Suppression of Bragg reflection glitches of a single‐crystal diamond anvil cell by a polycapillary half‐lens in high‐pressure XAFS spectroscopy

In combination with a single‐crystal diamond anvil cell (DAC), a polycapillary half‐lens (PHL) re‐focusing optics has been used to perform high‐pressure extended X‐ray absorption fine‐structure measurements. It is found that a large divergent X‐ray beam induced by the PHL leads the Bragg glitches from single‐crystal diamond to be broadened significantly and the intensity of the glitches to be reduced strongly so that most of the DAC glitches are efficiently suppressed. The remaining glitches can be easily removed by rotating the DAC by a few degrees with respect to the X‐ray beam. Accurate X‐ray absorption fine‐structure (XAFS) spectra of polycrystalline Ge powder with a glitch‐free energy range from ?200 to 800 eV relative to the Ge absorption edge are obtained using this method at high pressures up to 23.7 GPa, demonstrating the capability of PHL optics in eliminating the DAC glitches for high‐pressure XAFS experiments. This approach brings new possibilities to perform XAFS measurements using a DAC up to ultrahigh pressures.     

A sub‐micrometer resolution hard X‐ray microprobe system of BL8C at Pohang Light Source

A microprobe system has been installed on the nanoprobe/XAFS beamline (BL8C) at PLS‐II, South Korea. Owing to the reproducible switch of the gap of the in‐vacuum undulator (IVU), the intense and brilliant hard X‐ray beam of an IVU can be used in X‐ray fluorescence (XRF) and X‐ray absorption fine‐structure (XAFS) experiments. For high‐spatial‐resolution microprobe experiments a Kirkpatrick–Baez mirror system has been used to focus the millimeter‐sized X‐ray beam to a micrometer‐sized beam. The performance of this system was examined by a combination of micro‐XRF imaging and micro‐XAFS of a beetle wing. These results indicate that the microprobe system of the BL8C can be used to obtain the distributions of trace elements and chemical and structural information of complex materials.     

Characteristics of a tapered undulator for the X‐ray absorption fine‐structure technique at PLS‐II

An in‐vacuum undulator (IVU) with a tapered configuration was installed in the 8C nanoprobe/XAFS beamlime (BL8C) of the Pohang Light Source in Korea for hard X‐ray nanoprobe and X‐ray absorption fine‐structure (XAFS) experiments. It has been operated in planar mode for the nanoprobe experiments, while gap‐scan and tapered modes have been used alternatively for XAFS experiments. To examine the features of the BL8C IVU for XAFS experiments, spectral distributions were obtained theoretically and experimentally as functions of the gap and gap taper. Beam profiles at a cross section of the X‐ray beam were acquired using a slit to visualize the intensity distributions which depend on the gap, degree of tapering and harmonic energies. To demonstrate the effect of tapering around the lower limit of the third‐harmonic energy, V K‐edge XAFS spectra were obtained in each mode. Owing to the large X‐ray intensity variation around this energy, XAFS spectra of the planar and gap‐scan modes show considerable spectral distortions in comparison with the tapered mode. This indicates that the tapered mode, owing to the smooth X‐ray intensity profile at the expense of the highest and most stable intensity, can be an alternative for XAFS experiments where the gap‐scan mode gives a considerable intensity variation; it is also suitable for quick‐XAFS scanning.     

X‐ray beam‐position feedback system with easy‐to‐use beam‐position monitor

X‐ray beam‐position stability is indispensable in cutting‐edge experiments using synchrotron radiation. Here, for the first time, a beam‐position feedback system is presented that utilizes an easy‐to‐use X‐ray beam‐position monitor incorporating a diamond‐fluorescence screen. The acceptable range of the monitor is above 500 µm and the feedback system maintains the beam position within 3 µm. In addition to being inexpensive, the system has two key advantages: it works without a scale factor for position calibration, and it has no dependence on X‐ray energy, X‐ray intensity, beam size or beam shape.     

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.     

