The capabilities of an electrically cooled energy‐dispersive x‐ray detector for quantitative x‐ray fluorescence analysis

The capabilities of the Si PIN diode x‐ray detector were determined and compared with those of a standard Si(Li) detector. The x‐ray fluorescence (XRF) analysis systems assembled with these two detectors included annular radioisotope excitation sources of Cd‐109 and Fe‐55. The systems were calibrated for sensitivity and quantification was performed with fundamental parameters software. Based on the analysis of the standard reference material NIST 2710 (Montana soil), the elemental sensitivities and the limits of detection of both systems were obtained. The elemental sensitivities of the Si PIN detector for fluorescence x‐rays in the energy range up to 10 keV were comparable to those of the Si(Li) detector. At higher fluorescence x‐ray energies the sensitivity of the Si PIN detector gradually decreased and was smaller by a factor of ～4 at 20 keV. The reason was mainly the small thickness of the sensitive volume of the Si PIN diode (0.2 mm) and therefore the smaller relative efficiency of this detector. The assessed limits of detection (LODs) were comparable for the two detectors, which was mainly due to the lower spectral background of the Si PIN detector in excitation with the Cd‐109 source as a result of its smaller sensitive thickness. The accuracy of elemental determinations for the two detectors was comparable and within the limits of the assessed uncertainties, which were calculated considering all the steps of the analysis, i.e. spectrum measurement and analysis, sensitivity calibration and quantification. Copyright © 2004 John Wiley & Sons, Ltd.     

Semiconductor Peltier‐cooled detectors for x‐ray fluorescence analysis

We discuss recent results obtained in the development of Si(Li), Si p–i–n, CdTe p–i–n and CdZnTe x‐ray detectors with Peltier coolers for fabrication of laboratory and portable XRF analyzers. The characteristics of Si(Li) Peltier‐cooled detectors are close to those of detectors cooled with the liquid nitrogen and remain the most preferred type of detectors for the tasks of x‐ray fluorescence analysis. Considerable success was obtained in the improvement of the characteristics of CdTe p–i–n detectors and CdZnTe detectors with a metal–semiconductor–metal structure, effective in the energy range up to 100 keV. The spectra of all detectors are presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Calculation of attenuation and x‐ray fluorescence intensities for non‐parallel x‐ray beams

With the nowadays widespreaded use of x‐ray optics in x‐ray fluorescence analysis, large convergence or divergence angles can occur. This experimental situation violates a basic assumption of the usual fundamental parameter quantification procedure. In order to take beam divergences in micro x‐ray fluorescence analysis into account, a way of calculating fluorescence intensities numerically by Monte Carlo integration is described. For three examples of typical micro‐XRF set‐ups the fluorescence intensities and their deviation from the parallel beam geometry are calculated. Furthermore, we propose a new approach with ‘equivalent angles’ which correct for the beam divergences in fundamental parameter methods. Copyright © 2003 John Wiley & Sons, Ltd.     

Quantitative thickness determination using x‐ray fluorescence: application to multiple layers

The fundamental parameter method using x‐ray fluorescence was applied to the quantitative determination of single and multiple layer thicknesses using a compact experimental setup. Focused white‐beam radiation was obtained from a high‐voltage Mo x‐ray tube and the fluorescence spectra were acquired using a Peltier‐cooled Si solid‐state detector. The results show that in the case of single layers the accuracy of the thicknesses obtained is very good whereas for multiple layer structures the agreement is poorer, especially for the thinnest layers. This indicates a possible drawback of the standard‐free thickness determination scheme based on fundamental parameters for complex samples. Copyright © 2004 John Wiley & Sons, Ltd.     

Portable x‐ray fluorescence spectrometer with a pyroelectric x‐ray generator

A portable x‐ray fluorescence spectrometer was assembled with an x‐ray generator that was driven by a 9 V dry electric battery. Several possible optimum geometries of the x‐ray generator and detector were evaluated, and the results showed that the intensity of fluorescent x‐rays was strong enough when the angle between the x‐ray generator and detector was as small as 30°. The geometrically optimized x‐ray spectrometer was applied to the analysis of paints, plastics and aluminum foils. Pigments in paint and toxic elements in plastic could be easily detected with on‐site analysis. Fe in aluminum foil was quantitatively determined down to the sub‐% level. The detection limit of Fe was 180 ppm for 100 s of measurement. Copyright © 2005 John Wiley & Sons, Ltd.     

