Quantitative electron probe microanalysis: Fluorescence correction uncertainty

Summary In order to evaluate the fluorescence correction uncertainty in electron probe microanalysis, effects of two general types were investigated. The effects of uncertainty in 1. microprobe operational variables, including X-ray emergence angle and operating voltage, and 2. errors in model input parameters, such as fluorescence yield factors and mass attenuation coefficients, were evaluated. The major conclusion of this study is, that even in cases requiring large fluorescence corrections, microprobe operation at high (30°) X-ray emergences angles, and at the lowest voltage compatible with a reasonable X-ray output is entirely satisfactory. This conclusion is reached by substituting into existing fluorescence correction models reasonable input parameter errors, X-ray emergence angles, and operating voltages. Results show that absolute compositional errors vary quite slowly with X-ray emergence angle and operating voltage. The chief source of error among input parameters is the fluorescence yield factor. The role of model selection as a source of potential error is also discussed.

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Zusammenfassung Für die Ermittlung der Unsicherheit der Fluoreszenzkorrektur bei der Elektronenstrahl-Mikroanalyse sind zwei prinzipielle Effekte zu berücksichtigen: 1. Unsicherheiten, bedingt durch den Austrittswinkel der Röntgenstrahlung und die Beschleunigungsspannung und 2. fehlerhafte Parameter, wie Fluoreszenzausbeute und Massenschwächungskoeffizienten. Das wichtigste Ergebnis der vorliegenden Arbeit ist, daß die Mikrosondenanalyse sogar in Fällen, die eine große Fluoreszenzkorrektur erwarten lassen, und selbst bei großem Austrittswinkel (30°) und bei niedrigster Spannung mit einer erträglichen Impulsausbeute völlig zufriedenstellend ist. Dieses Ergebnis wurde erhalten, nachdem annehmbare Parameter für Abnahmewinkel und Beschleunigungsspannung in bekannte Fluoreszenzkorrektur-Modelle eingesetzt worden waren. Die Resultate zeigen, daß der absolute Fehler für die Zusammensetzung nur wenig mit dem Abnahmewinkel variiert. Der Faktor für die Fluoreszenzausbeute ist die hauptsächliche Fehlerquelle. Die Auswahl der Korrekturverfahren als eine Quelle für einen möglichen Fehler wird ebenfalls diskutiert.

     

Quantitative electron probe microanalysis: Uncertainty in the atomic number correction

Summary The atomic number effect in quantitative electron probe microanalysis has been considered from the point of view of error propagation. The results indicate that the chief causes of analysis uncertainty are poorly known electron backscattering factors and mean ionization potential values. Operating variables such as working voltage or X-ray take-off angle cannot be manipulated so as to reduce the effect of the uncertainties. However, the overall analysis uncertainty remains nearly constant over the entire range of working voltages practical for microanalysis.

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Zusammenfassung Der Atomnummerneffekt bei der quantitativen Elektronenstrahlmikroanalyse wurde im Hinblick auf seinen Beitrag zum Analysenfehler untersucht. Danach ist die Hauptursache für den Fehler die Ungenauigkeit der Rückstreufaktoren und der mittleren Ionisationspotentiale. Die Arbeitsbedingungen, wie Abnahmewinkel der Röntgenstrahlung oder Beschleunigungsspannung, können nicht so gewählt werden, daß diese Ungenauigkeit verringert wird. Der gesamte Analysenfehler bleibt jedoch fast über den ganzen für die Elektronenstrahlmikroanalyse üblichen Bereich der Anregungsspannung konstant.

     

A method to correct defocused element distribution maps in electron probe microanalysis

Element distribution maps obtained on electron microprobes via the beam scan method with wavelength-dispersive spectrometers reveal a defocusing effect if they are taken at sufficiently small magnification. This effect, which occurs where the Bragg condition of the spectrometer is not adequately met, can be avoided or corrected by various methods. A method is presented here to correct defocused element distribution maps with the help of corresponding maps obtained on homogeneous standards.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

A computer program for use in quantitative electron probe microanalysis

Summary A computer program for use in the conversion of electron probe X-ray intensity ratios into chemical compositions has been written. The inclusion of several of the more successful correction procedures facilitates the comparison of these procedures and allows an investigator to select the correction procedure which will give the best results for the system being studied. Theoretical calibration calculations of the intensity ratio versus composition can be performed and these results can be plotted by machine. The program has been designed to be as versatile as possible and still retain simple experimental input requirements. Some results obtained using recently published correction procedure are discussed.

