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     

Correction procedures in electron probe microanalysis of bulk samples

In recent years many of the advances in quantitative microprobe analysis have come from the improved ability to model the complex physics in the computer. This has enabled the accuracy of normal bulk analysis to be improved-right down to the very light elements as far as boron-and has extended the technique to the analysis of multiple thin films and layered samples. It has also allowed the user to shortcut the use of standards, though at the cost of somewhat reduced accuracy. Thus the analyst has come to rely more and more on correction procedures of increasing complexity, yet at the same time must understand their limitations. It is likely that in future the computer itself will be able to accumulate the best practice of expert users, advising the newcomer how these procedures can be best applied and where they are most likely to be in error.     

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.     

Grazing-emission electron probe microanalysis of particles near the substrate edge

The distribution of X-ray radiation from a small particle, situated near the sharp edge of a flat substrate and excited by an electron beam, is analyzed theoretically taking into account the effects of the radiation reflection and its partial penetration through the substrate lateral surface. It has been shown that in some cases this dependence is strongly related to the distribution of primary X-ray sources above the substrate, which allows to use the signal — grazing-angle dependence for structure investigations of particles. The proposed technique was tested in experiments with CaCO₃ particles, situated on a pure Si substrate and exposed to a highly concentrated HNO₃ environment. Comparison of the observed angle dependencies for Ca and O characteristic X-ray radiation with calculated results revealed the intrinsic structure of the particles caused by their preliminary chemical treatment.     

Accuracy of film thickness determination in electron probe microanalysis

The thickness of copper films (100–450 nm) on silicon substrates was determined by electron probe microanalysis (EPMA) applying (z) procedures of Pouchou and Pichoir. Film thickness was calculated from experimental k-ratios analyzed with electron energies between 6 and 30 keV using commercial software (LAYERF distributed by CAMECA). The influence of the incident electron energy and X-ray line chosen for analysis on the results was investigated. Accuracy of film thickness determination was evaluated by comparison with Rutherford backscattering spectroscopy (RBS) and secondary ion mass spectrometry (SIMS). The difference between layer thicknesses determined with EPMA and RBS is in general less than 2%, if EPMA measurements are performed with various electron energies. Layer thicknesses determined with Cu-L are mostly closer to values obtained by RBS than those derived from Cu-K radiation. Preliminary SIMS measurements yielded inconsistent results and, thus, cannot be used in this case to determine the layer thickness of Cu films on Si accurately.     

Secondary electron microanalysis

Secondary electron microanalysis is described as a nonconventional method to observe microareas at sample surfaces. The method is characterized by a high lateral and depth resolution and additionally by a typical sensitivity to localized electric potentials and electron work functions. The limits of the method for measurement at high vacuum conditions in conventional scanning electron microscopes are described in connection with electron-sample interactions. Examples for investigations of distributions of localized electric potentials, electron work functions at semiconductors, ferroelectrics and electric ceramics are given.     

X-ray microanalysis of 1.5-10 μm particles in metallurgical research

The importance of particle X-ray microanalysis for contemporary metallurgical research has been accentuated. Corrections in the formulae for the geometric modelling method and simplifications in the calculation procedure are introduced. Conditions for successful application of the peak to background ratio method were outlined. Besides these two methods related to isolated particles a new extrapolation method for matrix embedded particles is developed and comments to the particle weight fraction estimation method for the same kind of particles are given.     

Electron probe microanalysis of SiO2-coated minerals: Subsurface phases in quartz

Crystal fragments of biotite, garnet, and spinel were mounted together in one block which afterwards was sawn into several pieces; each piece was coated with SiO₂ of varying thickness, up to 7.9m. Electron probe microanalysis was carried out at various accelerating voltages of the major elements present, using the non-SiO₂-coated minerals as reference standard.Calibration curves, depth below the surface versus ratios of X-ray yields, have been established with the ultimate goal to use them for a (semi)-quantification of elements present in subsurface phases in quartz, a common host mineral in rocks.     

Assessing the size-dependent chemical speciation of soil particles using electron probe X-ray microanalysis

Soils of the Pereemnaya river catchment, East Siberia, Russia, characterized by high percentage of particles under 10 μm size and the almost total absence of clay minerals, were studied using ultra-thin window electron probe X-ray microanalysis (EPMA). Three subfractions – 10–5 μm, 1–5 μm and <1 μm were distinguished within <10 μm fraction on the basis of mineralogical composition and chemistry peculiarities. Besides the single particles characterization, the bulk chemistry of specified subfractions and their contributions to the bulk soil chemistry were evaluated. It was shown that concentrations of alkali and alkaline-earth metals within <10 μm fraction increased in the row (5–10 μm) < (1–5 μm) < (<1 μm). The presence of two mica types – low-Fe and rich-Fe – was detected in all the subfractions. Being compared with the soil bulk chemistry, the data obtained for fraction <10 μm show that this fraction is the major source of alkali and alkaline-earth metals and consequently the main contributor to element release due to weathering.     

