques to large surfaces and fast deposition rates, and development of a system for deposition of CNWs in the continuous mode.
5024031
Development and Performance Analysis of Carbon Nanowall-Based Mass Sensor.
In this study, a mass sensor was fabricated using a carbon nanowalls, and its performance was analyzed. The substrate that was used to fabricate the mass sensor was a polyimide film, on which a SiO2 insulating layer and a copper electrode were deposited using an RF magnetron sputter. Thereafter, a carbon nanowalls was grown on the substrate until its size was 5 by 5 mm. The growth times of the completely grown carbon nanowalls were 20, 25, and 30 minutes, respectively. The performance of the mass sensors fabricated based on different carbon nanowalls grown for various growth times was analyzed according to the changing mass from 1 to 5 mg.
105849418
Constructing in-chip micro-supercapacitors of 3D graphene nanowall/ruthenium oxides electrode through silicon-based microfabrication technique
Abstract The rapid development of sensor networks for smart industry requires comparable tiny power sources that can deliver high energetic performance and be mass-produced via the existed semi-conductor process. In this paper, novel 3D in-chip micro-supercapacitors (MSCs) based on hierarchical electrodes were developed through silicon-based microfabrication techniques by depositing graphene nanowall (GNW)/ruthenium oxides (RuOx) core-shell hybrids on the silicon scaffolds that are generated from deep reactive ion etching (DRIE). Conformal coating of RuOx on individual graphene nanoflakes was realized via reactive sputtering technique to benefit capacitance enhancement, while the orderly aligned GNW facilitated fast ions and electrons transfer. By harnessing both the merits of huge active surface area of the 3D hierarchical electrode architectures and the excellent electrochemical behaviors of the GNW/RuOx hybrids, the assembled MSCs exhibited areal energy, power densities of 15.1 μWh cm−2 and 2.49 mW cm−2, respectively. In parallel with our novel in-chip strategy by leveraging the bulk volume of Si substrate to create sidewall for effective area enhancement at footprint, the embedment of electrode nanostructures inside the substrate may also give a new concept of MSCs design towards protecting the fragile electrode materials and making the subsequent device encapsulation with ease.
103086550
Self-supported 3D NiCo-LDH/Gr composite nanosheets array electrode for high-performance supercapacitor
Abstract Graphene film (GF) and graphene nanowall (GW) are first grown on conductive nickel foams (NF) by a chemical vapor deposition (CVD) method. Then the nickel cobalt layered double hydroxides (NiCo-LDHs) nanosheets arrays are directly deposited on the NF, GF/NF and GW/NF by a facile hydrothermal method to form three-dimensional (3D) porous NiCo-LDH/Gr composite electrodes. The electrochemical performance and morphology of the obtained self-supported NiCo-LDH/NF, NiCo-LDH/GF/NF and NiCo-LDH/GW/NF composite electrodes are analyzed and observed. It shows that the NiCo-LDH/GF/NF composite electrode exhibits excellent capacitive properties (2690 F g-1 at 5 A g−1), which is 2.0 and 1.5 times of that of NiCo-LDH/NF and NiCo-LDH/GW/NF. The outstanding capacity of the NiCo-LDH/GF/NF electrode is ascribed to the numerous channels for rapid electron transport provided by the self-supported and high-quality GF. In addition, an asymmetric supercapacitor (ASC) is fabricated by using NiCo-LDH/GF/NF electrode. The optimized NiCo-LDH/GF/NF//AC device delivers a maximum energy density of 50.2 Wh kg−1, a high power density of 8002 W kg-1 at 17.6 Wh kg−1, and powers two green light-emitting-diodes for more than 3 min after charging 1 min. Therefore, the NiCo-LDH/Gr/NF composite electrode is a potential candidate in electrochemical energy storage device.
96688891
Carbon nanowalls as platinum support for fuel cells
Platinum catalysts supported on carbon nanowalls (Pt/CNW) were prepared by a solution-reduction method. It is shown that Pt nanoparticles with a mean diameter of 3.5 nm are well dispersed along domain boundaries in each CNW. In addition, it is shown that the Pt/CNW has high electrochemical active surface area and utilization, comparable to those for commercially available T–Pt/CB with good performance. Such high electrocatalytic activity could be attributed to the high electric conductivity of CNW and the improvement of electronic properties of Pt nanoparticles on the domain boundaries, in addition to the high dispersion of Pt particles.
122283890
Electron field emission enhancement of carbon nanowalls by plasma surface nitridation
Carbon nanowalls (CNWs) are two-dimensional carbon nanostructures consisting of stacked graphene sheets standing vertically on the substrate. The sharp edges of CNWs provide us with opportunities for applications as electron field emitter arrays. The effects of nitrogen plasma (NP) treatment on the surface of CNWs have been investigated in order to improve the electron field emission properties. The electron emission current from the edges of CNWs was drastically increased by the NP treatment. Morphological and chemical changes in the CNWs after the NP treatment were characterized using scanning electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy.
