Simultaneous soft X-ray transmission and emission microscopy

Novel low-energy X-ray fluorescence (LEXRF) system based on a multiple Si drift detector (SDD) configuration has been developed and implemented in the European TwinMic X-ray microspectroscopy station operating at the Italian synchrotron radiation facility ELETTRA. The setup, hosting up to eight large-area SDDs with specially adapted readout electronics, has demonstrated excellent performance for elemental analysis in the 280–2200 eV photon energy range, which covers the K and L edges of light elements, starting from C. The great advantage is the simultaneous acquisition of LEXRF, absorption and phase contrast maps, providing complementary information on elemental composition and morphology of specimen at submicrometer length scales.     

Formation of Mn-oxide clusters in Mn-implanted SiO2 probed by soft X-ray emission and absorption spectroscopy

Mn⁺-implanted a-SiO₂-samples were studied with the help of soft X-ray emission and absorption spectroscopy (Si L_2,3 3d3s → 2p_3/2,1/2 and Mn L_2,3 3d4s → 2p_3/2,1/2 emission transitions) using synchrotron excitation. The samples were obtained using a pulsed ion source (ion beam current density ∼2-7 mA/cm², E_impl. = 30 keV, ion fluence ∼2 × 10¹⁷ cm⁻², pulse duration 400 μs) without thermal annealing. It was established that Mn-ion provides a formal valence state 2+, so arranging in implanted a-SiO₂ the low-sized MnO antiferromagnetic clusters probably of crystalline type. The data obtained well coincides with the electronic spin resonance results reported earlier.     

Airborne interferometer for atmospheric emission and solar absorption

The interferometer for emission and solar absorption (INTESA) is an infrared spectrometer designed to study radiative transfer in the troposphere and lower stratosphere from a NASA ER-2 aircraft. The Fourier-transform spectrometer (FTS) operates from 0.7 to 50 mum with a resolution of 0.7 cm(-1). The FTS observes atmospheric thermal emission from multiple angles above and below the aircraft. A heliostat permits measurement of solar absorption spectra. INTESA's calibration system includes three blackbodies to permit in-flight assessment of radiometric error. Results suggest that the in-flight radiometric accuracy is ~0.5 K in the mid-infrared.     

X-ray optic characteristics of microchannel plates studied by X-ray absorption spectroscopy

The X-ray absorption spectra of white and black microchannel plates (MCPs) have been studied in the energy range from 80 to 250 eV. Data on the fine X-ray absorption near edge structure are presented. A new approach is described, which allows the effect of various treatments on the X-ray optic characteristics of MCPs to be studied. In particular, it is established that the thermal reduction of MCPs in hydrogen increases the critical reflection angle for long-wavelength X-rays in the channels.     

Imaging by using proton-induced quasi-monochromatic X-ray emission

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of ≈4–23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl₃$H₂O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Kα) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of ≈10 mm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (<100 mm) was highly contrasted by this method. The spatial resolution of the picture was ≈20 mm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.     

Imaging by using proton-induced quasi-monochromatic X-ray emission

Quasi-monochromatic X-ray emission induced by MeV-proton bombardment onto metallic targets was applied to radiography of small samples. The X-ray energy was adjusted in the range of ≈4–23 keV by changing the target material. The radiograms were recorded on an imaging plate. A small phantom made of Lucite was prepared for the test of photography using a contrast medium (RuCl₃·H₂O; ruthenium chloride). To clearly observe the image of the contrast agent, the photon energy was chosen to be 23.17 keV (Cd Kα) which is slightly above the K-absorption edge of Ru at 22.12 keV. Only the image of the contrast agent was successfully extracted by subtracting the image taken by 21.18-keV X-rays (Pd Kα) from that obtained by the 23.17-keV photons. Also images of a small fish sample were taken using a point-like X-ray source excited by a proton microbeam with a diameter of ≈10 μm. In this experiment, the X-ray energy was adjusted to 4.51 keV (Ti Kα) to obtain a strong attenuation by Ca in the bones. A fine structure of the bones in the thin caudal fin (<100 μm) was highly contrasted by this method. The spatial resolution of the picture was ≈20 μm. Performance of the above technique based on the proton-induced quasi-monochromatic X-ray emission is discussed in comparison to conventional methods.     

Wavelength-dependent model of Kr flash lamp emission and absorption

We present a simple model of the angular intensity distribution of linear flash lamps for laser pumping application, which also takes into account the plasma column absorption during flash pulse. The model parameters are derived by single-shot measurements of plasma emission and transmission, performed with an imaging spectrometer and a CCD detector. The model consists in a linear superposition, wavelength by wavelength, of a surface (opaque) and a volume (transparent) emitter and represents a good approximation of the time-averaged lamp emission and absorption for pulse durations from 50 mus to 2 ms. This model is a suitable tool for reflector optimization of flash-lamp-pumped solid-state lasers, allowing complete wavelength-dependent ray tracing with currently available computing power. Some sample applications are also shown and discussed, with results of ray tracing for a slab laser and evaluation of the effects of lamp blackbody emission for several laser active media and flash lamp excitation pulses.     

K X-ray emission cross sections by proton bombardment

X-ray emission cross sections by proton impact ionization of K-shell electrons are presented. These values are based upon weighted orthonormal fits to all the relevant experimental information available from the literature. Several methods for reducing possible statistical inconsistency among experimental data points are discussed in order to reach precise and accurate cross section estimates. Present results are compared to analytical cross section formulae and to variously fitted values.     

