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The reaction of MesP=CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the 'abnormal' (C(4)-substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented 'normal' C(2) adduct, Me2IMe → P(Mes)=CPh2 (2). Particularly striking is the asymmetric and weak bonding of the NHC to the P=C moiety in 2. DFT calculations indicate that the P=C natural bond order in 2 (1.54) still reflects significant π-character to the bond (cf. MesP=CPh2: NBO = 1.98). Further computational analysis suggests that π-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct.

We investigated the electronic structure of the vacancy-ordered $4d$-transition-metal monoxide $\mathrm{NbO}\phantom{\rule{0.28em}{0ex}}({\mathrm{Nb}}_{3}{\mathrm{O}}_{3})$ using angle-integrated soft- and hard-x-ray photoelectron spectroscopies as well as ultraviolet angle-resolved photoelectron spectroscopy. We found that density-functional-based band-structure calculations can describe the spectral features accurately provided that self-interaction effects are taken into account. In the angle-resolved spectra we were able to identify the so-called `vacancy' band that characterizes the ordering of the vacancies. This together with the band-structure results indicate the important role of the very large inter-Nb-$4d$ hybridization for the formation of the ordered vacancies and the high thermal stability of the ordered structure of niobium monoxide.

Polar catastrophe at the interface of oxide materials with strongly correlated electrons has triggered a flurry of new research activities. The expectations are that the design of such advanced interfaces will become a powerful route to engineer devices with novel functionalities. Here, we investigate the initial stages of growth and the electronic structure of the spintronic Fe3O4/MgO(001) interface. Using soft x-ray absorption spectroscopy, we have discovered that the so-called A-sites are ompletely missing in the first Fe3O4 monolayer. This discovery allows us to develop an unexpected but elegant growth principle in which, during deposition, the Fe atoms are constantly on the move to solve the divergent electrostatic potential problem, thereby ensuring epitaxy and stoichiometry at the same time. This growth principle provides a new perspective for the design of interfaces.

Two distinct ferromagnetic phases are present in LaMn0.5Co0.5O3 for which the spin-only magnetic moment calculated from the high temperature dc susceptibility is found to be unusually high. Such a high moment can only be accounted for by assigning the valence state of the cations to Mn2+-Co4+. This is unrealistic as the earlier report based on X-ray absorption spectroscopy (XAS) has suggested the valence state to be mainly Mn4+-Co2+ with traces of Co3+. Also from our studies using XAS, it is found that the valence state is mainly Mn4+-Co2+. In addition, no notable difference is observed in the minor Co3+ present in both phases. Our results based on X-ray magnetic circular dichroism studies (XMCD) reveal the presence of ``distinct'' high orbital moment associated with Co2+ for both phases. Thus it is found that the distinctness of the orbital moment also plays a vital role in determining the magnetic moment and T-c of both phases of LaMn0.5Co0.5O3. By considering the orbital moment obtained from XMCD, the anomaly in the paramagnetic susceptibility is resolved and thus we are able to assign the valence state to Mn4+-Co2+ configuration. The difference in the magnitude of orbital moment in both phases is believed to be due to the crystal field effects.

We have studied the far-infrared (far-IR) charge dynamics of an equilibrated pure oxygen doped La2CuO4+0.0315 under slow-cooled and fast-cooled conditions. The superconducting transition temperature (Tc) for the slow-cooled and that for the fast-cooled processes were respectively found to be close to the two intrinsic Tc's: One at 30 K and the other at 15 K. Direct comparison with our previous results and other far-IR and Raman studies on single crystalline La2-xSrxCuO4, we conclude that the topology of the pristine electronic phases that are responsible for the two intrinsic Tc's is holes arranged into two-dimensional (2D) square lattices., Submitted to PRB

The yield of secondary electrons emitted from an epitaxial three monolayer (3 ML) NiO(1 0 0)/Ag(1 0 0) film excited by soft X-ray linearly polarized synchrotron radiation at the Ni L 2,3 absorption threshold has been measured for different values of the thickness of a MgO(1 0 0) capping layer. Compared with the as grown 3 ML NiO(1 0 0)/Ag(1 0 0) film, we observe a significant enhancement by about a factor 1.2 of the secondary electron emission for the capped 8 ML MgO(1 0 0)/3 ML NiO(1 0 0)/Ag(1 0 0) sample. A further substantial yield enhancement by a factor 1.6 with respect to the uncapped NiO sample is observed after deposition of an additional 8 ML MgO(1 0 0) film, for a total capping layer thickness of 16 ML. The observed secondary electron yield enhancement is discussed in terms of modified electronic structure, surface work function changes, and characteristic electron propagation lengths.

