Search

Over the past four decades, energy microsources based on piezoelectric energy harvesting have been intensively studied for applications in autonomous sensor systems. The research is triggered by the request for replacing standard lead-based piezoelectric ceramics with environmentally friendly lead-free materials and potential deployment of energy-harvesting microsystems in internet of things, internet of health, ‘place and leave’ sensors in infrastructures and agriculture monitoring. Moreover, futher system miniaturization and co-integration of functions are required in line with a desired possibility to increase the harvested power density per material volume. Thus, further research efforts are necessary to develop more sustainable materials/systems with high-performance. This paper gives a comprehensive overview on the processing and functional testing the lead-free bulk materials and thin films and discusses their potential in the applications in the stress- and strain-driven piezoelectric energy harvesting. This includes the methodology of estimation of the substrate clamping and orientation/texture effects in the thin films, and identification of orientations offering high figure of merit. The ability to control film orientation of different lead-free materials is reviewed and the expected piezoelectric performances are compared with the ones reported in literature.

Copper oxide thin films have been successfully synthesized through a metal–organic chemical vapor deposition (MOCVD) approach starting from the copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate), Cu(tmhd)2, complex. Operative conditions of fabrication strongly affect both the composition and morphologies of the copper oxide thin films. The deposition temperature has been accurately monitored in order to stabilize and to produce, selectively and reproducibly, the two phases of cuprite Cu2O and/or tenorite CuO. The present approach has the advantages of being industrially appealing, reliable, and fast for the production of thin films over large areas with fine control of both composition and surface uniformity. Moreover, the methylammonium lead iodide (MAPI) active layer has been successfully deposited on the ITO/Cu2O substrate by the Low Vacuum Proximity Space Effusion (LV-PSE) technique. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) analyses have been used to characterize the deposited films. The optical band gap (Eg), ranging from 1.99 to 2.41 eV, has been determined through UV-vis analysis, while the electrical measurements allowed to establish the p-type conductivity behavior of the deposited Cu2O thin films with resistivities from 31 to 83 Ω cm and carrier concentration in the order of 1.5–2.8 × 1016 cm−3. These results pave the way for potential applications of the present system as a hole transporting layer combined with a perovskite active layer in emergent solar cell technologies.

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 (VO

International audience; Novel adducts of lithium hexafluoroacetylacetonato {Li(hfa)} with polyethers (monoglyme = {CH3OCH2CH2OCH3}, diglyme = {CH3O(CH2CH2O)2CH3}, triglyme = {CH3O(CH2CH2O)3CH3} and tetraglyme {CH3O(CH2CH2O)4CH3} have been synthesized through a single step reaction and characterized by FT-IR spectroscopy, 1H, and 13C NMR, single crystal X-ray diffraction studies along with thermal analysis.

The photocatalytic approach is known to be one of the most promising advanced oxidation processes for the tertiary treatment of polluted water. In this paper, β-NaYF4/TiO2 composite films have been synthetized through a novel sol–gel/spin-coating approach using a mixture of β-diketonate complexes of Na and Y, and Yb3+, Tm3+, Gd3+, Eu3+ as doping ions, together with the TiO2 P25 nanoparticles. The herein pioneering approach represents an easy, straightforward and industrially appealing method for the fabrication of doped β-NaYF4/TiO2 composites. The effect of the doped β-NaYF4 phase on the photocatalytic activity of TiO2 for the degradation of methylene blue (MB) has been deeply investigated. In particular, the upconverting TiO2/β-NaYF4: 20%Yb, 2% Gd, x% Tm (x = 0.5 and 1%) and the downshifting TiO2/β-NaYF4: 10% Eu composite films have been tested on MB degradation both under UV and visible light irradiation. An improvement up to 42.4% in the degradation of MB has been observed for the TiO2/β-NaYF4: 10% Eu system after 240 min of UV irradiation.

