Simulation of chemical activity of corrugated graphene within density functional theory predicts an enhancement of its chemical activity if the ratio of height of the corrugation (ripple) to its radius is larger than 0.07. Further growth of the curvature of the ripples results in appearance of midgap states which leads to an additional strong increase of chemisororption energy. These results open a way for tunable functionalization of graphene, namely, depending of curvature of the ripples one can provide both homogeneous (for small curvatures) and spot-like (for large curvatures) functionalization.
We present a structural analysis of the graphene/Ru(0001) system obtained by surface x-ray diffraction. The data were fit using Fourier-series expanded displacement fields from an ideal bulk structure, plus the application of symmetry constraints. The shape of the observed superstructure rods proves a reconstruction of the substrate, induced by strong bonding of graphene to ruthenium. Both the graphene layer and the underlying substrate are corrugated, with peak-to-peak heights of (0.82 +/- 0.15) A and (0.19 +/- 0.02) A for the graphene and topmost Ru-atomic layer, respectively. The Ru-corruga…
The Moiré structure of epitaxial graphene mono layer grown on 6H-SiC(0001) has been investigated recently by grazing incidence fast atom diffraction, and the results were compared with the calculation of the structure \textit{ab initio} and exact diffraction codes. We review these results and present a complementary approach using the Hard Wall Model to extract information without any \textit{a priori}. Reversely, taking advantage of previous exact calculations we evaluate quantitatively the performance of this simplified approach by comparing predictions using the same potential energy surfac…
Free-standing exfoliated monolayer graphene is an ultra-thin flexible membrane, which exhibits out of plane deformation or corrugation. In this paper, a technique is described to measure the band structure of such free-standing graphene by angle-resolved photoemission. Our results show that photoelectron coherence is limited by the crystal corrugation. However, by combining surface morphology measurements of the graphene roughness with angle-resolved photoemission, energy dependent quasiparticle lifetime and bandstructure measurements can be extracted. Our measurements rely on our development …
It is shown that for monolayer graphene electrons are confined on a perfect two dimensional surface. The implications for the electronic properties of corrugated graphene are discussed in view of a derivation of the constrained relativistic dynamics for the massless carriers in two dimensions. Surface curvature is related to a series of phenomena with practical applications such as curvature induced p-n junctions, band gap opening and decoherence. We also establish a bending free energy by treating graphene as a soft electronic membrane.
Density functional theory (DFT) modeling of the physisorption of four different types of molecules (toluene, bromine dimmer, water and nitrogen dioxide) over and above graphene ripples has been performed. For all types of molecules changes of charge transfer and binding energies in respect to flat graphene is found. The changes in electronic structure of corrugated graphene and turn of π-orbitals of carbon atoms in combination with chemical structure of adsorbed molecules are proposed as the causes of difference with the perfect graphene case and variety of adsorption properties of different t…
Recent studies show that periodic potentials can generate superlattice Dirac points at energies in graphene (is the Fermi velocity of graphene and G is the reciprocal superlattice vector). Here, we perform scanning tunneling microscopy and spectroscopy studies of a corrugated graphene monolayer on Rh foil. We show that the quasi-periodic ripples of nanometer wavelength in the corrugated graphene give rise to weak one-dimensional (1D) electronic potentials and thereby lead to the emergence of the superlattice Dirac points. The position of the superlattice Dirac point is space-dependent and show…
The electromagnetic radiation of electrons in the corrugated graphene in the presence of the transport electric current in the ballistic regime is studied. Radiation of the similar nature can be observed in undulator and wiggler. We considered here an impact of the ripples in the monolayer graphene on its electromagnetic properties. The electromagnetic radiation was actually calculated with a use of the standard electromagnetic theory. Two cases, of regular and random structures are analyzed. Nonlinear relation between the random height function h(x,y) and the gauge field is shown to create th…
We study the changes induced by the effective gauge field due to ripples on the low energy electronic structure of graphene. We show that zero energy Landau levels will form, associated to the smooth deformation of the graphene layer, when the height corrugation, $h$, and the length of the ripple, $l$, are such that $h^2 / (l a) \gtrsim 1$, where $a$ is the lattice constant. The existence of localized levels gives rise to a large compressibility at zero energy, and to the enhancement of instabilities arising from electron-electron interactions including electronic phase separation. The combine…
