Structure Properties Of Graphene Research Articles

Structural Properties of Graphene

Graphene, a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice with six carbon atoms, are of two types due to their bonding. Due to its structural uniqueness, properties of the grapheme is found to be very different and important in application point of view. Hence, the authors have studied the structural properties as co-ordination number, coordinates, distances of nearest atoms from 1st to 5th, analytically using two dimensional coordinate system taking one atom of a unit cell at the origin. Furthermore, packing fraction is also calculated, as the property is very important to study absorption/adsorption of different atoms into the sheet of it.

Electron-beam chemistry in graphene - Effect of environmental SEM parameters on patterning and defect engineering

The engineering of defects in low-dimensional materials can enable the modulation of their optical, electrical, thermal, and structural properties. We have previously shown the ability to engineer precision patterned defects in graphene by electron beam irradiation in a controlled water vapor ambient within an environmental scanning electron microscope (ESEM). However, the relationship between instrumental parameters and structural changes in graphene are unexplored. Here, we investigate the relationships between parameters such as pressure, electron dose, and acceleration voltage on the electronic and structural properties of graphene as probed by Raman spectroscopy. There are dependencies on all of the studied parameters but electron dose is the dominant parameter that shows the most intense levels of structural modulation. Interestingly, control of instrumental parameters allows for the precision tailoring of features such as resolution (as determined by the beamskirting effect), doping, and functionalization – all of which make this process powerful for precision tuning of 2D materials and adds an enhanced technique for the development of next-generation electronics.

Platinum Nanocrystals Embedded in Three-Dimensional Graphene for High-Performance Li-O2 Batteries.

Graphene is considered as a promising cathode candidate for Li-O2 batteries because of its excellent electronic conductivity and oxygen adsorption capacity. However, for Li-O2 batteries, the self-stacking effect caused by two-dimensional (2D) structural properties of graphene is not conducive to the rapid oxygen transport and mass transfer process, thereby affecting the electrode kinetics. Here, we successfully prepared three-dimensional (3D) graphene with different scales by plasma-enhanced chemical vapor deposition and physical pulverization strategies, in which CH4 is the carbon source and H2/Ar mixed gas is the etching gas. Meanwhile, we fabricated 3D graphene-based Pt nanocatalysts by an ultraviolet-assisted construction strategy and then applied them in Li-O2 batteries. Systematic studies reveal a special relevance between electrochemical performance and graphene particle size, and the smaller-sized 3D graphene can better maintain the microstructure distribution in both the Pt embedding process and electrochemical applications, which is beneficial to the transport of oxygen and Li ions, lowering the decomposition energy barrier of Li2O2, and further obtaining reduced charge overpotential (0.22 V) and prolonged cycle life for Li-O2 batteries. Finally, we anticipate that this work could promote the practical application of 2D materials and larger-sized 3D materials in Li-O2 batteries.

Prediction of Exchange-Correlation Energy of Graphene Sheets from Reverse Degree-Based Molecular Descriptors with Applications.

Over the past few years, the popularity of graphene as a potential 2D material has increased since graphene-based materials have applications in a variety of fields, including medicine, engineering, energy, and the environment. A large number of graphene sheets as well as an understanding of graphene’s structural hierarchy are critical to the development of graphene-based materials. For a variety of purposes, it is essential to understand the fundamental structural properties of graphene. Molecular descriptors were used in this study to investigate graphene sheets’ structural behaviour. Based on our findings, reverse degree-based molecular descriptors can significantly affect the exchange-correlation energy prediction. For the exchange-correlation energy of graphene sheets, a linear regression analysis was conducted using the reverse general inverse sum indeg descriptor, . From , a set of reverse topological descriptors can be obtained all at once as a special case, resulting in a model with a high correlation coefficient (R between 0.896 and 0.998). Used together, these reverse descriptors are graphed in relation to their response to graphene. Based on this study’s findings, it is possible to predict the exchange correlation energy as well as the geometric structures of graphene sheets with very little computational cost.

