11,900 research outputs found
Recommended from our members
In-situ resonant band engineering of solution-processed semiconductors generates high performance n-type thermoelectric nano-inks.
Thermoelectric devices possess enormous potential to reshape the global energy landscape by converting waste heat into electricity, yet their commercial implementation has been limited by their high cost to output power ratio. No single "champion" thermoelectric material exists due to a broad range of material-dependent thermal and electrical property optimization challenges. While the advent of nanostructuring provided a general design paradigm for reducing material thermal conductivities, there exists no analogous strategy for homogeneous, precise doping of materials. Here, we demonstrate a nanoscale interface-engineering approach that harnesses the large chemically accessible surface areas of nanomaterials to yield massive, finely-controlled, and stable changes in the Seebeck coefficient, switching a poor nonconventional p-type thermoelectric material, tellurium, into a robust n-type material exhibiting stable properties over months of testing. These remodeled, n-type nanowires display extremely high power factors (~500 µW m-1K-2) that are orders of magnitude higher than their bulk p-type counterparts
Cyclic Density Functional Theory : A route to the first principles simulation of bending in nanostructures
We formulate and implement Cyclic Density Functional Theory (Cyclic DFT) -- a
self-consistent first principles simulation method for nanostructures with
cyclic symmetries. Using arguments based on Group Representation Theory, we
rigorously demonstrate that the Kohn-Sham eigenvalue problem for such systems
can be reduced to a fundamental domain (or cyclic unit cell) augmented with
cyclic-Bloch boundary conditions. Analogously, the equations of electrostatics
appearing in Kohn-Sham theory can be reduced to the fundamental domain
augmented with cyclic boundary conditions. By making use of this symmetry cell
reduction, we show that the electronic ground-state energy and the
Hellmann-Feynman forces on the atoms can be calculated using quantities defined
over the fundamental domain. We develop a symmetry-adapted finite-difference
discretization scheme to obtain a fully functional numerical realization of the
proposed approach. We verify that our formulation and implementation of Cyclic
DFT is both accurate and efficient through selected examples.
The connection of cyclic symmetries with uniform bending deformations
provides an elegant route to the ab-initio study of bending in nanostructures
using Cyclic DFT. As a demonstration of this capability, we simulate the
uniform bending of a silicene nanoribbon and obtain its energy-curvature
relationship from first principles. A self-consistent ab-initio simulation of
this nature is unprecedented and well outside the scope of any other systematic
first principles method in existence. Our simulations reveal that the bending
stiffness of the silicene nanoribbon is intermediate between that of graphene
and molybdenum disulphide. We describe several future avenues and applications
of Cyclic DFT, including its extension to the study of non-uniform bending
deformations and its possible use in the study of the nanoscale flexoelectric
effect.Comment: Version 3 of the manuscript, Accepted for publication in Journal of
the Mechanics and Physics of Solids,
http://www.sciencedirect.com/science/article/pii/S002250961630368
Reversible, Opto-Mechanically Induced Spin-Switching in a Nanoribbon-Spiropyran Hybrid Material
It has recently been shown that electronic transport in zigzag graphene
nanoribbons becomes spin-polarized upon application of an electric field across
the nanoribbon width. However, the electric fields required to experimentally
induce this magnetic state are typically large and difficult to apply in
practice. Here, using both first-principles density functional theory (DFT) and
time-dependent DFT, we show that a new spiropyran-based, mechanochromic polymer
noncovalently deposited on a nanoribbon can collectively function as a dual
opto-mechanical switch for modulating its own spin-polarization. These
calculations demonstrate that upon mechanical stress or photoabsorption, the
spiropyran chromophore isomerizes from a closed-configuration ground-state to a
zwitterionic excited-state, resulting in a large change in dipole moment that
alters the electrostatic environment of the nanoribbon. We show that the
electronic spin-distribution in the nanoribbon-spiropyran hybrid material can
be reversibly modulated via noninvasive optical and mechanical stimuli without
the need for large external electric fields. Our results suggest that the
reversible spintronic properties inherent to the nanoribbon-spiropyran material
allow the possibility of using this hybrid structure as a resettable,
molecular-logic quantum sensor where opto-mechanical stimuli are used as inputs
and the spin-polarized current induced in the nanoribbon substrate is the
measured output.Comment: Accepted by Nanoscal
Elucidation of role of graphene in catalytic designs for electroreduction of oxygen
Graphene is, in principle, a promising material for consideration as
component (support, active site) of electrocatalytic materials, particularly
with respect to reduction of oxygen, an electrode reaction of importance to
low-temperature fuel cell technology. Different concepts of utilization,
including nanostructuring, doping, admixing, preconditioning, modification or
functionalization of various graphene-based systems for catalytic
electroreduction of oxygen are elucidated, as well as important strategies to
enhance the systems' overall activity and stability are discussed
- …