45 research outputs found
Detection mechanism in highly sensitive ZnO nanowires network gas sensors
Metal-oxide nanowires are showing a great interest in the domain of gas
sensing due to their large response even at a low temperature, enabling
low-power gas sensors. However their response is still not fully understood,
and mainly restricted to the linear response regime, which limits the design of
appropriate sensors for specific applications. Here we analyse the non-linear
response of a sensor based on ZnO nanowires network, both as a function of the
device geometry and as a response to oxygen exposure. Using an appropriate
model, we disentangle the contribution of the nanowire resistance and of the
junctions between nanowires in the network. The applied model shows a very good
consistency with the experimental data, allowing us to demonstrate that the
response to oxygen at room temperature is dominated by the barrier potential at
low bias voltage, and that the nanowire resistance starts to play a role at
higher bias voltage. This analysis allows us to find the appropriate device
geometry and working point in order to optimize the sensitivity. Such analysis
is important for providing design rules, not only for sensing devices, but also
for applications in electronics and opto-electronics using nanostructures
networks with different materials and geometries
A high aspect ratio Fin-Ion Sensitive Field Effect Transistor: compromises towards better electrochemical bio-sensing
The development of next generation medicines demand more sensitive and
reliable label free sensing able to cope with increasing needs of multiplexing
and shorter times to results. Field effect transistor-based biosensors emerge
as one of the main possible technologies to cover the existing gap. The general
trend for the sensors has been miniaturisation with the expectation of
improving sensitivity and response time, but presenting issues with
reproducibility and noise level. Here we propose a Fin-Field Effect Transistor
(FinFET) with a high heigth to width aspect ratio for electrochemical
biosensing solving the issue of nanosensors in terms of reproducibility and
noise, while keeping the fast response time. We fabricated different devices
and characterised their performance with their response to the pH changes that
fitted to a Nernst-Poisson model. The experimental data were compared with
simulations of devices with different aspect ratio, stablishing an advantage in
total signal and linearity for the FinFETs with higher aspect ratio. In
addition, these FinFETs promise the optimisation of reliability and efficiency
in terms of limits of detection, for which the interplay of the size and
geometry of the sensor with the diffusion of the analytes plays a pivotal role.Comment: Article submitted to Nano Letter
Asymmetric Franck-Condon factors in suspended carbon nanotube quantum dots
Electronic states and vibrons in carbon nanotube quantum dots have in general
different location and size. As a consequence, the conventional
Anderson-Holstein model, coupling vibrons to the dot total charge only, may no
longer be appropriated in general. Here we explicitly address the role of the
spatial fluctuations of the electronic density, yielding space-dependent
Franck-Condon factors. We discuss the consequent marked effects on transport
which are compatible with recent measurements. This picture can be relevant for
tunneling experiments in generic nano-electromechanical systems.Comment: 4+ pages, 3 figures (2 color, 1 BW
Persistent enhancement of the carrier density in electron irradiated InAs nanowires
We report a significant and persistent enhancement of the conductivity in
free-standing non intentionnaly doped InAs nanowires upon irradiation in ultra
high vacuum. Combining four-point probe transport measurements performed on
nanowires with different surface chemistries, field-effect based measurements
and numerical simulations of the electron density, the change of the
conductivity is found to be caused by the increase of the surface free carrier
concentration. Although an electron beam of a few keV, typically used for the
inspection and the processing of materials, propagates through the entire
nanowire cross-section, we demonstrate that the nanowire electrical properties
are predominantly affected by radiation-induced defects occuring at the
nanowire surface and not in the bulk.Comment: 18 pages, 5 figure
Inhomogeneous Si-doping of gold-seeded InAs nanowires grown by molecular beam epitaxy
We have investigated in-situ Si doping of InAs nanowires grown by molecular
beam epitaxy from gold seeds. The effectiveness of n-type doping is confirmed
by electrical measurements showing an increase of the electron density with the
Si flux. We also observe an increase of the electron density along the
nanowires from the tip to the base, attributed to the dopant incorporation on
the nanowire facets whereas no detectable incorporation occurs through the
seed. Furthermore the Si incorporation strongly influences the lateral growth
of the nanowires without giving rise to significant tapering, revealing the
complex interplay between axial and lateral growth.This work was supported by the ANR through the
Project No. ANR-11-JS04-002-01, and the Ministry of
Higher Education and Research, Nord-Pas de Calais
Regional Council and FEDER through the “Contrat de
Projets Etat Region (CPER) 2007-2013.” P.C. is the recipient of an Australian Research Council
Future Fellowship (project number FT120100498)
Single-hole transistor in p-type GaAs/AlGaAs heterostructures
A single-hole transistor is patterned in a p-type, C-doped GaAs/AlGaAs
heterostructure by AFM oxidation lithography. Clear Coulomb blockade resonances
have been observed at T=300 mK. A charging energy of ~ 1.5 meV is extracted
from Coulomb diamond measurements, in agreement with the lithographic
dimensions of the dot. The absence of excited states in Coulomb diamond
measurements, as well as the temperature dependence of Coulomb peak heights
indicate that the dot is in the multi-level transport regime. Fluctuations in
peak spacings larger than the estimated mean single-particle level spacing are
observed.Comment: 4 pages, 5 figure
PRAP-CVD: A Novel Technique to Deposit Intrinsically Conductive Polymers
Polymers provide extraordinary opportunities for functionalizing surfaces integrated into flexible devices contributing to a significant advancement in thin-film technologies. Both the advantageous characteristics of conventional polymers (e.g. low weight, flexibility) and the functional physical properties of conventional semiconductors (e.g. absorption and emission of light and a tuneable conductivity) can be found in polymers providing innovative materials. Among polymers with heterocyclic structures, called conjugated polymers, polythiophene remains one of the most intensely researched materials in the field of so called organic electronics owing to the relatively facile and well-established synthetic modifications of the corresponding monomers and its derivatives. In particular, poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most promising owing to its exceptional stability, transparency, and electrical conductivity. Nevertheless it is difficult to process PEDOT into thin-films by traditional solution-based methods. Plasma Radicals Assisted Polymerisation via Chemical Vapour Deposition (PRAP-CVD) is a novel technique able to overcome the challenges caused by the conventional techniques
Aharonov-Bohm oscillations in the presence of strong spin-orbit interactions
We have measured highly visible Aharonov-Bohm (AB) oscillations in a ring
structure defined by local anodic oxidation on a p-type GaAs heterostructure
with strong spin-orbit interactions. Clear beating patterns observed in the raw
data can be interpreted in terms of a spin geometric phase. Besides h/e
oscillations, we resolve the contributions from the second harmonic of AB
oscillations and also find a beating in these h/2e oscillations. A resistance
minimum at B=0T, present in all gate configurations, is the signature of
destructive interference of the spins propagating along time-reversed paths.Comment: 4 pages, 3 figures, published versio
Magneto-transport Subbands Spectroscopy in InAs Nanowires
We report on magneto-transport measurements in InAs nanowires under large
magnetic field (up to 55T), providing a direct spectroscopy of the 1D
electronic band structure. Large modulations of the magneto-conductance
mediated by an accurate control of the Fermi energy reveal the Landau
fragmentation, carrying the fingerprints of the confined InAs material. Our
numerical simulations of the magnetic band structure consistently support the
experimental results and reveal key parameters of the electronic confinement.Comment: 13 Pages, 5 figure