1,721,048 research outputs found
ELECTRONIC PROPERTY OF NA-DOPED EPITAXIAL GRAPHENES ON SIC
Full text linkThe electronic property of epitaxial graphenes with Na adsorption or intercalation is studied with the use of pseudopotential density functional method. It is found that the charge transfer and the Na binding energy show strong coverage dependence. Calculated energetics shows that Na prefers the intercalation between the buffer and top graphene layers to the adsorption on top graphene layer. The buffer layer is inert to Na adsorption on top graphene layer but it is charged when Na atoms are intercalated. This indicates that the conduction of epitaxial graphenes can be affected significantly by Na intercalation.X1119sciescopu
Re-emergent direct-indirect band gap transitions in carbon nanotubes under shear strains
No full textElectronic structures of single-walled carbon nanotubes under varying shear strains are studied with the use of pseudopotential density functional method. We present a new scheme to induce shear strains in one-dimensional materials like nanotubes without introducing artificial edge atoms. It is found that the band gap of semiconducting zigzag nanotubes exhibits reemerging direct-indirect transitions as they are twisted. The breaking of the three-fold rotational symmetry and the electron-hole symmetry of corresponding graphitic band structures under shear is shown to be the origin of the behavior in the band gap. (C) 2008 Elsevier Ltd. All rights reserved.X114sciescopu
SELF-ASSEMBLED METAL ATOM CHAINS ON GRAPHENE NANORIBBONS
Full text linkElectronic and magnetic properties of alkali and alkaline-earth metal doped graphene nanoribbons (GNRs) are studied by the pseudopotential density functional method. Strong site dependence is observed in metal adsorption on GNRs, and the adsorbed metal atoms are found to spontaneously form atomic chains in a particular form of GNRs. Such doped GNRs exhibit intriguing magnetic properties such as hysteresis and spin compensation as metal atoms switch from one edge to another at alternating gate voltages. Our study shows that the metal atoms can be used as reagents that can identify the edge atomic structures of GNRs and also as gate-driven spin valves that control the spin current in GNRs.X1170sciescopu
Frictional modes of barrel shaped piston rings under flooded lubrication
No full textA friction force measurement system using the floating liner method was developed to study the frictional behavior of piston rings. The measurement system was designed to control the effect of the secondary piston motion and to control temperatures of the cylinder wall and oil. The friction force between the barrel shaped piston ring and the cylinder liner was measured under flooded oil supply conditions. The measured friction forces were classified into five frictional modes with regard to the combination of predominant lubrication regimes (boundary, mixed and hydrodynamic lubrication) and stroke regions (mid-stroke and dead centers). The modes were identified on a Stribeck diagram, where the friction coefficients were evaluated both at mid-stroke and at the dead centers. (C) 2000 Published by Elsevier Science Ltd
Controlling Energy Gap of Bilayer Graphene by Strain
No full textUsing the First principles calculations, we show that mechanically tunable electronic energy gap is realizable in bilayer graphene if different homogeneous strains are applied to the two layers. It is shown that the size of the energy gap can be simply controlled by adjusting the strength and direction of these strains. We also show that the effect originates from the occurrence of strain-induced pseudoscalar potentials in graphene. When homogeneous strains with different strengths are applied to each layer of bilayer graphene. transverse electric fields across the two layers can be generated without any external electronic sources, thereby opening an energy gap. The results demonstrate a simple mechanical method of realizing pseudoelectromagnetism in graphene and suggest a maneuverable approach to fabrication of electromechanical devices based on bilayer graphene.X11110103sciescopu
Crossover in the adsorption properties of alkali metals on graphene
No full textThe adsorption of alkali metals (AMs) on single layer graphene is studied using first principles methods. We observe a common trend in the binding distance, the charge transfer, and the work function (W) at certain coverage of AMs with increase in the proportion rho (adatom/C atom) of the graphene covered by the AM. A dip in these properties occurs at rho approximate to 0.04 for all AMs except Li, for which it occurs at rho approximate to 0.08. This behavior is due to a transition of adsorbed metals from individual atoms to two-dimensional metallic sheets that exert a depolarization effect. W of graphene exhibits asymmetric dependence on rho : a dip in the adatom layer side but saturation on the graphene side, which is in contrast to the case of bulk graphite.X116260sciescopu
Effects of strain on electronic properties of graphene
Full text linkWe present first-principles calculations of electronic properties of graphene under uniaxial and isotropic strains, respectively. The semimetallic nature is shown to persist up to a very large uniaxial strain of 30% except a very narrow strain range where a tiny energy gap opens. As the uniaxial strain increases along a certain direction, the Fermi velocity parallel to it decreases quickly and vanishes eventually, whereas the Fermi velocity perpendicular to it increases by as much as 25%. Thus, the low energy properties with small uniaxial strains can be described by the generalized Weyl's equation while massless and massive electrons coexist with large ones. The work function is also predicted to increase substantially as both the uniaxial and isotropic strain increases. Hence, the homogeneous strain in graphene can be regarded as the effective electronic scalar potential.X11348Ysciescopu
Fabrication of Highly Conductive and Transparent Carbon Nanotube Thin Films using Layer-by-Layer Self Assembly Method
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