Soft X-ray Energy Region Research Articles

Electron transfer in LiMn1.5Ni0.5O4 during charging studied with soft X-ray spectrometry.

This is the first report on analyzing the chemical state of Li-ion battery electrodes at different states of charge by using a wavelength-dispersive spectrometer, which has a two-order improved energy resolution in the soft X-ray energy region compared with that of a conventional energy-dispersive X-ray analyzer. Electrodes containing LiMn1.5Ni0.5O4 were charged to prepare Li0.5Mn1.5Ni0.5O4 and λ-Mn0.75Ni0.25O2. The soft X-ray emission spectra obtained from those materials show that the O-K emission signal was drastically decreased throughout the charging process. This suggests that O-2p electron contributed to the electrochemical oxidation. The density of states and Bader charge evaluated from ab initio calculation support this result.

Multiedge X-ray Absorption Spectroscopy Part II: XANES Analysis of Bridging and Terminal Chlorides in Hexachlorodipalladate(II) Complex.

X-ray absorption spectroscopy is a unique experimental technique that can provide ground state electronic structure information about transition metal complexes with unoccupied d-manifold. The quantitative treatments of pre-edge and rising-edge features have already been developed for the sulfur- and chlorine-ligand K-edge excitations. The complementarity of using multiple core excitation edges from hard, tender, and soft X-ray energy regions has been defined for the first paper of this series. The given study provides compelling evidence for the transferability of the empirical transition dipole integral from ligand K-edge to metal L-edge and back to ligand K-edge in the tender X-ray energy range. The case study was performed for a series of homoleptic chloropalladium compounds at the chlorine K- and palladium L-edges. We propose the method described here to be generally applicable for other core level excitations, where complementarity of ground state electronic structural information from XANES analysis can provide the complete electronic structure description.

Study of structural and optical properties of zirconium carbide (ZrC) thin-films deposited by ion beam sputtering for soft x-ray optical applications

Compound materials have shown stable and enhanced optical performance in soft x-ray energy region. However, the growth related change in structural and chemical properties lead to affect their performances. In the present study, thin films of different thicknesses of ZrC compound material were deposited on Si (100) substrate. Optical response of ZrC thin film was measured in soft x-ray energy region using Indus-1 reflectivity beamline. It was found that the soft x-ray reflectivity data of ZrC thin films cannot be explained with Henke's tabulated data. To understand this disagreement a detailed structural and chemical investigation was carried out using x-ray reflectivity, grazing incidence x-ray diffraction, atomic force microscopy and x-ray photoelectron spectroscopy techniques. It was found that the presence of unreacted carbon along with small oxygen in ZrC matrix is responsible for variation in optical constant value. Details of the investigations are discussed.

Development of an in-vacuum diffractometer for resonant soft X-ray scattering

Resonant soft X-ray scattering measurements become one of powerful techniques to probe charge, orbital and spin orderings in strongly correlated electron systems. We have developed new in-vacuum diffractometer with a large vacuum chamber to solve experimental limitations of in-vacuum measurement in soft X-ray energy region, and for future instrumental developments. In this paper, the features of the diffractometer are presented.

Characteristic oxygen K-edge circular dichroism spectra of amino acid films by improved measurement technique

Circular dichroism (CD) spectroscopy in the soft x-ray energy region is a new tool to study the local structure of chiral materials. In this paper, we introduce a method to measure high-quality CD spectra in the oxygen K-edge energy region. Characteristic CD spectra of thin films of the amino acids L-tyrosine and L-aspartic acid are reported and compared with those of films of L-alanine and L-serine. The signals from the oxygen 1s → π∗ transitions of COO-, which is a common moiety in these amino acids, reflect the local geometry of each amino acid.

