Silvia Rizzato

Bismuth ferrite (BiFeO₃, BFO) is a lead-free perovskite that combines robust ferroelectricity and antiferromagnetism at room temperature, making it one of the most extensively studied room-temperature multiferroics for spintronics, sensors, and multifunctional devices. In bulk ceramics, however, Bi volatility, oxygen-vacancy-driven leakage, and parasitic phases complicate synthesis and obscure intrinsic ferroic response. This review critically revisits the fundamental physical properties of bulk BiFeO₃ ceramics by elucidating the relationships between crystal structure, defect chemistry, processing, and ferroic functionalities. Particular emphasis is placed on the evolution of the understanding of the intrinsic ferroelectric, magnetic, dielectric, and magnetoelectric properties of bulk BiFeO₃, highlighting the landmark experimental and theoretical studies that have shaped the current picture of this material. The review further examines A-site (Bi) and B-site (Fe) substitutions and selected co-doping strategies, assessing how they modify structural stability and ferroic behavior. Finally, representative performance benchmarks for undoped and doped bulk ceramics are compared, and the remaining challenges toward achieving reproducible room-temperature magnetoelectric functionality are critically discussed. Overall, this review provides a unified framework linking crystal chemistry, processing methods, microstructure, doping engineering, and ferroic functionalities, offering practical guidelines for the rational design of high-performance BiFeO₃-based bulk ceramics for next-generation multifunctional devices.

Acute skin toxicity after radiation treatments highlights the need for improved dose monitoring and measurement, as the treatment planning system does not accurately estimate skin dose. Wearable radiation detectors may be the solution for most in vivo dosimetry needs, but they require innovative materials. The purpose of this work is to overcome the challenges that limit accurate skin dosimetry by exploring the use of hydrogenated amorphous silicon (a-Si:H) fabricated on a flexible polyimide substrate for direct radiation detection. The a-Si:H detector was fabricated on a 125 μ m polyimide substrate with a thickness of 3.6–10 μ m. The detector’s response to the build-up region of the percentage depth dose (PDD) of the MV photon beam was compared to Geant4 radiation transport simulations and benchmarked to Attix ionization chamber measurements. Angular dependency and surface field factors at the phantom surface were compared to Attix IC. The PDD measurement is within 2% of Geant4’s simulation and the Attix chamber’s response from 150 μ m to 25 mm in a plastic water phantom. All samples showed linear dose responses with 0.37% reproducibility. The a-Si:H device matches the Attix chamber for surface field factor measurements (6–10 MV photon beams, for 5 to 25 cm field sizes). The angular dependence (−60° to +60°) compared to the Attix IC confirms the sensor’s WED of 150 ± 5 µ m. This study demonstrates that a-Si:H sensors on flexible plastic substrates have a potential for accurate surface dose measurements and agree with reference detectors. This thin, flexible detector provides real time measurements and is stable under high radiation doses. The possibility to assemble with ease an array of a-Si:H pixels over large areas with different sizes and shapes, makes this technology attractive for in vivo dosimetry.

The HASPIDE project of INFN exploits hydrogenated amorphous silicon (a-Si:H) as a sensitive material for innovative detectors, mainly focused on dosimetry both for standard and FLASH radiotherapy, but also fo other applications. The detector, deposited on a thin and flexible substrate of polyimide, has been developed with different contacts configurations during past years, giving rise to the necessity to compare them in order to determine which configuration is best, for a specific application. In particular, three types of contacts are under exam in this work: the first one is a classical n-i-p junction, where a thick layer of intrinsic a-Si:H material is sandwiched between n- and p-doped layers of hydrogenated amorphous silicon; the second configuration is a charge-selective contacts device (CSC), where the doped regions are replaced with metal oxides which selectively enhance the mobility of one charge-carrier, blocking the other and the last one is the hybrid type, in which the intrinsic region is coupled with a n-doped layer on the bottom and a hole selective metal oxide on the top. This work aims to give a comparison in the performance of three devices differing only in the contact configuration, in terms of dark current analysis and sensitivity to X-ray beams, so that the characteristics of each one can be analyzed and exploited.