An easy approach is presented to determine vapor pressures of complexes and thus to evaluate “a priori” their suitability as precursors for AP-MOCVD or spatial ALD. Fluorinated Mg and Ca compounds have been applied to the AP-MOCVD of MF2 films.

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.

A tri-metallic precursor mixture has been used to deposit Bi(1−x)DyxFeO3 film on conductive SrTiO3:Nb(100) substrates. A fine adjustment of the film composition is the key enabling an accurate tuning of the film piezoelectric and optical properties.

In this paper, we present integrated lead-free energy converters based on a suitable MEMS fabrication process with an embedded layer of LiNbO3. The fabrication technology has been developed to realize micromachined self-generating transducers to convert kinetic energy into electrical energy. The process proposed presents several interesting features with the possibility of realizing smaller scale devices, integrated systems, miniaturized mechanical and electromechanical sensors, and transducers with an active layer used as the main conversion element. When the system is fabricated in the typical cantilever configuration, it can produce a peak-to-peak open-circuit output voltage of 0.208 V, due to flexural deformation, and a power density of 1.9 nW·mm−3·g−2 at resonance, with values of acceleration and frequency of 2.4 g and 4096 Hz, respectively. The electromechanical transduction capability is exploited for sensing and power generation/energy harvesting applications. Theoretical considerations, simulations, numerical analyses, and experiments are presented to show the proposed LiNbO3-based MEMS fabrication process suitability. This paper presents substantial contributions to the state-of-the-art, proposing an integral solution regarding the design, modelling, simulation, realization, and characterization of a novel transducer.

The use of natural compounds with biocidal activity to fight the growth of bacteria responsible for foodborne illness is one of the main research challenges in the food sector. This study reports the preparation and physicochemical characterization of chitosan nanoparticles loaded with Thymus capitatus (Th-CNPs) and Origanum vulgare (Or-CNPs) essential oils. The nanosystems were obtained by ionotropic gelation technique with high encapsulation efficiency (80–83%) and loading capacity (26–27%). Nanoparticles showed a spherical shape, bimodal particle size distribution, and good stability (zeta potential values &gt, 40 mV). The treatment of the nanosuspensions at different temperatures (4 and 40 °C) and storage times (7, 15, 21, and 30 days) did not affect their physicochemical parameters and highlights their reservoir ability for essential oils also under stressful conditions. Both Or-CNPs and Th-CNPs exhibited an enhanced bactericidal activity against foodborne pathogens (S. aureus, E. coli, L. monocytogenes) than pure essential oils. These ecofriendly nanosystems could represent a valid alternative to synthetic preservatives and be of interest for health and food safety.

A careful engineering of the central metal coordination spheres provides adducts with excellent properties for application as precursors in vapor phase and solution processes. The family of precursors under study concerns the fluorinated metal-organic β-diketonates of alkaline, alkaline-earth and rare-earth metals adducted with a polyether, with general formula M(hfa)n·L (M = Ca, Na, Y, Yb, Er, Tm; Hhfa = 1,1,1,5,5,5 hexafluoroacetylacetone, L = diglyme or tetraglyme). Mass transport properties, such as volatility and thermal stability, of these adducts have been deeply analyzed through thermogravimetric analysis and differential scanning calorimetric measurements. These properties are rationalized in relation to the metal coordination sphere in the precursors and their applications. In particular, the precursors under focus have been applied to metal organic chemical vapor deposition and a combined sol–gel/spin-coating approach. Both methods allow us to obtain selectively and reproducibly CaF2 and NaYF4 phases with several combinations of lanthanide doping ions, using a proper mixture of fluorinated precursors. A careful optimization of both synthetic strategies is the key point for the production of different lanthanide-doped binary and multicomponent fluoride films, i.e., CaF2:Yb3+,Er3+; CaF2:Yb3+,Tm3+; CaF2:Yb3+,Er3+,Tm3+ and NaYF4:Yb3+,Er3+; NaYF4:Yb3+,Tm3+, with suitable morphologies, compositions and crystalline structures. The films show very promising upconversion properties, thus pointing to their appealing applications in photovoltaic systems and white light emission devices.

