X-ray absorption spectroscopy (XAS) is an extremely flexible experimental technique for determining both the oxidation state and the local environment of a given element in a material. The Next-Generation Advanced Materials (Next-GAME) project was created with the aim of bringing X-ray instruments back into common research centers that can at least partially support the research that until a few years ago was relegated only to synchrotrons. It is precisely in this context that our project takes place, aimed at the creation of a compact and user-friendly laboratory XAS spectrometer without sacrificing its energy resolution. Precisely for this purpose, an in-depth study on the geometry of monochromators was carried out, combining an analytical approach with the results obtained through ray tracing simulations. This dual approach has allowed us to highlight the effects that geometric parameters have on the resolving properties of the instrument, enabling us to maximize the ratio between performance and cost. In order to reduce the overall dimensions as much as possible without degrading the resolution, we opted for a Johansson-type cylindrically bent crystal. This crystal, if compared with the commonly used Johann crystals, allows to reduce drastically chromatic aberrations and, in addition, allows to use, exploiting Ge[220] reflection and subsequent harmonics, a single crystal to fully cover the energy range 5 − 15 keV of our interest containing the K-lines of the 3d transition metals and the L-lines of the 5d transition metals.
La spettroscopia di assorbimento di raggi X (XAS) è una tecnica sperimentale estremamente flessibile attraverso cui è possibile effettuare analisi su molteplici materiali innovativi. Il progetto Next-Generation Advanced Materials (Next-GAME) nasce con lo scopo di riportare all’interno dei comuni centri di ricerca strumenti a raggi X che possano, almeno in parte, affiancare la ricerca che fino a pochi anni fa era relegata ai soli sincrotroni. E’ proprio in questo contesto che si colloca il nostro progetto, finalizzato alla realizzazione di uno spettrometro XAS da laboratorio compatto e facile da utilizzare senza però sacrificare la risoluzione energetica dello strumento. Proprio a tal fine è stato effettuato uno studio approfondito sulla geometria dei cristalli monocromatori, affiancando ad un approccio analitico i risultati ottenuti attraverso simulazioni di ray tracing. Questo duplice approccio ha consentito di mettere in luce gli effetti che i parametri geometrici hanno sulle proprietà risolutive dello strumento, consentendoci di massimizzare il rapporto tra prestazioni e costi. Al fine di ridurre il più possibile gli ingombri senza degradare la risoluzione ci siamo indirizzati verso la scelta di un cristallo cilindrico tipo Johansson. Tale scelta, se comparata con i più comuni cristalli Johann, consente di ridurre le aberrazioni cromatiche e, in aggiunta, permette di utilizzare, sfruttando la riflessione Ge[220] e successive armoniche, un singolo cristallo per coprire interamente l’intervallo energetico 5−15 keV di nostro interesse contenente le linee-K dei metalli di transizione 3d e le linee-L dei metalli di transizione 5d.
Performance analysis and simulations of a laboratory X-ray absorbtion spectrometer
FLORIO, PIERO
2021/2022
Abstract
X-ray absorption spectroscopy (XAS) is an extremely flexible experimental technique for determining both the oxidation state and the local environment of a given element in a material. The Next-Generation Advanced Materials (Next-GAME) project was created with the aim of bringing X-ray instruments back into common research centers that can at least partially support the research that until a few years ago was relegated only to synchrotrons. It is precisely in this context that our project takes place, aimed at the creation of a compact and user-friendly laboratory XAS spectrometer without sacrificing its energy resolution. Precisely for this purpose, an in-depth study on the geometry of monochromators was carried out, combining an analytical approach with the results obtained through ray tracing simulations. This dual approach has allowed us to highlight the effects that geometric parameters have on the resolving properties of the instrument, enabling us to maximize the ratio between performance and cost. In order to reduce the overall dimensions as much as possible without degrading the resolution, we opted for a Johansson-type cylindrically bent crystal. This crystal, if compared with the commonly used Johann crystals, allows to reduce drastically chromatic aberrations and, in addition, allows to use, exploiting Ge[220] reflection and subsequent harmonics, a single crystal to fully cover the energy range 5 − 15 keV of our interest containing the K-lines of the 3d transition metals and the L-lines of the 5d transition metals.File | Dimensione | Formato | |
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Executive_Summary___Piero_Florio___Politecnico_di_Milano.pdf
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Descrizione: Executive Summary
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Performance_analysis_and_simulations_of_a_laboratory_X_ray_Absorption_Spectrometer_[PIERO_FLORIO].pdf
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Descrizione: TESI DEFINITIVA
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12.01 MB
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12.01 MB | Adobe PDF | Visualizza/Apri |
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https://hdl.handle.net/10589/197364