103202467
Highly conductive Na-embedded carbon nanowalls for hole-transport-material-free perovskite solar cells without metal electrodes
New generation solar cells are necessary to replace current silicon solar panels for low cost and high energy conversion efficiency. The perovskite photovoltaic device is a rising star among the 3rd generation solar cells due to its rapidly increased energy conversion efficiency. Recently invented Na-embedded carbon (Na@C) nanowalls, which possess ultrahigh conductivity and a large accessible surface area, are a very promising electrode material. Herein, the Na@C nanowall material was demonstrated as an excellent counter electrode for HTM-free perovskite solar cells (PSCs), leading to a high power conversion efficiency of 8.89% under the AM 1.5G simulated sunlight. This efficiency is almost two times as high as that (4.56%) of a PSC with regular graphene synthesized via chemical exfoliation of graphite.
19588598
Synthesis of carbon nanowall by plasma-enhanced chemical vapor deposition method.
Plasma-enhanced chemical vapor deposition (PECVD) is widely used for the synthesis of carbon materials, such as diamond-like carbons (DLCs), carbon nanotubes (CNTs) and carbon nanowalls (CNWs). Advantages of PECVD are low synthesis temperature compared with thermal CVD and the ability to grow vertically, free-standing structures. Due to its self-supported property and high specific surface area, CNWs are a promising material for field emission devices and other chemical applications. This article reviews the recent process on the synthesis of CNW by the PECVD method. We briefly introduce the structure and properties of CNW with characterization techniques. Growth mechanism is also discussed to analyze the influence of plasma conditions, substrates, temperature, and other parameters to the final film, which will give a suggestion on parameter modulation for desired film.
94875878
Plasma techniques for nanostructured carbon materials synthesis. A case study: carbon nanowall growth by low pressure expanding RF plasma
A short description of approaches for carbon nanostructures synthesis is made and the advantages of using plasma during the growth are presented. As a particular example of a plasma based technique we detail the process of downstream carbon nanowall (CNW) synthesis by a radiofrequency expanding plasma beam. The technique combines magnetron sputtering for catalyst deposition and plasma enhanced chemical vapor deposition (main gas: argon, active gas: hydrogen, precursor gas: acetylene) for carbon growth in a single reactor. The analysis focuses on the correlation between the material properties and the plasma characteristics measured at different points along the flow axis, aiming to reveal the importance of plasma species in the growth process. The material properties were investigated by scanning and transmission electron microscopy, whereas the plasma data were obtained by optical emission spectroscopy, Langmuir probes and mass spectrometry. CNWs with a large area and well isolated from each other are obtained at an optimum distance from the precursor injection point where the plasma presents an enhanced content of carbon nanoclusters. The possible processes responsible for the growth are discussed.
104371633
Effect of nitrogen configuration on carbon nanowall surface: Towards the improvement of electrochemical transduction properties and the stabilization of gold nanoparticles
Abstract In this work, unintentionally nitrogen doped carbon nanowall (CNW) films, deposited on silicon substrates, were treated in argon plasma admixed with nitrogen (Ar/N2) or oxygen (Ar/O2). X-ray photoelectron spectroscopy (XPS) showed that oxygen functional groups have been incorporated in various amounts with high nitrogen doping concentration (∼12.5–13.5 at%. for Ar/N2 and Ar/O2 gas mixtures). More importantly, nitrogen configuration on the surface has been modified after the treatment. The electrochemical reactivity of the CNW electrodes, before and after the treatment, was investigated by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy. The CV results indicate that the pyrrolic nitrogen can play a key role in the electrochemical transaction improvement. In addition, deposition of gold (Au) nanoparticles (NPs) onto CNW samples and their interaction with CNWs has been discussed through XPS results. It was suggested that a certain nitrogen configuration there is a promotion of electron donation from nitrogen to the Au NPs. Such findings open the way to design nitrogen doped carbon materials with specific nitrogen configuration to improve electrochemical properties and to prepare better platform for Au NPs for use in catalysis and sensor applications.
122368874
Fabrication of vertically aligned carbon nanowalls using capacitively coupled plasma-enhanced chemical vapor deposition assisted by hydrogen radical injection
Two-dimensional carbon nanostructures (carbon nanowalls) were fabricated using capacitively coupled radio-frequency plasma-enhanced chemical vapor deposition assisted by H radical injection. Carbon nanowalls were grown on Si, SiO2, and sapphire substrates without catalyst, and independent of substrate materials. Correlation between carbon nanowall growth and fabrication conditions, such as carbon source gases was investigated. In the case using C2F6/H2 system, aligned carbon nanowalls were grown vertically on the substrate, while carbon nanowalls grown using CH4/H2 system were waved and thin (<10 nm). In the case of the deposition without H radical injection, on the other hand, carbon nanowalls were not fabricated.
