Recent optical conductivity experiments of doped graphene in the infrared regime reveal a strong background in the energy region between the intra and interband transitions difficult to explain within conventional pictures. We propose a phenomenological model taking into account the marginal Fermi liquid nature of the quasiparticles in graphene near the neutrality point that can explain qualitatively the observed features. We also study the electronic Raman signal and suggest that it will also be anomalous.
The electronic and structural properties of (i) boron doped graphene sheets, and (ii) the chemisorption processes of hydrogen adatoms on the boron doped graphene sheets have been examined by {\it ab initio} total energy calculations.
Nitrogen-doped graphene was recently synthesized and was reported to be a catalyst for hydrogen dissociative adsorption under a perpendicular applied electric field (F). In this work, the diffusion of H atoms on N-doped graphene, in the presence and absence of an applied perpendicular electric field, is studied using density functional theory. We demonstrate that the applied field can significantly facilitate the binding of hydrogen molecules on N-doped graphene through dissociative adsorption and diffusion on the surface. By removing the applied field the absorbed H atoms can be released effi…
Two-dimensional alloys of carbon and nitrogen represent an urgent interest due to prospective applications in nanomechanical and optoelectronic devices. Stability of these chemical structures must be understood as a function of their composition. The present study employs hybrid density functional theory and reactive molecular dynamics simulations to get insights regarding how many nitrogen atoms can be incorporated into the graphene sheet without destroying it. We conclude that (1) C:N=56:28 structure and all nitrogen-poorer structures maintain stability at 1000 K; (2) stability suffers from …
Novel uses for 2-dimensional materials like graphene and hexagonal boron nitride (h-BN) are being frequently discovered especially for membrane and catalysis applications. Still however, a great deal remains to be understood about the interaction of environmentally and industrially elevant molecules such as water with these materials. Taking inspiration from advances in hybridising graphene and h-BN, we explore using density functional theory, the dissociation of water, hydrogen, methane, and methanol on graphene, h-BN, and their isoelectronic doped counterparts: BN doped graphene and C doped …
In this paper, the effect of B and N doping on the phonon induced thermal conductivity of graphene has been investigated. This study is important when one has to evaluate the usefulness of electronic properties of B and N doped graphene. We have performed the calculations by employing density functional perturbation theory(DFPT) to calculate the inter-atomic forces=force constants of pristine/doped graphene. Thermal conductivity calculations have been carried out by making use of linearized Boltzmann transport equations (LBTE) under single-mode relaxation time approximation (RTA). The thermal …
Since advanced Silicon-based device components are moderately chemically tunable, doped graphene has emerged as a promising candidate to replace this semiconducting material in flexible miniaturized electronic devices. Indeed, heteroatom co-doping (i.e. with boron and/or nitrogen) is an appealing strategy to tune both its structural and electronic properties, possibly inducing a band gap in graphene. However, presently synthesized BN-doped carbon-based materials are randomly doped, leading to their electronic properties not being reproducible. Using first-principles techniques, the present stu…
As a possible way of modifying the intrinsic properties of graphene we study the doping of graphene by embedded boron clusters with density functional theory. Cluster doping is technologically relevant as the cluster implantation technique can be readily applied to graphene. We find that B7 clusters embedded into graphene and graphene nanoribbons are structurally stable and locally metallize the system. This is done both by the reduction of the Fermi energy and by the introduction of boron states near the Fermi level. A linear chain of boron clusters forms a metallic "wire" inside the graphene…
Graphene nanomeshes (GNMs), formed by creating a superlattice of pores in graphene, possess rich physical and chemical properties. Many of these properties are determined by the pore geometry. In this work, we use first principles calculations to study the magnetic and electronic properties of metal-doped nitrogen-passivated GNMs. We find that the magnetic behaviour is dependent on the pore shape (trigonal vs. hexagonal) as dictated by the number of covalent bonds formed between the 3$d$ metal and the passivating N atoms. We also find that Cr and V doped trigonal-pore GNMs, and Ti doped GNMs a…
