Substrate induced proximity effect in superconducting niobium nanofilms

Structural and superconducting properties of high quality Niobium nanofilms with different thicknesses are investigated on silicon oxide and sapphire substrates. The role played by the different substrates and the superconducting properties of the Nb films are discussed based on the defectivity of the films and on the presence of an interfacial oxide layer between the Nb film and the substrate. The X-ray absorption spectroscopy is employed to uncover the structure of the interfacial layer. We show that this interfacial layer leads to a strong proximity effect, specially in films deposited on a SiO$_2$ substrate, altering the superconducting properties of the Nb films. Our results establish that the critical temperature is determined by an interplay between quantum-size effects, due to the reduction of the Nb film thicknesses, and proximity effects

Dimensional crossover and incipient quantum size effects in superconducting niobium nanofilms

Superconducting and normal state properties of sputtered Niobium nanofilms have been systematically investigated, as a function of film thickness in a d=9-90 nm range, on different substrates. The width of the superconducting-to-normal transition for all films remained in few tens of mK, thus remarkably narrow, confirming their high quality. We found that the superconducting critical current density exhibits a pronounced maximum, three times larger than its bulk value, for film thickness around 25 nm, marking the 3D-to-2D crossover. The extracted magnetic penetration depth shows a sizeable enhancement for the thinnest films, aside the usual demagnetization effects. Additional amplification effects of the superconducting properties have been obtained in the case of sapphire substrates or squeezing the lateral size of the nanofilms. For thickness close to 20 nm we also measured a doubled perpendicular critical magnetic field compared to its saturation value for d>33 nm, indicating shortening of the correlation length and the formation of small Cooper pairs in the condensate. Our data analysis evidences an exciting interplay between quantum-size and proximity effects together with strong-coupling effects and importance of disorder in the thinnest films, locating the ones with optimally enhanced critical properties close to the BCS-BEC crossover regime

Proximity array device: a novel photon detector working in long wavelengths

We present here an innovative photon detector based on the proximity junction array device (PAD) working at long wavelengths. We show that the vortex dynamics in PAD undergoes a transition from a Mott insulator to a vortex metal state by application of an external magnetic field. The PAD also evidences a Josephson I-V characteristic with the external field dependent tunneling current. At high applied currents, we observe a dissipative regime in which the vortex dynamics is dominated by the quasi-particle contribution from the normal metal. The PAD has a relatively high photo-response even at frequencies below the expected characteristic frequency while, its superconducting properties such as the order parameter and the Josephson characteristic frequency can be modulated via external fields to widen the detection band. This device represents a promising and reliable candidate for new high-sensitivity long-wavelength detectors. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Shape-resonant superconductivity in nanofilms: from weak to strong coupling

Ultrathin superconductors of different materials are becoming a powerful platform to find mechanisms for enhancement of superconductivity, exploiting shape resonances in different superconducting properties. Here we evaluate the superconducting gap and its spatial profile, the multiple gap components, and the chemical potential, of generic superconducting nanofilms, considering the pairing attraction and its energy scale as tunable parameters, from weak to strong coupling, at fixed electron density. Superconducting properties are evaluated at mean field level as a function of the thickness of the nanofilm, in order to characterize the shape resonances in the superconducting gap. We find that the most pronounced shape resonances are generated for weakly coupled superconductors, while approaching the strong coupling regime the shape resonances are rounded by a mixing of the subbands due to the large energy gaps extending over large energy scales. Finally, we find that the spatial profile, transverse to the nanofilm, of the superconducting gap acquires a flat behavior in the shape resonance region, indicating that a robust and uniform multigap superconducting state can arise at resonance.Comment: 7 pages, 4 figures. Submitted to the Proceedings of the Superstripes 2016 conferenc

Biochemical­­– and biophysical–induced barriergenesis in the blood brain barrier: a review of barriergenic factors for use in in vitro models

Central nervous system (CNS) pathologies are a prevalent problem in aging populations, creating a need to understand the underlying events in these diseases and develop efficient CNS‐targeting drugs. The importance of the blood‐brain barrier (BBB) has become evident, acting both as a physical barrier to drug entry into the CNS, and potentially as the cause or aggravator of CNS diseases. The development of a biomimetic BBB in vitro model is required for the understanding of BBB‐related pathologies and in the screening of drugs targeting the CNS. There is currently a great interest in understanding the influence of biochemical and biophysical factors, as these have the potential to greatly improve the barrier function of brain microvascular endothelial cells (BMECs). Recent advances in understanding how these may regulate barriergenesis in BMECs can help promote the development of improved BBB in vitro models, and therefore novel interventional therapies for pathologies related to its disruption. This review provides an overview of specific biochemical and biomechanical cues in the formation of the BBB, with a focus on in vitro models and how these might recapitulate BBB function

