Characteristic X-ray Lines Research Articles

Comparison of experimental and theoretical X-ray intensities from (In)GaAs specimens investigated by energy-dispersive X-ray spectroscopy in a transmission electron microscope

Experimental measurements of X-ray line intensity ratios in a transmission electron microscope are compared over several orders of magnitude of sample thicknesses, from the nm- to the mm- range, with Monte-Carlo simulations using two different software packages. It is shown that the form of the thickness dependence of the K/L ratio of characteristic X-ray lines for GaAs is reproduced qualitatively, but the numerical differences between software packages are large. A scheme is presented for improving the simple k-factor method, taking explicitly into account the thickness dependence that remains even after application of the usual absorption and fluorescence corrections. This is done in first-order approximation by linear regression. The improvement in determining the correct indium concentration in specimens of InGaAs is calculated to be 1at%.

Photo-recombination in highly charged Ne, Si, S and Ar ions

X-ray resolved Dielectronic Recombination studies of highly charged Ne, Si, S and Ar ions were performed in an electron beam ion trap. The prominent Δn = 1 DR transitions have been detected via the Kα and higher characteristic x-ray lines. The centroid energy shift between the KLM resonances identified through the Kα and Kβ photons indicate sensitivity to the intermediate state sublevel population and therefore to the dynamics of DR. In addition, several Δn = 2 transitions were clearly observed in the spectrum.

The direct measurement of the signal charge behavior in pnCCDs with subpixel resolution

In the MPI-Halbleiterlabor (MPI-HLL) we are developing fully depleted pn-type Charge Coupled Devices (pnCCD) with a thick radiation-sensitive region. Since 1997, the mesh experiment has been established as an unique technique to determine an X-ray interaction position with subpixel resolution. In order to investigate the signal charge behavior in pnCCDs, we performed the mesh experiment using various characteristic X-ray lines. Cu-L (0.9 keV), Al-K (1.5 keV) and Ti-K (4.5 keV) were used and the device operated under various conditions, e.g. register voltages. We obtained the restored pixel images for various X-ray event patterns. The photon entrance window of the back illuminated pnCCD shows highly uniform detection efficiency within a pixel. We measured the charge cloud size generated by an X-ray photon inside the CCD. The measured charge cloud sizes are around 6 μ m (rms) depending on the X-ray energy. The operation with different register conditions revealed asymmetries and regions with a weaker electric field around pixel boundaries.

Determination of lanthanides by source excited energy dispersive X-ray fluorescence (EDXRF) method after preconcentration with ammonium pyrrolidine dithiocarbamate (APDC)

A new analytical procedure for determination of lanthanides in environmental samples after chemical separation from major matrix elements on DOWEX 50W-X8 resin followed by preconcentration with chelating agent ammonium pyrrolidine dithiocarbamate (APDC) and analyses of thin targets by energy dispersive X-ray fluorescence (EDXRF) method using 109Cd as the source of excitation was presented. Characteristic Lα X-ray lines of the lanthanides were used for calculations of the net peak area and mass concentrations. The influence of pH value of the solution and addition of organic matter on the complexation was investigated. Percentage of recovery of each lanthanide after separation on DOWEX 50W-X8 resin was also determined. Accuracy of the method was tested on standard reference materials and real environmental samples (red mud material). For that purpose samples of standard reference materials and red mud were prepared as thick targets and directly analyzed (without the separation step) by EDXRF method using 241Am as the excitation source. In that case lanthanides concentrations were determined over their characteristic Kα X-ray lines and results were compared with those obtained after separation/preconcentration step described above. Results showed that selected lanthanides made stable complexes with APDC in the alkaline medium with the maximum recovery at pH = 8. The presence of organic matter slightly modified the complexation by means of somewhat higher recovery percentage at pH lower than 7 and approx. 20% lower recovery at pH higher than 7. Recovery of the elements after separation on DOWEX 50W-X8 resin and preconcentration with APDC at pH = 8 varied from 91.4% (Pr) to only 24.9% in the case of Dy. Concentrations of lanthanides measured in standard reference material and environmental samples of red mud after microwave digestion, separation on DOWEX 50W-X8 resin, preconcentration with APDC at pH = 8 and recalculation on the percentage of recovery were in good agreement with certified values in the case of SRM as well as with the concentrations obtained by direct determination over Kα lines using 241Am excitation source in the case of red mud leading to the conclusion that presented method was applicable for the determination of lanthanides in real environmental samples.

