Search

Journal of analytical atomic spectrometry 37(1), 114 - 129 (2022). doi:10.1039/D1JA00271F, Redox processes activated by environmental factors have been identified as the main cause of the chromatic alterations of a number of artists' pigments, including the yellow pigment orpiment (As$_2$S$_3$). Although a general comprehension of the mechanisms has been provided through characterization of degradation compounds of As$_2$S$_3$, experimental evidences to prove how other paint components and how different environmental agents influence the formation pathways of specific secondary compounds are still lacking. Thus, it becomes fundamental to develop a methodological strategy which enable achieving a discrimination among the causes affecting the chemical stability of more heterogenous As$_2$S$_3$-based paints and defining the mechanism through which the alteration establishes and evolves, with the ultimate goal of optimizing the preventive conservation measures of unique masterpieces. In this paper, we propose a comprehensive multi-material and multi-method approach based on the combination of synchrotron radiation X-ray micro-analytical techniques (i.e., X-ray diffraction, X-ray fluorescence and X-ray absorption near edge structure spectroscopy at S K-/Ag L$_3$-/As K-edges) and vibrational micro-spectroscopy methods to unveil the causes and mechanism of darkening of ���fake-gilded��� decorations in tempera paintings, originally consisting of an unusual mixture of A$_2$S$_3$ and metallic silver (Ag$^0$). Such degradation process is a not yet understood phenomenon threatening a series of Old Master paintings, including those by the Italian painters Cimabue and Pietro Lorenzetti. The high specificity, sensitivity and lateral resolution of the employed analytical methods allowed providing first-time evidence for the presence of black acanthite ($��$-Ag$_2$S), mimetite [Pb$_5$(AsO$_4$)$_3$Cl] and syngenite [K$_2$Ca(SO$_4$)$_2$��H$_2$O] as degradation products of the ���fake-gilded��� decorations in the Maest�� by Cimabue (Church of Santa Maria dei Servi, Bologna, Italy). Furthermore, the study of the painting combined with that of tempera paint mock-ups permitted to explore and define the environmental agents and internal factors causing the darkening, by proving that: (i) Ag$^0$ and moisture are key-factors for triggering the transformation of As$_2$S$_3$ to $��$-Ag$_2$S and As-oxides; (ii) S$^2$--ions arising from the degradation of A$_2$S$_3$ are the main responsible for the formation of $��$-Ag$_2$S; (iii) light exposure strengthens the tendency of the paint components towards alteration. Based on our findings, we finally propose a degradation mechanism of As$_2$S$_3$/Ag$^0$-based tempera paints., Published by ChemSoc, Cambridge

Image registration procedure for correlative Nano-Spectroscopy and Nano-Diffraction experiments. Detailed description of the python-based GUI script and validation using different modalities of microscopic imaging. Automated identification of isolated nanoparticles for analysis at selected nano-lab instruments and focused X-ray beamlines., WP15 - Correlative Nano-Spectroscopy and Nano-Diffraction

Protein aggregation is a hallmark of several severe neurodegenerative disorders such as Huntington's, Parkinson's, or Alzheimer's disease. Metal ions play a profound role in protein aggregation and altered metal-ion homeostasis is associated with disease progression. Here we utilize \(\mu\)-X-ray fluorescence imaging in combination with rapid freezing to resolve the elemental distribution of phosphorus, sulfur, potassium, and zinc in huntingtin exon-1-mYFP expressing HeLa cells. Using quantitative XRF analysis, we find a threefold increase in zinc and a 10-fold enrichment of potassium that can be attributed to cellular stress response. While the averaged intracellular ion areal masses are significantly different in aggregate-containing cells, a local intracellular analysis shows no different ion content at the location of intracellular inclusion bodies. The results are compared to corresponding experiments on HeLa cells forming pseudoisocyanine chloride aggregates. As those show similar results, changes in ion concentrations are not exclusively linked to huntingtin exon-1 amyloid formation.