Starting from fluorinated metal–organic β-diketonates, we report the synthesis of undoped and lanthanide-doped alkaline-earth fluoride (Er3+,Tm3+,Yb3+ tri-doped CaF2) thin films through two different chemical approaches: a metal–organic chemical vapor deposition (MOCVD) method and a combined sol–gel/spin-coating procedure. Both chemical approaches have the advantage of being very reliable and reproducible for the fast production of thin films with a high degree of uniformity over large areas. The fluorinated metal precursors act as a single-source in both processes, and an accurate control of the process parameters allows the optimization of the doped CaF2 films. X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray analysis have been used to characterize the deposited films. Upconversion emission, typical of the lanthanide ions, in the visible and near infrared regions upon laser excitation at 980 nm is clearly observable. The emissions are in the central region of the CIE1931 color coordinate space.

A new tetraglyme adduct of sodium hexafluoroacetylacetonate [Na(hfa)·tetraglyme] has been synthesized and successfully used, together with the RE(hfa)3·diglyme (RE = Y, Yb, Er) complexes, in the synthesis of hexagonal phase NaYF4:Yb3+,Er3+ upconverting films through a facile sol–gel method.

We report the synthesis of novel heterobimetallic precursors of the formula [RE(hfa)4]-[Na·tetraglyme]+ [RE = Y, Gd; Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme = 2,5,8,11,14-pentaoxapentadecane], which can be efficiently used as a single source for the metal-organic chemical vapor deposition of NaREF4 films.

In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg = 3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤ 0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

An innovative sol–gel process, using a mixture of Na(hfa)·tetraglyme and RE(hfa)3·diglyme (RE = Y, Yb, Tm) complexes, has been optimized to produce upconverting β-NaYF4:Yb3+/Tm3+ thin films. The X-ray diffraction (XRD) analysis confirms that the new sol–gel preparation route yields reproducibly and selectively the hexagonal Na(Y1.5Na0.5)F6 structure (β-NaYF4) without any impurity phases, since no peaks of the cubic NaYF4, YOF, Y2O3 or NaF phases were observed. This final goal has been achieved through an accurate optimization of the operative parameters such as the molar ratio of the precursor mixture, the aging time of the sol, the spin coating procedure and the annealing temperature. Field-emission scanning electron microscopy (FE-SEM) images indicate that the morphology of the surfaces, grain dimensions and thickness are strongly related to the processing parameters, with the hexagonal phase films having a very uniform morphology. Energy dispersive X-ray (EDX) analyses established the film composition in terms of dopant ions, which are responsible for the upconverting properties of the material. Luminescence measurements under laser excitation at 980 nm confirmed the promising upconversion properties of the β-NaYF4:Yb3+/Tm3+ films.

This work reports two new silver metalorganic precursors for the chemical vapor deposition of Ag metallic coatings. Both precursors are based on β-diketonate adducts, namely, Ag(hfac)(L) (H-hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione), where L is 1,10-phenanthroline (phen) or 2,5,8,11-tetraoxadodecane (triglyme). Using these ligands, the designed precursors have better solubility in alcoholic solvents and are less toxic and costly than previously reported ones. The new precursors have been characterized and their crystallographic structure solved. With the new triglyme precursor, [Ag(triglyme)2]+[Ag(hfac)2]−, pure metallic Ag coatings made of Ag nanoparticles about 20 nm in diameter were succesfully deposited on glass and Si substrates using Aerosol Assisted Metalorganic CVD (AA-CVD).