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 c…
Two-dimensional graphene exhibits many fascinating properties such as ballistic electronic conduction and quantum Hall effect at room temperature.1-4 Graphene doped electrochemically or through charge-transfer with electron-donor and -acceptor molecules,5-7 shows marked changes in electronic structure, with characteristic signatures in the Raman spectra.5-10 Substitutional doping, universally used in tuning properties of semiconductors, could be a powerful tool to control the electronic properties of graphene. Here, we present the structure and properties of boron and nitrogen doped graphenes,…
We built graphene nanoflakes doped or not with $C$ atoms in the $sp^3$ hybridization or with $Si$ atoms. These nanoflakes are isolated, i.e. are not connected to any object (substrate or junction). We used a modified tight binding method to compute the $π$ and $σ$ density of states. The nanoflakes are semiconducting (due to the armchair geometry of their boundaries) when their are pure but the become conducting when doped because doping removes the degeneracy of the density of states levels. Moreover, we showed that the $π$ Fermi level and the Fermi level of both $π$ and $σ$ electrons are not …
Li and Na attachment to free tetracyanoethylene (TCNE) molecules and TCNE adsorbed on doped graphene is studied using density functional theory. While TCNE is adsorbed only weakly on ideal graphene, we identified a configuration in which TCNE is chemisorbed on Al-doped graphene via molecule C atom and a surface oxygen atom. Up to four (five) Li and Na atoms can be stored on both free (adsorbed) TCNE with binding energies stronger than cohesive energies of the Li and Na metals. When storing up to three atoms per molecule, it should be possible to avoid reduction of common battery electrolytes. …
High-quality nitrogen-doped graphene on nickel is prepared by exploiting both the catalytic properties of nickel and the solubility of nitrogen atoms into its bulk. Following the standard chemical vapor deposition procedure, a previously nitrogen-doped nickel substrate is exposed to carbon-containing precursors so that nitrogen atoms, segregating to the surface, remain trapped in the growing graphene network. Morphological and chemical characterization by scanning tunneling microscopy and X-ray photoelectron spectroscopy demonstrates that the process yields a flat, wide, continuous nitrogen-do…
Graphene halfly doped with H or F possesses local magnetization at the undoped C sites. Thus the Seebeck coefficient is different for each spin channel and its sign also changes depending on the spin polarization. Deposition of doped graphene on the C-face 4H-SiC(0001) with two buffer layers substantially varies the electronic and thermoelectric properties. These properties are efficiently calculated from the semiclassical Boltzmann equations, using the maximally-localized Wannier-functions interpolation of the band structures obtained with the density-functional theory. Our results indicate l…
A method for determining the type of charge carrier, electron or hole, which is transferred from metal contacts to graphene, is described. The Dirac point is found to shift toward more negative (positive) gate voltages for electron (hole) doping by shortening of the interelectrode spacing. The shift of the Dirac point is accompanied by an enhancement of the electron-hole conductivity asymmetry. Experimentally determined carrier types may be explained in terms of the metal work functions modified by interactions with graphene.
We have studied the interaction of water and graphene doped with nitrogen in different configurations, namely, graphitic and pyridinic nitrogen, by means of the van der Waals density functional. We found that the local nitrogen configuration plays a key role in determining the stable water configuration, while the dispersion force is responsible for the water adsorption. With the graphitic nitrogen, water prefers to orient with its oxygen toward the surface, whereas for the pyridinic nitrogen it prefers to orient with its hydrogens toward the surface, because nitrogen is positively and negativ…
We use first-principles density-functional calculations to determine the frequency shift of the A$'_1$-${\bf K}$ phonon (Raman D band) in monolayer graphene, as a function of the charge doping. A detailed DFT study on the electron-phonon coupling and the phonon line width of E$_{2g}$-${\bm Γ}$ and A$'_1$-${\bf K}$ phonons are also performed for graphene multi-layers. Furthermore, we explain the experimentally observed '1/(Number of Layers)' behaviour of the Raman G band position after including the dynamic response treated within time dependent perturbation theory.