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Zusammenfassung Ein Computerprogramm wurde geschrieben, um Intensitätsverhältnisse der Elektronenstrahlmikroanalyse in chemische Zusammensetzungen umzurechnen. Die Einfügung einiger besonders erfolgversprechender Korrekturverfahren erleichtert den Vergleich dieser Verfahren und ermöglicht dem Bearbeiter, jenes Korrekturverfahren auszuwählen, das für das eben untersuchte System die besten Ergebnisse liefert. Die theoretischen Berechnungen des Intensitätsverhältnisses in Abhängigkeit von der Zusammensetzung können als Eichung durchgeführt werden und diese Ergebnisse kann die Maschine ausdrucken. Das Programm wurde so vielseitig wie möglich erstellt, beinhaltet aber dennoch einfache experimentelle Eingabemöglichkeiten. Einige Ergebnisse, die durch den Gebrauch kürzlich veröffentlichter Korrekturverfahren erhalten wurden, werden diskutiert.

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Résumé Un programme d'ordinateur servant à convertir les rapports d'intensité de rayons X de sonde électronique en compositions chimiques a été rédigé. L'inclusion de plusieurs procédures de correction parmi celles qui ont obtenu le plus de succès facilite la comparaison de ces procédures et permet à l'investigateur de choisir la procédure de correction qui, à son avis, donnera les meilleurs résultats pour lè système étudié. Des calculs théoriques de calibrage entre le rapport d'intensité et la composition peuvent être faits et ces résultats peuvent être rapportés sur graphique mécaniquement. De par sa conception, le programme jouit du maximum de souplesse tout en gardant le plus de simplicité possible aux données expérimentales nécessaires à l'entrée. Certains résultats obtenus à l'aide de procédures de correction récemment publiés, font l'objet de discussions.

     

An improved Born approximation for the electron impact ionization of atomic hydrogen

A two-electron continuum wave function satisfying exact asymptotic boundary conditions (see [1]) is simplified in the high energy limit for asymmetric kinematics. The long range correlation between the fast escaping electron and the target atom in a low continuum state is properly taken into account, and corrects therefore the major shortcoming of the ordinary Born approximation. This improved Born approximation has been employed to calculate triply differential ionization cross sections at intermediate energies.     

The distribution of light elements in biological cells measured by electron probe X-ray microanalysis of cryosections.

The intracellular distribution of the elements carbon, nitrogen, and oxygen was measured in cultured rat hepatocytes by energy dispersive electron probe X-ray microanalysis of 100-nm-thick freeze-dried cryosections. Electron irradiation with a dose up to 106 e/nm2 caused no or merely negligible mass loss in mitochondria and in cytoplasm. Cell nuclei lost carbon, nitrogen, and-to a clearly higher extent-oxygen with increasing electron irradiation. Therefore, electron doses less than 3 x 105 e/nm2 were used to measure the subcellular compartmentation of carbon, nitrogen, and oxygen in cytoplasm, mitochondria, and nuclei of the cells. The subcellular distribution of carbon, nitrogen, and oxygen reflects the intracellular compartmentation of various biomolecules. Cells exposed to inorganic mercury before cryofixation showed an increase of oxygen in nuclei and cytoplasm. Concomitantly the phosphorus/nitrogen ratio decreased in mitochondria. The data suggest mercury-induced production of ribonucleic acid (RNA) and decrease of adenosine triphosphate (ATP). Although biomolecules cannot be identified by X-ray microanalysis, measurements of the whole element spectrum including the light elements carbon, nitrogen, and oxygen can be useful to study specific biomolecular activity in cellular compartments depending on the functional state of the cell.     

Characterization of a laser‐nitrided titanium alloy by electron backscattered diffraction and electron probe microanalysis

After a laser gas nitriding treatment of the Ti‐7.5Al (atom %) titanium‐based alloy, we used a combination of electron backscattered diffraction (EBSD) in scanning electron microscope and electron probe microanalysis (EPMA) techniques in order to efficiently characterize the different phases in the resolidified layer. Representative measurements of chemical composition and reliable determination of crystal structure were possible for each phase of the complex microstructure. The reaction zone is formed by a mixture of isostructural TiN phases with dendritic and/or ‘coarse’ needles morphology, fixed into a α′‐Ti matrix (martensite) with a thin needle aspect. The nitrogen solubility was found to remain very low in the α′‐Ti matrix (up to 2–3 atom %), while in the TiN phase, an aluminum solubility as high as 4 atom % was measured, reducing drastically the nitrogen content into a Ti₇₉N₁₇Al₄ chemical composition. Copyright © 2005 John Wiley & Sons, Ltd.     

