59 research outputs found
Tight binding description of the electronic response of a molecular device to an applied voltage
We analyze the effect of an external electric field on the electronic
structure of molecules which have been recently studied as molecular wires or
diodes. We use a self-consistent tight binding technique which provides results
in good agreement with ab initio calculations and which may be applied to a
large number of molecules. The voltage dependence of the molecular levels is
mainly linear with slopes intimately related to the electronic structure of the
molecules. We emphasize that the response to the applied voltage is an
important feature which governs the behavior of a molecular device
Solid phase epitaxy amorphous silicon re-growth: some insight from empirical molecular dynamics simulation
The modelling of interface migration and the associated diffusion mechanisms
at the nanoscale level is a challenging issue. For many technological
applications ranging from nanoelectronic devices to solar cells, more knowledge
of the mechanisms governing the migration of the silicon amorphous/crystalline
interface and dopant diffusion during solid phase epitaxy is needed. In this
work, silicon recrystallisation in the framework of solid phase epitaxy and the
influence on orientation effects have been investigated at the atomic level
using empirical molecular dynamics simulations. The morphology and the
migration process of the interface has been observed to be highly dependent on
the original inter-facial atomic structure. The [100] interface migration is a
quasi-planar ideal process whereas the cases [110] and [111] are much more
complex with a more diffuse interface. For [110], the interface migration
corresponds to the formation and dissolution of nanofacets whereas for [111] a
defective based bilayer reordering is the dominant re-growth process. The study
of the interface velocity migration in the ideal case of defect free re-growth
reveals no difference between [100] and [110] and a decrease by a mean factor
of 1.43 for the case [111]. Finally, the influence of boron atoms in the
amorphous part on the interface migration velocity is also investigated in the
case of [100] orientation
Process Optimization and Downscaling of a Single Electron Single Dot Memory
This paper presents the process optimization of a single-electron nanoflash
electron memory. Self-aligned single dot memory structures have been fabricated
using a wet anisotropic oxidation of a silicon nanowire. One of the main issue
was to clarify the process conditions for the dot formation. Based on the
process modeling, the influence of various parameters (oxidation temperature,
nanowire shape) has been investigated. The necessity of a sharp compromise
between these different parameters to ensure the presence of the memory dot has
been established. In order to propose an aggressive memory cell, the
downscaling of the device has been carefully studied. Scaling rules show that
the size of the original device could be reduced by a factor of 2. This point
has been previously confirmed by the realization of single-electron memory
devices
Adsorption behavior of conjugated {C}3-oligomers on Si(100) and HOPG surfaces
A pi-conjugated {C}3h-oligomer involving three dithienylethylene branches
bridged at the meta positions of a central benzenic core has been synthesized
and deposited either on the Si(100) surface or on the HOPG surface. On the
silicon surface, scanning tunneling microscopy allows the observation of
isolated molecules. Conversely, by substituting the thiophene rings of the
oligomers with alkyl chains, a spontaneous ordered film is observed on the HOPG
surface. As the interaction of the oligomers is different with both surfaces,
the utility of the Si(100) surface to characterize individual oligomers prior
to their use into a 2D layer is discussed
Molecular rectifying diodes from self-assembly on silicon
We demonstrate a molecular rectifying junction made from a sequential
self-assembly on silicon. The device structure consists of only one conjugated
(p) group and an alkyl spacer chain. We obtain rectification ratios up to 37
and threshold voltages for rectification between -0.3V and -0.9V. We show that
rectification occurs from resonance through the highest occupied molecular
orbital of the p-group in good agreement with our calculations and internal
photoemission spectroscopy. This approach allows us to fabricate molecular
rectifying diodes compatible with silicon nanotechnologies for future hybrid
circuitries
High Conductance Ratio in Molecular Optical Switching of Functionalized Nanoparticle Self-Assembled Nanodevices
Self-assembled functionalized nano particles are at the focus of a number of
potential applications, in particular for molecular scale electronics devices.
Here we perform experiments of self-assembly of 10 nm Au nano particles (NPs),
functionalized by a dense layer of azobenzene-bithiophene (AzBT) molecules,
with the aim of building a light-switchable device with memristive properties.
We fabricate planar nanodevices consisting of NP self-assembled network
(NPSANs) contacted by nanoelectrodes separated by interelectrode gaps ranging
from 30 to 100 nm. We demonstrate the light-induced reversible switching of the
electrical conductance in these AzBT NPSANs with a record on/off conductance
ratio up to 620, an average value of ca. 30 and with 85% of the devices having
a ratio above 10. Molecular dynamics simulation of the structure and dynamics
of the interface between molecular monolayers chemisorbed on the nano particle
surface are performed and compared to the experimental findings. The properties
of the contact interface are shown to be strongly correlated to the molecular
conformation which in the case of AzBT molecules, can reversibly switched
between a cis and a trans form by means of light irradiations of well-defined
wavelength. Molecular dynamics simulations provide a microscopic explanation
for the experimental observation of the reduction of the on/off current ratio
between the two isomers, compared to experiments performed on flat
self-assembled monolayers contacted by a conducting cAFM tip.Comment: pdf files : publication and supporting informatio
Silicon dry oxidation kinetics at low temperature in the nanometric range: Modeling and experiment
Kinetics of silicon dry oxidation are investigated theoretically and
experimentally at low temperature in the nanometer range where the limits of
the Deal and Grove model becomes critical. Based on a fine control of the
oxidation process conditions, experiments allow the investigation of the growth
kinetics of nanometric oxide layer. The theoretical model is formulated using a
reaction rate approach. In this framework, the oxide thickness is estimated
with the evolution of the various species during the reaction. Standard
oxidation models and the reaction rate approach are confronted with these
experiments. The interest of the reaction rate approach to improve silicon
oxidation modeling in the nanometer range is clearly demonstrated
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