Research and Analysis of Graphene Coatings Based on Knowledge Mapping

Graphene coating is a new type of coating made by using the unique structural properties of graphene. It has broad application prospects of anticorrosive coatings, conductive coatings and heat-dissipating coatings. In order to study the development of graphene coating technology research, we use CiteSpace information visualization software, based on the literature of 8 813 articles in the research and application of graphene coatings in Web of Science database from 2010 to 2018. From the perspective of literature measurement, we apply the knowledge map to research the national, discipline and related hotspot analysis of graphene coating research, cited literatures and research frontier status. By comparing and analyzing the literature information on the field of graphene coating research and application at home and abroad, the research progresses and development trend of graphene coatings can be evaluated from the disciplinary distribution and research fronts. It is pointed out that the wear resistance of graphene coatings is the focus of the future research.

A DFT study on the electronic structure of in-plane heterojunctions of graphene and hexagonal boron nitride nanoribbons

The structural similarity between hexagonal boron nitride (h-BN) and graphene nanoribbons allows forming heterojunctions with small chain stress. The insulation nature of the former and the quasi-metallic property of the latter make them attractive for flat optoelectronics. Recently, shapes of graphene and h-BN domains were precisely controlled, creating sharp graphene/h-BN interfaces. Here, we investigated the electronic and structural properties of graphene (h-BN) nanoribbon domains of different sizes sandwiched between h-BN (graphene) nanoribbons forming in-plane heterojunctions. Different domain sizes for the non-passivated zigzag edge termination were studied. Results showed that the charge density is localized in the edge of the heterojunctions, regardless of the domain size. The systems with graphene domains are metallic, presenting null band gaps. The ones with the h-BN island are small-bandgap semiconductors with the highest bandgap value around 0.2 eV. The calculated bandgap has the same magnitude of the certain threshold for density functional theory. As a general trend, these materials exhibit a ferromagnetic behavior, which can be useful for magnetic applications at the nanoscale.

Synthesis and physical characterization of magnetron sputtered Graphene-CdS bilayer

CdS/Graphene Nano composites have been extetinsively investigated in the field of basic industrial research and electronic device applications because of their unique physical, chemical properties and photo stability under visible‐light irradiation. In this study, we explore the electrical properties of Cadmium sulfide with the addition of graphene. CdS/Graphene hybrid was fabricated by simple RF magnetron sputtering method using CdS as a sputtering source. The hybrid material formation and structural properties of Graphene, CdS, CdS/Graphene have been discussed using XRD, FTIR, Raman, and UV–vis spectroscopy techniques. Herein, we present a facile and efficient method for hybridization of CdS Nano-sphere with graphene Nano sheet and subsequent investigation of enhancement of current of the hybrid material. Field emission scanning electron microscopy (FESEM) micrographs reveal the formation of CdS nanospheres and homogeneous scattering on the surface of graphene sheets. The UV absorption spectrum of CdS/Graphene hybrid presented a red-shifted. The enhancement in the current of CdS/Graphene hybrid has been observed due to the generation of electron-hole pairs. Also, current-voltage (I-V) characteristics of an as-grown thin film of the hybrid are conducted using 4-point probe measurement and revealed their semiconducting nature with a drastic enhancement of electrical conductivity.

Exfoliation and Noncovalent Functionalization of Graphene Surface with Poly-N-Vinyl-2-Pyrrolidone by In Situ Polymerization.

Heteroatom functionalization on a graphene surface can endow the physical and structural properties of graphene. Here, a one-step in situ polymerization method was used for the noncovalent functionalization of a graphene surface with poly-N-vinyl-2-pyrrolidone (PNVP) and the exfoliation of graphite into graphene sheets. The obtained graphene/poly-N-vinyl pyrrolidone (GPNVP) composite was thoroughly characterized. The surface morphology of GPNVP was observed using field emission scanning electron microscopy and high-resolution transmission electron microscopy. Raman spectroscopy and X-ray diffraction studies were carried out to check for the exfoliation of graphite into graphene sheets. Thermogravimetric analysis was performed to calculate the amount of PNVP on the graphene surface in the GPNVP composite. The successful formation of the GPNVP composite and functionalization of the graphene surface was confirmed by various studies. The cyclic voltammetry measurement at different scan rates (5–500 mV/s) and electrochemical impedance spectroscopy study of the GPNVP composite were performed in the typical three-electrode system. The GPNVP composite has excellent rate capability with the capacitive property. This study demonstrates the one-pot preparation of exfoliation and functionalization of a graphene surface with the heterocyclic polymer PNVP; the resulting GPNVP composite will be an ideal candidate for various electrochemical applications.