146170683
Controllable growth of vertically oriented graphene for high sensitivity gas detection
Directly synthesize vertical graphene nano-petals (VGNPs) on SiO2 substrate by PACVD, the growth temperature is significantly reduced and reaches at 550 °C. We utilize the unique topography of VGNPs to investigate the ammonia gas sensitivity and realize the ppt level detection ability.
98687956
Initial growth process of carbon nanowalls synthesized by radical injection plasma-enhanced chemical vapor deposition
We synthesized carbon nanowalls (CNWs) using radical injection plasma-enhanced chemical vapor deposition. The initial growth process of CNWs was investigated with and without O2 gas addition to a C2F6 capacitively coupled plasma with H radical injection. In the case of the CNW synthesis without the addition of O2 gas, scanning electron microscopy (SEM), transmission electron microscopy, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy revealed that a 10-nm-thick interface layer composed of nanoislands was formed on a Si substrate approximately 1 min prior to CNW formation. In contrast, with O2 gas addition, SEM and XPS revealed that an interface layer was not formed and that CNWs were grown directly from nanoislands. Moreover, Raman spectroscopy suggested that the interface layer was composed of amorphous carbon and that O2 gas addition during CNW growth is effective for achieving a high graphitization of CNWs. Therefore, O2 gas addition has the effect of reducing the amorphicity and disorde...
93118712
RF-PECVD synthesis of carbon nanowalls and their field emission properties
Abstract Carbon nanowalls (CNWs) were successfully fabricated on various substrates by radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene, argon and hydrogen without aid of any catalyst or substrate pretreatment. The influence of synthesis parameters on the field emission behaviors of CNWs was investigated in depth. The results showed that the morphology and microstructure of CNWs could be adjusted by growth parameters (temperature, pressure and gas flow rate), and CNWs with sharp edges displayed good field emission properties. Especially, the sample prepared under the pressure of 300 Pa and the temperature of 650 °C with H 2 flow rate of 120 sccm exhibited the best field emission performance (the turn-on and threshold fields were 4.7 and 6.0 V/μm, respectively). In addition, the field emission characteristics of CNWs after stability test had no obvious deterioration; however, the morphology and microstructure of CNWs changed.
34987345
Controlled synthesis of large-scale, uniform, vertically standing graphene for high-performance field emitters.
Large-scale, uniform, vertically standing graphene with atomically thin edges are controllably synthesized on copper foil using a microwave-plasma chemical vapor deposition system. A growth mechanism for this system is proposed. This film shows excellent field-emission properties, with low turn-on field of 1.3 V μm(-1) , low threshold field of 3.0 V μm(-1) and a large field-enhancement factor more than 10 000.
93640508
Synthesis of carbon nanosheets by inductively coupled radio-frequency plasma enhanced chemical vapor deposition
Abstract An ultrathin sheet-like carbon nanostructure, carbon nanosheet, has been effectively synthesized with CH4 diluted in H2 by an inductively coupled radio-frequency plasma enhanced chemical vapor deposition. Nanosheets were obtained without catalyst over a wide range of deposition conditions and on a variety of substrates, including metals, semiconductors and insulators. Scanning electron microscopy shows that the sheet-like structures stand on edge on the substrate and have corrugated surfaces. The sheets are 1 nm or less in thickness and have a defective graphite structure. Raman spectra show typical carbon features with D and G peaks at 1350 and 1580 cm−1, respectively. The intensity ratio of these two peaks, I(D)/I(G), increases with methane concentration or substrate temperature, indicating that the crystallinity of the nanosheets decreases. Infrared and thermal desorption spectroscopies reveal hydrogen incorporation into the carbon nanosheets.
135776014
Synthesis of carbon nanowalls by plasma-enhanced chemical vapor deposition in a CO/H2 microwave discharge system
Abstract Synthesis of carbon nanowalls was performed by a plasma-enhanced chemical vapor deposition in a CO/H 2 microwave discharge system. At the optimum CO/H 2 feed ratio of 46 sccm/4 sccm, the aligned carbon nanowalls with thickness of about several tens of nanometers were able to be synthesized. The extremely high growth rate of 1 μm min − 1 was obtained in our system with a relatively low microwave discharge power of 60 W for a growth area of 1 cm 2 . An optical emission spectroscopy was performed to clarify the characteristics of a CO/H 2 discharge system.
96230368
Non-Catalytic Low-Temperature Synthesis of Carbon Nanofibers by Plasma-Enhanced Chemical Vapor Deposition in a CO/Ar/O2 DC Discharge System
Catalyst-free low-temperature growth of carbon nanofibers was performed by a plasma-enhanced chemical vapor deposition using a CO/Ar/O2 DC discharge system. At the optimum oxygen concentration of O2/CO = 0.002–0.005, vertically aligned carbon nanofibers with a diameter of about 10–50 nm can be synthesized at temperatures as low as 90 °C without any catalyst materials. It is concluded that the addition of a small amount of O2 is the key to the synthesis of carbon nanofibers without a catalyst, because it suppresses the isotropic deposition of amorphous carbon while allowing the anisotropic linear growth of crystallized carbon materials.