A finite Schottky barrier and large contact resistance between monolayer MoS2 and electrodes are the major bottlenecks in developing high-performance field-effect transistors (FETs) that hinder the study of intrinsic quantum behaviors such as valley-spin transport at low temperature. A gate-tunable graphene electrode platform has been developed to improve the performance of MoS2 FETs. However, intrinsic misalignment between the work function of pristine graphene and the conduction band of MoS2 results in a large threshold voltage for the FETs, because of which Ohmic contact behaviors are obser…
Utilizing the strengths of nitrogen doped graphene quantum dot (N-GQD) as a substrate, here in, we have shown that one can stabilize the catalytically more active planar Au 20 (P-Au 20 ) compared to the thermodynamically more stable tetrahedral structure (T-Au 20 ) on an N-GQD. Clearly, this simple route avoids the usage of traditional transition metal oxide substrates which have been suggested and used for stabilizing the planar structure for a long time. Considering the experimental success in the synthesis of N-GQDs and in the stabilization of Au nanoparticles on N-doped graphene, we expect…
We present a method for decoupling epitaxial graphene grown on SiC(0001) by intercalation of a layer of fluorine at the interface. The fluorine atoms do not enter into a covalent bond with graphene, but rather saturate the substrate Si bonds. This configuration of the fluorine atoms induces a remarkably large hole density of p \approx 4.5 \times 1013 cm-2, equivalent to the location of the Fermi level at 0.79 eV above the Dirac point ED .
Graphene has vast promising applications on the nanoelectronics and spintronics because of its unique magnetic and electronic properties. Making use of an ab initio spin-polarized density functional theory, implemented by the method of Heyd-Scuseria-Ernzerhof 06(HSE06) hybrid functional, the properties of nitrogen substitutional dopants in semi-metal monolayer graphene were investigated. We found from our calculation, that introducing nitrogen doping would possibly break energy degeneracy with respect to spin(spin symmetry breaking) at some doping concentrations with proper dopant configuratio…
Employing density-functional theory (DFT) calculations, the generalized-stacking-fault energy (GSFE) curves along two crystallographic slips, glide and shuffle, for both pristine graphene and impurity of boron (B) or nitrogen (N) doped graphene were examined. The effects of B and N doping on the GSFE were clarified and correlated with local electron interactions and bonding configurations. The GSFE data were then used to analyze dislocation dipole and core structure, and subsequently combined with the Peierls-Nabarro (P-N) model to examine the role of doping on several key characteristics of d…
While the mechanical distortions change the electronic properties of graphene significantly, the effects of electronic manipulation on its mechanical properties have not been known. Using first-principles calculation methods, we show that, when graphene expands isotropically under equibiaxial strain, both the electron and hole doping can maintain or improve its ideal strength slightly and enhance the critical breaking strain dramatically. Contrary to the isotropic expansions, the electron doping decreases the ideal strength as well as critical strain of uniaxially strained graphene while the h…
A promising material for hydrogen storage at room temperature-Al doped graphene was proposed theoretically by using density functional theory calculation. Hydrogen storage capacity of 5.13 wt% was predicted at T = 300 K and P = 0.1 Gpa with adsorption energy Eb = -0.260 eV/H2. This is close to the target of 6 wt% and satisfies the requirement of immobilization hydrogen with Eb of -0.2 ~ -0.4 eV/H2 at ambient temperature and modest pressure for commercial applications specified by U.S. Department of Energy. It is believed that the doped Al varies the electronic structures of both C and H2. The …
A principle of enhancement CO adsorption was developed theoretically by using density functional theory through doping Al into graphene. The results show that the Al doped graphene has strong chemisorption of CO molecule by forming Al-CO bond, where CO onto intrinsic graphene remains weak physisorption. Furthermore, the enhancement of CO sensitivity in the Al doped graphene is determined by a large electrical conductivity change after adsorption, where CO absorption leads to increase of electrical conductivity upon via introducing large amount of shallow acceptor states. Therefore, this newly …
Sulfur and nitrogen dual doped graphene have been extensively investigated in the field of oxygen reduction reaction, supercapacitors and batteries, but their magnetic and absorption performance have not been explored. Besides, the effects of doping sequence of sulfur and nitrogen atoms on the morphology, structural property and the corresponding microwave absorption performance of the dual doped graphene remain unexplored. In this work, nitrogen and sulfur dual doped graphene with different doping sequence were successfully prepared using a controllable two steps facile thermal treatment meth…
Graphitic nitrogen-doped graphene is an excellent platform to study scattering processes of massless Dirac fermions by charged impurities, in which high mobility can be preserved due to the absence of lattice defects through direct substitution of carbon atoms in the graphene lattice by nitrogen atoms. In this work, we report on electrical and magnetotransport measurements of high-quality graphitic nitrogen-doped graphene. We show that the substitutional nitrogen dopants in graphene introduce atomically sharp scatters for electrons but long-range Coulomb scatters for holes and, thus, graphitic…
Spectra of the C1s core hole, created in XPS and screened by electronic excitations in pristine and doped graphene, are calculated and discussed. We find that singular effects in the lineshapes are not possible in the pristine graphene, and their observation should be connected with the doping. However, the structure of the low energy excitation spectrum in the region where the singular behaviour is expected leads to asymmetries in the core hole lineshapes in pristine graphene similar to those in doped graphene. This makes the analysis more complex than in the case of metals and may lead to in…
Possible stably-ordered substitutional structures based on a graphene-type crystal lattice are considered. A kinetic model of atomic ordering in metal-doped graphene with stoichiometric (1/8, 1/4, 1/2) and nonstoichiometric compositions is developed. Inasmuch as the intrasublattice and intersublattice 'interchange' ('mixing') energies are competitively different for graphene-based lattice, kinetic curves of the long-range order (LRO) parameters may be nonmonotonic for the structures described by two or three LRO parameters.