Изучение парамагнитных свойств графеновых структур, полученных при воздействии ультразвука на чистый графит в органических реагентах

Изучение парамагнитных свойств графеновых структур, полученных при воздействии ультразвука на чистый графит в органических реагентах

Biological and structural properties of graphene oxide/curcumin nanocomposite incorporated chitosan as a scaffold for wound healing application

AimsThe purpose of this research is to fabricate chitosan (CS)/graphene oxide (GO)/curcumin (Cur) 3D scaffolds through the freeze-drying method for wound dressing applications. Main methodsGO is produced by Hammer's method; then, it is characterized by X-ray diffraction and TEM analysis. Fabricated scaffolds are characterized by FTIR, FESEM, AFM, water vapor transmission rate, PBS absorption, contact angle, tensile strength, porosity measurement, biodegradability, and drug release methods. The cell viability and morphology of NIH/3 T3 cells are investigated by WST assay kit and FESEM analysis, and the antibacterial activity of scaffolds is determined by the optical density (OD) method. The photothermal antibacterial activity is characterized by NIR irradiation, too. Key findingsThe mean pore diameter of scaffolds adjusted by the incorporation of about 0–1.5%wt. of GO/Cur nanocomposite into CS matrix, decreasing from 87 to 40 μm that can be attributed to the intermolecular bonds between CS and GO/Cur nanocomposite. Besides, the PBS absorption of scaffolds enhances by the addition of GO/Cur, especially 1% of it. Furthermore, the overall average of cell viability of nanocomposite scaffolds is about 95%, and the FESEM images show that NIH/3T3 fibroblasts well spread on the nanocomposite scaffolds. GO/Cur has a significant influence on the antibacterial activity of CS scaffolds as CS/GO/Cur 0.5 scaffold diminishes the bacterial growth to about 52% of the control sample's growth. SignificanceThe results evidence the antibacterial CS/GO/Cur scaffolds are excellent supports for cell growth and proliferation, and they could be promising candidates for wound dressing applications.

Epitaxial Graphene Growth on the Step‐Structured Surface of Off‐Axis C‐Face 3C‐SiC(1¯1¯1¯)

Graphene layers grown on the C‐face SiC exhibit quite different structural and electronic properties compared with those grown on the Si‐face SiC. Herein, the growth and structural properties of graphene on the off‐axis C‐face 3C‐SiC() are studied. The as‐grown 4° off‐axis 3C‐SiC() exhibits highly periodic steps with step height of ≈0.75 nm and terrace width of ≈50 nm. After annealing at 1800 °C under 850 mbar argon atmosphere, relatively uniform large graphene domains can be grown. The low‐energy electron microscopy (LEEM) results demonstrate that one monolayer (ML) to four‐ML graphene domains are grown over several micrometers square, which enables us to measure micro low‐energy electron diffraction (μ‐LEED) on the single graphene domain. The μ‐LEED pattern collected on the monolayer domain mainly exhibits four sets of graphene (1 × 1) spots, indicating the presence of graphene grains with different azimuthal orientations in the same graphene sheet. Raman spectra collected on the graphene domains show rather small D peaks, indicating the presence of less defects and higher crystalline quality of the graphene layers grown on the C‐face off‐axis 3C‐SiC().

Green synthesis, characterization and potential application of reduced graphene oxide

This study investigates the structure and composition of graphene produced by thermal reduction of graphene oxide (GO) at various temperatures, for short time (5 min). The influence of reduction temperature on the structural properties of graphene was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier Transform Infrared (FTIR) spectroscopy, UV–Vis spectroscopy, thermogravimetric analysis (TGA), Raman and X-ray photoelectron spectroscopy (XPS). We demonstrated that by controlling the temperature in the annealing process, we can design materials with desired composition to meet the necessities for future or existing applications. The synthesized materials proved to have great potential in the atenolol adsorption from wastewater at room temperature (61% removal efficiency after 30 min).