102248589
Effect of the aromatic precursor flow rate on the morphology and properties of carbon nanostructures in plasma enhanced chemical vapor deposition
Understanding the effects of the synthesis parameters on the morphology and electrochemical properties of nanocarbon layers is a key step in the development of application-tailored nanostructures. In this paper we used an aromatic carbon as a new kind of precursor for the synthesis of carbon based nanostructures by plasma enhanced chemical vapor deposition (PECVD). Complex precursor molecules enable a new degree of influence over the atomic structure of PECVD synthesized carbons. Here, we report on the synthesis and characterization of the nanostructures resulting from varied flow rates of p-xylene used as carbon precursor. By changing the flow rate of the precursor, three different morphologies with graphitic character were synthesized. The resulting structures were carbon nanofibers (CNF), freestanding carbon nanowalls (fCNW) and interconnected carbon nanowalls (iCNW), formed at flow rates of 3 ml h−1, between 1 and 3 ml h−1 and less than 1 ml h−1, respectively. Structural characterization by transmission electron microscopy and Raman spectroscopy indicate a lower defect density for the CNF in comparison to the CNW nanostructures. The electrochemical characterization of the oxygen reduction reaction onset potential and effective surface area feature a significantly higher onset at around −171 mV and an electrochemically active surface area of 0.76 μm−1 for the iCNW compared to −196 mV, 0.61 μm−1 and 0.22 μm−1 for the fCNW and CNF, respectively. The similarities in defect density and differences in activity observed for the iCNW and fCNF suggest that the kind of the defects determines the electrochemical properties. Thus, the iCNW was identified as the most appropriate morphology for further investigations.
98769536
Carbon nanowalls synthesis by means of atmospheric dcPECVD method
Carbon nanowalls (CNWs) were grown by atmospheric dc plasma enhanced chemical vapour deposition method. Maintaining plasma at atmospheric pressure give us possibility to synthetize CNWs at high rate. By using two different liquid carbon sources we can control CNWs density. Growth of sparsely distributed CNWs can be achieved by using ethanol, while hexane gives densely packed CNWs films.
17095228
Growth of carbon nanowalls at atmospheric pressure for one-step gas sensor fabrication
Carbon nanowalls (CNWs), two-dimensional "graphitic" platelets that are typically oriented vertically on a substrate, can exhibit similar properties as graphene. Growth of CNWs reported to date was exclusively carried out at a low pressure. Here, we report on the synthesis of CNWs at atmosphere pressure using "direct current plasma-enhanced chemical vapor deposition" by taking advantage of the high electric field generated in a pin-plate dc glow discharge. CNWs were grown on silicon, stainless steel, and copper substrates without deliberate introduction of catalysts. The as-grown CNW material was mainly mono- and few-layer graphene having patches of O-containing functional groups. However, Raman and X-ray photoelectron spectroscopies confirmed that most of the oxygen groups could be removed by thermal annealing. A gas-sensing device based on such CNWs was fabricated on metal electrodes through direct growth. The sensor responded to relatively low concentrations of NO2 (g) and NH3 (g), thus suggesting high-quality CNWs that are useful for room temperature gas sensors.PACS: Graphene (81.05.ue), Chemical vapor deposition (81.15.Gh), Gas sensors (07.07.Df), Atmospheric pressure (92.60.hv)
49548472
Synthesis of carbon nanowalls from a single-source metal-organic precursor
In this work, the deposition of carbon nanowalls (CNWs) by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) is investigated. The CNWs are electrically conducting and show a large specific surface area, which is a key characteristic to make them interesting for sensors, catalytic applications or energy-storage systems. It was recently discovered that CNW films can be deposited by the use of the single-source metal-organic precursor aluminium acetylacetonate. This precursor is relatively unknown in combination with the ICP-PECVD deposition method in literature and, thus, based on our previous publication is further investigated in this work to better understand the influence of the various deposition parameters on the growth. Silicon, stainless steel, nickel and copper are used as substrate materials. The CNWs deposited are characterized by scanning electron microscopy (SEM), Raman spectroscopy and Auger electron spectroscopy (AES). The combination of bias voltage, the temperature of the substrate and the substrate material had a strong influence on the morphology of the graphitic carbon nanowall structures. With regard to these results, a first growth model for the deposition of CNWs by ICP-PECVD and aluminium acetylacetonate is proposed. This model explains the formation of four different morphologies (nanorods as well as thorny, straight and curled CNWs) by taking the surface diffusion into account. The surface diffusion depends on the particle energies and the substrate material and thus explains the influence of these parameters.