The electronic structure of a single layer graphene on Ru(0001) is compared with that of a single layer hexagonal boron nitride nanomesh on Ru(0001). Both are corrugated sp2 networks and display a pi-band gap at the K point of their 1 x 1 Brillouin zone. Graphene has a distinct Fermi surface which indicates that 0.1 electrons are transferred per 1 x 1 unit cell. Photoemission from adsorbed xenon identifies two distinct Xe 5p1/2 lines, separated by 240 meV, which reveals a corrugated electrostatic potential energy surface. These two Xe species are related to the topography of the system and hav…
In graphene based materials, the energy storage capacity is usually improved by rich porous structures with extremely high surface area. By utilizing surface corrugations, this work shows an alternative strategy to activate graphene materials for large capacitance. We demonstrate how to simply fabricate such activated graphene and how these surface structures helped to realize considerable specific capacitance (e.g., electrode capacitance of ~340 F g-1 at 5 mV s-1 and device capacitance of ~ 343 F g-1 at 1.7 A g-1) and power performance (e.g., power density of 50 and 2500 W kg-1 at the energy …
Functional nano-templates enable self-assembly of otherwise impossible arrangements of molecules. A particular class of such templates is that of sp2 hybridized single layers of hexagonal boron nitride or carbon (graphene) on metal supports. If the substrate and the single layer have a lattice mismatch, superstructures are formed. On substrates like rhodium or ruthenium these superstructures have unit cells with ~3 nm lattice constant. They are corrugated and contain sub-units, which behave like traps for molecules or quantum dots, which are small enough to become operational at room temperatu…
The ability to engineer the electronic band structure and, more strikingly, to access new exotic phase of matter has been the cornerstone of the advance of science and technology. Twisting van der Waals materials to form moiré superlattice is a powerful paradigm and can drive graphene from a normal metallic state into an insulating, superconducting, or ferromagnetic states. Here, we present a new route to create non-trivial band structure and consequently an exotic phase of matter via lithographically patterned strain (lattice deformation). This method is used to realize an artificially corrug…
A generalized Dirac equation is derived in order to describe charge carriers moving in corrugated graphene, which is the case for temperatures above 10°K due to the presence of flexural phonons. Such interaction is taken into account by considering an induced metric, in the same spirit as the general relativity approach for the description of fermionic particle moving in a curved space-time. The resulting equation allows to include in a natural way the presence of other phonon branches as well as an external electromagnetic field. It also predicts non-linear effects which are not present in th…
Theoretical research has predicted that ripples of graphene generates effective gauge field on its low energy electronic structure and could lead to zero-energy flat bands, which are the analog of Landau levels in real magnetic fields. Here we demonstrate, using a combination of scanning tunneling microscopy and tight-binding approximation, that the zero-energy Landau levels with vanishing Fermi velocities will form when the effective pseudomagnetic flux per ripple is larger than the flux quantum. Our analysis indicates that the effective gauge field of the ripples results in zero-energy flat …
Propagating edge and interfacial states in corrugated graphene: Robustness and configurability
University of Science and Technology Houari Boumediene（哈乌阿里·布麦迪内科技大学）；Ecole Supérieure des Sciences des Aliments et des Industries Agroalimentaires（食品科学与食品工业高等学院）；The University of Hong Kong（香港大学）；Ohio University（俄亥俄大学）
Periodically corrugated epitaxial graphene and hexagonal boron nitride (h-BN) on metallic substrates are considered as perspective templates for the self-assembly of nanoparticles arrays. By using first-principles calculations, we determine binding energies and diffusion activation barriers of metal adatoms on graphene and h-BN. The observed chemical trends can be understood in terms of the interplay between charge transfer and covalent bonding involving the adatom d electrons. We further investigate the electronic effects of the metallic substrate and find that periodically corrugated templat…
Results from first principles density functional theory (DFT) calculations and classical molecular dynamics (CMD) simulations are presented on moire-corrugation of graphene (gr). We find that the moire-corrugated graphene could be surprisingly stable against the perfectly flat gr-sheet as pointed out by CMD simulations and DFT calculations. We also show that using the cost-effective CMD approach one can simulate graphene on e.g. Ru(0001) with a correct binding registry and reasonable corrugation and adhesion energy. A new force field has been parameterized for the interface using an angular-de…
A new mechanism that induces charge density variations in corrugated graphene is proposed. Here it is shown how the interplay between lattice deformations and exchange interactions can induce charge separation, i.e., puddles of electrons and holes, for realistic deformation values of the graphene sheet. The induced charge density lies in the range of $10^{11}-10^{12}$ cm$^{-2}$, which is compatible with recent measurements.