Calcium fluoride represents one of the most efficient hosts for up-conversion or down-conversion emissions. A simple metal organic chemical vapor deposition approach is applied to the fabrication of CaF2 nanostructured thin films using the fluorinated “second-generation” β-diketonate compound Ca(hfa)2•diglyme•H2O as a Ca-F single-source precursor. The versatility of the process is demonstrated for the fabrication of up-converting Yb/Er or Yb/Tm codoped CaF2 films on Si, quartz, and glass substrates. The Ln(hfa)3•diglyme (Ln = Tm, Er, Yb) precursors are used as sources of the doping ions. Structural, morphological, and compositional characterization of the films shows the formation of polycrystalline CaF2 films with a very uniform surface and suitable doping. In fact, an appropriate tuning of the mixture composition, i.e., the Ca:Ln ratio in the multicomponent source, permits the deposition of films with the desired stoichiometry. The films show promising up-conversion properties in the visible and near infrared regions upon laser excitation for both doping mixtures.

Metal-Organic Chemical Vapor Deposition (MOCVD) has been applied to the fabrication of lanthanum cobaltite (LaCoO 3 ) films on MgO (001) and LaAlO 3 (001) substrates. The films have been deposited using a multi-metal source, consisting of the La (hfa) 3 •diglyme and Co (tta) 2 •tmeda (H-hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = CH 3 O-(CH 2 CH 2 O) 2 CH 3 , Htta = α-thenoyltrifluoroacetone; tmeda = N,N,N′,N′-tetramethyl-ethylendiammine) precursor mixture. Structural and morphological characterization of films, carried out using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), proved the present MOCVD approach a suitable effective route for the growth of pure LaCoO 3 films. Composition and purity has been assessed through energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses.

Metal-Organic Chemical Vapor Deposition (MOCVD) has been applied to the fabrication of BiFeO 3 on dielectric SrTiO 3 and conducting SrTiO 3 :Nb (100) substrates. Films have been deposited using a mixed bi-metallic source, consisting of Bi(phenyl) 3 and Fe(tmhd) 3 , (phenyl = -C 6 H 5, H-tmhd = 2,2,6,6-tetramethyl-3,5-heptandione) precursor mixture. The chemical, structural and morphological characterizations of films have been carried out by energy dispersive X-ray analysis, X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Local piezoelectric properties have been investigated by piezoresponce force microscopy (PFM) and piezoelectric force spectroscopy (PFS). Structural and morphological characterizations point to the formation of homogeneous and flat surfaces for BiFeO 3 films. Different ferroelectric/piezoelectric domains have been observed depending on the structure/morphology of the samples.

The complex, Mn(hfa)2•tmeda [(H-hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentandione, tmeda = N,N,N′,N′-tetramethylethylendiamine)], is synthesized in a single-step reaction and characterized by elemental analysis, thermal analysis, and infrared (IR) spectroscopy. The solid-state crystal structure of Mn(hfa)2•tmeda provides evidence of a mononuclear structure. The thermal analyses show that the complex is thermally stable and can be evaporated to leave less than 2% residue. The complex properties are compared with the first generation, commercially available MnII and MnIII precursors, Mn(acac)2 (Hacac = acetylacetone) and Mn(tmhd)3 (Htmhd = 2,2,6,6-tetramethyl-3,5-heptanedione), respectively. Mn(hfa)2•tmeda represents the first example of manganese(II) precursor that can be used in the liquid phase without decomposition, thus providing constant evaporation rates, even for long deposition times. It is successfully applied to the reduced-pressure, metal-organic (MO)CVD of the Mn3O4 phase.