Structural properties of graphene on copper substrates

Introduction. Studies of the substrate influence on graphene properties are relevant due to the high sensitivity of this two-dimensional material to the smallest effects. At the same time, studies dedicated to the separation of direct substrate influence and residual synthesis effects on graphene properties are not described in the literature in sufficient detail. Materials and methods. This paper presents the results of a study of the structural properties of as-grown and transferred graphene on copper substrates by Raman spectroscopy and atomic force microscopy. Results and discussion. Using Raman spectroscopy, we found that the mechanical strain in the as-grown grapheme is increased, while negligibly small in transferred graphene, the strain coefficients being of 0.22– 0.33 and ∼ 0 %, respectively. Using atomic force microscopy, we showed that this effect does not relate to the copper surface irregularities: the average roughness of the substrate surface for as-grown graphene was of 20.4 nm, while for the transferred graphene it was of 62.0 nm, the height difference being of almost an order of magnitude greater for the latter. This contradiction was explained in terms of residual synthesis effects present in case of as-grown graphene. Conclusion. Taking into account the analyzed substrate effects is important both for the refinement of methods for the initial characterization of as-grown graphene, and for practical applications requiring graphene transfer to corrugated and perforated substrates, membranes and objects of complex shape.

First-principles study on structural stability of graphene oxide and catalytic activity of nitric acid

The stability and electronic structure properties of graphene fumigated by nitric acid are systematically studied by the first-principles method based on ultrasoft pseudopotentials. The model of graphene oxide fumigated by nitric acid is built based on the 2 × 2 supercell model with orthogonal graphene unit cells, which contains 15 carbon and 2 oxygen atoms. The results show that the fumigated graphene containing a carbon atom bonded to an oxygen atom is a stable structure with lower energy, which is consistent with the experimental result. In addition, the mechanical stability analysis shows <inline-formula><tex-math id="Z-20191212071737-1">\begin{document}${ {C_{66}} > 0,\;{C_{11}} > 0,\;{C_{11}}{C_{22}} > C_{12}^2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20191304_Z-20191212071737-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20191304_Z-20191212071737-1.png"/></alternatives></inline-formula>, which satisfies the mechanical stability condition. By analyzing the reactant and product, it can be concluded that the nitric acid acts as catalyst. Moreover, the process of graphene oxidation catalyzed by nitric acid is endothermic and the reaction needs heating. By analyzing the electronic properties of the structure, the graphene oxide is determined to be an intrinsic semiconductor with a direct band gap of 1.12 eV and work function of 5.28 eV. These results provide theoretical basis for preparing the graphene oxide and its applications in the field of optoelectronic devices.

Role of oxygen functional groups for improved performance of graphene-silicone composites as a thermal interface material

We report the findings of our experimental investigation on the performance of reduced graphene oxide (rGO)/silicone composite as a thermal interface material (TIM) influenced by the loading factor, surface functionality, and structural properties of graphene. The experimental data reveals that in addition to the loading factor, the thermal conductance of TIMs is greatly impacted by the density of oxygen-functionality (phenolic group) in rGO, and the morphological and structural properties introduced during the thermal reduction (deoxygenation) of graphene oxide to rGO. In particular, the phenolic groups prominently formed on the basal plane of rGO play a significant role in decreasing the interfacial thermal resistance. The results also show that the larger sp2 graphitic structures and the morphological properties of rGO increase the degree of dispersion in the matrix. A dynamic interplay between these factors determines the final value of the thermal conductance observed for different composites. An optimum combination of these factors led to the maximum thermal conductance (541 W/m2K) for the T-rGO600 (thermally-reduced graphene oxide processed at 600 °C)/silicone composite. The proposed underlying physics backed by the experimental data should be useful in designing high thermal performance TIMs with carbonaceous nanomaterials, including carbon nanotubes, graphene nanoplatelets, and carbon blacks acting as additives.

