1,568 research outputs found
Enhanced shot noise in carbon nanotube field-effect transistors
We predict shot noise enhancement in defect-free carbon nanotube field-effect
transistors through a numerical investigation based on the self-consistent
solution of the Poisson and Schrodinger equations within the non-equilibrium
Green functions formalism, and on a Monte Carlo approach to reproduce injection
statistics. Noise enhancement is due to the correlation between trapping of
holes from the drain into quasi-bound states in the channel and thermionic
injection of electrons from the source, and can lead to an appreciable Fano
factor of 1.22 at room temperature.Comment: 4 pages, 4 figure
Shot noise suppression in quasi one-dimensional Field Effect Transistors
We present a novel method for the evaluation of shot noise in quasi
one-dimensional field-effect transistors, such as those based on carbon
nanotubes and silicon nanowires. The method is derived by using a statistical
approach within the second quantization formalism and allows to include both
the effects of Pauli exclusion and Coulomb repulsion among charge carriers. In
this way it extends Landauer-Buttiker approach by explicitly including the
effect of Coulomb repulsion on noise. We implement the method through the
self-consistent solution of the 3D Poisson and transport equations within the
NEGF framework and a Monte Carlo procedure for populating injected electron
states. We show that the combined effect of Pauli and Coulomb interactions
reduces shot noise in strong inversion down to 23 % of the full shot noise for
a gate overdrive of 0.4 V, and that neglecting the effect of Coulomb repulsion
would lead to an overestimation of noise up to 180 %.Comment: Changed content, 7 pages,5 figure
Engineering interband tunneling in nanowires with diamond cubic or zincblende crystalline structure based on atomistic modeling
We present an investigation in the device parameter space of band-to-band
tunneling in nanowires with a diamond cubic or zincblende crystalline
structure. Results are obtained from quantum transport simulations based on
Non-Equilibrium Green's functions with a tight-binding atomistic Hamiltonian.
Interband tunneling is extremely sensitive to the longitudinal electric field,
to the nanowire cross section, through the gap, and to the material. We have
derived an approximate analytical expression for the transmission probability
based on WKB theory and on a proper choice of the effective interband tunneling
mass, which shows good agreement with results from atomistic quantum
simulation.Comment: 4 pages, 3 figures. Final version, published in IEEE Trans.
Nanotechnol. It differs from the previous arXiv version for the title and for
some changes in the text and in the reference
Il restauro dei dipinti "olio su tela"
none3Il testo condensa la lunga ed eterogenea attività didattica relativa all’argomento, innanzitutto quella svolta dai tre autori, a vario titolo, presso l’Università di Bologna. Molte affermazioni, cos’ come tutta l’iconografia, derivano direttamente dalla poliedrica e trentennale attività dello “Studio di Restauro G.M.Costanini”. nel tempo, cambiano i materiali e le tecniche di restauro, ma ciò che dovrebbe rimanere saldo per chi è coinvolto in problemi di restauro è la capacità di una lettura sistematica dell’opera d’arte e del suo stato di conservazione e la possibilità di elaborare o valutare gli interventi adatti per rallentare l’inevitabile degrado dei materiali. Per queste ragioni, tutto quello che qui riguarda direttamente i dipinti olio su tela, nella sua articolazione e sistemazione, risulta certamente proficuo anche nell’approccio al restauro di altre categorie di opere d’arte.noneCostantini G.M.; Costato Costantini R.; Fiori C.Costantini G.M.; Costato Costantini R.; Fiori C
Field-Effect Transistors with Doped Reservoirs and Realistic Geometry
The authors would like to make corrections to some results presented in IEEE Trans. Electron Devices, Vol. 53, No. 8, pp. 1782-1733, Aug. 2006
Simulation of hydrogenated graphene Field-Effect Transistors through a multiscale approach
In this work, we present a performance analysis of Field Effect Transistors
based on recently fabricated 100% hydrogenated graphene (the so-called
graphane) and theoretically predicted semi-hydrogenated graphene (i.e.
graphone). The approach is based on accurate calculations of the energy bands
by means of GW approximation, subsequently fitted with a three-nearest neighbor
(3NN) sp3 tight-binding Hamiltonian, and finally used to compute ballistic
transport in transistors based on functionalized graphene. Due to the large
energy gap, the proposed devices have many of the advantages provided by
one-dimensional graphene nanoribbon FETs, such as large Ion and Ion/Ioff
ratios, reduced band-to-band tunneling, without the corresponding disadvantages
in terms of prohibitive lithography and patterning requirements for circuit
integration
Drift velocity peak and negative differential mobility in high field transport in graphene nanoribbons explained by numerical simulations
We present numerical simulations of high field transport in both suspended
and deposited armchair graphene nanoribbon (A-GNR) on HfO2 substrate. Drift
velocity in suspended GNR does not saturate at high electric field (F), but
rather decreases, showing a maximum for F=10 kV/cm. Deposition on HfO2 strongly
degrades the drift velocity by up to a factor of 10 with respect to suspended
GNRs in the low-field regime, whereas at high fields drift velocity approaches
the intrinsic value expected in suspended GNRs. Even in the assumption of
perfect edges, the obtained mobility is far behind what expected in
two-dimensional graphene, and is further reduced by surface optical phonons.Comment: 4 pages, 4 figure
A semi-analytical model of Bilayer Graphene Field Effect Transistor
Bilayer graphene has the very interesting property of an energy gap tunable
with the vertical electric field. We propose an analytical model for a
bilayer-graphene field-effect transistor, suitable for exploring the design
parameter space and to find a device structure with promising performance in
terms of transistor operation. Our model, based on the effective mass
approximation and ballistic transport assumptions, takes into account
bilayer-graphene tunable gap and self polarization, and includes all
band-to-band tunneling current components, which are shown to represent the
major limitation to transistor operation, because the limited achievable energy
gap is not sufficient to obtain a large Ion/Ioff ratio
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