Light‐switching‐light optical transistor based on metallic nanoparticle cross‐chains geometry incorporating Kerr nonlinearity

In this research work, we propose all‐optical transistor based on metallic nanoparticle cross‐chains geometry. The geometry of the proposed device consists of two silver nanoparticle chains arranged along the x‐ and z‐axis. The x‐chain contains a Kerr nonlinearity, the source beam is set at the left side of the later, while the control beam is located at the top side of the z‐chain. The control beam can turn ON and OFF the light transmission of an incoming light. We report a theoretical model of a very small all‐optical transistor proof‐of‐conceptmade of optical ‘light switching light'concept. We show that the transmission efficiency strongly depends on the control beam and polarization of the incoming light. We investigate the influence of a perfect reflector and reflecting substrate on the transmission of the optical signal when the control beam is turned ON and OFF. These new findings make our unique design a potential candidate for future highly‐integrated optical information processing chips.     

The energy dispersive scheme of X‐ray fluorescence analysis with a crystal polarizer and polycapillary optics

The efficiency of the polarization scheme based on polycapillary optics and a diamond crystal polarizer was demonstrated. The scheme provides suppression of the background of scattered radiation in measuring X‐ray fluorescence spectra. A quasi‐parallel X‐ray beam with an angular divergence of 4.2 mrad was formed by a microfocus source with a copper anode and polycapillary half‐lens. Simultaneous polarization and monochromatization of radiation was obtained with a crystal of natural diamond, which was set at the diffraction reflection (113). The degree of polarization of CuK_α1 spectral line and the maximum radiation flux were respectively equal to 99.86% and 5 · 10⁶ photon/s. In the direction orthogonal to the plane of diffraction, the maximum attenuation of the background was up to 19 dB.     

Large‐acceptance diamond planar refractive lenses manufactured by laser cutting

For the first time, single‐crystal diamond planar refractive lenses have been fabricated by laser micromachining in 300 µm‐thick diamond plates which were grown by chemical vapour deposition. Linear lenses with apertures up to 1 mm and parabola apex radii up to 500 µm were manufactured and tested at the ESRF ID06 beamline. The large acceptance of these lenses allows them to be used as beam‐conditioning elements. Owing to the unsurpassed thermal properties of single‐crystal diamond, these lenses should be suitable to withstand the extreme flux densities expected at the planned fourth‐generation X‐ray sources.     

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.     

Application of glancing‐emergent‐angle fluorescence for polarized XAFS studies of single crystals

X‐ray absorption fine‐structure (XAFS) data were obtained for the V K‐edge for a series of anisotropic single crystals of (Cr_xV_1–x)₂O₃. The data and the results were compared for the as‐prepared bulk single crystals (measured in fluorescence in two different orientations) and those ground to powder (measured in transmission). For the bulk single crystals, the glancing‐emergent‐angle (GEA) method was used to minimize fluorescence distortion. The reliability of the GEA technique was tested by comparing the polarization‐weighted single‐crystal XAFS data with the experimental powder data. These data were found to be in excellent agreement throughout the entire energy range. Thus, it was possible to reliably measure individual V–V contributions parallel and perpendicular to the c axis of the single crystals, i.e. those unavailable by powder data XAFS analysis. These experiments demonstrate that GEA is a premiere method for non‐destructive high‐photon‐count in situ studies of local structure in bulk single crystals.     

Transmission‐mode diamond white‐beam position monitor at NSLS

Two transmission‐mode diamond X‐ray beam position monitors installed at National Synchrotron Light Source (NSLS) beamline X25 are described. Each diamond beam position monitor is constructed around two horizontally tiled electronic‐grade (p.p.b. nitrogen impurity) single‐crystal (001) CVD synthetic diamonds. The position, angle and flux of the white X‐ray beam can be monitored in real time with a position resolution of 500 nm in the horizontal direction and 100 nm in the vertical direction for a 3 mm × 1 mm beam. The first diamond beam position monitor has been in operation in the white beam for more than one year without any observable degradation in performance. The installation of a second, more compact, diamond beam position monitor followed about six months later, adding the ability to measure the angular trajectory of the photon beam.     

