Energy Gap In Graphene Research Articles

Pseudomagnetic Moment in Graphene in Time-Dependent Electric Field

We study the dynamics of graphene ring in the presence of time-dependent electric field, where the Dirac particles in graphene ring interact with external electromagnetic fields. Using the Dirac Hamiltonian in electromagnetic field, we obtain the pseudomagnetic moment of the Dirac particles around a graphene ring. It is shown that the appeared pseudomagnetic moment term essentially can be in control by time-dependent electric field, and also it depends on the energy gap of graphene. It seems that one can construct a logic system in graphene and also in semiconductors by the pseudomagnetic moment term.

Controllable N-Doping of Graphene

Opening and tuning an energy gap in graphene are central to many electronic applications of graphene. Here we report N-doped graphene obtained by NH3 annealing after N(+)-ion irradiation of graphene samples. First, the evolution of the graphene microstructure was investigated following N(+)-ion irradiation at different fluences using Raman spectroscopy, showing that defects were introduced in plane after irradiation and then restored after annealing in N2 or in NH3. Auger electron spectroscopy (AES) of the graphene annealed in NH3 after irradiation showed N signal, however, no N signal was observed after annealing in N2. Last, the field-effect transistor (FET) was fabricated using N-doped graphene and monitored by the source-drain conductance and back-gate voltage (Gsd-Vg) curves in the measurement. The transport property changed compared to that of the FET made by intrinsic graphene, that is, the Dirac point position moved from positive Vg to negative Vg, indicating the transition of graphene from p-type to n-type after annealing in NH3. Our approach, which provides a physical mechanism for the introduction of defect and subsequent hetero dopant atoms into the graphene material in a controllable fashion, will be promising for producing graphene-based devices for multiple applications.

Tunneling conductance in gapped graphene-based normal metal–insulator–superconductor junctions: Case of massive Dirac electrons

We study the quantum transport property in a gapped graphene-based normal metal–insulator–superconductor junctions ( NG/ IG/ SG), in the limit of a thin barrier. The charged fermions in NG/ IG/ SG structure are treated as massive relativistic particles. Based on Andreev and normal reflections in normal-superconductor graphene-based junction and BTK formalism, the tunneling conductance’s in terms of some different electrostatic superconductor, U 0 and barrier, V 0 potential are obtained. Using the experimental based values of the Fermi energy in the NG and SG ( E FN and E FN + U 0, respectively), energy gap in graphene 2 mv F 2 and superconducting order parameter, Δ, it is shown that the conductance spectra of such system represent a new behavior, i.e. if we take | E FN - mv F 2 | → 0 , it becomes as a step function of V 0. This behavior of charge transportation can be considered as a nano switch.

Energy bands of atomic monolayers of various materials: Possibility of energy gap engineering

The mobility of graphene is very high because the quantum Hall effects can be observed even at room temperature. Graphene has the potential of the material for novel devices because of this high mobility. But the energy gap of graphene is zero, so graphene cannot be applied to semiconductor devices such as transistors, LEDs, etc. In order to control the energy gaps, we propose atomic monolayers which consist of various materials besides carbon atoms. To examine the energy dispersions of atomic monolayers of various materials, we calculated the electronic states of these atomic monolayers using density functional theory with structural optimizations. The quantum chemical calculation software Gaussian 03 was used under periodic boundary conditions. The calculation method is LSDA/6-311G(d,p), B3LYP/6-31G(d), or B3LYP/6-311G(d,p). The calculated materials are C (graphene), Si (silicene), Ge, SiC, GeC, GeSi, BN, BP, BAs, AlP, AlAs, GaP, and GaAs. These atomic monolayers can exist in the flat honeycomb shapes. The energy gaps of these atomic monolayers take various values. Ge is a semimetal; AlP, AlAs, GaP, and GaAs are indirect semiconductors; and others are direct semiconductors. We also calculated the change of energy dispersions accompanied by the substitution of the atoms. Our results suggest that the substitution of impurity atoms for monolayer materials can control the energy gaps of the atomic monolayers. We conclude that atomic monolayers of various materials have the potential for novel devices.

The formation of an energy gap in graphene on ruthenium by controlling the interface

In this work, we have investigated the spectral function of graphene on a monolayer of intercalated gold on Ru(0001) using angle-resolved photoemission spectroscopy (ARPES). The intercalation leads to a decoupling of the graphene film, as documented by emergence of the characteristic linear π-bands near the Fermi level. However, a band gap at the band crossing is observed. We relate this gap opening to the broken symmetry of the two carbon sublattices, induced by the special lattice mismatch of the graphene and the intercalated gold monolayer.

