1,721,018 research outputs found
Electronic properties of one-dimensional pentacene crystals
No full textThe electronic properties of an infinite row of freestanding, aligned side-by-side, pentacene molecules are derived as a function of the intermolecular overlap integral and the chemical potential shift. We use a semiclassical approximation and a first principles tight binding method to obtain conductance and mobility of this one-dimensional crystal as a function of temperature and gate voltage. For two values of the intermolecular overlap, energy bands show a metallic behavior. For all the other values, a bandgap is present and evolves with the intermolecular overlap following a typical modulation. The magnitude of the scattering parameters estimated by the observed conductivity is coherent with the existing literature values. These findings could be relevant for the implementation of organic-based sensors
Andreev Spectroscopy of Molecular States in Resonant and Charge Accumulation Regime
No full textMolecular electronics represents the ultimate step of the miniaturization process of the integrated circuits. Including molecules in manmade devices may introduce novel functionalities in nanodevices, such as the possibility to interact with biological environments with tremendous implications in several fields. With these motivations, we present a Bogoliubov-de Gennes description of the transport properties of a Normal-metal/molecule/Superconductor (N/m/S) junction formed by contacting an annular molecule (m) (e.g., a benzene molecule) with a normal (N) and a superconducting electrode (S). Differently from N/m/N junctions, the superconducting correlations in S play a crucial role in determining the transparency of the system. We demonstrate that the zero-bias differential conductance of the device is strongly suppressed in presence of charge accumulation on the molecule, while a resonant transmission with maximum conductance is observed when the charge stored on the molecule is negligible. We explain these findings observing that the space distribution of molecular quantum states is strongly affected by the Andreev mechanism, which represents the dominant scattering process at the m/S interface when the energy of the incident quasi-particle is below the superconducting energy gap. The relevance of these findings is briefly discussed
a-axis tilt grain boundaries for YBa2Cu3O7-x Superconducting Quantum Interferometers
No full textSuperconducting quantum interference devices (SQUIDs) have been fabricated using YBa2Cu3O72x
@100# 45°-tilt grain-boundary Josephson junctions based on a controllable biepitaxial technique.
These devices are characterized by large characteristic voltages, desirable magnetic-flux-to-voltage
transfer parameters and low flux noise. An energy resolution of 1.6310230 J/Hz at liquid helium has
been measured, which is the lowest value reported for biepitaxial SQUIDs. These junctions exhibit
a phenomenology different from traditional @001# 45°-tilt biepitaxials probably due to the absence
of p junctions. The performance of the presented SQUIDs demonstrates that significant
improvements in the biepitaxial technique are possible, and the resulting devices have potential for
applications
Radiation induced degradation in a 150-nm CMOS SPADs device
No full textThe effects induced by radiation on an innovative photo-sensor consisting of Single-Photon Avalanche Diodes arrays, implemented in a 150-nm CMOS technology, are presented. Samples were irradiated with a proton beam at different doses, and the impact of radiation-induced damage on the performance of the devices in terms of Dark Count Rate has been estimated. Furthermore, possible methods to reduce the impact of radiation-induced damage are discussed
Quantum waveguide theory of the Josephson effect in multiband superconductors
Full text linkWe formulate a quantum waveguide theory of the Josephson effect in multiband superconductors, with special emphasis on iron-based materials. By generalizing the boundary conditions of the scattering problem, we first determine the Andreev levels spectrum and then derive an explicit expression for the Josephson current which generalizes the formula of the single-band case. In deriving the results, we provide a second quantization field theory, allowing us to evaluate the current-phase relation and the Josephson current fluctuations in multiband systems. We present results for two different order parameter symmetries, namely s ± and s ++ , which are relevant in multiband systems. The obtained results show that the s ± symmetry can support π states which are absent in the s ++ case. We also argue that there is a certain fragility of the Josephson current against phase fluctuations in the s ++ case. The temperature dependence of the Josephson critical current is also analyzed and we find, for both the order parameter symmetries, remarkable violations of the Ambegaokar-Baratoff relation. The results are relevant in view of possible experiments aimed at investigating the order parameter symmetry of multiband superconductors using mesoscopic Josephson junctions
Radiation induced degradation in a 150-nm CMOS SPADs device
No full textThe effects induced by radiation on an innovative photo-sensor consisting of Single-Photon Avalanche Diodes arrays, implemented in a 150-nm CMOS technology, are presented. Samples were irradiated with a proton beam at different doses, and the impact of radiation-induced damage on the performance of the devices in terms of Dark Count Rate has been estimated. Furthermore, possible methods to reduce the impact of radiation-induced damage are discussed
Characterization of the Radiation-Induced Damage in a PEN (Polyethylene Naphthalate) Scintillation Detector †
No full textThe radiation hardness of a Polyethylene Naphthalate (PEN) thin film scintillator has been characterized in terms of the light yield loss after irradiation with 11 MeV protons and 1 MeV electrons. The light yield distributions induced by excitation with radioactive sources have been measured on samples irradiated with different doses and the induced light loss has been computed. Results showed the good radiation hardness behaviors of PEN scintillators, with a light yield loss of ~15% at 10 Mrad and ~35% at the maximum delivered dose of 80 Mrad
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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