The initiation and termination steps of the anionic polymerization of P=C bonds have been modeled. The initiation step was investigated through the stoichiometric reaction of MesP=CPh2 (1) with RLi (R = Me or n-Bu). In each case, the addition was highly regioselective with the formal attack of R– at phosphorus to give the carbanion Li[Mes(R)P–CPh2] (3a, R = Me; 3b, R = n-Bu). To simulate the termination step in the anionic polymerization of 1, carbanions 3a and 3b were quenched in situ with various electrophiles. Through these reactions, several new tertiary phosphines have been prepared, namely, Mes(Me)P–CPh2H (4a), Mes(n-Bu)P–CPh2H (4b), Mes(Me)P–CPh2Me (6a), Mes(Me)P–CPh2–P(NEt2)2 (7a), Mes(Me)P–CPh2–SiMe2H (8a), and Mes(Me)P–CPh2–SiMe3 (9a). In addition, compounds 4a, 7a, 8a, and 9a were characterized by X-ray crystallography. Most of the metrical parameters are typical of tertiary phosphines; however, the P–CPh2H bonds were elongated in all cases reflecting the considerable steric bulk surrounding this bond. Unexpectedly, an unusually large 31P–31P coupling constant (2JPP > 200 Hz) was observed for 7a both in solution and the solid state. This observation may be rationalized by a through space P···P interaction. This rationale is further supported by the short P···P distance [P(1)—P(2) = 2.966(1) Å; cf. Σ rvdw = 3.7 Å] and a small P–C–P bond angle for 7a [P(1)–C(11)–P(1) = 99.17(9)°].Key words: phosphaalkenes, phosphorus polymers, phosphines, anionic polymerization.

Superconducting transition temperature (Tc) as a function of oxygen concentration for hexagonal rubidium tungsten bronzes RbxWOy with 2.80 ≤ y ≤ 3.07 and x = 0.19, 0.23, and 0.27 has been systematically investigated. Three regions corresponding to Tc 3 K (superconductivity enhanced region) were identified in Tc–y phase diagram for Rb0.19WOy and Rb0.23WOy. No superconductivity enhanced region was observed for Rb0.27WOy. The superconductivity suppressed region shifts toward higher oxygen content as rubidium concentration increases. The local ordering of the intercalated rubidium atoms might be responsible for the intriguing Tc–y phase diagram of RbxWOy.

The oxidation behavior of an Fe48Cr15C15Mo14B6Er2 bulk metallic glass (Fe-BMG) was studied over the temperature range of 600–725 � C in dry air. The oxidation kinetics of the glassy alloy followed a two-stage parabolic rate law at T � 650� C, while the single-stage linear rate was observed at higher temperatures (T � 675 � C). The oxidation rates of the Fe-BMG at T � 625 � C were much lower than those of the commercial 304 stainless steel (304 SS), revealing the excellent oxidation resistance of the amorphous alloy. A continuous, thin layer of chromium oxide (Cr2O3) containing some iron was formed at T � 650 � C, while typical hump iron oxides intermixed with minor amounts of Cr2O3 and MoO2 were observed at T � 675 � C. In addition, a substrate phase transformation from the amorphous structure to Fe-Cr and FeCrMo crystalline phases was detected after the oxidation. Very likely, the formation of the non-protective Fe3O4 and MoO2 breaks the scale integrity and allows the rapid cation/anion transportation, resulting in the fast linear-kinetics behavior of the Fe-BMG at T � 675 � C.