The environmental aging effect of doped graphene is investigated as a function of the organic doping species, humidity, and the number of graphene layers adjacent to the dopant by studies of the Raman spectroscopy, x-ray and ultraviolet photoelectron spectroscopy, scanning electron microscopy, infrared spectroscopy, and electrical transport measurements. It is found that higher humidity and structural defects induce faster degradation in doped graphene. Detailed analysis of the spectroscopic data suggest that the physical origin of the aging effect is associated with the continuing reaction of…
We present a new way to enhance the electron-phonon coupling constant and the critical superconducting temperature of graphene, significantly beyond all reported values. Using density functional theory, we explore the application effects of the tensile biaxial strain on the lithium intercalated graphene. Both effects together, the presence of adatom and the strain, trigger enhancement of critical temperature, up to 300\%, compared to non-strained lithium intercalated graphene.
Using density functional theory, we present a comparative study of the electronic properties of BN-doped graphene monolayer, bilayer, trilayer, and multilayer systems. In addition, we address a superlattice of pristine and BN-doped graphene. Five doping concentrations between 12.5% and 75% are considered, for which we obtain band gaps from 0.02 eV to 2.43 eV. We show that the effective mass varies between 0.007 and 0.209 free electron masses, resembling a high mobility of the charge carriers.
For carbon-based materials, in contrast to metal surfaces, the relationship between strain and reactivity is not yet established, even though there are literature reports on strained graphene. Knowledge of such relationships would be extremely beneficial for understanding the reactivity of graphene-based surfaces and finding optimisation strategies which would make these materials more suitable for targeted applications. Here we investigate the effects of compressive and tensile strain (up to +/-5%) on the structure, electronic properties and the reactivity of pure, N-doped and P-doped graphen…
Graphene/silicon heterostructures have attracted tremendous interest as a new platform for diverse electronic and photonic devices such as barristors, solar cells, optical modulators, and chemical sensors. The studies to date largely focus on junctions between graphene and lightly-doped silicon, where a Schottky barrier is believed to dominate the carrier transport process. Here we report a systematic investigation of carrier transport across the heterojunctions formed between graphene and highly-doped silicon. By varying the silicon doping level and the measurement temperature, we show that t…
We study the superconducting phases of the two-dimensional honeycomb lattice of graphene. We find two spin singlet pairing states, s-wave and an exotic $p+ip$ that is possible because of the special structure of the honeycomb lattice. At half filling, the $p+ip$ phase is gapless and superconductivity is a hidden order. We discuss the possibility of a superconducting state in metal coated graphene.
Recent theoretical considerations have demonstrated that freestanding graphene doped with alkali metals (AC x ) supports strong Dirac and weak acoustic plasmons. Here we show that when AC x is deposited on a metallic surface, the intense Coulomb screening completely washes out these collective modes. However, even small increase of separation between AC x and metallic surface causes recovery of AC x plasmonic properties and especially the enhancement of acoustic plasmons intensities not present in the freestanding case. We further provide the physical background of these intriguing phenomena. …
In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully u…
We calculate electron-hole generation and recombination rates for Coulomb scattering (Auger recombination and impact ionization) in Graphene. The conduction and valence band dispersion relation in Graphene together with energy and momentum conservation requirements restrict the phase space for Coulomb scattering so that electron-hole recombination times can be much longer than 1 ps for electron-hole densities smaller than $10^{12}$ cm$^{-2}$.