Total reflection x‐ray fluorescence analysis—a review

Total reflection x‐ray fluorescence analysis (TXRF) is a special energy‐dispersive x‐ray analytical technique extending XRF down to the ultra trace element range. Detection limits of picograms or nanograms per gram levels are reached with x‐ray tube excitation. Using synchrotron radiation as excitation source, femtogram levels are detectable, particularly important for Si wafer surface analysis. TXRF is specially suited for applications in which only a very small amount of sample is available, as only a few micrograms are required for the analysis. In this review, an overview of theoretical principles, advantages, instrumentation, quantification and application is given. Chemical analysis as well as surface analysis including depth profiling and thin‐film characterization is described. Special research results on extension to low‐Z elements, excitation with synchrotron radiation and x‐ray absorption spectroscopy (XAS) for chemical speciation at trace levels are reviewed. Copyright © 2007 John Wiley & Sons, Ltd.     

Laboratory vacuum spectrometer for the soft x‐ray region

A laboratory surface x‐ray absorption near edge structure ((S)XANES) spectrometer used for measurements in the soft x‐ray region is described. The x‐ray beam path of the spectrometer is enclosed in a vacuum chamber directly connected to the x‐ray generator output port. With this setup, the absorption of the x‐rays in the air is avoided. The developed spectrometer uses a monochromator equipped with cylindrically bent PET(002), KAP(001), and Ge(111) crystals of different Rowland radii working in the Johann focusing geometry. Nine stepping motors are used to control the positions of the monochromator, receiving slit, sample, and detectors. An x‐ray photon energy available in experiment ranges from about 1 keV to 5 keV. A registration of the photoelectrons emitted from the sample with the channeltron is used to carry out surface‐sensitive measurements. The performance of the developed spectrometer is illustrated by spectra measured at the absorption K‐edges of several elements from the Na‐Ti set. Copyright © 2008 John Wiley & Sons, Ltd.     

X‐ray fluorescence analysis with a pyroelectric x‐ray generator

Several types of handy x‐ray fluorescence spectrometers are presented. The results obtained with a Niton spectrometer are presented as a goal to develop a laboratory‐made spectrometer using an Amptek Cool‐X pyroelectric x‐ray generator. A small and cheap charge‐up x‐ray emitting device and its spectrum are also presented. Handy x‐ray spectrometers are now progressing rapidly and the detection limits are in the range of a few ppm for certain elements. Copyright © 2005 John Wiley & Sons, Ltd.     

Pressure study of monoclinic ReO2 up to 1.2 GPa using X‐ray absorption spectroscopy and X‐ray diffraction

The crystal and local atomic structure of monoclinic ReO₂ (α‐ReO₂) under hydrostatic pressure up to 1.2 GPa was investigated for the first time using both X‐ray absorption spectroscopy and high‐resolution synchrotron X‐ray powder diffraction and a home‐built B₄C anvil pressure cell developed for this purpose. Extended X‐ray absorption fine‐structure (EXAFS) data analysis at pressures from ambient up to 1.2 GPa indicates that there are two distinct Re—Re distances and a distorted ReO₆ octahedron in the α‐ReO₂ structure. X‐ray diffraction analysis at ambient pressure revealed an unambiguous solution for the crystal structure of the α‐phase, demonstrating a modulation of the Re—Re distances. The relatively small portion of the diffraction pattern accessed in the pressure‐dependent measurements does not allow for a detailed study of the crystal structure of α‐ReO₂ under pressure. Nonetheless, a shift and reduction in the (011) Bragg peak intensity between 0.4 and 1.2 GPa is observed, with correlation to a decrease in Re—Re distance modulation, as confirmed by EXAFS analysis in the same pressure range. This behavior reveals that α‐ReO₂ is a possible inner pressure gauge for future experiments up to 1.2 GPa.     

X‐ray absorption and x‐ray fluorescence for the characterization of titanium oxide‐modified HPLC silicas

Titanium oxide grafted on to the surfaces of chromatographic silica was investigated by x‐ray fluorescence (XRF) and x‐ray absorption (XAS) spectroscopy and the latter used before and after the extensive use of this material as a support for reversed‐phase high‐performance liquid chromatography (RP‐HPLC). XRF indicated the formation of a complete 2:1 monolayer whereas XAS suggested the presence of more than one titanium oxide structure. These structures show some slight modification after immobilization of PMOS and use in HPLC. Copyright © 2005 John Wiley & Sons, Ltd.     

