Heavy-fermion-like state in a transition metal oxide LiV2O4 single crystal: indication of Kondo resonance in the photoemission spectrum

We have performed a vacuum ultraviolet laser excited photoemission spectroscopy on a d-electron heavy-fermion-like material LiV2O4 single crystal. We observed a sharp peak structure in the density of states at approximately 4 meV above the Fermi level (E(F)). The evolution of the peak height corresponds well with the crossover behavior to the heavy-fermion-like state as observed in the thermal and transport properties. The position, shape, and temperature (T) dependence of the peak structure is quite similar to the Kondo resonance observed in conventional f-electron heavy Fermion compounds.

Orbital-assisted metal-insulator transition in VO2

We found direct experimental evidence for an orbital switching in the V 3d states across the metal-insulator transition in VO2. We have used soft-x-ray absorption spectroscopy at the V L2,3 edges as a sensitive local probe and have determined quantitatively the orbital polarizations. These results strongly suggest that, in going from the metallic to the insulating state, the orbital occupation changes in a manner that charge fluctuations and effective bandwidths are reduced, that the system becomes more one dimensional and more susceptible to a Peierls-like transition, and that the required massive orbital switching can only be made if the system is close to a Mott insulating regime.

Controlling orbital moment and spin orientation in CoO layers by strain

We have observed that CoO films grown on different substrates show dramatic differences in their magnetic properties. Using polarization dependent x-ray absorption spectroscopy at the Co L2,3 edges, we revealed that the magnitude and orientation of the magnetic moments strongly depend on the strain in the films induced by the substrate. We presented a quantitative model to explain how strain together with the spin-orbit interaction determine the 3d orbital occupation, the magnetic anisotropy, as well as the spin and orbital contributions to the magnetic moments. Control over the sign and direction of the strain may, therefore, open new opportunities for applications in the field of exchange bias in multilayered magnetic films.

Spectroscopy of stripe order in La1.8Sr0.2NiO4 using resonant soft x-ray diffraction

Strong resonant enhancements of the charge-order and spin-order superstructure-diffraction intensities in La1.8Sr0.2NiO4 are observed when x-ray energies in the vicinity of the Ni L2,3 absorption edges are used. The pronounced photon-energy and polarization dependences of these diffraction intensities allow for a critical determination of the local symmetry of the ordered spin and charge carriers. We found that not only the antiferromagnetic order but also the charge-order superstructure resides within the NiO2 layers; the holes are mainly located on in-plane oxygens surrounding a Ni2+ site with the spins coupled antiparallel in close analogy to Zhang-Rice singlets in the cuprates.

Improved Synthesis of 2,2‘-Dibromo-9,9‘-spirobifluorene and Its 2,2‘-Bisdonor-7,7‘-bisacceptor-Substituted Fluorescent Derivatives

Pure 2,2'-Dibromo-9,9'-spirobifluorene was synthesized by a method that did not involve troublesome dibromination of 9,9'-spirobifluorene or Sandmeyer reaction of 2,2'-diamino-9,9'-spirobifluorene. A series of donor-acceptor orthogonally substituted 9,9'-spirobifluorene was subsequently prepared showing rich variation of fluorescence in solution and in solid state. [reaction: see text]

Synthesis, Characterization, and Photophysical Properties of Os(II) Diimine Complexes [Os(N∧N)(CO)2I2] (N∧N = Bipyridine, Phenanthroline, and Pyridyl Benzoxazole)

A new series of Os(II) diimine complexes with the general formula [Os(N(wedge)N)(CO)(2)I(2)], N(wedge)N = 2,2'-bipyridine (bpy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (dbubpy) (2), 4,7-diphenyl-1,10-phenanthroline (dpphen) (3), 2-(2'-pyridyl)benzoxazole (pboz) (4), and 5-tert-butyl-2-(2'-pyridyl)benzoxazole (bupboz) (5), were synthesized and characterized by spectroscopic methods and by a single-crystal X-ray diffraction study on the dpphen complex 3. The corresponding photophysical properties were studied using UV-vis and emission spectrometry. The resulting phosphorescence features both in solution and as a solid film, in combination with the MO calculation, lead us to conclude that the emissions originate from mixed halide-to-ligand (XLCT approximately 70%) and metal-to-ligand (MLCT approximately 30%) transitions instead of the typical MLCT transition. Using complexes 4 and 5 as the dopant emitters, we evaluated their potential to serve as a phosphor for organic light emitting diodes by examining their electroluminescent performances. Reddish orange electroluminescence centered around 600 nm was observed for organic light emitting diodes (OLEDs) fabricated using complex 5 as the emitter; the device efficiency was shown to be as high as 2.8% (and 5.0 cd/A or 2.7 lm/W), and the peak luminance was shown to be 5600 cd/m(2) at a driving voltage of approximately 15 V.

Orbital symmetry and electron correlation in NaxCoO2

Measurements of polarization-dependent soft x-ray absorption reveal that the electronic states determining the low-energy excitations of NaxCoO2 have predominantly a(1g) symmetry with significant O 2p character. In contrast to the prediction of band theory, doping-dependent O 1s x-ray absorption shows a large transfer of spectral weight, providing spectral evidence for strong electron correlations of the layered cobaltates. We also found that NaxCoO2 exhibits a charge-transfer electronic character rather than a Mott-Hubbard character.

