Growth Of Vertical Graphene Research Articles

Vertical Graphene Growth on LDH Nanosheets and Carbon Cloth Nanofibers with NiCo Nanoparticles as a Freestanding Host for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries have been recognized as one of the excellent candidates for next-generation energy storage batteries because of their high energy density and low cost and low pollution. However, lithium-sulfur batteries have been challenged by low conductivity, low sulfur utilization, poor cycle life, and the shuttle effect of polysulfides. To address these problems, we report here an independent mixed sulfur host. First, NiCoAl-layered double hydroxide (LDH) nanosheets were uniformly grown on carbon cloth (CC) by a hydrothermal method. Then, vertical graphene (VG) was uniformly vertically grown on the composite structures to form VG@LDH/CC by a plasma enhanced chemical vapor deposition (PECVD) method. Graphene and LDH nanosheets forming a three-dimensional mesh structure can effectively physically block lithium polysulfides, store singlet sulfur, and improve the conductivity of the cathode. In addition, during the growth of graphene, the Ni and Co ions in the LDH nanosheets are reduced to NiCo nanoparticles, which can enhance the chemical adsorption of polysulfides, thus effectively mitigating the "shuttle effect" and improving the electrical conductivity of the material. The lithium sulfur batteries with derived sulfur anodes (VG@LDH/CC-S) exhibited excellent electrochemical properties, including excellent rate performance (780.8 mAh g-1 at 3C) and impressive cycling stability (capacity decay of about 0.0755% per cycle after 750 cycles at 0.5C).

Direct Growth of Vertical Graphene on Fiber Electrodes and Its Application in Alternating Current Line-Filtering Capacitors.

Fiber-shaped electrochemical capacitors (FSECs) have garnered substantial attention to emerging portable, flexible, and wearable electronic devices. However, achieving high electronic and ionic conductivity in fiber electrodes while maintaining a large specific surface area is still a challenge for enhancing the capacitance and rapid response of FSECs. Here, we present an electric-field-assisted cold-wall plasma-enhanced chemical vapor (EFCW-PECVD) method for direct growth of vertical graphene (VG) on fiber electrodes, which is incorporated in the FSECs. The customized reactor mainly consists of two radio frequency coils: one for plasma generation and the other for substrate heating. Precise temperature control can be achieved by adjusting the conductive plates and the applied power. With induction heating, only the substrate is heated to above 500 °C within just 5 min, maintaining a low temperature in the gas phase for the growth of VG with a high quality. Using this method, VG was easily grown on metallic fibers. The VG-coated titanium fibers for FSECs exhibit an ultrahigh rate performance and quick ion transport, enabling the conversion of an alternating current signal to a direct current signal and demonstrating outstanding filtering capabilities.

Growth of vertical graphene by plasma-enhanced chemical vapor deposition and its applications

As one of the most abundant elements on earth, carbon has a profound influence on human development. Currently, various carbon materials, especially graphene and carbon nanotube, have attracted our intensive attention. In particular, graphene, on which sp2-hybridized carbon atoms compose one layer, is widely applied for its distinctive structure and features. Yet, the structure of a material determines its properties. As an unusual graphene material with a unique structure, vertical graphene (VG) grown with plasma enhanced chemical vapor deposition (PECVD) reveals an exposed sharp edge, perpendicular-to-substrate orientation, non-stacking morphology, and great surface-to-volume ratio. These characteristics highlight the prospect of VG as an attractive material with extensive usage. This paper focuses on the preparation of VG, including the growth mechanism and factors affecting the growth process, then introduces some typical applications related to the property of VG. Finally, we will briefly summarize the structure, properties, and applications of VG.

Controllable Fabrication of Vertical Graphene with Tunable Growth Nature by Remote Plasma-Enhanced Chemical Vapor Deposition.