Polarization resolved, Raman scattering response due to E$_{2g}$ phonon in monolayer graphene has been investigated in magnetic fields up to 29 T. The hybridization of the E$_{2g}$ phonon with only the fundamental inter Landau level excitation (involving the n=0 Landau level) is observed and only in one of the two configurations of the circularly crossed polarized excitation and scattered light. This polarization anisotropy of the magneto-phonon resonance is shown to be inherent to relatively strongly doped graphene samples, with carrier concentration typical for graphene deposited on SiO$_2$.
The next-nearest neighbor interaction (NNN) is included in a tight-binding calculation of the electronic spectrum and conductivity of doped graphene. As a result, we observe a wide variation of the conductivity behavior, since the Fermi energy and the resonance peak are not shifted by the same amount. Such effect can have a profound effect in the idea of explaining the minimal conductivity of graphene as a consequence of impurities or defects. Finally, we also estimate the mean free path and relaxation time due to resonant impurity scattering.
The effects of biaxial strain on the impurity-induced magnetism in P-doped graphene (P-graphene) and N-doped silicene (N-silicene) are studied by means of spin-polarized density functional calculations, using the supercell approach. The calculations were performed for three different supercell sizes $4\times 4$, $5\times 5$, and $6\times 6$, in order to simulate three different dopant concentrations 3.1, 2.0 and 1.4 %, respectively. For both systems, the calculated magnetic moment is 1.0 $μ_B$ per impurity atom for the three studied concentrations. From the analysis of the electronic structure…
The conductivity of doped graphene is considered taking into account scattering by short-range nonsymmetric defects, when the longitudinal and transverse components of conductivity tensor appear to be different. The calculations of the anisotropic conductivity tensor are based on the quasiclassical kinetic equation for the case of monopolar transport at low temperatures. The effective longitudinal conductivity and the transverse voltage, which are controlled by orientation of sample and by gate voltage (i.e. doping level), are presented.
Substances such as the ``telephone number compound'' Sr14Cu24O41 are intrinsically hole-doped. The involved interplay of spin and charge dynamics is a challenge for theory. In this article we propose to describe hole-doped Heisenberg spin rings by means of complete numerical diagonalization of a Heisenberg Hamiltonian that depends parametrically on hole positions and includes the screened Coulomb interaction among the holes. It is demonstrated that key observables like magnetic susceptibility, specific heat, and inelastic neutron scattering cross section depend sensitively on the dielectric co…
Based on first principles density functional theory calculations we explored energetics of oxygen reduction reaction over pristine and nitrogen-doped graphene with different amounts of nitrogen doping. The process of oxygen reduction requires one more step then same reaction catalyzed by metals. Results of calculations evidence that for the case of light doped graphene (about 4% of nitrogen) energy barrier for each step is lower than for the same process on Pt surface. In contrast to the catalysis on metal surface the maximal coverage of doped graphene is lower and depends on the corrugation o…
We calculate the photoemission spectra of suspended and epitaxial doped graphene using an ab initio cumulant expansion of the Green's function based on the GW self-energy. Our results are compared to experiment and to standard GW calculations. For doped graphene on a silicon carbide substrate, we find, in contrast to earlier calculations, that the spectral function from GW only does not reproduce experimental satellite properties. However, ab initio GW plus cumulant theory combined with an accurate description of the substrate screening results in good agreement with experiment, but gives no p…
First principles based DFT calculations performed to insight structural and electronic properties of Boron doped Magnesium atom decorated graphene sheet for application of hydrogen storage. The four H2 molecules stably binds magnesium atom with Boron doped graphene sheet. The average binding energy extracted in the range-0.566 to -0.687 eV/H2.Partial density of states of complex system shows s and d orbitals of H2 molecule and Mg atom at -0.1eV overlaps of main peaks indicates strong hybridizing and binding of s and d orbitals of H2 and Mg atom respectively. The gravimetric capacity of studied…
The nonlinear response of electrons (holes) in doped graphene on ac pumping is considered theoretically for the frequency region above the energy relaxation rate but below the momentum and carrier-carrier scattering rates. Temporally-dependent heating of electrons by a strong ac field, which is described within the energy balance approach, leads to an effective generation of high-order harmonics. The efficiency of up-conversion of the 1 mm radiation into the third harmonic by a single-layer graphene is about 10^{-7} at pumping level ~100 kW/cm^2, room temperature, and concentration ~5 x 10^{11…
Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasi-classical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level m = E_F/v_F^2.