Background New CD36 mutations are constantly being identified, although no study has specifically targeted a Taiwanese population. CD36 deficiency can result in dyslipid state and slow clearance of chylomicron. This could be linked to more frequent lipemic donations. Study Design and Methods We used flow cytometric methods to study the CD36 deficiency in 640 regular volunteer platelet apheresis donors from Taipei blood centre. The coding exons of CD36 gene were sequenced in CD36-deficient individuals, and the allele frequencies of CD36 variants were determined in the larger population by mutation-specific PCR and oligonucleotide hybridization. Visual inspection of lipemic plasma was routinely performed on samples taken before commencement of apheresis. Individuals found to have lipemic plasma are deferred until next donation. We investigated the link between positive lipemic deferral record and low platelet CD36 expression status. Results We found four donors (0·6%) with type I CD36 deficiency (both platelets and monocytes CD36null) and six (1·0%) with type II CD36 deficiency (PLT: CD36null, monocyte: CD36low). Six CD36 genetic variants were identified, two of them were novel, all but one are found exclusively in CD36null and CD36low expressors. Subjects with CD36 genetic variants also displayed deficient or reduced CD36 on monocytes. Donors with null or low PLT CD36 expression were more likely to have a lipemic deferral record than control subjects with normal PLT CD36 expression (X2 = 27·36, odds ratio = 2·6, 95% conference interval: 1·8–3·8, P < 0·0001). Conclusion Through this study, we established a donor registry to supply CD36-negative platelets for patients in need.

The oxidation behavior of FeCoNi, FeCoNiCr, and FeCoNiCrCu equi-molar alloys was studied over the temperature range 800–1000 °C in dry air. The ternary and quaternary alloys were single-phase, while the quinary alloy was two-phase. In general, the oxidation kinetics of the ternary and quinary alloys followed the two-stage parabolic rate law, with rate constants generally increasing with temperature. Conversely, three-stage parabolic kinetics were observed for the quaternary alloy at T ≥ 900°C. The additions of Cr and Cu enhanced the oxidation resistance to a certain extent. The scales formed on all the alloys were triplex and strongly dependent on the alloy composition. In particular, on the ternary alloy, they consist of an outer-layer of CoO, an intermediate layer of Fe3O4, and an inner-layer of CoNiO2 and Fe3O4. Internal oxidation with formation of FeO precipitates was also observed for this alloy, which had a thickness increasing with temperature. The scales formed on the quaternary alloy consisted of an outer layer of Fe3O4 and CoCr2O4, an intermediate layer of FeCr2O4 and NiCr2O4, and an inner layer of Cr2O3. Finally, the scales formed on the quinary alloy are all heterophasic, consisting of an outer layer of CuO, an intermediate-layer of CuO and Fe3O4, and an inner-layer of Fe3O4, FeCr2O4, and CuCrO2. The formation of Cr2O3 on the quaternary alloy and possibly that of CuCrO2 on the quinary alloy was responsible for the reduction of the oxidation rates as compared to the ternary alloy.

We have measured B K-edge X-ray absorption spectra of Mg 1-x Al x B 2 (x=0.0 ~ 0.4) using bulk-sensitive total fluorescence yield (TFY) at room temperature and 30 K. In contrast to previous reports no peaks near 192 eV and 194 eV could be observed after repeated scraping, indicating their origin being due to surface contamination. These clean spectra show a peak right above the absorption threshold, anticipated from transition to the unoccupied B 2p states. Except in the intermediate Al doping range of x ~ 0.1 to 0.28 the threshold peak intensity decreases, consistent with pσ-hole filling. The increase of peak intensity in the intermediate range is correlated with structural phase transition.

An oxygen concentration dependent metal-nonmetal (MN) transition was observed for Rb 0.23 WO y with 2.80 3.04, the ρ RT of the Rb 0.23 WO y exhibits a four orders of magnitude increase with a value of 5 Ω cm. Correspondingly, the lattice constant along c-direction slightly shortens as oxygen concentration increases from 2.80 to 3.08. The observed results suggest that the hybridization between W 5d (t 2g ) and O 2p orbitals might be responsible for the MN transition. In addition, similar measurements were performed for Rb x WO 3.04 and Rb x WO 2.85 with 0.19 < x < 0.27. No rubidium concentration dependent MN transition was observed, indicating the electronic structure of the host WO y is not modified significantly by varying the soluble rubidium concentration.