As an important member of the graphene family, vertical graphene (VG) has broad applications like field emission, energy storage, and sensors owing to its fascinating physical and chemical properties. Among various fabrication methods for VG, plasma enhanced chemical vapor deposition (PECVD) is most employed because of the fast growth rate at relatively low temperature for the high-quality VG. However, to date, relations between growth manner of VG and growth parameters such as growth temperature, dosage of gaseous carbon source, and electric power to generate plasma are still less known, which in turn hinder the massive production of VG for further applications. In this study, the growth behavior of VG was studied as functions of temperature, plasma power, and gas composition (or chamber pressure). It was found that the growth behavior of VG is sensitive to the growth conditions mentioned above. Although conditions with high growth temperature, large flow rate of mixed gas of methane and carrier gases, and high plasma power may be helpful for the fast growth of VG, brunching of VG is simultaneously enhanced, which in turn decreases the vertical growth nature of VG. High-quality VG can be achieved by optimizing the growth parameters. It was revealed that the vertical growth nature of VG is governed by the electric field at the interfacial layer between VG and the substrate, for which its strength is influenced by the density of plasma. These findings are important for the general understanding of the VG growth and provided a feasible way for the controllable fabrication of VG using the remote PECVD method which is usually believed to be unsuitable for the fabrication of VG.

Plasma low-energy ion flux induced vertical graphene synthesis

Vertical graphene (VG) is a promising material for energy-storage, sensor, and electronic applications, owing to excellent structural, mechanical, and electrical properties. An existing method for synthesizing VG is plasma-enhanced chemical vapor deposition under high plasma ion-energy interaction on carbon surface. However, since this method can cause substrate damage, device performance degradation, and internal defects in VG, a new synthesis method using low-ion-energy is required. Accordingly, it is necessary to understand how the plasma low-ion energy contributes to the nucleation and growth of VG by interaction with the surface, but the reported studies are limited to the high-ion-energy region. Here, we report on the effects of low-energy ion flux in plasma-induced growth of vertical graphene and found the key plasma parameter for the VG growth and nucleation in a low-ion-energy environment and successfully controlled the nucleation of VG. VG deposition and plasma parameter measurements were performed in a radiofrequency inductively coupled plasma. In the low-energy region, the growth rate and nucleation of VG depended strongly on ion density, and insufficient ion flux formed highly disordered carbon. Based on these findings, VG nucleation was controlled by tailoring the ion energy and density under conditions where disordered carbon was formed.

Controllable modulation of patterned vertical graphene through macro-geometries for high current field emitters

In this work, in-situ growth of vertical graphene (VG) in controllable patterns was achieved through macro-geometric modulation of nickel substrates, followed by the adjustment of growth density and size of VG. When VG was grown in controllable patterns, the turn-on electric field decreased from 1.04 V/μm for initial VG to 0.69 V/μm and the current variation of patterned vertical graphene (PVG, 7%) was obviously lower than that of initial VG (23%). The outstanding field emission properties of PVG were essentially attributable to the weakening of field shielding. The COMSOL simulation demonstrated that PVG reduced field shielding and VG grown on Ni aggregation provided stronger contribution to field emission. In addition, structural stability of VG and connection between VG and substrate were observed in SEM and TEM. The results had implications in understanding the influence of structural stability on field emission properties by observing the cross section of VG-substrate and the nano-structure evolution of VG before and after field emission.

Analytical modelling to study the magnetic field-assisted growth of graphene in the reactive plasma

A theoretical model has been developed to study the impact of a magnetic field on the growth of vertically aligned graphene sheets using plasma deposition techniques. The present model incorporates the dynamics of negatively charged electrons and positively charged ions and active neutral radicals of reactive gases in the complex plasma comprising Ar, C2H2, and H2 gases and deposition of these gaseous phase plasma species in the form of vertically aligned graphene sheets. The dynamics and deposition of the plasma particles can be controlled or enhanced by various process parameters and use of external magnetic field is one of the most promising way to enhance the deposition of species. In the present work, the growth of vertical graphene in a plasma environment has been studied with and without external magnetic field. The analytical simulations of the developed model revealed the significant enhancement in the growth of vertically aligned graphene sheets when magnetic field is applied in the plasma reactor. Our findings of the analytical simulations are in line with existing experimental observations.

Vertical graphene growth process optimization for use in cellular identification

Vertical graphene growth process optimization for use in cellular identification

Fluorobenzene and Water-Promoted Rapid Growth of Vertical Graphene Arrays by Electric-Field-Assisted PECVD.

