Search

The aim of this study is to investigate the feasibility of manufacturing thin real-time relative dosimeters for clinical radiotherapy (RT) with potential applications for transmission monitoring in vivo dosimetry and pre-treatment dose verifications. Thin (≈1 μm) layers of a high sensitivity, wide bandgap semiconductor, the inorganic perovskite CsPbCl3, have been grown for the first time by magnetron sputtering on plastic substrates equipped with electrode arrays. Prototype devices have been tested in real-time configuration to evaluate the dose delivered by a 6 MV photon beam from a linear accelerator. Linearity of the charge with the dose has been verified over three order of magnitudes, linearity of the current signal with the dose rate has been also successfully tested in the range 0.5-4.3 Gy/min. The combination of high sensitivity per unit volume and wide bandgap provides high signal-to-noise ratios, up to 70, even at moderate applied voltages. The Schottky diode configuration allows the detector to operate without bias voltage (null bias).The blocking-barrier structure allows to confine the active volume within sub-millimetric sizes, a quite attractive feature in view to increase granularity and achieve the high spatial resolutions required in modern RT techniques. All the above-mentioned features indeed pave the way to a novel generation of flexible, transmission, real time dosimeters for clinical radiotherapy.

Introduction: This paper deals with the class of versatile semiconducting materials called perovskites, which have been deposited for the first time on flexible substrates and then tested for radiation detection monitoring applications.Methods: Lead halide inorganic perovskite, CsPbCl3, 0.4–1 μm-thick films have been grown on plastic flexible substrates equipped with interdigitated electrodes (IDEs) by magnetron sputtering at room temperature.Results: First measurements in realtime configuration are reported for a 1–µm thick prototype under proton beams with energy in the range 100–228 MeV and 1–10 nA extraction currents, of interest for protontherapy applications.Discussion: Experimental results evidence good performances of our sample as a real-time monitoring device. Current stability under UV and proton beam exposure has been tested in the range 0.1–120 s, as well as reproducibility under multiple exposures. The measured current signal proved to be linearly dependent on the extraction currents at a given proton energy. Linearity of the current signal of the device with proton fluxes was also proved within two order of magnitude range, about 107–109 p/s. These promising results, when coupled with easyness of fabrication, low processing costs and high versatility of electrode configurations, all features characterizing the manufacturing process, put into evidence lead halide perovskites as promising candidates for real-time radiation detection in protontherapy.

Abstract Inorganic metal halide perovskites are relevant semiconductors for optoelectronic devices. The successful deposition of thin films of CsPbBr3 and CsPbCl3 has recently been obtained by Radio-Frequency magnetron sputtering. In this work we compare the morphological, structural and optical characteristics of the two materials obtained with this deposition technique. A detailed photoluminescence (PL) spectroscopy study of the as-grown samples was conducted at the macro and micro scale in a wide temperature range (10-300 K) to fully characterize the PL on sample areas of square centimeters, to assess the origin of the inhomogeneous broadening and to quantify the PL quantum yield quenching. Our results prove that this technique allows for the realization of high quality nanometric films with controlled thickness of relevance for optoelectronic applications.

Halide perovskites are a novel class of semiconductors that have attracted great interest in recent decades due to their peculiar properties of interest for optoelectronics. In fact, their use ranges from the field of sensors and light emitters to ionizing radiation detectors. Since 2015, ionizing radiation detectors exploiting perovskite films as active media have been developed. Recently, it has also been demonstrated that such devices can be suitable for medical and diagnostic applications. This review collects most of the recent and innovative publications regarding solid-state devices for the detection of X-rays, neutrons, and protons based on perovskite thin and thick films in order to show that this type of material can be used to design a new generation of devices and sensors. Thin and thick films of halide perovskites are indeed excellent candidates for low-cost and large-area device applications, where the film morphology allows the implementation on flexible devices, which is a cutting-edge topic in the sensor sector.