Diamond X‐ray beam‐position monitoring using signal readout at the synchrotron radiofrequency

Single‐crystal diamond is a material with great potential for the fabrication of X‐ray photon beam‐position monitors with submicrometre spatial resolution. Low X‐ray absorption combined with radiation hardness and excellent thermal‐mechanical properties make possible beam‐transmissive diamond devices for monitoring synchrotron and free‐electron laser X‐ray beams. Tests were made using a white bending‐magnet synchrotron X‐ray beam at DESY to investigate the performance of a position‐sensitive diamond device using radiofrequency readout electronics. The device uniformity and position response were measured in a 25 µm collimated X‐ray beam with an I‐Tech Libera `Brilliance' system. This readout system was designed for position measurement and feedback control of the electron beam in the synchrotron storage ring, but, as shown here, it can also be used for accurate position readout of a quadrant‐electrode single‐crystal diamond sensor. The centre‐of‐gravity position of the F4 X‐ray beam at the DORIS III synchrotron was measured with the diamond signal output digitally sampled at a rate of 130 Msample s^?1 by the Brilliance system. Narrow‐band filtering and digital averaging of the position signals resulted in a measured position noise below 50 nm (r.m.s.) for a 10 Hz bandwidth.     

A fast energy‐dispersive multi‐element detector for X‐ray absorption spectroscopy

In this paper results are presented from fluorescence‐yield X‐ray absorption fine‐structure spectroscopy measurements with a new seven‐cell silicon drift detector (SDD) module. The complete module, including an integrated circuit for the detector readout, was developed and realised at DESY utilizing a monolithic seven‐cell SDD. The new detector module is optimized for applications like XAFS which require an energy resolution of ～250–300 eV (FWHM Mn Kα) at high count rates. Measurements during the commissioning phase proved the excellent performance for this type of application.     

Development of dispersive XAFS system for analysis of time‐resolved spatial distribution of electrode reaction

Apparatus for a technique based on the dispersive optics of X‐ray absorption fine structure (XAFS) has been developed at beamline BL‐5 of the Synchrotron Radiation Center of Ritsumeikan University. The vertical axis of the cross section of the synchrotron light is used to disperse the X‐ray energy using a cylindrical polychromator and the horizontal axis is used for the spatially resolved analysis with a pixel array detector. The vertically dispersive XAFS (VDXAFS) instrument was designed to analyze the dynamic changeover of the inhomogeneous electrode reaction of secondary batteries. The line‐shaped X‐ray beam is transmitted through the electrode sample, and then the dispersed transmitted X‐rays are detected by a two‐dimensional detector. An array of XAFS spectra in the linear footprint of the transmitted X‐ray on the sample is obtained with the time resolution of the repetition frequency of the detector. Sequential measurements of the space‐resolved XAFS data are possible with the VDXAFS instrument. The time and spatial resolutions of the VDXAFS instrument depend on the flux density of the available X‐ray beam and the size of the light source, and they were estimated as 1 s and 100 µm, respectively. The electrode reaction of the LiFePO₄ lithium ion battery was analyzed during the constant current charging process and during the charging process after potential jumping.     

Pixelated transmission‐mode diamond X‐ray detector

Fabrication and testing of a prototype transmission‐mode pixelated diamond X‐ray detector (pitch size 60–100 µm), designed to simultaneously measure the flux, position and morphology of an X‐ray beam in real time, are described. The pixel density is achieved by lithographically patterning vertical stripes on the front and horizontal stripes on the back of an electronic‐grade chemical vapor deposition single‐crystal diamond. The bias is rotated through the back horizontal stripes and the current is read out on the front vertical stripes at a rate of ～1 kHz, which leads to an image sampling rate of ～30 Hz. This novel signal readout scheme was tested at beamline X28C at the National Synchrotron Light Source (white beam, 5–15 keV) and at beamline G3 at the Cornell High Energy Synchrotron Source (monochromatic beam, 11.3 keV) with incident beam flux ranges from 1.8 × 10^?2 to 90 W mm^?2. Test results show that the novel detector provides precise beam position (positional noise within 1%) and morphology information (error within 2%), with an additional software‐controlled single channel mode providing accurate flux measurement (fluctuation within 1%).     

miXAFS: a program for X‐ray absorption fine‐structure data analysis

A new program called miXAFS for the analysis of X‐ray absorption fine‐structure (XAFS) data is presented. miXAFS can analyze the XAFS functions simultaneously for all measured X‐ray absorption edges of the constituent elements in a sample under the constraints for the structural parameters over the edges. The program provides a surface plot of the R‐factor as a function of two structural parameters, which is useful to validate the optimized structural parameters. The structural parameters can be obtained from the XAFS data in a few steps using the setting file and batch process. The program, which is coded in MATLAB and freely available, runs on Macintosh and Windows operating systems. It has a graphical user interface and loads experimental data and XAFS functions in a variety of ASCII data formats.     

