Littérature scientifique sur le sujet « Standardless analysis »

Electron beam X-ray microanalysis with semiconductor energy-dispersive spectrometry (EDS) performed with standards and calculated matrix corrections can yield quantitative results with a distribution such that 95% of analyses fall within ±5% relative for major and minor constituents. Standardless methods substitute calculations for the standard intensities, based either on physical models of X-ray generation and propagation (first principles) or on mathematical fits to remotely measured standards (fitted standards). Error distributions have been measured for three different standardless analysis procedures with a suite of microanalysis standards including metal alloys, glasses, minerals, ceramics, and stoichiometric compounds. For the first-principles standardless procedure, the error distribution placed 95% of analyses within ±50% relative, whereas for two commercial fitted standards procedures, the error distributions placed 95% of analyses within ±25% relative. The implication of these error distributions for the accuracy of analytical results is considered, and recommendations for the use of standardless analysis are given.

The ϕ(ρz) models developed during the recent years (Gaussian, PAP, XPP) have been shown by several authors to improve significantly the capability of quantitative x-ray microanalysis, mainly in the field of light elements, tilted specimens, and layered specimens. An increasing number of users is now able to take advantage of these models, since some of them have been implemented in EPMA or EDS commercial softwares.However, most of the reported successful applications are the result of analyses with standards, where the basic data are the relative x-ray intensities (also called k-ratios). Indeed, analyses with standards are well adapted to the electron microprobes, and permit to obtain very accurate results. But in the scanning electron microscopes (SEM), the operations of acquiring, processing and handling the EDS spectra of all the required standards are really time consuming. It is why an EDS standardless mode giving satisfactory quantitative results would be so useful, even for those laboratories which can also operate an electron microprobe for the applications requiring the highest degree of accuracy.

The main difficulty in the quantitative mineral analysis of rocks is connected with the variable nature of the mineral species. In the present paper a combined method (and a corresponding computer program) is proposed, which practically overcomes this difficulty. This method is based on linear equations, which are a combination of the chemical mass-balance equations with those of the quantitative X-ray diffractometry, and can perform (completely or partly) both the quantification and the chemical characterization of the minerals on several rock samples simultaneously, demanding only easily accessible initial information, such as: (i) major element (oxide) compositions for the samples; (ii) qualitative mineral composition of the samples; (iii) X-ray intensities for one or few nonoverlapped reflections of the crystalline minerals (not necessarily of all): (iv) some characteristic data for the phases (i.e., chemical composition data), if these are accurately known. Where it is possible the minerals may be expressed via end members. The samples may contain amorphous phases and/or phases without X-ray data. From the general case some very simple partial cases are derived, demanding less initial information. This method has the following advantages over the previous ones of similar philosophy: (i) drastic reduction of the number of required samples; (ii) sufficiency of equations for any analytical problem; (iii) possibility of performing partial analysis when a complete one is impossible; (iv) possibility of using the same end member in more than one solid solution. Analysis examples are given.

In truly standardless electron microprobe analysis, generated X-ray intensities calculated from first principles are combined with a detector efficiency model. Though already used for energy dispersive (ED) analysis, the application of this concept to wavelength dispersive (WD) analysis is problematic, mainly because the reflectivity of spectrometer crystals is not well known. However, the need to carry out standard measurements with every batch of WD analyses can be avoided by using stored intensity data, and interpolation may be used when no standard is available. An empirical adjustment factor allowing for changes in spectrometer efficiency with time can be applied as necessitated by the variability of the spectrometer characteristics and the accuracy required. A similar approach to background corrections, based on measured continuum intensities, can be used. While the convenience of standardless WD analysis is attainable only at the expense of reduced accuracy, it can have a useful role where high accuracy is not needed or as a preliminary to applying a more rigorous routine using standards.

A method for quantitative phase analysis without standards (QPAWS) has been published in 1977 and has gained considerable interest, as the calibration for quantitative XRD may sometimes be difficult. Standards for quantitatative XRD are not generally available, and in many cases even the pure phases cannot be obtained.The QPAWS method is based on (i) analysis of all phases present in the samples, (ii) foreknowledge of mass absorption coefficients (MAC)(iii) measuring samples which contain all phases in varying concentrations. In this method the number of samples used is equal to the number of phases to be analysed.