NiO thin films were grown through metalorganic chemical vapour deposition (MOCVD) on quartz and LaAlO3 (001) single crystal substrates. Two different volatile and thermally stable nickel β-diketonate adducts, Ni(hfa)2·tmeda and Ni(tta)2·tmeda [H-hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentandione; tmeda = N,N,N′,N′-tetramethylethylendiamine, Htta = 2-thenoyltrifluoroacetone], were applied as precursors for NiO film growth. The comprehensive study, applying two different precursors and changing the processing parameters, allowed for morphological control of the deposited NiO films. The AFM analyses indicated different values of roughness for NiO films obtained from the two different precursors and those from Ni(tta)2·tmeda showed a lower roughness. In addition, UV-Vis and ellipsometric measurements on NiO films grown from the Ni(tta)2·tmeda show higher transparency, fewer defects/impurities, better crystallinity and a higher refractive index than films deposited using the Ni(hfa)2·tmeda source. Raman spectroscopy confirmed the antiferromagnetic nature of the NiO layers. Work functions, around 5.1 eV, were measured by Kelvin Probe Force Microscopy for NiO films grown from Ni(tta)2·tmeda. The relationship between the precursor/substrate nature and film properties allowed us to define the best precursor and conditions for the MOCVD growth of good quality NiO films.

In the present work we describe the process of formation of methylammonium lead iodide perovskite (MAPbI(3)) by reaction between [001] oriented PbI2 thin films and MAI. The reaction leads to a rapid change in the optical properties with the formation of a brown phase having a large band in the visible range and a contribution in the near-UV range (375 nm). X-ray diffraction analyses indicate that the MAI + PbI2 as-obtained material mainly consists of a highly oriented matrix of MAI that intermixes with the Pb-I precursor. A chemical exfoliation of the initial PbI2 structure with the massive intercalation of the methylammonium iodide ions suitably describes the optical and structural findings. Short thermal treating (100 degrees C) of this as-obtained sample results in the formation of a second oriented intermediate phase, attributed to the presence of a low-dimensional perovskite structure. Such low-dimensional metastable phase is no longer visible by increasing the annealing time or the annealing temperature (150 degrees C), with the 3D MAPbI(3) tetragonal phase left in the XRD pattern.

Thin films of CaCu3Ti4O12 (CCTO) are successfully deposited by metal-organic (MO)CVD on (001)SrTiO3 substrates. An interesting approach, based on a molten multi-component precursor source, is applied. The molten mixture consists of the Ca(hfa)2 center dot tetraglyme, Ti(tmhd)2(OiPr)2, and Cu(tmhd)2 [Hhfa?=?1,1,1,5,5,5-hexafluoro-2,4-pentanedione; tetraglyme?=?2,5,8,11,14-pentaoxapentadecane; Htmhd?=?2,2,6,6-tetramethyl-3,5-heptandione; OiPr?=?iso-propoxide] precursors. It is also found that, in the present case of a relatively large lattice mismatch (similar to 5%), the epitaxial growth can be achieved by a careful optimization of deposition parameters. Film structural and morphological characterization is carried out using several techniques; X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A complete comparison between films deposited by two main processes is carried out in order to understand the kinetic and thermodynamic issues involved in the MOCVD epitaxial growth.

Porous La0.8Sr0.2MnO3 (LSMO) films have been prepared by metal organic chemical vapor deposition (MOCVD) technique for solid oxide fuel cell (SOFC) applications. LSMO samples have been deposited on yttria-stabilized zirconia (YSZ) electrolyte pellets. The adopted in situ strategy involves a molten mixture consisting of the La(hfa)3·diglyme, Sr(hfa)2·tetraglyme, and Mn(tmhd)3 [Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = bis(2-methoxyethyl)ether; tetraglyme = 2,5,8,11,14-pentaoxapentadecane; Htmhd = 2,2,6,6-tetramethyl-3,5-heptandione] precursors. It has been shown that porous LSMO films can be obtained through an accurate tuning of processing parameters, which affect the nucleation and growth processes. The structural and compositional characterizations of these films, carried out by X-ray diffraction (XRD) and energy dispersive X-ray analysis, point to the formation of a single polycrystalline La0.8Sr0.2MnO3 phase. The field emission scanning electron microscopy (FE-SEM) images confirm the formation of porous films. To evaluate the electrochemical activity of the cathodic films, an investigation by impedance spectroscopy (IS) has been performed.