Radiation Hardness and Defects Activity in PEA2PbBr4 Single Crystals

Metal halide perovskites (MHPs) are low-temperature processable hybrid semiconductor materials with exceptional performances that are revolutionizing the field of optoelectronic devices. Despite their great potential, commercial deployment is hindered by MHPs lack of stability and durability, mainly attributed to ions migration and chemical interactions with the device electrodes. To address these issues, 2D layered MHPs have been investigated as possible device interlayers or active material substitutes to reduce ion migration and improve stability. Here we consider the 2D perovskite PEA2PbBr4 that was recently discussed as very promising candidate for X-ray direct detection. While the increased resilience of PEA2PbBr4 detectors have already been reported, the physical mechanisms responsible for such improvement compared to the standard "3D" perovskites are not still fully understood. To unravel the charge transport process in PEA2PbBr4 crystals thought to underly the device better performance, we adapted an investigation technique previously used on highly resistive inorganic semiconductors, called photo induced current transient spectroscopy (PICTS). We demonstrate that PICTS can detect three distinct trap states (T1, T2, and T3) with different activation energies, and that the trap states evolution upon X-ray exposure can explain PEA2PbBr4 superior radiation tolerance and reduced aging effects. Overall, our results provide essential insights into the stability and electrical characteristics of 2D perovskites and their potential application as reliable and direct X-ray detectors

Nanocrack-induced leakage current in AlInN/AlN/GaN

Here we report on the study of nano-crack formation in Al1−xInxN/AlN/GaN heterostructures, on its association with composition fluctuation and on its local electrical properties. It is shown here that indium segregation at nano-cracks and threading dislocations originating from the non-pseudomorphic AlN interlayer could be the cause of the high reverse-bias gate leakage current of Ni/Au Schottky contacts on Al1−xInxN/AlN/GaN heterostructures and significantly affects the contact rectifying behavior. Segregation of indium around crack tips in Al1−xInxN acting as conductive paths was assessed with conductive atomic force microscopy

Clinical relevance of an objective - limit of detection - limit of quantification - based flow cytometry approach for measurable residual disease assessment in acute myeloid leukemia. A post-hoc analysis of the GIMEMA AML1310 trial

Using a multiparametric flow cytometry (MFC) assay, we assessed the predictive power of a threshold calculated applying the criteria of limit of detection (LOD) and limit of quantitation (LOQ) in adult patients affected with Acute Myeloid Leukemia (AML). This was a post-hoc analysis of 261 patients enrolled in the GIMEMA AML1310 prospective trial. According to the protocol design, using the predefined MRD threshold of 0.035% bone marrow residual leukemic cell (RLC) calculated on mononuclear cells, 154 (59%) were negative (MRD<0.035%) and 107 (41%) were positive (MRD≥0.035%). Using LOD and LOQ, we selected the following categories of patients: 1) LODneg if RLC were below LOD (74; 28.4%); 2) LODpos-LOQneg if RLC were between LOD and LOQ (43; 16.5%); and 3) LOQpos if RLC were above LOQ (144; 54.4%). Two-year overall survival (OS) of these 3 categories was 75.4% vs. 79.8% vs. 66.4%, respectively (p=0.1197). Due to superimposable outcome, LODneg and LODpos-LOQneg categories were combined. Two-year OS of LODneg/LODpos- LOQneg patients was 77.0% versus 66.4% of LOQpos individuals (P=0.043). Such a figure was challenged in multivariate analysis (p=0.048, HR 0.628, 95% CI 0.396-0.997) that confirmed the independent role of LOD-LOQ approach in influencing OS. In the AML1310 protocol, using the threshold of 0.035%, 2-year OS of MRD<0.035% and MRD≥0.035% patients was 74.5% vs. 66.4%, respectively (p=0.3521). In conclusion, the use of LOD-LOQ method results in a more sensitive detection of MRD that, in turn, translates in a more accurate recognition of patients with different outcome

Use of Measurable Residual Disease to Evolve Transplant Policy in Acute Myeloid Leukemia: A 20-Year Monocentric Observation