Optics express 30(18), 31519 - 31529 (2022). doi:10.1364/OE.454863, Diffraction-limited hard X-ray optics are key components for high-resolution microscopy, in particular for upcoming synchrotron radiation sources with ultra-low emittance. Diffractive optics like multilayer Laue lenses (MLL) have the potential to reach unprecedented numerical apertures (NA) when used in a crossed geometry of two one-dimensionally focusing lenses. However, minuscule fluctuations in the manufacturing process and technical limitations for high NA X-ray lenses can prevent a diffraction-limited performance. We present a method to overcome these challenges with a tailor-made refractive phase plate. With at-wavelength metrology and a rapid prototyping approach we demonstrate aberration correction for a crossed pair of MLL, improving the Strehl ratio from 0.41(2) to 0.81(4) at a numerical aperture of 3.3 × 10$^{−3}$. This highly adaptable aberration-correction scheme provides an important tool for diffraction-limited hard X-ray focusing., Published by Soc., Washington, DC

Metallomics 14(11), mfac069 (2022). doi:10.1093/mtomcs/mfac069, Visualizing the endogenous distribution of elements within plant organs affords key insights in the regulation of trace elements in plants. Hyperaccumulators have extreme metal(loid) concentrations in their tissues, which make them useful models for studying metal(loid) homeostasis in plants. X-ray-based methods allow for the nondestructive analysis of most macro and trace elements with low limits of detection. However, observing the internal distributions of elements within plant organs still typically requires destructive sample preparation methods, including sectioning, for synchrotron X-ray fluorescence microscopy (XFM). X-ray fluorescence microscopy-computed tomography (XFM–CT) enables “virtual sectioning” of a sample thereby entirely avoiding artefacts arising from destructive sample preparation. The method can be used on frozen-hydrated samples, as such preserving “life-like” conditions. Absorption and Compton scattering maps obtained from synchrotron XFM–CT offer exquisite detail on structural features that can be used in concert with elemental data to interpret the results. In this article we introduce the technique and use it to reveal the internal distribution of hyperaccumulated elements in hyperaccumulator plant species. XFM–CT can be used to effectively probe the distribution of a range of different elements in plant tissues/organs, which has wide ranging applications across the plant sciences., Published by RSC Publ., Cambridge

Advances in X-Ray/EUV Optics and Components XVII : [Proceedings] - SPIE, 2022. - ISBN 97815106546489781510654655 - doi:10.1117/12.2633458 Advances in X-Ray/EUV Optics and Components XVII, San Diego, United States, 21 Aug 2022 - 26 Aug 2022; Proceedings of SPIE 12240, 122400J (2022). doi:10.1117/12.2633458 special issue: "SPIE Optical Engineering + Applications", While modern x-ray microscopes at synchrotron radiation sources and free-electron lasers require x-ray optics of highest quality, these optics often show aberrations due to limitations in fabrication technology. Based on ptychography, we determine these aberrations and fabricate tailor made refractive phase plates to compensate for them. Starting from the aberrated optics, diffraction-limited beams can be generated by introducing the phase plate behind these optics. In addition, the wavefront can be modified to generate custom beams for special needs, such as donut-shaped beams with orbital angular momentum or for structured-illumination microscopy. The nanofocused beam can be engineered in shape and phase by introducing specially designed phase plates. We introduce a general scheme for wavefront engineering and illustrate it with a numerical example., Published by SPIE, Bellingham, Wash.

Journal of synchrotron radiation 29(6), 1407 - 1413 (2022). doi:10.1107/S1600577522008025, X-ray diffraction with high spatial resolution is commonly used to characterize(poly)crystalline samples with, for example, respect to local strain, residualstress, grain boundaries and texture. However, the investigation of highlyabsorbing samples or the simultaneous assessment of high-Zmaterials by X-rayfluorescence have been limited due to the utilization of low photon energies.Here, a goniometer-based setup implemented at the P06 beamline of PETRAIII that allows for micrometre spatial resolution with a photon energy of 35 keVand above is reported. A highly focused beam was achieved by using compoundrefractive lenses, and high-precision sample manipulation was enabled by agoniometer that allows up to 5D scans (three rotations and two translations).As experimental examples, the determination of local strain variations inmartensitic steel samples with micrometre spatial resolution, as well as thesimultaneous elemental distribution for high-Zmaterials in a thin-film solar cell,are demonstrated. The proposed approach allows users from the materials-science community to determine micro-structural properties even in highly absorbing samples., Published by Wiley-Blackwell, [S.l.]

