High-resolution Soft X-ray Emission Research Articles

Hydrogen-Bonded Structures of Water Molecules in Hydroxy-Functionalized Nanochannels of Columnar Liquid Crystalline Nanostructured Membranes Studied by Soft X-ray Emission Spectroscopy.

Here, we report a synchrotron-based high-resolution soft X-ray emission spectroscopy study on hydrogen-bonded structures of water molecules in the self-organized, hydroxy-group-functionalized one-dimensional nanochannels of liquid crystalline nanostructured membranes. The water molecules confined in the uncharged hydroxy-functionalized nanochannels (which have a diameter of about 1.5 nm) exhibit hydrogen-bonded structures close to those of bulk liquid water, even directly interacting with diol groups. These hydrogen-bonded structures contrast with the more distorted hydrogen bonding of water molecules confined in self-organized channels with a diameter of 0.6 nm formed by an analogous nanostructured membrane with a cationic moiety, which was explained by the ability of the channel functional groups to donate and accept hydrogen bonds in a confined space and the nanochannel diameter.

Ion Selectivity of Water Molecules in Subnanoporous Liquid-Crystalline Water-Treatment Membranes: A Structural Study of Hydrogen Bonding.

We demonstrate hydrogen‐bonded structures of water in self‐organized subnanoporous water treatment membranes obtained using synchrotron‐based high‐resolution soft X‐ray emission spectroscopy. The ion selectivity of these water treatment membranes is usually understood by the size compatibility of nanochannels in the membrane with the Stokes radius of hydrated ions, or by electrostatic interaction between charges inside the nanochannels and such ions. However, based on a comparison between the hydrogen‐bonded structures of water molecules in the nanochannels of the water treatment membrane and those surrounding the ions, we propose a definite contribution of structural consistency among the associated hydrogen‐bonded water molecules to the ion selectivity. Our observation delivers a novel concept to the design of water treatment membranes where water molecules in the nanochannel can be regarded as a part of the material that controls the ion selectivity.

Distinguishing between High- and Low-Spin States for Divalent Mn in Mn-Based Prussian Blue Analogue by High-Resolution Soft X-ray Emission Spectroscopy.

We combine Mn L2,3-edge X-ray absorption, high resolution Mn 2p-3d-2p resonant X-ray emission, and configuration-interaction full-multiplet (CIFM) calculation to analyze the electronic structure of Mn-based Prussian blue analogue. We clarified the Mn 3d energy diagram for the Mn(2+) low-spin state separately from that of the Mn(2+) high-spin state by tuning the excitation energy for the X-ray emission measurement. The obtained X-ray emission spectra are generally reproduced by the CIFM calculation for the Mn(2+) low spin state having a stronger ligand-to-metal charge-transfer effect between Mn t2g and CN π orbitals than the Mn(2+) high spin state. The d-d-excitation peak nearest to the elastic scattering was ascribed to the Mn(2+) LS state by the CIFM calculation, indicating that the Mn(2+) LS state with a hole on the t2g orbital locates near the Fermi level.

Transmission-grating spectrometer for highly efficient and high-resolution soft X-ray emission studies

A high-resolution soft X-ray emission spectrometer has been developed for site-specific electronic structure analysis of functional materials in the photon energy range of 50–600eV on the in-vacuum undulator beamline BL3U of the UVSOR facility. In order to realize the high detection efficiency without sacrificing the energy resolution to the signal intensity, the present X-ray emission spectrometer adopts an optical design, which was originally adopted in the field of astrophysics such as Chandra X-ray observatory. This new-type X-ray emission spectrometer consists of a Wolter type I mirror, a freestanding transmission grating, and a charge coupled device (CCD) detector, allowing the focusing with 20 times larger acceptance angle (1.5×10−3sr) than commercially available compact spectrometers with reflection-type gratings such as VG-SCIENTA XES350. The X-ray emission energy resolution of 15–34meV has successfully been achieved in the photon energy of 60–100eV by using a transmission grating with the groove density of 5555lines/mm.

High-resolution soft X-ray emission spectrograph at advanced light source

Abstract The progress of valence electronic spectroscopy with X-rays has been largely limited by the challenge of fine instrumentation. Relatively weak scattering cross-section and/or limited (coarse) energy resolution restrict X-ray spectroscopy to address fundamental issues in condensed-matter electron physics. Depending on the nature of excitations, high brightness photon beam from third-generation synchrotron facilities helps raise the count rates to a detectable limit over the noise level. Over the past decade, it has been realized that high-resolution resonant inelastic soft X-ray scattering has the potential to play an important role in understanding complex phenomena observed in highly correlated systems. Driven by such demand, we have developed a soft X-ray emission spectrograph based on variable line spacing (VLS) gratings to work in the soft X-ray and deep UV (the M edge of transition metals) regime. The slit-less design coupled with high quality optical elements and a high quantum efficiency (QE) in-vacuum CCD detector greatly improves the overall throughput. The M edge spectrograph has been demonstrated to have a resolving power better than 10,000 and will be used in conjunction with meV-resolution beamline (MERLIN) at the Advanced Light Source at Lawrence Berkeley National Laboratory.

