Fabrication Of High Quality Graphene Research Articles

Synthesis and properties of polypropylene-graphene nanocomposite

Graphene being 2D crystalline material has attracted broad and deep interest all over the world due to its good physical, chemical, mechanical and electrical property with high shape asymmetry. Fabrication of high-quality graphene is becoming increasingly important to work on its various properties and application prospects. Recent progress on the hybrid material-based nanomaterial has greater prospects in many applications. In this investigation, commercial graphite powder is preferred as the precursor and two different solvents showing different exfoliation efficiencies, i.e., N-Methyl-2-pyrrolidone and 1-Methylnaphthalene are employed as exfoliation media. Ball milling technique, known to have successfully produced nanomaterials in large scale, is employed in this work to produce multi- layered graphene sheets. Multi-layer graphene’s are made with high aspect ratio with modifications in process parameter. The exfoliated multi-layered graphene is incorporated as filler material with polypropylene matrix to develop polymer nanocomposites. The enhanced mechanical stability of the polypropylene/graphene nanocomposite and its respective morphology is studied in this work which has applications in photovoltaics, electronic devices and facial reconstruction.

High-quality graphene from the surface of CrFeCoNiC high-entropy alloy

Graphene has shown many attractive properties while the difficulties in the fabrication of high-quality graphene have been a significant bottleneck in its applications. Here we report the discovery of high-quality graphene obtained from the solidified equiatomic CrFeCoNiC high-entropy alloy. Graphite flakes can be peeled off from the surface of the as-cast CrFeCoNiC high-entropy alloy, and single or multilayer graphene can be further exfoliated. The mechanical properties of the graphene are investigated by an atomic force microscope, and the result confirms the discovery of high-quality graphene. The transmission electron microscopy and Raman spectroscopy are applied to further characterize the quality of the graphene and show that the graphene has high-quality with few defects, comparable to the graphene obtained from highly oriented pyrolytic graphite. The thermodynamic calculation is applied to investigate the solidification process of the high-entropy alloy and reveals the mechanism of the formation of graphite on the surface.

Growth Conditions of Graphene Grown in Chemical Vapour Deposition (CVD)

The fabrication of high quality graphene has become the main interest in current chemical vapour deposition (CVD) method due to the scalability for mass production of graphene-based electronic devices. The quality of graphene is determined by defect density, number of layers and properties changed such as electron mobility, transparency and conductivity as compared to the pristine graphene. Here, we did a study on the effects of reaction conditions such as methane, CH4 concentration and deposition time towards the quality of graphene produced. We found that by lowering both CH4 concentration down to 20% and deposition time to 5 min, a better quality graphene was produced with higher I2D/IG ratio of 0.82 compared to other reaction condition. Through the analysis, we concluded that there are two important parameters to be controlled to obtain high quality graphene.

Electrochemical Fabrication of High Quality Graphene in Mixed Electrolyte for Ultrafast Electrothermal Heater

High quality graphene sheets have been considered as a promising candidate in several industrial applications due to their excellent electronic and thermal conductivity. However, the mass production of high quality graphene sheets from graphite bulk is still facing great challenges. Here we demonstrated a new approach to prepare high quality graphene by mixing a solution of oxalic acid and hydrogen peroxide as the electrolyte. The reaction did not involve the oxidation of graphite and thus exfoliated graphene possesses a uniform lateral size (2–6 μm, 78.1%), low oxygen content (2.41 at. %), few structure defects, and high conductivity of 26 692 S m–1. The optimized mixed electrolyte is environmental friendly, cheap and safe, and most importantly it is easy to be removed through low temperature heating, which facilitates graphene purification. An electrothermal heater, made from highly concentrated graphene ink (8.5 mg mL–1) on A4-size paper or polyester, exhibits excellent performance: a rapid rise of tem...