Flexible hydrogenated amorphous silicon (a-Si:H) detectors are attractive candidates for clinical dosimetry, particularly for applications requiring lightweight devices and operation without external bias. In this work, three flexible a-Si:H detector architectures are experimentally compared under clinical photon and electron beams: a conventional n-i-p diode, a charge selective contact (CSC) detector, and a very thin p-i-n diode. All detectors show excellent dose linearity under both irradiation modalities. However, large differences in sensitivity are observed at zero bias, exceeding two orders of magnitude across architectures. The conventional n-i-p device shows a response that is limited by the internal electric field, while CSC and very thin p-i-n detectors achieve sensitivities in the pC/cGy range without applied bias. Electron beams yield higher charge per unit dose than photons, compatible with a larger local energy deposition in the active layer. The results demonstrate that sensitivity in flexible a-Si:H dosimeters is governed by contact design and intrinsic layer thickness rather than by active volume alone. Taken together, the present results suggest that combining charge selective contacts with thinner intrinsic layers may represent a promising strategy to further enhance zero-bias sensitivity. These findings provide clear design guidelines for the development of flexible dosimeters for surface and transmission measurements in advanced radiotherapy.

The INFN HASPIDE project investigates hydrogenated amorphous silicon (a-Si:H) as an innovative detector technology for dosimetry in FLASH radiotherapy. Conventional dosimeters, such as ionization chambers, show non-linear behavior when exposed to ultra-high dose-per-pulse beams used in FLASH radiotherapy, where several Grays are delivered in microsecond pulses. Thanks to its radiation hardness, mechanical flexibility and compatibility with large-area deposition, a-Si:H is a promising material for in-vivo and surface dosimetry. This work presents the response of a thin a-Si:H detector exposed to a high-dose-per-pulse 10 MeV electron beam, together with an analytical model used to describe the single-pulse dynamics and extract quantitative parameters. Measurements were performed at the University of Torino using a modified clinical LINAC operated in Ultra High Dose Rate regime, where the single-pulses satisfy the FLASH criteria. The a-Si:H detector, read out with a TetrAMM picoammeter (100 kHz sampling frequency), resolves individual radiation pulses with high repeatability. Both pulse charge and peak current scale linearly with the applied electric field up to 6 V (2.4 V/μm), beyond which the readout electronics saturates. The analytical model is validated through direct comparison with raw data, showing excellent agreement in extracted pulse parameters.

Plasmonic nanostructures enable strong electromagnetic field confinement, offering significant potential for sensing, spectroscopy, and nanophotonic applications. In this study, we present the design, simulation, fabrication, and experimental validation of triangular gold nanodisk arrays fabricated using colloidal lithography—a scalable and cost-effective technique. Finite Element Method (FEM) simulations reveal that these structures exhibit strong near-field confinement, angle-robust plasmonic resonances (little shift from 0° to 80° incidence) and polarization-independent behavior (due to the high symmetry of the array), with maximum electric field enhancement reaching 310 in a 10 nm dielectric gap. Experimental reflectance measurements confirm the simulated absorptance spectra, demonstrating excellent agreement across various gap thicknesses. Results indicate that thinner gap layers favor stronger field enhancement, while thicker gaps offer sharper resonance dips beneficial for sensing applications. This work highlights the potential of colloidal lithography-fabricated triangular nanodisk arrays as practical platforms for plasmon-enhanced devices. To our knowledge, this is the first demonstration of triangular metal–insulator–metal (MIM) nanodisk arrays fabricated via a scalable colloidal process, achieving performance comparable to e-beam-fabricated structures