The response of resistive In2O3−x sensing devices was investigated as a function of the NO2 concentration in different operative conditions. Sensing layers are 150 nm thick films manufactured by oxygen-free room temperature magnetron sputtering deposition. This technique allows for a facile and fast manufacturing process, at same time providing advantages in terms of gas sensing performances. The oxygen deficiency during growth provides high densities of oxygen vacancies, both on the surface, where they are favoring NO2 absorption reactions, and in the bulk, where they act as donors. This n-type doping allows for conveniently lowering the thin film resistivity, thus avoiding the sophisticated electronic readout required in the case of very high resistance sensing layers. The semiconductor layer was characterized in terms of morphology, composition and electronic properties. The sensor baseline resistance is in the order of kilohms and exhibits remarkable performances with respect to gas sensitivity. The sensor response to NO2 was studied experimentally both in oxygen-rich and oxygen-free atmospheres for different NO2 concentrations and working temperatures. Experimental tests revealed a response of 32%/ppm at 10 ppm NO2 and response times of approximately 2 min at an optimal working temperature of 200 °C. The obtained performance is in line with the requirements of a realistic application scenario, such as in plant condition monitoring.

Due to their high optical efficiency, low-cost fabrication and wide variety in composition and bandgap, halide perovskites are recognized nowadays as real contenders for the development of the next generation of optoelectronic devices, which, among others, often require high quality over large areas which is readily attainable by vacuum deposition. Here, we report the amplified spontaneous emission (ASE) properties of two CsPbBr3 films obtained by single-step RF-magnetron sputtering from a target containing precursors with variable compositions. Both the samples show ASE over a broad range of temperatures from 10 K up to 270 K. The ASE threshold results strongly temperature dependent, with the best performance occurring at about 50 K (down to 100 µJ/cm2), whereas at higher temperatures, there is evidence of thermally induced optical quenching. The observed temperature dependence is consistent with exciton detrapping up to about 50 K. At higher temperatures, progressive free exciton dissociation favors higher carrier mobility and increases trapping at defect states with consequent emission reduction and increased thresholds. The reported results open the way for effective large-area, high quality, organic solution-free deposited perovskite thin films for optoelectronic applications, with a remarkable capability to finely tune their physical properties.

By means of time-resolved photoluminescence (TR-PL) spectroscopy, we present a detailed investigation of the carrier relaxation dynamics in a CsPbBr3 bulk sample and microcrystal ensemble at cryogenic temperature on a picosecond time scale. We provide evidence of a long temperature-dependent cooling rate for the excitons and free carriers population, with an initial cooling time constant of a few tens of picoseconds. A relaxation bottleneck in the thermalization process was found that cannot be explained by the Auger effect or hot phonon population, since we address a very low excitation regime, not commonly investigated in literature, where such processes are not effective. Adding a continuous wave optical bias to the picosecond excitation, we probed the photoinduced PL decrease of the localized states and the photoinduced PL increase of the population in the high energy states. A long recovery time from the photoinduced PL decrease was found for localized states and quite significant differences were detected, depending on the resonance/off resonance bias used in the experiment.

Large-area CsPbCl3 films in the range 0.1–1.5 μm have been grown by radio frequency (RF)-magnetron sputtering on glass substrates by means of a one-step procedure. Three structural phase transitions have been detected, which are associated with hysteresis behavior in the electrical current when measured as a function of temperature in the range 295–330 K. Similarly, photoluminescence (PL) experiments in the same temperature range bring evidence of a non-monotonic shift of the PL peak. Detailed electrical characterizations evidenced how phase transitions are not influencing detrimentally the electrical transport properties of the films. In particular, the activation energy (0.6–0.8 eV) extracted from the temperature-dependent film resistivity does not appear to be correlated with phase changes. A non-linear trend of the photoconductivity response as a function of a ultra violet (UV) 365 nm light emitting diode (LED) power has been interpreted considering the presence of an exponential tail of intragap defects. Thermally stimulated currents after exposure with the same LED measured from room temperature up to 370 K showed no evidence of trapping effects due to intragap states on the electrical transport properties at room temperature of the films. As a consequence, measured photocurrents at room temperature appear to be well reproducible and stable in time, which are attractive features for possible future applications in photodetection.