Photoemission spectroscopic evidence of gap anisotropy in an f-electron superconductor

We used low-temperature ultrahigh-resolution (360 microeV) photoemission spectroscopy with a laser as a photon source (Laser-PES) to study the superconducting (SC) gap of an f-electron superconductor CeRu2. The unique combination of the large escape depth expected from the known universal behavior and extremely high-energy resolution has enabled us to directly measure the bulk SC gap of an f-electron superconductor for the first time. The present study provides direct evidence for an anisotropic SC gap in CeRu2, and also demonstrates the potential of Laser-PES in investigating unconventional superconductivity realized in correlated d- and f-electron superconductors.

Determination of the orbital moment and crystal-field splitting in LaTiO3

Utilizing a sum rule in a spin-resolved photoelectron spectroscopic experiment with circularly polarized light, we show that the orbital moment in LaTiO3 is strongly reduced from its ionic value, both below and above the Ne el temperature. Using Ti L2,3 x-ray absorption spectroscopy as a local probe, we found that the crystal-field splitting in the t2g subshell is about 0.12-0.30 eV. This large splitting does not facilitate the formation of an orbital liquid.

Ordering of hydrogen bonds in high-pressure low-temperature H2O

The near K-edge structure of oxygen in liquid water and ices III, II, and IX at 0.25 GPa and several low temperatures down to 4 K has been studied using inelastic x-ray scattering at 9884.7 eV with a total energy resolution of 305 and 175 meV. A marked decrease of the preedge intensity from the liquid phase and ice III to ices II and IX is attributed to ordering of the hydrogen bonds in the proton-ordered lattice of the latter phases. Density functional theory calculations including the influence of the Madelung potential of the ice IX crystal correctly account for the remaining preedge feature. Furthermore, we obtain spectroscopic evidence suggesting a possible new phase of ice at temperatures between 4 and 50 K.

Derivative of α,β-Dicyanostilbene: Convenient Precursor for the Synthesis of Diphenylmaleimide Compounds, E−Z Isomerization, Crystal Structure, and Solid-State Fluorescence

A convenient and efficient procedure was developed for preparing 3,4-diaryl-substituted maleimides through the improved synthesized diaryl-substituted fumaronitrile. The synthesis of diphenyl-substituted fumaronitrile derivatives from phenylacetonitrile compounds was analyzed and improved. We found the stoichiometry of the sodium methoxide and the concentration of the starting material, phenylacetonitrile derivatives, were crucial for the high yield and easy purification of the products. Particularly, bis(4-bromophenyl)fumaronitrile, bis(3-trifluoromethylphenyl)fumaronitrile, and bis(4-methoxyphenyl)fumaronitrile were isolated in good yields of 70-90% by simple suction filtration. In addition, (1)H NMR provided compelling evidence that the E-Z isomerization was involved in the formation reaction of the maleimide compounds from either fumaronitrile or maleonitrile derivatives. Single-crystal X-ray structures of these three fumaronitrile derivatives, the first three of the kind, were obtained, revealing the nonplanar molecular structure. We ascribe the strong solid-state fluorescence of these diphenylfumaronitrile derivatives to the nonplanar structure that inhibits the close packing of the molecule aggregation and thus the fluorescence quenching.

Spin and orbital magnetic moments of Fe3O4

We present measurements of the spin and orbital magnetic moments of Fe3O4 by using SQUID and magnetic circular dichroism in soft x-ray absorption. The measurements show that Fe3O4 has a noninteger spin moment, in contrast to its predicted half-metallic feature. Fe3O4 also exhibits a large unquenched orbital moment. Calculations using the local density approximation including the Hubbard U method and the configuration interaction cluster-model suggest that strong correlations and spin-orbit interaction of the 3d electrons result in the noninteger spin and large orbital moments of Fe3O4.

Different look at the spin state of Co(3+) ions in a CoO(5) pyramidal coordination

Using soft-x-ray absorption spectroscopy at the Co L(2,3) and O K edges, we demonstrate that the Co3+ ions with the CoO5 pyramidal coordination in the layered Sr2CoO3Cl compound are unambiguously in the high spin state. Our result questions the reliability of the spin state assignments made so far for the recently synthesized layered cobalt perovskites and calls for a reexamination of the modeling for the complex and fascinating properties of these new materials.

Orbital ordering in La0.5Sr1.5MnO4 studied by soft X-ray linear dichroism

We found that the conventional model of orbital-ordering of 3x(2)-r(2)/3y(2)-r(2) type in the e(g) states of La0.5Sr1.5MnO4 is incompatible with measurements of linear dichroism in the Mn 2p-edge x-ray absorption, whereas these e(g) states exhibit predominantly cross-type orbital ordering of x(2)-z(2)/y(2)-z(2). LDA+U band-structure calculations reveal that such a cross-type orbital-ordering results from a combined effect of antiferromagnetic structure, Jahn-Teller distortion, and on-site Coulomb interactions.

