Pokročilé instrumentace a metody pro charakterizace materiálů

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Investigating plasma morphology at material boundaries under varying ambient pressures
(Elsevier, 2025-12-01) Mohan, Megha; Prochazka, David; You, Yi; Riedel, Jens; Gornushkin, Igor; Ročňáková, Ivana; Papula, Martin; Pořízka, Pavel; Kaiser, Jozef
Laser-Induced Breakdown Spectroscopy (LIBS) is a widely used technique for elemental analysis. The analysis of the obtained LIBS spectra generally assumes plasma homogeneity. However, using focused laser beams for interrogation, LIBS probes materials on the microscale and is, thus, prone to artefacts from sample heterogeneities on the micrometre scale. An ablation at a material boundary of two matrices may result in a significant inhomogeneity in the plasma plume, which can severely impact the accuracy of quantitative analysis. Since this propagation of the surface morphology into the plasma plume is driven by the plasma expansion, its final impact is strongly pressure dependent. This study examines the influence of varying ambient pressures (7-1000 mbar) on plasma morphology, spectral characteristics, and key plasma properties such as electron number density at a well-defined Cu-Sn boundary, in comparison with the results obtained using homogeneous alloys. Several approaches of plasma imaging with bandpass filters, spectroscopy, and Radon transform-based 3D reconstruction were employed to analyse elemental distribution, signal-to-noise (SNR) and signal-to-background (SBR) ratios, as well as electron number densities. The 3D reconstructions revealed a pronounced plasma asymmetry for the ablation at the material boundary, in contrast to the near-axial symmetry observed for the ablation of homogeneous alloys. At lower pressures, this distinct elemental separation in plasma persisted, while higher pressures led to an increased collisional mixing and homogenization. SNR and SBR were consistently lower for ablation at the boundary compared to homogeneous samples. These findings highlight how boundary ablation contributes to plasma inhomogeneities in LIBS analysis of heterogeneous materials and emphasize the need to account for these effects when using LIBS for elemental mapping of fine heterogeneous structures.
On the non-universality of distance metrics in laser-induced breakdown spectroscopy
(The Royal Society of Chemistry, 2025-06-05) Vrábel, Jakub; Képeš, Erik; Nedělník, Pavel; Záděra, Antonín; Pořízka, Pavel; Kaiser, Jozef
The ability to measure similarity between high-dimensional spectra is crucial for numerous data processing tasks in spectroscopy. Many popular machine learning algorithms depend on, or directly implement, a form of similarity or distance metric. Despite its profound influence on algorithm performance and sensitivity to signal fluctuations, the selection of an appropriate metric remains often neglected within the spectroscopic community. This work aims to shed light on the metric selection process in Laser-Induced Breakdown Spectroscopy (LIBS) and study consequences for data analysis and analytical performance in selected applications. We studied six relevant distance metrics: Euclidean, Manhattan, cosine, Siamese, fractional, and mutual information. We assessed their response to changes in sample composition, additive noise, and signal intensity. Our results show specific vulnerabilities of commonly used metrics, such as the Euclidean metric's high sensitivity to additive noise and the cosine metric's sensitivity to spectral shifts. The Siamese metric stood out in the majority of studied cases and outperformed others in a direct comparison within the spectra classification task. This work provides basic guidelines for selecting metrics in various contexts. The methodology is general and can be directly extended to other spectroscopic techniques that possess comparable data properties.
Chlorine determination in cement paste samples using laser-induced breakdown spectroscopy and non-matching matrix calibration samples
(Royal Society of Chemistry, 2025-06-05) Kratochvilová, Lucie; Prochazka, David; Opravil, Tomáš; Pořízka, Pavel; Kaiser, Jozef
This paper deals with determining the chlorine content in cement matrixes using non-matching calibration samples made from microsilica and potassium chloride. We aimed to make easy-to-prepare calibration samples and determine the chlorine content in cement paste samples. To create proper cement paste samples, it is necessary to allow the concrete to mature for 28 days. Also, this methodology enables faster calibration and higher throughput in routine analysis. To suppress the matrix effect, we tested several strategies of signal normalization and then compared the reference (known) and the predicted chlorine content. Best results were obtained when we normalized the intensity of the chlorine line by a parameter proportional to the particle number density which was a priori determined by the intensity of the hydrogen emission line (H alpha) and full width at half-maximum (FWHM). With this parameter, we obtained a high-reliability coefficient for the calibration curve (R2 = 0.99) and the best prediction for total chloride content in cement paste, with a sum of mean squares of the prediction error of 0.22 wt%.
Porous 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 Benjamin
This 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.
Automated 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, Andreas
This 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.

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