ENEA Portici Research Centre

This paper reports a simple and economical method for the fabrication of nanopatterned optical fiber nanotips. The proposed patterning approach relies on the use of the nanosphere lithography of the optical fiber end facet. Polystyrene (PS) nanospheres are initially self-assembled in a hexagonal array on the surface of water. The created pattern is then transferred onto an optical fiber tip (OFT). The PS monolayer colloidal crystal on the OFT is the basic building block that is used to obtain different periodic structures by applying further treatment to the fiber, such as metal coating, nanosphere size reduction and sphere removal. Ordered dielectric and metallo-dielectric sphere arrays, metallic nanoisland arrays and hole-patterned metallic films with feature sizes down to the submicron scale are achievable using this approach. Furthermore, the sizes and shapes of these periodic structures can be tailored by altering the fabrication conditions. The results indicate that the proposed self-assembly approach is a valuable route for the development of highly repeatable metallo-dielectric periodic patterns on OFTs with a high degree of order and low fabrication cost. The method can be easily extended to simultaneously produce multiple fibers, opening a new route to the development of fiber-optic nanoprobes. Finally, we demonstrate the effective application of the patterned OFTs as surface-enhanced Raman spectroscopy nanoprobes. A simple way is used to make nanopatterned tips for optical fibres by combining self-assembly of nanospheres with nanofabrication processes. Nanostructures fabricated on optical fibre tips can be used to realize exceptional light trapping and manipulation on the nanoscale, which can be harnessed for sensing applications. The ability of nanospheres to self-assemble into hexagonal arrays is promising for achieving such nanostructures. Marco Pisco at the University of Sannio in Italy and co-workers have demonstrated a new approach for realizing nanoprobes. They created a self-assembled hexagonal array of polystyrene nanospheres on a water surface and then transferred it to an optical fibre tip. The team then modified the periodic structure by employing processes based on thermal evaporation, plasma etching and sonication. They demonstrated this method by using it to produce probes for surface-enhanced Raman spectroscopy.

In optoelectronics, inkjet printing (IJP) technology is being developed as an alternative to the traditional techniques for organic materials deposition. In this work, we report the fabrication of organic light-emitting diodes (OLEDs) on the flexible substrate by studying the effect of a surface chemical treatment on the inkjet printed polymer film morphology. The employed piranha treatment increases the substrate surface energy and improves the wettability, thus inducing a decrease in the IJ printed drop thickness. The IJ printed polymer (poly(9,9-dihexyl-9H-fluorene-2,7-diyl)) is the hole-transporting layer (HTL) of a hybrid structure in which the other layers are deposited by vacuum thermal evaporation. Furthermore, in order to determine the effect of the IJ deposition method on the manufactured OLED performances, we compare them to those of devices fabricated using standard technologies. With this aim, OLEDs with the same structure are fabricated by replacing the IJ printed polymer with a spin-coated film employing the same polymer solution. The electrical and optical properties of the electroluminescent devices are investigated and discussed. Despite the lack of thickness uniformity in IJ printed film, which is an intrinsic, technological limit, OLEDs with IJ printed HTL show electro-optical characteristics that are similar to the ones of OLEDs with spin-coated HTL.

This work, framed in the IEA SHC Task 51 "Solar Energy in Urban Planning", presents an illustrative perspective of solar energy in urban planning through the analysis of 34 international case studies conducted in 10 countries. The aim here is to examine challenges, barriers and opportunities for active solar systems and passive solar strategies by taking into consideration interrelated technical and non-technical aspects in ongoing and completed projects. It focuses on exposing potential pitfalls and illustrating lessons learned in case studies divided into three categories: (i) existing urban areas, (ii) new urban areas, and (iii) solar landscapes. The analysis has yielded insights into the solar energy strategy adoption, the evaluation of solar energy production, solar irradiation and daylighting, and the architectural quality, sensitivity and visibility of the solar systems for urban planning. The outcomes have implications to stimulate successful practices in implementing solar strategies in urban planning and facilitating their replicability worldwide by avoiding common mistakes.

In-situ synchrotron X-ray diffraction (XRD) was used to monitor the thermal decomposition (thermolysis) of Cd thiolates precursors embedded in a polymer matrix and the nucleation of CdS nanoparticles. A thiolate precursor/polymer solid foil was heated to 300 degrees C in the X-ray diffraction setup of beamline W1.1 at Hasylab, and the diffraction curves were each recorded at 10 degrees C. At temperatures above 240 degrees C, the precursor decomposition is complete and CdS nanoparticles grow within the polymer matrix forming a nanocomposite with interesting optical properties. The nanoparticle structural properties (size and crystal structure) depend on the annealing temperature. Transmission electron microscopy (TEM) and photoluminescence (PL) analyses were used to characterize the nanoparticles. A possible mechanism driving the structural transformation of the precursor is inferred from the diffraction features arising at the different temperatures.