Field emission arrays for medical x-ray imaging

Experiments demonstrate the feasibility of using microfabricated cold field emission cathodes in x-ray sources for medical imaging. Electron beam currents of 25mA at voltages of 25kV have been used to produce x-ray source focal spot diameters of 0.2mm. Analysis of both filtered and unfiltered x-ray spectra from molybdenum anodes show clear characteristic x-ray lines. These x-ray source characteristics are consistent with the requirements for human breast imaging.

Time-resolved investigation of ionization processes in the Dresden Electron Beam Ion Source

The emission of characteristic x-ray lines of iron and krypton ions was measured in dependence on the confinement time in an Electron Beam Ion Source, the DRESDEN EBIS. Primarily the measurement was focused on x-ray lines from dielectronic recombination (DR) processes. Due to the sharp resonant character of DR processes the formation of individual ion charge states can be observed at different electron energies (resonance energies) with time-resolved energy-dispersive x-ray spectroscopy. In the case of iron ions, experimentally observed resonance energies are compared to resonance energies calculated with the Flexible Atomic Code (FAC). Further, on outer-shell Kα x-ray satellites of krypton ions are time-resolve analyzed to construct the evolution of the ionization of krypton ions in the electron beam.

Distribution of calcium carbonate and silicone elastomer in a flame retardant system based on ethylene–acrylate copolymer, chalk and silicone elastomer and its effect on flame retardant properties

AbstractA combination of microscopy studies (SEM, ESEM/EDX, and TEM/EDX) is proven to be useful in locating chalk particles and silicone elastomer in a flame retardant system based on ethylene–acrylate copolymer, chalk, and silicone elastomer. The dispersion of the two additives was also obtained. The chalk particles were visually observed (at a certain degree of magnification), and the silicone elastomer was detected using characteristic X‐ray mapping and line scans. The analysis provided a good contrast between chalk particles and silicone elastomer in the surrounding polymer matrix. It is shown that dispersion of the additives depends on the mixing conditions, where tougher mixing conditions improve dispersion. A discussion is given on how dispersion correlates with the flame retardant properties of this system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2085–2095, 2006

Comment on “Direct evidence of nanocluster-induced luminescence in InGaN epifilms” [Appl. Phys. Lett. 86, 021911 (2005)

In a recent letter, Chang et al. claim to have obtained “Direct evidence of nanocluster-induced luminescence in InGaN epifilms.” The work comprises measurements by x-ray diffraction XRD , scanning electron microscopy SEM , energy dispersive x-ray spectrometry EDS , and cathodoluminescence CL of a 0.2 m thick In0.186Ga0.814N layer on a GaN buffer layer grown by metal organic chemical vapor deposition MOCVD . The authors present an XRD scan on a symmetric 0002 reflection where the InGaN-related diffraction peak is shown to have two components. This observation is interpreted as “clear and direct evidence of phase separation.” Vegard’s law is used directly to obtain the “two” compositions in the InxGa1−xN film, allegedly corresponding to x=0.125 and x=0.223. Subsequently, the authors present an SEM/CL surface image of the InxGa1−xN film where they identify brighter and darker regions on a 1 m length scale. In addition, EDS measurements at electron beam energies of 15 keV in the so-called “nanoclusters” were performed. By comparing the intensity of the In and Ga characteristic x-ray lines the authors argue that the “nanoclusters” observed in the SEM image correspond to In-rich regions. Finally, the paper presents spatially resolved CL results showing a two component CL peak whose relative intensities vary with the beam position in the sample surface. Besides an overstretching of the term “nano,” which is clear even for an audience outside the field see the length scale of 1 m in Fig. 2 , the interpretation and conclusions inferred from the experimental results in Ref. 1 have the potential to mislead unwary readers. Consequently, a more careful examination is mandatory. This comment highlights a few ambiguous issues and attempts to provide some clarification. Starting from the XRD results, it should be stressed that the observation of two out-of-plane lattice constants, c1 and c2, cannot be interpreted as evidence of two phases. This “direct” deduction of phase segregation is, in fact, based on an incorrect application of Vegard’s neglecting the strain effects of in a strained epitaxial system. This common mis-

