Structural and Electronic Properties of Graphene Oxide for Different Degree of Oxidation1

In the last year, the investigation of two-dimensional materials as graphene oxide is a fundamental goal to produce innovative devices with wide range of applications in many areas. In the present work, we report a systematic study of structural and electronic properties of graphene oxide for different oxidations levels (25%, 50%, 75%, 100%) using density functional calculations for electronic ground state and a statistical approach on carbon-carbon bond length obtained after the geometric optimization of graphene covered with epoxide and hydroxyl functional groups. The theoretical models proposed and studied here are accord with the well-known experimental data. Our statistical results of the carbon-carbon bond length shown that hydroxyl groups disturbs the structure of graphene more than epoxide groups, however, both hydroxyl and epoxide groups are responsible of the change of hybridization sp2 to sp3, while the degree of oxidation increase. In addition, our electronic structure calculations confirm that with low degree of oxidation, the graphene oxide is semiconductor, and with full degree of oxidation graphene oxide is an insulating material. The minimum of total energy is found when the graphene oxide has full coverage. This work can contribute to understand the plasticity and ductility properties of graphene oxide recently reported

Plasmon modes of graphene nanoribbons with periodic planar arrangements

Among their amazing properties, graphene and related low-dimensional materials show quantized charge-density fluctuations—known as plasmons—when exposed to photons or electrons of suitable energies. Graphene nanoribbons offer an enhanced tunability of these resonant modes, due to their geometrically controllable band gaps. The formidable effort made over recent years in developing graphene-based technologies is however weakened by a lack of predictive modeling approaches that draw upon available ab initio methods. An example of such a framework is presented here, focusing on narrow-width graphene nanoribbons, organized in periodic planar arrays. Time-dependent density-functional calculations reveal unprecedented plasmon modes of different nature at visible to infrared energies. Specifically, semimetallic (zigzag) nanoribbons display an intraband plasmon following the energy-momentum dispersion of a two-dimensional electron gas. Semiconducting (armchair) nanoribbons are instead characterized by two distinct intraband and interband plasmons, whose fascinating interplay is extremely responsive to either injection of charge carriers or increase in electronic temperature. These oscillations share some common trends with recent nanoinfrared imaging of confined edge and surface plasmon modes detected in graphene nanoribbons of 100–500 nm width.C. V. G. acknowledges the financial support of “Secretaria Nacional de Educación Superior, Ciencia, Tecnología e Innovación” (SENESCYT-ECUADOR). All authors thank Dr. V. M. Silkin from the University of the Basque Country for his invaluable support in developing the TDDFT code.Peer reviewe

Innovative full wave modeling of plasmon propagation in graphene by dielectric permittivity simulations based on density functional theory

We report on an ab initio technique for modeling the electromagnetic response of graphene in the THz range. Quantum mechanical calculations are performed using linear response density functional theory, and compared with a semiphenomenological model derived from the Kubo formula. We present a novel concept of dispersive conductivity, which goes beyond the Kubo-Drude model and results in a self-consistent constitutive relation for the analysis of plasmon propagation in complex nanosystems. The rigorous characterization of the constitutive relation may be inserted in electromagnetic fullwave solvers, providing a new paradigm for nanoelectronic computations at THz frequencies