The role of structural and dynamical disorder in semiconductors is a topic of fundamental relevance because of its contribution to the spectral line shape of the photoluminescence, and it plays a major role in ruling the carrier transport properties at the band edge. In this regard, a class of semiconductors, i.e., halide perovskites, deeply investigated in the last decade, shows a peculiar degree of disorder, which has only been recently under investigation. The interest to study disorder in halide perovskites is related to the large set of innovative applications of this class of materials, spanning from energy harvesting to high brilliance incoherent and coherent light emitters. In this perspective, we show that quantitative information on the disorder in halide perovskites can be extracted by deep analysis of the photoluminescence in different experimental conditions. Our study, conducted on a large set of samples of a metal halide perovskite, CsPbBr 3 , prepared with various synthesis/deposition methods, clarifies the relative weight of the static and dynamic contributions. A comparison with theoretical predictions is provided, gaining insights into the exciton/carrier–phonon interaction in metal halide perovskites. [ABSTRACT FROM AUTHOR]

Inorganic CsPbBr3 perovskite devices have been manufactured and tested as dosimeters under both conventional and Intensity Modulated Radiotherapy (IMRT) X-ray beams. Samples showed a very good linear dependence of the collected charge/current on dose/dose rates in the range of 0.1–5.0 Gy/0.1–4.0 Gy/min of interest for clinical applications. A device sensitivity of about 70 nC/Gy mm3 compares favorably with other solid-state dosimeters. The first verification of an IMRT dose profile of a prostate cancer treatment, performed by moving the perovskite device on a 10 cm-long profile with a 0.5 mm pitch, showed agreement within 5% with the dose distribution required by the treatment planning system.

Caesium lead halide perovskites were recently demonstrated to be a relevant class of semiconductors for photonics and optoelectronics. Unlike CsPbBr3 and CsPbI3, the realization of high-quality thin films of CsPbCl3, particularly interesting for highly efficient white LEDs when coupled to converting phosphors, is still a very demanding task. In this work we report the first successful deposition of nanocrystalline CsPbCl3 thin films (70–150 nm) by radio frequency magnetron sputtering on large-area substrates. We present a detailed investigation of the optical properties by high resolution photoluminescence (PL) spectroscopy, resolved in time and space in the range 10–300 K, providing quantitative information concerning carriers and excitons recombination dynamics. The PL is characterized by a limited inhomogeneous broadening (~15 meV at 10 K) and its origin is discussed from detailed analysis with investigations at the micro-scale. The samples, obtained without any post-growth treatment, show a homogeneous PL emission in spectrum and intensity on large sample areas (several cm2). Temperature dependent and time-resolved PL spectra elucidate the role of carrier trapping in determining the PL quenching up to room temperature. Our results open the route for the realization of large-area inorganic halide perovskite films for photonic and optoelectronic devices.

We studied electrically active defects in CsPbBr3 polycrystalline films and single crystals samples using the thermally stimulated currents (TSC) technique in the temperature range 100–400 K. Below room temperature, both polycrystalline and single-crystals TSC emission is composed by a quasi-continuum of energy levels in the range 0.1–0.3 eV, and capture cross sections ~10−21 cm2. Above room temperature, TSC analysis reveals the presence of defect states in the range 0.40–0.52 eV only in polycrystalline samples, whereas these intermediate energy states are absent in TSC detected in single crystals. In polycrystalline films, the occupancy changes of an energy level at 0.45 eV strongly influences the room temperature photoconductivity, giving rise to slow transients due to defect passivation. In single-crystals, where intermediate energy states are absent, the photoconductivity response during illumination is almost stable and characterized by fast rise/decay times, a promising result for future applications of this material in photodetection and dosimetry.

