Simulation of layer measurement with confocal micro‐XRF

A simple model to simulate the measurement of layered structures with confocal micro X‐ray fluorescence (micro‐XRF) was developed and implemented as a computer program. The model assumes monochromatic excitation, considers at the moment only K lines, and simplifies the volume defined by excitation and detection foci as a circle area. First simulation results and comparison with data acquired using the Atominstitut confocal micro‐XRF spectrometer are very promising. The simulation software enables us to perform parameter studies to have a better understanding of the analysis of layered structures with confocal micro‐XRF. Copyright © 2014 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.     

A confocal set‐up for micro‐XRF and XAFS experiments using diamond‐anvil cells

A confocal set‐up is presented that improves micro‐XRF and XAFS experiments with high‐pressure diamond‐anvil cells (DACs). In this experiment a probing volume is defined by the focus of the incoming synchrotron radiation beam and that of a polycapillary X‐ray half‐lens with a very long working distance, which is placed in front of the fluorescence detector. This set‐up enhances the quality of the fluorescence and XAFS spectra, and thus the sensitivity for detecting elements at low concentrations. It efficiently suppresses signal from outside the sample chamber, which stems from elastic and inelastic scattering of the incoming beam by the diamond anvils as well as from excitation of fluorescence from the body of the DAC.     

A simple calibration procedure of polycapillary based portable micro‐XRF spectrometers for reliable quantitative analysis of cultural heritage materials

Portable micro‐X‐ray fluorescence (micro‐XRF) spectrometers mostly utilize a polycapillary X‐ray lens along the excitation channel to collect, propagate and focus down to few tens of micrometers the X‐ray tube radiation. However, the polycapillary X‐ray lens increases the complexity of the quantification of micro‐XRF data because its transmission efficiency is strongly dependent on the lens specifications and the propagated X‐ray energy. This feature results to a significant and not easily predicted modification of the energy distribution of the primary X‐ray tube spectrum. In the present work, we propose a simple calibration procedure of the X‐ray lens transmission efficiency based on the fundamental parameters approach in XRF analysis. This analytical methodology is best suited for compact commercial and portable micro‐XRF spectrometers. The developed calibration procedure is validated through the quantitative analysis of a broad range of samples with archeological relevance such as glasses, historical copper alloys, silver and gold alloys offering an overall accuracy of less than 10%–15%. Copyright © 2015 John Wiley & Sons, Ltd.     

Toward sub‐micro‐XRF working at nanometer range using capillary optics

Capillary optics are used for X‐ray fluorescence micro‐analysis using the Cu Kα line provided by a rotating anode. The excitation beam is focused using a polycapillary lens on a Co–Ti sample. Cylindrical glass capillaries of various diameters are fitted to the X‐ray detector (Energy Dispersive X‐Ray (EDX) analyzer) and displaced along the irradiated zone of the sample. The fluorescence is studied as a function of capillary position. Good agreement is found between experimental and calculated lateral widths of the fluorescence collection, taken into account the cylindrical capillary critical angles relevant in the experiment. The influence of the cylindrical capillary diameter on the signal level detected is studied to estimate the possibility of lateral resolution increase of X‐ray fluorescence technique both in‐lab and in synchrotron environment. Copyright © 2013 John Wiley & Sons, Ltd.     

Element‐selective three‐dimensional imaging of microparticles with a confocal micro‐PIXE arrangement

A detailed report about the confocal experiment and the corresponding data analysis is presented to determine local atomic concentrations in a thick sample with a micrometer resolution. X‐ray emission from a quartz substrate, loaded by aerosol particles, was induced by a scanning proton microbeam and observed by an Si(Li) spectrometer whose field of view was narrowed by a polycapillary lens. A series of X‐ray images were recorded at different positions of the sample along the microbeam axis when the particles were driven through the sensitive microvolume. The concentrations reconstructed in three dimensions were used to extract penetration profiles of the strongest X‐ray emitters (Fe, Ca, S) in an aerosol sample together with the surface profile of the matrix (Si). The results show exponentially dumped depth profiles with characteristic length depending on particle size. Copyright © 2009 John Wiley & Sons, Ltd.     