Dissociative Photoionization of Methyl Thiochloroformate, ClC(O)SCH3, Following Sulfur 2p, Chlorine 2p, Carbon 1s, and Oxygen 1s Excitations

The electronic transitions and the dissociative ionic photoionization mechanisms of gaseous ClC(O)SCH(3) have been investigated at the VUV and soft X-ray energy regions of S 2p, Cl 2p, C 1s, and O 1s core edges using tunable synchrotron radiation and time-of-flight mass spectrometry. The relative abundances of the ionic fragments were obtained from both PEPICO (photoelectron photoion coincidence) and PEPIPICO (photoelectron photoion photoion coincidence) spectra. The presence of a moderate site- and element-specific fragmentation effects and its implication regarding chemical reactions were analyzed. The relationship of the current results with the interstellar chemistry is also a goal of this piece of work.

Soft x-ray excited optical luminescence: Some recent applications

X-ray excited optical luminescence (XEOL) studies of several classes of light emitting materials excited using soft x rays (photon energy ranging from 10 to 2500 eV) are presented. We show that XEOL with soft x rays (short penetration depths) is often site specific and is ideally suited for the study of light emitting thin films and devices. Several examples including porous silicon, organic light emitting diode materials, and CdS based nanostructures are used to illustrate the unique properties of XEOL and its applications in the soft x-ray energy region.

Quantitative studies of the photoabsorption of carbonyl sulphide in the valence-shell, S 2p, 2s and C 1s inner-shell regions (4–360 eV) by dipole electron impact spectroscopies

Electronic excitation spectra and absolute photoabsorption oscillator strengths (cross-sections) have been measured in the UV, VUV and soft X-ray energy regions for the valence- and inner- (S 2p, 2s, C 1s) shell photoabsorption of carbonyl sulphide (OCS) from 5 to 360 eV using low-resolution (∼1 eV fwhm) dipole (e, e) spectroscopy. The absolute oscillator strength scale has been determined using valence-shell TRK (i.e., S(0)) sum-rule normalization. The discrete structures, as well as the continuum structures, in the valence region also have been studied at high resolution (∼0.05 eV fwhm) from 4 to 32 eV. The presently reported high- and low-resolution absolute photoabsorption oscillator strengths are compared with previously published data (from the direct photoabsorption measurements) in those limited energy regions where such data exist. Evaluation of the S(−2) sum using the presently reported absolute differential photoabsorption oscillator strength data gives a static dipole polarizability for carbonyl sulphide in excellent agreement (within 2%) with previously reported polarizability values. Other dipole sums S( u) ( u=−1, −3 to −6, −8, −10) and logarithmic dipole sums L( u) ( u=−1 to −6) are also determined from the presently reported absolute differential photoabsorption oscillator strength data.

Greatly enhanced soft x-ray generation from femtosecond-laser-produced plasma by using a nanohole-alumina target

By making an array of nanoholes on an alumina target, x-ray emission from laser-produced plasma can be greatly enhanced even in soft x-ray energy regions (<0.25 keV). X-ray fluence enhancement around 30 times was achieved in the 5–25 nm wavelength range. The enhancement increases as the ionization level of Al becomes higher and the x-ray wavelength becomes shorter. Over 50-fold enhancement was obtained at a soft x-ray wavelength around 6 nm, which corresponds to the emission from Al8+,9+ ions. X-ray pulse duration was 17 ps, which is much shorter than that obtained by using the prepulse technique.

Quantitative studies of the photoabsorption and photoionization of PCl 3 in the valence and inner (P 2p,2s; Cl 2p,2s) shell regions

Electronic excitation spectra and absolute photoabsorption oscillator strengths (cross sections) have been measured in the vacuum ultraviolet and soft X-ray energy regions for the valence and inner (P 2p,2s; Cl 2p,2s) shell photoabsorption of phosphorus trichloride (PCl 3) from 5 to 350 eV (1 eV fwhm) using dipole (e,e) spectroscopy. The discrete structures in the valence region and in the vicinity of the phosphorus 2p and chlorine 2p inner shells have also been studied at higher resolution (0.05–0.1 eV fwhm). Evaluation of the S(−2) sum using the presently reported absolute photoabsorption oscillator strength data gives a dipole polarizability for PCl 3 within 1% of the experimental value. The photoionization efficiency, ionic photofragmentation branching ratios, and absolute partial oscillator strengths for molecular and dissociative photoionization have also been determined for PCl 3 by dipole (e,e+ion) coincidence spectroscopy from the first ionization threshold up to the chlorine 2s edge.

