2,275 research outputs found
Strain engineering on graphene towards tunable and reversible hydrogenation
Graphene is the extreme material for molecular sensory and hydrogen storage
applications because of its two-dimensional geometry and unique
structure-property relationship. In this Letter, hydrogenation of graphene is
discussed in the extent of intercoupling between mechanical deformation and
electronic configuration. Our first principles calculation reveals that the
atomic structures, binding energies, mechanical and electronic properties of
graphene are significantly modified by the hydrogenation and applied strain.
Under an in-plane strain of 10 %, the binding energies of hydrogen on graphene
can be improved by 53.89 % and 23.56 % in the symmetric and anti-symmetric
phase respectively. Furthermore the instability of symmetrically bound hydrogen
atoms under compression suggests a reversible storage approach of hydrogen. In
the anti-symmetric phase, the binding of hydrogen breaks the sp2 characteristic
of graphene, which can be partly recovered at tensile strain. A charge density
based analysis unveils the underline mechanisms. The results reported here
offer a way not only to tune the binding of hydrogen on graphene in a
controllable and reversible manner, but also to engineer the properties of
graphene through a synergistic control through mechanical loads and hydrogen
doping
Engineering graphene by oxidation: a first principles study
Graphene epoxide, with oxygen atoms lining up on pristine graphene sheets, is
investigated theoretically in this Letter. Two distinct phases: metastable
clamped and unzipped structures are unveiled in consistence with experiments.
In the stable (unzipped) phase, epoxy group breaks underneath sp2 bond and
modifies the mechanical and electronic properties of graphene remarkably. The
foldable epoxy ring structure reduces its Young's modulus by 42.4%, while
leaves the tensile strength almost unchanged. Epoxidation also perturbs the pi
state and opens semiconducting gap for both phases, with dependence on the
density of epoxidation. In the unzipped structures, localized states revealed
near the Fermi level resembles the edge states in graphene nanoribbons. The
study reported here paves the way for oxidation-based functionalization of
graphene-related materials.Comment: 17 pages (4 figures, 1 table
Strain Engineering of Antimonene by a First-principles Study: Mechanical and Electronic Properties
In this work, we investigate the mechanical and electronic properties of
monolayer antimonene in its most stable beta-phase using first-principles
calculations. The upper region of its valence band is found to solely consist
of lone pair p-orbital states, which are by nature more delocalized than the
d-orbital states in transition metal dichalcogenides, implying superior
transport performance of antimonene. The Young's and shear moduli of
beta-antimonene are observed to be ~25% higher than those of bulk antimony,
while the hexagonal lattice constant of the monolayer reduces significantly
(~5%) from that in bulk, indicative of strong inter-layer coupling. The ideal
tensile test of beta-antimonene under applied uniaxial strain highlights ideal
strengths of 6 GPa and 8 GPa, corresponding to critical strains of 15% and 17%
in the zigzag and armchair directions, respectively. During the deformation
process, the structural integrity of the material is shown to be better
preserved, albeit moderately, in the armchair direction. Interestingly, the
application of uniaxial strain in the zigzag and armchair directions unveil
direction-dependent trends in the electronic band structure. We find that the
nature of the band gap remains insensitive to strain in the zigzag direction,
while strain in the armchair direction activates an indirect-direct band gap
transition at a critical strain of 4%, owing to a band switching mechanism. The
curvature of the conduction band minimum increases during the transition, which
suggests a lighter effective mass of electrons in the direct-gap configuration
than in the free-standing state of equilibrium. The work function of
free-standing beta-antimonene is 4.59 eV and it attains a maximum value of 5.07
eV under an applied biaxial strain of 4%
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