Littérature scientifique sur le sujet « Angle Resolved - XRF »

The x-ray source of our instrument is a rotating anode system with a silver target. It is flanged to a He-filled monochromator chamber. The photon energy of the x-rays for the excitation of characteristic specimen radiation can be tuned continuously from IkeV to 30 keV. The cross-section of the beam - monochromatic or polychromatic tube radiation - leaving the monochromator chamber is variable within 0.1 and 100mm2. A Be-window separates the evacuable specimen chamber from the monochromator chamber. The specimen holder allows for a linear movement of the specimen in x- and y-direction normal to the beam of incident x-radiation and allows a laterally resolved analysis. A rotation around an axis normal to the incident x-ray beam enables investigations under variable incidence- and take-off angles. X-ray detection is performed by an energy dispersive system.

X-ray micro fluorescence imaging refers to the use of an x-ray beam as a probe to excite XRF in a specimen and produce a spatially resolved image of the element distribution. The advantages of high sensitivity and low background, together with the nondestructive nature of the measurement, have lead to applications of x-ray microfluorescence analysis in biology, geology, materials science, as well as in the area of nondestructive evaluation. Previous reports have described the development of an x-ray microprobe which uses a conventional source of x-rays to produce a 10-μm beam. This paper describes improvements to the microprobe which have increased the beam power and the solid angle of detection. The data collection and display software have also been enhanced.

Ultra-thin platinum (Pt) films were deposited on Si (100) substrates at 160°C by magnetron sputtering and subsequently annealed to form silicides. The thickness of the Pt x Si films was found to be approximately 4 nm as determined by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) analysis shows that these films consist of PtSi and Pt 2 Si phases, and a multi-layer configuration of SiO x/ PtSi/Pt 2 Si/Si was detected by angle-resolved XPS. However, the Pt 3 Si phase was not detected by X-ray diffraction (XRD).

AbstractSynchrotron X-ray diffraction (XRD) is a powerful technique to study in situ and in real-time the structural and kinetic processes of pressure-induced phase transformations. This paper presents the experimental set-up developed at beamline ID27 of the ESRF to perform time-resolved angle dispersive XRD in the Paris-Edinburgh cell. It provides a practical guide for the acquisition of isobaric-isothermal kinetic data and the construction of transformation-time plots. The interpretation of experimental data in terms of reaction mechanisms and transformation rates is supported by an overview of the kinetic theory of solid-solid transformations, with each step of data processing illustrated by experimental results of relevance to the geosciences. Reaction kinetics may be affected by several factors such as the sample microstructure, impurities or differential stress. Further high-pressure kinetic studies should investigate the influence of such processes, in order to acquire kinetic information more akin to natural or technological processes.

Single crystals of 2-methylbenzimidazolium perchlorate were prepared for the first time with a slow evaporation method from an aqueous solution of a mixture of 2-methylbenzimidazole (MBI) crystals and perchloric acid HClO4. The crystal structure was determined by single crystal X-ray diffraction (XRD) and confirmed by XRD of powder. Angle-resolved polarized Raman and Fourier-transform infrared (FTIR) absorption spectra of crystals consist of lines caused by molecular vibrations in MBI molecule and ClO4− tetrahedron in the region ν = 200–3500 cm−1 and lattice vibrations in the region of 0–200 cm−1. Both XRD and Raman spectroscopy show a protonation of MBI molecule in the crystal. An analysis of ultraviolet-visible (UV-Vis) absorption spectra gives an estimation of an optical gap Eg~3.9 eV in the crystals studied. Photoluminescence spectra of MBI-perchlorate crystals consist of a number of overlapping bands with the main maximum at Ephoton ≅ 2.0 eV. Thermogravimetry-differential scanning calorimetry (TG-DSC) revealed the presence of two first-order phase transitions with different temperature hysteresis at temperatures above room temperature. The higher temperature transition corresponds to the melting temperature. Both phase transitions are accompanied by a strong increase in the permittivity and conductivity, especially during melting, which is similar to the effect of an ionic liquid.

