Backward electronic Tamm states in graphene-based heterostructures

We study the electronic surface waves (the so-called Tamm states) localized at the interface between a graphene-based superlattice and a homogeneous graphene by applying suitable electrodes on a graphene sheet. The magnitude as well as the sign of the slope of the Tamm dispersive curve can be flexibly tuned just by varying the external voltage. Particularly, in addition to the conventional forward Tamm states, backward Tamm states in which the wave vector of the electronic surface wave is antiparallel with the group velocity can be realized.     

Anisotropic pairing symmetry effect on crossed Andreev reflection in a graphene-based transistor

Crossed Andreev reflection (CAR) under the influence of anisotropic pairing symmetry is considered. It is shown that CAR is sensitive to the Fermi energy and the orientation of the gap. In addition, the oscillatory period of CAR can be not only tunable by the potential energy in the superconductor region, it also can be modulated by the length of the superconductor region. The physical origination for those phenomena has also been analyzed.     

Valley polarized electronic transport through a line defect in graphene: An analytical approach based on tight-binding model

We develop a tight-binding theory to study the electronic transport through an extended line defect in monolayer graphene. After establishing an analytical expression of the transmission probability, we clarify the following issues concerning the valley polarization in the electronic transport process. Firstly, we find that the valley polarization is robust in the total linear dispersion region. More interestingly, we find that the lattice deformation around the line defect play an important role in tuning the incident angle for complete transmission. Finally, we indicate that next nearest neighbor interaction only causes a small suppression to the valley polarization.     

Palladium atoms and its dimers adsorbed on graphene: First-principles study

In this work we have studied the stabilty, electronic and magnetic properties of Pd adatoms and dimers adsorbed on graphene system using first-principles calculations. The adsorption energies for Pd adatom and its dimer have been found to range from −0.986 to −1.135 eV and −0.165 to −1.101 eV, respectively, which signify stable configuration and future utilization of this system in catalysis. A shift but no separation of π and π^? bands at the Dirac point has been observed in case of Pd dimer adsorption in perpendicular configuration, which can be accounted for the breaking of symmetry of the graphene structure due to adsorption. 64-68% spin polarization P(E_F) and 1.944-1.990 μ_B magnetic moment have been observed for Pd dimers adsorbed on graphene in perpendicular configuration for different sites. The unequal values of partial density of states for 4d and 5s orbitals of Pd dimers at Fermi level have been found to be responsible for the generation of high spin polarization.     

Magnetotransport in a graphene monolayer with two tunable magnetic barriers

The magnetotransport property for a monolayer graphene with two turnable magnetic barriers has been investigated by the transfer-matrix method. We show that the parameters of barrier height, width, and interval between two barriers affect the electron wave decaying length, which determine the conductance with parallel or antiparallel magnetization configuration, and consequently the tunneling magnetoresistance (TMR) for the system. Interestingly, a graphene attached by two barriers with different heights can produce a resonant TMR peak at low energy region one order of magnitude larger than that for the system with two same height barriers because that the asymmetry of magnetic barriers block the electron transmission in the case of antiparallel magnetization configuration. The results obtained here may be useful in understanding of electron tunneling in graphene and in designing of graphene-based nanodevices.     

石墨烯在分析科学中的应用新进展

石墨烯因其独特的物理、化学性质在理论和应用研究上引起广泛关注,在电化学、分析化学及生命分析化学等领域具有很好的应用前景。本文简要介绍了石墨烯的制备和功能化修饰,并概述了近年来石墨烯和氧化石墨烯等材料在样品前处理、传感器、荧光分析及质谱分析等方面的应用进展。     

Graphene grown on transition metal substrates: Versatile templates for organic molecules with new properties and structures

