3,333 research outputs found
Static dielectric response and Born effective charge of BN nanotubes from {\it ab initio} finite electric field calculations
{\it Ab initio} investigations of the full static dielectric response and
Born effective charge of BN nanotubes (BN-NTs) have been performed for the
first time using finite electric field method. It is found that the ionic
contribution to the static dielectric response of BN-NTs is substantial and
also that a pronounced chirality-dependent oscillation is superimposed on the
otherwise linear relation between the longitudinal electric polarizability and
the tube diameter (), as for a thin dielectric cylinderical shell. In
contrast, the transverse dielectric response of the BN-NTs resemble the
behavior of a thin (non-ideal) conducting cylindrical shell of a diameter of
\AA, with a screening factor of 2 for the inner electric field. The
medium principal component of the Born effective charge corresponding
to the transverse atomic displacement tangential to the BN-NT surface, has a
pronounced -dependence (but independent of chirality), while the large
longitudinal component exhibits a clear chirality dependence (but
nearly -independent), suggesting a powerful way to characterize the diameter
and chirality of a BN-NT.Comment: submitted to PR
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Methods of tailoring the deposition of metals using self-assembled monolayers
In some aspects, the present disclosure provides methods of depositing a metal onto a nanomaterial which has been passivized with a self-assembled monolayer at a weakened point in the topography of the nanomaterial. In some embodiments, the weakened point is caused by the curvature of the topography. This method may be used to prepare electronic devices such as memory modules.Board of Regents, University of Texas Syste
First-Principle Description of Correlation Effects in Layered Materials
We present a first-principles description of anisotropic materials
characterized by having both weak (dispersion-like) and strong covalent bonds,
based on the Adiabatic--Connection Fluctuation--Dissipation Theorem within
Density Functional Theory. For hexagonal boron nitride the in-plane and out of
plane bonding as well as vibrational dynamics are well described both at
equilibrium and when the layers are pulled apart. Also bonding in covalent and
ionic solids is described. The formalism allows to ping-down the deficiencies
of common exchange-correlation functionals and provides insight towards the
inclusion of dispersion interactions into the correlation functional.Comment: Accepted for publication in Physical Review Letter
Excitons and Many-Electron Effects in the Optical Response of Single-Walled Boron Nitride Nanotubes
We report first-principles calculations of the effects of quasiparticle
self-energy and electron-hole interaction on the optical properties of
single-walled BN nanotubes. Excitonic effects are shown to be even more
important in BN nanotubes than in carbon nanotubes. Electron-hole interactions
give rise to complexes of bright (and dark) excitons, which qualitatively alter
the optical response. Excitons with binding energy larger than 2 eV are found
in the (8,0) BN nanotubes. Moreover, unlike the carbon nanotubes, theory
predicts that these exciton states are comprised of coherent supposition of
transitions from several different subband pairs, giving rise to novel
behaviors.Comment: 4 pages, 4 figure
Excitons in boron nitride nanotubes: dimensionality effects
We show that the optical absorption spectra of boron nitride (BN) nanotubes
are dominated by strongly bound excitons. Our first-principles calculations
indicate that the binding energy for the first and dominant excitonic peak
depends sensitively on the dimensionality of the system, varying from 0.7 eV in
bulk hexagonal BN via 2.1 eV in the single sheet of BN to more than 3 eV in the
hypothetical (2,2) tube. The strongly localized nature of this exciton dictates
the fast convergence of its binding energy with increasing tube diameter
towards the sheet value. The absolute position of the first excitonic peak is
almost independent of the tube radius and system dimensionality. This provides
an explanation for the observed "optical gap" constancy for different tubes and
bulk hBN [R. Arenal et al., to appear in Phys. Rev. Lett. (2005)].Comment: 5 pages, 2 figure
Broad boron sheets and boron nanotubes: An ab initio study of structural, electronic, and mechanical properties
Based on a numerical ab initio study, we discuss a structure model for a
broad boron sheet, which is the analog of a single graphite sheet, and the
precursor of boron nanotubes. The sheet has linear chains of sp hybridized
sigma bonds lying only along its armchair direction, a high stiffness, and
anisotropic bonds properties. The puckering of the sheet is explained as a
mechanism to stabilize the sp sigma bonds. The anisotropic bond properties of
the boron sheet lead to a two-dimensional reference lattice structure, which is
rectangular rather than triangular. As a consequence the chiral angles of
related boron nanotubes range from 0 to 90 degrees. Given the electronic
properties of the boron sheets, we demonstrate that all of the related boron
nanotubes are metallic, irrespective of their radius and chiral angle, and we
also postulate the existence of helical currents in ideal chiral nanotubes.
Furthermore, we show that the strain energy of boron nanotubes will depend on
their radii, as well as on their chiral angles. This is a rather unique
property among nanotubular systems, and it could be the basis of a different
type of structure control within nanotechnology.Comment: 16 pages, 17 figures, 2 tables, Versions: v1=preview, v2=first final,
v3=minor corrections, v4=document slightly reworke
Magneto-mechanical interplay in spin-polarized point contacts
We investigate the interplay between magnetic and structural dynamics in
ferromagnetic atomic point contacts. In particular, we look at the effect of
the atomic relaxation on the energy barrier for magnetic domain wall migration
and, reversely, at the effect of the magnetic state on the mechanical forces
and structural relaxation. We observe changes of the barrier height due to the
atomic relaxation up to 200%, suggesting a very strong coupling between the
structural and the magnetic degrees of freedom. The reverse interplay is weak,
i.e. the magnetic state has little effect on the structural relaxation at
equilibrium or under non-equilibrium, current-carrying conditions.Comment: 5 pages, 4 figure
Graphitic-BN Based Metal-free Molecular Magnets From A First Principle Study
We perform a first principle calculation on the electronic properties of
carbon doped graphitic boron nitride graphitic BN. It was found that carbon
substitution for either boron or nitrogen atom in graphitic BN can induce
spontaneous magnetization. Calculations based on density functional theory with
the local spin density approximation on the electronic band structure revealed
a spin polarized, dispersionless band near the Fermi energy. Spin density
contours showed that the magnetization density originates from the carbon atom.
The magnetization can be attributed to the carbon 2p electron. Charge density
distribution shows that the carbon atom forms covalent bonds with its three
nearest neighbourhood. The spontaneous magnetization survives the curvature
effect in BN nanotubes, suggesting the possibility of molecular magnets made
from BN. Compared to other theoretical models of light-element or metal-free
magnetic materials, the carbon-doped BN are more experimentally accessible and
can be potentially useful.Comment: 8 pages, 4 figure
Corporate entrepreneurship champions: mapping the past and present states of the field for future advancements
Purpose
The purpose of this study is to critically examine and review the extant research on corporate entrepreneurship champions in the broader area of corporate entrepreneurship and to uncover the avenues for advancement of the scholarship with the purpose of engaging CE champions towards the upliftment of organisations in particular, and younger workforce in general.
Design/methodology/approach
In this study, authors employ bibliometric analysis through a review of 274 papers fetched from Web of Science and Scopus databases.
Findings
The authors set the agenda for future research and policy by elucidating research themes and potential research questions by bringing out twelve themes classified into five basic themes, three niche themes, three motor themes, and one key theme, while also providing the methodological inputs for carrying out this agenda.
Originality/value
This study adopts a unique lens of investigation in contextualising the role of self-efficacy, employee engagement, and career choice for the younger workforce
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