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- ItemTowards high loading cesium lead halide nanocomposites for radiation detection(IOP Publishing, 2025-01-01) Král, Jan; Děcká, Kateřina; Zabloudil, Vojtěch; Liška, Petr; Hájek, František; Horák, Michal; Čuba, Václav; Mihóková, Eva; Auffray, EtiennetteCesium lead halide nanocrystals (NCs) and their nanocomposites have attracted a lot of attention in the field of radiation detection thanks to their excellent luminescent properties, especially their potential for fast timing. However, most research on their nanocomposites focuses on low loadings (around 1 wt%) which is insufficient for detecting high-energy X-rays or gamma-rays. There have been only few reports exploring materials with higher loadings but all with limited success in terms of transparency of the final material. In our work, we present nanocomposites of cesium lead halide NCs with loading up to 40 wt%. We employ innovative surface functionalization of the NCs to enhance their dispersion within the matrix, thereby improving the final material transparency. We display the NC dispersion within the matrix using confocal photoluminescence microscopy and we then characterise the radioluminescent properties of nanocomposites of cesium lead bromide (CPB) and cesium lead bromochloride NCs with varying chloride content. To asses their performance as radiation detectors, we measure their timing capabilities under X-rays. Our findings reveal a significant improvement in time resolution under X-rays from previously published 300 ps for CPB polymer nanocomposites to 215 ps. When combined with increased stopping power of high NC content, this advancement holds great promise for practical applications, e.g. in time-of-flight positron emission tomography and computed tomography or high energy physics.
- ItemPorous titanium/hydroxyapatite interpenetrating phase composites with optimal mechanical and biological properties for personalized bone repair(Elsevier, 2025-01-01) Oliver Urrutia, Carolina; Kashimbetova, Adelia; Slámečka, Karel; Casas Luna, Mariano; Matula, Jan; Koledová, Zuzana; Kaiser, Jozef; Čelko, Ladislav; Montufar Jimenez, Edgar BenjaminThis study introduces the first fabrication of porous titanium/hydroxyapatite interpenetrating phase composites through an innovative processing method. The approach combines additive manufacturing of a customized titanium skeleton with the infiltration of an injectable hydroxyapatite foam, followed by in situ foam hardening at physiological temperature. This biomimetic process circumvents ceramic sintering and metal casting, effectively avoiding the formation of secondary phases that can impair mechanical performance. Hydroxyapatite foams, prepared using two foaming agents (polysorbate 80 and gelatine), significantly reinforce the titanium skeleton while preserving the microstructural characteristics essential for osteoinductive properties. The strengthening mechanisms rely on the conformation of the foams to the titanium surface, thereby enabling stable mechanical interlocking and effective interfacial stress transfer. This, combined with the mechanical constriction of phases, enhances damage tolerance and mechanical reliability of the interpenetrating phase composites. In addition, the interpenetrating phase composites feature a network of concave pores with an optimal size for bone repair, support human osteoblast proliferation, and exhibit mechanical properties compatible with bone, offering a promising solution for the efficient and personalized reconstruction of large bone defects. The results demonstrate a significant advancement in composite fabrication, integrating the benefits of additive manufacturing for bone repair with the osteogenic capacity of calcium phosphate ceramics.
- ItemSpatially confined magnetic shape-memory Heuslers: Implications for nanoscale devices(Elsevier, 2025-01-01) Takhsha Ghahfarokhi, Milad; Horký, Michal; Nasi, Lucia; Kosogor, Anna; Trevisi, Giovanna; Casoli, Francesca; Arregi Uribeetxebarria, Jon Ander; Brescia, Rosaria; Uhlíř, Vojtěch; Albertini, FrancaMagnetic shape-memory (MSM) Heuslers are among the most promising materials for thermo-magneto-mechanical applications. However, the knowledge about the martensitic transformation (which is the basis of the multifunctionality in these materials) as a function of size reduction in the submicron scale is still very limited. Here, we aim to bridge this knowledge gap by investigating the behavior of these materials upon nanoscale confinement. We customize a top-down approach by patterning arrays of submicron epitaxial Ni-Mn-Ga structures with lateral sizes down to similar to 70 nm, using a Cr hard mask on MgO(001) substrate. The structures include straight stripes, radial stripes, squares and triangles. The martensitic transformation temperature, sharpness, thermal hysteresis and magnetic characteristics of the material are investigated upon spatial confinement. Transmission electron microscopy techniques including Geometric Phase Analysis (GPA) algorithm, and quantitative theoretical analysis of stress help us to evaluate the martensitic transformation of Ni-Mn-Ga starting from continuous films and down to sub-micron patterns. We show that the size-dependent internal stress relaxation plays a primary role in broadening the martensitic transformation of the material, reducing thermal hysteresis, and pushing the transformation toward higher temperatures in the sub-micron structures. These findings highlight the importance of stress considerations upon incorporation of MSM Heusler materials into nanoscale functional devices.
