Doping monolayer graphene with single atom substitutions

Magnetic properties of transition metal Mn, Fe and Co dimers on monolayer phosphorene

We studied the geometries, electronic structure and magnetic properties of substitutional doping and adsorption of transition metal (Mn, Fe and Co) dimers on phosphorene monolayer in the framework of the generalized gradient approximation (GGA) and GGA + U. Electronic band structures and magnetic properties were dependent on the doping type and dopant materials. For Mn and Fe substitutional and adsorption dimers, we obtained semiconducting band structures with spin polarization. However, we found a half-metallic feature in Co substitutional dimer while the Co adsorption dimer showed a semiconducting behavior without any spin polarization. With GGA + U, all the systems showed spin polarized semiconducting band structures except Co adsorption dimer which remained unaffected. The hybridization between transition metal (TM) and phosphorene sheet contributed to suppressing the magnetic moment of TM dimers. For instance, the total magnetic moments of -2.0, 4.24 and 1.28 μ B/cell for Mn, Fe and Co substitutional dimers were obtained while the Mn and Fe adsorption dimers showed magnetic moments of -1.69 and 0.46 μ B/cell. These magnetic moments were enhanced with GGA + U. The same magnetic ground states were obtained both from GGA and GGA + U approaches except for the Mn dimers. We observed that the Mn and Fe substitutional dimers showed an out-of-plane magnetization while an in-plane magnetization was observed in Co substitutional dimer. The Mn adsorption dimer still displayed a perpendicular magnetization whereas the Fe adsorption dimer had an in-plane magnetization. We found that the both GGA and GGA + U showed the same magnetization direction in all the systems.

Tunable magnetism in metal adsorbed fluorinated nanoporous graphene

Developing nanostructures with tunable magnetic states is crucial for designing novel data storage and quantum information devices. Using density functional theory, we investigate the thermodynamic stability and magnetic properties of tungsten adsorbed tri-vacancy fluorinated (TVF) graphene. We demonstrate a strong structure-property relationship and its response to external stimuli via defect engineering in graphene-based materials. Complex interplay between defect states and the chemisorbed atom results in a large magnetic moment of 7 μB along with high in-plane magneto-crystalline anisotropy energy (MAE) of 17 meV. Under the influence of electric field, spin crossover effect accompanied by a change in the MAE is observed. The ascribed change in spin-configuration is caused by the modification of exchange coupling between defect states and a change in the occupation of d-orbitals of the metal complex. Our predictions open a promising way towards controlling the magnetic properties in graphene based spintronic and non-volatile memory devices.

Transformation between divacancy defects induced by an energy pulse in graphene

The mutual transformations among the four typical divacancy defects induced by a high-energy pulse were studied via molecular dynamics simulation. Our study revealed all six possible mutual transformations and found that defects transformed by absorbing energy to overcome the energy barrier with bonding, debonding, and bond rotations. The reversibility of defect transformations was also investigated by potential energy analysis. The energy difference was found to greatly influence the transformation reversibility. The direct transformation path was irreversible if the energy difference was too large. We also studied the correlation between the transformation probability and the input energy. It was found that the transformation probability had a local maxima at an optimal input energy. The introduction of defects and their structural evolutions are important for tailoring the exceptional properties and thereby performances of graphene-based devices, such as nanoporous membranes for the filtration and desalination of water.

Large spin-filtering effect in Ti-doped defective zigzag graphene nanoribbon

Through first-principles calculations using the nonequilibrium Green's function formalism together with density functional theory, we study the conductance of double-vacancy zigzag graphene nanoribbons doped with four transition metal atoms Ti, V, Cr and Fe. We show that Ti doping induces large spin-filtering with an efficiency in excess of 90% for bias voltages below 0.5 V, while the other metal adatoms do not induce large spin filtering. This is despite the fact that the Ti dopant possesses small spin moment, while large moments reside on V, Cr and Fe dopants. Our analysis shows that the suppression of transmission in the spin-down channel in the Ti-doped graphene nanoribbon, thus the large spin filtering efficiency, is due to transmission anti-resonance arising from destructive quantum interference. These findings suggest that the decoration of graphene with titanium, and possibly other transition metals, can act as effective spin filters for nanospintronic applications.

