Raman Spectra in Irradiated Graphene: Line Broadening, Effects of Aging and Annealing

The results of measurements of the Raman spectra in the same group of monolayer graphene samples, successively subjected to irradiation with different ions, prolonged aging, and annealing under different conditions, are considered. Changes in the position, width, and intensity of the Raman lines are analyzed in the study of the following problems: comparison of the results of irradiation with various ions, the influence of prolonged aging on the spectra of irradiated samples, the mechanism of broadening of Raman scattering lines caused by an increase in the density of radiation defects, the consequences of annealing of radiation damages in vacuum and in the atmosphere of the forming gas, the contribution of doping and lattice deformation to the shift of the position of the Raman lines after annealing. The results obtained made it possible to determine the level of stability of defects introduced by radiation, to reveal the possibility of restoring the damaged lattice using annealing. Since the results relate to graphene deposited on a widely used SiO2/Si substrate, they may be of interest when using ion irradiation to change the properties of graphene in appropriate devices.

Localization of Charge Carriers in Monolayer Graphene Gradually Disordered by Ion Irradiation

Gradual localization of charge carriers is studied in a series of microsize samples of monolayer graphene fabricated on the common large scale film and irradiated by different doses of C+ ions with energy 35 keV. Measurements of the temperature dependence of conductivity and magneto-resistance in fields up to 4 T show that at low disorder, the samples are in the regime of weak localization and antilocalization. Further increase of disorder leads to strong localization regime, when conductivity is described by the variable-range-hopping (VRH) mechanism. A crossover from the Mott regime to the Efros-Shklovskii regime of VRH is observed with decreasing temperature. Theoretical analysis of conductivity in both regimes shows a remarkably good agreement with experimental data.

On the X-Ray Edge Problem in Graphene

We calculate the core-hole spectral density in a pristine graphene, where the density of states of itinerant electrons goes linearly to zero at the Fermi level. We consider explicitly two models of electron-hole interaction. In the unscreened Coulomb interaction model, the spectral density is similar to that in metal (for local interaction). Thus there is no δ-function singularity in the core-hole spectral density. In the local interaction model, the δ-function singularity survives, but the interaction leads to the appearance of the background in the spectral density.

Diffraction limit of light in curved space

Overcoming the diffraction limit is crucial for obtaining high-resolution images and observing fine microstructures.With this conventional difficulty still puzzling us and the prosperous development of wave dynamics of light interacting with gravitational fields in recent years,how spatial curvature affects the diffraction limit is an attractive and important question.Here we investigate the issue of the diffraction limit and optical resolution on two-dimensional curved space—surfaces of revolution(SORs)with constant or variable spatial curvature.We show that the diffraction limit decreases and the resolution is improved on SORs with positive Gaussian curvature,opening a new avenue to super-resolution.The diffraction limit is also influenced by the propagation direction,as well as the propagation distance in curved space with variable spatial curvature.These results provide a possible method to control the optical resolution in curved space or equivalent waveguides with varying refractive index distribution and may allow one to detect the presence of the nonuniform strong gravitational effect by probing locally the optical resolution.