The interest in graphene (a carbon monolayer) adsorbed on metal surfaces goes back to the 60's, long before isolated graphene was produced in the laboratory. Owing to the carbon-metal interaction and the lattice mismatch between the carbon monolayer and the metal surface, graphene usually adopts a rippled structure, known as moiré, that confers it interesting electronic properties not present in isolated graphene. These moiré structures can be used as versatile templates where to adsorb, isolate and assemble organic-molecule structures with some desired geometric and electronic properties. In this review, we first describe the main experimental techniques and the theoretical methods currently available to produce and characterize these complex systems. Then, we review the diversity of moiré structures that have been reported in the literature and the consequences for the electronic properties of graphene, attending to the magnitude of the lattice mismatch and the type of interaction, chemical or physical, between graphene and the metal surface. Subsequently, we address the problem of the adsorption of single organic molecules and then of several ones, from dimers to complete monolayers, describing both the different arrangements that these molecules can adopt as well as their physical and chemical properties. We pay a special attention to graphene/Ru(0001) due to its exceptional electronic properties, which have been used to induce long-range magnetic order in tetracyanoquinodimethane (TCNQ) monolayers, to catalyze the (reversible) reaction between acetonitrile and TCNQ molecules and to efficiently photogenerate large acenes.     

Electronic structure and optical properties of non-metallic modified graphene: a first-principles study

In this paper, the electronic structure and stability of the intrinsic, B-, N-, Si-, S-doped graphene are studied based on first-principles calculations of density functional theory. Firstly, the intrinsic, B-, N-, Si-, S-doped graphene structures are optimized, and then the forming energy, band structure, density of states, differential charge density are analyzed and calculated. The results show that B- and Si-doped systems are p-type doping, while N is n-type doping. By comparing the forming energy, it is found that N atoms are more easily doped in graphene. In addition, for B-, N-, Si-doped systems, it is found that the doping atoms will open the band gap, leading to a great change in the band structure of the doping system. Finally, we systematically study the optical properties of the different configurations. By comparison, it is found that the order of light sensitivity in the visible region is as follows: S-doped> Si-doped> pure > B-doped > N-doped. Our results will provide theoretical guidance for the stability and electronic structure of non-metallic doped graphene.     

Facile preparation of graphene nitride by irradiating MHz ultrasound

The present study aimed at developing a simple sonochemical method to prepare graphene nitride from the mixture of graphite and aqueous ammonia solution. Ultrasound of 1.6 MHz was irradiated to the sample in a fabricated sonoreactor at predetermined ultrasonic power and duration. The one-pot method succeeded in the preparation of graphene nitride. The generation was proven by XPS analysis in finding N1S peak in the spectrum. Detail analysis of N1s peak suggested that the major nitrogen species was pyrrolic type. Furthermore, the presence of CO bond proved the oxidation by OH radical. The reaction product had the value of N/C as high as 0.08, which is comparable to reported values for ultrasonic preparation of graphene nitride. The fact indicates that the significance of chemical effects of MHz range ultrasound, and the finding of the simple preparation method will accelerate practical application of graphene nitride.     

Theoretical study of 1D gradient photonic structures with quartic polynomial dielectric profile formed by AllGa1-lAs varying pressure and temperature under oblique incidence

In this work it is presented a theoretical study of the optical properties of 1D photonic systems with gradient dielectric profile layers of quartic polynomial type, using the dielectric Al_lGa_1-lAs being the Al concentration along the width of the slab as the gradient function, when external parameters as the pressure and the temperature are considered. It is shown that the proposed gradient profile admits an analytic approach supported on the method of series to find the solutions of the wave equations for the TE and TM polarizations. Also, it is proposed a new regression model for the calculation of the dielectric value of Al_lGa_1-lAs as a function of the pressure and temperature. The results showed that the increase in the pressure shifts and changes the transmission bands due to the decrease in the dielectric mean value of the gradient slab. On the other hand, it is found that the increase in the temperature shifts the transmission bands to lower frequencies but without changing their shape distribution. Considering the inclusion of graphene, it is observed its effect on the distribution of the transmission bands at different frequencies depending on the graphene properties. It is expected that the proposed structure can be contribute to the development of new devices when the pressure, the temperature and the chemical potential of graphene are used as external tunable parameters.