Analysis and comparison of three Coleoptera families in organic and conventional orchards within the Etna Regional Park (Catania, Sicily)

The objective of this work was to compare two agricultural management systems, organic and conventional, in the Etna Regional Park. The influence in both spatial and temporal dimensions, that natural habitats adjacent to these two different managed agricultural systems have on Coleoptera biocoenosis in orchards was also studied. This comparison was done through standardised data and multivariate analysis using a multi-taxa approach. Specifically, three families of the Order Coleoptera, namely Carabidae, Tenebrionidae and Staphylinidae (excluding Aleocharinae and Scydmaeninae) were studied.peer-reviewe

Photo-physical Properties of Perovskites on Curved Surfaces

Organic-inorganic metal halide perovskites (MHPs) have recently attracted increasing attention as highly-efficient light-harvesting materials for photovoltaic applications. The technical ease of solution processing of these materials is one of their major advantages on the route towards fabrication of low-cost solar cells and optoelectronic devices. However, the precise control of crystallization and morphology of MHPs deposited from solutions, considered crucial for enhancing the final photovoltaic performance, still remains challenging. Firstly, the PhD thesis focuses on novel and thus far unexplored issues of crystallization mechanisms and photo-physical characterization of polycrystalline MAPbI3 and MAPbBr3 coated via one-step solution processing onto the surface of elongated, cylinder-shaped, quartz substrates with unprecedentedly high curvatures (diameters of 80 to 1800 ÎŒm). The obtained results are then compared with the ones gathered for deposits of polycrystalline MAPbI3 and MAPbBr3 on planar substrates. Secondly, the deposits of polycrystalline MAPbI3 and MAPbBr3 on cylindrical substrates are used to track the changes in photoluminescence (PL) and photocurrent (PC) of these materials in the presence of various gaseous media. In particular, the advantages offered by small cross-sectional dimensions and the cylindrical geometry of thus obtained deposits of MAPbI3 and MAPbBr3 made it possible to easily combine them with simple gas-flow observation chambers having both optical and electrical accesses. This approach enabled to perform simultaneous measurements of PL and PC for polycrystalline deposits of MAPbI3 and MAPbBr3 exposed to the precisely controlled flow of different gaseous media, including technologically important oxygen (O2) and nitrogen (N2). Thus, an insight could be gained into the role and importance of surface defects for the general optoelectronic properties, such as photo-brightening and photo-bleaching, as well as long-term stability of these materials. Thirdly, a study of selective photo-bleaching of MAPbI3 under illumination with specific wavelengths is performed. For the first time this type of experiments were performed under precisely controlled atmosphere of either O2 or N2, additional insight could be gained on the influence of these gaseous media on the mechanism of selective, wavelength-dependent photo-bleaching in MAPbI3. Lastly, a study of the photo-induced charge transfer in a model system of the MAPbI3/TiO2 interface is carried out. Specifically, a contactless technique based on a combination of low-temperature electron spin resonance (ESR) with in situ illumination is used to directly track the photo-carriers at the MAPbI3/TiO2 interface. In particular, this approach shows that the ESR signal intensity of paramagnetic defects in TiO2 (Ti3+-related centers) markedly changes upon illumination of the MAPbI3/TiO2 interface. It is then inferred that the presented novel methodology can be used to monitor the flow of light-excited electrons from MAPbI3 to TiO2. Altogether, in addition to exploring morphological and photo-physical aspects of thin polycrystalline films of two archetypal MHPs, that is MAPbI3 and MAPbBr3, coated onto strongly curved substrates, this PhD dissertation also provides a novel approach for designing MHPs-based devices. In particular, it paves the way for designing sensitive differential gas sensors, which are expected to function under various environmental conditions

Differential Response of the Photoluminescence and Photocurrent of Polycrystalline CH(3)NH(3)PbI(3 )and CH3NH3PbBr3 to the Exposure to Oxygen and Nitrogen

