1,465 research outputs found
Oriented Graphene Nanoribbons Embedded in Hexagonal Boron Nitride Trenches
Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the
potential to be used in high-performance graphene-based semiconductor
electronics. However, controlled growth of GNRs on dielectric substrates
remains a challenge. Here, we report the successful growth of GNRs directly on
hexagonal boron nitride substrates with smooth edges and controllable widths
using chemical vapour deposition. The approach is based on a type of template
growth that allows for the in-plane epitaxy of mono-layered GNRs in
nano-trenches on hexagonal boron nitride with edges following a zigzag
direction. The embedded GNR channels show excellent electronic properties, even
at room temperature. Such in-plane hetero-integration of GNRs, which is
compatible with integrated circuit processing, creates a gapped channel with a
width of a few benzene rings, enabling the development of digital integrated
circuitry based on GNRs.Comment: 32 pages, 4 figures, Supplementary informatio
A First-Principles Study of Zinc Oxide Honeycomb Structures
We present a first-principles study of the atomic, electronic, and magnetic
properties of two-dimensional (2D), single and bilayer ZnO in honeycomb
structure and its armchair and zigzag nanoribbons. In order to reveal the
dimensionality effects, our study includes also bulk ZnO in wurtzite,
zincblende, and hexagonal structures. The stability of 2D ZnO, its nanoribbons
and flakes are analyzed by phonon frequency, as well as by finite temperature
ab initio molecular-dynamics calculations. 2D ZnO in honeycomb structure and
its armchair nanoribbons are nonmagnetic semiconductors but acquire net
magnetic moment upon the creation of zinc-vacancy defect. Zigzag ZnO
nanoribbons are ferromagnetic metals with spins localized at the oxygen atoms
at the edges and have high spin polarization at the Fermi level. However, they
change to nonmagnetic metal upon termination of their edges with hydrogen
atoms. From the phonon calculations, the fourth acoustical mode specified as
twisting mode is also revealed for armchair nanoribbon. Under tensile stress
the nanoribbons are deformed elastically maintaining honeycomblike structure
but yield at high strains. Beyond yielding point honeycomblike structure
undergo a structural change and deform plastically by forming large polygons.
The variation in the electronic and magnetic properties of these nanoribbons
have been examined under strain. It appears that plastically deformed
nanoribbons may offer a new class of materials with diverse properties.Comment: http://prb.aps.org/abstract/PRB/v80/i23/e23511
Elastic and plastic deformation of graphene, silicene, and boron nitride honeycomb nanoribbons under uniaxial tension: A first-principles density-functional theory study
This study of elastic and plastic deformation of graphene, silicene, and
boron nitride (BN) honeycomb nanoribbons under uniaxial tension determines
their elastic constants and reveals interesting features. In the course of
stretching in the elastic range, the electronic and magnetic properties can be
strongly modified. In particular, it is shown that the band gap of a specific
armchair nanoribbon is closed under strain and highest valance and lowest
conduction bands are linearized. This way, the massless Dirac fermion behavior
can be attained even in a semiconducting nanoribbon. Under plastic deformation,
the honeycomb structure changes irreversibly and offers a number of new
structures and functionalities. Cagelike structures, even suspended atomic
chains can be derived between two honeycomb flakes. Present work elaborates on
the recent experiments [C. Jin, H. Lan, L. Peng, K. Suenaga, and S. Iijima,
Phys. Rev. Lett. 102, 205501 (2009)] deriving carbon chains from graphene.
Furthermore, the similar formations of atomic chains from BN and Si nanoribbons
are predicted.Comment: http://prb.aps.org/abstract/PRB/v81/i2/e02410
Large Electronic Anisotropy and Enhanced Chemical Activity of Highly Rippled Phosphorene
We investigate the electronic structure and chemical activity of rippled
phosphorene induced by large compressive strains via first-principles
calculation. It is found that phosphorene is extraordinarily bendable, enabling
the accommodation of ripples with large curvatures. Such highly rippled
phosphorene shows a strong anisotropy in electronic properties. For ripples
along the armchair direction, the band gap changes from 0.84 to 0.51 eV for the
compressive strain up to -20% and further compression shows no significant
effect, for ripples along the zigzag direction, semiconductor to metal
transition occurs. Within the rippled phosphorene, the local electronic
properties, such as the modulated band gap and the alignments of frontier
orbitals, are found to be highly spatially dependent, which may be used for
modulating the injection and confinement of carriers for optical and
photovoltaic applications. The examination of the interaction of a physisorbed
NO molecule with the rippled phosphorene under different compressive strains
shows that the chemical activities of the phosphorene are significantly
enhanced at the top and bottom peaks of the ripples, indicated by the enhanced
adsorption and charge transfer between them. All these features can be ascribed
to the effect of curvatures, which modifies the orbital coupling between atoms
at the ripple peaks
Mechanical and Electronic Properties of MoS Nanoribbons and Their Defects
We present our study on atomic, electronic, magnetic and phonon properties of
one dimensional honeycomb structure of molybdenum disulfide (MoS) using
first-principles plane wave method. Calculated phonon frequencies of bare
armchair nanoribbon reveal the fourth acoustic branch and indicate the
stability. Force constant and in-plane stiffness calculated in the harmonic
elastic deformation range signify that the MoS nanoribbons are stiff quasi
one dimensional structures, but not as strong as graphene and BN nanoribbons.
Bare MoS armchair nanoribbons are nonmagnetic, direct band gap
semiconductors. Bare zigzag MoS nanoribbons become half-metallic as a
result of the (2x1) reconstruction of edge atoms and are semiconductor for
minority spins, but metallic for the majority spins. Their magnetic moments and
spin-polarizations at the Fermi level are reduced as a result of the
passivation of edge atoms by hydrogen. The functionalization of MoS
nanoribbons by adatom adsorption and vacancy defect creation are also studied.
The nonmagnetic armchair nanoribbons attain net magnetic moment depending on
where the foreign atoms are adsorbed and what kind of vacancy defect is
created. The magnetization of zigzag nanoribbons due to the edge states is
suppressed in the presence of vacancy defects.Comment: 11 pages, 5 figures, first submitted at November 23th, 200
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