7730496
Process-specific mechanisms of vertically oriented graphene growth in plasmas
Applications of plasma-produced vertically oriented graphene nanosheets (VGNs) rely on their unique structure and morphology, which can be tuned by the process parameters to understand the growth mechanism. Here, we report on the effect of the key process parameters such as deposition temperature, discharge power and distance from plasma source to substrate on the catalyst-free growth of VGNs in microwave plasmas. A direct evidence for the initiation of vertical growth through nanoscale graphitic islands is obtained from the temperature-dependent growth rates where the activation energy is found to be as low as 0.57 eV. It is shown that the growth rate and the structural quality of the films could be enhanced by (a) increasing the substrate temperature, (b) decreasing the distance between the microwave plasma source and the substrate, and (c) increasing the discharge power. The correlation between the wetting characteristics, morphology and structural quality is established. It is also demonstrated that morphology, crystallinity, wettability and sheet resistance of the VGNs can be varied while maintaining the same sp3 content in the film. The effects of the substrate temperature and the electric field in vertical alignment of the graphene sheets are reported. These findings help to develop and optimize the process conditions to produce VGNs tailored for applications including sensing, field emission, catalysis and energy storage.
139171989
Vertically-oriented graphene nanowalls: Growth and application in Li-ion batteries
Abstract Vertically-oriented graphene nanowalls (VGNWs) have been successfully synthesized under different experimental conditions (such as flow rate of argon, growth temperature, plasma power as well as deposition time) on copper foils in the reactive methane and argon environment using a capacitively coupled plasma-enhanced horizontal tube furnace deposition system. It is shown that the morphology and structure of VGNWs can be effectively tailored by experimental conditions. Furthermore, the growth mechanism of VGNWs produced in the plasma-based approach has been investigated. The synthesized VGNWs are used as anode materials in Li-ion batteries and the batteries show outstanding cycle efficiency (~99%). The specific capacity of coin-type cells can be improved by adjusting the experimental parameters and reaches 400 mAh g−1 in the first charge-discharge cycle. This work is particularly important for the development of an advanced process for the synthesis and application of carbon-based nanomaterials.
139527712
Direct synthesis of vertical graphene nanowalls on glass substrate for thermal management
Vertical few layered graphene (VG) nanoflakes were directly synthesized on traditional glass substrate by the plasma-assisted chemical vapor deposition, where the extremely low growing temperature (<560 °C) and short time (<30 min) were involved. The VG microstructure could be well-controlled by tuning the plasma power, growth time and growth temperature. Raman, TEM, and SEM were used to determine the quality and single size of the VG. Because of the unique three-dimensional structure with high surface area, the VG network can provide superior thermal management capabilities, which has been demonstrated by the scalable frost removal. We believed that this hybrid system consisting of vertical graphene nanowalls and glass substrates has great potentials for future transparent 'green-warmth' constructions.
55625175
Morphology, Microstructure, and Hydrogen Content of Carbon Nanostructures Obtained by PECVD at Various Temperatures
Carbon nanostructures were obtained by acetylene injection into an argon plasma jet in the presence of hydrogen. The samples were synthesized in similar conditions, except that the substrate deposition temperatures were varied, ranging from 473 to 973 K. A strong dependence of morphology, structure, and graphitization upon was found. We obtained vertical aligned carbon nanotubes (VA-CNTs) at low temperatures as 473 K, amorphous carbon nanoparticles (CNPs) at temperatures from about 573 to 673 K, and carbon nanowalls (CNWs) at high temperatures from 773 to 973 K. Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, elastic recoil detection analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to substantiate the differences in these material types. It is known that hydrogen concentration modifies strongly the properties of the materials. Different concentrations of hydrogen-bonded carbon could be identified in amorphous CNP, VA-CNT, and CNW. Also, the H : C ratios along depth were determined for the obtained materials.
97499514
Synthesis and electrical characterization of n-type carbon nanowalls
Nitrogen-incorporated carbon nanowalls are prepared by microwave plasma-enhanced chemical vapor deposition using acetylene and methane. n-type conduction in the nanowalls is confirmed by Hall- and Seebeck-effect measurements. We show that increasing the amount of C2 radicals by adding Ar enables catalyst-free growth of nanowalls at a high rate up to about 1 μm/min and reduces the deposition temperature (TD) down to around 650 °C. A substrate pretreatment using diamond powder results in a composite of nanowalls and nanocrystalline diamond films, suggesting that the nanowall growth is limited by gas-phase conditions rather than surface conditions. The low conductivity nanowalls for low TD exhibit thermal activation in the Arrhenius plot, indicative of semiconducting conduction, while the high conductivity nanowalls for high TD are almost temperature independent, indicative of quasimetallic conduction. The high conductivity is attributed to a global increase in the sp2 cluster size and crystallinity, which i...