Radiative Auger Effect and Extended X-Ray Emission Fine Structure (EXEFS)

Radiative Auger spectra are weak X-ray emission spectra near the characteristic X-ray lines. Radiative Auger process is an intrinsic energy-loss process in an atom when a characteristic X-ray photon is emitted, due to an atomic many-body effect. The energy loss spectra correspond to the unoccupied conduction band structure of materials. Therefore the radiative Auger effect is an alternative tool to the X-ray absorption spectroscopy such as EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure), and thus it is named EXEFS (Extended X-ray Emission Fine Structure). By the use of a commercially available X-ray fluorescence spectrometer or an electron probe microanalyzer (EPMA), which are frequently used in materials industries, we can obtain an EXEFS spectrum within 20 min. The radiative Auger effect, as an example, demonstrates that the study on atomic many-body effects has become a powerful tool for crystal and electronic structure characterizations. The EXEFS method has already been used in many industries in Japan. Reviews about the applications and basic study results on the radiative Auger effect are reported in this paper.

Calculation of the contributions of scattering effects to the X-ray fluorescent intensities for light matrix samples

The contributions of scattering effects to the X-ray fluorescent intensities were calculated by considering the intensity of scattered primary fluorescence radiation that is scattered into the direction of detector, the secondary enhancement by coherent scattering radiation and incoherent scattering radiation for light matrix samples on the basis of the theoretical calculations. Relative intensities for nine different characteristic X-ray lines for the synthesized fused disks were calculated and compared with the measured relative intensities. It was found from this study that the contributions of scattering effects to the fluorescent intensities of analytes in fused disk samples are sizeable. Moreover, the magnitude of contribution of scattering effects increases with the increase of atomic number of analyte or/and the decrease of the content of the fluorescent element in the fused disk samples, which is about several percents of that excited by primary radiation, or even more than 10% for PbLβ 1. The average relative error of the calculated relative intensities compared with the measured values is 0.93% after scattering effects was considered, while the average relative error of the values calculated by NRLXRF for the same lines is 2.75%. The calculated relative intensities after considering the scattering effects are more agreeable to the measured values. Therefore, more accurate results for fundamental parameter method are expected with the consideration of scattering effects, especially for light matrix samples.

Femtosecond laser induced X-ray emission from metal alloys, polymers and color filters

Various material surfaces were irradiated on a moving stage with focused laser pulses from a conventional 1 kHz femtosecond laser system, and X-ray emission spectra were measured during the laser ablation of the materials. Sharp K or L characteristic X-ray lines from the elements contained in the materials were clearly observed in a range of 2–15 keV. Signals due to copper and zinc were recognizable within a few minutes when a brass surface was irradiated. Poly(vinyl chloride) gave a marked emission originating from chlorine. When a color glass filter was irradiated, the detection of cobalt and arsenic was possible even though the amounts of these components were estimated to be less than 1 wt.% by using an electron probe microanalyzer. Time-integrated emission spectra in the visible region were also monitored during the femtosecond laser ablation of these materials. The emission spectra in the visible region were complicated owing to peaks originating from air components and white continuum emissions. Thus, the elemental analysis by femtoseond laser induced X-ray is considered to be useful for some samples. The etched trenches left at the surfaces after the laser ablation were examined with an optical microscope. The trench width varied with the materials, which may be attributed to changes in the irradiation area giving maximum counts of X-ray emission.

