253 research outputs found
Functionalization of BN Honeycomb structure by Adsorption and Substitution of Foreign atoms
We carried out first-principles calculations within Density Functional Theory
to investigate the structural, electronic and magnetic properties of
boron-nitride (BN) honeycomb structure functionalized by adatom adsorption, as
well as by the substitution of foreign atoms for B and N atoms. For periodic
high density coverage, most of transition metal atoms and some of group
3A, 4A, and 6A elements are adsorbed with significant binding energy and modify
the electronic structure of bare BN monolayer. While bare BN monolayer is
nonmagnetic, wide band gap semiconductor, at high coverage of specific adatoms
it can achieve magnetic metallic, even half-metallic ground states. At low
coverage, the bands associated with adsorbed atoms are flat and the band
structure of parent BN is not affected significantly. Therefore, adatoms and
substitution of foreign atoms at low coverage are taken to be the
representative of impurity atoms yielding localized states in the band gap and
resonance states in the band continua. Notably, the substitution of C for B and
N yield donor and acceptor like magnetic states in the band gap. Localized
impurity states occurring in the gap give rise to interesting properties for
electronic and optical application of the single layer BN honeycomb structure.Comment: 10 pages, 6 figures, 4 table
Variable and reversible quantum structures on a single carbon nanotube
The band gap of a semiconducting single wall carbon nanotube decreases and
eventually vanishes leading to metalization as a result of increasing radial
deformation. This sets in a band offset between the undeformed and deformed
regions of a single nanotube. Based on the superlattice calculations, we show
that these features can be exploited to realize various quantum well structures
on a single nanotube with variable and reversible electronic properties. These
quantum structures and nanodevices incorporate mechanics and electronics.Comment: 7 pages, 4 figures, To be appear in PR
Dissociation of H2O at the vacancies of single layer MoS2
Cataloged from PDF version of article.Based on first-principles density functional theory and finite temperature molecular dynamics calculations, we predict that H2O can be dissociated into its constituents O and H at specific vacancy defects of single-layer MoS2 honeycomb structure, which subsequently are bound to fourfolded Mo and twofolded S atoms surrounding the vacancy, respectively. This exothermic and spontaneous process occurs, since the electronegativity and ionization energy of Mo are smaller than those of H. Once desorbed from twofolded S atoms, H atoms migrate readily on the MoS2 surface and eventually form free H-2 molecules to be released from the surface. Present results are critical for acquiring clean and sustainable energy from hydrogen
Perpendicular growth of carbon chains on graphene from first-principles
Cataloged from PDF version of article.Based on first-principles calculations we predict a peculiar growth process, where carbon adatoms adsorbed to graphene readily diffuse above room temperature and nucleate segments of linear carbon chains attached to graphene. These chains grow longer on graphene through insertion of carbon atoms one at a time from the bottom end and display a self-assembling behavior. Eventually, two allotropes of carbon, namely graphene and cumulene, are combined to exhibit important functionalities. The segments of carbon chains on graphene become chemically active sites to bind foreign atoms or large molecules. When bound to the ends of carbon chains, transition metal atoms, Ti, Co, and Au, attribute a magnetic ground state to graphene sheets and mediate stable contacts with interconnects. We showed that carbon chains can grow also on single-wall carbon nanotubes
Hydrogen storage of calcium atoms adsorbed on graphene: First-principles plane wave calculations
Based on the first-principles plane wave calculations, we showed that Ca
adsorbed on graphene can serve as a high-capacity hydrogen storage medium,
which can be recycled by operations at room temperature. Ca is chemisorbed by
donating part of its 4s-charge to the empty -band of graphene. At the
end adsorbed Ca atom becomes positively charged and the semi-metallic graphene
change into a metallic state. While each of adsorbed Ca atoms forming the (4x4)
pattern on the graphene can absorb up to five H_2 molecules, hydrogen storage
capacity can be increased to 8.4 wt % by adsorbing Ca to both sides of graphene
and by increasing the coverage to form the (2x2) pattern. Clustering of Ca
atoms is hindered by the repulsive Coulomb interaction between charged Ca
atoms.Comment: 5 pages, 3 figure
Hydrogen storage of calcium atoms adsorbed on graphene: First-principles plane wave calculations
Based on the first-principles plane wave calculations, we showed that Ca
adsorbed on graphene can serve as a high-capacity hydrogen storage medium,
which can be recycled by operations at room temperature. Ca is chemisorbed by
donating part of its 4s-charge to the empty -band of graphene. At the
end adsorbed Ca atom becomes positively charged and the semi-metallic graphene
change into a metallic state. While each of adsorbed Ca atoms forming the (4x4)
pattern on the graphene can absorb up to five H_2 molecules, hydrogen storage
capacity can be increased to 8.4 wt % by adsorbing Ca to both sides of graphene
and by increasing the coverage to form the (2x2) pattern. Clustering of Ca
atoms is hindered by the repulsive Coulomb interaction between charged Ca
atoms.Comment: 5 pages, 3 figure
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