Carbon Atoms In Graphene Research Articles

Ni-Doped Epitaxial Graphene Monolayer on the Ni(111) Surface

Nickel-doped graphene has been synthesized from propylene on a Ni(111) surface and studied using scanning tunneling microscopy (STM) and density functional theory (DFT). It is established that nickel centers are formed during graphene synthesis on the Ni(111) surface by both chemical vapor deposition (CVD) and temperature-programmed growth (TPG); apparently, they are always present in graphene synthesized on Ni(111). The centers are observed in STM images as single defects or defect chains and identified by DFT calculations as Ni atoms in carbon bivacancies. These nickel atoms are positively charged and may be of interest for single-atom catalysis. The incorporated Ni atoms should remain in graphene after the detachment from the substrate since they bound more strongly with carbon atoms in graphene than with substrate nickel atoms.

Novel Sr5(PO4)2SiO4-graphene nanocomposites for applications in bone regeneration in vitro

This work mainly focused on the development of novel nanocomposites with combination of strontium phosphosilicates (SPS: Sr5(PO4)2SiO4) and graphene (G) for bone regeneration applications. Firstly, we have adopted the sol-gel method to synthesize the rod shaped nanosized SPS powder using CTAB as a surface morphology directing agent. Secondly, we have attempted a new approach to grow the graphene on the nanosized SPS by chemical vapour deposition technique, whereas SPS acts as self catalyst for the generation of graphene. The Raman analysis proved the existence of graphene with a few layers in G@SPS nanocomposites. The XPS confirms the presence of sp2 hybridized carbon atoms in graphene by detecting peak position at 284.4 eV. In vitro apatite study demonstrates the deposition of needle like shaped amorphous apatite layer on G@SPS. The 50–250 µg/ml of G@SPS were assessed to examine its in vitro cytocompatibility behaviour using mBMSCs and found to stimulation of cell proliferation. The G@SPS possesses relative alkaline phosphatase activity, calcium deposition and osteogenic differentiation ability. Also, G@SPS shown no toxicity on HUVECs and significantly encouraged the cell proliferation. Therefore, this finding provides the development of G@SPS nanocomposites with improved biological properties can acts potential candidate for future bone tissue engineering applications.

A New Approach of Mathematical Analysis of Structure of Graphene as a Potential Material for Composites.

The new analysis of a simplified plane model of single-layered graphene is presented in this work as a potential material for reinforcement in ultralight and durable composites. However, owing to the clear literature discrepancies regarding the mechanical properties of graphene, it is extremely difficult to conduct any numerical analysis to design parts of machines and devices made of composites. Therefore, it is necessary to first systemize the analytical and finite element method (FEM) calculations, which will synergize mathematical models, used in the analysis of mechanical properties of graphene sheets, with the very nature of the chemical bond. For this reason, the considered model is a hexagonal mesh simulating the bonds between carbon atoms in graphene. The determination of mechanical properties of graphene was solved using the superposition method and finite element method. The calculation of the graphene tension was performed for two main directions of the graphene arrangement: armchair and zigzag. The computed results were verified and referred to articles and papers in the accessible literature. It was stated that in unloaded flake of graphene, the equilibrium of forces exists; however, owing to changes of inter-atom distance, the inner forces occur, which are responsible for the appearance of strains.

Atomic mechanism of strong interactions at the graphene/sapphire interface

For atomically thin two-dimensional materials, interfacial effects may dominate the entire response of devices, because most of the atoms are in the interface/surface. Graphene/sapphire has great application in electronic devices and semiconductor thin-film growth, but the nature of this interface is largely unknown. Here we find that the sapphire surface has a strong interaction with some of the carbon atoms in graphene to form a C-O-Al configuration, indicating that the interface interaction is no longer a simple van der Waals interaction. In addition, the structural relaxation of sapphire near the interface is significantly suppressed and very different from that of a bare sapphire surface. Such an interfacial C-O-Al bond is formed during graphene growth at high temperature. Our study provides valuable insights into understanding the electronic structures of graphene on sapphire and remote control of epitaxy growth of thin films by using a graphene–sapphire substrate.

