260 research outputs found
A Field Effect Transitor based on the Mott Transition in a Molecular Layer
Here we propose and analyze the behavior of a FET--like switching device, the
Mott transition field effect transistor, operating on a novel principle, the
Mott metal--insulator transition. The device has FET-like characteristics with
a low ``ON'' impedance and high ``OFF'' impedance. Function of the device is
feasible down to nanoscale dimensions. Implementation with a class of organic
charge transfer complexes is proposed.Comment: Revtex 11pages, Figures available upon reques
A RAIRS, TPD and femtosecond laser-induced desorption study of CO, NO and coadsorbed CO + NO on Pd(111)
Here we present a systematic study of the adsorption and laser induced desorption of CO, NO and CO + NO from a Pd(111) surface at a number of different coverages. We begin by characterising the surfaces using reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). Experiments show that NO displaces pre-adsorbed CO considerably, but that CO has a much smaller effect on pre-adsorbed NO. In both cases, the preferred binding sites of CO are occupied by NO, displacing it to less favourable adsorption sites. Femtosecond laser induced desorption (fs-LID) shows that desorption of CO on Pd(111) follows a power law and is fairly independent of CO coverage, but for NO on Pd(111) we observe a clear deviation from a power law curve at higher coverages, with saturation being observed. This suggests that the cross-section for LID of NO is much larger than that for CO and that NO on Pd(111) is more photoactive than CO on Pd(111). Interestingly, for CO + NO on Pd(111) we find that coadsorption has a strong influence on the photodesorption process and that the structure of the overlayer is also important in controlling the photodesorption products, regardless of the order in which the two molecules are dosed
Theory of the Eigler-swith
We suggest a simple model to describe the reversible field-induced transfer
of a single Xe-atom in a scanning tunneling microscope, --- the Eigler-switch.
The inelasticly tunneling electrons give rise to fluctuating forces on and
damping of the Xe-atom resulting in an effective current dependent temperature.
The rate of transfer is controlled by the well-known Arrhenius law with this
effective temperature. The directionality of atom transfer is discussed, and
the importance of use of non-equlibrium-formalism for the electronic
environment is emphasized. The theory constitutes a formal derivation and
generalization of the so-called Desorption Induced by Multiple Electron
Transitions (DIMET) point of view.Comment: 13 pages (including 2 figures in separate LaTeX-files with
ps-\specials), REVTEX 3.
Wave packet propagation study of the charge transfer interaction in the F^- -Cu(111) and -Ag(111) systems
The electron transfer between an ion and and
surfaces is studied by the wave packet propagation method in order to determine
specifics of the charge transfer interaction between the negative ion and the
metal surface due to the projected band gap. A new modeling of the ion
is developed that allows one to take into account the six quasi-equivalent
electrons of which are {\it a priori} active in the charge transfer
process. The new model invokes methods of constrained quantum dynamics. The
six-electron problem is transformed to two one-electron problems linked via a
constraint. The projection method is used to develop a wave packet propagation
subject to the modeling constraint. The characteristics (energy and width) of
the ion ion level interacting with the two surfaces are determined and
discussed in connection with the surface projected band gap.Comment: 34 pages, Revtex, 9 figures (postscript
Measurement of the Optical Conductivity of Graphene
Optical reflectivity and transmission measurements over photon energies
between 0.2 and 1.2 eV were performed on single-crystal graphene samples on a
transparent SiO2 substrate. For photon energies above 0.5 eV, graphene yielded
a spectrally flat optical absorbance of (2.3 +/- 0.2)%. This result is in
agreement with a constant absorbance of pi*alpha, or a sheet conductivity of
pi*e^2/2h, predicted within a model of non-interacting massless Dirac Fermions.
This simple result breaks down at lower photon energies, where both spectral
and sample-to-sample variations were observed. This "non-universal" behavior is
explained by including the effects of doping and finite temperature, as well as
contributions from intraband transitions.Comment: 9 pages, 4 figures, Phys. Rev. Lett. 101, 196405 (2008
Electron-phonon effects and transport in carbon nanotubes
We calculate the electron-phonon scattering and binding in semiconducting
carbon nanotubes, within a tight binding model. The mobility is derived using a
multi-band Boltzmann treatment. At high fields, the dominant scattering is
inter-band scattering by LO phonons corresponding to the corners K of the
graphene Brillouin zone. The drift velocity saturates at approximately half the
graphene Fermi velocity. The calculated mobility as a function of temperature,
electric field, and nanotube chirality are well reproduced by a simple
interpolation formula. Polaronic binding give a band-gap renormalization of ~70
meV, an order of magnitude larger than expected. Coherence lengths can be quite
long but are strongly energy dependent.Comment: 5 pages and 4 figure
Electrically Driven Light Emission from Individual CdSe Nanowires
We report electroluminescence (EL) measurements carried out on three-terminal
devices incorporating individual n-type CdSe nanowires. Simultaneous optical
and electrical measurements reveal that EL occurs near the contact between the
nanowire and a positively biased electrode or drain. The surface potential
profile, obtained by using Kelvin probe microscopy, shows an abrupt potential
drop near the position of the EL spot, while the band profile obtained from
scanning photocurrent microscopy indicates the existence of an n-type Schottky
barrier at the interface. These observations indicate that light emission
occurs through a hole leakage or an inelastic scattering induced by the rapid
potential drop at the nanowire-electrode interface.Comment: 12 pages, 4 figure
Tunable few-electron double quantum dots and Klein tunnelling in ultra-clean carbon nanotubes
Quantum dots defined in carbon nanotubes are a platform for both basic
scientific studies and research into new device applications. In particular,
they have unique properties that make them attractive for studying the coherent
properties of single electron spins. To perform such experiments it is
necessary to confine a single electron in a quantum dot with highly tunable
barriers, but disorder has until now prevented tunable nanotube-based
quantum-dot devices from reaching the single-electron regime. Here, we use
local gate voltages applied to an ultra-clean suspended nanotube to confine a
single electron in both a single quantum dot and, for the first time, in a
tunable double quantum dot. This tunability is limited by a novel type of
tunnelling that is analogous to that in the Klein paradox of relativistic
quantum mechanics.Comment: 21 pages including supplementary informatio
- …