Bottom‐up engineering of diamond micro‐ and nano‐structures

Engineering nanostructures from the bottom up enables the creation of carefully sculpted complex structures that are not accessible via top down fabrication techniques, in particular, complex periodic structures for applications in photonics and sensing. In this work a proof of principle that bottom up approach can be adopted and utilized for sculpting devices from diamond is proposed and demonstrated. A realization of periodic structures is achieved by growing nanoscale single crystal diamond through a defined pattern. Optical wave‐guiding of a narrow band emission attributed to the SiV defects in diamond is demonstrated by overgrowth on a thin diamond membrane. In addition, an array of hexagonal microdisks with diameter sizes ranging from 1 to 4 μm is demonstrated. The bottom up approach for diamond opens up new avenues for devices fabrication and sculpting three dimensional structures.     

Development of a two‐dimensional imaging system of X‐ray absorption fine structure

A two‐dimensional imaging system of X‐ray absorption fine structure (XAFS) has been developed at beamline BL‐4 of the Synchrotron Radiation Center of Ritsumeikan University. The system mainly consists of an ionization chamber for I₀ measurement, a sample stage, and a two‐dimensional complementary metal oxide semiconductor (CMOS) image sensor for measuring the transmitted X‐ray intensity. The X‐ray energy shift in the vertical direction, which originates from the vertical divergence of the X‐ray beam on the monochromator surface, is corrected by considering the geometrical configuration of the monochromator. This energy correction improves the energy resolution of the XAFS spectrum because each pixel in the CMOS detector has a very small vertical acceptance of ～0.5 µrad. A data analysis system has also been developed to automatically determine the energy of the absorption edge. This allows the chemical species to be mapped based on the XANES feature over a wide area of 4.8 mm (H) × 3.6 mm (V) with a resolution of 10 µm × 10 µm. The system has been applied to the chemical state mapping of the Mn species in a LiMn₂O₄ cathode. The heterogeneous distribution of the Mn oxidation state is demonstrated and is considered to relate to the slow delocalization of Li⁺‐defect sites in the spinel crystal structure. The two‐dimensional‐imaging XAFS system is expected to be a powerful tool for analyzing the spatial distributions of chemical species in many heterogeneous materials such as battery electrodes.     

X‐ray position‐sensitive duo‐lateral diamond detectors at SOLEIL

The performance of a diamond X‐ray beam position monitor is reported. This detector consists of an ionization solid‐state chamber based on a thin single‐crystal chemical‐vapour‐deposition diamond with position‐sensitive resistive electrodes in a duo‐lateral configuration. The detector's linearity, homogeneity and responsivity were studied on beamlines at Synchrotron SOLEIL with various beam sizes, intensities and energies. These measurements demonstrate the large and homogeneous (absorption variation of less than 0.7% over 500 µm × 500 µm) active area of the detector, with linear responses independent of the X‐ray beam spatial distribution. Due to the excellent charge collection efficiency (approaching 100%) and intensity sensitivity (0.05%), the detector allows monitoring of the incident beam flux precisely. In addition, the in‐beam position resolution was compared with a theoretical analysis providing an estimation of the detector's beam position resolution capability depending on the experimental conditions (X‐ray flux, energy and readout acquisition time).     

Confocal full‐field X‐ray microscope for novel three‐dimensional X‐ray imaging

A confocal full‐field X‐ray microscope has been developed for use as a novel three‐dimensional X‐ray imaging method. The system consists of an X‐ray illuminating `sheet‐beam' whose beam shape is micrified only in one dimension, and an X‐ray full‐field microscope whose optical axis is normal to the illuminating sheet beam. An arbitral cross‐sectional region of the object is irradiated by the sheet‐beam, and secondary X‐ray emission such as fluorescent X‐rays from this region is imaged simultaneously using the full‐field microscope. This system enables a virtual sliced image of a specimen to be obtained as a two‐dimensional magnified image, and three‐dimensional observation is available only by a linear translation of the object along the optical axis of the full‐field microscope. A feasibility test has been carried out at beamline 37XU of SPring‐8. Observation of the three‐dimensional distribution of metallic inclusions in an artificial diamond was performed.