Non‐invasive time‐course imaging of apoptotic cells by confocal Raman micro‐spectroscopy

Confocal Raman micro‐spectroscopy (CRMS) was used to measure time‐course spectral images of live cells undergoing apoptosis without using molecular labels or other invasive procedures. Human breast cancer cells (MDA‐MB‐231) were exposed to 300 µM etoposide to induce apoptosis, and Raman spectral images were acquired from the same cells at 2‐h intervals over a period of 6 h. The purpose‐built inverted confocal Raman micro‐spectrometer integrated an environmental enclosure and wide‐field fluorescence imaging. These key instrumental elements allowed the cells to be maintained under sterile physiological conditions (37 °C, 5% CO₂) and enabled viability and apoptosis assays to be carried out on the cells at the end of CRMS measurements. The time‐course spectral images corresponding to DNA Raman bands indicated an increase in signal intensity in apoptotic cells, which was attributed to DNA condensation. The Raman spectral images of lipids indicated a high accumulation of membrane phospholipids and highly unsaturated non‐membrane lipids in apoptotic cells. This study demonstrates the potential of CRMS for label‐free time‐course imaging of individual live cells. This technique may become a useful tool for in vitro toxicological studies and testing of new pharmaceuticals, as well as other time‐dependent cellular processes, such as cell differentiation, cell cycle and cell–cell interactions. Copyright © 2010 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.     

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.     

Depth‐selective elemental imaging of microSD card by confocal micro XRF analysis

A semiconductor device, a microSD card, was measured by using two XRF instruments. 2D elemental images were obtained using a micro‐XRF system with a spatial resolution of 10 µm. Elemental distributions of the near‐surface region of the sample were clearly shown. Titanium was observed in the resin constituting the sample. Nickel and gold were observed on a terminal and localization of the sample. Elemental distribution of copper reflected the circuit structure of the measurement area that was in the neighborhood of the sample surface. Moreover, the elemental depth distributions of the sample were measured by using a confocal micro‐XRF instrument. The confocal micro‐XRF instrument was constructed in the laboratory with fine‐focus polycapillary x‐ray optics. The depth resolution of the developed spectrometer was 13.7 µm at an energy of Au Lβ (11.4 keV). The elemental images obtained at near‐surface by confocal micro‐XRF were the same as the results obtained from 2D micro‐XRF. However, different Cu images were obtained at a depth of several tens of micrometers. This indicates that microSD cards consist of a few different Cu‐circuit structure designs. The elemental depth distributions of each circuit structure of the semiconductor device were clearly shown by confocal micro‐XRF. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of matrix effects on portable and stationary XRF spectrometers for cultural heritage samples

In this work, we compare the matrix effects for two different X-ray fluorescence spectrometers, a portable and a stationary one, in order to evaluate their performances in terms of scattering radiation for different matrices. Five reference materials were analyzed: orchard leaves (NBS-1571), clay (ISE-954), bone ash (NIST-1400), 70% copper alloy (BCR-691) and 22 ct gold alloy (Fisher). The results obtained showed similar behavior for both spectrometers. The lowest background was obtained for the light matrix and an increase was observed for intermediate atomic number matrices, reaching a maximum for copper and gold alloys.     

X-radiography of cultural heritage materials using handheld XRF spectrometers

This study investigated the feasibility, repeatability, and limitations of using handheld X-ray fluorescence spectrometers to perform radiography with thorough safety measures. Radiography is a well-established nondestructive technique commonly used in the field of cultural heritage preservation but not easily accessible to many. Equipped with X-ray generating tubes, handheld spectrometers could potentially assist performing radiographic tasks off-site due to their portability and increasing availability. These spectrometers are designed to work at close range within a limited voltage range and wattage, so the exposure settings should be modified for the spectrometers to generate big enough X-ray beams to irradiate the artifacts and enough radiation to penetrate through them to produce useful radiographs. Using a Bruker Tracer 5i, the effective beam spread angle, which was computed from several test shots, was used to determine the constant relation between the area of irradiation and the X-ray source to image-receptor distance. Based on inverse square law and the total wattage limitation of the spectrometer, current and exposure time were recalculated to produce informative radiographs. Because of the limitations of the tested spectrometer, this method is best applicable to an area smaller than 9 cm, with the scanning distance shorter than half a meter. The spectrometer cannot be used to radiograph materials that require higher voltage than it can produce.     

XRF induced by PIXE: Comparison with radioisotope XRF

XRF induced by PIXE (XRF-PIXE) using silver as a primary target was compared with a standard radioisotope XRF system using Cd-109 as a primary exciting source, for the analysis of single-element thin standards. The sensitivity of the two methods were determined for elements from Cl to Mo. XRF is found to be more sensitive for elements from Cl to Mn, whereas XRF-PIXE is found to be more suitable for elements from Fe to Mo. Both techniques can be considered as complementary to each other.     