On the graphene Hamiltonian operator

We solve a second-order elliptic equation with quasi-periodic boundary conditions defined on a honeycomb lattice that represents the arrangement of carbon atoms in graphene. Our results generalize those found by Kuchment and Post (Commun Math Phys 275(3):805–826, 2007) to characterize not only the stability but also the instability intervals of the solutions. This characterization is obtained from the solutions of the energy eigenvalue problem given by the lattice Hamiltonian. We employ tools of the one-dimensional Floquet theory and specify under which conditions the one-dimensional theory is applicable to the structure of graphene. The systematic study of such stability and instability regions provides a tool to understand the propagation properties and behavior of the electrons wavefunction in a hexagonal lattice, a key problem in graphene-based technologies.

Klein collimation by rippled graphene superlattice

The hybridization of and orbitals of carbon atoms in graphene depends on the surface curvature. Considering a single junction between flat and rippled graphene subsystems, it is found an accumulation of charge in the rippled subsystem due to Klein penetration phenomenon that gives rise to n–p junction. Using this fact, we show that the momentum distribution of electrons in ballisitically propagating beam can be selective without a waveguide, or external electric, and/or magnetic fields in graphene strip under experimentally feasible one-dimensional periodic potential. Such a potential is created with the aid of superlattice that consists of periodically repeated graphene pieces with different hybridizations of carbon orbits, produced by variation of the graphene surface curvature. The charge redistribution and selected transmission of electrons, caused by the superlattice, allows to control the electron focusing in the considered system by simply changing the element properties in the superlattice.

How hydrogen sticks to graphene

The 2-D sheet of sp2-hybridized carbon atoms in graphene helps grant the material unique and useful chemical, material, and electronic properties. Adding hydrogen atoms to the carbons can improve those properties—for example, by turning graphene into a semiconductor. New laboratory and computational experiments reveal how energy dissipates through a graphene sheet when hydrogen atoms strike it, making C–H bond formation possible (Science 2019, DOI: 10.1126/science.aaw6378). Alec. M. Wodtke of the University of Gottingen and the Max Planck Institute for Biophysical Chemistry was experimenting with hydrogen scattering from metal surfaces when his group observed that graphene grown on platinum behaved differently. Hydrogen and metal atoms collide like billiard balls, he says, but when hydrogen hits a graphene carbon it doesn’t bounce off, it forms a bond. Wodtke’s collaborator, Thomas F. Miller III of the California Institute of Technology, used computational models to better understand what happens. When st...

First-principles study of a vertical spin switch in atomic scale two-dimensional platform

Abstract High in-plane charge carrier mobility and long spin diffusion length makes graphene a unique material for spin-based devices. However, in a vertical graphene junction, the 2pz orbitals of carbon atoms in graphene can be tuned via suitable magnetic substrates; this would affect the spin injection into graphene. Here, a vertical spin switch has been designed by embedding a single layer of graphene as a tunnel layer between the Ni (1 1 1) substrate. Periodic density functional approach in conjunction with Julliere’s model is used to calculate the tunnel magnetoresistance (TMR). Further, single-layered hexagonal Boron Nitride (h-BN) is sandwiched between the graphene and Ni (1 1 1) substrate to understand the role of hybridization at the interface on TMR. Our calculation shows that in contrast to the graphene junction, a much higher TMR value is obtainable in the case of the graphene/h-BN multi-tunnel junction (MTJ). The TMR in graphene junction is found to decrease with the increase of an externally applied electric field, and drops to zero for a field greater than equal to 0.16 V/A. Similar phenomenon was observed in the case of h-BN/graphene MTJ, where TMR value remains unchanged for electric field up to 0.1 V/A beyond which it drops to zero. The change in hybridization and charge-carrier-population at the interface modifies the magnetic exchange interaction and magnetic anisotropy resulting in a spin flip at interface, leads to rapid drop in TMR after a threshold electric field. The high and tunable TMR value suggests h-BN assisted high performance graphene based vertical spin switch.

Recent Progress on Germanene and Functionalized Germanene: Preparation, Characterizations, Applications, and Challenges.

A new family of single-atom-thick 2D germanium-based materials with graphene-like atomic arrangement, germanene and functionalized germanene, has attracted intensive attention due to their large bandgap and easily tailored electronic properties. Unlike carbon atoms in graphene, germanium atoms tend to adopt mixed sp2 /sp3 hybridization in germanene, which makes it chemically active on the surface and allows its electronic states to be easily tuned by chemical functionalization. Impressive achievements in terms of the applications in energy storage and catalysis have been reported by using germanene and functionalized germanene. Herein, the fabrication of epitaxial germanene on different metallic substrates and its unique electronic properties are summarized. Then, the preparation strategies and the fundamental properties of hydrogen-functionalized germanene (germanane or GeH) and other ligand-terminated forms of germanene are presented. Finally, the progress of their applications in energy storage and catalysis, including both experimental results and theoretical predictions, is analyzed.