Catalytic conversion of CHx and CO2 on non-noble metallic impurities in graphene

Density functional theory (DFT) was applied to investigate the geometric, electronic, and magnetic properties of CHx (x = 0, 1, 2, 3, 4) species on non-noble metal embedded graphene (NNM-graphene). It was found that the different stabilities of CHx species can modify the electronic structures and magnetic properties of NNM-graphene systems. The carbonaceous reforming reactions include conversion of CHx (x = 0, 1, 2 and 3) species by hydrogen molecules (H2) to form CHx+2 species or oxidation of C atoms by oxygen molecules to form CO2. In the hydrogenation reactions, deposited C atoms can be converted easily into CHx species overcoming small energy barriers. In comparison, coadsorption of C and O2 to generate CO2 encounters relatively larger energy barriers on the NNM-graphene. Hence, the coadsorption of CHx and H2 as the starting state is energetically more favorable and formation of CHx species can reduce amounts of carbon deposition. Among the NNM-graphene substrates studied, moderate adsorption energies and low reaction barriers of CHx species are more likely to occur on the Co-graphene surface, thus the hydrogenation reaction is able to inhibit carbon deposition on the NNM-graphene surface while maintaining high activity.

JS, Gomes MAF, Herrmann HJ. Crumpling Damaged Graphene

Through molecular mechanics we find that non-covalent interactions modify the fractality of crumpled damaged graphene. Pristine graphene membranes are damaged by adding random vacancies and carbon-hydrogen bonds. Crumpled membranes exhibit a fractal dimension of 2.71 ± 0.02 when all interactions between carbon atoms are considered, and 2.30 ± 0.05 when non-covalent interactions are suppressed. The transition between these two values, obtained by switching on/off the non-covalent interactions of equilibrium configurations, is shown to be reversible and independent on thermalisation. In order to explain this transition, we propose a theoretical model that is compatible with our numerical findings. Finally, we also compare damaged graphene membranes with other crumpled structures, as for instance polymerised membranes and paper sheets, that share similar scaling properties.

Improving low-energy boron/nitrogen ion implantation in graphene by ion bombardment at oblique angles

Ion implantation is a widely adopted approach to structurally modify graphene and tune its electrical properties for a variety of applications. Further development of the approach requires a fundamental understanding of the mechanisms that govern the ion bombardment process as well as establishment of key relationships between the controlling parameters and the dominant physics. Here, using molecular dynamics simulations with adaptive bond order calculations, we demonstrate that boron and nitrogen ion bombardment at oblique angles (particularly at 70°) can improve both the productivity and quality of perfect substitution by over 25%. We accomplished this by systematically analyzing the effects of the incident angle and ion energy in determining the probabilities of six distinct types of physics that may occur in an ion bombardment event, including reflection, absorption, substitution, single vacancy, double vacancy, and transmission. By analyzing the atomic trajectories from 576,000 simulations, we identified three single vacancy creation mechanisms and four double vacancy creation mechanisms, and quantified their probability distributions in the angle-energy space. These findings further open the door for improved control of ion implantation towards a wide range of applications of graphene.

A non-destructive n-doping method for graphene with precise control of electronic properties via atomic layer deposition

Graphene applications require high precision control of the Fermi level and carrier concentration via a nondestructive doping method. Here, we develop an effective n-doping technique using atomic layer deposition (ALD) of ZnO thin films on graphene through a reactive molecular layer. This ALD doping method is nondestructive, simple, and precise. The ZnO thin films on graphene are uniform, conformal, of good quality with a low density of pinholes, and finely tunable in thickness with 1 Å resolution. We demonstrate graphene transistor control in terms of the Dirac point, carrier density, and doping state as a function of the ZnO thickness. Moreover, ZnO functions as an effective thin-film barrier against air-borne water and oxygen on the graphene, resulting in extraordinary stability in air for graphene devices. ZnO ALD was also applied to other two-dimensional materials including MoS2 and WSe2, which substantially enhanced electron mobility.

Catalysis with two-dimensional materials and their heterostructures

Graphene and other 2D atomic crystals are of considerable interest in catalysis because of their unique structural and electronic properties. Over the past decade, the materials have been used in a variety of reactions, including the oxygen reduction reaction, water splitting and CO2 activation, and have been shown to exhibit a range of catalytic mechanisms. Here, we review recent advances in the use of graphene and other 2D materials in catalytic applications, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals). We discuss the advantages of these materials for catalysis and the different routes available to tune their electronic states and active sites. We also explore the future opportunities of these catalytic materials and the challenges they face in terms of both fundamental understanding and the development of industrial applications.

