Quantitative determination of site occupancy of multi-rare-earth elements doped into Ca2SnO4 phosphor by electron channeling microanalysis

X-ray fluorescence analysis based on electron channeling effects in transmission electron microscopy (TEM) was performed on Ca₂SnO₄ phosphor materials doped with Eu³⁺/Y³⁺ at various concentrations, which showed red photoluminescence associated with the ⁵D₀-⁷F₂ electric dipole transition of Eu³⁺ ions. The method provided direct information on which host element site dopant elements occupy, the results of which were compared with those of X-ray diffraction (XRD)-Rietveld analysis. The obtained results indicated that while it is not favorable for a part of Eu³⁺ to occupy the smaller Sn⁴⁺ site, this is still energetically better than creating Ca vacancies or any other of the possible charge balance mechanisms. The local lattice distortions associated with dopant impurities with different ionic radii were also examined by TEM-electron energy-loss spectroscopy (TEM-EELS). The change in PL intensity as a function of dopant concentration is discussed based on the experimental results, although the general concept of concentration quenching applies.     

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.     

Mapping the Distribution of Doping Elementsin Electrolytically Doped Manganese Dioxideby EFTEM and EELS

Summary.  Energy-filtering transmission electron microscopy (EFTEM) and electron energy-loss spectrometry (EELS) have been used to measure the distribution of titanium in titanium-doped electrolytic manganese dioxide, which consists of large particle agglomerates of some micrometer diameter. In contrast to previous investigations, where the distribution of the doping elements can only be investigated at the thinnest regions of the agglomerates, we describe an improved procedure which allows to measure the concentration of the dopant not only at the thinner edges of the particle agglomerate, but also in the interior. The titanium distribution maps showed that titanium is enriched on the surface of the agglomerates and in pores penetrating into their interior. Within the agglomerates, titanium is evenly distributed, and in manganese dioxide the titanium concentration could be analyzed quantitatively by EELS spectrometry. Based on these results, suggestions for possible improvements of the doping process and for the preparation of the product are given. Received November 29, 2000. Accepted (revised) December 12, 2000     

EELS nanoanalysis for investigating both chemical composition and bonding of interlayers in composites

The paper is concerned with the application of analytical transmission electron microscopy (TEM) to characterize both chemical composition and bond state of the elements detected in interlayers in C- and SiC-fibre reinforced composites. The chemical bond state of nanometre-sized regions is characterized by means of electron energy loss spectroscopy (EELS), where respective information is gained by analysing energy loss near edge structures (ELNES). In this context results of Si-L₂₃ ELNES investigations are presented concerning the chemical bonding of silicon with carbon, nitrogen and oxygen. The specific bond state of silicon is revealed by recording series of EEL spectra at high energy resolution across the fibre/ matrix interlayers of interest. Moreover, the element distribution is imaged by energy-filtered TEM.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

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.     

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     

Structural and Chemical Analysis of Materials with High Spatial Resolution

 An understanding of the correlation between microstructures and properties of materials require the characterization of the material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen and on the scattering power of the atoms (ions) present in the analyzed column. The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the electron charge density distribution of the bulk (defect-free) material. The different techniques are described and applied to different problems in materials science. It will be shown that nearly atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments in electron microscopy instrumentation will result in atomic resolution in the foreseeable future.     

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.     

Diffuse-reflectance Fourier transform-infrared spectroscopic microanalysis of the flavonolignans

Diffuse-reflectance Fourier transform-infrared spectroscopic (DRIFT) microanalysis (10 g samples) of a selected series of flavonoids was studied, comparing to transmission FT-IR spectroscopic analysis of the same samples at the mg level. DRIFT was shown to be a useful, sample-saving and reliable IR technique for the structural analysis and compound identification of the mainSilybum genus 3-OH-flavonolignans (silybin, isosilybin, silydianin, silychristin and isosilychristin) and the dihydroflavonol taxifolin.     

Electron probeX-ray microanalysis for the assessment of homogeneity of candidate reference materials at the nanogram level

A new approach to the assessment of homogeneity for powder samples of candidate reference materials with the help of electron probeX-ray micro-analysis (EPMA) is proposed. It is based on the utilisation of the Kolmogorov—Smirnov statistics coupled with the Akaike Information Criterion in the processing of the quantitative EPMA data. The evaluation of three IAEA candidate reference materials with the described approach is discussed.     