Because of their excellent photoelectric properties, organic-inorganic metal halide perovskites (MHPs), such as methylammonium lead triiodide, CH3NH3PbI3 (MAPbI(3)), and methylammonium lead tribromide, CH3NH3PbBr3 (MAPbBr(3)), are of great interest for the emerging MHPs-based photovoltaic technology. Despite extensive research efforts focused on physicochemical aspects of both MAPbI(3) and MAPbBr(3), the impact of environmental extremes, including various gaseous media, on their photo-electric properties remains poorly understood. In this context, here, the MHPs-based gas-sensing elements were grown by one-step solution process on the outer surface of cylindrical in shape quartz substrates with diameters varying in the range of 80-1100 mu m. The elongated cylinder-shaped geometry and high surface-to-volume ratios of the thus-prepared deposits revealed advantageous for designing miniature, light-transparent gas-flow chambers and made it possible to investigate the photoluminescence (PL) and photocurrent (PC) responses of both MHPs exposed to the precisely controlled recurrent flow of either O-2 or N-2. In addition, we could also collect the PL responses for the deposits of MAPbI(3 )and MAPbBr(3), positioned side-by-side close to each other and therefore simultaneously exposed to identical environmental conditions. Specifically, we found that under exposure to O-2 the PL responses of MAPbI(3) and MAPbBr(3 )were markedly opposite; i.e., the PL decreased for MAPbI(3), whereas it increased for MAPbBr(3). In contrast, under the exposure to N-2, the PL of MAPbI(3 )increased, while it decreased for MAPbBr(3). A considerably differential behavior was also found for the PC responses. In particular, under recurrent exposures to both gaseous media, the PL and PC responses of MAPbBr(3) correlated, whereas for MAPbI(3) they anticorrelated. In conclusion, the distinctly opposite PL and PC responses of polycrystalline deposits of MAPbI(3) and MAPbBr(3 )to O-2 and N-2 reported herein point to markedly contrasting properties of the surface carrier traps and defects for these two MHPs. This study also evidences that a side-by-side arrangement of elongated cylindrically shaped substrates coated with two different MHPs, due to their differential responses to exposure to O-2 or N-2, can function as a simple differential gas detector

Effect of Thermal Cycling on the Structural Evolution of Methylammonium Lead Iodide Monitored around the Phase Transition Temperatures

Optoelectronic devices and solar cells based on organometallic hybrid perovskites have to operate over a broad temperature range, which may contain their structural phase transitions. For instance, the temperature of 330 K, associated with the tetragonal-cubic transformation, may be crossed every day during the operation of solar cells. Therefore, the analysis of thermal cycling effects on structural and electronic properties is of significant importance. This issue is addressed in the case of methylammonium lead iodide (CH3NH3PbI3) across both structural phase transitions (at 160 and 330 K). In situ synchrotron radiation X-ray diffraction (XRD) data recorded between 140 and 180 K show the emergence of a boundary phase between the orthorhombic and tetragonal phases, which becomes more abundant with successive thermal cycles. At high temperatures, around 330 K, an incommensurately modulated tetragonal phase is formed upon repeated crossings of the phase boundary between tetragonal and cubic phases. These alterations, which indicate a gradual evolution of the material under operating conditions of photovoltaic devices, are further documented by electrical resistivity and heat capacity measurements

Light-induced charge transfer at the CH3NH3PbI3/TiO2 interface-a low-temperature photo-electron paramagnetic resonance assay

The performance of organic-inorganic metal halide perovskites-based (MHPs) photovoltaic devices critically depends on the design and material properties of the interface between the light-harvesting MHP layer and the electron transport layer (ETL). Therefore, the detailed insight into the transfer mechanisms of photogenerated carriers at the ETL/MHP interface is of utmost importance. Owing to its high charge mobilities and well-matched band structure with MHPs, titanium dioxide (TiO2) has emerged as the most widely used ETL material in MHPs-based photovoltaic devices. Here, we report a contactless method to directly track the photo-carriers at the ETL/MHP interface using the technique of low-temperature electron paramagnetic resonance (EPR) in combination with in situ illuminations (Photo-EPR). Specifically, we focus on a model nanohybrid material consisting of TiO2-based nanowires (TiO(2)NWs) dispersed in the polycrystalline methylammonium lead triiodide (MAPbI(3)) matrix. Our approach is based on observation of the light-induced decrease in intensity of the EPR signal of paramagnetic Ti3+ (S=1/2) in non-stoichiometric TiO(2)NWs. We associate the diminishment of the EPR signal with the photo-excited electrons that cross the ETL/MHP interface and contribute to the conversion of Ti3+ states to EPR-silent Ti2+ states. Overall, we infer that the technique of low-temperature Photo-EPR is an effective strategy to study the transfer mechanisms of photogenerated carriers at the ETL/MHP interface in MAPbI(3)-based photovoltaic and photoelectronic systems

Quantum spin-liquid states in an organic magnetic layer and molecular rotor hybrid

The exotic properties of quantum spin liquids (QSLs) have continually been of interest since Anderson's 1973 ground-breaking idea. Geometrical frustration, quantum fluctuations, and low dimensionality are the most often evoked material's characteristics that favor the long-range fluctuating spin state without freezing into an ordered magnet or a spin glass at low temperatures. Among the few known QSL candidates, organic crystals have the advantage of having rich chemistry capable of finely tuning their microscopic parameters. Here, we demonstrate the emergence of a QSL state in [EDT-TTF-CONH2](2)(+)[BABCO(-)] (EDT-BCO), where the EDT molecules with spin-1/2 on a triangular lattice form layers which are separated by a sublattice of BCO molecular rotors. By several magnetic measurements, we show that the subtle random potential of frozen BCO Brownian rotors suppresses magnetic order down to the lowest temperatures. Our study identifies the relevance of disorder in the stabilization of QSLs