Native defects in ultra-high vacuum grown graphene islands on Cu(1 1 1)

We present a scanning tunneling microscopy (STM) study of native defects in graphene islands grown by ultra-high vacuum decomposition of ethylene on Cu(1 1 1). We characterize these defects through a survey of their apparent heights, atomic-resolution imaging, and detailed tunneling spectroscopy. Bright defects that occur only in graphene regions are identified as C site point defects in the graphene lattice and are most likely single C vacancies. Dark defect types are observed in both graphene and Cu regions, and are likely point defects in the Cu surface. We also present data showing the importance of bias and tip termination to the appearance of the defects in STM images and the ability to achieve atomic resolution. Finally, we present tunneling spectroscopy measurements probing the influence of point defects on the local electronic landscape of graphene islands.

Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling

Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.

Phosphorus and cobalt co-doped reduced graphene oxide bifunctional electrocatalyst for oxygen reduction and evolution reactions

P and Co co-doped reduced graphene oxide has been developed and studied, which exhibits great potential in catalyzing not only oxygen reduction but also oxygen evolution, and can be used as a promising non-precious bifunctional electrocatalyst.

DFT investigation of Ni-doped graphene: catalytic ability to CO oxidation

Theoretical investigations predict that Ni-doped graphene is a promising catalyst for CO oxidation at mild temperatures.

Novel insights into l-cysteine adsorption on transition metal doped graphene: influences of the dopant and the vacancy

Unprotonated l-cysteine is docked on single-vacancy and double-vacancy graphenes doped with transition metals from Sc to Zn. The adsystems exhibit interesting adsorption stability and magnetism.

Substitutional 4d and 5d impurities in graphene

We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals.

High catalytic activity for CO oxidation on single Fe atom stabilized in graphene vacancies

The geometric, electronic and catalytic characters of Fe atom embedded graphene (including monovacancy and divacancy) are investigated using the first-principles method, which gives a reference on designing graphene-based catalysts for CO oxidation.

Defect stabilized gold atoms on graphene as potential catalysts for ethylene epoxidation: a first-principles investigation

The defects on graphene make Au atoms active while being monodisperse and superior for ethylene epoxidation.

Exploring the stability and electronic structure of beryllium and sulphur co-doped graphene: a first principles study

First principles density functional theory calculations have been performed to explore the stability, structural and electronic properties of Be and S co-doped graphene sheets.

Plasmon-enhanced strong visible light photocatalysis by defect engineered CVD graphene and graphene oxide physically functionalized with Au nanoparticles

The strong visible light photocatalytic activity of defect-controlled CVD graphene (GR) and graphene oxide (GO) hybrids through physical functionalization with Au atoms has been demonstrated here.

Probing individual point defects in graphene via near-field Raman scattering

The Raman scattering D-peak in graphene is spatially localised in close proximity to defects. Here, we demonstrate the capability of tip-enhanced Raman spectroscopy (TERS) to probe individual point defects, even for a graphene layer with an extremely low defect density. This is of practical interest for future graphene electronic devices. The measured TERS spectra enable a direct determination of the average inter-defect distance within the graphene sheet. Analysis of the TERS enhancement factor of the graphene Raman peaks highlights the preferential enhancement and symmetry-dependent selectivity of the D-peak intensity caused by zero-dimensional Raman scatterers.

A single iron site confined in a graphene matrix for the catalytic oxidation of benzene at room temperature

Coordinatively unsaturated (CUS) iron sites are highly active in catalytic oxidation reactions; however, maintaining the CUS structure of iron during heterogeneous catalytic reactions is a great challenge. Here, we report a strategy to stabilize single-atom CUS iron sites by embedding highly dispersed FeN4 centers in the graphene matrix. The atomic structure of FeN4 centers in graphene was revealed for the first time by combining high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy with low-temperature scanning tunneling microscopy. These confined single-atom iron sites exhibit high performance in the direct catalytic oxidation of benzene to phenol at room temperature, with a conversion of 23.4% and a yield of 18.7%, and can even proceed efficiently at 0°C with a phenol yield of 8.3% after 24 hours. Both experimental measurements and density functional theory calculations indicate that the formation of the Fe═O intermediate structure is a key step to promoting the conversion of benzene to phenol. These findings could pave the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.