Development of a novel aspherical mirror bender for an active grating

A novel monolithic mechanical bender has been designed and fabricated to meet the requirements of an active polynomial grating in a new soft X-ray scattering and emission beamline at the National Synchrotron Radiation Research Center, Taiwan. This compact bender achieves nearly fixed center point under different bending conditions. Moreover, the compact bender can be bent to a desirable third-order polynomial surface profile to cancel the defocus and coma aberrations using two PZT actuators. Theoretical analysis reveals that the grating has unprecedented spectral resolving power. A detailed mechanical analysis has been conducted and a prototype bender was fabricated and tested. The results indicate that the performance of the bender is excellent and is therefore suitable to be used in the active grating.

Magnetic dichroism and spin structure of antiferromagnetic NiO(001) films

We find that Ni L2 edge x-ray magnetic linear dichroism is fully reversed for NiO(001) films on materials with reversed lattice mismatch. We relate this phenomenon to a preferential stabilization of magnetic S domains with main spin component either in or out of the plane, via dipolar interactions. This suggests a way to selectively control spin structures in 3d systems with small spin-orbit coupling.

Ortho-substituent effect on fluorescence and electroluminescence of arylamino-substituted coumarin and stilbene

[structure: see text] Newly synthesized arylamino-substituted coumarins and stilbenes show enhanced fluorescence emission (bluer and brighter) both in solution and in solid film. Pure blue efficient electroluminescence with 2.7% and 4.1% of external quantum efficiency can be achieved with MeC1 and XTPS, respectively.

The colourful fluorescence from readily-synthesised 3,4-diaryl-substituted maleimide fluorophores

A new synthesis procedure has been developed for a series of maleimide-based fluorophores, exhibiting a large variation of emission spectra spanning the entire visible range.

Ferromagnetism induced by clustered Co in Co-doped anatase TiO2 thin films

We investigated ferromagnetism of a newly discovered ferromagnetic semiconductor Co-doped anatase TiO2 thin film, using the magnetic circular dichroism (MCD) at the Co L(2,3) absorption edges. The magnetic moment was observed to be approximately 0.1 micro(B)/Co in the measurements, but the MCD spectral line shape is nearly identical to that of Co metal, showing that the ferromagnetism is induced by a small amount of clustered Co. With thermal treatments at approximately 400 degrees C, the MCD signal increases, and the moment reaches up to approximately 1.55 micro(B)/Co, which is approximately 90% of the moment in Co metal. In the latter case, the cluster size was observed to be 20-60 nm.

Readily synthesised arylamino fumaronitrile for non-doped red organic light-emitting diodes

Bright (maximum 10034 cd m(-2), 455 cd m(-2) at 20 mA cm(-2)) and efficient (maximum 2.4% at 4 mA cm(-2)) red (lambda(max)el 634-636 nm) organic light-emitting diodes employ arylamino-substituted fumaronitrile as the novel host emitter, which is readily prepared and easily purified.

Ginsenoside Rb1 enhances peripheral nerve regeneration across wide gaps in silicone rubber chambers

Silicone rubber chambers filled with collagen containing ginsenoside Rb1 (GRb1) were used to repair lesioned rat sciatic nerves with 15-mm gaps between stumps. Six weeks after implantation, histology of the nerve regenerated in the chambers filled with GRb1 and collagen contained larger axons than those in the chambers with collagen only. This study showed that the GRb1 could exert a positive influence on nerve regeneration when using silicone rubber tubes.

Dosimetric analysis of urinary morbidity following prostate brachytherapy (125I vs. 103Pd) combined with external beam radiation therapy

The purpose of this analysis was to correlate isotope selection with the urinary symptoms of patients who received a combination of external beam radiotherapy (EBRT) and a transperineal interstitial permanent prostate brachytherapy (TIPPB) boost with either a (103)palladium ((103)Pd) or a (125)iodine ((125)I) radioisotope. Postimplant dosimetry was performed to evaluate both urethral dose and implant quality. The American Urologic Association (AUA) scores in both the (125)I and (103)Pd groups were similar initially. However, at 1, 3, 6, and 12 months of follow-up, the mean AUA scores for the (125)I and (103)Pd patients were 18 +/- 6 vs. 11 +/- 9, 17 +/- 7 vs. 11 +/- 7, 10 +/- 3 vs. 9 +/- 4, and 14 +/- 8 vs. 7 +/- 5, respectively (P < 0.01). The only significant difference between the postimplant dose-volume histogram (DVH) of the (125)I and (103)Pd implants was the minimum dose that 90% of the urethra received (D(90)). The increased AUA score of the (125)I group was weakly correlated (R(2) = 0.20) with the D(90) dose but that of the (103)Pd patients was not (R(2) = 0.00). This suggests that the higher AUA score of the (125)I patients was not necessarily the result of the higher D(90) dose. Thus, patients who received (103)Pd experienced less urinary morbidity than those implanted with (125)I. We recommend further validating these findings in prospective studies in which the quality of the (125)I and (103)Pd implants can be evaluated.