LiNbO3 Thin Films through a Sol-Gel/Spin-Coating Approach Using a Novel Heterobimetallic Lithium-Niobium Precursor.

Lithium niobate is a lead-free material which has attracted considerable attention due to its excellent optical, piezoelectric, and ferroelectric properties. This research is devoted to the synthesis through an innovative sol-gel/spin-coating approach of polycrystalline LiNbO3 films on Si substrates. A novel single-source hetero-bimetallic precursor containing lithium and niobium was synthesized and applied to the sol-gel synthesis. The structural, compositional, and thermal characteristics of the precursor have been tested through attenuated total reflection, X-ray photoelectron spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The LiNbO3 films have been characterized from a structural point of view with combined X-ray diffraction and Raman spectroscopy. Field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy have been used to study the morphological and compositional properties of the deposited films.

Highly stable CsPbBr3 perovskite phases from new lead ß-diketonate glyme adducts.

Lead is one of the key metals of the all-inorganic lead halide perovskites. This work tailors novel architectures of lead's coordination sphere using a ß-diketone (H-hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione) and a glyme (monoglyme, diglyme, triglyme, or tetraglyme) ligand. The coordination chemistry and thermal behaviour of these "Pb(hfa)2·glyme" adducts have been analysed through FT-IR spectroscopy, 1H and 13C NMR analyses, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Single-crystal X-ray diffraction studies provide evidence of the formation of a monomeric Pb(hfa)2·monoglyme structure. In order to validate the potentiality of these "Pb(hfa)2·glyme" precursors for the fabrication of Pb-based halide perovskites, a facile, one-step and low-temperature solution approach has been applied to prepare CsPbBr3 microcrystals with a process carried out in air under atmospheric pressure. Pure stoichiometric CsPbBr3 powders, obtained using Cs(hfa) and Br2 as cesium and bromide sources, respectively, show excellent stability under atmospheric conditions. Better results are obtained in terms of yield and stability from the diglyme and tetraglyme lead adducts. Field emission scanning electron microscopy (FE-SEM) indicates a good uniform morphology of cubic grains, while the structure and the 1 : 1 : 3 stoichiometry of Cs : Pb : Br are confirmed by X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX), respectively. Tauc plots derived from absorption spectroscopy point to optical energy band-gaps (Eg) in the 2.21-2.27 eV range, in agreement with literature data. The present research elucidates the potential of these novel "Pb(hfa)2·glyme" adducts as promising lead precursors for CsPbBr3 perovskite synthesis, paving the way for their implementation in various technological applications.

Fabrication of Europium-Doped CaF2 Films via Sol-Gel Synthesis as Down-Shifting Layers for Solar Cell Applications.

In the present work, an in-depth study on the sol-gel process for the fabrication of Eu-doped CaF2 materials in the form of thin films has been addressed for the production of down-shifting layers. Fine-tuning of the operative parameters, such as the annealing temperature, substrate nature and doping ion percentage, has been finalized in order to obtain Eu(III)-doped CaF2 thin films via a reproducible and selective solution process for down-shifting applications. An accurate balance of such parameters allows for obtaining films with high uniformity in terms of both their structural and compositional features. The starting point of the synthesis is the use of a mixture of Ca(hfa)2•diglyme•H2O and Eu(hfa)3•diglyme adducts, with a suited ratio to produce 5%, 10% and 15% Eu-doped CaF2 films, in a water/ethanol solution. A full investigation of the structural, morphological and compositional features of the films, inspected using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX), respectively, has stated a correlation between the annealing temperature and the structural characteristics and morphology of the CaF2 thin films. Interestingly, crystalline CaF2 films are obtained at quite low temperatures of 350-400 °C. The down-shifting properties, validated by taking luminescence measurements under UV excitation, have allowed us to correlate the local environment in terms of the degree of symmetry around the europium ions with the relative doping ion percentages.

Highly Tunable MOCVD Process of Vanadium Dioxide Thin Films: Relationship between Structural/Morphological Features and Electrodynamic Properties.

The monoclinic structures of vanadium dioxide are widely studied as appealing systems due to a plethora of functional properties in several technological fields. In particular, the possibility to obtain the VO2 material in the form of thin film with a high control of structure and morphology represents a key issue for their use in THz devices and sensors. Herein, a fine control of the crystal habit has been addressed through an in-depth study of the metal organic chemical vapor deposition (MOCVD) synthetic approach. The focus is devoted to the key operative parameters such as deposition temperature inside the reactor in order to stabilize the P21/c or the C2/m monoclinic VO2 structures. Furthermore, the compositional purity, the morphology and the thickness of the VO2 films have been assessed through energy dispersive X-ray (EDX) analyses and field-emission scanning electron microscopy (FE-SEM), respectively. THz time domain spectroscopy is used to validate at very high frequency the functional properties of the as-prepared VO2 films.