Monte Carlo simulation code for confocal 3D micro‐beam X‐ray fluorescence analysis of stratified materials

Stratified materials are of great importance for many branches of modern industry, e.g. electronics or optics and for biomedical applications. Examination of chemical composition of individual layers and determination of their thickness helps to get information on their properties and function. A confocal 3D micro X‐ray fluorescence (3D µXRF) spectroscopy is an analytical method giving the possibility to investigate 3D distribution of chemical elements in a sample with spatial resolution in the micrometer regime in a non‐destructive way. Thin foils of Ti, Cu and Au, a bulk sample of Cu and a three‐layered sandwich sample, made of two thin Fe/Ni alloy foils, separated by polypropylene, were used as test samples. A Monte Carlo (MC) simulation code for the determination of elemental concentrations and thickness of individual layers in stratified materials with the use of confocal 3D µXRF spectroscopy was developed. The X‐ray intensity profiles versus the depth below surface, obtained from 3D µXRF experiments, MC simulation and an analytical approach were compared. Correlation coefficients between experimental versus simulated, and experimental versus analytical model X‐ray profiles were calculated. The correlation coefficients were comparable for both methods and exceeded 99%. The experimental X‐ray intensity profiles were deconvoluted with iterative MC simulation and by using analytical expression. The MC method produced slightly more accurate elemental concentrations and thickness of successive layers as compared to the results of the analytical approach. This MC code is a robust tool for simulation of scanning confocal 3D µXRF experiments on stratified materials and for quantitative interpretation of experimental results. Copyright © 2011 John Wiley & Sons, Ltd.     

Distribution of selected elements in atherosclerotic plaques of apoE/LDLR‐double knockout mice assessed by synchrotron radiation‐induced micro‐XRF spectrometry

Apolipoprotein E and LDL receptor double‐knockout (apoE/LDLR^?/?) mice represent a reliable experimental model of atherosclerosis. The aim of the present study was to examine the elemental content of atherosclerotic plaques using synchrotron radiation‐induced micro x‐ray fluorescence (XRF) spectrometry. Numerous essential and trace elements were detected in cross‐sections of aortic roots collected from 6‐month‐old apoE/LDLR^?/? mice fed with chow diet. Two‐dimensional maps of the elemental distribution and point recordings were compared with images of consecutive sections stained histologically, allowing precise localization of the analyzed elements in morphologically defined areas of aortic lesion. The sulphur was detected in areas occupied by macrophages and smooth muscle cells. Iron was observed in high concentrations in cardiac and smooth muscle, blood clots and in adjacent coronary vessels. Lower concentrations of iron were seen in the regions of plaques rich in macrophages and lipids. Copper was detected in higher amounts only in cardiac muscle and its concentration in plaques was very low. There was a quite high content of calcium in aortic plaque areas containing lipids and macrophages. Much higher concentrations of calcium were observed in mineral deposits, mostly located in the aortic media. Similar distribution was also characteristic for phosphorus. Zinc was observed in moderately low concentrations in atheromas. Higher content of zinc was seen in smooth musculature, in cardiac muscle and in mineral concretions. The presented results provide a substantial morphological and physicochemical background for further investigations aiming to evaluate pharmacological and dietary treatment of atherosclerosis in an apoE/LDLR^?/? mouse model. Copyright © 2008 John Wiley & Sons, Ltd.     

In situ confocal micro‐Raman spectroscopic investigation of rearrangement kinetics and phase evolution of UHMWPE during annealing

Ultrahigh molecular weight polyethylene was investigated using in situ confocal micro‐Raman spectroscopy during annealing at 110.0 °C. Based on the Raman spectra, crystalline, amorphous, and all‐trans noncrystalline fractions were recognized to evaluate rearrangement kinetics during isothermal annealing at 110.0 °C and phase evolution during cooling from 110.0 to 30.0 °C. For the crystalline fraction, a substantial increase from 0.600 ± 0.001 to 0.639 ± 0.008 was observed during the first 24.2 min of annealing; a very gradual increase from 0.639 ± 0.001 to 0.679 ± 0.001 occurred during the following 114.6 min. For the amorphous phase fraction, conversely, a sharp decrease from 0.240 ± 0.000 to 0.213 ± 0.004 was exhibited during the first 24.2 min of annealing, and then, a flat decrease happened from 0.213 ± 0.004 to 0.192 ± 0.001 as time expanded to 138.8 min. For the all‐tans noncrystalline fraction, a gradual decrease was shown from 0.160 ± 0.000 at 0.0 min to 0.128 ± 0.001 at 138.8 min. The rearrangement rate constant K was obtained to be 0.632 by an Avrami equation. During cooling from 110.0 to 30.0 °C, there were two phase evolution regions: region 1 from 110.0 to 90.0 °C and region 2 from 90.0 to 30.0 °C. The crystal lamella thickened faster in region 1 than in region 2. The amorphous layer continually decreased in content in the combined region of 1 and 2. The all‐trans noncrystalline phase obviously decreased in region 1 and then almost maintained a constant level in region 2. Copyright © 2014 John Wiley & Sons, Ltd.     