Highly collimated synchrotron sources are the essential ingredient of novel radiology and micro-radiology techniques for materials science. medicine and biology-with contrast based on the refractive index rather than on absorption. We were able to implement a real-time version of such techniques. Successful test studies included thin-foil breaking and electrodeposition processes in the areas concerning materials properties. Meanwhile. extensive effort was dedicated to obtain high-quality X-ray images of live specimens on a microscopic scale and in real time. These tests achieved a lateral resolution better than 2 mum and a time per image of 10 ms, with clear potential for further improvements. The images revealed in great detail moving parts of different specimens. opening the way to a wide variety of applications in the life sciences, medicine and materials science. (C) 2001 Published by Elsevier Science B.V.

X-ray absorption near-edge fine structure (XANES) spectroscopy from N K-edge measurement was employed to examine the crystal structure of metallorganic vapor phase epitaxy (MOVPE) grown Mg-doped GaN (GaN:Mg) films. The result showed that Mg doping induced crystal stacking faults to occur at the film surface causing a fraction of hexagonal phase to transform into cubic phase. As a consequence of this, XANES spectra of the films were found to vary with the dopant concentration and to lose pure hexagonal character when examined with the incident angle θ of the X-ray beam. Spectral characteristic variation between the two phases allows us to estimate the phase composition of the samples. The trend of increasing cubic phase component in dopant concentration is consistent with the observed Normaski optical micrograph.

X-ray absorption near edge structure (XANES) spectra of crystalline (c)- and amorphous (a)-Si–C–N thin films were measured at the C, N, and Si K edge using the fluorescence and sample drain current modes. A sharp peak similar to the C 1s core exciton in chemical vapor deposition diamond is observed, which can be assigned to the transition from the C 1s to sp3 hybridized states in c-Si–C–N. The C K edge XANES spectrum of a-Si–C–N contains a relatively large 1s→π* peak, implying that carbon atoms in the a-Si–C–N film are bonded largely in graphite-like sp2 configurations. A shift of the a-Si–C–N π* peak towards the lower energy by ∼0.3 eV relative to that of c-Si–C–N is observed, which can be attributed to a higher degree of disorder-induced localization of excited electrons. Both a- and c-Si–C–N N K-edge XANES spectra resemble that of α-Si3N4. The Si K-edge absorption spectra of the Si–C–N thin films indicate a proportional combination of local Si–N and Si–C bonds. The increase of the binding energies of e...

This study measures the x-ray-absorption spectra of a series of nanodiamond thin films with grain diameters ranging from 3.5 nm to $5\ensuremath{\mu}\mathrm{m}$ at the C $K$-edge using the sample drain current mode at room temperature. Resonance peaks resembling the C $1s$ core exciton are observed. The exciton state and conduction band edge are found to shift to higher energies with the decrease of the grain size indicative of the presence of the quantum confinement effect.

This work investigates charge redistribution in a series of Ni-Cu alloys using x-ray photoemission spectroscopy (XPS) and Ni/Cu ${L}_{3,2}$- and $K$-edge x-ray-absorption near-edge structure (XANES). XPS results show that the constituent $d$ bands are well separated and shifted to a slightly higher binding energy upon dilution into the other host, indicating that the atomic sites in the alloy are not as well screened relative to the pure metal. However, no significant $d$-band narrowing is observed, suggesting that there is modest $d\ensuremath{-}d$ interaction in the alloys. In contrast to the XPS observation, XANES results show a reduction in white-line intensity at both edges relative to the pure metal suggesting that both Ni and Cu sites gain $d$ charge. The unoccupied Ni $d$ band is far from fully occupied even at infinite dilution. The discrepancy between the implications of the XPS and XANES results is dealt with using a charge redistribution model in which $s\ensuremath{-}p\ensuremath{-}d$ rehybridization takes place at both sites within the framework of electroneutrality and electronegativity considerations. It appears that both Ni and Cu gain a small but measurable amount of $d$ charge in alloy formation through rehybridization (loss of non-$d$ conduction charge). Possible connection between these results and the disappearance of ferromagnetism in ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}$ alloys at $xg0.6$ is discussed.