Momentum selectivity and anisotropy effects in the nitrogenK-edge resonant inelastic x-ray scattering from GaN

High-resolution soft x-ray emission and absorption spectra near the N $K$-edge of wurtzite GaN are presented. The experimental data are interpreted in terms of full-potential electronic structure calculations. The absorption spectra, compared with calculations including core hole screening, indicate partial core hole screening in the absorption process. The resonantly excited x-ray emission spectra show pronounced dispersion of spectral structures, which is attributed to effects of momentum conservation in the resonant inelastic x-ray scattering (RIXS) process. In development of GaN based optoelectronics, momentum selectivity in RIXS can be utilized to control development of band structure in GaN nanostructures.

Design of a novel transmission-grating spectrometer for soft X-ray emission studies

The design of a transmission-grating spectrometer for high-resolution soft X-ray emission studies has been proposed. It is different from conventional types of soft X-ray emission spectrometers; that is, the spectrometer has a Wolter type I mirror, a free-standing transmission grating, and a back-illuminated CCD. A high collection angle up to 1.5 × 10 −3 sr is achieved by utilizing the Wolter mirror as a prefocusing system. The CCD is mounted at 1400 mm downstream of the grating on a Rowland torus mount. Diffracted X-rays are detected by the CCD in the normal incidence geometry, resulting in high detection efficiency. The energy resolution is limited by the figure errors of the optical elements and the spatial resolution of the detector. The ray-tracing results confirm that the aberrations do not practically degrade the energy resolution.

Influence of shallow core-level hybridization on the electronic structure of post-transition-metal oxides studied using soft X-ray emission and absorption

The influence of shallow core-level hybridization on the electronic structure of the post-transition metal oxides ZnO, CdO, In 2 O 3 , and SnO 2 has been investigated using high-resolution soft x-ray emission and absorptionspectroscopies. Synchrotron radiation excited O K α emission spectra provide a direct measure of the O 2p partial density of states and shallow core-level hybridization for this series of transparent conducting materials and reveal significant mixing of O 2p and shallow-core metal d states for ZnO, CdO, and In 2 O 3 . The experimental data are compared with local density approximation and tight-binding band structure calculations and with previous experimental determinations of direct and indirect band gaps. Rocksalt CdO, bixbyite In 2 O 3 , and rutile SnO 2 all adopt structures with metal cations in sites with locally centrosymmetric coordination. This prevents hybridization of O 2p states with metal 4d states at the zone center, but mixing away from Γ leads to indirect band gaps for CdO and In 2 O 3 . A revised value for the lowest indirect band gap in CdO is proposed and the overall trends in the band gap are discussed in terms of the separation between O 2p and metal 4d states. The experimental investigation has been extended to study the effects of Sn doping in In 2 O 3 .

Soft X-ray emission and absorption spectroscopy of hydrofullerene

Abstract High-resolution soft X-ray emission and absorption spectra in the C K region of hydrofullerene, which probably consists mainly of C 60 H 36 , were measured using highly brilliant synchrotron radiation to identify its molecular structure and electronic structure. Comparison with the C2p-DOS spectra, calculated by discrete variational (DV) Xα molecular orbital calculations, of three possible C 60 H 36 isomers, showed that the measured X-ray spectra approximately agreed with the calculated C2p-DOS spectra of the T-symmetry isomer. The X-ray spectral features were explained by the electronic structure hybridized between the sp 2 and sp 3 carbon atoms of the T-symmetry C 60 H 36 .

Soft x-ray emission spectrometer for undulator radiation

An experimental system for high-resolution soft x-ray emission spectroscopy was made. The experimental system is designed to be attached to the undulator beamlines. Spectrometer uses the Rowland circle geometry in which input slit, spherical grating, and multichannel detector lie on the focal circle. Three blazed holographic gratings are changeable in the vacuum. The Rowland circle radii of gratings are 5, 7, and 10 m and their line densities are 600, 1200, and 2400 lines/mm, respectively. The available photon energy is from 30 to 1200 eV. The resolution ΔE is achieved to 0.06 eV by 50 μ-input-slit width for hν=120 eV. Several experimental results measured by this system are presented.

Electronic structure of high Tc superconductors by x-ray emission spectroscopy

We report high resolution soft x-ray emission spectroscopy measurements which provide direct information on the partial Cu 3d and O 2p electronic states of copper oxide-based ceramic superconductors (La2CuO4,La1.85Sr0.15CuO4, YBa2Cu3O7, and Bi2Sr2CaCu3O8. The discussion refers to XPS/UPS data and LDP theory. The main conclusions are that: (i) the excitation spectra show well localized Cu 3d states in all the perovskite-related compounds (though less so than in CuO), (ii) Cu 3d-O 2p hybridization is not that predicted by LDF theory, (iii) O 2p states are band-like.