Vertical graphene (VG) arrays show exposed sharp edges, ultra-low electrical resistance, large surface-to-volume ratio, and low light reflectivity, thus having great potential in emerging applications, including field emission, sensing, energy storage devices, and stray light shields. Although plasma enhanced chemical vapor deposition (PECVD) is regarded as an effective approach for the synthesis of VG, it is still challenging to increase the growth rate and height of VG arrays simultaneously. Herein, a fluorobenzene and water-assisted method to rapidly grow VG arrays in an electric field-assisted PECVD system is developed. Fluorobenzene-based carbon sources are used to produce highly electronegative fluorine radicals to accelerate the decomposition of methanol and promote the growth of VG. Water is applied to produce hydroxyl radicals in order to etch amorphous carbon and accelerate the VG growth. The fastest growth rate can be up to 15.9µm h-1 . Finally, VG arrays with a height of 144µm are successfully synthesized at an average rate of 14.4µm h-1 . As a kind of super black material, these VG arrays exhibit an ultra-low reflectance of 0.25%, showing great prospect in stray light shielding.

Conversion of vertical-to-planar graphene by morphing of copper nanostructure during a moderate temperature plasma process

The plasma-enhanced chemical vapor deposition process enables the growth of graphene at a moderate temperature, but it is vertical graphene (VG) with a large number of defects. In this letter, we report a successful method to obtain planar graphene by morphing of Cu nanostructure during a modified Ar/CH4 plasma process at 600 °C. The insertion of meshed metal shields within the plasma region reduces the magnitude of ions bombardment on the substrate. In this circumstance, the evaporated Cu with a thickness of 200 nm on a black Si template is permitted to diffuse and form a planar film. The reduced plasma etching allows the growth of VG leaves and they are converted into planar multilayer graphene during the Cu morphing process. The crystal defect on planar graphene is minimum, where the values of Raman ID/IG and ID’/IG are 1.91 ± 0.06 and 0.20 ± 0.02, respectively.

Nano-and micro-engineered vertical graphene/Ni for superior optical absorption

Black coatings benefit from low reflectance or high light absorption are utilized in multifarious optical applications. Due to their unique three-dimensional nanostructure and π-band optical transitions, vertical graphene (VG) has drawn great attention to the field of black coatings. However, how the morphology of VGs affects reflectance has not been comprehensively disclosed yet. In addition, the morphology of the substrate for VG growth also affects the absorption properties. Here, we report a nano-and micro-engineered VG/Ni structure based on VG and laser-modified nickel foil, which possesses omnidirectional low reflectance of ∼0.25% over the visible range. A larger spacing of graphene nanowalls is more conducive to the formation of light traps and improves the absorption property. Besides, the surface of nickel substrate by laser irradiation presents a “cauliflower-like” microstructure, which further enhances light-trapping ability.

PECVD of Vertical Graphene: Local Plasma or Nonlocal Plasma?

Using the plasma-enhanced chemical vapor deposition method, we grow vertical graphene thin films onto SiO2/Si substrates, which is a special format of graphene composed of numerous macroscopically uniformly distributed graphene flakes approximately vertically arranged. The growth parameters, including the growth temperature, growth time and plasma power, are systematically studied and optimized. Most importantly, the function of plasma has been revealed. In the same deposition machine, we have altered the plasma electrode and heater configurations, and found that the vertical graphene can only grow in local plasma environment. That is, the samples have to be well immersed in the plasma sheath electric field. In this way, the vertical growth of graphene and the local enhancement of electric field can form a positive feedback loop, resulting in the continuous growth of vertical graphene. This experiment clarifies the function of plasma electric field in the vertical graphene growth, and can offer hints for the growth of other vertical two-dimensional materials as well. The vertical graphene films are scalable, transfer-free and lithographically patternable, which is compatible with standard semiconductor processing and promising for optoelectronic applications. We have characterized the optical properties of the as-grown vertical graphene films, where a nearly zero transmittance is observed for 1100–2600[Formula: see text]nm wavelengths, indicating a superstrong absorption in the black colored vertical graphene.