This study measures X-ray absorption spectra of crystalline (c)-Si–C–N thin film at the C and Si K-edge using the sample drain current mode, and at the N K-edge using the fluorescent mode. A resonance peak resembling the C 1s core exciton in CVD-diamond/Si is observed, and a broad feature occurring in the energy range between ∼290 and 300 eV can be assigned to the antibonding C 2p–Si 3sp hybridized states and the C 2p–N 2sp hybridized states as well. Analysis of the N K-edge near edge absorption spectra reveals a similar feature in c-Si–C–N and a-Si3N4, suggesting that nitrogen atoms generally have similar local environment in these two materials. Moreover, results obtained from Si K-edge absorption spectra for c-Si–C–N demonstrate a proportional combination of local Si–N and Si–C bonds, associated with the local tetrahedral C–Si–N3 as well as the long-range ordered atomic structure around Si atoms.

Purpose: to report on unusual imaging presentations in renal transitional cell carcinoma (TCC) Material and Methods: Imaging studies of 140 cases of pathologically proven renal TCC were retrospectively studied with the focus on unusual presentations Results: Unusual imaging manifestations were found in 20 cases (14.3%). These findings were classified into 5 categories: perirenal abscesses or perirenal hematomas in 6 cases; parenchymal masses in 5; undue thickening of the hydronephrotic wall in 4; “tuberculoid” pyelograms in 3; and tumors with massive necrosis in 2 Conclusion: Deceptive imaging presentations may occur in renal TCC. Recognition of these presentations may help to prevent delay in diagnosis

We present the electronic structure of ferrimagnetic ${\mathrm{Zn}}_{\mathit{x}}$${\mathrm{Ni}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ compounds obtained by a combination of O K-edge x-ray-absorption measurements and first-principles spin-unrestricted calculations using the pseudofunction method. The two distinct preedge features are found to vary systematically as a function of the Zn content. From both experimental and theoretical analyses, we find that substitution of Ni with Zn enhances localization of the 3d states of Fe on the octahedral sites, so that the O 2p\char21{}Fe 3d hybridized states can be resolved into two distinct twofold and threefold features. \textcopyright{} 1996 The American Physical Society.

Ni and Fe L3,2-edge magnetic circular dichroism (MCD) and Cr K-edge x-ray absorption near-edge structure measurements have been performed for the Py/Cr(tCr)/Py (Py=Ni80Fe20) trilayers with tCr=5, 10, 15, 20, and 25 A. The MCD asymmetry ratios in the Ni and Fe L3-edges spectra are found strongly affected by the thickness of the Cr layer. The moments of the Fe and Ni 3d states are found, respectively, to decrease and increase suddenly when tCr increases beyond 20 A. The measured magneto-optical Kerr effect hysteresis loops show a ferromagnetic-to-antiferromagnetic phase transition at about the same Cr-layer thickness. The transition of the magnetic property is found to correlate with the structural transition of the Cr spacer layer from a pseudomorphic fcc-like structure to a bcc structure.

The origin of the Curie temperature enhancement of EuO upon Gd doping is studied by using soft x-ray absorption spectroscopy on epitaxial pure and Gd-doped EuO thin films. Temperature- and doping-dependent changes in the oxygen K edge spectra provide information about the correlation of magnetism and lattice. Band-structure calculations reveal that these spectral changes as well as the increase of the Curie temperature to 125 K for Gd-doped EuO cannot be explained by electron doping alone. The compression of the crystal lattice due to the incorporation of the smaller Gd${}^{3+}$ ions plays also an important role.

Physical review / B 85, 235106 (2012). doi:10.1103/PhysRevB.85.235106, Published by APS, College Park, Md.

A type of GaAs-based ferromagnetic semiconductor, (Ga, Cr)As, was successfully prepared by low-temperature molecular-beam epitaxy. The (Ga, Cr)As thin film shows a flat surface up to the Cr content x=0.18. However, when Cr content x exceeded 0.20, the roughness of the film became larger. The ferromagnetic ordering of the semiconductor sample with the Cr content of x=0.11 was observed. The electronic structures of (Ga, Cr)As were characterized by x-ray absorption spectroscopy (XAS). The XAS spectra show different line shapes in different Cr content.

Zinc-blende CrAs/GaAs multilayers were grown by molecular beam epitaxy. It was certified that each CrAs layer maintains an epitaxial relationship with the zinc-blende GaAs structure judging from the reflection high-energy electron diffraction observation. The film contains thicker zinc- blende CrAs layers in total than the CrAs thin film directly grown on the GaAs substrate which has the critical thickness of 3 nm. It was clarified that the optimum thicknesses of CrAs and GaAs to keep a good epitaxial relationship are 2 ML and 2 ML, respectively. The electronic structure of the multilayer is thought to be close to that of the (Ga, Cr)As thin film which has 50% of Cr content judging from x-ray absorption spectroscopy measurements.