La fluorescence des rayons X (XRF) est un outil analytique qualitatif et quantitatif pour la caractérisation élémentaire de nombreux types de matériaux ; elle est non destructive, rapide et convient à l'analyse d'une large gamme d'éléments. La méthode est basée sur l'excitation d'un analyte par un faisceau primaire de rayons X qui induit l'émission de la fluorescence X de l'échantillon. L'objectif de l'analyse quantitative par fluorescence X est d’établir la relation entre la concentration des éléments avec les intensités de fluorescence mesurées. Cependant, cette tâche n'est pas simple puisque les intensités de fluorescence apparentes dépendent de la fraction pondérale de l’élément dans l'analyte, de la composition de la matrice, de la géométrie du dispositif expérimental, des paramètres de la source de rayons X primaires et du système de détection, etc. Les informations quantitatives peuvent être obtenues en appliquant des approches théoriques ou empiriques. Un des objectifs de cette thèse est d'étudier les performances d’une installation miniaturisée de fluorescence X destinée à l'analyse des actinides par leurs raies XL (12 keV < E < 17 keV), implantée dans le laboratoire d’analyses de l’installation ATALANTE (CEA Marcoule). Le dispositif expérimental comprend un tube à rayons X à anode d'Ag qui irradie un échantillon, un détecteur au silicium à dérive (SDD) et un monochromateur HOPG cylindrique. Ce dernier élément est placé entre l'échantillon et le système de détection et agit comme un filtre passe-bande en modifiant la distribution spectrale du rayonnement de fluorescence. De cette manière, les spectres peuvent être enregistrés dans la gamme d'énergie d'intérêt, tout en réduisant le taux de comptage dû aux rayonnements parasites. Le monochromateur HOPG du dispositif expérimental couvre la gamme d'énergie d'intérêt qui permet d'analyser les éléments de Z moyen (Se, Rb, Sr, Y, etc.) et Z élevé (principalement U, Np, Pu, Am et Cm) par leurs raies K et L, respectivement. Le second objectif de ce travail est d'affiner l'algorithme classique de quantification basé sur les paramètres fondamentaux en tenant compte des modifications de la distribution spectrale par le cristal HOPG. En effet, les spectres mesurés avec un système de fluorescence classique peuvent être traités avec succès en utilisant une méthode théorique basée sur des équations mathématiques sans nécessiter d’étalons. Il s’agit de la méthode dite des paramètres fondamentaux (PF). Cependant, pour traiter avec précision les spectres mesurés avec la présente configuration, il est nécessaire de connaître la fonction de transmission du cristal HOPG. L'étude détaillée de l’instrumentation miniature et des phénomènes physiques mis en jeu a été réalisée en utilisant la méthode de Monte Carlo pour le transport des rayonnements, avec le code PENELOPE. Ensuite, pour mieux comprendre les propriétés de réflexion du cristal de HOPG, des simulations d’optique des rayons X ont été réalisées à l'aide du logiciel XRT afin de modéliser la réponse du cristal cylindrique de HOPG et représenter pas à pas l'ensemble de détection. La réponse du système optique développé a été simulée en utilisant des spectres expérimentaux enregistrés sans le monochromateur HOPG comme données d'entrée. Le modèle de simulation a été validé par la comparaison avec des données expérimentales pour différents échantillons liquides contenant des éléments Z moyens (quelques dizaines de mg.L-1), ce qui a permis de caractériser la fonction de transfert du cristal HOPG. Ensuite, celle-ci a pu être importée avec succès dans le logiciel PyMCA, basé sur les paramètres fondamentaux, afin de fournir des résultats quantitatifs. Pour conclure, il est démontré que le couplage du code Monte Carlo PENELOPE et des simulations XRT peut être utilisé pour prédire les réponses spectrales de l’instrumentation de fluorescence miniature pour différentes conditions géométriques dans le but de contribuer à l'améliorer
X-ray fluorescence (XRF) is qualitative and quantitative analytical tool for elemental analysis of many types of materials; it is non-destructive, fast and is suitable for the analysis of the wide range of elements. The method is based on the excitation of an analyte by a beam of primary X-rays to induce the emission of X-ray fluorescence from the sample. The goal of the quantitative XRF analysis is to relate the elemental concentrations to the measured fluorescence intensities. However, this task is not straightforward since the apparent fluorescence intensities are dependent on the weight fraction of an analyte, matrix composition, geometry of the experimental setup, parameters of the primary X-ray source and detection system, etc.. The quantitative information can be obtained applying theoretical or empirical approaches. One of the aims of this thesis is to investigate the performances of the miniaturised XRF setup intended to the analysis of actinides by their L X-ray lines (12 keV < E < 17 keV) installed in the analysis laboratory within ATALANTE facility (CEA Marcoule). The experimental setup includes an Ag-anode X-ray tube which irradiates a sample, a silicon drift detector (SDD) and a cylindrical HOPG monochromator. The latter element is positioned between the sample and the detection system and in such a geometry, it acts as a bandpass filter modifying the spectral distribution of the fluorescence radiation. In this manner, the spectra can be recorded in the energy range of interest reducing the burden on the detection system from an unwanted radiation. The HOPG monochromator of the experimental setup cover the energy range of interest and permits to analyse analysis of medium-Z (Se, Rb, Sr, Y, etc.) and high-Z (mainly U, Np, Pu, Am, and Cm) elements by their K and L X-ray lines, respectively. The second goal of this work is to refine the classical quantification algorithm based on the fundamental parameters taking into account the modifications of the spectral distribution by the HOPG crystal. Indeed, spectra measured with a classical XRF system can be successfully processed using a theoretical method based on mathematical equations without standards. Such method is called the fundamental parameters (FP) method. However, in order to process accurately the spectra measured with the present setup, it arises the necessity to know the transmission function of the HOPG filter. The detailed investigation of the miniature setup and of the physical phenomena involved was performed utilizing the Monte Carlo method for the radiation transport with the PENELOPE code. In addition, to establish a better understanding of the reflection properties of the HOPG crystal, ray-tracing simulations were performed using the dedicated the ray-tracing package XRT to model the cylindrical HOPG crystal and represent step by step the entire detection channel. The response of the developed optical system was simulated applying the experimental spectra recorded without the HOPG monochromator as an input data. The validity of the simulation model has been approved through the comparison with experimental data for different liquid samples containing medium-Z elements (a few tens of mg.L-1),what allowed to define the HOPG transfer function. Next, the estimated transfer function could be successfully applied in the FP-based software PyMCA to provide quantitative results. To conclude, it is demonstrated that the coupling of the PENELOPE Monte Carlo code and XRT simulations can be used to predict the spectral responses of the miniature setup under different geometrical conditions in order to help to improve it