Absolute oscillator strenghts for the valence-shell photoabsorption (2–200 eV) and the molecular and dissociative photoionization (11–80 eV) of nitrogen dioxide

The valence-shell photoabsorption spectrum and absolute differential oscillator strengths (cross sections) of nitrogen dioxide have been measured at 1 eV FWHM resolution from the visible up to the soft X-ray energy region (2–200 eV) using dipole ( e, e) spectroscopy. The discrete spectral structures from 1.6 to 30 eV have also been studied at higher resolution (0.05 eV FWHM), and absolute oscillator strength values have been determined for the 2 B 1 ← 2 A 1 and 2BP 2 ← 2 A 1 systems as well as for the Rydberg states at higher energies. Comparisons have been made to previously reported absolute optical measurements in those limited energy regions where such data exist. The accuracy of the absolute oscillator strengths of nitrogen dioxide have been critically evaluated by comparison of the static electric—dipole polarizability of nitrogen dioxide derived from the present data using the S(−2) sum rule with those determined from dielectric constant measurements in the literature. In addition, dipole ( e, e + ion) coincidence spectroscopy has been used to obtain the photoion branching ratios, absolute photoionization efficiencies, and absolute partial differential oscillator strengths for the molecular and dissociative photoionization channels of nitrogen dioxide from the first ionization threshold up to 80 eV. Some qualitative deductions have been made concerning the dipole-induced breakdown pathways of nitrogen dioxide under UV, VUV, and soft X-ray radiation.

High-resolution beamline 9.3.2 in the energy range 30–1500 eV at the Advanced Light Source: Design and performance

Bending magnet beamline 9.3.2 at the Advanced Light Source (ALS) was designed for high resolution spectroscopy with the capability for delivering circularly polarized light in the soft x-ray energy region using three gratings. The monochromator is a fixed included-angle spherical grating monochromator (SGM) and was originally used at SSRL as a prototype for later insertion-device-based monochromators for the ALS. For operation at the ALS, the toroidal pre-mirror used at SSRL was replaced by a horizontally focusing and a vertically focusing mirror in the Kirkpatrick-Baez configuration. Circularly polarized radiation is obtained by inserting a water-cooled movable aperture in front of the vertically focusing mirror to allow selecting the beam either above or below the horizontal plane. To maintain a stable beam intensity through the entrance slit, the photocurrent signals from the upper and lower jaws of the entrance slit are utilized to set a feedback loop with the vertically deflecting mirror piezoelectric drive. The beamline end station has a movable platform that accommodates two experimental chambers enabling the synchrotron radiation to be directed to either one of the two experimental chambers without breaking the vacuum. © 1996 American Institute of Physics.

High resolution soft X-ray bending magnet beamline 9.3.2 with circularly polarized radiation capability at the Advanced Light Source

Bending magnet beamline 9.3.2 at the Advanced Light Source (ALS) was designed for high resolution spectroscopy in the soft x-ray energy region, covering a range from 30 eV to 1500 eV with three gratings. The monochromator itself is a standard fixed included angle 55 m spherical grating monochromator and was originally used at the Stanford Synchrotron Radiation Laboratory (SSRL) as a prototype for later insertion device based monochromators for the ALS. For operations at the ALS, the toroidal pre-mirror used at SSRL to vertically focus onto the entrance slit and horizontally focus onto the exit slit was replaced by two separate crossed mirrors (Kirkpatrick-Baez configuration). Circularly polarized radiation is obtained by inserting a water-cooled movable aperture in front of the vertically focusing mirror to allow selecting the beam either above or below the horizontal plane. To maintain a stable beam intensity through the entrance slit, the photocurrent signals from the upper and lower jaws of the entrance slit are utilized to set a feedback loop with the vertically deflecting mirror Piezoelectric drive. The beamline end station has a rotatable platform (through 60°) that accommodates two experimental chambers, enabling the synchrotron radiation to be directed to either one without breaking vacuum.