The synthesis, physical, photocatalytic, and antibacterial properties of MgO and graphene nanoplatelets (GNPs) nanocomposites are reported. The crystallinity, phase, morphology, chemical bonding, and vibrational modes of prepared nanomaterials are studied. The conductive nature of GNPs is tailored via photocatalysis and enhanced antibacterial activity. It is interestingly observed that the MgO/GNPs nanocomposite with optimized GNPs content show a significant photocatalytic activity (97.23% degradation) as compared to bare MgO (43%) which makes it the potential photocatalyst for purification of…
Currently, the fundamental factors that control the oxygen reduction reaction (ORR) activity of graphene itself, in particular the dependence of the ORR activity on the number of exposed edge sites remain elusive, mainly due to limited synthesis routes of achieving small size graphene. In this work, the synthesis of low oxygen content (< 2.5 +/-0.2 at %), few layer graphene nanosheets with lateral dimensions smaller than a few hundred nm was achieved using a combination of ionic liquid assisted grinding of high purity graphite coupled with sequential centrifugation. We show for the first time,…
Graphene layers are stable, hard, and relatively inert. We study how tensile stress affects $σ$ and $π$ bonds and the resulting change in the chemical activity. Stress affects more strongly $π$ bonds that can become chemically active and bind to adsorbed species more strongly. Upon stretch, single C bonds are activated in a geometry mixing $120^{o}$ and $90^{o}$; an intermediate state between $sp^{2}$ and $sp^{3}$ bonding. We use ab-initio density functional theory to study the adsorption of hydrogen on large clusters and 2D periodic models for graphene. The influence of the exchange-correlati…
Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low costs remains a grand challenge. Here, we report a hybrid material of Co3O4 nanocrystals grown on reduced graphene oxide (GO) as a high-performance bi-functional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). While Co3O4 or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisin…
By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from -7% (compression) to +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H2O compared with the adsorption on a planar surface, and the charge transfer between the wa…
The contact strength, adhesion and friction, between graphene and an incommensurate crystalline substrate such as {\it h}-BN depends on their relative alignment angle $θ$. The well established Novaco-McTague (NM) theory predicts for a monolayer graphene on a hard bulk {\it h}-BN crystal face a small spontaneous misalignment, here $θ_{NM}$\,$\simeq$\,0.45 degrees which if realized would be relevant to a host of electronic properties besides the mechanical ones. Because experimental equilibrium is hard to achieve, we inquire theoretically about alignment or misalignment by simulations based on d…
Graphene on copper is a system of high technological relevance, as Cu is one of the most widely used substrates for the CVD growth of graphene. However, very little is known about the details of their interaction. One approach to gain such information is studying the superlattices emerging due to the mismatch of the two crystal lattices. However, graphene on copper is a low-corrugated system making both their experimental and theoretical study highly challenging. Here, we report the observation of a new rotational Moire superlattice of CVD graphene on Cu (111), characterized by a periodicity o…
Pt/Graphene and Pt/MnO2-Graphene catalysts have been prepared by microwave-assisted polyol process. Electrochemical results show that Pt/MnO2-Graphene has higher electrocatalytic activity and stability. Furthermore, carbon riveted Pt/MnO2-Graphene catalyst has been designed and synthesized on the basis of in situ carbonization of L-ascorbic acid. The stability for carbon riveted Pt/MnO2-catalyst is significantly enhanced.