137629939
Direct synthesis of multi-layer graphene film on various substrates by microwave plasma at low temperature
Abstract We introduce a possible route for vertically standing multi-layer graphene films (VMGs) on various substrates at low temperature by electron cyclone resonance microwave plasma. VMG films on various substrates, including copper sheet, glass and silicon oxide wafer, were analyzed by studying their structural, electrical, and optical properties. The density and temperature of plasma were measured using Cylindrical Langmuir probe analysis. The morphologies and microstructures of multi-layer graphene were characterized using field emission scattering electron microscope, high resolution transmission electron microscope, and Raman spectra measurement. The VMGs on different substrates at the same experimental conditions synthesized the wrinkled VMGs with different heights. In addition, the transmittance and electrical resistance were measured using ultra-violet visible near-infrared spectroscopy and 4 probe point surface resistance measurement. The VMGs on glass substrate obtained a transmittance of 68.8% and sheet resistance of 796 Ω/square, whereas the VMGs on SiO 2 wafer substrate showed good sheet resistance of 395 Ω/square and 278 Ω/square. The results presented herein demonstrate a simple method of synthesizing of VMGs on various substrates at low temperature for mass production, in which the VMGs can be used in a wide range of application fields for energy storage, catalysis, and field emission due to their unique orientation.
133067554
Synthesis of vertically aligned carbon nanoflakes by hot-wire chemical vapor deposition: Influence of process pressure and different substrates
Abstract The vertically aligned carbon nanoflakes thin films were synthesized on Si (100) and alkali free borosilicate glass substrates at relatively low substrate temperature of 400 °C, without any catalyst or surface pre-treatment, using hot-wire chemical vapor deposition (HWCVD) technique. Raman Spectroscopy studies reveal that the crystallinity of the films increases with increase in process pressure. Our studies show that HWCVD is a versatile technique for the synthesis of these films at low temperature compared to plasma enhanced CVD on both semiconducting Si as well as insulating glass substrates.
97193772
Low temperature growth of graphene film by microwave assisted surface wave plasma CVD for transparent electrode application
Here, we report the synthesis of a graphene film on Cu foil by microwave assisted surface wave plasma chemical vapor deposition (MW-SWP-CVD) at a low pressure and temperature using a hydrocarbon gas. Raman spectroscopy and transmission electron microscopy (TEM) studies clearly show deposited carbon films that consist of few layer graphene sheets. Deposition of graphene films with a few layers structure was achieved at a temperature as low as 240 °C. In the nucleation and growth process, carbon radicals are formed with hydrogen termination in the surface wave plasma, which absorb continuously on the Cu surface to form sp2 carbon and eventually a graphene structure. The transparency and conductivity characteristics of the transferred graphene films show suitability for flexible electronics applications.
12560717
Low-temperature plasma enhanced chemical vapour deposition of carbon nanotubes
Abstract Vertically aligned carbon nanotubes were selectively grown at temperatures as low as 120 °C by plasma enhanced chemical vapour deposition. We investigated the effects of acetylene, ethylene and methane as carbon source gases together with ammonia as an etchant and nickel as catalyst material. The diluted acetylene plasma gave the highest nanotube growth rate and showed the most intense C 2 Swan bands in optical emission. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapour deposition (1.2–1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result allows more cost-effective nanotube production, direct growth of nanotubes onto low-temperature substrates like plastics, and could facilitate carbon nanotube integration into sensitive nanoelectronic devices.
137112472
Pecvd synthesis of 2d nanostructured carbon material
Abstract Carbon nanowalls were synthesised by downstream deposition in an expanding radiofrequency argon plasma beam discharge injected with acetylene and hydrogen. The obtained layers have been investigated by Scanning and Transmission Electron Microscopy, Selected Area Electron Diffraction, and Raman Spectroscopy. We present the influence of the substrate type on the material characteristics and report on the possibility to obtain free standing carbon nanowall layers. Also, the importance of pressure values and argon carrier mass flow rate during the deposition process is discussed in relation to the quality of the nanostructured material.
95772506
Vertical growth of carbon nanowalls using rf plasma-enhanced chemical vapor deposition
Two-dimensional carbon nanostructures (carbon nanowalls) were fabricated by capacitively coupled, radio-frequency (rf) plasma-enhanced chemical vapor deposition (PECVD) employing fluorocarbon/hydrogen (H) mixtures. Correlation between carbon nanowall growth and fabrication conditions, such as the carbon source gases, was investigated. In addition, H atom density in the plasma was measured using vacuum ultraviolet absorption spectroscopy (VUVAS), in order to discuss the growth mechanism of carbon nanowalls.
120564409
Growth of Carbon Nanowalls on a SiO2 Substrate by Microwave Plasma-Enhanced Chemical Vapor Deposition
We investigated the growth process of carbon nanowalls (CNWs) on a SiO2 substrate by microwave plasma-enhanced chemical vapor deposition (MPECVD). It is revealed that the CNWs are grown at the fine-textured structure on the SiO2 and the growth process does not require the catalyst. The CNW initially has a semicircular shape. The height, thickness, and mesh size increase with growth time. It is found that the height of CNWs as a function of time obeys the square root law. Extremely high growth rate, approximately 10 µm/h, is achieved, in contrast to previous studies.
