96 research outputs found
Opposite effects of NO on electrical injection in porous silicon gas sensors
The electrical conductance of porous silicon fabricated with heavily doped
p-type silicon is very sensitive to NO. A concentration of 10 ppb can be
detected by monitoring the current injection at fixed voltage. However, we show
that the sign of the injection variations depends on the porous layer
thickness. If the thickness is sufficiently low -- of the order of few
\micro\meter{} -- the injection decreases instead of increasing. We discuss the
effect in terms of an already proposed twofold action of NO, according to
which the free carrier density increases, and simultaneously the energy bands
are bent at the porous silicon surface.Comment: 3 pages, 3 figures, requires SIunits packag
Role of microstructure in porous silicon gas sensors for NO
Electrical conductivity of porous silicon fabricated form heavily doped
p-type silicon is very sensitive to NO, even at concentrations below 100
ppb. However, sensitivity strongly depends on the porous microstructure. The
structural difference between sensitive and insensitive samples is
independently confirmed by microscopy images and by light scattering behavior.
A way to change the structure is by modifying the composition of the
electrochemical solution. We have found that best results are achieved using
ethanoic solutions with HF concentration levels between 13% and 15%.Comment: 3 pages, 4 figures, package SIunits require
Time-Resolved Fluorescence Spectroscopy of Molecularly Imprinted Nanoprobes as an Ultralow Detection Nanosensing Tool for Protein Contaminants
: Currently, optical sensors based on molecularly imprinted polymers (MIPs) have been attracting significant interest. MIP sensing relies on the combination of the MIP's selective capability, which is conveyed to the polymeric material by a template-assisted synthesis, with optical techniques that offer exquisite sensitivity. In this work, we devised an MIP nanoparticle optical sensor for the ultralow detection of serum albumin through time-resolved fluorescence spectroscopy. The Fluo-nanoMIPs (∅~120 nm) were synthetized using fluorescein-O-methacrylate (0.1×, 1×, 10× mol:mol versus template) as an organic fluorescent reporter. The ability of 0.1× and 1×Fluo-nanoMIPs to bind albumin (15 fM-150 nM) was confirmed by fluorescence intensity analyses and isothermal titration calorimetry. The apparent dissociation constant (Kapp) was 30 pM. Conversely, the 10× fluorophore content did not enable monitoring binding. Then, the time-resolved fluorescence spectroscopy of the nanosensors was studied. The 1×Fluo-nanoMIPs showed a decrease in fluorescence lifetime upon binding to albumin (100 fM-150 nM), Kapp = 28 pM, linear dynamic range 3.0-83.5 pM, limit of detection (LOD) 1.26 pM. Selectivity was confirmed testing 1×Fluo-nanoMIPs against competitor proteins. Finally, as a proof of concept, the nanosensors demonstrated detection of the albumin (1.5 nM) spiked in wine samples, suggesting a possible scaling up of the method in monitoring allergens in wines
Characterization-Based Modeling of Retriggering and Afterpulsing for Passively Quenched CMOS SPADs
The current trend in the design of systems based on CMOS SPADs is to adopt smaller technological nodes, allowing the co-integration of additional electronics for the implementation of complex digital systems on chip. Due to their simplicity, a way to reduce the area occupied by the integrated electronics is the use of passive quenching circuits (PQCs) instead of active (AQCs) or mixed (MQCs) ones. However, the recharge phase in PQCs is slower, so the device can be retriggered before this phase ends. This paper studies the phenomena of afterpulsing and retriggering, depending on the characteristics of the SPADs and the working conditions. In order to do that, a test chip containing SPADs of different size has been characterized in several operating environments. A mathematical model has been proposed for fitting afterpulsing phenomenon. It is shown that retriggering can be also described in terms of this model, suggesting that it is linked to carriers trapped in the shallow levels of the semiconductor and that should be taken into account when considering the total amount of afterpulsing events.Junta de Andalucía TIC 233
Scalar f0(980) and sigma(500) meson exchange in phi decays into pi0pi0gamma
The complementarity between Chiral Perturbation Theory and the Linear Sigma
Model is exploited to study production in radiative decays,
where the effects of the scalar resonance, and those of its more
controversial partner, should become manifest via the decay chain. The recently reported data
on coming from the VEPP-2M collider in
Novosibirsk and the DANE -factory in Frascati can be reasonably
described in our approach, which we propose as a promising first step towards
more detailed analyses. The contribution, which appears as a
moderately narrow peak at the high part of the dipion mass spectrum, can be
interpreted as the isoscalar member of the scalar nonet with a large coupling and an coupling suppressed by almost ideal
- mixing. Indeed, the mixing angle in the flavour basis is found
to be , if the -propagator is approximated by a
simple Breit-Wigner, or , if an improved two-channel
analysis is performed. The resonance, which is then strongly
coupled to pion pairs, yields a tiny contribution because, in our approach, its
coupling to kaon pairs is proportional to and thus quite
small.Comment: 18 pages, 4 figures; new treatment of the f0 propagator added and
Comments on previous work correcte
Demonstrating the high sensitivity of MoS2 monolayers in direct x-ray detectors
Two-dimensional transition metal dichalcogenides (TMDCs) are demonstrated to be appealing semiconductors for optoelectronic applications, thanks to their remarkable properties in the ultraviolet-visible spectral range. Interestingly, TMDCs have not yet been characterized when exposed to x rays, although they would be ideal candidates for optoelectronic applications in this spectral range. They benefit from the high cross section of the constituent heavy atoms, while keeping the absorption very low, due to the ultrathin structure of the film. This encourages the development of photodetectors based on TMDCs for several applications dealing with x rays, such as radioprotection, medical treatments, and diagnosis. Given the atomic thickness of TMDCs, they can be expected to perform well at low dose measurements with minimal perturbation of the radiation beam, which is required for in vivo applications. In this paper, the use of TMDCs as active materials for direct x-ray detection is demonstrated, using a photodetector based on a MoS2 monolayer (1L-MoS2). The detector shows a response to x rays in the range of 101–102 keV, at dose rates as low as fractions of mGy/s. The sensitivity of 1L-MoS2 reaches values in the range of 108–109 µC Gy−1 cm−3, overcoming the values reported for most of the organic and inorganic materials. To improve the x-ray photoresponse even further, the 1L-MoS2 was coupled with a polymeric film integrating a scintillator based on terbium-doped gadolinium oxysulfide (Gd2O2S:Tb). The resulting signal was three times larger, enabled by the indirect x ray to visible photoconversion mechanism. This paper might pave the way toward the production of ultrathin real-time dosimeters for in vivo applications.Peer Reviewe
Charge asymmetries in e+e- -> pi+ pi- gamma at the phi resonance
We consider the forward-backward pion charge asymmetry for the
e^{+}e^{-}\to\pi^{+}\pi^{-}\gamma process. At tree level we consider
bremsstrahlung and double resonance contributions. Although the latter
contribution is formally sub-leading, it is enhanced at low dipion invariant
mass due to resonant effects. We consider also four alternative models
to describe the final state radiation at the loop level: Resonance Chiral
Perturbation Theory, Unitarized Chiral Perturbation Theory, Kaon Loop Model and
Linear Sigma Model. The last three models yield results compatible with
experimental data. The Kaon Loop Model requires an energy dependent phase to
achieve the agreement.Comment: Revised version, conclusions changed, 11 pages, 8 figs, version to
appear in PL
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