Early bearing and vegetative growth of 153 Sicilian olive accessions

In 2014, an olive germplasm collection was established in south-western Sicily, Italy. The collection included 153 Sicilian accessions and 3 international varieties (reference), each with 7 trees, spaced at 5×2 m and trained to hedgerow system. The aim of the trial was to study early growth and yield responses of the accessions to super-high planting density (SHD). Trunk cross sectional area, tree height, pruning weights, shoot positioning, blooming and fruit yield (kg tree-1) were measured in 2015 and 2016. Based on trunk growth and amount of prunings, the 153 accessions were separated into four categories of vigor as it follows: very high vigor (6 accessions), high vigor (13), medium vigor (131), and low vigor (3). In 85% of the accessions, the majority of shoots were born on the central part of the main stem, indicating prevalent mesotony. Constant early blooming (100% of trees in trial in both years) was recorded in 7 accessions (‘Nebba 1’, ‘Nocellara di Licata’, ‘Olivo di Monaci’, ‘Olivo di Monaci 1’, ‘Olivo di Mandanici’, ‘Verdella’, and ‘Calatina’), with ‘Nocellara di Licata’ and ‘Verdella’ bearing no fruit at the end. Accessions in the very high and low vigor categories produced no fruit, determining a lack of relationship between early bearing and tree vigor

CHEMICAL AND SENSORY CHARACTERISTICS OF FIVE LOQUAT CULTIVARS

Fruit quality can be evaluated by combining chemical-physical and sensory analyses. In this trial, both instrumental and sensory analyses were carried out on fruit of 5 loquat cultivars (Nespolone di Trabia, Sanfilippara, Virticchiara, Marcen\uf2 and Golden Nugget), with the aim of assessing their commercial quality. Fruit weight, transversal and longitudinal diameter, total soluble solid content (TSS), and titratable acidity (TA) were measured. In addition, a sensory profile of each cultivar was defined by a trained panel, which generated 16 attributes. The highest fruit weight was found in \u2018Golden Nugget\u2019 and \u2018Sanfilippara\u2019; the latter exhibited also the highest flesh/seed ratio. Total soluble solid content ranged from 18.0 \ub0brix in \u2018Virticchiara\u2019 to 12.6 \ub0brix in \u2018Nespolone di Trabia\u2019, whereas titratable acidity was highest in \u2018Sanfilippara\u2019. \u2018Golden Nugget\u2019 showed the best flesh color whilst \u2018Sanfilippara\u2019 had the best peel color. \u2018Virticchiara\u2019 had the highest intensity of sweet and the lowest intensity of sour and astringent. \u2018Nespolone di Trabia\u2019 showed the highest intensity of sour, while \u2018Marcen\uf2\u2019 and \u2018Sanfilippara\u2019 showed the highest intensity of astringent. Both instrumental and sensory analyses revealed good quality traits in fruit of \u2018Virticchiara\u2019 and \u2018Sanfilippara\u2019. The former in terms of taste and TSSC/TA ratio; the latter for appearance. Our results indicated that some local varieties, often replaced by foreign cultivars, should be reconsidered for the market

Early bearing and vegetative growth of 153 Sicilian olive accessions

In 2014, an olive germplasm collection was established in south-western Sicily, Italy. The collection included 153 Sicilian accessions and 3 international varieties (reference), each with 7 trees, spaced at 5×2 m and trained to hedgerow system. The aim of the trial was to study early growth and yield responses of the accessions to super-high planting density (SHD). Trunk cross sectional area, tree height, pruning weights, shoot positioning, blooming and fruit yield (kg tree-1) were measured in 2015 and 2016. Based on trunk growth and amount of prunings, the 153 accessions were separated into four categories of vigor as it follows: very high vigor (6 accessions), high vigor (13), medium vigor (131), and low vigor (3). In 85% of the accessions, the majority of shoots were born on the central part of the main stem, indicating prevalent mesotony. Constant early blooming (100% of trees in trial in both years) was recorded in 7 accessions (‘Nebba 1’, ‘Nocellara di Licata’, ‘Olivo di Monaci’, ‘Olivo di Monaci 1’, ‘Olivo di Mandanici’, ‘Verdella’, and ‘Calatina’), with ‘Nocellara di Licata’ and ‘Verdella’ bearing no fruit at the end. Accessions in the very high and low vigor categories produced no fruit, determining a lack of relationship between early bearing and tree vigor