Account of the background in wavelength dispersive X-ray electron probe microanalysis based on the simulation of bremsstrahlung X-radiation

The potentials of six approximation functions described in the literature and used to simulate bremsstrahlung X-radiation in electron probe microanalysis are analyzed within a uniform approach. An algorithm based on the use of wave spectra is proposed for determining the parameters of the functions. It is found that the calculated values of some parameters of approximation functions considerably differ from those presented by the authors of the functions. It is found that the quality of approximating bremsstrahlung X-radiation is strongly affected by the method of calculating the average atomic number of the sample and the corrections for matrix effects. In the wavelength range 0.1 ≤ λ ≤ 1.2 nm for atomic numbers 10 ≤ Z ≤ 83 and accelerating voltages 15 ≤ E ₀ ≤ 25 kV, the best function ensures background estimation with a relative standard deviation of 3–6%, which is comparable with the relative standard deviation of the direct background measurement in routine electron probe microanalysis. The use of the calculation method of the background account at λ > 1.2 nm is complicated because of the significant uncertainty of the absorption factor in the long-wavelength region for the majority of elements.     

Quantitative electron probe microanalysis for the characterization of thin carbon-boron layers in fusion devices

Summary The first wall of the fusion device TEXTOR at the Forschungszentrum Jülich has been coated in situ with an amorphous hydrogen rich carbon/boron film (a-C/B:H) which reduces plasma impurities caused by the plasma surface interaction. The results of the coating process of the 35 m² large inner wall surface have been controlled by a recently developed modification of the quantitative electron probe microanalysis, which has been applied to 12 samples from specified positions inside the tokamak. The quantification itself is based on a Monte Carlo simulation of electron trajectories providing very accurate results for X-ray intensities emitted by elements present in the electron bombarded sample. The Monte Carlo results are used in the present work to calibrate the measured X-ray intensities emitted by boron and carbon from the a-C/B:H layers deposited on pure silicon substrates. As a result the total deposited mass of the layer per area unit as well as the composition of the layers (except hydrogen) could be determined very accurately. The relative errors were less than 7%. The limit of detectability were found to be in the range of one monolayer for boron as well as for carbon.     

Influence of the topography of zinc coated sheet on the results of electron probe microanalysis

As far as possible, electron probe microanalyses (EPMA) must be carried out on optimally smooth surfaces. When analyzing technical surfaces with a roughness resulting from the rolling or coating process, EPMA results are biased, which has consequences especially when determining element mass layer in the detection limit area. This effect was tested and a corrective process was developed on electrolytically galvanized and hot-dip galvanized steel sheet of varying roughness.     

A single-molecule probe based on intramolecular electron transfer

Detecting structure, dynamics, and chemical reactions at the single-molecule level represents the ultimate degree of sensitivity for sensing and imaging. There is a tremendous need to develop new molecular systems and methodology for single-molecule-based sensing. This work presents for the first time the single-molecule spectroscopy of a new molecular probe which uses an intramolecular electron transfer mechanism to detect binding, local structure, and interfacial processes. Moreover, we show how information about the interaction of these probes with their environment is obtained from an analysis of the intensity, duration and time-varying behavior of the single-molecule fluorescence.     

Influence of different correction models on investigations of carbonaceous insulating films by electron beam X-ray microanalysis

Normally quantitative investigations of insulators by electron beam X-ray microanalysis are made possible by coating special samples with thin evaporated carbon films. This, however, will fail if the samples themselves contain carbon as polysilastyrene {[(CH₃)₂Si]_x (CH₃)C₆H₅Si}_n, which is used for the preparation of silicon carbide. Samples of polysilastyrene, together with reference layers (pure silicon) were investigated using different equipment (JEOL, CAMECA) and with varying correction procedures (ZAF, PAP). Compared with the results of reference measurements (elementary analysis, NMR) it appears that the PAP correction procedure is better suited for solving this problem than the classical ZAF correction procedure.