Polycapillary X-ray Lens Research Articles

Ultrafast time resolved x-ray diffraction, extended x-ray absorption fine structure and x-ray absorption near edge structure

Ultrafast time resolved x-ray absorption and x-ray diffraction have made it possible to measure, in real time, transient phenomena structures and processes induced by optical femtosecond pulses. To illustrate the power of these experimental methods, we present several representative examples from the literature. (I) Time resolved measurements of photon/electron coupling, electron/phonon interaction, pressure wave formation, melting and recrystallization by means of time resolved x-ray diffraction. (II) Ultrafast x-ray absorption, EXAFS, for the direct measurement of the structures and their kinetics, evolved during electron transfer within molecules in liquid phase. (III) XANES experiments that measure directly pathway for the population of high spin states and the study of the operating mechanism of dye activated TiO2 solar cell devices. The construction and use of novel polycapillary x-ray lenses that focus and collimate hard x-rays efficiently are described.

Size-Resolved Source Apportionment of Aerosol Particles with a Confocal Micro X-Ray Fluorescence Spectrometer

A laboratory confocal micro X-ray fluorescence (micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) in the excitation channel and a polycapillary parallel X-ray lens (PPXRL) in the detection channel was used to carry out the size-resolved source apportionment of aerosol particles. The PPXRL in the detection channel both increased the collection angle of the detector and improved the signal-to-noise ratio of the X-ray spectrum. When this confocal micro-XRF spectrometer was used to carry out the quantitative XRF analysis of single aerosol particles with smaller size than that of the overlapping foci of the PFXRL and the PPXRL, the sensitivity was corrected by using a Gaussian function. The size-resolved “fingerprint database” for the air pollution sources was established based on the quantitative XRF results for single aerosol particles. The size-resolved aerosol particles on hazy-foggy days in Beijing were apportioned.

A deep view in cultural heritage—confocal micro X-ray spectroscopy for depth resolved elemental analysis

Quantitative X-ray fluorescence (XRF) and particle induced X-ray emission (PIXE) techniques have been developed mostly for the elemental analysis of homogeneous bulk or very simple layered materials. Further on, the microprobe version of both techniques is applied for 2D elemental mapping of surface heterogeneities. At typical XRF/PIXE fixed geometries and exciting energies (15–25 keV and 2–3 MeV, respectively), the analytical signal (characteristic X-ray radiation) emanates from a variable but rather extended depth within the analyzed material, according to the exciting probe energy, set-up geometry, specimen matrix composition and analyte. Consequently, the in-depth resolution offered by XRF and PIXE techniques is rather limited for the characterization of materials with micrometer-scale stratigraphy or 3D heterogeneous structures. This difficulty has been over-passed to some extent in the case of an X-ray or charged particle microprobe by creating the so-called confocal geometry. The field of view of the X-ray spectrometer is spatially restricted by a polycapillary X-ray lens within a sensitive microvolume formed by the two inter-sectioned focal regions. The precise scanning of the analyzed specimen through the confocal microvolume results in depth-sensitive measurements, whereas the additional 2D scanning microprobe possibilities render to element-specific 3D spatial resolution (3D micro-XRF and 3D micro-PIXE). These developments have contributed since 2003 to a variety of fields of applications in environmental, material and life sciences. In contrast to other elemental imaging methods, no size restriction of the objects investigated and the non-destructive character of analysis have been found indispensable for cultural heritage (CH) related applications. The review presents a summary of the experimental set-up developments at synchrotron radiation beamlines, particle accelerators and desktop spectrometers that have driven methodological developments and applications of confocal X-ray microscopy including depth profiling speciation studies by means of confocal X-ray absorption near edge structure (XANES) spectroscopy. The solid mathematical formulation developed for the quantitative in-depth elemental analysis of stratified materials is exemplified and depth profile reconstruction techniques are discussed. Selected CH applications related to the characterization of painted layers from paintings and decorated artifacts (enamels, glasses and ceramics), but also from the study of corrosion and patina layers in glass and metals, respectively, are presented. The analytical capabilities, limitations and future perspectives of the two variants of the confocal micro X-ray spectroscopy, 3D micro-XRF and 3D micro-PIXE, with respect to CH applications are critically assessed and discussed.