Pseudospin–orbital coupling for pseudospintronic device in graphene

We investigate the coupling of graphene pseudospin to orbital motion of the Dirac particles in mock relativistic and low energy limits in analogy to semiconductor spin–orbit coupling. We suggest harnessing these effects for nanoscale electronic applications under an artificial atomic structure, consisting of a graphene ring and a charged nano-sized dot, wherein a large pseudospin–orbital strength can be achieved by accelerating the Dirac particles around the ring, due to the small energy gap in graphene and the large radial electric field due to the charged quantum dot. We compare the pseudo SOC effects experienced by Dirac particles in graphene to the conventional Rashba SO effects experienced by electrons in semiconductors, effectively implementing spintronics in graphene.

Energy gaps and a zero-field quantum Hall effect in graphene by strain engineering

Owing to the fact that graphene is just one atom thick, it has been suggested that it might be possible to control its properties by subjecting it to mechanical strain. New analysis indicates not only this, but that pseudomagnetic behaviour and even zero-field quantum Hall effects could be induced in graphene under realistic amounts of strain. Among many remarkable qualities of graphene, its electronic properties attract particular interest owing to the chiral character of the charge carriers, which leads to such unusual phenomena as metallic conductivity in the limit of no carriers and the half-integer quantum Hall effect observable even at room temperature1,2,3. Because graphene is only one atom thick, it is also amenable to external influences, including mechanical deformation. The latter offers a tempting prospect of controlling graphene’s properties by strain and, recently, several reports have examined graphene under uniaxial deformation4,5,6,7,8. Although the strain can induce additional Raman features7,8, no significant changes in graphene’s band structure have been either observed or expected for realistic strains of up to ∼15% (refs 9, 10, 11). Here we show that a designed strain aligned along three main crystallographic directions induces strong gauge fields12,13,14 that effectively act as a uniform magnetic field exceeding 10 T. For a finite doping, the quantizing field results in an insulating bulk and a pair of countercirculating edge states, similar to the case of a topological insulator15,16,17,18,19,20. We suggest realistic ways of creating this quantum state and observing the pseudomagnetic quantum Hall effect. We also show that strained superlattices can be used to open significant energy gaps in graphene’s electronic spectrum.

Effect of the tensile force on the electronic energy gap of graphene sheets

The external force can make a graphene sheet tighten and change its electronic structure. By using the tight-binding method, the energy bands of graphene sheets with zigzag shaped edges and armchair shaped edges drawn by the tensile force are investigated based on considering the nearest-neighbor interaction, and the analytic relations between the energy gaps besides the energy bands of π-electrons for two types of graphene sheets and the tensile force are obtained . Through numerical calculation, we found that the energy gaps broaden as the tensile force increases besides that the tensile force can make graphene open an energy gap,and moreover, the energy gap of graphene with zigzag edges broadens more easily.

XeF 2 and F-atom reactions with Si: their significance for plasma etching : Daniel L. Flamm, Dale E. Ibbotson, John A. Mucha and Vincent M. Donnelly. Solid St. Technol., 117 (April 1983)

Necessity of opening of energy gap in the band structure of, otherwise a zero gap semiconductor, graphene, is a must for its use in fabrication of high speed electronic devices. One such technique, for opening of energy gap in graphene, is by way of doping the pristine graphene with boron or nitrogen. Besides many important applications, to which B- and N-doped graphene has been put, the one very important for solving the global energy crisis is by way of its capacity for hydrogen storage. In this paper electronic structure of B- and N-doped graphene has been studied by using Density Functional Theory, as implemented in WIEN2K code. PBE-GGA (Perdew–Burke–Ernzerhof 96) pseudo-potential is used for solving the Schrodinger equation in self-consistent manner and to account for the exchange and correlation effects through the use of Generalized Gradient Approximation. The band structure calculations reveal that whereas a band gap opens at the symmetry point K both for B- and N-doped graphene, the center of the gap (i.e., the Dirac point in pristine graphene) is shifted above the Fermi level by about 2.20 eV for B-doped graphene, and shifted down the Fermi level by about the same amount for N-doped graphene, when the doping level was kept 25% in each case. The energy gap opened was found to be about 0.30 eV for B-doped graphene and 0.45 eV for N-doped graphene. The linear dispersion characteristics obtained at Dirac point for pristine graphene, almost vanish for B-/N-doped graphene, due to symmetry breaking and opening of energy gap. The band structure and Density of States of B-/N-doped graphene are found also to depend on the choice of cell parameters.