Elemental composition of marine sponges from the Berlengas natural park, western Portuguese coast

AbstractAnalytical studies of sponges have recently become a matter of interest, since these organisms have been reported to accumulate high levels of some elements, including heavy metals, which may have an anthropogenic origin, allowing their application as environmental pollution indicators. In the present work, 35 sponges collected in August 1998 at the Berlengas Natural Park were classified and analysed by secondary target energy‐dispersive x‐ray fluorescence spectrometry (EDXRF). Some major, minor and trace elements could be determined: Al, Si, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr, Zr, I and Pb. To assess some local influences on the sponge composition, two sediment samples were also taken from the area and analysed. Besides these elements, sponges are constituted by fairly high percentages of elements that do not emit characteristic x‐ray lines. Therefore, absorption corrections for quantitative calculations were carried out taking into account the ratio between the inelastic and elastic scattered incident radiation from a silver secondary target to calculate the mean atomic number of the light matrix. Calibration was performed using chemical compounds and standard reference materials. Precision, accuracy and detection limits for the range of elements determined by the method are particularly suitable for the chemical analysis of these organisms. Results for the sediment chemical composition indicated the existence of high Ca and low Si levels and confirmed the absence of any trace metal contamination in the region. The sponge composition showed low Si contents, even in siliceous specimens. Certain high elemental contents determined in some species indicated a clear selective bioaccumulation of particular trace elements, such as Ni, Zn and As, which is not dependent on local influences. Copyright © 2003 John Wiley & Sons, Ltd.

Implementation of a spectrum fitting procedure using a robust peak model

AbstractThe need for an accurate description of characteristic x‐ray lines has led to the development of complex peak models that combine a Gauss, a shelf and a tail function. Via relationships that describe the shelf and tail parameters as a function of the energy, it is possible to reduce the number of fit parameters significantly. In this work, we carried out an experiment to study the shelf and tail parameters obtained with an HPGe detector. We observed a strong discontinuity in the shelf and tail parameters around the K‐edge energy of Ge. This indicates that these parameters are strongly dependent on the mass‐attenuation coefficient of the detector material. Therefore, we propose relationships that describe those parameters as a function of the energy and the mass‐attenuation coefficient. The implementation of these relationships in a fitting procedure results in a more robust fitting procedure with a much smaller number of fitting parameters. Excellent fits for HPGe spectra can be obtained. Because the detector dependence seems to be fairly general, we could successfully apply the model to Si(Li) spectra also. Copyright © 2003 John Wiley & Sons, Ltd.

Radiation applications in art and archaeometry: X-ray fluorescence applications to archaeometry. Possibility of obtaining non-destructive quantitative analyses

The possibility of obtaining quantitative XRF analysis in archaeometric applications is considered in the following cases: (i) Examinations of metallic objects with irregular surface: coins, for instance. (ii) Metallic objects with a natural or artificial patina on the surface. (iii) Glass or ceramic samples for which the problems for quantitative analysis rise from the non-detectability of matrix low Z elements. The fundamental parameter method for quantitative XRF analysis is based on a numerical procedure involving he relative values of XRF lines intensity. As a consequence it can be applied also to the experimental XRF spectra obtained for metallic objects if the correction for the irregular shape consists only in introducing a constant factor which does not affect the XRF intensity relative value. This is in fact possible in non-very-restrictive conditions for the experimental set up. The finenesses of coins with a superficial patina can be evaluated by resorting to the measurements of Rayleigh to Compton scattering intensity ratio at an incident energy higher than the one of characteristic X-ray. For glasses and ceramics the measurements of the Compton scattered intensity of the exciting radiation and the use of a proper scaling law make possible to evaluate the matrix absorption coefficients for all characteristic X-ray line energies.