Controlling material thickness and element interdiffusion at the interface is crucial for many applications of core-shell nanowires. Herein, we report the thickness-controlled and conformal growth of a Sb2Te3 shell over GeTe and Ge-rich Ge-Sb-Te core nanowires synthesized via metal-organic chemical vapor deposition (MOCVD), catalyzed by the Vapor–Liquid–Solid (VLS) mechanism. The thickness of the Sb2Te3 shell could be adjusted by controlling the growth time without altering the nanowire morphology. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were employed to examine the surface morphology and the structure of the nanowires. The study aims to investigate the interdiffusion, intactness, as well as the oxidation state of the core-shell nanowires. Angle-resolved X-ray photoelectron spectroscopy (XPS) was applied to investigate the surface chemistry of the nanowires. No elemental interdiffusion between the GeTe, Ge-rich Ge-Sb-Te cores, and Sb2Te3 shell of the nanowires was revealed. Chemical bonding between the core and the shell was observed.

Tensile and compressive tests were performed on extruded Mg-10Gd-2Y-0.5Zr (mass fraction, %) alloy specimens with different tilt angles relative to extrusion direction. The microstructures were examined by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM). Calculations of the orientation factors for basal slip were done for that existed texture. The results show that the alloy doesn’t show tensile-compressive yield strength asymmetry, and the highest flow stress is appeared along the extrusion direction. Meanwhile the extruded textures are much more randomized. The reason may be that the addition of rare-earth is benefit to activate the non-basal slips, especially pyramidal <c+a>slip. The reduction of c/a ratio is helpful to enhance the symmetry of the Mg crystal, which decreases the critical resolved shear stress of <c+a> slip.

Transmembrane proteins function within a continuous layer of biologically relevant lipid molecules that stabilizes their structures and modulates their activities. Structures and interactions of biological membrane–protein complexes or “memteins” can now be elucidated using native nanodiscs made by poly(styrene co-maleic anhydride) derivatives. These linear polymers contain a series of hydrophobic and polar subunits that gently fragment membranes into water-soluble discs with diameters of 5–50 nm known as styrene maleic acid lipid particles (SMALPs). High-resolution structures of memteins that include endogenous lipid ligands and posttranslational modifications can be resolved without resorting to synthetic detergents or artificial lipids. The resulting ex situ structures better recapitulate the in vivo situation and can be visualized by methods including cryo-electron microscopy (cryoEM), electron paramagnetic resonance (EPR), mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy, small angle x-ray scattering (SAXS), and x-ray diffraction (XRD). Recent progress including 3D structures of biological bilayers illustrates how polymers and native nanodiscs expose previously inaccessible membrane assemblies at atomic resolution and suggest ways in which the SMALP system could be exploited for drug discovery.