Modulated Ar/CH4 Plasma by Metal Shield for Enhancing the PECVD Growth of Vertical Graphene

This paper presents the direct growth of vertical graphene (VG) using a metal shield (MS)-assisted plasma-enhanced chemical vapor deposition (PECVD) method. The 300 [Formula: see text] Ar/CH4 plasma is used to grow VG at 600∘C for 30 min on a 200 mm Si wafer. Without MS, the high Ar+ physical and H+ chemical rate etching of plasma prevents the growth of VG. The installation of 1 MS helps reduce the etching by reducing the ions density in the lower plasma zone and allows localized growth of VG as dark spots on the Si wafer. The crystal quality of VG grown by Ar/CH4 plasma with 1 MS is satisfyingly good with a narrow Raman I(G) peak within 36–40 cm−1, and the thickness of individual VG leaf is few-layer graphene since I(2D)[Formula: see text](G) is [Formula: see text]. The installation of 2 MS further improves the coverage, size, and population density of VG on the Si wafer by further lowering the ions density in the lower plasma zone. Further annealing of VG at 1040∘C in an Ar/H2/CH4 environment can repair the carbon sp2 but it is almost not required as the hydrogen atoms can etch the VG and reduce its coverage on a 200 mm Si wafer.

Chloroform-Assisted Rapid Growth of Vertical Graphene Array and Its Application in Thermal Interface Materials.

With the continuous progress in electronic devices, thermal interface materials (TIMs) are urgently needed for the fabrication of integrated circuits with high reliability and performance. Graphene as a wonderful additive is often added into polymer to build composite TIMs. However, owing to the lack of a specific design of the graphene skeleton, thermal conductivity of graphene‐based composite TIMs is not significantly improved. Here a chloroform‐assisted method for rapid growth of vertical graphene (VG) arrays in electric field‐assisted plasma enhanced chemical vapor deposition (PECVD) system is reported. Under the optimum intensity and direction of electric field and by introducing the highly electronegative chlorine into the reactor, the record growth rate of 11.5 µm h−1 is achieved and VG with a height of 100 µm is successfully synthesized. The theoretical study for the first time reveals that the introduction of chlorine accelerates the decomposition of methanol and thus promotes the VG growth in PECVD. Finally, as an excellent filler framework in polymer matrix, VG arrays are used to construct a free‐standing composite TIM, which yields a high vertical thermal conductivity of 34.2 W m−1 K−1 at the graphene loading of 8.6 wt% and shows excellent cooling effect in interfacial thermal dissipation of light emitting diode.

In-situ growth of vertical graphene on titanium by PECVD for rapid sterilization under near-infrared light

Alternative antimicrobials are urgently needed due to the antibiotic resistance. Herein, vertical graphene has been in-situ prepared on medical titanium (VG@Ti) by plasma-enhanced chemical vapor deposition for rapid sterilization under near-infrared light. The physicochemical properties, photothermal effect, antibacterial activity, and biocompatibility of VG@Ti were systematically investigated. The results indicated that the thickness of vertical graphene film increased with the augmentation of reaction temperature. Graphene films showed a vertical distribution on medical titanium, which improved the corrosion resistance, hydrophobicity as well as antibacterial ability against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) under near-infrared light. Inhibition rates of 93.3% and 99.1% were achieved for E. coli and S. aureus, respectively, when VG@Ti was exposed to near-infrared light (808 nm) with 0.8 W/cm2 for 10 min. Moreover, vertical graphene on titanium surface exhibit no obvious cytotoxicity to osteoblasts cells. The in vivo results confirmed that vertical graphene with near-infrared light could kill bacteria efficiently and showed no obvious toxicity.

Insights into the Mechanism for Vertical Graphene Growth by Plasma-Enhanced Chemical Vapor Deposition.

Vertically oriented graphene (VG) has attracted attention for years, but the growth mechanism is still not fully revealed. The electric field may play a role, but the direct evidence and exactly what role it plays remains unclear. Here, we conduct a systematic study and find that in plasma-enhanced chemical vapor deposition, the VG growth preferably occurs at spots where the local field is stronger, for example, at GaN nanowire tips. On almost round-shaped nanoparticles, instead of being perpendicular to the substrate, the VG grows along the field direction, that is, perpendicular to the particles’ local surfaces. Even more convincingly, the sheath field is screened to different degrees, and a direct correlation between the field strength and the VG growth is observed. Numerical calculation suggests that during the growth, the field helps accumulate charges on graphene, which eventually changes the cohesive graphene layers into separate three-dimensional VG flakes. Furthermore, the field helps attract charged precursors to places sticking out from the substrate and makes them even sharper and turn into VG. Finally, we demonstrate that the VG-covered nanoparticles are benign to human blood leukocytes and could be considered for drug delivery. Our research may serve as a starting point for further vertical two-dimensional material growth mechanism studies.