Polycapillary‐optics‐based micro‐XANES and micro‐EXAFS at a third‐generation bending‐magnet beamline

A focusing system based on a polycapillary half‐lens optic has been successfully tested for transmission and fluorescence µ‐X‐ray absorption spectroscopy at a third‐generation bending‐magnet beamline equipped with a non‐fixed‐exit Si(111) monochromator. The vertical positional variations of the X‐ray beam owing to the use of a non‐fixed‐exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K‐edge is approximately 200 µm on the lens input side and this was reduced to ～1 µm for the focused beam. Beam sizes (FWHM) of 12–16 µm, transmission efficiencies of 25–45% and intensity gain factors, compared with the non‐focused beam, of about 2000 were obtained in the 7–14 keV energy range for an incoming beam of 0.5 × 2 mm (vertical × horizontal). As a practical application, an As K‐edge µ‐XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant.     

Quadruplex CARS micro‐spectroscopy

We demonstrate a technique for simultaneous detection of coherent anti‐Stokes Raman scattering (CARS) at four vibrational frequencies, using simple passive optical elements and without spectrally resolved detection. The technique is based on pump and Stokes femtosecond pulses selectively exciting vibrational resonances through spectral focusing. By replicating the pump and Stokes pair into four pairs, each traveling through appropriate glass elements, we simultaneously excite four different vibrational frequencies. The resulting CARS is a periodic train of intensities detected by a single photomultiplier and frequency analyzed to retrieve its Fourier coefficients. We demonstrate detection of methanol and ethanol mixtures in water and quantitative determination of their concentration owing to the improved chemical selectivity of this quadruplex CARS scheme. Copyright © 2012 John Wiley & Sons, Ltd.     

Multielement analysis of lichen samples using XRF methods. Comparison with ICP‐AES and FAAS

This research presents the contents of Ca, Fe, Zn, Br, Rb, Sr and Pb in lichen samples used as biomonitors of air pollution collected in Havana. Statistical comparisons were made among the results obtained in three campaigns during three years. Two X‐Ray Fluorescence (XRF) methods were used, employing for excitation an annular ¹⁰⁹Cd source and a Mo X‐ray tube with a molybdenum secondary target. In both cases, matrix effects were corrected by the use of normalization for the Compton scattered peak; in this way the determination is more efficient. For quality control of the results, biological Certified Reference Materials were analyzed and were made comparisons between XRF, Inductively Coupled Plasma‐Atomic Emission Spectrometry and Flame Atomic Absorption Spectrophotometry. No significant differences were found between the different techniques. The elemental distribution patterns obtained for each metal were associated with different pollution sources, thus contributing to the assessment of air pollution in Havana. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of multivariate linear regression methods in micro‐Raman spectrometric quantitative characterization

Chemical imaging was used in this study as a powerful analytical tool to characterize pharmaceuticals in solid form. The majority of analyses are evaluated with bilinear modelling using only the pure component spectra or just the chemical images themselves to estimate the concentrations in each pixel, which are far from true quantitative determination. Our aim was to create more accurate concentration images using regression methods. For the first time in chemical imaging, variable selections with interval partial least squares (PLS) and with genetic algorithms (PLS‐GA) were applied to increase the efficiency of the models. These were compared to numerous bilinear modelling and multivariate linear regression methods such as univariate regression, classical least squares (CLS), multivariate curve resolution–alternating least squares (MCR‐ALS), principal component regression (PCR) and partial least squares (PLS). Two component spray‐dried pharmaceuticals were used as a model. The paper is shown that, in contrast to the usual way of using either external validation or cross‐validation, both should be performed simultaneously in order to get a clear picture of the prediction errors and to be able to select the appropriate models. Using PLS with variable selection, the root mean square errors were reduced to 3% per pixel by keeping only those peaks that are truly necessary for the estimation of concentrations. It is also shown that interval PLS can point out the best peak for univariate regression, and can thereby be of great help even when regulations allow only univariate models for product quality testing. Variable selection, besides yielding more accurate overall concentrations across a Raman map, also reduces the deviation among pixel concentrations within the images, thereby increasing the sensitivity of homogeneity studies. Copyright © 2015 John Wiley & Sons, Ltd.