Depth Elemental Imaging of Forensic Samples by Confocal micro-XRF Method

Micro-XRF is a significant tool for the analysis of small regions. A micro-X-ray beam can be created in the laboratory by various focusing X-ray optics. Previously, nondestructive 3D-XRF analysis had not been easy because of the high penetration of fluorescent X-rays emitted into the sample. A recently developed confocal micro-XRF technique combined with polycapillary X-ray lenses enables depth-selective analysis. In this paper, we applied a new tabletop confocal micro-XRF system to analyze several forensic samples, that is, multilayered automotive paint fragments and leather samples, for use in the criminaliztics. Elemental depth profiles and mapping images of forensic samples were successfully obtained by the confocal micro-XRF technique. Multilayered structures can be distinguished in forensic samples by their elemental depth profiles. However, it was found that some leather sheets exhibited heterogeneous distribution. To confirm the validity, the result of a conventional micro-XRF of the cross section was compared with that of the confocal micro-XRF. The results obtained by the confocal micro-XRF system were in approximate agreement with those obtained by the conventional micro-XRF. Elemental depth imaging was performed on the paint fragments and leather sheets to confirm the homogeneity of the respective layers of the sample. The depth images of the paint fragment showed homogeneous distribution in each layer expect for Fe and Zn. In contrast, several components in the leather sheets were predominantly localized.

Size-resolved source apportionment of aerosol particles using polycapillary X-ray lens with a plateau in its focal spot

A laboratory micro X-ray fluorescence spectrometer based on a special polycapillary X-ray lens (PXRL) was used to carry out the source apportionment of aerosol particles. In the curve of the distribution of the X-ray intensity in the focal spot of the special PXRL, there was a plateau with a diameter of 21.3 μm in which the distribution of the X-ray intensity was homogeneous. The gain in flux density in the plateau of the PXRL is 1490. The uniformity of this plateau was 2.9%. This was helpful for the quantitative X-ray fluorescence analysis of a single aerosol particle with smaller size than that of the plateau of the PXRL. The fingerprint database of aerosol particles with given sizes from various air pollution sources was established with the single particle analysis method. The size-resolved source apportionment of aerosol particles in haze in Beijing city was performed with this fingerprint database.

Sample Surface and Near-surface Analysis by Confocal 3D XRF Spectrometer

We have developed a confocal 3D-XRF spectrometer in combination with polycapillary X-ray lenses and a laboratory X-ray source. The depth resolutions of the 3D-XRF configuration estimated by scanning of Au and Cr thin foils were approximately 50 μm for AuLα, and 100 μm for CrKα, respectively. The capacity of the depth-sensitive analysis of the confocal setup was investigated by scanning a thick plastic reference sample concluding trace metals of Ti, Cr, Co and Pb. The depth sensitivity in deeper region was significantly decreased than that in the surface region because of the absorption of X-ray irradiation and X-ray fluorescence in the material. The calculated LLD values of Cr at each depth were 9.4 mg/kg at 300 μm, 23 mg/kg at 500 μm, 38 mg/kg at 700 μm, 77 g/kg at 900 μm, and 110 mg/kg at 1100 μm, respectively. 3D elemental analysis with the confocal XRF setup was demonstrated for an electrical Cu cable covered with PVC. The 3D elemental images agreed well with the actual distributions of the sample. The confocal 3D-XRF has a great advantage for 3D elemental analysis as well as nondestructive depth analysis at ambient pressure.

Grazing Exit Micro X-ray Fluorescence Analysis of a Hazardous Metal Attached to a Plant Leaf Surface Using an X-ray Absorber Method

If human beings or animals repeatedly ingest plant leaves contaminated with minute quantities of hazardous metals (Pb, As, Hg, Cd, etc.), the metals will gradually accumulate in their bodies. When the quantities of the metals in the bodies reach toxic levels, they may cause serious symptoms of poisoning. Therefore, it is significant to detect and analyze the minute quantities of hazardous metals that attach to plant leaves in terms of epidemiology and disease prevention. We developed grazing exit micro X-ray fluorescence analysis (GE-micro-XRF), which was expected to analyze the localized surface of an aqueous plant leaf with a much faster and simpler sample treatment than with conventional analytical methods, to detect Pb attached to a surface of a leaf of Camellia hiemalis. A micro X-ray beam was produced by using a polycapillary X-ray lens. GE-v-XRF is a grazing exit X-ray analysis (GE-XA) method in which X-rays emitted from only the near-surface region of a specimen are selectively detected under a grazing exit angle condition (extremely low exit angle near 0 degrees). In any GE-XA method, X-rays emitted from inside the specimen must be absorbed inside the specimen and attenuated when X-rays pass through the specimen. However, we deduced that X-rays emitted from inside aqueous organic material such as a plant leaf are scarcely absorbed because X-ray absorption in any aqueous organic material is much smaller than that in most metallic and semiconductor materials, which was analyzed with GE-XA methods. Therefore, we have developed a novel GE-micro-XRF method in which a chip of a silicon wafer is placed between the analyzed leaf and an X-ray detector as an absorber of the X-rays emitted from inside the leaf. As a result of GE-XRF analysis of a leaf dipped in Pb standard solution using the X-ray absorber, we have for the first time selectively detected X-rays emitted from the near-surface region of an aqueous plant leaf. Therefore, we have detected X-rays emitted from Pb with much higher peak/background ratios (P/B ratios) as compared to those of conventional XRF analysis. In the analysis, we also found a difference in element distributions between the leaf surface and its interior. Therefore, we observed and analyzed a cross section of the leaf with a SEM-EDX to confirm the validity of this result. The result of the analysis of the cross section has been in excellent agreement with that of the XRF analysis.