- ItemAutomated detection of element-specific features in LIBS spectra(ROYAL SOC CHEMISTRY, 2024-11-27) Gajarská, Zuzana; Faruzelová, Anna; Képeš, Erik; Prochazka, David; Pořízka, Pavel; Kaiser, Jozef; Lohninger, Hans; Limbeck, AndreasThis work introduces a novel semi-automatic approach to identify elemental lines in spectra obtained via laser-induced breakdown spectroscopy (LIBS). The algorithm is based on unique spectral fingerprints of individual elements that are configured into comb-like filters. The element-specific filters are then correlated with measured spectra for semi-supervised qualitative analysis of samples. Spectral variations are accommodated by adjusting the micro-parameters of the comb filter. This step ensures accurate results despite minor deviations from the instrument's ideal calibration due to instrumental fluctuations, e.g., drift in spectral calibration or line broadening. Additionally, the algorithm can autonomously detect spectral interference regions, aiding the analyst in verifying spectral lines where such interference may occur. The paper presents a comprehensive overview of the algorithm and discusses the main concepts, parameters, optimization steps, and limitations using Echelle spectra of two standard reference materials with different complexity: borosilicate glass (NIST 1411) and low-alloyed steel (SUS1R). Furthermore, the transferability of the approach to different scenarios and real-life applications is demonstrated using a single-channel Czerny-Turner spectrum of an amalgam filling extracted from a hyperspectral image of a human tooth. A demo of the algorithm is publicly available for non-commercial purposes.
- ItemA Comparative Study of the Impact of La2O3 and La2Zr2O7 Dispersions on Molybdenum Microstructure, Mechanical Properties, and Fracture(SPRINGER, 2024-10-23) Tkachenko, Serhii; Slámečka, Karel; Bednaříková, Vendula; Remešová, Michaela; Gejdoš, Pavel; Ksenzova, Olha; Valášek, Daniel; Dvořák, Karel; Šulák, Ivo; Gálíková, Markéta; Baláž, Matej; Deák, Andréa; Cihlář, Jaroslav; Čelko, LadislavWe report, for the first time, the effect of lanthanum zirconate (La2Zr2O7) particles on the microstructure and mechanical behavior of an experimental molybdenum oxide dispersion-strengthened alloy. The focus was on the preparation of the novel Mo-La2Zr2O7 composite using high-energy ball milling and spark plasma sintering and on the comparison of its microstructural and mechanical properties with pure Mo and Mo-La2O3 ODS alloy counterparts. Mechanical properties were assessed using a Vickers hardness test at room temperature and a three-point flexural test in the temperature range from - 150 to 150 degrees C. The microstructure of the studied materials and their fracture behavior were evaluated using x-ray diffraction, energy-dispersive x-ray spectroscopy, and scanning electron and transmission electron microscopy. The strengthening effect of La2Zr2O7 particles was found to be lower than that of La2O3 particles, resulting in a 30-35% lower yield stress and flexural strength of the Mo-La2Zr2O7 alloy compared to the Mo-La2O3 alloy. The experimental Mo-La2Zr2O7 alloy exhibited low plasticity and no distinct ductile-to-brittle transition temperature (DBTT) in the tested temperature range, unlike pure Mo and the Mo-La2O3 alloy, which had the DBTT of 63 and 1 degrees C, respectively. Fracture occurred mainly in a brittle intergranular manner in the entire testing temperature range, while the counterpart materials showed localized plastic stretching at grain boundaries and within grains at and above the transition region. The observed behavior was primarily related to lower strengthening and brittleness as well as less effective grain boundary purification.