Selective Area Band Engineering of Graphene using Cobalt-Mediated Oxidation

This study reports a scalable and economical method to open a band gap in single layer graphene by deposition of cobalt metal on its surface using physical vapor deposition in high vacuum. At low cobalt thickness, clusters form at impurity sites on the graphene without etching or damaging the graphene. When exposed to oxygen at room temperature, oxygen functional groups form in proportion to the cobalt thickness that modify the graphene band structure. Cobalt/Graphene resulting from this treatment can support a band gap of 0.30 eV, while remaining largely undamaged to preserve its structural and electrical properties. A mechanism of cobalt-mediated band opening is proposed as a two-step process starting with charge transfer from metal to graphene, followed by formation of oxides where cobalt has been deposited. Contributions from the formation of both CoO and oxygen functional groups on graphene affect the electronic structure to open a band gap. This study demonstrates that cobalt-mediated oxidation is a viable method to introduce a band gap into graphene at room temperature that could be applicable in electronics applications.

Room-Temperature, Low-Barrier Boron Doping of Graphene

Doping graphene with boron has been difficult because of high reaction barriers. Here, we describe a low-energy reaction route derived from first-principles calculations and validated by experiments. We find that a boron atom on graphene on a ruthenium(0001) substrate can replace a carbon by pushing it through, with substrate attraction helping to reduce the barrier to only 0.1 eV, implying that the doping can take place at room temperature. High-quality graphene is grown on a Ru(0001) surface and exposed to B2H6. Scanning tunneling microscopy/spectroscopy and X-ray photoelectron spectroscopy confirmed that boron is indeed incorporated substitutionally without disturbing the graphene lattice.

Nitrogen Doping Enables Covalent-Like π-π Bonding between Graphenes

The neighboring layers in bilayer (and few-layer) graphenes of both AA and AB stacking motifs are known to be separated at a distance corresponding to van der Waals (vdW) interactions. In this Letter, we present for the first time a new aspect of graphene chemistry in terms of a special chemical bonding between the giant graphene "molecules". Through rigorous theoretical calculations, we demonstrate that the N-doped graphenes (NGPs) with various doping levels can form an unusual two-dimensional (2D) π-π bonding in bilayer NGPs bringing the neighboring NGPs to significantly reduced interlayer separations. The interlayer binding energies can be enhanced by up to 50% compared to the pristine graphene bilayers that are characterized by only vdW interactions. Such an unusual chemical bonding arises from the π-π overlap across the vdW gap while the individual layers maintain their in-plane π-conjugation and are accordingly planar. The existence of the resulting interlayer covalent-like bonding is corroborated by electronic structure calculations and crystal orbital overlap population (COOP) analyses. In NGP-based graphite with the optimal doping level, the NGP layers are uniformly stacked and the 3D bulk exhibits metallic characteristics both in the in-plane and along the stacking directions.

Proximity-induced magnetism in transition-metal substituted graphene

We investigate the interactions between two identical magnetic impurities substituted into a graphene superlattice. Using a first-principles approach, we calculate the electronic and magnetic properties for transition-metal substituted graphene systems with varying spatial separation. These calculations are compared for three different magnetic impurities, manganese, chromium, and vanadium. We determine the electronic band structure, density of states, and Millikan populations (magnetic moment) for each atom, as well as calculate the exchange parameter between the two magnetic atoms as a function of spatial separation. We find that the presence of magnetic impurities establishes a distinct magnetic moment in the graphene lattice, where the interactions are highly dependent on the spatial and magnetic characteristic between the magnetic and carbon atoms, which leads to either ferromagnetic or antiferromagnetic behavior. Furthermore, through an analysis of the calculated exchange energies and partial density of states, it is determined that interactions between the magnetic atoms can be classified as an RKKY interaction.

Geometric stability, electronic structure, and intercalation mechanism of Co adatom anchors on graphene sheets

We perform a systematic study of the adsorption of Co adatom on monolayer and bilayer graphene sheets, and the calculated results are compared through the van der Waals density functional (vdW-DF) and the generalized gradient approximation of Perdew, Burke and Ernzernhof (GGA + PBE) methods. For the single Co adatom, its adsorption energy at vacancy site was found to be larger than at the high-symmetry adsorption sites. For the different vdW corrections, the calculated adsorption energies of Co adatom on grapheme substrates are slightly changed to some extent, but they do not affect the most preferable adsorption configurations. NEB calculations prove that the Co adatom has smaller energy barrier within pristine bilayer graphene (PBG) than that on the upper layer, indicating the high mobility of Co atom anchors at overlayer and easily aggregates. For the PBG substrate, the Co adatom intercalates into graphene sheets with a large energy barrier (9.29 eV). On the bilayer graphene with a single-vacancy (SV), the Co adatom can easily be trapped at the SV site and intercalates into graphene sheets with a much lower energy barrier (2.88 eV). These results provide valuable information on the intercalation reaction and the formation mechanism of metal impurity in graphene sheets.