Tungsten nitride (WNx) thin films were produced by reactive dc magnetron sputtering of tungsten in an Ar–N2 gas mixture. The influence of the deposition power on the properties of tungsten nitride has been analyzed and compared with that induced by nitrogen content variation in the sputtering gas. A combined analysis of structural, electrical and optical properties on thin WNx films obtained at different deposition conditions has been performed. It was found that at an N2 content of 14% a single phase structure of W2N films was formed with the highest crystalline content. This sputtering gas composition was subsequently used for fabricating films at different deposition powers. Optical analysis showed that increasing the deposition power created tungsten nitride films with a more metallic character, which is confirmed with resistivity measurements. At low sputtering powers the resulting films were crystalline whereas, with an increase of power, an amorphous phase was also present. The incorporation of an excess of nitrogen atoms resulted in an expansion of the W2N lattice and this effect was more pronounced at low deposition powers. Infrared analysis revealed that in WNx films deposited at low power, chemisorbed N2 molecules did not behave as ligands whereas at high deposition power they clearly appeared as ligands around metallic tungsten. In this study, the influence of the most meaningful deposition parameters on the phase transformation reaction path was established and deposition conditions suitable for producing thermally stable and highly crystalline W2N films were found.

Precision medicine is continuously demanding for novel point of care systems, potentially exploitable also for in-vivo analysis. Biosensing probes based on Lab-On-Fiber Technology have been recently developed to meet these challenges. However, devices exploiting standard label-free approaches (based on ligand/target molecule interaction) suffer from low sensitivity in all cases where the detection of small molecules at low concentrations is needed. Here we report on a platform developed through the combination of Lab-On-Fiber probes with microgels, which are directly integrated onto the resonant plasmonic nanostructure realized on the fiber tip. In response to binding events, the microgel network concentrates the target molecule and amplifies the optical response, leading to remarkable sensitivity enhancement. Moreover, by acting on the microgel degrees of freedom such as concentration and operating temperature, it is possible to control the limit of detection, tune the working range as well as the response time of the probe. These unique characteristics pave the way for advanced label-free biosensing platforms, suitably reconfigurable depending on the specific application.

We report on a method for integrating sub-wavelength resonant structures on top of optical fiber tip. Our fabrication technique is based on direct milling of the glass on the fiber facet by means of focused ion beam. The patterned fiber tip acts as a structured template for successive depositions of any responsive or functional overlay. The proposed method is validated by depositing on the patterned fiber a high refractive index material layer, to obtain a 'double-layer' photonic crystal slab supporting guided resonances, appearing as peaks in the reflection spectrum. Morphological and optical characterizations are performed to investigate the effects of the fabrication process. Our results show how undesired effects, intrinsic to the fabrication procedure should be taken into account in order to guarantee a successful development of the device. Moreover, to demonstrate the flexibility of our approach and the possibility to engineering the resonances, a thin layer of gold is also deposited on the fiber tip, giving rise to a hybrid photonic-plasmonic structure with a complementary spectral response and different optical field distribution at the resonant wavelengths. Overall, this work represents a significant step forward the consolidation of Lab-on-Fiber Technology.

An important support in Demand Response (DR) programs can be provided by the Electric Vehicles (EVs). EVs may behave as a load to the grid, a supplier of electricity to the grid or an energy storage device. Thanks to the smart grid enabling technologies, Utilities can manage EVs charging time and rates, gather EVs-detailed meter data and, therefore, implement DR programs. In the present paper an overview on DR definitions and a classification of the types of customers involved and implementable programs is reported. Then a special focus on EVs integration in DR programs is given, stressing the valuable services that EVs in smart grid asset can provide.

Abstract The integration of structures supporting Bloch surface waves (BSWs) with optical fibers is highly desirable, since it would enable the development of high‐figure‐of‐merit miniaturized all‐fiber optrodes, opening new pathways within the “lab‐on‐fiber” roadmap. Here, the first experimental demonstration of grating‐assisted excitation of BSWs on the tip of single‐mode fibers in the near‐infrared region is provided. This is attained via fabrication of a 1D diffraction grating on the fiber facet, and subsequent deposition of a 1D photonic crystal. In spite of a resonance broadening due to grating‐induced morphological perturbations, the measured Q ‐factor of 50 is still higher than typical lab‐on‐tip plasmonic‐probe benchmarks. With a view toward biomolecular sensing, a surface sensitivity of 1.22 nm nm −1 of homogeneous overlay deposited over the active region, which is in line with most plasmonic optrodes largely used in connection with optical fibers, is evaluated. The results also highlight the current limitations and the challenges to face for the development of advanced BSW‐based fiber‐tip platforms for biological sensing applications.

