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.     

ED‐XRF set‐up for size‐segregated aerosol samples analysis

The knowledge of size‐segregated elemental concentrations in atmospheric particulate matter (PM) gives a useful contribution to the complete chemical characterisation; this information can be obtained by sampling with multi‐stage cascade impactors. In this work, samples were collected using a low‐pressure 12‐stage Small Deposit Impactor and a 13‐stage rotating Micro Orifice Uniform Deposit Impactor^?. Both impactors collect the aerosol in an inhomogeneous geometry, which needs a special set‐up for X‐ray analysis. This work aims at setting up an energy dispersive X‐ray fluorescence (ED‐XRF) spectrometer to analyse quantitatively size‐segregated samples obtained by these impactors. The analysis of cascade impactor samples by ED‐XRF is not customary; therefore, as additional consistency test some samples were analysed also by particle‐induced X‐ray emission (PIXE), which is more frequently applied to size‐segregated samples characterised by small PM quantities. A very good agreement between ED‐XRF and PIXE results was obtained for all the detected elements in samples collected with both impactors. The good inter‐comparability proves that our methodology is reliable for analysing size‐segregated samples by ED‐XRF technique. The advantage of this approach is that ED‐XRF is cheaper, easier to use, and more widespread than PIXE, thus promoting an intensive use of multi‐stage impactors. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

A modular system for XRF and XRD applications consisting of a microfocus X‐ray source and different capillary optics

In recent years, new components for x‐ray analysis have been developed: capillary optics, microfocus x‐ray tubes and compact detectors, e.g. energy‐dispersive detectors without liquid nitrogen cooling. Microfocus tubes have a relatively low power but their brightness is up to 100 times higher than for normal x‐ray tubes which are used in diffractometry. A combination of these tubes with highly efficient capillary optical elements allows one to obtain parallel or focused beams of high intensity. Combining such a special source with detectors of different kinds, a compact system can be realized which may be successfully used in micro‐XRF, in diffraction and microdiffraction, etc. The system presented is designed in a modular way so that the components may be replaced by each other. Some examples of applications of such systems are reported. Copyright © 2004 John Wiley & Sons, Ltd.     

Nondestructive elemental depth profiling of Japanese lacquerware ‘Tamamushi‐nuri’ by confocal 3D‐XRF analysis in comparison with micro GE‐XRF

We have applied recently two XRF (micro x‐ray fluorescence) methods [micro‐Grazing Exit XRF (GE‐XRF) and confocal 3D‐XRF] to Japanese lacquerware ‘Tamamushi‐nuri.’ A laboratory grazing‐exit XRF (GE‐XRF) instrument was developed in combination with a micro‐XRF setup. A micro x‐ray beam was produced by a single capillary and a pinhole aperture. Elemental x‐ray images (2D images) obtained at different analyzing depths by micro GE‐XRF have been reported. However, it was difficult to directly obtain depth‐selective x‐ray spectra and 2D images. A 3D XRF instrument using two independent polycapillary x‐ray lenses and two x‐ray sources (Cr and Mo targets) was also applied to the same sample. 2D XRF images of a Japanese lacquerware showed specific distributions of elements at the different depths, indicating that ‘Tamamushi‐nuri’ lacquerware has a layered structure. The merits and disadvantages of both the micro GE‐XRF and confocal micro XRF methods are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Novel high‐resolution silicon drift detectors

Silicon drift detectors (SDDs) are used as energy‐dispersive detectors for x‐ray fluorescence analysis in commercial systems. Because of the low capacitance of the readout anode, achieved by the device topology and by the integration of the first FET on the chip, noise contributions are very small, allowing good energy resolution at low shaping times and high count rates. Typical energy resolution is better than 147 eV FWHM at 5.9 keV (Mn Kα), at ?10°C. This allows the chips to be cooled with a thermoelectric element, avoiding the use of liquid nitrogen. SDD chips are produced at MPI‐Halbleiterlabor in Munich with different geometries and areas. Recently, a new SDD has been developed which places the anode and the integrated JFET at the margin of the chip where it can easily be shielded from direct irradiation with the use of a collimator. The new layout allows the design of a readout anode with smaller area and therefore reduces the capacitance to values of about 120 fF compared with 200–250 fF with standard SDDs. The result is an improvement in energy resolution down to 128 eV at ?15°C. A second effect is the enhancement of the peak‐to‐background values to 6000 homogeneously across the active area of the detector. Copyright © 2004 John Wiley & Sons, Ltd.     

