2,653 research outputs found
Energy-transfer rate in a double-quantum-well system due to Coulomb coupling
We study the energy-transfer rate for electrons in a double-quantum-well
structure, where the layers are coupled through screened Coulomb interactions.
The energy-transfer rate between the layers (similar to the Coulomb drag effect
in which the momentum transfer rate is considered) is calculated as functions
of electron densities, interlayer spacing, the temperature difference of the
2DEGs, and the electron drift velocity in the drive layer. We employ the full
wave vector and frequency dependent random-phase approximation at finite
temperature to describe the effective interlayer Coulomb interaction. We find
that the collective modes (plasmons) of the system play a dominant role in the
energy transfer rates. The contribution of optical phonons to the transfer
rates through the phonon mediated Coulomb coupling mechanism has also been
considered.Comment: LaTex, 5 pages, 4 figures, uses grafik.sty (included
Directed Growth of Hydrogen Lines on Graphene: High Throughput Simulations Powered by Evolutionary Algorithm
We set up an evolutionary algorithm combined with density functional
tight-binding (DFTB) calculations to investigate hydrogen adsorption on flat
graphene and graphene monolayers curved over substrate steps. During the
evolution, candidates for the new generations are created by adsorption of an
additional hydrogen atom to the stable configurations of the previous
generation, where a mutation mechanism is also incorporated. Afterwards a
two-stage selection procedure is employed. Selected candidates act as the
parents of the next generation. In curved graphene, the evolution follows a
similar path except for a new mechanism, which aligns hydrogen atoms on the
line of minimum curvature. The mechanism is due to the increased chemical
reactivity of graphene along the minimum radius of curvature line (MRCL) and to
sp bond angles being commensurate with the kinked geometry of hydrogenated
graphene at the substrate edge. As a result, the reaction barrier is reduced
considerably along the MRCL, and hydrogenation continues like a mechanical
chain reaction. This growth mechanism enables lines of hydrogen atoms along the
MRCL, which has the potential to overcome substrate or rippling effects and
could make it possible to define edges or nanoribbons without actually cutting
the material.Comment: 10 pages of main text, 37 pages of supplementary information, 1
supplementary vide
Quantum Transport Characteristics of Lateral pn-Junction of Single Layer TiS3
Using density functional theory and nonequilibrium Greens functions-based
methods we investigated the electronic and transport properties of monolayer
TiS3 pn-junction. We constructed a lateral pn-junction in monolayer TiS3 by
using Li and F adatoms. An applied bias voltage caused significant variability
in the electronic and transport properties of the TiS3 pn-junction. In
addition, spin dependent current-voltage characteristics of the constructed
TiS3 pn-junction were analyzed. Important device characteristics were found
such as negative differential resistance and rectifying diode behaviors for
spin-polarized currents in the TiS3 pn-junction. These prominent conduction
properties of TiS3 pn-junction offer remarkable opportunities for the design of
nanoelectronic devices based on a recently synthesized single-layered material
Ag and Au Atoms Intercalated in Bilayer Heterostructures of Transition Metal Dichalcogenides and Graphene
The diffusive motion of metal nanoparticles Au and Ag on monolayer and
between bilayer heterostructures of transition metal dichalcogenides and
graphene are investigated in the framework of density functional theory. We
found that the minimum energy barriers for diffusion and the possibility of
cluster formation depend strongly on both the type of nanoparticle and the type
of monolayers and bilayers. Moreover, the tendency to form clusters of Ag and
Au can be tuned by creating various bilayers. Tunability of the diffusion
characteristics of adatoms in van der Waals heterostructures holds promise for
controllable growth of nanostructures.Comment: accepted, APL Ma
Chiral single-wall gold nanotubes
Based on first-principles calculations we show that gold atoms can form both
free-standing and tip-suspended chiral single-wall nanotubes composed of
helical atomic strands. Free-standing, infinite (5,5) tube is found to be
energetically the most favorable. While energetically less favorable, the
experimentally observed (5,3) tube stretching between two tips corresponds to a
local minimum in the string tension. Similarly, the (4,3) tube is predicted as
a favorable structure yet to be observed experimentally. Analysis of band
structure, charge density, and quantum ballistic conductance suggests that the
current on these wires is less chiral than expected, and there is no direct
correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma
-AlN-Mg(OH) vdW Bilayer Heterostructure: Tuning the excitonic characteristics
Motivated by recent studies that reported the successful synthesis of
monolayer Mg(OH) [Suslu \textit{et al.}, Sci. Rep. \textbf{6}, 20525
(2016)] and hexagonal (\textit{h}-)AlN [Tsipas \textit{et al}., Appl. Phys.
Lett. \textbf{103}, 251605 (2013)], we investigate structural, electronic, and
optical properties of vertically stacked -AlN and Mg(OH), through
\textit{ab initio} density-functional theory (DFT), many-body quasi-particle
calculations within the GW approximation, and the Bethe-Salpeter equation
(BSE). It is obtained that the bilayer heterostructure prefers the
stacking having direct band gap at the with Type-II band
alignment in which the valance band maximum and conduction band minimum
originate from different layer. Regarding the optical properties, the imaginary
part of the dielectric function of the individual layers and hetero-bilayer are
investigated. The hetero-bilayer possesses excitonic peaks which appear only
after the construction of the hetero-bilayer. The lowest three exciton peaks
are detailedly analyzed by means of band decomposed charge density and the
oscillator strength. Furthermore, the wave function calculation shows that the
first peak of the hetero-bilayer originates from spatially indirect exciton
where the electron and hole localized at -AlN and Mg(OH),
respectively, which is important for the light harvesting applications.Comment: Accepted by Physical Review
Strong Coupling Characterisation of Quasi-1D polarons in cylindrical QW-wires
Cataloged from PDF version of article.We retrieve, within the strong-coupling theory, the quasi-one dimensional analog of the standard optical polaron relevant to a cylindrical quantum well wire. Under the assumption of perfect confinement the ground state binding energy, effective polaronic mass and the phonon-coupling-induced potential well profiles are given as a function of the wire radius and the electron-phonon interaction strength
Monte-Carlo simulation of localization dynamics of excitons in ZnO and CdZnO quantum well structures
Localization dynamics of excitons was studied for ZnO/MgZnO and CdZnO/MgZnO
quantum wells (QW). The experimental photoluminescence (PL) and absorption data
were compared with the results of Monte Carlo simulation in which the excitonic
hopping was modeled. The temperature-dependent PL linewidth and Stokes shift
were found to be in a qualitatively reasonable agreement with the hopping
model, with accounting for an additional inhomogeneous broadening for the case
of linewidth. The density of localized states used in the simulation for the
CdZnO QW was consistent with the absorption spectrum taken at 5 K.Comment: 4 figures, to appear in J. Appl. Phy
Spintronic properties of zigzag-edged triangular graphene flakes
Cataloged from PDF version of article.We investigate quantum transport properties of triangular graphene flakes with zigzag edges by using first principles calculations. Triangular graphene flakes have large magnetic moments which vary with the number of hydrogen atoms terminating its edge atoms and scale with its size. Electronic transmission and current-voltage characteristics of these flakes, when contacted with metallic electrodes, reveal spin valve and remarkable rectification features. The transition from ferromagnetic to antiferromagnetic state under bias voltage can, however, terminate the spin polarizing effects for specific flakes. Geometry and size dependent transport properties of graphene flakes may be crucial for spintronic nanodevice applications. (C) 2010 American Institute of Physics. [doi:10.1063/1.3489919
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