The Impact of X-Ray Radiation on Chemical and Optical Properties of Triple-Cation Lead Halide Perovskite: from the Surface to the Bulk

Understanding the effects of X-rays on halide perovskite thin films is critical for accurate and reliable characterization of this class of materials, as well as their use in detection systems. In this study, advanced optical imaging techniques are employed, both spectrally and temporally resolved, coupled with chemical characterizations to obtain a comprehensive picture of the degradation mechanism occurring in the material during photoemission spectroscopy measurements. Two main degradation pathways are identified through the use of local correlative physico-chemical analysis. The first one, at low X-Ray fluence, shows minor changes of the surface chemistry and composition associated with the formation of electronic defects. Moreover, a second degradation route occurring at higher fluence leads to the evaporation of the organic cations and the formation of an iodine-poor perovskite. Based on the local variation of the optoelectronic properties, a kinetic model describing the different mechanisms is proposed. These findings provide valuable insight on the impact of X-rays on the perovskite layers during investigations using X-ray based techniques. More generally, a deep understanding of the interaction mechanism of X-rays with perovskite thin films is essential for the development of perovskite-based X-ray detectors and solar for space applications.     

Customizable and Reconfigurable Surface Properties of Printed Micro-objects by 3D Direct Laser Writing via Nitroxide Mediated Photopolymerization

Photoactivated Reversible Deactivation Radical Polymerization (RDRP) technologies have emerged very recently in the field of 3D printing systems especially at the macroscale in vat-photopolymerization-based processes such as digital light processing (DLP). Contrary to conventional free radical photopolymerization, photoRDRP in 3D printing leads to 3D objects with living character and thus confers them the unique ability to be post-modified after fabrication. While 3D direct laser writing (3D DLW) by two photon polymerization has become a standard for fabrication of complex 3D micro-objects, the use of RDRP and its associated benefits has so far been under-investigated at that scale. Herein, a photoresist suitable for 3D DLW based on nitroxide mediated photopolymerization (NMP2) is developed. The photopolymerization efficiency for fabrication of micro-structures and their subsequent post-modification are investigated regarding the laser power and the wavelength of excitation. Moreover, highly tunable, precise, and successive surface patterning of 2D and 3D multi-material microstructures are demonstrated thanks to the spatial and temporal control offered by the photo-induced post-modification. This work highlights new directions to be explored in order to accelerate the adoption of RDRP in 3D printing based on photopolymerization.     

Nanoliter Liquid Packaging in a Bioresorbable Microsystem by Additive Manufacturing and its Application as a Controlled Drug Delivery Device

Precise packaging of nanoliter amounts of liquid in a microsystem is important for many biomedical applications. However, existing liquid encapsulation technologies have limitations in terms of liquid waste, evaporation, trapped bubbles, and liquid degradation. In this study, multiple additive manufacturing techniques for nanoliter liquid packaging in bioresorbable microsystems is used. Two-photon photolithography is used for bioresorbable reservoir fabrication, while inkjet printing (IJP) is used for precise nanoliter liquid packaging. Dual IJP allows for micro-reservoirs to be filled with precise amounts of drug solution and subsequently and rapidly sealed with a layer of lipids mixed with Fe₃O₄ nanoparticles. Combining these two printing techniques can overcome the previous limitations of liquid encapsulation technologies. To demonstrate the relevance of this technique, a wirelessly activated, bioresorbable multi-reservoir microcapsule that can be used for controlled drug delivery is presented. The microcapsules and their content are shown to be stable during fabrication, storage, and operation. Multiple cargo release events are triggered independently by the local melting of the sealing layer, resulting from magnetically induced Fe₃O₄ nanoparticle heating. The operation of the capsule is demonstrated in tissue phantoms and in vitro cell cultures.     

Synthesis of 6‐Substituted 7‐Bomoazabicyclo[2.2.1]heptanes via Nucleophilic Addition to 3‐Bromo‐1‐azoniatricyclo[2.2.1.0]‐heptane Bromide

We describe herein an efficient method for the preparation of a functionalised bicyclic framework (6‐substituted 7‐bromo‐aza‐bicyclo[2.2.1]heptane) through the selective opening of the aziridium 2 with organocuprates in up to 90% yield. These interesting chiral building blocks were then utilised as novel ligands in the rearrangement of epoxides to afford chiral allylic alcohols.     

Formation and Etching of the Insulating Sr-Rich V5+ Phase at the Metallic SrVO3 Surface Revealed by Operando XAS Spectroscopy Characterizations

In the search of low cost and more efficient electronic devices, here the properties of SrVO₃ transparent conductor oxide (TCO) thin film are investigated, both visible-range optically transparent and highly conductive, it stands as a promising candidate to substitute the standard indium-tin-oxide (ITO) in applications. Its surface stability under water (both liquid and vapor) and other gaseous atmospheres is especially addressed. Through the use of spectroscopy characterizations, X-ray photoemission and operando X-ray absorption measurements, the formation of a thin Sr-rich V⁵⁺ layer located at the surface of the polycrystalline SrVO₃ film with aging is observed, and for the first time how it can be removed from the surface by solvating in water atmosphere. The surface recovery is associated to an etching process, here spectroscopically characterized in operando conditions, allowing to follow the stoichiometric modification under reaction. Once exposed in oxygen atmosphere, the Sr-rich V⁵⁺ layer forms again. The findings improve the understanding of aging effects in perovskite oxides, allowing for the development of functionalized films in which it is possible to control or to avoid an insulating surface layer. This constitutes an important step towards the large-scale use of V-based TCOs, with possible implementations in oxide-based electronics.