Electronic Properties Of Monolayer Graphene Research Articles

A perspective of recent advances in PECVD-grown graphene thin films for scientific research and technological applications

The purpose of this review is to provide a perspective on some of the recent advances in applying graphene thin films, including monolayer and multilayer graphene sheets synthesized by a scalable approach based on plasma-enhanced chemical vapor deposition (PECVD), to scientific research and technologies. The technological applications present here include the use of graphene in flexible electronics, for anticorrosion of metals, and for Si-based technologies including superlubricity and optoelectronics. In the case of fundamental scientific research, we demonstrate that periodic patterns of nanoscale strain distributions in monolayer graphene can lead to local giant pseudomagnetic fields as well as global modifications to the electronic properties of monolayer graphene, including strain-induced valley Hall signals and quantized Landau levels in the absence of external magnetic fields, edge states, as well as increasing electronic correlation with increasing strain. These findings suggest new approaches towards developing emerging quantum states with tunable electronic correlation based on graphene straintronics.

An Overview of the Electronic Structure of Monolayer Graphene

Monolayer graphene is a nanostructured material that consists of layers of graphene, each layer of single-layer graphene consists of a layer of carbon atoms that are interconnected in a hexagonal lattice. The crystal structure of monolayer graphene is two dimensional and carbon atoms are inserted in a hexagonal lattice. The band structure of monolayer graphene includes two main bands that located at points K and K’ considered as quantum bands of electrons and holes. The electronic properties of monolayer graphene include the movement of electrons at very high speed and maintaining their spin. Also, monolayer graphene has unique optical properties and can be used as an optical switcher in electronic devices. Which from the basis of the contemporary technology of graphene and is progressing, therefor, research in this field is important and this research was carried out in a library method and its purpose is to investigate the electronic structure of single – layer graphene.

Substrate effect on the electronic properties of graphene on vicinal Pt(1 1 1)

The atomic structure and electronic properties of monolayer graphene on a curved multi-nano-vicinal Pt (111) substrate are investigated with a low-energy electron diffraction, scanning tunneling microscopy and angle-resolved photoemission spectroscopy. Despite graphene grows continuously over the terraces and step bunching areas, the spatial periodicity also varies by varying the vicinal angle of the substrate. This superperiodicity has been evidenced by splitting of first order Pt spots in LEED and from STM. The photoemission spectroscopy unravels that the linearly dispersing π band of graphene is affected by the step periodicity as evidenced by the opening of bandgaps. The gaps opening occurs at the intersection of the main graphene band with Umklapp bands due to the superperiodicity of the one-dimensional nanostructured substrate. The energy and momentum locations of the minigaps change with the superperiodicity, which is related to the spatial periodicity and vicinal angle of the substrate. Our results show a simple way to tune the electronic properties of epitaxial graphene by tuning the substrate vicinality.

Magnetotransport in hybrid InSe/monolayer graphene on SiC

The magnetotransport properties of a hybrid InSe/monolayer graphene in a SiC system are systematically studied. Compared to those of its bare graphene counterpart, in InSe/graphene, we can effectively modify the carrier density, mobility, effective mass, and electron–electron (e–e) interactions enhanced by weak disorder. We show that in bare graphene and hybrid InSe/graphene systems, the logarithmic temperature (lnT) dependence of the Hall slope R H = δR xy /δB = δρ xy /δB can be used to probe e–e interaction effects at various temperatures even when the measured resistivity does not show a lnT dependence due to strong electron–phonon scattering. Nevertheless, one needs to be certain that the change of R H is not caused by an increase of the carrier density by checking the magnetic field position of the longitudinal resistivity minimum at different temperatures. Given the current challenges in gating graphene on SiC with a suitable dielectric layer, our results suggest that capping a van der Waals material on graphene is an effective way to modify the electronic properties of monolayer graphene on SiC.

Influence of oxide substrates on monolayer graphene doping process by thermal treatments in oxygen

The structural and the electronic properties of monolayer graphene made by chemical vapor deposition and transferred on various oxide substrates (SiO2, Al2O3, and HfO2) are investigated by Raman Spectroscopy and Atomic Force Microscopy in order to highlight the influence of the substrate on the features of p-doping obtained by O2 thermal treatments. By varing the treatment temperature up to 400 °C, the distribution of the reaction sites of the substrates is evaluated. Their total concentration and the consequent highest doping available is determined and it is shown that this latter is linked to the water affinity of the substrate. Finally, by varing the exposure time to the gas up to 2 h, the kinetics of doping is investigated. The doping process is found to be better described by a diffusion limited kinetic model, ascribable to the diffusion of O2 in the interstitial space between graphene and the substrate. After this step, the doping process is completed by a faster redox reaction between O2 adsorbed to graphene and interstitial H2O.