A hydrothermal reacting approach to prepare few-layer graphene from bulk graphite

The paper presents a simple, efficient and high-quality method for preparing few-layer graphene during the hydrothermal synthesis of magnesium silicate hydroxide (MSH) using bulk graphite as initial material. This type of graphene was characterized by high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Results show that the graphene obtained using this method is coated on the outer surface of MSH nanoparticles and stacked by 8–12 single graphene sheets with an approximate interlayer spacing of 0.34 nm. The graphene-MSH interface connects via chemical bonds of C-OH, CO and CH that formed between carbon atoms in graphene and active oxygen atoms and/or hydroxyl groups in MSH. This simple solution-phase approach offers a greater possibility in the large-yield, environmental and lattice-perfect produce of graphene using only bulk graphite as the raw material.

A transport isolation by orbital hybridization transformation toward graphene nanoribbon-based nanostructure integration

Among feature-rich graphene-related materials, graphene nanoribbon (GNR)-based nanostructures are particularly attractive because they can provide tunable and excellent electronic properties. However, the integration of high-quality GNR-based nanostructures on a large scale is still an open area. In this paper, a novel idea is proposed: transport isolation. By a construction of different orbital hybridizations of the carbon atoms in graphene, the GNR regions and functionalized graphene regions are integrated. In the hybrid system, the functionalized graphene regions play the role of the isolation barrier. Based on the first principle calculation, it is demonstrated that about 0.6 nm wide hydrogenated graphene is enough to reliably isolate the GNR regions. Besides, it is revealed that once the armchair GNRs (AGNRs) are fully isolated by functionalized graphene, their band gaps are basically maintained and are weakly dependent on the width of functionalized graphene regions. In addition, the transport characteristics of those isolated AGNRs are verified to be similar to the pristine AGNRs at the device level. The above virtues infer our method can effectively produce a reliable isolation, verified by a simulation of device integration demo. We hope it can provide an intriguing option for the integration of GNR-based nanostructures.

Spin dynamics in graphene-like nanocarbon, graphene and their nitrogen adatom derivatives

Ulterior computational device is atomic electron in which information route would be precision spin gyration. This demands to investigate spin dynamics in realistic graphene. Our scenario presents spin transport data obtained using electron spin resonance spectroscopy, over 123–473 K for graphene, graphene-like nanocarbon (GNCs) and their nitrogen (N)-doped derivatives. Variations in dispersion widths and anisotropy in effective g-factor indicated modifications in spin–lattice, and spin–spin relaxation time, for both systems after N loading. Particularly, for GNCs contributions of orbital moments to spin inhomoginities are reduced. It resembles with variations observed for spin–orbit coupling constant and spin-flip factor. Flip of spin is more favorable, for N-GNCs, due to retardation in momentum- and spin relaxation rate. Nitrogen narrowed down mid gap states in GNCs and has profound impact on modifications in pseudo chemical potential with reduced density of states, effective magnetic moment, and spin and defect concentration. The variations in spin parameters are opposite, especially, for N-graphene. The spin susceptibility indicated that, there are ~ 10 non-interacting spins per 100 carbon atoms in graphene, and GNCs which is reduced by 50%, especially, for spin correlated, N-GNCs. Atomically engineered spin degrees of constraints are useful for spintronic applications.

Scalable fabrication of ultrathin free-standing graphene nanomesh films for flexible ultrafast electrochemical capacitors with AC line-filtering performance

The commercialized aluminum electrolytic capacitors (AECs) currently used for alternating current (AC) line-filtering have low specific capacitances, making them usually the largest components in electronic circuits. Herein, an ultrathin free-standing graphene nanomesh film (GMF) with uniform and dense nanoholes has been successfully fabricated by an in-situ carbothermal reduction strategy on the basis of spontaneously assembled graphene hybrid film. Due to the carbothermal reduction reaction between carbon atoms of graphene and the metal oxide nanoparticles in-situ generated during assembly process, in-plane nanopores are generated within graphene film. The pore size and density of GMF can be conveniently tuned by annealing temperature. With large ion-accessible surface area, efficient ion diffusion and electron transport pathways, the typical GMF-based electrochemical capacitor (EC) exhibits a high volumetric capacitance of up to 7.6 F cm−3 at 120 Hz, unprecedented power density of up to 3000 W cm−3, ultrafast frequency response with a phase angle of −82.3°, and a short resistor-capacitor time constant of 0.32 ms at 120 Hz, as well as long-term cycling stability. The performances of these ECs are superior to those of the state-of-the-art carbon-based ECs for this purpose; thus, it is promising to replace commercialized AECs for AC line-filtering in future electronics.