Fundamental characteristics of polycapillary x‐ray optics combined with glass conical pinhole for micro x‐ray fluorescence spectrometry

AbstractWe have developed a new micro x‐ray fluorescence spectrometry (µ‐XRF) instrument using polycapillary x‐ray lens (PCXL) combined with glass conical pinhole (GCP). The x‐rays focused by the PCXL were focused again by the GCP. The size of the obtained x‐ray microbeam was estimated by a wire scanning method. In our instrument, the size of the x‐ray microbeam end was 25 µm for Cr Kα at 0.5 mm from the GCP. The divergence angle of x‐ray microbeam was 15 mrad. In order to evaluate the performance of our instrument, the gain (x‐ray flux density) was estimated. The gain in our instrument was corrected by comparison of the intensity per unit area for a Cu pinhole aperture. The gain thus obtained was approximately 1400. This highly intense micro x‐ray beam will be useful for micro‐XRF analysis. Copyright © 2009 John Wiley & Sons, Ltd.

Focusing synchrotron radiation using a polycapillary half-focusing X-ray lens for imaging

An imaging system based on a polycapillary half-focusing X-ray lens (PHFXRL) and synchrotron radiation source has been designed. The focal spot size and the gain in power density of the PHFXRL were 22 microm (FWHM) and 4648, respectively, at 14.0 keV. The spatial resolution of this new imaging system was better than 5 microm when an X-ray charge coupled device with a pixel size of 10.9 x 10.9 microm was used. A fossil of an ancient biological specimen was imaged using this system.

Identification of origin of single aerosol particles using polycapillary X-ray lens

A micro X-ray fluorescence (Micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) and a laboratory X-ray source was designed to carry out the XRF analysis of single aerosol particles. The minimum detection limit (MDL) of this Micro-XRF spectrometer was 9 ppm for the Fe-Kα. The percentage of the particles of vehicle exhaust among aerosol particles was studied in Beijing, Chinese capital, during the test of odd–even driving restrictions for Beijing 2008 Olympics Games. This Micro-XRF spectrometer had potential applications in the analysis of single aerosol particles.

Development and application of glancing incident X-ray fluorescence spectrometry using parallel polycapillary X-ray lens

A new glancing incident X-ray fluorescence (GIXRF) spectrometer using parallel polycapillary X-ray lens has been developed. Integrated with a Zr filter and slits, a highly collimated and monochromatic X-ray beam has been achieved. This method eliminated the monochromator used in the conventional GIXRF method. Moreover the parallel X-ray lens increased the acceptance solid angle and hence increases intensities of the excitation spectrum. In this paper, this method has been applied in analysis of single crystal and film sample.

X-ray Energy Dependence of the Properties of the Focused Beams Produced by Polycapillary X-ray Lens

We investigated X-ray energy distribution in an X-ray microbeam produced by a polycapillary X-ray lens in combination with a sealed-type X-ray tube. This polycapillary X-ray lens has an output focal distance (OFD) of approximately 15 mm. The size of the X-ray microbeam and its OFD were estimated by using a wire scanning method. In our case, the sizes of the X-ray microbeams at the output focal distance were 49 microm for Mo L(alpha), 36 microm for W L(alpha), and 28 microm for Mo K(alpha). The spot sizes depend on the energy of the X-ray fluorescence. The reason for the energy dependence is that X-ray capillary optics is based on the principle of propagation through glass capillaries by means of X-ray total external reflection. The evaluated OFD values of Mo L(alpha) and Mo K(alpha) were slightly changed in 17 microm. However, a deviation of 100 microm from the OFD caused only a 3% increase of the focal spot size. Therefore, we concluded that the OFD showed no significant dependence on X-ray energy.