The Role of the Oxygen Impurity on the Electronic Properties of Monolayer Graphene: A Density-Functional Study

Oxidation during the fabrication of a two-dimensional carbon-based system (graphene) can not be avoided so that will affect the electronic properties of the system. In this study, we investigate the effect of the oxygen impurity on the electronic properties of monolayer graphene using density functional theory calculations. The calculations were performed using the (3×3) supercell model and were validated by the (1×1) supercell calculations. We find that by increasing the oxygen concentration from 6%, 11%, 17%, 33% and 50%, the band gap enhanced from 0.1 to 2.48 eV. An analysis using the partial density-of-states projected to the atoms confirmed that strong hybridizations between O − Py and C − Pz orbitals are responsible for inducing the enhancement of the bandgap. Therefore, we conclude that oxygen atoms are highly sensitive to changes in the electronic properties of monolayer graphene.

Spatially Resolved Modification of Graphene’s Band Structure by Surface Oxygen Atoms

We present the spatially resolved modification of the topography and electronic properties of monolayer graphene by a low dosage of atomic oxygen on the nanometer scale. Using the combination of an ultrahigh-vacuum scanning tunneling microscope and a gas beam of oxygen atoms, we show that the surface O-atoms, even at a low coverage of O/C = ∼1/150, serve as p-type dopants that leads to site-dependent partial and full graphene band modifications up to a gap of a few hundred millielectronvolts. The degree of modification and the number of O-atom-induced charge-holes per area are inversely proportional to the distance between the measuring position and the location of the nearest adsorbate. However, the number of holes contributed per oxygen atom is found to be a site-independent constant of 0.15 ± 0.05. For a small population of adsorbates taller than 4 A, the graphene energy bands are no longer resolved; instead, our tunneling spectra show very spatially localized but highly dense states over a wide potent...

Energetic Stabilities, Structural and Electronic Properties of Monolayer Graphene Doped with Boron and Nitrogen Atoms

The structural, energetic, and electronic properties of single-layer graphene doped with boron and nitrogen atoms with varying doping concentrations and configurations have been investigated here via first-principles density functional theory calculations. It was found that the band gap increases with an increase in doping concentration, whereas the energetic stability of the doped systems decreases with an increase in doping concentration. It was observed that both the band gaps and the cohesive energies also depend on the atomic configurations considered for the substitutional dopants. Stability was found to be higher in N-doped graphene systems as compared to B-doped graphene systems. The electronic structures of B- and N-doped graphene systems were also found to be strongly influenced by the positioning of the dopant atoms in the graphene lattice. The systems with dopant atoms at alternate sublattices have been found to have the lowest cohesive energies and therefore form the most stable structures. These results indicate an ability to adjust the band gap as required using B and N atoms according to the choice of the supercell, i.e., the doping density and substitutional dopant sites, which could be useful in the design of graphene-based electronic and optical devices.

Changes in work function due to NO2 adsorption on monolayer and bilayer epitaxial graphene on SiC(0001)

The electronic properties of monolayer graphene grown epitaxially on SiC(0001) are known to be highly sensitive to the presence of ${\mathrm{NO}}_{2}$ molecules. The presence of small areas of bilayer graphene, on the other hand, considerably reduces the overall sensitivity of the surface. We investigate how ${\mathrm{NO}}_{2}$ molecules interact with monolayer and bilayer graphene, both free-standing and on a SiC(0001) substrate. We show that it is necessary to explicitly include the effect of the substrate in order to reproduce the experimental results. When monolayer graphene is present on SiC, there is a large charge transfer from the interface between the buffer layer and the SiC substrate to the molecule. As a result, the surface work function increases by 0.9 eV after molecular adsorption. A graphene bilayer is more effective at screening this interfacial charge, and so the charge transfer and change in work function after ${\mathrm{NO}}_{2}$ adsorption is much smaller.

Modulating the Electronic Properties of Monolayer Graphene Using a Periodic Quasi-One-Dimensional Potential Generated by Hex-Reconstructed Au(001).

The structural and electronic properties of monolayer graphene synthesized on a periodically reconstructed substrate can be widely modulated by the generation of superstructure patterns, thereby producing interesting physical properties, such as magnetism and superconductivity. Herein, using a facile chemical vapor deposition method, we successfully synthesized high-quality monolayer graphene with a uniform thickness on Au foils. The hex-reconstruction of Au(001), which is characterized by striped patterns with a periodicity of 1.44 nm, promoted the formation of a quasi-one-dimensional (1D) graphene superlattice, which served as a periodic quasi-1D modulator for the graphene overlayer, as evidenced by scanning tunneling microscopy/spectroscopy. Intriguingly, two new Dirac points were generated for the quasi-1D graphene superlattice located at -1.73 ± 0.02 and 1.12 ± 0.12 eV. Briefly, this work demonstrates that the periodic modulation effect of reconstructed metal substrates can dramatically alter the electronic properties of graphene and provides insight into the modulation of these properties using 1D potentials.

Low-Bias Terahertz Amplitude Modulator Based on Split-Ring Resonators and Graphene

Split-ring resonators represent the ideal route to achieve optical control of the incident light at THz frequencies. These subwavelength metamaterial elements exhibit broad resonances that can be easily tuned lithographically. We have realized a design based on the interplay between the resonances of metallic split rings and the electronic properties of monolayer graphene integrated in a single device. By varying the major carrier concentration of graphene, an active modulation of the optical intensity was achieved in the frequency range between 2.2 and 3.1 THz, achieving a maximum modulation depth of 18%, with a bias as low as 0.5 V.

