Modeling disorder in graphene (original) (raw)
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JETP Letters, 2011
One of the important research fields in the phys ics of graphene is its functionalization by various adsorbed atoms, molecules, and chemically active groups. As a consequence, modified graphene can acquire new properties necessary for its particular technical applications. The transport properties of graphene are most crucial for its application as a base element in new generation microelectronic devices. It was convincingly demonstrated in experiments that ion bombardment of graphene [1], as well as deposi tion of atomic hydrogen [2] or fluorine [3] on it, makes it possible to open a transport quasigap in the nearest vicinity of the Dirac point in the graphene spectrum. In turn, this may initiate a metal-insulator transition in such a system as it occurs in disordered systems with massive carriers . The mentioned quasigap appears because the defects induce the impurity resonance states near the Dirac point. Moreover, the resonant defects of this type are always present in a certain amount in graphene prepared, for example, by micro mechanical cleavage . Theoretical analysis based on the simplest models of adsorbed atoms demonstrated that these defects should indeed strongly affect the electron density of states and conductivity of graphene . However, only those cases, in which the adsor bent induced impurity levels were strongly hybridized with the host spectrum, have been studied in detail. In this work, we consider possible modifications induced in the electronic spectrum of graphene by defects of the same type but for the opposite case of weak hybrid ization of the impurity level.
Effect of disorder on the electronic properties of graphene: A theoretical approach
Physical Review B, 2012
In order to manipulate the properties of graphene, its very important to understand the electronic structure in presence of disorder. We investigate, within a tight-binding description, the effects of disorder in the on-site (diagonal disorder) term in the Hamiltonian as well as in the hopping integral (off-diagonal disorder) on the electronic dispersion and density of states by the augmented space recursion method. Extrinsic off-diagonal disorder is shown to have dramatic effects on the twodimensional Dirac-cone, including asymmetries in the band structures as well as the presence of discontinuous bands (because of resonances) in certain limits. Disorder-induced broadening, related to the scattering length (or life-time) of Bloch electrons, is modified significantly with increasing strength of disorder. We propose that our methodology is suitable for the study of the effects of disorder in other 2D materials, such as a boron nitride mono layer.
The Ground State of Graphene and Graphene Disordered by Vacancies
2012
Graphene clusters consisting of 24 to 150 carbon atoms and hydrogen termination at the zigzag boundary edges have been studied, as well as clusters disordered by vacancy(s). Density Function Theory and Gaussian03 software were used to calculate graphene relative stability, desorption energy, band gap, density of states, surface shape, dipole momentum and electrical polarization of all clusters by applying the hybrid exchange-correlation functional Beke-Lee-Yang-Parr. Furthermore, infrared frequencies were calculated for two of them. Different basis sets, 6-31g**, 6-31g* and 6-31g, depending on the sizes of clusters are considered to compromise the effect of this selection on the calculated results. We found that relative stability and the gap decreases according to the size increase of the graphene cluster. Mulliken charge variation increase with the size. For about 500 carbon atoms, a zero HOMO-LUMO gap amount is predicted. Vacancy generally reduces the stability and having vacancy affects the stability differently according to the location of vacancies. Surface geometry of each cluster depends on the number of vacancies and their locations. The energy gap changes as with the location of vacancies in each cluster. The dipole momentum is dependent on the location of vacancies with respect to one another. The carbon-carbon length changes according to each covalence band distance from the boundary and vacancies. Two basis sets,
Impurity and vacancy effects in graphene
Low Temperature Physics, 2012
A Green function analysis has been developed for quasiparticle spectrum of a 2D graphene sheet in presence of different types of substitutional disorder, including vacancies. The anomalous character of impurity effects in this system is demonstrated, compared to those in well known doped semiconductors, and explained in terms of conical singularities in the band spectrum of pure graphene. The criteria for appearance of localized states on clusters of impurity scatterers and for qualitative restructuring of band spectrum are established and a possibility for a specific metal/insulator transition at presence of vacancies is indicated. PACS: 03.65.Pm Relativistic wave equations; 71.30.+h Metal-insulator transitions and other electronic transitions; 71.55.-i Impurity and defect levels.
Spectral function of graphene with short-range impurity centers
Low Temperature Physics, 2008
Spectral function of graphene with point substitutional defects is calculated for different impurity concentrations. It is demonstrated that features in the spectral function of graphene observed in ARPES experiments can be caused by the presence of a well-defined resonance state and are clearly pronounced at the impurity concentrations, which are of the order of the critical concentration for the impurity induced spectrum rearrangement. PACS: 71.23.-k Electronic structure of disordered solids; 71.55.-i Impurity and defect levels; 81.05.Uw Carbon, diamond, graphite.
Resonant impurity band induced by point defects in graphene
EPL (Europhysics Letters), 2009
It is pointed out that point defects on graphene are strongly correlated and can not be treated as independent scatters. In particular, for large on-site defect potential, it is shown that defects induce an impurity band with density of state characterized by the Wigner semi-circle law. We find that the impurity band enhances conductivity to the order of 4e 2 /h and explains the absence of strong localization. Furthermore,the impurity band supports ferromagnetism with the induced magnetic moment approaching 1µB per defect in the limit of infinite quasi-particle lifetime.
Critical wavefunctions in disordered graphene
Journal of Physics: Condensed Matter, 2012
In order to elucidate the presence of non-localized states in doped graphene, an scaling analysis of the wave function moments known as inverse participation ratios is performed. The model used is a tight-binding hamiltonian considering nearest and next-nearest neighbors with random substitutional impurities. Our findings indicate the presence of non-normalizable wave functions that follow a critical (power-law) decay, which are between a metallic and insulating behavior. The power-law exponent distribution is robust against the inclusion of next-nearest neighbors and on growing the system size.
Disorder and electronic transport in graphene
Journal of Physics: Condensed Matter, 2010
In this review, we provide an account of the recent progress in understanding electronic transport in disordered graphene systems. Starting from a theoretical description that emphasizes the role played by band structure properties and lattice symmetries, we describe the nature of disorder in these systems and its relation to transport properties. While the focus is primarily on theoretical and conceptual aspects, connections to experiments are also included. Issues such as short versus long-range disorder, localization (strong and weak), the carrier density dependence of the conductivity, and conductance fluctuations are considered and some open problems are pointed out.
2006
Defects in graphene are of crucial importance for its electronic and magnetic properties. Here impurity effects on the electronic structure of surrounding carbon atoms are considered and the distribution of the local densities of states (LDOS) is calculated. As the full range from near field to the asymptotic regime is covered, our results are directly accessible by scanning tunnelling microscopy
Disorder Induced Localized States in Graphene
Physical Review Letters, 2006
We consider the electronic structure near vacancies in the half-filled honeycomb lattice. It is shown that vacancies induce the formation of localized states. When particle-hole symmetry is broken, localized states become resonances close to the Fermi level. We also study the problem of a finite density of vacancies, obtaining the electronic density of states, and discussing the issue of electronic localization in these systems. Our results have also relevance for the problem of disorder in d-wave superconductors.