Controlling defects in graphene for optimizing the electrical properties of graphene nanodevices

Structural defects strongly impact the electrical transport properties of graphene nanostructures. In this Perspective, we give a brief overview of different types of defects in graphene and their effect on transport properties. We discuss recent experimental progress on graphene self-repair of defects, with a focus on in situ transmission electron microscopy studies. Finally, we present the outlook for graphene self-repair and in situ experiments.

Electronic interaction between nitrogen atoms in doped graphene

Many potential applications of graphene require either the possibility of tuning its electronic structure or the addition of reactive sites on its chemically inert basal plane. Among the various strategies proposed to reach these objectives, nitrogen doping, i.e., the incorporation of nitrogen atoms in the carbon lattice, leads in most cases to a globally n-doped material and to the presence of various types of point defects. In this context, the interactions between chemical dopants in graphene have important consequences on the electronic properties of the systems and cannot be neglected when interpreting spectroscopic data or setting up devices. In this report, the structural and electronic properties of complex doping sites in nitrogen-doped graphene have been investigated by means of scanning tunneling microscopy and spectroscopy, supported by density functional theory and tight-binding calculations. In particular, based on combined experimental and simulation works, we have systematically studied the electronic fingerprints of complex doping configurations made of pairs of substitutional nitrogen atoms. Localized bonding states are observed between the Dirac point and the Fermi level in contrast with the unoccupied state associated with single substitutional N atoms. For pyridinic nitrogen sites (i.e., the combination of N atoms with vacancies), a resonant state is observed close to the Dirac energy. This insight into the modifications of electronic structure induced by nitrogen doping in graphene provides us with a fair understanding of complex doping configurations in graphene, as it appears in real samples.

TM atoms on B/N doped defective graphene as a catalyst for oxygen reduction reaction: a theoretical study

N-doping can effectively improve the binding strength of metal atoms with divacancies and some TM–VN2 serve as promising ORR catalysts.

Electronic and magnetic properties of an AlN monolayer doped with first-row elements: a first-principles study

Two-dimensional (2D) magnetic materials are the focus of one of the most active areas of nano-materials research.

Anomalous twisting strength of tilt grain boundaries in armchair graphene nanoribbons

The critical instability twist rate of graphene nanoribbons can be improved by grain boundaries.

Graphyne-supported single Fe atom catalysts for CO oxidation

We demonstrate that graphyne is a good substrate for single Fe atom catalysts, which have high catalytic activity for CO oxidation.

Energetics of atomic scale structure changes in graphene

An overview of theoretical and experimental studies concerned with energetics of atomic scale structure changes in graphene, including thermally activated and electron irradiation-induced processes.

Multiple CO2 capture in stable metal-doped graphene: a theoretical trend study

A systematic trend study of carbon dioxide capture on metal-doped single vacancy/double vacancy graphene.

Stability and spectroscopy of single nitrogen dopants in graphene at elevated temperatures

Single nitrogen (N) dopants in graphene are investigated using atomic-resolution scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). Using an in situ heating holder at 500 °C provided us with clean graphene surfaces, and we demonstrate that isolated N substitutional atoms remain localized and stable in the graphene lattice even during local sp(2) bond reconstruction. The high stability of isolated N dopants enabled us to acquire 2D EELS maps with simultaneous ADF-STEM images to map out the local bonding variations. We show that a substitutional N dopant causes changes in the EELS of the carbon (C) atoms it is directly bonded to. An upshift in the π* peak of the C K-edge EELS of ∼0.5 eV is resolved and supported by density functional theory simulations.

Direct in situ observations of single Fe atom catalytic processes and anomalous diffusion at graphene edges

Single-atom catalysts are of great interest because of their high efficiency. In the case of chemically deposited sp(2) carbon, the implementation of a single transition metal atom for growth can provide crucial insight into the formation mechanisms of graphene and carbon nanotubes. This knowledge is particularly important if we are to overcome fabrication difficulties in these materials and fully take advantage of their distinct band structures and physical properties. In this work, we present atomically resolved transmission EM in situ investigations of single Fe atoms at graphene edges. Our in situ observations show individual iron atoms diffusing along an edge either removing or adding carbon atoms (viz., catalytic action). The experimental observations of the catalytic behavior of a single Fe atom are in excellent agreement with supporting theoretical studies. In addition, the kinetics of Fe atoms at graphene edges are shown to exhibit anomalous diffusion, which again, is in agreement with our theoretical investigations.