Accurate assessment of the antibacterial activity of graphene requires consideration of both the graphene fabrication method and, for supported films, the properties of the substrate. Large-area graphene films produced by chemical vapor deposition were grown directly on copper substrates or transferred on a gold substrate and their effect on the viability and proliferation of the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli were assessed. The viability and the proliferation of both bacterial species were not affected when they were grown on a gra…
Single atom catalysts (SACs) present the ultimate level of catalyst utilization, which puts them in the focus of current research. For this reason, their understanding is crucial for the development of new efficient catalytic systems. Using Density Functional Theory calculations, model SACs consisted of nine metals (Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt and Au) on four different supports (pristine graphene, N- and B-doped graphene and graphene with single vacancy) were analyzed. Among them, only graphene with a single vacancy enables the formation of SACs, which are stable in terms of aggregation and…
The exceptional conducting nature of graphene makes it a viable candidate for enhancing the effectiveness of photocatalytic and biomedical nanomaterials. Herein, the immobilization of monodispersed silicon dioxide (SiO2) nanoparticles on multiple graphene layers is demonstrated for intercalation of graphene nanoplatelets (GNPs). Interestingly, the loading of graphene nanoplatelets with SiO2 nanoparticles enhances the photocatalytic efficiency from 46% to 99%. For biomedical applications, it is found that 75% of Gram positive and 50% of Gram negative bacteria have been killed, hence bacterial p…
The paper presents the author view on spin-rooted properties of graphene supported by numerous experimental and calculation evidences. Dirac fermions of crystalline graphene and local spins of graphene molecules are suggested to meet a strict demand - different orbitals for different spins- which leads to a large spectrum of effects caused by spin polarization of electronic states. The consequent topological non-triviality, making graphene topological insulator, and local spins, imaging graphene chemical activity, are proposed to discuss such peculiar properties of graphene as high temperature…
Graphite is one of the most chemically inert materials. Its elementary constituent, monolayer graphene, is generally expected to inherit most of the parent material's properties including chemical inertness. Here we show that, unlike graphite, defect-free monolayer graphene exhibits a strong activity with respect to splitting molecular hydrogen, which is comparable to that of metallic and other known catalysts for this reaction. We attribute the unexpected catalytic activity to surface corrugations (nanoscale ripples), a conclusion supported by theory. Nanoripples are likely to play a role in …
Graphene pseudohalides are natural candidates for use in molecular sensing due to their greater chemical activity as compared to both graphene halides and pristine graphene. Though their study is still in its infancy, being hindered until recently by the unavailability of both selective and efficient procedures for their synthesis, they promise to considerably widen the application potential of chemically modified graphenes. Herein, we employ vdW-DFT to study the structural and electronic properties of two selected graphene pseudohalides namely cyanographone and isocyanographone and investigat…
Low-cost graphene sponge electrodes were functionalized with two-dimensional (2D) materials, i.e., borophene and hexagonal boron nitride (hBN), using a one-step, hydrothermal self-assembly method. Borophene and hBN-modified graphene sponge anode and N-doped graphene sponge cathode were employed for electrochemical degradation of model persistent contaminants of emerging concern in one-pass, flow through mode, and using low-conductivity supporting electrolyte. Functionalization of the reduced graphene oxide (RGO) coating with 2D materials led to specific modifications in the electrode electroca…
Direct growth of large-area vertically stacked two-dimensional (2D) van der Waal (vdW) materials is a prerequisite for their high-end applications in integrated electronics, optoelectronics and photovoltaics. Currently, centimetre- to even metre-scale monolayers of single-crystal graphene (MLG) and hexagonal boron nitride (h-BN) have been achieved by epitaxial growth on various single-crystalline substrates. However, in principle, this success in monolayer epitaxy seems extremely difficult to be replicated to bi- or few-layer growth, as the full coverage of the first layer was believed to term…
Defects change essentially not only electronic but also chemical properties of graphene being centers of its chemical activity. Their functionalization is a way to modify electronic and crystal structure of graphene which may be important for graphene-based nanoelectronics. Using hydrogen as an example, we have simulated a chemistry of imperfect graphene for a broad class of defects (Stone-Wales defects, bivacancy, nitrogen substitution impurity, and zigzag edges) by density functional calculations. We have studied also an effect of finite width of graphene nanoribbons on their chemical proper…