Analytical electron microscopy of materials

Analytical electron microscopy enables combined crystallographic and chemical information with a high spatial resolution to be gained from microregions of electron-transparent specimens. This is reached by the combined application of imaging, diffraction and spectroscopic methods, using either a dedicated scanning transmission electron microscope or a conventional high-resolution electron microscope (having a strong objective lens) equipped with suitable X-ray or electron spectrometers. Of the diffraction methods especially the technique of convergent beam diffraction is used, yielding valuable information on crystal structures, lattice parameter changes, symmetry variations and crystal perfection, respectively. For chemical analysis, either energy-dispersive X-ray spectroscopy (EDX) is used or electron energy loss spectroscopy (EELS). Finally, high-resolution electron microscopy in the lateral resolution range of some 0.1 nm allows the reliable geometrical inspection of extreme microregions.     

Standardless X-ray analysis of bulk specimens

The paper gives an overview of the problems of Standardless analysis of bulk specimens by energy dispersive spectrometry (EDS) in scanning electron microscopes (SEM). The interest is concentrated on the present (and future) developments. The influence of the fluorescence excited by the continuum is discussed. Some improvements are proposed for the ionization cross-section. The difficulties due to the Coster-Kronig radiationless transitions are mentioned for the L lines. Emphasis is put on the necessity of an accurate modelling of the detector window, in order to be able to calculate reliably the efficiency of detection, mainly for the ultra-light elements. It is shown that some hypotheses such as the continuity of the fluorescence yield with the atomic number, which are currently accepted for heavier elements, could be wrong in the field of ultra-light elements. The capability of Standardless analysis in special situations is discussed: analysis at oblique electron beam incidence, analysis of specimens with a thin conductive coating, analysis of stratified specimens.     

Spectroscopic imaging techniques for characterization of polymer morphologies: a combination of infrared and electron microscopy

The morphological characterization of polymer blends consisting of polyamide and poly(tetrafluoroethylene) using FT-IR spectroscopy and electron microscopy is described. To enhance the lateral resolution - one of the main limits in infrared spectroscopy - a combination with scanning electron microscopy and analytical electron microscopic methods of a transmission electron microscope was made. The possibilities of electron energy loss spectroscopy and energy filtered transmission electron microscopy (EFTEM) in the area of polymer characterization are outlined.     

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     

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.     

Application of emission spectrometer with laser sampler to microanalysis of pigments from Hubert Robert’s canvas painting

Laser-induced breakdown spectroscopy has been applied to layer-by-layer pigment material microanalysis from the different sections of Hubert Robert’s (1733–1808) painting “Landscape of a Pool with an Obelisk and Ruins of an Aqueduct”. This painting consists of two sections and, therefore, requires thorough examination of the pigments from both sections in order to identify their authenticity. The data obtained on the elemental composition of the paint layers including the ground layer alongside with art examination have formed the basis for the identification, attribution and restoration of both investigated sections of the painting.     

Characterization of individual atmospheric particles by element mapping in electron probe microanalysis

In this paper procedures for the characterization of individual aerosol particles by element mapping in the electron microprobe are presented. The number, size and qualitative chemical composition of particles is derived from a combination of secondary or backscattered electron images and element distribution maps. Accuracy of the size distribution and reliability of the qualitative analysis procedure were checked with silicate samples. In order to obtain a semi-quantitative estimate of the chemical composition of individual particles the count rates taken from element distribution maps are corrected for matrix and geometric effects using particle ZAF procedures.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Ultrastructure and microanalysis of silica bodies in Dactylis Glomerata L.

Silica bodies of orchard grass (Dactylis glomerata L.) were analysed by transmission electron microscopy and X-ray microanalysis. Silica bodies are inserted into the epidermis of the leaf and consist of a rather compact amorphous silica and low carbon. In particular regions of the interface between silica body and cell wall, silica is crossed by electron opaque strands, which are similar to filaments of the cell wall and most probably represent cellulose fibrils. The presence of a higher carbon content in this region than in the compact silica supports this notion. Cells with silicified walls or lumen were found apart from typical silica bodies. They most likely represent early or intermediate stages of silica body formation. Some epidermal cells showed silica deposits between protoplast and cell wall with small but regularly detected nitrogen and phosphorus peaks indicating a particular extracellular chemical composition probably involved in silica accumulation.     

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.     

Local and surface analysis within an analytical electron microscope

Analytical transmission electron microscopes have the ability to display at very high spatial resolution both the structural information of solid specimens prepared as thin films and the spectroscopic information related either to electronic properties or to the elemental composition. An example of study, by electron energy loss spectroscopy, of small spherical silicon particles is given as an illustration of the performances of the technique.