ABSTRACT A good light trapping scheme is necessary to improve the performance of amorphous/microcrystalline silicon tandem cells. This is generally achieved by using a highly reflective transparent conducting oxide/metal back contact plus an intermediate reflector between the component cells. In this work, the use of doped silicon oxide as alternative n‐layer in micromorph solar cells is proposed as a means to obtain high current values using a simple Ag back contact and no extra reflector between the component cells n‐doped silicon oxide layers with a wide range of optical and electrical properties have been prepared. The influence of different deposition regimes on the material properties has been studied. The main findings are the following: (i) when carbon dioxide is added to the gas mixture, sufficiently high hydrogen dilution is necessary to widen the transition region from highly conductive microcrystalline‐like films to amorphous material characterized by low electrical conductivity; (ii) lower refractive index values are found with lower deposition pressure. Optimal n‐doped silicon oxide layers have been used in both component cells of micromorph devices, adopting a simple Ag back contact. Higher current values for both cells are obtained in comparison with the values obtained using standard n‐doped microcrystalline silicon, whereas similar values of fill factor and open circuit voltage are measured. The current enhancement is particularly evident for the bottom cell, as revealed by the increased spectral response in the red/infrared region. The results prove the high potential of n‐doped silicon oxide as ideal reflector for thin‐film silicon solar cells. Copyright © 2011 John Wiley & Sons, Ltd.

First and second-order Raman analysis on annealed silicon nitride films is reported. Possible formation of amorphous Si nanoparticles after an intermediate treatment is deduced from the occurrence of a resonant spectrum. After nucleation of Si nanocrystals, with a model description of the first-order spectra it is possible to access information regarding mean radius, size dispersion, and crystalline phase fraction consistent with the fundamental data derived from microscopy. Substantial increase in second to first order intensity ratio is also observed: Enhanced electron–phonon coupling in both amorphous and crystalline Si nanoparticles is suggested.

inhibition, which may constitute possible lead compounds for the development of antiviral agents in Covid-19 treatment.

Ge nanoclusters (NCs), synthesized by ion implantation and annealing up to 900 °C, result small (∼2 nm) and amorphous in Si3N4, crystalline and much larger in SiO2. The NCs ripening and crystallization kinetics in Si3N4 is retarded by larger interfacial energy and lower diffusivity of Ge in comparison to SiO2. Ge NCs absorb light more efficiently when embedded in Si3N4 than in SiO2. A significant effect of the barrier height on absorption was evidenced, in agreement with effective mass theory predictions. The smaller bandgap of Ge NCs embedded in Si3N4 and their closeness is promising features for light harvesting applications.

Abstract We report on the fabrication process of a sensing device obtained by ink‐jet printing of polyaniline suspension on alumina substrates. We optimized the inkjet parameters (amplitude and duration of jetting impulse, jetting frequency, substrate velocity) to obtain thin polyaniline lines as sensitive layers and we analyzed the morphology of PANI lines on substrate. Device response towards ammonia are also discussed and compared with reference device obtained by spin‐coating.

Nanostructured glass substrates endowed with high aspect ratio one-dimensional corrugations are prepared by defocused ion beam erosion through a self-organized gold (Au) stencil mask. The shielding action of the stencil mask is amplified by co-deposition of gold atoms during ion bombardment. The resulting glass nanostructures enable broadband anti-reflection functionality and at the same time ensure a high efficiency for diffuse light scattering (Haze). It is demonstrated that the patterned glass substrates exhibit a better photon harvesting than the flat glass substrate in p-i-n type thin film a-Si:H solar cells.

Abstract. An application of regression relationships depending on geomorphic parameters is proposed to predict the amount of the average annual suspended sediment yield at different sections of the drainage network. Simple and multiple regression relationships, utilising the drainage density and the hierarchical anomaly index as independent variables, based on data from 20 river basins of different size located in Italy, are here tested. An application is also shown for a small river basin located in central Italy where it is possible to compare the obtained suspended sediment yield estimates with reservoirs siltation data. The results confirm the potential applicability of regression equations for estimating the suspended sediment yield depending on the topological behaviours of the river network. A discussion of the reliability of the method for ungauged basins is also provided, which puts in light the necessity of additional tests to support the application of the approach to small size watersheds.