Energy Dispersive X-ray Fluorescence spectrometry (EDXRF) is a non-destructive analytical technique that allows multi-element analysis of a large variety of materials in a relatively fast and simple way, and is used in a broad range of areas. This technique resorts to calibrated standard samples for each type of sample to be analysed, as well as the knowledge of Fundamental Parameters (FP). The use of standards have several drawbacks to consider such as the unavailability of standards for certain types of materials, the associated monetary costs, and inaccuracy of the standard’s measurements. On the other hand, the inaccuracy of Fundamental Parameters limits the accuracy of the quantification. Furthermore, FP used by quantification software are included in built-in tabulation inaccessible to the user. EDXRF spectrometers employed in triaxial geometry allow the experimental measurement of the Rayleigh-to-Compton scattering intensity ratio. The measurement of these ratios of standard samples permits a method for determination of the average atomic number Zavg of unknown samples. In this work, using the Geant4 toolkit, a code is implemented to simulate the X-ray spectrum obtained from employing a triaxial geometry spectrometer, aiming for both elemental quantification from the characteristic peaks and the determination of Compton-to-Rayleigh scattering ratio. Simulation results are compared with experimental measurements of standard reference materials, showing a good agreement for the simulated peak intensities, as well as for the simulated scattering ratios. Zn K-shell FP are calculated using the multiconfiguration Dirac-Fock approach, presenting good agreement when comparing with the available values in literature. A comparison of K-shell fluorescence yield and partial fluorescence yield values is presented, regarding different references from which a comprehensive set of values can be used for atomic relaxation libraries. These comparisons point that further studies should be employed before changing Geant4 library for atomic relaxation.