Quantitative electron probe microanalysis of Y-Ba-Cu-O superconducting materials

The high temperature superconductor YBa₂Cu₃O_7–x has been studied by quantitative electron probe microanalysis (EPMA). After investigation of appropriate standards and choice between three different matrix correction methods this technique provides very accurate analytical results including those for oxygen. The quantitative results even allow the determination of the stoichiometry with deviations less than 2% relative. The application of computercontrolled EPMA is demonstrated by the characterization of the microstructure of a ceramic Y-Ba-Cu-O sample. Finally the properties of copperL ₂ andL ₃ valence band spectra are presented for compounds with copper in different valence state.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Quality of electron probe X-ray microanalysis determinations obtained from laboratory reference materials of the coppery alloys and basaltic glasses

Nine coppery alloys and five basaltic glasses have been quantitatively evaluated as the reference materials to employ in electron probe X-ray microanalysis. The optimum conditions for measurements were selected considering the dependence of intensity and detection limit on the conditions of the X-ray radiation excitation and analytical signal recording. The homogeneity of basaltic glasses and coppery alloys has been examined. The dependence of electron probe X-ray microanalysis accuracy on the homogeneity of reference materials was studied in the reference materials of coppery alloys.Six data sets comprising the average concentrations, standard deviations, relative standard deviations, confidence interval and the z-score of data quality were calculated for 50 control samples: 10 alloys, 14 glasses, 2 metals, 24 minerals and oxides. The average compositions of every control sample were derived in 8–16 analyses. The measured values were corrected for matrix effects applying the original program. These series of concentrations have been compared with each other and with the certified/recommended values using 2-pair selective Student's t-test.The results gained from both laboratory reference materials and certified glass reference materials show comparable accuracy. The quality of all available results complies with the “applied geochemistry” category of performance (2nd category). The laboratory reference materials give comparable accuracy to certified reference materials and can be used for calibrating microprobe techniques, as well as data quality control. The application of laboratory reference materials in microanalysis of silicate minerals and coppery alloys allows reliable analytical data to be acquired. The applications in mineralogy and metallurgy can be extended successfully to the targets when certified reference materials are not available.     

Speciation of sulfur in individual aerosol particles from work places by wavelength-dispersive electron-probe microanalysis

The oxidation state of sulfur has been determined by measuring the energy shift of the S K line by wavelength-dispersive electron-probe microanalysis. On flat polished samples the energy shift between sulfate (S⁺⁶) and sulfide (S^-2) was 1.3 eV, in good agreement with previous literature data. The observed energy shift of the S K line is dominated by the change of the valence state of sulfur—the effects of co-ordination geometry and nearest neighbours are small. The relationship between the energy shift of the S K line and the oxidation number of sulfur is linear, to a first approximation. The effect of particle geometry on the position of the S K line is usually small and introduces an error of approximately half an oxidation number. The apparent sulfur valence states observed for individual aerosol particles from work places in a nickel refinery are highly variable and most probably result from different mixtures of the two end-members sulfide and sulfate.     

Thermal stability of beam sensitive atmospheric aerosol particles in electron probe microanalysis at liquid nitrogen temperature

Thin-window electron probe X-ray microanalysis offers new analytical possibilities for low-Z detection (i.e. elements with low atomic number; such as C, N and O). However, the quantitative analysis of individual particles raises some practical questions concerning the technique. From the analytical point of view, beam damage is one of the most important problems due to its big impact on the analysis of individual atmospheric particles. The dependence of the beam-damage effect on the type of collection substrate was studied using standard aerosol particles. Different metallic substrates were rigorously tested in relation to the beam damage effects to different kinds of beam sensitive particles. Ammonium sulfate, ammonium nitrate, sodium nitrate as well as sulfuric acid droplets were analyzed using a liquid nitrogen cooled sample stage on different metallic substrates such as Be, Al, Si and Ag. The obtained results confirm that the use of Be as a collection surface offers some advantages in order to minimize the damage to beam sensitive particles, as suggested in earlier research.     

Interference technique in grazing-emission electron probe microanalysis of submicrometer particles

The distribution of X-ray radiation from a small particle, situated on a flat support and excited by an electron beam, is analyzed theoretically. The interference pattern, appearing within the region of grazing take-off angles, is shown to contain valuable information about the particle structure and composition. It also provides the resources for extracting this information that are valid even in conditions of extremely low signals (e.g. for very small samples), when the effect of background suppression for angles of the total reflection region is insufficient. Characteristic elements of the interference pattern are found that are relatively independent on the noise caused by the support radiation. Algorithms for this noise correction and elimination are proposed. An approximate formalism for the particle structure retrieval, based on the Fourier-transformation properties, is described. Potential applications of the proposed technique are illustrated with numerical models of spherical and hemispherical particles, both homogeneous and of ‘core-and-shell’ structures, with total sizes between 30 and 200 nm. The additional possibilities of studying the shape, structure and elemental composition of small particles have been demonstrated. The general conditions of the experimental realization of proposed methods are discussed.     