135916691
DC plasma enhanced growth of oriented carbon nanowall films by HFCVD
Abstract Two dimensional graphitic carbon structures, commonly referred to as carbon nanowalls (CNW), are raising increasing interest in the scientific community. Their surface area is theoretically twice that of the closed boundary structures, such as carbon nanotubes, making them extremely attractive for chemical and biosensor applications. In this work CNW, with maximum longitudinal dimension ranging from 10 to 200 nm and wall thickness lower than 5 nm, have been grown in a HFCVD reactor on Si substrates. The growth precursors consisted of methane diluted into He noble gas. The effect of a DC plasma on the growth rate and film morphology was explored. The experimental setup consisted of a two grid system which allowed to vary independently the plasma voltage and current density on the substrate surface. An increase of growth rate was observed as the film thickness increased from a few nanometers to about 200 nm when the substrate current density was increased from 0 to 3.5 mA/cm 2 for 30 min.
7580862
Synthesis and characterization of carbon nanowalls on different substrates by radio frequency plasma enhanced chemical vapor deposition
Abstract A radio frequency plasma enhanced chemical vapor deposition system was used for the successful growth of thin vertical carbon nanowalls, also known as vertical graphene, on various substrates. Transmission electron microscopy studies confirmed the presence of vertical graphene walls, which are tapered, typically consisting of 10 layers at the base tapering off to 2 or 3 layers at the top. The sides of the walls are facetted at quantized angles of 30° and the facetted sides are usually seamless. Growth occurs at the top open edge which is not facetted. Hydrogen induced etching allows for nucleation of branch walls apparently involving a carbon onion-like structure at the root base. Characterization by a superconducting quantum interference device showed magnetic hysteresis loops and weak ferromagnetic responses from the samples at room temperature and below. Temperature dependence of the magnetization revealed a magnetic phase transition around T  = 50 K highlighting the coexistence of antiferromagnetic interactions as well as ferromagnetic order.
139611299
Efficient and controllable growth of vertically oriented graphene nanosheets by mesoplasma chemical vapor deposition
Abstract Owing to the unique nanoarchitecture and graphene in nature, the vertically oriented graphene nanosheets (VGN) possesses many promising properties and holds great potential for various applications. Although the plasma-enhanced chemical vapor deposition (PECVD) techniques have been the effective and widely used approaches, they remain the challenge for the controllable and efficient growth of VGN for the mass and intended applications. Also, each method provides limited structures. Herein, for the first time, we report a synthesis of VGN with various controllable structures and fast growth rates by mesoplasma CVD at Ar-H2-CH4 gas mixture. Five types of structures, including cauliflower-like, petal-like, quasi-maze-like, maze-like, and floc-like structures are synthesized by simply adjusting the growth parameters. The growth dynamics and structure transition of VGN are analyzed from the aspect of the deposition precursor density and the H/C ratio. Even at no H2 addition, VGN is synthesized at mesoplasma condition and an extremely high rate of 18.08 μm/min is obtained, which is at least one order of magnitude faster than any other methods reported. This work provides a new route to increase the growth rate of VGN and also demonstrates the advantages of mesoplasma CVD for the growth of high quality films with high efficiency.
97306163
Understanding growth of carbon nanowalls at atmospheric pressure using normal glow discharge plasma-enhanced chemical vapor deposition
Abstract Synthesis of carbon nanowalls (CNWs) at atmospheric pressure is realized by using a negative normal glow discharge, which differs from prior low-pressure plasma-enhanced chemical vapor deposition methods for CNW growth and holds great potential for mass-production of CNWs. The glow discharge is characterized for electrical and optical properties. The resulting CNW structures are analyzed using transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy. The CNW growth process is examined for effects of discharge regime, discharge duration (growth time), hydroxyl radicals (water vapor), and local current density. Possible CNW growth mechanism and critical process parameters to the CNW growth and evolution are identified. OH radicals play an essential role in the initial nucleation process, but excess OH radicals accelerate the oxidation of CNWs. For a fixed growth time, there exists an optimum feed gas relative humidity and an optimum current density (∼40% and ∼9.17 A/m2, respectively, in the current work) for the growth of large and less defective CNWs with a high degree of crystallinity. Results obtained in this study can be used to tailor final properties of the as-grown CNWs for various applications.
96275591
Solution plasma exfoliation of graphene flakes from graphite electrodes
Graphene flakes were successfully produced by a simple method named a solution plasma process. The plasma was generated between two carbon electrode tips which were immersed in distilled water. The production approach is a continuous energy accumulation induced by focusing of plasma streamers on the surface of electrodes. This focused energy produces thermal gradient zones where a proper energy level is produced. Concisely, the energy is enough to extract graphene layers from the graphite structure but not enough to break covalent C–C bonds within the graphene sheets. Optical emission spectroscopy results showed the decomposition of carbon from the graphite electrodes with different intensities for the carbon species. Transmission electron microscopy images confirmed the hexagonal honeycomb structure of the graphene flakes. Furthermore, broadening of the 2D band in the Raman spectra revealed that the graphene flakes were disordered multilayers.