Alterations in ambipolar characteristic of graphene due to adsorption of Escherichia coli bacteria

In order to evaluate the interaction between biomaterials and graphene from the perspective of its ambipolar characteristic, we have investigated the alteration in ambipolarity of graphene-based field effect transistors (G-FET) after the adsorption of Escherichia coli (E. coli) bacteria onto its graphene layer. We confirmed a positive shift in the ambipolar curve of the G-FETs after the adsorption of E. coli, presumably due to the negative charge of the adsorbed E. coli. However, we did not observe any decrease in the electron mobility or conductivity of the G-FETs, which implied that E. coli did not chemically react with the carbon atoms of graphene, nor introduce any damage on the graphene lattice, but were only physically adsorbed onto the graphene surface. These findings may extend the prominence of graphene as a stable yet sensitive material to be fully utilized in future biosensing applications. These results were then compared to those of ferritin adsorption, which is a protein shell and biomaterial like E. coli, and radical oxygen doping onto the graphene surface.

A Self-Repairing Cathode Material for Lithium-Selenium Batteries: Se-C Chemically Bonded Selenium-Graphene Composite.

Lithium-selenium batteries, employing selenium as a cathode material, exhibit some notable advantages, such as high discharge rates and good cycling performance, due to their high electrical conductivity, high output voltages, and high volumetric capacity density. However, an important problem, termed the "shuttle effect", can lead to capacity decay in Li-Se cells (and in Li-S cells), which arises from aggregation and the loss of Se or S from the cathode into the electrolyte. In this work, in order to solve this problem, a new self-repairing system has been devised, in which some Se atoms are chemically bonded to the carbon atoms of graphene and act as reclaiming points for dissociated Se atoms through the establishment of -Se-Se-Se- chains. Se-decorated graphene (Se-GE) was first constructed through a facile high-energy ball-milling process. Its formation was confirmed by XRD, SEM, HRTEM, XPS, and Raman analyses. As we anticipated, in examining cell properties, the as-prepared Se-GE composite underwent an initial capacity decay in the first 20 cycles (from 1050 mAh g-1 to 750 mAh g-1 , ca. 29 % loss), but the capacity then reverted to 970 mAh g-1 (ca. 92 % of the initial value). Other measurements were also consistent with the recapture of dissociated Se atoms.

Functional group dependence of spin magnetism in graphene oxide

We evaluated graphene oxides (GOs) synthesized by different methods in terms of magnetism and chemical structure. GO samples were synthesized by Brodie and Hummers methods, which are labeled as BGO and HGO, respectively. The temperature dependence of magnetic susceptibility indicates an order of magnitude larger localized spin concentration of HGO (Ns=2×1019) than that of BGO (Ns=2×1018). The FT-IR spectra for GO exhibits peaks for hydroxyl, carboxyl, epoxy and carbonyl groups in spite of absence of any peak for graphite. Interestingly, the peak around 1224cm−1 attributed to COH stretching for HGO is larger than that for BGO, while the peak around 1050cm−1 for COC stretching is larger for BGO. The difference of functional groups between HGO and BGO explains the larger spin magnetism for HGO. In the case of introduction of epoxy group, oxygen atom bonds to adjacent carbon atoms, remaining symmetry regarding A, B sub-lattices of graphene lattice. On the other hand, attaching hydroxyl group occurs randomly on carbon atoms of graphene and breaks symmetry of A, B-sublattices, resulting in the emergence of the localized states and the spin magnetism.

Exfoliation of Graphene in Ionic Liquids: Pyridinium versus Pyrrolidinium

Exfoliation is an elegant physical technique to directly obtain graphene from graphite. A search for high-performance exfoliation solvents is actively pursued nowadays. We report potentials of mean force and free energies, characterizing steered separation of graphene sheets and their subsequent solvation by room-temperature ionic liquids (RTILs). The exfoliation performance of N-butylpyridinium bis(trifluoromethanesulfonyl)imide [BPY][TFSI] is compared to that of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide [PYR][TFSI]. Both RTILs are shown to exhibit comparable exfoliation performance, which is superior to the performance of 1-ethyl-3-methylimidazolium tetrafluoroborate by ∼20 kJ mol–1 nm–1. The sulfur atom of TFSI– contributes an essential portion of the solvation enthalpy due to its dispersive attraction to carbon atoms of graphene. Both RTILs maintain a single, moderately defined shell around the graphene surface. [BPY][TFSI] and [PYR][TFSI] are suitable starting compounds to engi...