High‐resolution x‐ray analysis with multilayer gratings

Periodic multilayers are nowadays widely used to perform x‐ray analysis in the soft x‐ray range (photon energy lower than 1 keV). However, they do not permit to obtain high‐resolution spectra such as natural or synthetic crystals. Thus, multilayers cannot resolve interferences between close x‐ray lines. It has been shown and demonstrated experimentally that patterning a grating profile within a multilayer structure leads to a diffractive optics with improved resolving power. We illustrate the use of an Mo/B₄C multilayer grating in the Fe L and C K spectral ranges, around 700 and 280 eV, respectively. First, in the Fe L range, the improved spectral resolution enables us to distinguish the Fe Lα and Lβ emissions (separated by 13 eV). In addition, using a sample made of a mix of LiF and an iron ore, we show that it is possible to easily resolve the F K and Fe L emissions. These examples demonstrate that an improved x‐ray analysis can be obtained with multilayer gratings when there is the need to study samples having elements giving rise to close emission lines. Second, in the C K range, by comparing C Kα spectra from B₄C and cellulose, we show that the shape of the emission band is sensitive to the chemical state of the carbon atom. Copyright © 2009 John Wiley & Sons, Ltd.     

Characterization of x‐rays emerging from between reflector and sample carrier in reflector‐assisted TXRF analysis

The possible application of an Si reflector, which is placed just above the sample carrier in total reflection x‐ray fluorescence (TXRF) analysis, was investigated. The x‐rays that were emitted from an Mo tube and passed between the Si reflector and the Si sample carrier were analyzed with an Si drift detector. In our experimental setup, the angle between the reflector and the sample carrier can be changed by adjusting the inclination of the reflector. The intensity of the x‐rays that emerged from between the two Si surfaces drastically changed depending on the reflector angle. At a proper reflector angle, this intensity showed a maximum and, in addition, the Compton peak in the x‐ray spectrum was suppressed. When this x‐ray beam was used for excitation of TXRF signals, the highest intensity of x‐ray fluorescence emitted from the sample was detected, indicating that these experimental conditions are useful for the enhancement of TXRF intensities. Copyright © 2004 John Wiley & Sons, Ltd.     

The advantages of using digital signal processing in polarized x‐ray fluorescence analysis

Improving the specificity and productivity of XRF is of great relevance for the determination of trace elements in samples of diverse origin. The advantages of using digital signal processing in energy‐dispersive polarized x‐ray fluorescence analysis are demonstrated by comparing the instrumental sensitivities achieved with those obtained by using a conventional analogue signal processing‐based spectrometer. A compact geometry secondary target arrangement was designed to increase the effective solid angles and to reduce the distances between secondary target, sample and detector, thus achieving larger x‐ray fluxes for both the excitation and detection process, resulting in improved instrumental sensitivities. The performance of both spectrometers was evaluated for two different detectors: an Si(Li) detector and a thermoelectrically cooled passivated‐implanted planar silicon detector (X‐PIPS). The uncertainties achieved and accuracy are illustrated for the analysis of a group of sediment and organic‐origin certified reference materials using two different quantitative procedures. Copyright © 2006 John Wiley & Sons, Ltd.     

The multi‐purpose hard X‐ray beamline BL10 at the DELTA storage ring

The layout and the characteristics of the hard X‐ray beamline BL10 at the superconducting asymmetric wiggler at the 1.5 GeV Dortmund Electron Accelerator DELTA are described. This beamline is equipped with a Si(111) channel‐cut monochromator and is dedicated to X‐ray studies in the spectral range from ～4 keV to ～16 keV photon energy. There are two different endstations available. While X‐ray absorption studies in different detection modes (transmission, fluorescence, reflectivity) can be performed on a designated table, a six‐axis kappa diffractometer is installed for X‐ray scattering and reflectivity experiments. Different detector set‐ups are integrated into the beamline control software, i.e. gas‐filled ionization chambers, different photodiodes, as well as a Pilatus 2D‐detector are permanently available. The performance of the beamline is illustrated by high‐quality X‐ray absorption spectra from several reference compounds. First applications include temperature‐dependent EXAFS experiments from liquid‐nitrogen temperature in a bath cryostat up to ～660 K by using a dedicated furnace. Besides transmission measurements, fluorescence detection for dilute sample systems as well as surface‐sensitive reflection‐mode experiments are presented.     