Effect of oxygen adsorption on the local properties of epitaxial graphene on SiC (0001)

The effect of oxygen adsorption on the local structure and electronic properties of monolayer graphene grown on SiC (0001) has been studied by means of low-energy electron microscopy (LEEM), microprobe low-energy electron diffraction (\ensuremath{\mu}LEED), and microprobe angle resolved photoemission (\ensuremath{\mu}ARPES). We show that the buffer layer of epitaxial graphene on SiC (0001) is partially decoupled after oxidation. The monitoring of the oxidation process demonstrates that the oxygen saturates the Si dangling bonds, breaks some Si--C bonds at the interface, and intercalates the graphene layer. Accurate control over the oxidation parameters enables us to tune the charge density modulation in the layer.

Zero-mode anomalies of massless Dirac electron in graphene

A brief review is given on singularities appearing in electronic properties of monolayer graphene at the Dirac point from a theoretical point of view. The topics include effective-mass description of electronic states, singular behavior of the conductivity including the Hall effect and nonuniversality of the minimum conductivity, and the singular diamagnetic response to uniform and spatially varying magnetic field.

Inhomogeneous electronic properties of monolayer graphene on Ru(0001)

Inhomogeneous electronic properties of monolayer graphene on Ru(0001)

Tuning the electronic properties of monolayer graphene by the periodic aligned graphene nanoribbons

The 2 p z tight-binding model has been used to investigate the electronic properties of ribbon–graphene hybrid systems. This system is constructed by zigzag graphene nanoribbons aligned periodically on monolayer graphene. It was found that for such systems the electronic properties would be strongly influenced by the geometric structure of graphene nanoribbons, such as the width and the period of the ribbons. In addition, the stacking arrangement between graphene nanoribbons and monolayer graphene also plays a dominant role in determining the band structures in the low-energy region. These geometric structure effects can be well understood through the density of state calculations. Such hybrid structures lead to interesting novel features, dissimilar from those of single layer graphene, and could serve as a platform for the studies of device applications.

The interaction of Xe and Xe + K with graphene

We have investigated the electronic properties of monolayer graphene with adsorbed layers of xenon or potassium, or a combination of the two. The formation of the first Xe layer is characterized by a dipole polarization which is quenched by a second Xe layer. By comparing K on Xe on graphene to K on bare graphene, we determine the K contribution to trigonal warping and mass renormalization due to electron–phonon coupling. The former is found to be small but significant, while the latter is shown to be negligible. Thus, previously determined values of electron–phonon coupling for K on graphene are shown to be intrinsic to doped graphene and not determined by the proximity of K ions to the graphene.

Periodicity, work function and reactivity of graphene on Ru(0001) from first principles

Using density functional theory (DFT), a detailed analysis of the energetic and electronic properties of monolayer graphene on Ru(0001) was performed. Firstly, we demonstrate that the corrugated (12×12)C/(11×11)Ru structure is an absolute minimum among smaller and larger commensurabilities. Secondly, we show that the reduced work function originates from the charge depletion in the graphene skeleton states at bonded carbon atoms, in contrast to the assumed n-doping of π states. We further propose that the higher-lying regions of the graphene layer form an array of electronically disconnected nanographene islands. Finally, we explore the adsorption properties of this template with respect to metals by comparing the adsorption of Au and Pt single atoms. A 1.1 eV (0.7 eV) preference is found for Au (Pt) atop adsorption in the low region with 0.2–0.3 eV selectivity for the (hcp, top) locations, in agreement with recent experiments on Pt clusters.

Electronic transport in chemical vapor deposited graphene synthesized on Cu: Quantum Hall effect and weak localization

We report on electronic properties of graphene synthesized by chemical vapor deposition (CVD) on copper then transferred to SiO2/Si. Wafer-scale (up to 4 in.) graphene films have been synthesized, consisting dominantly of monolayer graphene as indicated by spectroscopic Raman mapping. Low temperature transport measurements are performed on microdevices fabricated from such CVD graphene, displaying ambipolar field effect (with on/off ratio ∼5 and carrier mobilities up to ∼3000 cm2/V s) and “half-integer” quantum Hall effect, a hall-mark of intrinsic electronic properties of monolayer graphene. We also observe weak localization and extract information about phase coherence and scattering of carriers.

Electronic properties of monolayer graphene in the presence of the uniform magnetic and modulated electric fields

The influence of modulated electric fields on low-energy Landau levels (LLs) of single-layer graphene is investigated by the Peierls tight-binding model. Such fields strongly affect the electronic properties of LLs, i.e., they split the LLs into the parabolic bands, produce the extra band-edge states, break the state degeneracy, and increase the dimensionality. The extra band-edge states make the density of states (DOS) exhibits many pairs constructed by the two square-root divergent peaks. The energy spacing between the pair peaks is proportional to the electric field strength ( V 0), and the peak intensity displays an inverse proportion to V 0. However, DOS is independent of the modulated period. Furthermore, the dependence of the peak frequency on the electric field strength is also discussed in detail. The predicted results could be verified by the experimental measurements.