Formation of Silicene Nanosheets on Graphite.

The extraordinary properties of graphene have spurred huge interest in the experimental realization of a two-dimensional honeycomb lattice of silicon, namely, silicene. However, its synthesis on supporting substrates remains a challenging issue. Recently, strong doubts against the possibility of synthesizing silicene on metallic substrates have been brought forward because of the non-negligible interaction between silicon and metal atoms. To solve the growth problems, we directly deposited silicon on a chemically inert graphite substrate at room temperature. Based on atomic force microscopy, scanning tunneling microscopy, and ab initio molecular dynamics simulations, we reveal the growth of silicon nanosheets where the substrate-silicon interaction is minimized. Scanning tunneling microscopy measurements clearly display the atomically resolved unit cell and the small buckling of the silicene honeycomb structure. Similar to the carbon atoms in graphene, each of the silicon atoms has three nearest and six second nearest neighbors, thus demonstrating its dominant sp2 configuration. Our scanning tunneling spectroscopy investigations confirm the metallic character of the deposited silicene, in excellent agreement with our band structure calculations that also exhibit the presence of a Dirac cone.

Density functional theory calculations on transition metal atoms adsorbed on graphene monolayers

Transition metal atom adsorption on graphene monolayers has been elucidated using periodic density functional theory under hybrid and generalized gradient approximation functionals. More specifically, we examined the adsorption of Cu, Fe, Zn, Ru, and Os on graphene monolayers by calculating, among others, the electronic density-of-states spectra of the adatom-graphene system and the overlap populations of the adatom with the nearest adsorbing graphene carbon atoms. These calculations reveal that Cu form primarily covalent bonds with graphene atoms via strong hybridization between the adatom orbitals and the sp band of the graphene substrate, whereas the interaction of the Ru and Os with graphene also contain ionic parts. Although the interaction of Fe with graphene atoms is mostly covalent, some charge transfer to graphene is also observed. The interaction of Zn with graphene is weak. Mulliken population analysis and charge contour maps are used to elucidate charge transfers between the adatom and the substrate. The adsorption strength is correlated with the metal adsorption energy and the height of the metal adatom from the graphene plane for the geometrically optimized adatom-graphene system. Our analysis shows that show that metal adsorption strength follows the adatom trend Ru≈Os>Fe>Cu>Zn, as verified by corresponding changes in the adsorption energies. The increased metal-carbon orbital overlap for the Ru relative to Os adatom is attributed to hybridization defects.

Observation of Ferromagnetic Semiconductor Behaviors from Graphene Doped with Manganese-Oxide By Electrochemical Method

Ferromagnetic semiconductors have attracted much attention in the field of spintronic application, because future electronic devices will have a switchable magnetic ordering in semiconductors for exploiting spin rather than charge. The key importance of the magnetic semiconductor is the Curie temperature to maintain the ferromagnetic ordering at room temperature. A high Curie temperature above room temperature has been shown in carbon-based materials. Recently, graphene which is an atomically monolayer graphite, has been an important issue for future spin electronic devices due to the high mobility and superb material properties. Especially, a theoretical result showed that graphene with defects behaves like a diluted magnetic semiconductor (DMS). In general, sp2 hybridized carbon atoms in graphene have an unsaturated dangling bond, which induces various surface modifications. Therefore, doping onto graphene easily leads to modification of the electronic structure, magnetic property, and carrier density. In this work, we report an electrochemical doping of manganese-oxide onto graphene, and also investigate the ferromagnetic semiconductor behavior from the manganese-oxide doped graphene. We have doped a manganese-oxide onto graphene by an electrochemical method. Graphene showed a clear ferromagnetic semiconductor behavior after doping of manganese-oxide. The manganese-oxide doped graphene has a coercive field (Hc) of 232 Oe at 10 K, and has the Curie temperature of 270 K from the temperature-dependent resistivity using transport measurement. The ferromagnetism of manganese-oxide doped graphene attributes to the double-exchange from the coexistence of Mn3+ and Mn4+ on the surface of graphene. In addition, the semiconducting behavior is caused by the formation of manganese-oxide on graphene.