Measurable residual disease (MRD) is increasingly employed as a biomarker of quality of complete remission (CR) in intensively treated acute myeloid leukemia (AML) patients. We evaluated if a MRD-driven transplant policy improved outcome as compared to a policy solely relying on a familiar donor availability. High-risk patients (adverse karyotype, FLT3-ITD) received allogeneic hematopoietic cell transplant (alloHCT) whereas for intermediate and low risk ones (CBF-AML and NPM1-mutated), alloHCT or autologous SCT was delivered depending on the post-consolidation measurable residual disease (MRD) status, as assessed by flow cytometry. For comparison, we analyzed a matched historical cohort of patients in whom alloHCT was delivered based on the sole availability of a matched sibling donor. Ten-years overall and disease-free survival were longer in the MRD-driven cohort as compared to the historical cohort (47.7% vs. 28.7%, p = 0.012 and 42.0% vs. 19.5%, p = 0.0003). The favorable impact of this MRD-driven strategy was evident for the intermediate-risk category, particularly for MRD positive patients. In the low-risk category, the significantly lower CIR of the MRD-driven cohort did not translate into a survival advantage. In conclusion, a MRD-driven transplant allocation may play a better role than the one based on the simple donor availability. This approach determines a superior outcome of intermediate-risk patients whereat in low-risk ones a careful evaluation is needed for transplant allocation

Conferenze divulgative presso scuole/Enti nell'ambito del Progetto Lauree Scientifiche

Le sfide dei Nuovi Materiali Quali e quante sono le applicazioni dei nuovi materiali? Solo per citare alcuni esempi: Lampadine a pellicola. Pellicole flessibili saranno in uso prima nei display dei telefonini ed entreranno presto anche nelle case, in sostituzione delle normali lampadine. Energia solare. La quantità di energia che arriva dal sole è circa 10000 volte il consumo globale di energia. Come utilizzare al meglio questa enorme riserva energetica? Quali saranno i materiali che miglioreranno l’efficienza e diminuiranno i costi dell’energia solare fotovoltaica? Nanoelettronica. L’attuale microelettronica è in crisi... come potremo “aiutarla”? In che modo la ricerca sta cercando di risolvere i problemi relativi all’eccessiva miniaturizzazione dei dispositivi elettronici

Surface and Defect States in Semiconductors Investigated by Surface PhotovoltageDefects in Semiconductors

The aim of this chapter is a throughout description and discussion of surface photovoltage spectroscopy. The basic physical principles, experimental details, and relevant results of the method are described, and the capability of the method to extract material properties like optical band gap and defect-related states is discussed. The method presents several advantages, as it allows for the identification of conduction versus valence band nature of the defect-related transitions and the defect level positions within the band gap. Moreover, it allows for the detection of relatively low densities of surface defects as well as their cross-sections. The application of the method to different materials and structures is discussed, ranging from bulk semiconductors to low-dimensional systems, to nanostructures

Surface photovoltage spectroscopy characterization of Al1-xInxN/AlN/GaN heterostructures

We report on MOCVD grown Al1-xInxN/AlN/GaN heterostructures with different AlN (interlayer) thicknesses, investigated by Surface Photovoltage Spectroscopy. The different contributions to SPV spectra from all the layers present within the structure have been analyzed. Below the GaN band gap SPV analysis has been performed, and the observed peaks related to red, yellow and green defect states in GaN. The density of the two dimensional electron gas (2DEG) forming at the interface has been measured. A band gap shift has been detected and its dependence on the 2DEG electron density at the AlN/GaN interface has been analyzed on the basis of the Moss Burstein and renormalization effects

Electrical Transport and 2DEG Properties Evaluation in InAlN/AlN/ GaN Heterostructures

In0.14 Al0.86N/AlN/GaN heterostructures with different AlN interlayer thicknesses (0-7.5nm) and different barrier layer thicknesses have been investigated by Current-Voltage (I-V) characteristics with Schottky contacts in a planar back-to-back configuration at 300K. Changes in the slope of I-V characteristic have been observed for increasing bias and attributed to the onset of electrical conduction at the AlN/GaN interface, where the two-dimensional electrons gas (2DEG) is located. A new model has been proposed to extract the 2DEG properties from the room temperature I-V measurements. By accurate modelling of the heterostructure and by using the 1-D Schrödinger Poisson solver, the characteristics of the two-dimensional electrons gas (2DEG) forming at the AlN/GaN interface have been calculated. By comparing I-V and Hall Effect results, we assessed the reliability of common I-V analyses in the determination of the major transport properties of the 2DEG. Capacitance-Voltage measurements are under study for further analysis and also to compare the extracted results from proposed model and other methods