156 research outputs found
Nonequilibrium electron charging in carbon-nanotube-based molecular bridges
We evidence the importance of electron charging under nonequilibrium
conditions for carbon-nanotube-based molecular bridges, using a self-consistent
Green's function method with an extended Huckel Hamiltonian and a
three-dimensional Poisson solver. Our analysis demonstrates that such feature
is highly dependent on the chirality of the carbon nanotube as well as on the
type of the contact metal, conditioning in a nongeneralized way the system's
conduction mechanism. Based on its impact on transport, we argue that
self-consistency is essential for the current-voltage calculations of
semiconducting nanotubes, whereas less significant in the case of metallic
ones.Comment: 4 pages, 4 figure
Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions
We calculate quantum transport for metal-graphene nanoribbon heterojunctions
within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is
paid on both the chemical aspects of the interface bonding as well the
one-dimensional electrostatics along the ribbon length. Band-bending and doping
effects strongly influence the transport properties, giving rise to conductance
asymmetries and a selective suppression of the subband formation. Junction
electrostatics and p-type characteristics drive the conduction mechanism in the
case of high work function Au, Pd and Pt electrodes, while contact resistance
becomes dominant in the case of Al.Comment: 4 pages, 5 figure
Theoretical study of the role of metallic contacts in probing transport features of pure and defected graphene nanoribbons
Understanding the roles of disorder and metal/graphene interface on the electronic and transport properties of graphene-based systems is crucial for a consistent analysis of the data deriving from experimental measurements. The present work is devoted to the detailed study of graphene nanoribbon systems by means of self-consistent quantum transport calculations. The computational formalism is based on a coupled Schrödinger/Poisson approach that respects both chemistry and electrostatics, applied to pure/defected graphene nanoribbons (ideally or end-contacted by various fcc metals). We theoretically characterize the formation of metal-graphene junctions as well as the effects of backscattering due to the presence of vacancies and impurities. Our results evidence that disorder can infer significant alterations on the conduction process, giving rise to mobility gaps in the conductance distribution. Moreover, we show the importance of metal-graphene coupling that gives rise to doping-related phenomena and a degradation of conductance quantization characteristics
Insulator-metal transition in biased finite polyyne systems
A method for the study of the electronic transport in strongly coupled
electron-phonon systems is formalized and applied to a model of polyyne chains
biased through metallic Au leads. We derive a stationary non equilibrium
polaronic theory in the general framework of a variational formulation. The
numerical procedure we propose can be readily applied if the electron-phonon
interaction in the device hamiltonian can be approximated as an effective
single particle electron hamiltonian. Using this approach, we predict that
finite polyyne chains should manifest an insulator-metal transition driven by
the non-equilibrium charging which inhibits the Peierls instability
characterizing the equilibrium state.Comment: to appear at EPJ
Local Coordination Modulates the Reflectivity of Liquefied Si-Ge Alloys
The properties of liquid Si-Ge binary systems at melting conditions deviate
from those expected by the ideal alloy approximation. Particularly, a
non-linear dependence of the dielectric functions occurs with the reflectivity
of liquid Si-Ge being 10\% higher at intermediate Ge content than in pure Si or
Ge. Using \textit{ab initio} methodologies, we revealed a direct correlation
between reflectivity and atomic coordination, discovering that Si-Ge's higher
local coordination drives the aforementioned optical behavior. These findings
extend the physical understanding of liquefied semiconductors and hold the
promise of further generalization
Electron backscattering from stacking faults in SiC by means of \textit{ab initio} quantum transport calculations
We study coherent backscattering phenomena from single and multiple stacking
faults (SFs) in 3C- and 4H-SiC within density functional theory quantum
transport calculations. We show that SFs give rise to highly dispersive bands
within both the valance and conduction bands that can be distinguished for
their enhanced density of states at particular wave number subspaces. The
consequent localized perturbation potential significantly scatters the
propagating electron waves and strongly increases the resistance for -doped
systems. We argue that resonant scattering from SFs should be one of the
principal degrading mechanisms for device operation in silicon carbide.Comment: 5 pages, 4 figure
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