In PV applications, under mismatching conditions, it is necessary to adopt a maximum power point tracking (MPPT) technique which is able to regulate not only the voltages of the PV modules of the array but also the DC input voltage of the inverter. Such a technique can be considered a hybrid MPPT (HMPPT) technique since it is neither only distributed on the PV modules of the PV array or only centralized at the input of the inverter. In this paper a new HMPPT technique is presented and discussed. Its main advantages are the high MPPT efficiency and the high speed of tracking which are obtained by means of a fast estimate of the optimal values of PV modules voltages and of the input inverter voltage. The new HMPPT technique is compared with simple HMPPT techniques based on the scan of the power versus voltage inverter input characteristic. The theoretical analysis and the results of numerical simulations are widely discussed. Moreover, a laboratory test system, equipped with PV emulators, has been realized and used in order to experimentally validate the proposed technique.

Abstract In this study, site-specific natural background levels (NBLs) were determined for 18 elements (Al, As, Be, Cd, Co, Cu, Cr, Fe, Hg, K, Mn, Mo, Ni, Pb, Tl, U, V, and Zn) in two sediment cores collected offshore the Bagnoli-Coroglio brownfield site (Gulf of Pozzuoli, southern Italy) to accurately assess the degree of contamination and the historical trends in Heavy Metals (HMs) enrichment. This objective was pursued taking in account the high temporal and spatial variability of the geochemical properties of the area due to the local geothermal activity. Moreover, the temporal variation of Polycyclic Aromatic Hydrocarbons (PAHs) was investigated. 226 Ra was used as an extraordinary marker to confirm 210 Pb dating. It especially allowed defining the geochronological framework of the sediment core closer the brownfield up to around 1500, providing compelling support to correlate the investigated elements’ occurrences with natural geogenic dynamic. Sediment samples were accurately dated and analyzed for chemical and particle size composition. The contamination factor (Cf) and the pollution load index (PLI) showed very high enrichment of Cd, Cu, Hg, Pb, and Zn. The contamination profiles of HMs and PAHs follow the same pattern in both sediment cores, increasing from deep to upper layers. The highest contamination levels for HMs and PAHs were observed between 10 and 30 cm, corresponding to the periods of most intense industrial activity. Decreasing trends of pollutants were observed in the surface layers (0–10 cm), probably affected by a natural attenuation process due to the cessation of industrial activities.

Schottky‐barrier solar cells (SBSCs) represent low‐cost candidates for photovoltaics applications. The engineering of the interface between absorber and front electrode is crucial for reducing the dark current, blocking the majority carriers injected into the electrode, and reducing surface recombination. The presence of tailored interfacial layers between the metal electrode and the semiconductor absorber can improve the cell performance. In this work, the interface of a graphene/n‐type Si SBSC by introducing a graphene‐based derivative (GBD) layer meant to reduce the Schottky‐barrier height (SBH) and ease the charge collection are engineered. The chemical vapor deposition (CVD) parameters are tuned to obtain the two graphene films with different structure and electrical properties: few‐layer graphene (FLG) working as transparent conductive electrode and GBD layer with electron‐blocking and hole‐transporting properties. Test SBSCs are fabricated to evaluate the effect of the introduction of GBD as interlayer into the FLG/n‐Si junction. The GBD layer reduces the recombination at the interface between graphene and n‐Si, and improves the external quantum efficiency (EQE) with optical bias from 50 to 60%. The FLG/GBD/n‐Si cell attains a power conversion efficiency (PCE) of ≈5%, which increase to 6.7% after a doping treatment by nitric acid vapor.

We present our blind predictions for the Statistical Assessment of the Modeling of Proteins and Ligands (SAMPL), ninth challenge, focusing on the binding of WP6 (carboxy-pillar[6]arene) with ammonium/diammonium cationic guests. Host-guest binding free energies have been calculated using the recently developed virtual double system single box approach, based on the enhanced sampling of the bound and unbound end-states followed by fast switching nonequilibrium alchemical simulations [M. Macchiagodena et al., J. Chem. Theory Comput. 16, 7160 (2020)]. As far as Pearson and Kendall coefficients are concerned, performances were acceptable and, in general, better than those we submitted for calixarenes, cucurbituril-like open cavitand, and beta-cyclodextrines in previous SAMPL host-guest challenges, confirming the reliability of nonequilibrium approaches for absolute binding free energy calculations. In comparison with previous submissions, we found a rather large mean signed error that we attribute to the way the finite charge correction was addressed through the assumption of a neutralizing background plasma.