Preserving thin layer of GO for direct growth of VG using a low-etch shielded PECVD

The growth of vertical graphene (VG) on thin graphene oxide (GO) may provide a semi-insulating VG-GO. Unfortunately, the highly energetic plasma will etch out the GO template layer. In this communication, we report the use of a meshed shield to lower the physical etching on the substrate during plasma-enhanced chemical vapor deposition (PECVD). The medium-temperature of 600 °C and high-power of 300 WRF managed to grow higt h-quality VG on GO during the shielded PECVD process. GO was only slightly reduced after the process. The synthesized VG-GO film is effective as a lateral heat spreader. The heating of the peripheral heat sink was increased from 1.35 to 8.14 KW−1 with the presence of a VG-GO film. The reduction in lateral thermal resistance was better than GO and VG alone.

Vertical Graphene Growth on AlCu4Mg Alloy by PECVD Technique

Vertical graphene, which belongs to nanomaterials, is a very promising tool for improving the useful properties of long-used and proven materials. Since the growth of vertical graphene is different on each base material and has specific deposition setting parameters, it is necessary to examine each base material separately. For this reason, a full factor design of experiment was performed with 26 = 64 rounds, which contained additional 5 central points, i.e., a total of 69 rounds of individual experiments, which was to examine the effect of input factors Temperature, Pressure, Flow, CH4, Plasma Power, and Annealing in H2 on the growth of vertical graphene on aluminum alloy AlCu4Mg. The deposition was performed using plasma-enhanced chemical vapor deposition (PECVD) technology. Mainly, the occurrence of graphene was analyzed, which was confirmed by Raman spectroscopy, as well as its thickness. The characterization was performed using electron and transmission microscopy, including an atomic force microscope. It was found that the growth of graphene occurred in 7 cases and its thickness is affected only by the interaction flow (sccm) × pretreatment H2 (sccm).

ТЕОРЕТИЧНА МОДЕЛЬ ФОРМУВАННЯ ДВОВИМІРНИХ НАНОСТРУКТУР ВЕРТИКАЛЬНОГО ГРАФЕНУ ПІД ДІЄЮ ПЛАЗМИ

Vertically oriented graphene nanostructures have been grown for more than decade, but the mechanisms of their formation are still unclear. A multifactor model is proposed, which is verified by comparison with experimental data and describes the processes of growth of the structure of vertical graphene in plasma. The role of chemical and physical processes that cannot be directly characterized by available experimental methods, such as surface diffusion of adatoms and radicals under the action of ions, has been studied. Ion bombardment is a key factor that significantly accelerates the growth rate through the formation of surface defects and, consequently, increases the energy of surface adsorption. Hydrocarbon radicals formed on the substrate under the bombardment diffuse to the graphene nanosheets and serve as the main source of the construction material. Thus, the leading role in the formation of vertical graphene belongs to surface diffusion, rather than direct deposition from the gas phase. The temperature of the sample is also an important parameter, which affects the growth process according to the following mechanism: at low temperatures the adsorption from the gas phase is more intense, but the diffusion processes are slowed down; elevated temperatures have the opposite effect. The surface density of graphene nanosheets, which can be controlled at the stage of nucleation, strongly affects the height of the structure due to the redistribution of ion fluxes during the growth: as the nanosheets grow, the ion current density decreases to the side edge of the sheet and increases to the upper edge. This process leads to a decrease in the ion current density at the side edge of the nanosheet, and, as a consequence, to a change in the dependence of the graphene sheet length on time: from a saturated curve or a quasilinear time dependence to a parabolic dependence. The assumption of surface diffusion of hydrocarbon radicals as the dominant growth mechanism is consistent with existing experimental data; these results confirm the physical model, and also bring a deeper understanding of the physics of growth of vertical graphene.

Vertical graphene growth on uniformly dispersed sub-nanoscale SiOx/N-doped carbon composite microspheres with a 3D conductive network and an ultra-low volume deformation for fast and stable lithium-ion storage

Vertical graphene growth on subnanoscopically and homogeneously dispersed SiOx and carbon composite microspheres shows fast and stable lithium ion storage behavior.