Successful deposition of CsPbX3 (X = Br, Cl) thin films (50-500 nm) on several kind of substrates has been realized by Radio-Frequency Magnetron Sputtering. The technique allows for high homogeneity of the samples on large areas (several cm2) not only in terms of morphology but also referring to the optical properties. In particular, high resolution (in space, spectrum and time) photoluminescence studies in a wide temperature range (10-300 K) reveal that the low inhomogeneous broadening comes from a submicron size disorder while no significant contribution arises from a micrometric or even larger disorder. Given the relevance of inorganic halide perovskites for innovative optoelectronic devices, our results prove the scalability of this technique. Moreover, the successful deposition on several different substrates open the route for an easy integration in multi-layered structures.

The present work reports the application of RF-magnetron sputtering technique to realize CsPbBr 3 70 nm thick films on glass substrate by means of a one-step procedure. The obtained films show highly uniform surface morphology and homogeneous thickness as evidenced by AFM and SEM investigations. XRD measurements demonstrate the presence of two phases: a dominant orthorhombic CsPbBr 3 and a subordinate CsPb 2 Br 5 . Finally, XPS data reveals surface bromine depletion respect to the stoichiometrical CsPbBr 3 composition, nevertheless photoluminescence spectroscopy results confirm the formation of a highly luminescent film. These preliminary results demonstrate that our approach could be of great relevance for easy fabrication of large area perovskite thin films. Future developments, based on this approach, may include the realization of multijunction solar cells and multicolor light emitting devices.

Halide perovskites are extremely interesting semiconductors for innovation in optoelectronics and photovoltaics. In particular, they are efficient emitters of both incoherent and coherent light and, therefore, of interest as active materials in lasers, light amplification systems (resonators and waveguides), and other photonic devices. Here, we present a set of experimental results concerning nonlinear effects in the radiative emission of CsPbBr3 films deposited by spin-coating on a silicon substrate and on metasurfaces realized by microspheres having a core of SiO2 and a shell of TiO2 (T-Rex). We evidence the presence of amplified spontaneous emission which, depending on the sample structure, shows different behavior as a function of the excitation power. In particular, we distinguish between two processes: light amplification by randomly arranged emitters and amplification by a quite ordered distribution of nanocrystals around a resonator. [ABSTRACT FROM AUTHOR]

CsPbCl3 perovskite is attracting increasing interest in ultraviolet (UV) detection due to its optical band gap and superior intrinsic optoelectronic properties. In this study, a novel one-step magnetron sputtering technique was applied for fabricating CsPbCl3 polycrystalline films on flexible plastic substrates with interdigitated contacts. The photoconductive response of 500 nm and 1 µm thick films to pulsed ultraviolet (UV) light in the 0.1–100 Hz frequency range and intensity of 10–500 W/m2 was tested at room temperature. The experimental results demonstrated the good performances of the CsPbCl3 films in terms of signal stability, fast response to transient signal, detectivity, light dynamic range, and dark current noise for the photodetection of pulsed UV light. [ABSTRACT FROM AUTHOR]

Intrinsic defects in CsPbBr3 microcrystalline films have been studied using thermally stimulated current (TSC) technique in a wide temperature range (100⁻400 K). Below room temperature, TSC emission is composed by a set of several energy levels, in the range 0.11⁻0.27 eV, suggesting a quasi-continuum distribution of states with almost constant density. Above room temperature, up to 400 K, the temperature range of interest for solar cells, both dark current and photocurrent, are mainly dominated by energy levels in the range 0.40⁻0.45 eV. Even if measured trap densities are high, in the range 1013⁻1016 cm−3, the very small capture cross-sections, about 10−26 m2, agree with the high defect tolerance characterizing this material.