Structural and electronic effects in metallocene catalysts studied by x‐ray techniques

A series of metallocenes, namely, [Cp₂ZrCl₂], [(MeCp)₂ZrCl₂], [(nBuCp)₂ZrCl₂], [(iBuCp)₂ZrCl₂], [(tBuCp)₂ZrCl₂], [Et(Ind)₂ZrCl₂], [Et(IndH₄)₂ZrCl₂], and [MeSi₂(Ind)₂ZrCl₂)] were analyzed by extended x‐ray absorption fine structure (EXAFS) and x‐ray photoelectron spectroscopy (XPS). Complementary techniques, UV–vis spectroscopy and cyclic and differential pulse voltammetry, were employed to characterize the organometallic complexes. The catalysts were evaluated in ethylene polymerization, having methylaluminoxane (MAO) as the cocatalyst, and the resulting polymers were characterized by gel permeation chromatography. The structural and electronic effects caused by the coordination sphere around the metal center and their effects on the catalytic activity and polymer characteristics are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Composition determination for complex and transmitting samples in x‐ray quantitative analysis

In this work, quantitative analysis of x‐ray fluorescence measurements of transmitting samples with complex chemical composition is considered. A method is presented for analytical solution of sample composition including matrix effects, independent of sample thickness and requiring no standards. The method uses fundamental parameters and measured fluorescence signal intensities, and is applicable to transmission geometry measurements for which standard analyses are not applicable. Limitations of the analysis presented here are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Determination of Mg and Ti in Ziegler–Natta catalysts by x‐ray fluorescence spectrometry

The metal content in Ziegler–Natta catalysts based on Ti and Mg derivatives could not be determined directly by x‐ray fluorescence (XRF) spectrometry owing to the instability of the catalyst. The samples were then calcined and the resultant Mg and Ti oxides were characterized by x‐ray diffraction (XRD). A series of synthetic standards were prepared with high‐purity MgO and TiO₂, since there were no available certified standards for the catalysts. Samples and standards were compressed with high‐purity H₃BO₃ flux. This protocol was shown to be reproducible, having a correlation coefficient of 0.9999. The metal contents determined by XRF were in accordance with those obtained by a complexometric titration (Mg) and a UV–visible spectrophotometric method (Ti). Copyright © 2004 John Wiley & Sons, Ltd.     

A high‐resolution X‐ray fluorescence spectrometer and its application at SSRF

A high‐resolution X‐ray fluorescence spectrometer based on Rowland circle geometry was developed and installed at BL14W1 XAFS beamline of Shanghai Synchrotron Radiation Facility. The spectrometer mainly consists of three parts: a sample holder, a spherically curved Si crystal, and an avalanche photodiode detector. The simplicity of the spectrometer makes it easily assembled on the general purpose X‐ray absorption beamline. X‐ray emission spectroscopy and high‐resolution X‐ray absorption near edge spectroscopy can be carried out by using this spectrometer. X‐ray emission preliminary results with high‐resolution about 3 eV of Mn compounds were obtained, which confirmed the feasibility of the spectrometer. The application about Eu (III) retention on manganese dioxide was also studied using this spectrometer. Compared with conventional X‐ray absorption fine structure spectroscopy technique, the fluorescence peak of probed element [Eu (III) Lα] and matrix constituents (Mn Kα) were discriminated using this technique, indicating its superiority in fluorescence detection. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of polycapillary x‐ray lens for x‐ray sources with various spot sizes

The performance of a polycapillary x‐ray lens (PCXRL) is related to the spot size of the x‐ray source. The transmission efficiency of the PCXRL decreases generally with the increase of the x‐ray source spot size. Both the output focal spot size of a focusing PCXRL and the divergence of a parallel PCXRL increase with increasing source spot size. A large source spot size results in more ‘escape halo’, which affects the measured transmission efficiency and the measured output focal spot size. Copyright © 2007 John Wiley & Sons, Ltd.     

Local structure of NiAl compounds investigated by extended X‐ray absorption fine‐structure spectroscopy

The local structures of pure NiAl and Ti‐, Co‐doped NiAl compounds have been obtained utilizing extended X‐ray absorption fine‐structure (EXAFS) spectroscopy. The results provide experimental evidence that Ni antisite defects exist in the Ni‐rich NiAl compounds. The site preference of Ti and Co has been confirmed. Ti occupies the Al sublattice, while Co occupies the Ni sublattice. The structure parameters obtained by EXAFS were consistent with the X‐ray diffraction results. Owing to the precipitation of α‐Cr, the local structure of NiAl‐Cr has not been obtained, making the site preference of Cr unclear.