Determination of thickness distribution and composition of thin coatings by EPMA: Application in the field of steel sheet production

A new method for the investigation of surface coatings by EPMA is presented. It is based on a physical model which takes into account the X-ray intensity depth distribution, the absorption and the electron backscattering effects at the interface between film and substrate. When combined with the concentration mapping (CM) technique, a two-dimensional film thickness distribution and the film composition can be determined simultaneously. Only bulk standards are required for this method.With some examples in the field of steel sheet production and electrogalvanizing the versatility of the method as well as its high sensitivity are pointed out. Particularly important for practical work is the applicability to almost any combinations of film and substrate materials as well as the wide thickness range from almost the total X-ray emergence depth down to the monolayer range.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Analytical,structural and electrical characterization of SiGe layers by electron microbeam techniques

k-ratios of Ge-L and Si-K measured at different beam energies allow to evaluate simultaneously composition and thickness of SiGe layers on a Si substrate. A simple technique applying backscattered electrons also enables estimation of composition of bulk SiGe and of composition and thickness of relatively thick (200 nm) SiGe layers on Si. Electron channeling patterns of pseudomorphic SiGe/Si structures and of pure Si substrate show no significant differences whereas in relaxed structures a smearing of the pattern with increasing density of misfit dislocations is observed. Under particular conditions the technique of the electron beam induced current permits imaging of recombination-active misfit dislocations with a spatial resolution around 0.2 m. Moreover, a repulsion of holes due to the valence-band offset in a n-Si/SiGe heterostructure was detected.     

The influence of collecting substrates on the single-particle characterization of real atmospheric aerosols

This work investigated the influence of three different collecting substrate materials, Ag and Al foils and grids for transmission electron microscopy (TEM grid), on the morphological and chemical compositional analysis of individual particles collected at an underground shopping area in Seoul, Korea. The feasibility of using each substrate in a quantitative single-particle analysis was evaluated by comparing particle morphologies, X-ray spectra, and elemental quantification results obtained for the three substrates. The morphologies and the quality of X-ray spectra for crystalline mineral particles were very similar among the three substrates. However, water-soluble, CNO-rich aerosols showed different morphologies among the three substrates, mainly due to the differences in the hygroscopic properties of the substrates. The quality of the X-ray spectra of the CNO-rich particles was optimal when collected on the TEM grid. To reliably assess the characteristic X-rays of the CNO-rich particles collected on the Ag and Al foils, appropriate data analysis had to be applied. Especially, the X-ray spectra of the CNO-rich particles collected on Al foil required a new background subtraction procedure. The overall relative abundances of the chemical species, obtained from the three collecting substrates, were in good agreement with each other and single-particle characterization of the real aerosol sample was feasible on the different substrates. However, the TEM grid substrate was the most appropriate for single-particle analysis of the water-soluble CNO-rich particles as: (i) it retains the original morphology and size of the particles, (ii) it allows high contrast in the backscattered electron image (BSEI) mode, and (iii) it provides a high peak-to-background ratio (P/B) with small and correctable interferences in the X-ray spectra.     

Characterization of Oil Fly Ash Particles by Electron Probe Microanalysis

Abstract

An automated electron microprobe was used to characterize more than 25000 fly ash particles with diameters between 1μm and 200μm, which were collected in two fractions from the stack of an oil fired power plant under two different burning conditions. Sample preparation procedures were developed to insure a quantitative particle transfer from the collection container to a Nuclepore filter and the automated localization of the carbonaceous particles in the backscattered electron image was optimized. Size distributions were measured and the results were interpreted in terms of the burning conditions of the power plant.     

The electron microanalyzer (EPMA): a powerful device for the microanalysis of filled polymeric materials

The electron probe microanalyzer is a device often used in the field of geology or in the glass and steel industries. However, it is barely known or used in the polymer field. Thus, in this paper, we investigate the use of electron probe microanalyzer for polymer microanalyses and compared it with a scanning electron microscope equipped with an energy dispersive spectrometer. To show the unique potential of this technique only develop in our lab for polymer application, three different samples were studied: (i) a fire protective epoxy‐based coating submitted to aging in salt water, (ii) the distribution of organometallic catalysts into a thermal isolative silicone polymer, and (iii) the fouling growth of milk protein (biopolymer) on a stainless steel surface. Compared to an energy dispersive spectrometer, with an electron probe microanalyzer it is possible to quickly create X‐ray mappings of low concentration elements at a good resolution, as well as allowing the interpretation of the mechanism of action for the three samples which was impossible using only an energy dispersive spectrometer because of its too low detection resolution. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification by Electron Probe Microbeam Analysis of Submicron Borides in Joints of Nickel Base Superalloys

The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM₂B₂ (M=Mo and M=Co, Cr) and the solid solution boride [Cr_1–x (Mo, W)_x]B.