V.J. Surya

Effect of surface doping on the band structure of graphene: a DFT study

AbstractnVarious techniques, like doping, vacancy creation, strain engineering are tried to open a gap in the bandstructure of graphene and in some cases the gap has opened up. However, when the gap opens up the Dirac cones disappear. Without Dirac cones, graphene loses all its novelty. So opening a gap in graphene, retaining Dirac cones has become a challenging task. We, through first principles study using Density Functional theory, have done band gap tuning investigations. We have succeeded in opening the band gap, retaining the Dirac cones. Surface doping (adsorption) of various elements are tried and finally surface doping of sulfur is found to induce band gap opening in graphene. The Dirac cones are retained and the graphene is now a semiconductor with fast moving massless Dirac Fermions. We are reporting this type of calculations for the first time.

Effect of multiple defects and substituted impurities on the band structure of graphene: a DFT study

In graphene, band gap opening and tuning are important technological challenges for device applications. Various techniques have been suggested to this technologically complicated problem. Here, we present an ab initio study on the band gap opening in graphene through vacancy, adding impurity atom in the vacancy and substitutional co-doping. In the case of graphene with single vacancy a direct band gap of ~1xa0eV is obtained. This is a spin polarized state. The graphene system with two monovacancies gives rise to an effective indirect band gap (pseudo gap) of ~1xa0eV. The graphene substitutionally doped with B and N is co-doped (tri-doped) with S. This tri-doped graphene has turned into a semiconductor (band gap ~1xa0eV). These graphene semiconductors are better than the other semiconductor because of the presence of massless Dirac fermions in addition to normal electrons. This will have lot of application in device industry compared to a pristine graphene because of the presence of a gap and Dirac fermions. This type of band gap opening, with this type of defects and impurities, we are reporting for the first time.

Quantum scar and breakdown of universality in graphene: A theoretical insight

Graphene has brought forward a lot of new physics. One of them is the emergence of massless Dirac fermions in addition to the electrons and these features are new to physics. In this theoretical study, the signatures for quantum scar and the breakdown of universality in graphene are investigated with reference to the presence of these two types of fermions. Taking the graphene quantum dot (QD) potential as the confining potential, the radial part of Dirac equations are solved numerically. Concentrations of the two component eigen-wavefunctions about classical periodic orbits emerge as the signatures for the quantum scar. The sudden variations, in the ratio of the radial wave-functions (large and small components), R(g/f), with mass ratio κ are the signatures for breakdown of universality in graphene. The breakdown of universality occurs for the states k = −1 and k = 1, and the state k = −1 is more susceptible to the breakdown of universality.