The electron-phonon coupling in potassium-doped graphene on Ir(111) is studied via the renormalization of the pi* band near the Fermi level, using angle-resolved photoemission spectroscopy. The renormalization is found to be fairly weak and almost isotropic, with a mass enhancement parameter of lambda= 0.28(6) for both the K-M and the K-G direction. These results are found to agree well with recent first principles calculations.
We compute, from first-principles, the frequency of the E2g, Gamma phonon (Raman G-band) of graphene, as a function of the charge doping. Calculations are done using i) the adiabatic Born-Oppenheimer approximation and ii) time-dependent perturbation theory to explore dynamic effects beyond this approximation. The two approaches provide very different results. While, the adiabatic phonon frequency weakly depends on the doping, the dynamic one rapidly varies because of a Kohn anomaly. The adiabatic approximation is considered valid in most materials. Here, we show that doped graphene is a specta…
Graphene, due to its exceptional properties, is a promising material for nanotechnology applications. In this context, the ability to tune the properties of graphene-based materials and devices with the incorporation of defects and impurities can be of extraordinary importance. Here we investigate the effect of uniaxial tensile strain on the electronic and magnetic properties of graphene doped with substitutional Ni impurities (Ni_sub). We have found that, although Ni_sub defects are non-magnetic in the relaxed layer, uniaxial strain induces a spin moment in the system. The spin moment increas…
We demonstrate generation of linearly polarized pulses from a passively Q-switched Erbium-doped fiber laser. The cavity was designed using only polarization maintaining (PM) fibers and components, resulting in linearly polarized output beam with degree of polarization (DOP) at the level of 97.6%. Reduced graphene oxide (rGO) was used as a saturable absorber for Q-switched operation. The laser was capable of delivering 1.85us pulses with 125nJ pulse energy at 115kHz repetition rate.
The nonlinear magneto-optic responses are investigated for gapped graphene and doped graphene in a perpendicular magnetic field. The electronic states are described by Landau levels, and the electron dynamics in an optical field is obtained by solving the density matrix in the equation of motion. In the linear dispersion approximation around the Dirac points, both linear conductivity and third order nonlinear conductivities are numerically evaluated for infrared frequencies. The nonlinear phenomena, including third harmonic generation, Kerr effects and two photon absorption, and four wave mixi…
We calculate core-level spectra for pristine and doped free-standing graphene sheets. Instructions for how to perform the calculations are given in detail. Although pristine graphene is not metallic the core-level spectrum presents low-energy tailing which is characteristic of metallic systems. The peak shapes vary with doping level in a characteristic way. The spectra are compared to experiments and show good agreement. We compare to two different pristine samples and to one doped sample. The pristine samples are one with quasi-free-standing epitaxial graphene on SiC obtained by hydrogen inte…
Active sites and catalytic mechanism of nitrogen-doped graphene in oxygen reduction reaction (ORR) have been extensively studied but are still inconclusive, partly due to the lack of an experimental method that can detect the active sites. It is proposed in this report that the active sites on nitrogen-doped graphene can be determined via the examination of its chemical composition change before and after ORR. Synchrotron-based X-ray photoelectron spectroscopy analyses of three nitrogen-doped multilayer graphene samples reveal that oxygen reduction intermediate OH(ads) which should chemically …
In this work, we present a semi-analytical expression for the temperature dependence of a spin-resolved dynamical density-density response function of massless Dirac fermions within the Random Phase Approximation. This result is crucial in order to describe thermodynamic properties of the interacting systems. In particular, we use it to make quantitative predictions for the paramagnetic spin susceptibility of doped graphene sheets. We find that, at low temperatures, the spin susceptibility behaves like $T^{-2}$ which is completely different from the temperature dependence of the magnetic susce…
Numerically solving the semiconductor Bloch equations within a phenomenological relaxation time approximation, we extract both the linear and nonlinear optical conductivities of doped graphene and gapped graphene under excitation by a laser pulse. We discuss in detail the dependence of second harmonic generation, third harmonic generation, and the Kerr effects on the doping level, the gap, and the electric field amplitude. The numerical results for weak electric fields agree with those calculated from available analytic perturbation formulas. For strong electric fields when saturation effects …