Sensing enhancement of a Fabry-Perot THz cavity using switchable VO2 mirrors.

We experimentally investigate the sensing properties of an open cavity operating in the THz regime and realized by employing as mirrors two thin vanadium dioxide (VO2) films grown on silicon parallel plates and separated by a variable length. The phase transition of VO2 is used to control the behavior of the system between two different responses: a high transmission mode to the incident radiation (VO2 in the insulating state) and a high sensitivity to tiny changes in the cavity refractive index (VO2 in the conducting state). In the first state, the low loss regime enables to adjust the cavity length and easily optimize the resonances due to the Fabry-Perot (FP) effect in the Si plates and in the cavity volume. The activation of the metallic-like state instead, by damping the FP oscillations in the plates, promotes the onset of a comb-like spectrum that can be exploited as a versatile tool for accurate sensing applications. Using both an analytical model and full-wave simulations, we estimate the device response to variation in the refractive index of the cavity volume, showing that the proposed structure can achieve sensitivity values among the highest reported for THz sensors.

Luminescent 1,10-Phenanthroline ß-Diketonate Europium Complexes with Large Second-Order Nonlinear Optical Properties.

Substitution of the diglyme ligand of [Eu(hfa)3(diglyme)] (where hfa is hexafluoroacetylacetonate) with a simple 1,10-phenanthroline leads to a six-fold increase of the product µßEFISH, as measured by the Electric-Field-Induced Second Harmonic generation (EFISH) technique. Similarly, [Eu(tta)3(1,10-phenanthroline)] (where Htta is 2-thenoyltrifluoroacetone) is characterized by a large second-order NLO response. Both 1,10-phenanthroline europium complexes have great potential as multifunctional materials for photonics.

Optimization of Oxygen Evolution Reaction with Electroless Deposited Ni-P Catalytic Nanocoating.

The low efficiency of water electrolysis mostly arises from the thermodynamic uphill oxygen evolution reaction. The efficiency can be greatly improved by rationally designing low-cost and efficient oxygen evolution anode materials. Herein, we report the synthesis of Ni-P alloys adopting a facile electroless plating method under mild conditions on nickel substrates. The relationship between the Ni-P properties and catalytic activity allowed us to define the best conditions for the electroless synthesis of highperformance Ni-P catalysts. Indeed, the electrochemical investigations indicated an increased catalytic response by reducing the thickness and Ni/P ratio in the alloy. Furthermore, the Ni-P catalysts with optimized size and composition deposited on Ni foam exposed more active sites for the oxygen evolution reaction, yielding a current density of 10 mA cm-2 at an overpotential as low as 335 mV, exhibiting charge transfer resistances of only a few ohms and a remarkable turnover frequency (TOF) value of 0.62 s-1 at 350 mV. The present study provides an advancement in the control of the electroless synthetic approach for the design and large-scale application of high-performance metal phosphide catalysts for electrochemical water splitting.

Polymer-Based Graphene Derivatives and Microwave-Assisted Silver Nanoparticles Decoration as a Potential Antibacterial Agent.

Nanocomposites obtained by the decoration of graphene-based materials with silver nanoparticles (AgNPs) have received increasing attention owing to their antimicrobial activity. However, the complex synthetic methods for their preparation have limited practical applications. This study aims to synthesize novel NanoHybrid Systems based on graphene, polymer, and AgNPs (namely, NanoHy-GPS) through an easy microwave irradiation approach free of reductants and surfactants. The polymer plays a crucial role, as it assures the coating layer/substrate compatibility making the platform easily adaptable for a specific substrate. AgNPs' loading (from 5% to 87%) can be tuned by the amount of Silver salt used during the microwave-assisted reaction, obtaining spherical AgNPs with average sizes of 5-12 nm homogeneously distributed on a polymer-graphene nanosystem. Interestingly, microwave irradiation partially restored the graphene sp2 network without damage of ester bonds. The structure, morphology, and chemical composition of NanoHy-GPS and its subunits were characterized by means of UV-vis spectroscopy, thermal analysis, differential light scattering (DLS), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray analysis (EDX), Atomic Force Microscopy (AFM), and High-Resolution Transmission Electron Microscopy (HRTEM) techniques. A preliminary qualitative empirical assay against the typical bacterial load on common hand-contacted surfaces has been performed to assess the antibacterial properties of NanoHy-GPS, evidencing a significative reduction of bacterial colonies spreading.