Improvement of spatial resolution of µ‐XRF by using a thin metal filter

An improvement of spatial resolution of µ‐XRF by using a thin metal filter was investigated. The size of the x‐ray beam focused by the polycapillary x‐ray lens depended on the energy of the characteristic x‐rays. Original spot sizes at the focal point were 48 µm for CrKα, 41 µm for NiKα, and 28 µm for MoKα, respectively. To make the x‐ray beam size small, Ti? Cu thin foil was placed between the output of the lens and the focal point as a metal filter to reduce the continuous x‐rays. Finally, the x‐ray microbeam size was improved to 30 µm by applying a filter. Clear 2D mapping images of Cr, Fe, and Ni in 300‐mesh stainless steel could be obtained by applying this filter. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of the detection limits in the analysis of some medium atomic number elements measured with a portable XRF and an external proton beam PIXE spectrometer system

A portable X‐ray fluorescence (XRF) spectrometer system was constructed using an Amptek Mini‐X X‐ray tube and an X‐123 compact spectrometer. The spectrometer is optimised for the best limits of detection. Its analytic properties are tested and compared with an analogous laboratory‐based instrument, an external beam proton‐induced X‐ray emission spectrometry (PIXE) setup. Depending on elements in question the thick target detection limits of this portable XRF device are comparable or even lower than the PIXE setup. Copyright © 2011 John Wiley & Sons, Ltd.     

Large‐surface‐area diamond (111) crystal plates for applications in high‐heat‐load wavefront‐preserving X‐ray crystal optics

Fabrication and results of high‐resolution X‐ray topography characterization of diamond single‐crystal plates with large surface area (10 mm × 10 mm) and (111) crystal surface orientation for applications in high‐heat‐load X‐ray crystal optics are reported. The plates were fabricated by laser‐cutting of the (111) facets of diamond crystals grown using high‐pressure high‐temperature methods. The intrinsic crystal quality of a selected 3 mm × 7 mm crystal region of one of the studied samples was found to be suitable for applications in wavefront‐preserving high‐heat‐load crystal optics. Wavefront characterization was performed using sequential X‐ray diffraction topography in the pseudo plane wave configuration and data analysis using rocking‐curve topography. The variations of the rocking‐curve width and peak position measured with a spatial resolution of 13 µm × 13 µm over the selected region were found to be less than 1 µrad.     

Quantitative or semi‐quantitative?–laboratory‐based WD‐XRF versus portable ED‐XRF spectrometer: results obtained from measurements on nickel‐base alloys

‘Semi‐quantitative’ analytical procedures are becoming more and more popular. Using such procedures, the question of the accuracy of results arises. The accuracy of an analytical procedure depends to a great extent on spectral resolution, counting statistics and matrix correction. Two ‘semi‐quantitative’ procedures are compared with a quantitative analytical program. Using a laboratory‐based wavelength‐dispersive x‐ray fluorescence (WD‐XRF) spectrometer and a portable energy‐dispersive x‐ray fluorescence (ED‐XRF) spectrometer, 28 different nickel‐base alloy Certified Reference Materials (CRMs) were analyzed. Line interferences and inaccurate matrix correction are reasons for deviations from the reference value. As the comparison shows, ‘semi‐quantitative’ analyses on the WD‐XRF spectrometer can be accepted as quantitative determinations. The investigations show that the results obtained with the portable ED‐XRF spectrometer do not meet the quality requirements of laboratory analysis, but they are good enough for field investigations. Copyright © 2004 John Wiley & Sons, Ltd.     

GE‐MXRF analysis of multilayer films

Polycapillary x‐ray optics (capillary x‐ray lens) is now popular in x‐ray fluorescence (XRF) analysis. Such an x‐ray lens can collect x‐rays emitted from an x‐ray source in a large solid angle and form a very intense x‐ray microbeam which is very convenient for micro x‐ray fluorescence (MXRF) analysis. In this paper, a new method called grazing exit micro x‐ray fluorescence analysis (GE‐MXRF), which combines an x‐ray lens used to form an intense XRF source was developed and applied in multilayer film analysis. Such a method can give the information of film composition, density, and thickness. Through two‐dimensional scan of the film sample, the information of film uniformity can be acquired; meanwhile, this method is also useful in adjusting experiment condition during the film preparation with metal vapor vacuum arc (MEVVA) source ion implantation. Copyright © 2008 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.     

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.     

Measurement of background components in wavelength dispersive X‐ray fluorescence spectrometry

Three components of the background have been investigated: first, characteristic radiation of the lamellas of the collimator excited by secondary x‐ray beam; second, secondary x‐ray beam scattered by the lamellas of the collimator; third, diffusive and incoherent scattering of the secondary x‐ray beam by the focusing crystal. The relationships between chemical content of the specimen and the intensity of the first and the second components were determined by a wavelength‐dispersive x‐ray spectrometer that has an energy‐dispersive x‐ray detector. The intensity of the third component was very low. It was not found in this experiment. Copyright © 2006 John Wiley & Sons, Ltd.     

