Browsing by Subject "61.48.Gh"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access Domain formation on oxidized graphene(American Physical Society, 2012-11-01) Topsakal, M.; Çıracı, SalimAbstract Using first-principles calculations within density functional theory, we demonstrate that the adsorption of a single oxygen atom results in significant electron transfer from graphene to oxygen. This strongly disturbs the charge landscape of the C-C bonds at the proximity. Additional oxygen atoms adsorbing to graphene prefer always the C-C bonds having the highest charge density and, consequently, they have the tendency to form domain structure. While oxygen adsorption to one side of graphene ends with significant buckling, the adsorption to both sides with similar domain pattern is favored. The binding energy displays an oscillatory variation and the band gap widens with increasing oxygen coverage. While a single oxygen atom migrates over the C-C bonds on the graphene surface, a repulsive interaction prevents two oxygen adatoms from forming an oxygen molecule. Our first-principles study together with finite-temperature ab initio molecular dynamics calculations conclude that oxygen adatoms on graphene can not desorb easily without the influence of external agents.Item Open Access Structural, mechanical, and electronic properties of defect-patterned graphene nanomeshes from first principles(American Physical Society, 2011) Şahin, H.; Çıracı, SalimMotivated by the state of the art method for fabricating high-density periodic nanoscale defects in graphene, the structural, mechanical, and electronic properties of defect-patterned graphene nanomeshes including diverse morphologies of adatoms and holes are investigated by means of first-principles calculations within density functional theory. It is found that various patterns of adatom groups yield metallic or semimetallic, even semiconducting, behavior and specific patterns can be in a magnetic state. Even though the patterns of single adatoms dramatically alter the electronic structure of graphene, adatom groups of specific symmetry can maintain the Dirac fermion behavior. Nanoholes forming nanomesh are also investigated. Depending on the interplay between the repeat periodicity and the geometry of the hole, the nanomesh can be in different states ranging from metallic to semiconducting including semimetallic states with the bands crossing linearly at the Fermi level. We showed that forming periodically repeating superstructures in a graphene matrix can develop a promising technique for engineering nanomaterials with desired electronic and magnetic properties.Item Open Access Structures of fluorinated graphene and their signatures(American Physical Society, 2011) Şahin, H.; Topsakal, M.; Çıracı, SalimRecent synthesis of fluorinated graphene introduced interesting stable derivatives of graphene. In particular, fluorographene (CF), namely, fully fluorinated chair conformation, is found to display crucial features, such as high mechanical strength, charged surfaces, local magnetic moments due to vacancy defects, and a wide band gap rapidly reducing with uniform strain. These properties, as well as structural parameters and electronic densities of states, are found to scale with fluorine coverage. However, most of the experimental data reported to date neither for CF nor for other CnF structures complies with the results obtained from first-principles calculations. In this study, we attempt to clarify the sources of disagreements. © 2011 American Physical Society.