Modulation of x-ray line intensity emitted by a periodic structure under electron excitation

We report on the intensity modulation of a characteristic x-ray line emitted by a periodic structure, as a function of the observation angle. This intensity variation takes place around the Bragg direction corresponding to the diffraction of the x-ray line by the emitting structure. An enhancement of the emitted radiation is observed and interpreted on the basis of the reciprocity theorem. The enhancement remains unchanged by varying the number of emitting periods. Following Yariv and Yeh [J. Opt. Soc. Am. 67, 438 (1977)], a possible application as x-ray resonator to achieve a distributed feedback soft x-ray laser is envisaged.

A method to measure the effective gas path length in the environmental or variable pressure scanning electron microscope.

A simple method is described to determine the effective gas path length when incident electrons scatter in the gas above the specimen. This method is based on the measurement of a characteristic x-ray line emitted from a region close to the incident beam. From various experimental measurements performed on various microscopes, it is shown that the effective gas path length may increase with the chamber pressure and that it is also often dependent of the type of x-ray bullet.

Two-wave X-ray optical diagnostics of Ge xSi 1− x/Si modulation-doped heterostructures

New X-ray optical methods—two-wave reflecto- and refractometry—have been used for the first time for the determination of Ge x Si 1− x /Si composition and exact measurements of multilayer heterostructure thicknesses. Both techniques are based on simultaneous measurements of two intense characteristic X-ray lines separated from the polychromatic X-ray probe by semitransparent monochromators. X-ray reflectometry of multilayer structures completely eliminates intensity drift influence and geometrical errors at small grazing angles. The refractometry technique provides direct determination of refractive index decrement and the respective value of x in a solid solution with ∼1% accuracy. Refractometry data are not influenced by mechanical strain and by presence of overlaying thin film structure.

Two-phase (ferroelectric and antiferroelectric) nuclei and diffuse phase transition in the vicinity of the ferroelectric–antiferroelectric–paraelectric triple point

X-ray studies of the crystal structure in Pb1−x(Li1/2La1/2)xZr1−yTiyO3 solid solutions at the phase transition from a paraelectric state into ordered states near the triple ferroelectric–antiferroelectric–paraelectric point of the “Ti-content–temperature” phase diagram are carried out. Analysis of the shape of characteristic x-ray lines indicates the presence of two-phase nuclei with ferroelectric and antiferroelectric types of dipole ordering in the crystal lattice of the solid solutions above the point of the paraelectric phase transition (the Curie temperature).

Complete Identification using Spectral Imaging, Compass, and Phaseid

The complete and accurate identification of all of the phases present in a sample is the ultimate goal of any materials investigator. The identification should include compositional as well as crystalline measurements for unique characterization. in an SEM, the composition of individual regions can be routinely determined via EDS or WDS analysis. The main limitation is the need to visually identify the individual regions from the images alone. A method to limit this restriction is to collect x-ray maps of the field-of-view. This technique has the benefit of providing the spatial distribution of the elemental species, but requires knowledge of all of the elements of interest before the start of the analysis and composition quantification cannot be performed with data only from the maps. Another disadvantage is the possibility that materials may have similar compositional analyses but may be different phases only manifested by crystallographic means.A better method of complete phase identification involves the collection and analysis of spectral images and the subsequent crystallographic phase identification via EBSD. Spectral imaging consists of the collection of complete EDS spectra at each location within a field-of-view. From this 3-D data set, a series of elemental maps may be extracted for visualizing the spatial distribution of any elements of interest. This data set is especially useful because elements, and even characteristic x-ray lines, can be fully analyzed after the data collection with total flexibility.

Measurement and interpretation of the low-energy wing of Fe K β1,3 characteristic X-ray line

Special profile of Fe K β 1,3 characteristic line emitted by free atoms is measured and compared with the theoretical Hartree–Fock calculations. It is shown that the low-energy wing structure, which is not resolved in the emission in solid state, can be well described by the superposition of the profiles corresponding to the 5D 4, 3P 4 and 3H 4 parent terms of the 3d 6 shell.