97687850
Synthesis of graphene nanosheets from petroleum asphalt by pulsed arc discharge in water
The synthesis of graphene nanosheets has been achieved by pulsed arc discharge in water with petroleum asphalt as a carbon source. The synthesized graphene nanosheets were examined by Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy and atomic force microscopy. The results indicate that most of as-synthesized graphene nanosheets have 2–5 layers, and small amounts of them have sheets in the range of 5–10 layers. The optical emission spectroscopy was used to monitor the arc discharge process, which indicates that the released hydrogen from asphalt may play a key role in the formation of graphene.
103807533
Rapid growth of micron-sized graphene flakes using in-liquid plasma employing iron phthalocyanine-added ethanol
Giant graphene flakes on the micron scale were synthesized and grown in plasmas in liquid-phase pure ethanol with added iron phthalocyanine (FePc) in a solvent. At atmospheric pressure, plasmas were generated in the gas phase filled with Ar and in the liquid phases comprising bubbles and liquid solutions. In the mixture of FePc in ethanol, nanographene sheets aggregated to form giant graphene flakes, as confirmed by the D, G, and 2D bands in the corresponding Raman spectra. Therefore, a bottom-up approach of graphite synthesis from pure ethanol with additives and a catalyst was realized by in-liquid plasma processing.
97167465
Patterning Vertically Oriented Graphene Sheets for Nanodevice Applications
Graphene has attracted growing interest in the past few years. Growing vertically oriented graphene sheets with a designed pattern is practically attractive for device applications based on graphene. Here we report a patterned synthesis of vertical graphene nanosheets using plasma-enhanced chemical vapor deposition. Both experimental and modeling results suggest that the electric field distribution above the substrate material plays a key role in the graphene coverage. Vertical graphene patterns can thus be designed through artificially designing the surface electric field distribution. A field-effect transistor (FET) sensor device has been demonstrated for detection of low-concentration gases using vertically patterned graphene sheets bridging a metal electrode gap.
136007513
Preparation and electron field emission of carbon nanowall by Cat-CVD
Carbon nanowall (CNW) films have been prepared by catalytic chemical vapor deposition using only CH4 gas. In the SEM images of the samples prepared at a substrate heating temperature, Ts, of 500 °C, the wall structures on the substrates were observed. In those prepared at Ts of 400 °C, however, the wall structure was not observed. The electron field emission from the CNW films was observed at small electric field. The wall width and height increased when the Raman intensity ratio, ID/IG, decreased. Then, the threshold electric field decreased. The smallest threshold electric field was 2.6 V/μm in this work.
96406561
Effect of hydrogen dilution in preparation of carbon nanowall by hot-wire CVD
Carbon nanowall films prepared on the stainless steel substrates by hot-wire chemical vapor deposition using CH 4 with different hydrogen dilution ratios and structure variation in the CNWs against hydrogen dilution have been studied. In the scanning electron microscope images, the wall height and width in the samples prepared with the hydrogen dilution ratio, H 2 /(CH 4 +H 2 ), between 10% and 25% were larger than that prepared without hydrogen dilution. In the Raman spectra for the samples prepared with the H 2 /(CH 4 +H 2 ) below 25%, the intensity ratio of the G peak to the D peak, I G /I D , increased with increasing the H 2 /(CH 4 +H 2 ). In the samples prepared with the H 2 /(CH 4 +H 2 ) over 25%, the wall size and the I G /I D decreased.
95898788
Oxygen atom loss coefficient of carbon nanowalls
Abstract Extremely high values of atomic oxygen loss coefficient on carbon nanowall (CNW) surface are reported. CNW layers consisting of interconnected individual nanostructures with average length of 1.1 μm, average thickness of 66 nm and surface density of 3 CNW/μm 2 were prepared by plasma jet enhanced chemical-vapor deposition using C 2 H 2 /H 2 /Ar gas mixtures. The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectrometry (RS) as well as X-ray photoelectron spectroscopy (XPS). The surface loss coefficient was measured at room temperature in a flowing afterglow at different densities of oxygen atoms supplied from inductively coupled radiofrequency O 2 plasma. The RF generator operated at 13.56 MHz and different nominal powers up to 900 W corresponding to different O-atom density in the afterglow up to 1.3 × 10 21  m −3 . CNW and several different samples of known coefficients for heterogeneous surface recombination of neutral oxygen atoms have been placed separately in the afterglow chamber and the O-atom density in their vicinity was measured with calibrated catalytic probes. Comparison of measured results allowed for determination of the loss coefficient for CNWs and the obtained value of 0.59 ± 0.03 makes this material an extremely effective sink for O-atoms.