L’analisi scientifica è da un po’ di tempo entrata nel mondo dei beni culturali, non sono più solo gli archeologi e gli storici dell’arte a occuparsi dello studio dei reperti archeologici e storici, ma anche gli scienziati sono entrati a gamba tesa portando le loro conoscenze al servizio di questa vasta gamma di materiali. Lo studio di reperti botanici e zoologici, le competenze chimiche e mineralogiche, lo studio di fenomeni fisici, ha permesso di porre e rispondere a nuove domande, colmando così lacune sulla storia dell’umanità. Reti commerciali, migrazioni, tecniche produttive, molte sono state le scoperte avvenute grazie anche all’intervento scientifico, oltre a fornire strumenti utili al restauro e alla conservazione dei reperti. Nei miei tre anni di dottorato mi sono occupato dell’applicazione dell’analisi in Fluorescenza a Raggi X (XRF) per analizzare campioni metallici e ceramici. Questa tecnica ha il vantaggio di poter essere applicata in maniera non invasiva e non distruttiva su un reperto per ottenere informazioni sulla sua composizione elementare. In particolare, il nostro obiettivo è quello di ottenere informazioni sui diversi strati che compongono un campione. Spesso, infatti, i manufatti presentano una struttura stratificata causata dal passaggio degli anni o dalla natura stessa dell’oggetto, che presenza una serie di decorazioni superficiali. L’impiego di tecniche non invasive permetterebbe quindi di ottenere informazioni più dettagliate anche su campioni al momento inaccessibili, in quanto troppo fragili o troppo preziosi. Lo studio si è quindi avvalso di tecniche a scansione angolare, per cui il segnale di fluorescenza caratteristica dipende sia dalla posizione dell’analita all’interno del campione, sia dalla struttura e composizione dello stesso, sia dalla geometria di analisi. Per valutare l’applicabilità delle tecniche sono stati analizzati tre casi diversi: campioni metallici preparati ad hoc in laboratorio, un campione ceramico, e un campione di lustro. Per i primi due campioni è stata applicata l’XRF a Risoluzione Angolare (AR-XRF) per cui il campione è stato ruotato con uno step angolare inferiore a un grado, e misurato ad ogni step. Nel caso dei campioni metallici i profili misurati sono stati confrontati direttamente con i profili calcolati usando il metodo dei Parametri Fondamentali. Nel caso del campione ceramico invece, sono stati confrontati i rapporti dei profili, in quanto la geometria del campione era piuttosto complessa. Nello studio sui campioni metallici, composti da una doratura depositata su una lamina di rame, è stato possibile calcolare lo spessore dello strato superficiale. Nel caso del campione di Majolica sono invece state studiate le varie decorazioni, valutando così anche diversi limiti della tecnica, in particolar modo nel caso in cui la composizione della decorazione sia simile alla composizione dello strato sottostante, o nel caso in cui avvengano processi di diffusione a lunghe distanze. In casi in cui invece lo spessore della decorazione era limitato e ben separato dallo strato sottostante, è stato possibile ottenere informazioni sua sulla composizione della decorazione che sul suo spessore. Infine, lo studio delle ceramiche lustrate è stato effettuato presso la linea XRF del Sincrotrone di Elettra, impiegando tecniche di analisi in radenza. In questo caso stato possibile solo evidenziare come il nano-strato di nano-particelle di argento, caratteristico di questa tipologia di campioni, sia effettivamente distinguibile applicando queste tecniche, in quanto il profilo di fluorescenza di tale elemento è molto diverso dagli altri. Rimangono comunque dei problemi, legati soprattutto all’analisi dati e all’allineamento che vanno ancora risolti, rendendo necessari ulteriori studi a riguardo.
In the last decades scientific analysis has been deeply employed in the world of cultural heritage, thus, archaeologists and art historians are no more the sole front line workers of this field. Scientists, and science, have joined the team, giving new inputs and tools for the study of historical and archaeological samples, allowing to explore new paths and receive new answers, collecting information otherwise inaccessible on human history and culture. New discoveries have been made on the trade networks, migrations and on the technologies employed; besides, science also gave precious inputs on conservation and restoring procedures, allowing to better preserve fragile and sensitive artifacts. In my three years as a PhD student, I worked on the application of X-Ray Fluorescence (XRF) analysis to analyze ceramic and metal samples. XRF is a non-invasive technique that retrieves the elemental composition of a sample. In particular the aim of my PhD project is to obtain information on the layered structure of an unknown sample, distinguishing and characterizing the different layers. Indeed, artifacts usually concerning the field of Cultural Heritage present a layered structure; sometimes it is due to the presence of alteration layers, other times, instead, the objects are made of different layers from the principle, for example in the case of a glazed ceramic or of a painting. The possibility to get this information in a non-invasive way will give the possibility to analyze objects that are nowadays unattainable, because they cannot be sampled. My project has, thus, focused on the analysis of three kinds of samples employing angular dependent techniques (Angle Resolved-XRF, Grazing Emission-XRF}, Grazing Incidence-XRF}); indeed, the fluorescence signal of an analyte depends on its position inside the sample, on the sample composition and on the geometry of analysis. The chosen specimens allowed to verify the feasibility of this analytical method in an increasing complexity: a gilded laboratory-made sample, a ceramic Majolica sherd, and an Italian renaissance lustered fragment. The first two samples have been analyzed through AR-XRF where the measure is performed while tilting the sample, one spectrum is collected for each tilting angle. In the case of the gilded sample the measured profiles have been compared directly with the calculated profiles employing the Fundamental Parameters method. For the ceramic Majolica sample, instead, we studied the ratio of the profiles, as the sample surface is not flat. In the study of the metallic samples, made of gilded copper plate, we could infer the thickness of the top-layer. While in the case of the Majolica sample, we studied the different decorations, evaluating the limits of the technique, in particular in the case that the top-layer composition is similar to the underling layer, or in the case of a long-range diffusion. Instead, in the case of two well-separate layers we could retrieve information on both the composition and the thickness of the layer. Finally, the study of the lustered ceramic has been carried out at the XRF beamline of the Elettra Synchrotron of Trieste, employing grazing techniques. In this case we could only highlight and distinguish the presence of the silver nanoparticles in the luster nanolayer, which is the peculiar feature of this kind of artifacts. However, there are still many questions left, especially concerning the data analysis and the alignment of the sample, which requires more investigations.