Observation of fluorapatite formation under hydrolysis of tetracalcium phosphate in the presence of KF by means of soft X-ray emission and absorption spectroscopy

The effect of fluoride on the hydrolysis of tetracalcium phosphate (TTCP; Ca₄(PO₄)₂O) in 0.1 mol/l KH₂PO₄ containing 62–83 mmol/l KF was studied with the help of X-ray fluorescence measurements. Fluorine X-ray emission and absorption spectra of the final product of hydrolysis and reference samples (CaF₂ and Ca₅(PO₄)₃F) were measured at Beamline BL-2C of Photon Factory (PF, Tsukuba). Based on these measurements we concluded that hydrolysis of TTCP in the presence of KF converts it into fluorapatite. Formation of CaF₂, which is often found in the hydrolysis of hydroxyapatite at high fluoride concentration, was not observed.     

X-ray absorption spectroscopy, simulation and modeling of Si-DLC films

Amorphous silicon-containing diamond-like carbon (Si-DLC) films were deposited on silicon wafers by Ar⁺ Ion Beam Assisted Deposition (IBAD) at various energy conditions. The films were examined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The Si K-edge X-ray Absorption Spectroscopy (XAS) results indicate that Si-DLC films have an amorphous structure, where each Si atom is coordinated to four carbon atoms or CH_n groups. This short-range order, where a Si atom is surrounded by four C atoms, was found in all Si-DLC films. The XANES spectra do not indicate Si coordination to oxygen atoms or phenyl rings, which are present in the precursor material. A structural model of Si-DLC is proposed based on XAS findings. Simulated X-ray absorption spectra of the model produced by FEFF8 show a good resemblance to the experimental data.     

Target characterization by PIXE, alpha spectrometry and X-ray absorption

We report on the thickness and homogeneity characterization of thin metallic targets of Zr-96 by means of alpha absorption spectrometry, Particle Induced X-ray Emission (PIXE) and X-ray absorption. The target thicknesses determined by means of the above mentioned methods are critically compared. The thicknesses were determined before and after irradiation with a 70 MeV beam of ¹⁴N ions.     

Structural properties of low-temperature grown ZnO thin films determined by X-ray diffraction and X-ray absorption spectroscopy

The epitaxial growth of ZnO thin films on Al₂O₃ (0001) substrates have been achieved at a low-substrate temperature of 150 °C using a dc reactive sputtering technique. The structures and crystallographic orientations of ZnO films varying thicknesses on sapphire (0001) were investigated using X-ray diffraction (XRD). We used angle-dependent X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to examine the variation of local structure. The XRD data showed that the crystallinity of the film is improved as the film thickness increases and the strain is fully released as the film thickness reached about 800 Å. The Zn K-edge XANES spectra of the ZnO films have a strong angle-dependent spectral feature resulting from the preferred c-axis orientation. The wurtzite structure of the ZnO films was explicitly shown by the XRD and EXAFS analysis. The carrier concentration, Hall mobility and resistivity of the 800 Å-thick ZnO film were 1.84 × 10¹⁹ cm^− 3, 24.62 cm²V^− 1s^− 1, and 1.38 × 10^− 2 Ω cm, respectively.     

Electronic structure in thin film organic semiconductors studied using soft X-ray emission and resonant inelastic X-ray scattering

The electronic structure of thin films of the organic semiconductors copper and vanadyl (VO) phthalocyanine (Pc) has been measured using resonant soft X-ray emission spectroscopy and resonant inelastic X-ray scattering. For Cu-Pc we report the observation of two discrete states near E_F. This differs from published photoemission results, but is in excellent agreement with density functional calculations. For VO-Pc, the vanadyl species is shown to be highly localized. Both dipole forbidden V 3d to V 3d*, and O 2p to V 3d* charge transfer transitions are observed, and explained in a local molecular orbital model.     

X-ray absorption of gold nanoparticles with thin silica shell

Silica-coated gold (Au) nanoparticles were prepared and their morphological and X-ray absorption properties were investigated. These core-shell type nanoparticles are very stable in aqueous media and may be suitable for an X-ray contrast agent in biological systems. Transmission electron micrographs confirmed well-separated and relatively homogeneous morphology of the nanoparticles in highly concentrated colloids. Peak position for Au plasmon resonance was red-shifted with increasing shell thickness. X-ray absorption by the colloids of silica-coated Au nanoparticles was stronger than that by those of silica-coated Agl nanoparticles, a recently investigated X-ray contrast agent, at similar experimental conditions.     

An X-ray absorption approach to mixed and metallicity-sorted single-walled carbon nanotubes

Carbon based structures have been widely studied by X-ray absorption (XAS), also called NEXAFS, which is a very useful bulk probing method that allows examining the unoccupied density of states (DOS) and the site selective bonding environment. Two very well known spectral features in the XAS core level spectrum are the σ* and π* bands, and both have been analyzed in several studies for graphitic-like systems. However, among all the carbon materials, the unique one-dimensional electronic properties attributed to single-walled carbon nanotubes (SWCNTs) exhibit features that reveal clearly their electronic structure in the core level XAS spectrum. In this article, we outline the C1s response in XAS, which is related to the DOS of the conduction band in SWCNTs and its fine structure, revealed by experiments performed on metallicity-sorted SWCNT material. The progress in the identification of changes in the site selective conduction band electronic structure with XAS is discussed in detail.