During this PhD thesis I researched the conditions to obtain a controlled electrodeposition of bismuth metal and bismuth selenide and the standardless determination of the thickness of electrodeposited thin films by means of a quantification method based on Monte Carlo simulations. The first part of this thesis was dedicated to the development of a new quantification method for the thickness determination of electroplated samples since the high variability of alloys makes impossible to use specific standards with a consequent lowering of the accuracy. The specimens were prepared with materials and features that made this study focused on the application in the electroplating sector. For this reason, films of varying thicknesses of nickel, palladium and gold have been deposited on copper and brass substrates. The study was conducted using EDS and XRF techniques and the results were compared with measurements of weight, SEM and XRF (current quantification method). Certified samples were also used as a comparison. The proposed method consists in constructing a calibration curve using simulated standards obtained from Monte Carlo algorithm in which the single electrons, or photons, interact with the substrate. The intensities are then normalized with respect to the pure elements (the only required standards to be measured) to minimize possible instrumental deviations; the calibration curve is used to derive the thickness of the samples. Taking into account that the current XRF quantification technique predicts an error of about 5 %, the results were encouraging for both techniques. In fact, a deviation from the expected values of about 9 % was obtained with EDS using DTSA-II software (consistent with results obtained with measured standards) while one of only about 4 % was obtained with XRF using XMI-MSIM software. The two different techniques are complementary and allow to analyse very different ranges of thicknesses. Beyond the accuracy, this procedure does not require standards of known thickness: therefore, its advantages consist in being very low-cost and it would allow to virtually analyse any type of coating having only available bulk samples of the pure elements to be identified. Regarding the electrodeposition processes, I have investigated the conditions for bismuth and bismuth selenide deposition since these materials have numerous properties that make them attractive for their use in technological devices. Currently, the films of these materials are obtained through vapour phase techniques to have good control over the deposition but the use of techniques in liquid phase, at ambient temperature and pressure, could considerably reduce the production costs. I found the conditions for an underpotential deposition to control the deposition of monolayer fractions on monocrystalline silver electrode. In this way both single layer and multilayer samples of bismuth and bismuth selenide were prepared. In addition to synthesise these compounds I tried to measure their thickness with the previously developed standardless method to obtain a better characterization of the deposits.

ABSTRACT Quantitative insights into the geochemistry and petrology of proximal impactites are fundamental to understand the complex processes that affected target lithologies during and after hypervelocity impact events. Traditional analytical techniques used to obtain major- and trace-element data sets focus predominantly on either destructive whole-rock analysis or laboratory-intensive phase-specific micro-analysis. Here, we present micro–X-ray fluorescence (µXRF) as a state-of-the-art, time-efficient, and nondestructive alternative for major- and trace-element analysis for both small and large samples (up to 20 cm wide) of proximal impactites. We applied µXRF element mapping on 44 samples from the Chicxulub, Popigai, and Ries impact structures, including impact breccias, impact melt rocks, and shocked target lithologies. The µXRF mapping required limited to no sample preparation and rapidly generated high-resolution major- and trace-element maps (~1 h for 8 cm2, with a spatial resolution of 25 µm). These chemical distribution maps can be used as qualitative multi-element maps, as semiquantitative single-element heat maps, and as a basis for a novel image analysis workflow quantifying the modal abundance, size, shape, and degree of sorting of segmented components. The standardless fundamental parameters method was used to quantify the µXRF maps, and the results were compared with bulk powder techniques. Concentrations of most major elements (Na2O–CaO) were found to be accurate within 10% for thick sections. Overall, we demonstrate that µXRF is more than only a screening tool for heterogeneous impactites, because it rapidly produces bulk and phase-specific geochemical data sets that are suitable for various applications within the earth sciences.

Abstract Algorithms for quantification by SEM/EDS always specify that the material being analyzed should be homogeneous. Every instruction on analysis by SEM/EDS warns against analyzing heterogeneous samples. However, in day-to-day analysis, it is extremely common to encounter samples which are heterogeneous and these samples must be analyzed. It is very common for an analyst to simply scan an entire field of view in the SEM, acquire an x-ray spectrum from this field of view, press the button for standardless quantification, and hope for the best. This work explores the magnitude of this problem and characterizes it with measurements. A solution is then proposed for performing this kind of analysis. The results of analyses of multiple areas showed larger variations than the variation between the area-weighted and gross spectrum calculations. The results obtained were consistent with the nominal bulk concentrations for homogeneous materials.