Journal of synchrotron radiation 29(3), 1-10 (2022). doi:10.1107/S1600577522002582, Scientific tasks aiming at decoding and characterizing complex systems and processes at high pressures set new challenges to modern X-ray diffraction instrumentation in terms of X-ray flux, focal spot size and sample positioning. Here, we present new developments at the Extreme Conditions Beamline (P02.2, PETRA III, DESY, Germany) that enable considerable improvements for the data collection at very high-pressures and small scattering volumes. Particularly, we describe the focusing the X-ray beam to the sub-micron level with controlled aberrations of the focusing compound refractive lenses due to the implementation of a correcting phase plate. This device provides a significant enhancement of the signal-to-noise ratio by conditioning the beam shape profile at the focal spot. A new sample alignment system with a small sphere of confusion enables single-crystal data collection from grains of micron to sub-micron dimensions subjected to pressures as high as 200 GPa. The combination of the technical development of the optical path and the sample alignment system contributes to research and benefits on various levels, including rapid and accurate diffraction mapping of the samples with the sub-micron resolution at multimegabar pressures., Published by Wiley-Blackwell, [S.l.]

Catalyst deactivation involves a complex interplay of processes taking place at different length and time scales. Understanding this phenomenon is one of the grand challenges in solid catalyst characterization. A process contributing to deactivation is carbon deposition (i. e., coking), which reduces catalyst activity by limiting diffusion and blocking active sites. However, characterizing coke formation and its effects remains challenging as it involves both the organic and inorganic phase of the catalytic process and length scales from the atomic scale to the scale of the catalyst body. Here we present a combination of hard X-ray imaging techniques able to visualize in 3-D the distribution, effect and nature of carbon deposits in the macro-pore space of an entire industrially used catalyst particle. Our findings provide direct evidence for coke promoting effects of metal poisons, pore clogging by coke, and a correlation between carbon nature and its location. These results provide a better understanding of the coking process, its relation to catalyst deactivation and new insights into the efficiency of the industrial scale process of fluid catalytic cracking.

JACS Au 1(6), 852 - 864 (2021). doi:10.1021/jacsau.1c00130, Ziegler-type catalysts are the grand old workhorse of the polyolefin industry, yet their hierarchically complex nature complicates polymerization activity–catalyst structure relationships. In this work, the degree of catalyst framework fragmentation of a high-density polyethylene (HDPE) Ziegler-type catalyst was studied using ptychography X-ray-computed nanotomography (PXCT) in the early stages of ethylene polymerization under mild reaction conditions. An ensemble consisting of 434 fully reconstructed ethylene prepolymerized Ziegler catalyst particles prepared at a polymer yield of 3.4 g HDPE/g catalyst was imaged. This enabled a statistical route to study the heterogeneity in the degree of particle fragmentation and therefore local polymerization activity at an achieved 3-D spatial resolution of 74 nm without requiring invasive imaging tools. To study the degree of catalyst fragmentation within the ensemble, a fragmentation parameter was constructed based on a k-means clustering algorithm that relates the quantity of polyethylene formed to the average size of the spatially resolved catalyst fragments. With this classification method, we have identified particles that exhibit weak, moderate, and strong degrees of catalyst fragmentation, showing that there is a strong heterogeneity in the overall catalyst particle fragmentation and thus polymerization activity within the entire ensemble. This hints toward local mass transfer limitations or other deactivation phenomena. The methodology used here can be applied to all polyolefin catalysts, including metallocene and the Phillips catalysts to gain statistically relevant fundamental insights in the fragmentation behavior of an ensemble of catalyst particles., Published by ACS Publications, Washington, DC