Simple Model of Nonlinear Spin Waves in Graphene Structures

A series of theoretical and experimental works is known which investigated the magnetic properties of graphene structures. This is due, among other things, to the prospects of using graphene as a material for the needs of the future nanoelectronics and spintronics. In particular, it is known about the presence of ferromagnetic properties at temperatures up to 200 C and above in a single-layer graphene films that are free from impurities. Previously there was proposed a quantum field theoretical model describing the possible mechanism of ferromagnetism in graphene as a result of spontaneous breaking of spin symmetry of the surface density of valence electrons. The possible spatial configurations of the localized spin density were described. In this paper we investigate such spatially localized nonlinear spin configurations of the valence electron density on the graphene surface such as kinks, and their interactions, as well as quasibound metastable states of the interacting kinks and antikinks, that are breathers. The spectrum of such breathers is investigated. It is shown that under certain conditions, this spectrum has a discrete sector, which, in turn, allows us to speak about the possibility of coherent quantum generation of spin waves in graphene structures, which is important in terms of practical applications in nanoelectronics and spintronics.

Geometric Multigrid for the Tight-Binding Hamiltonian of Graphene

In order to calculate the electronic properties of graphene structures a tight-binding approach can be used. The tight-binding formulation leads to linear systems of equations which are maximally i...

Graphene and related 2D materials: An overview of the Raman studies

After a brief overview of the discovery and the Raman study of new forms of carbons (intercalated graphite, carbon fiber, fullerenes, carbon nanotubes), the invaluable contribution of late Professor M. Dresselhaus is noted, and the 10 reviews and 9 contributions collected to present a picture of the current Raman investigations of graphene and related 2D materials (such as black phosphorus, MoS2) are introduced. Methods for numbering the graphene layers, the effects of external perturbations (temperature, pressure, doping, and magnetic field) on the phonons of graphene, characterization of the chemical and structural properties of graphene at the nanoscale level by tip‐enhanced Raman spectroscopy, surface enhanced Raman spectroscopy and hyperspectral imaging, and applications combining graphene and Raman spectroscopy are addressed. Copyright © 2017 John Wiley & Sons, Ltd.

Carbon Precursor Structures and Graphene on Palladium Nanoparticles

Due to their stable catalytic properties graphene-encapsulated metal nanoparticles (NPs) have come into the focus of heterogeneous catalysis. Research on graphene’s atomic structure is a prerequisite for understanding and controlling catalytic processes; however, it is still at its very beginning considering metal NPs. This atomic-scale scanning tunnelling microscopy study documents preliminary growth stages and the structural properties of graphene on highly oriented pyrolytic graphite (HOPG) supported palladium NPs. It is shown that an annealing of the NPs at ∼650 °C in a few tens of Langmuir of ethylene (ethene) leads first to a carbon precursor structure covering the NP’s (111) facets. At higher ethylene exposures, the precursor structure turns into single-layer graphene encapsulating the NPs. Graphene-encapsulated palladium NPs with a size larger than ∼30 nm exhibit mostly one single and an almost defect-free graphene sheet on a facet. In most of the cases, such a perfect growth does not take place o...

Alloyed surfaces: New substrates for graphene growth

We report a systematic ab-initio density functional theory investigation of Ni(111) surface alloyed with elements of group IV (Si, Ge and Sn), demonstrating the possibility to use it to grow high quality graphene. Ni(111) surface represents an ideal substrate for graphene, due to its catalytic properties and perfect matching with the graphene lattice constant. However, Dirac bands of graphene growth on Ni(111) are completely destroyed due to the strong hybridization between carbon pz and Ni d orbitals. Group IV atoms, namely Si, Ge and Sn, once deposited on Ni(111) surface, form an ordered alloyed surface with 3×3-R30° reconstruction. We demonstrate that, at variance with the pure Ni(111) surface, alloyed surfaces effectively decouple graphene from the substrate, resulting unstrained due to the nearly perfect lattice matching and preserves linear Dirac bands without the strong hybridization with Ni d states. The proposed surfaces can be prepared before graphene growth without resorting on post-growth processes which necessarily alter the electronic and structural properties of graphene.