Generation of experimental L x‐ray fluorescence cross‐sections for inter‐elements at inter‐energies EL1 ≤ E ≤ EK (computer program IGELCS)

The experimental values of L x‐ray fluorescence (XRF) cross‐sections are not available for all the elements in the range La–U, at all the photon energies E in the range EL1 ≤ E ≤ EK. To generate L XRF cross‐sections, where experimental measurements are not available, two empirical relations have been developed, one between the L XRF cross‐sections and photon energy and the other between the L XRF cross‐sections and atomic number. For the measured data on L XRF cross‐sections at incident energies between Ll and K edges of an element and the data on L XRF cross‐sections for elements in the range 57 ≤ Z ≤ 92 at an energy value, polynomial fits have been derived. The L XRF cross‐section values generated with the derived empirical relations were found to be in agreement with the experimental values within their experimental uncertainties. Subsequently, a software code IGELCS was developed to interpolate and to generate the cross‐sections at inter‐energies and for inter‐elements in a single computer run. The running of the software requires minimum input data on five elements at five common energies. Copyright © 2003 John Wiley & Sons, Ltd.     

Improvements of the low‐energy performance of a micro‐focus x‐ray source for XRF analysis with the SEM

X‐ray Fluorescence (XRF) with a scanning electron microscope (SEM) is a valuable completion of the analytical capabilities of SEMs. Small and compact micro‐focus x‐ray sources are mounted to the microscope chamber, and the x‐ray spectra are monitored with conventional EDS systems. Up to now the x‐ray tubes used for the micro‐focus x‐ray sources are equipped with beryllium windows about 100 µm thick. The poly‐capillary x‐ray lenses have their transmission maximum at photon energies around 10 keV. It drops down in both low‐ and high‐energy ranges. Hence, L‐radiation from an Mo or Rh target will be strongly attenuated, and the excitation of fluorescence in the soft x‐ray range becomes very ineffective. A new micro‐focus x‐ray source was developed. It is characterised by a lower self‐absorption in the tube target, thin beryllium windows and an x‐ray optics having a large distance between its foci and the maximum of transmission at about 5 keV. Thus K line fluorescence of light elements becomes effectively excited by the L‐radiation from Mo or Rh tube targets. The detection limit for sodium oxide in glass was found to be below 1 mass%. Copyright © 2009 John Wiley & Sons, Ltd.     

Development of a high‐resolution confocal micro‐XRF instrument equipped with a vacuum chamber

A confocal micro‐X‐ray fluorescence (micro‐XRF) instrument equipped with a vacuum chamber was newly developed. The instrument is operated under a vacuum condition to reduce the absorption of XRF in the atmosphere. Thin metal layers were developed to evaluate the confocal volume, corresponding to depth resolution. A set of thin metal layers (Al, Ti, Cr, Fe, Ni, Cu, Zr, Mo, and Au) was prepared by a magnetron sputtering technique. The depth resolutions of the new instrument were varied from 56.0 to 10.9 µm for an energy range from 1.4 to 17.4 keV, respectively. The lower limit of detection (LLD) was estimated by comparison with a glass standard reference material NIST SRM 621). The LLDs obtained by a conventional micro‐XRF were compared with the LLDs obtained by a confocal micro‐XRF instrument. The LLDs were improved in the measurement under confocal configuration because of the reduction of background intensity. Finally, layered materials related to forensic investigation were measured. The confocal micro‐XRF instrument was able to nondestructively obtain the distribution of light elements that cannot be detected by measurement in air. Copyright © 2013 John Wiley & Sons, Ltd.     

Broad‐beam PIXE and µ‐PIXE analysis of normal and in vitro demineralized dental enamel

Dental enamel has been widely studied by particle‐induced x‐ray emission (PIXE), but less attention was paid to its demineralization, which leads to caries formation. Using broad‐beam PIXE and µ‐PIXE, we investigated normal enamel and the in vitro formation of pre‐carious lesion in lactic acid solution, aiming also to evaluate intercusp differences within the same tooth. Broad‐beam PIXE was performed using 3.0 MeV protons, and µ‐PIXE maps of Ca, Fe and Zn were collected with 3.1 MeV protons at ～4 µm resolution. In normal enamel a differentiated Ca‐rich surface layer was observed, where Fe and Zn reached their highest levels. In deeper layers, Fe and Zn evidenced quasiperiodic patterns of maxima, possibly due to coupled diffusion‐reaction catalytic processes involved in the enamel growth. Both Fe and Zn appeared to be located in a few distinct types of pools. Near the surface, demineralization induced an increase of Fe, Cu, Zn, Sr and Pb with respect to Ca, attributed to partial hydroxyapatite dissolution and/or to chelate extraction and concentration of trace metals. Ca maps revealed limited changes in the surface layer and a massive loss in the inner enamel; here, Fe was almost depleted and Zn partially removed. The maps of Ca, Fe and Zn demonstrated major intercusp variations in both normal and altered enamel. Thus, broad‐beam PIXE and µ‐PIXE, which do not require (semi)thin sectioning of the tooth as the conventional methods, provide compositional and structural insight of normal dental enamel, of its intercusp variability and of the alterations produced by in vitro demineralization, largely not accessible to the current techniques, and highly relevant for understanding the incipient caries formation. Copyright © 2008 John Wiley & Sons, Ltd.     

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.