138 research outputs found
Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid
It is demonstrated theoretically that the absorptivity of bulk shear sagittal
waves by an ultra-thin layer of viscous fluid between two different elastic
media has a strong maximum (in some cases as good as 100%) at an optimal layer
thickness. This thickness is usually much smaller than the penetration depths
and lengths of transverse and longitudinal waves in the fluid. The angular
dependencies of the absorptivity are demonstrated to have significant and
unusual structure near critical angles of incidence. The effect of
non-Newtonian properties and non-uniformities of the fluid layer on the
absorptivity is also investigated. In particular, it is shown that the
absorption in a thin layer of viscous fluid is much more sensitive to non-zero
relaxation time(s) in the fluid layer than the absorption at an isolated
solid-fluid interface.Comment: 14 pages, 8 figure
Two-dimensional semiconducting nanostructures based on single graphene sheets with lines of adsorbed hydrogen atoms
It is shown that lines of adsorbed hydrogen pair atoms divide the graphene
sheet into strips and form hydrogen-based superlattice structures (2HG-SL). We
show that the forming of 2HG-SL drastically changes the electronic properties
of graphene from semimetal to semiconductor. The electronic spectra of "zigzag"
(n,0) 2HG-SL is similar to that of (n,0) carbon nanotubes and have a similar
oscillation of band gap with number n, but with non-zero minimal values. The
composite dual-periodic (n,0)+(m,0) 2HG-SLs of "zigzag" strips are analyzed,
with the conclusion that they may be treated as quasi-two-dimensional
heterostructures. We also suggest an experimental way of fabricating hydrogen
superlattices.Comment: 12 pages, 3 figure
On the Thermal Stability of Graphone
Molecular dynamics simulation is used to study thermally activated migration
of hydrogen atoms in graphone, a magnetic semiconductor formed of a graphene
monolayer with one side covered with hydrogen so that hydrogen atoms are
adsorbed on each other carbon atom only. The temperature dependence of the
characteristic time of disordering of graphone via hopping of hydrogen atoms to
neighboring carbon atoms is established directly. The activation energy of this
process is found to be Ea=(0.05+-0.01) eV. The small value of Ea points to
extremely low thermal stability of graphone, this being a serious handicap for
practical use of the material in nanoelectronics.Comment: 3 figure
Extreme structure and spontaneous lift of spin degeneracy in doped perforated bilayer graphenes
Extreme structure and spin states of doped and undoped perforated bigraphenes was studied using DFT simulations. It was found that folded nanopores possess extremely high curvature of 0.34 Å−1. Dramatic structural deformation causes severe changes of the chemical properties of carbon atoms localized at the nanopores converting the folded edges to local oxidative fragments. It was found that asymmetrical coordination of either Li, Ca, or Al to the nanopores is coupled with electron transfer from metal to edge carbon atoms and breakdown of local inversion symmetry. Li-, Ca-, and Al-doped perforated AA bigraphene revealed ferromagnetic spin ordering with magnetic moments of 0.38, 0.14, and 0.32μB/unit cell, respectively, and spin polarization energy gain of 0.037eV for Ca-doped superlattice. It was shown that ferromagnetic spin ordering of bigraphene nanopores contradicts to the Nagaoka's theorem, which excludes strong electron correlations as a reason of spin polarization. Spontaneous lift of spin degeneracy was interpreted in terms of perturbing intense local electrostatic fields from extra electron charges localized at the nanopore edges, coupled with breakdown of space inversion and local translation invariances. It was shown that spin energy splitting is proportional to the matrix elements calculated on Bloch states with opposite wavevectors and perturbing electrostatic fields
First-principles modeling of the polycyclic aromatic hydrocarbons reduction
Density functional theory modelling of the reduction of realistic
nanographene molecules (C42H18, C48H18 and C60H24) by molecular hydrogen
evidences for the presence of limits in the hydrogenation process. These limits
caused the contentions between three-fold symmetry of polycyclic aromatic
hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs.
Increase of the binding energy between nanographenes during reduction is also
discussed as possible cause of the experimentally observed limited
hydrogenation of studied nanographenes.Comment: 18 pages, 7 figures, accepted to J. Phys. Chem.
Metal-semiconductor (semimetal) superlattices on a graphite sheet with vacancies
It has been found that periodically closely spaced vacancies on a graphite
sheet cause a significant rearrange-ment of its electronic spectrum: metallic
waveguides with a high density of states near the Fermi level are formed along
the vacancy lines. In the direction perpendicular to these lines, the spectrum
exhibits a semimetal or semiconductor character with a gap where a vacancy
miniband is degenerated into impurity levels.Comment: 4 pages, 3 figure
The influence of size effect on the electronic and elastic properties of diamond films with nanometer thickness
The atomic structure and physical properties of few-layered oriented
diamond nanocrystals (diamanes), covered by hydrogen atoms from both sides are
studied using electronic band structure calculations. It was shown that energy
stability linear increases upon increasing of the thickness of proposed
structures. All 2D carbon films display direct dielectric band gaps with
nonlinear quantum confinement response upon the thickness. Elastic properties
of diamanes reveal complex dependence upon increasing of the number of
layers. All theoretical results were compared with available experimental data.Comment: 16 pages, 5 figures, 3 table
Superlattice Based on Graphene on a Strip Substrate
A graphene-based superlattice formed due to the periodic modulation of the
band gap has been investigated. Such a modulation is possible in graphene
deposited on a strip substrate made of silicon oxide and hexagonal boron
nitride. The advantages and some possible problems in the superlattice under
consideration are discussed. A model describing such a superlattice is proposed
and the dispersion relation between the energy and momentum of carriers has
been obtained using the transfer matrix method within this model.Comment: 6 pages, 3 figure
Spectral and mechanical properties of the materials structured with carbon nanotubes
Carbon nanotubes are considered as the good candidate to modify the surface properties of the organic and inorganic structures. Both the spectral and mechanical properties as well as quantum chemical simulation are discussed to explain the increase in transmission and hardness of the nanostructured polyvinyl alcohol films, magnesium fluoride, etc. The basic features of carbon nanotubes are regarded to their small refractive index, strong hardness of C⎯C bonds as well as complicated and unique mechanisms of charge carrier moving. The structures of the composite films and their mechanical properties are modeled too. The peculiarities of new nanostructured materials and their possible optoelectronics and display applications will be under consideration. The results have been supported by RFBR grant #10-03-00916 and RAS Presidium Program # 21
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