Metal-free synthesis of nanocrystalline graphene on insulating substrates by carbon dioxide-assisted chemical vapor deposition

The scalable, low-cost fabrication of high quality graphene is a subject of intense research. Here, a novel method to synthesize uniform and large area graphene films directly on various high-temperature resistant insulating substrates such as SiO2/Si, Al2O3 and quartz glass by low pressure chemical vapor deposition (LP-CVD) using a mild oxidant (CO2) and a carbon source (CH4), without the aid of any metallic species or catalysts, is reported. The resulting films are uniform and homogeneous on a large scale and comprise nanocrystalline graphene domains. Raman spectroscopy, UV–Vis spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy and electrical transport measurements were used for an initial characterization of the synthesized graphene films. The optical and electrical properties of the film can be easily tuned together with layer thickness by controlling process conditions, like temperature, chamber pressure and process gas composition. The obtained graphene films show excellent electrical transport properties with high charge carrier mobilities up to 720 cm2/(Vs). These directly grown graphene films are readily applicable in a wide range of application fields, such as sensors, transparent conductive coatings and electronic devices.

Fabrication of high-quality graphene by hot-filament thermal chemical vapor deposition

To the best of our knowledge, the previously reported graphene fabricated using catalytic chemical vapor deposition techniques contained a high defect density, which will hinder its opto-electronic properties. In this work, the effects of two crucial parameters, namely deposition time and hydrogen flow rate on the growth of graphene using a hot-filament thermal chemical vapor deposition technique were systematically studied. Fabrications were conducted at substrate and filament temperatures of 1000°C and 1750°C, respectively. Very low ID/IG ratios (≪0.1) were obtained for all the samples, which reflected the formation of high-quality graphene deposited on Cu foils. A quasi-static equilibrium copper vapor inside an alumina tube was found to be an important factor to obtain a low defect density graphene. A growth mechanism was then proposed, where the cuprous oxide (Cu2O) acted as a nucleation site for graphene growth.

Scalable fabrication of high quality graphene by exfoliation of edge sulfonated graphite for supercapacitor application

Graphene sheets with high quality and dispersibility were prepared by exfoliation of edge sulfonated graphite. Tosyl-graphene (TsG) dispersion in N-methyl-pyrrolidone (NMP) readily reached up to 16 mg mL−1 without any surfactants. TsG enjoys intact crystal planes and flexible framework. When employed as electrode material for supercapacitor, TsG shows outstanding specific capacitance of 180 F g−1 at a current density of 0.5 A g−1, and excellent cycling stability (only 2% loss after 10 000 cycles), which can offer enormously potential for super-capacitors and other highly desired energy storage devices.

Atomistic processes of grain boundary motion and annihilation in graphene

The motion and annihilation of a grain boundary (GB) in graphene are investigated by tight-binding molecular dynamics (TBMD) simulation and ab initio local density approximation total energy calculation. A meandering structure of the GB is found to be energetically more favorable than other structures, in good agreement with experiment. It is observed in the TBMD simulation that evaporation of carbon dimers and sequential Stone–Wales transformations of carbon bonds lead to rapid motion and annihilation of the GB. The dimer erection and evaporation are found to proceed by formation of an adatom due to bond breaking. These results shed interesting light on the fabrication of high-quality graphene.

High quality 2D crystals made by anodic bonding: a general technique for layered materials

Anodic bonding of nanolayers is an easy technique based on a simple apparatus, which has already proven successful in application in the fabrication of high quality graphene. Here we demonstrate its extension to the fabrication of high quality nanolayers from several layered materials. The strengths of this technique are its high throughput rate and ease of application. All fabrication parameters are controllable and need to be determined carefully. We report optimal parameters found for nine layered materials. In general, using optimal parameters results in high quality 2D layers, in most cases much larger than those obtained by ‘Scotch tape’ microcleavage, with higher yields and which are easily transferable to other substrates. Moreover the samples obtained are clean and the good optical contrast of these layers on the glass substrate makes their identification very easy. This is thus the technique of choice for making nanolayers in the laboratory from any layered material.

Facile fabrication of high quality graphene from expandable graphite: simultaneous exfoliation and reduction

High quality graphenes were prepared from low-cost expandable graphite via a facile hydrazine hydrate or concentrated ammonia-assisted quenching strategy.