Characterization of polycapillary X-ray lens for application in confocal three-dimensional energy-dispersive micro X-ray diffraction experiments

A confocal technology based on polycapillary X-ray optics is proposed to perform three-dimensional energy-dispersive micro X-ray diffraction. A three-dimensional energy-dispersive micro X-ray diffractometer based on a polycapillary focusing X-ray lens (PFXRL) in the excitation channel and a polycapillary parallel X-ray lens (PPXRL) in the detection channel has been designed. At 2\theta = 90^ \circ, the lateral resolution l_X \times l_Y of this diffractometer is 49.7 \times 49.9 \rm \micro m at 7.5 keV, and its depth resolution d_Z is 48.1 \rm \micro m at 8.0 keV. The total resolution of this diffractometer in \Delta d/d is 6.5% at 6.4 keV and 2\theta = 140.2^ \circ.

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

AbstractThe 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.

An energy dispersive micro X-ray diffractometer based on a combined system of polycapillary optics

An energy dispersive micro X-ray diffractometer based on a combined system of two polycapillary X-ray lenses is designed. The polycapillary X-ray lens in the excitation channel is either a polycapillary parallel X-ray lens (PPXRL) or a slightly focusing polycapillary X-ray lens (SFPXRL). The polycapillary X-ray lens in the detection channel is a PPXRL. At 6.4 keV and 2 θ = 141.5°, the total resolution of the diffractometer based on a SFPXRL in the excitation channel and a PPXRL in the detection channel in Δ d/ d is 4.8%.

A new film analysis method using polycapillary X-ray lens

Grazing emission X-ray fluorescence (GE-XRF) is a development of XRF related to total reflection XRF. This paper proposed a GE-MXRF setup involved a polycapillary X-ray lens. Polycapillary lens is an effective optics to obtain μm-size primary X-ray beam. Using this proposed setup, we applied it to the analysis of film samples, and the information of film thickness, composition and density can be acquired, which is very useful in semiconductor industry.

Development of confocal micro X-ray fluorescence instrument using two X-ray beams

A new confocal micro X-ray fluorescence instrument was developed. This instrument has two independent micro X-ray tubes with Mo targets. A full polycapillary X-ray lens was attached to each X-ray tube. Another half polycapillary lens was attached to a silicon drift X-ray detector (SDD). The focal spots of the three lenses were adjusted to a common position. The effects of the excitation of two X-ray beams were investigated. The instrument enabled highly sensitive three-dimensional X-ray fluorescence analysis. We confirmed that the X-ray fluorescence intensity from the sample increased by applying the two independent X-ray tubes in confocal configuration. Elemental depth profiling of black wheat was demonstrated with the result that each element in the surface coat of a wheat grain showed unique distribution.

Performances of synchrotron radiation microbeam focused by monolithic half focusing polycapillary X-ray lens

A monolithic half focusing polycapillary X-ray lens (MHFPXRL) composed of 289,000 capillaries is used to produce a synchrotron radiation microbeam. The energy dependence of the output focal distance, focal spot size, transmission efficiency, vertical beam position, and gain in flux density of this microbeam is studied in detail. There is a slight change in the output focal distance of the MHFPXRL when the X-ray energies change.

Development of Confocal 3D X-ray Fluorescence Instrument and Its Applications to Micro Depth Profiling

We have developed a confocal micro X-ray fluorescence instrument. Two independent X-ray tubes of Mo and Cr targets were installed to this instrument. Two polycapillary full X-ray lenses were attached to two X-ray tubes, and a polycapillary half X-ray lens was also attached to the X-ray detector (silicon drift detector, SDD). Finally, three focus spots of three lenses were adjusted at a common position. By using this confocal micro X-ray fluorescence instrument, depth profiling for layered samples were performed. It was found that depth resolution depended on energy of X-ray fluorescence that was measured. In addition, X-ray elemental maps were determined at different depths for an agar sample including metal fragments of Cu, Ti and Au. The elemental maps showed actual distributions of metal fragments in the agar, indicating that the confocal micro X-ray fluorescence is a feasible technique for non-destructive depth analysis and 3D X-ray fluorescence analysis.

Application of a combined system of polycapillary x-ray lens and toroidal mirror in micro-x-ray-absorption fine-structure facility

A micro-x-ray-absorption fine-structure facility based on a monolithic half focusing polycapillary x-ray lens (MHFPXRL), a toroidal mirror, and synchrotron radiation is proposed. The synchrotron radiation is focused by using a combined system of a MHFPXRL and a toroidal mirror. At 8.0keV, the synchrotron radiation beam with a 2.3×26-mm2 area is first focused into a beam spot with a 0.9×0.3-mm2 area by a toroidal mirror. This focused beam is then focused into a focal spot with a 21.4-μm diameter by using a MHFPXRL. The gain of power flux density in the focal spot of the combined system is 47 473. The focal distance of the MHFPXRL is 13.3mm. The transmitting extended x-ray-absorption fine-structure (EXAFS) spectrum of Ni foil and the fluorescent EXAFS spectrum of zinc in the zinc hyperaccumulator are measured.