In-situ observation and atomic resolution imaging of the ion irradiation induced amorphisation of graphene

Ion irradiation has been observed to induce a macroscopic flattening and in-plane shrinkage of graphene sheets without a complete loss of crystallinity. Electron diffraction studies performed during simultaneous in-situ ion irradiation have allowed identification of the fluence at which the graphene sheet loses long-range order. This approach has facilitated complementary ex-situ investigations, allowing the first atomic resolution scanning transmission electron microscopy images of ion-irradiation induced graphene defect structures together with quantitative analysis of defect densities using Raman spectroscopy.

Strain and orientation modulated bandgaps and effective masses of phosphorene nanoribbons

Passivated phosphorene nanoribbons, armchair (a-PNR), diagonal (d-PNR), and zigzag (z-PNR), were investigated using density functional theory. Z-PNRs demonstrate the greatest quantum size effect, tuning the bandgap from 1.4 to 2.6 eV when the width is reduced from 26 to 6 Å. Strain effectively tunes charge carrier transport, leading to a sudden increase in electron effective mass at +8% strain for a-PNRs or hole effective mass at +3% strain for z-PNRs, differentiating the (mh*/me*) ratio by an order of magnitude in each case. Straining of d-PNRs results in a direct to indirect band gap transition at either -7% or +5% strain and therein creates degenerate energy valleys with potential applications for valleytronics and/or photocatalysis.

Large capacitance enhancement induced by metal-doping in graphene-based supercapacitors: a first-principles-based assessment

Chemically doped graphene-based materials have recently been explored as a means to improve the performance of supercapacitors. In this work, we investigate the effects of 3d transition metals bound to vacancy sites in graphene with [BMIM][PF6] ionic liquid on the interfacial capacitance; these results are compared to the pristine graphene case with particular attention to the relative contributions of the quantum and electric double layer capacitances. Our study highlights that the presence of metal-vacancy complexes significantly increases the availability of electronic states near the charge neutrality point, thereby enhancing the quantum capacitance drastically. In addition, the use of metal-doped graphene electrodes is found to only marginally influence the microstructure and capacitance of the electric double layer. Our findings indicate that metal-doping of graphene-like electrodes can be a promising route toward increasing the interfacial capacitance of electrochemical double layer capacitors, primarily by enhancing the quantum capacitance.

Single adatom dynamics at monatomic steps of free-standing few-layer reduced graphene

Steps and their associated adatoms extensively exist and play prominent roles in affecting surface properties of materials. Such impacts should be especially pronounced in two-dimensional, atomically-thin membranes like graphene. However, how single adatom behaves at monatomic steps of few-layer graphene is still illusive. Here, we report dynamics of individual adatom at monatomic steps of free-standing few-layer reduced graphene under the electron beam radiations, and demonstrate the prevalent existence of monatomic steps even down to unexpectedly ultrasmall lateral size of a circular diameter of ~5 Å. Single adatom prefers to stay at the edges of the atomic steps of few-layer reduced graphene and evolve with the steps. Moreover, we also find that how the single adatom behaves at atomic step edges can be remarkably influenced by the type of adatoms and step edges. Such single adatoms at monatomic steps and ultrasmall atomic steps open up a new window for surface physics and chemistry for graphene-based as well as other two-dimensional materials.

Sublattice asymmetry of impurity doping in graphene: A review

In this review we highlight recent theoretical and experimental work on sublattice asymmetric doping of impurities in graphene, with a focus on substitutional nitrogen dopants. It is well known that one current limitation of graphene in regards to its use in electronics is that in its ordinary state it exhibits no band gap. By doping one of its two sublattices preferentially it is possible to not only open such a gap, which can furthermore be tuned through control of the dopant concentration, but in theory produce quasi-ballistic transport of electrons in the undoped sublattice, both important qualities for any graphene device to be used competetively in future technology. We outline current experimental techniques for synthesis of such graphene monolayers and detail theoretical efforts to explain the mechanisms responsible for the effect, before suggesting future research directions in this nascent field.