Non-reciprocity and asymmetric transmission in optical and plasmonic systems is a key element for engineering the one-way propagation structures for light manipulation. Here we investigate topological nanostructures covered with graphene-based meta-surfaces, which consist of a periodic pattern of sub-wavelength stripes of graphene winding around the (meta-) tube or (meta-)torus. We establish the relation between the topological and plasmonic properties in these structures, as justified by simple theoretical expressions. Our results demonstrate how to use strong asymmetric and chiral plasmonic …
Previous studies indicate that the properties of graphene oxide (GO) can be significantly improved by enhancing its graphitic domain size through thermal diffusion and clustering of functional groups. Remarkably, this transition takes place below the decomposition temperature of the functional groups and thus allows fine-tuning of graphitic domains without compromising with the functionality of GO. By studying the transformation of GO under mild thermal treatment, we directly observe this size enhancement of graphitic domains from originally 40 nm2 to 200 nm2 through an extensive transmission …
Nitrogen doping of the carbon is an important method to improve the performance and durability of catalysts for proton exchange membrane fuel cells by platinum-nitrogen and carbon-nitrogen bonds. This study shows that p-phenyl groups and graphitic N acting bridges linking platinum and the graphene/carbon black (the ratio graphene/carbon black=2/3) hybrid support materials achieved the average size of platinum nanoparticles with (4.88 +/- 1.79) nm. It improved the performance of the lower-temperature hydrogen fuel cell up to 0.934 W cm-2 at 0.60 V, which is 1.55 times greater than that of comme…
Metal heteroatoms dispersed in nitrogen-doped graphene display promising catalytic activity for fuel cell reactions such as the hydrogen evolution reaction (HER). Here we explore the effects of dopant concentration on the synergistic catalytic behaviour of a paired metal atom active site comprised of Co and Pt atoms. The metals are coordinated to six atoms in a vacancy of N-doped graphene. We find that HER activity is enhanced with increasing N concentration, where the free energy of hydrogen atom adsorption ranges from 0.23 to -0.42 eV as the doping changes from a single N atom doped in the p…
Intrinsic ripples with various configurations and sizes were reported to affect the physical and chemical properties of 2D materials. By performing molecular dynamics simulations and theoretical analysis, we use two geometric models of the ripple shape to explore numerically the distribution of ripples in graphene membrane. We focus on the ratio of ripple height to its diameter (t/D) which was recently shown to be the most relevant for chemical activity of graphene membranes. Our result demonstrates that the ripple density decreases as the coefficient t/D increases, in a qualitative agreement …
Facet-dependent Chemical Kinetics Governed Growth of Twisted Graphene Layers with Pre-designed Angles
School of Physical Science and Technology, ShanghaiTech University（上海科技大学物理科学与技术学院）；Center for Transformative Science, Shanghai Tech University（上海科技大学变革科学中心）；Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences（中国科学院上海微系统与信息技术研究所）；Suzhou Laboratory（苏州实验室）；Department of Chemistry, Technical University of Munich（慕尼黑工业大学化学系）
Enhancement of the chemical activity of graphene is evidenced by first-principles modelling of chemisorption of the hydrogen, fluorine, oxygen and hydroxyl groups on strained graphene. For the case of negative strain or compression, chemisorption of the single hydrogen, fluorine or hydroxyl group is energetically more favourable than those of their pairs on different sublattices. This behaviour stabilizes the magnetism caused by the chemisorption being against its destruction by the pair formations. Initially flat, compressed graphene is shown to buckle spontaneously right after chemisorption …
We present a graphene/Cu nanoparticle hybrids (G/CuNPs) system as a surface-enhanced Raman scattering (SERS) substrate for adenosine detection. The Cu nanoparticles wrapped around a monolayer graphene shell were directly synthesized on flat quartz by chemical vapor deposition in a mixture of methane and hydrogen. The G/CuNPs showed an excellent SERS enhancement activity for adenosine. The minimum detected concentration of the adenosine in serum was demonstrated as low as 5 nM, and the calibration curve showed a good linear response from 5 to 500 nM. The capability of SERS detection of adenosin…
While the basal plane of graphene is inert, defects in it are centers of chemical activity. An attractive application of such defects is towards controlled functionalization of graphene with foreign molecules. However, the interaction of the defects with reactive environment, such as ambient, decreases the efficiency of functionalization and makes it poorly controlled. Here, we report a novel approach to generate, monitor with time resolution, and functionalize the defects $\textit{in situ}$ without ever exposing them to the ambient. The defects are generated by an energetic Argon plasma and t…