Nanoplastics pose significant environmental and public health risks, prompting the need for sensitive, cost-effective, and rapid assays for ecotoxicity assessment. The present work proposes the use of a portable smartphone-based platform to enhance traditional Daphnia magna acute toxicity assays by integrating behavior analysis and heart rate measurements. The aim is to improve sensitivity in detecting toxic effects of nanoplastics. In particular, the study focused on nano-sized carboxylated polystyrene (PS) nanoparticles. Two variability factors that could influence biological effects of nanoplastics, the particle size and the age of the organisms, were considered. Results demonstrated that the application of the proposed integrated approach allowed the detection of early subtle effects such as a significant impact on the heart rate and behavior of Daphnia magna under short-term exposure to PS carboxylated nanoparticles. In particular, a stimulation of heart rate was observed for both neonates and adults either for 40 nm or 200 nm particles after 48 h exposure, presumably attributable to an interference of carboxylated PS NPs with adrenergic-type receptors. Behavioral alterations were detectable for 40 nm particles but not for 200 nm ones consisting of a decrease in velocity and alterations of trajectories. Obtained results demonstrated the suitability of the proposed smartphone platform for friendly and real-time integration of behavioral analysis with physiological outcome measurements during acute exposure of Daphnia magna to nano-sized carboxylated PS NPs, expanding the sensitivity of the traditional acute toxicity tests. It offers a novel, cost-effective, and field-applicable method for environmental monitoring of nanoparticle toxicity and impact.

Radiation damage tests in hydrogenated amorphous silicon (a-Si:H) flexible flux and dose-measuring devices have been performed with a 3 MeV proton beam, to evaluate combined displacement and total ionizing dose damage. The tested devices had two different configurations and thicknesses. The first device was a 2 μm thick n-i-p diode having a 5 mm x 5 mm area. The second device was a 5 μm thick charge selective contact detector having the same area. Both the devices were deposited on a flexible polyimide substrate and were irradiated up to the fluence of 10¹⁶ n_eq/cm². The response to different proton fluxes has been measured before irradiation and after irradiation at 10¹⁶ n_eq/cm² for charge-selective contacts and n-i-p devices. The effect of annealing for partial performance recovery at 100°C for 12 hours was also studied and a final characterization on annealed devices was performed. This test is the first combined displacement and total ionizing dose test on flexible a-Si:H devices.

The development of alternatives to animal models and traditional cell cultures has led to the emergence of organ-on-chip (OoC) systems, which replicate organ functions under both physiological and pathological conditions. These microfluidic platforms simulate key tissue interfaces—such as tissue–air, tissue–liquid, and tissue–tissue interactions—while incorporating biomechanical stimuli to closely resemble in vivo environments. This makes OoC systems particularly suitable for modeling biological barriers such as the skin, the placenta, and the blood–brain barrier, which play essential roles in maintaining homeostasis. This review explores various biological barrier models that can be replicated using the OoC technology, discussing the integration of induced pluripotent stem cells (iPSCs) to advance personalized medicine. Additionally, we examine the methods for assessing barrier formation, including real-time monitoring through integrated sensors, and discuss the advantages and challenges associated with these technologies. The potential of OoC systems in disease modeling, drug discovery, and personalized therapeutic strategies is also highlighted.

Understanding the function of the blood–brain barrier (BBB) in health and disease, as well as improving drug delivery across the BBB, remains a critical priority in neuroscience research. However, current in vitro models of the BBB have become increasingly complex and challenging to implement. In this study, we present a simplified microfluidic BBB model in which human umbilical vein endothelial cells (HUVECs) are cultured as a monolayer along a fibrin gel containing human pericytes and astrocytes. Remarkably, within just three days, the 3D co-culture significantly enhanced barrier formation and upregulated the expression of tight-junction proteins in HUVECs. These findings demonstrate that HUVECs, which have been extensively used for over 50 years to study vascular endothelium due to their ease of isolation and culture, can adapt their phenotype towards that of BBB endothelial cells under appropriate conditions. This microfluidic BBB model offers a valuable tool for drug development and for advancing our understanding of BBB physiology in both health and disease contexts.