We addressed the so-far unresolved issue concerning the Co valence in the superconducting bilayer hydrated Na(x)CoO(2) · yH(2)O (x∼0.35, y∼1.3) using soft x-ray absorption spectroscopy at the Co-L(2,3) and O-K edges. We find that the valence state of the Co lies in a narrow range from +3.3 to +3.4 for all studied Na(x)CoO(2) · yH(2)O samples and their deuterated analogue with T(c)'s ranging from 3.8 to 4.7 K. These valence values are far from the often claimed +3.7, the number based on the Na content only. We propose to modify the phase diagram accordingly, where the basic electronic structure of the superconducting phase is very close to that of the Na(0.7)CoO(2) system, suggesting that the presence of in-plane spin fluctuations could play an important role for the superconductivity.

Power and bandwidth requirements have become more stringent for DRAMs in recent years. This is largely because mobile devices (such as smart phones) are more intensively relying on the use of graphics. Current DDR memory I/Os operate at 5Gb/s with a power efficiency of 17.4mW/Gb/s (i.e., 17.4pJ/b)[1], and graphic DRAM I/Os operate at 7Gb/s/pin [3] with a power efficiency worse than that of DDR. High-speed serial links [5], with a better power efficiency of ∼1mW/Gb/s, would be favored for mobile memory I/O interface. However, serial links typically require long initialization time (∼1000 clock cycles), and do not meet mobile DRAM I/O requirements for fast switching between active, standby, self-refresh and power-down operation modes [4]. Also, traditional baseband-only (or BB-only) signaling tends to consume power super-linearly [4] for extended bandwidth due to the need of power hungry pre-emphasis, and equalization circuits.

Earth- and space-based observations provide synergistic information for space mission encounters by providing data over longer timescales, at different wavelengths and using techniques that are impossible with an in situ flyby. We report here such observations in support of the EPOXI spacecraft flyby of comet 103P/Hartley 2. The nucleus is small and dark, and exhibited a very rapidly changing rotation period. Prior to the onset of activity, the period was ∼16.4 hr. Starting in 2010 August the period changed from 16.6 hr to near 19 hr in December. With respect to dust composition, most volatiles and carbon and nitrogen isotope ratios, the comet is similar to other Jupiter-family comets. What is unusual is the dominance of CO2-driven activity near perihelion, which likely persists out to aphelion. Near perihelion the comet nucleus was surrounded by a large halo of water-ice grains that contributed significantly to the total water production. Fil: Meech, K. J.. Institute for Astronomy; Estados Unidos Fil: A’Hearn, M. F.. University of Maryland; Estados Unidos Fil: Adams, J. A.. Cornell University; Estados Unidos Fil: Bacci, P.. Centro Astronomico di Libbiano; Italia Fil: Bai, J.. Chinese Academy of Sciences; China Fil: Barrera, L.. Universidad Metropolitana de Ciencias de la Educacion; Chile Fil: Battelino, M.. Swedish Space Corporation; Suecia Fil: Bauer, J. M.. Jet Propulsion Laboratory; Estados Unidos Fil: Becklin, E.. Stratospheric Observatory for Infrared Astronomy; Estados Unidos Fil: Bhatt, B.. Indian Institute of Astrophysics; India Fil: Biver, N.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bockelee Morvan, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Bodewits, D.. University of Maryland; Estados Unidos Fil: Bohnhardt, H.. Gobierno de la Republica Federal de Alemania. Max Planck Institut Fur Astrophysik; Alemania Fil: Boissier, J.. Inst. di Radioastronomia; Italia Fil: Bonev, B. P.. Catholic University of America; Estados Unidos Fil: Borghini, W.. Osservatorio Astronomico Naturalistico di Casasco; Italia Fil: Brucato, J. R.. Osservatorio Astrofisico di Arcetri; Italia Fil: Bryssinck, E.. Brixiis Observatory; Bélgica Fil: Buie. M. W.. Southwest Research Institute; Estados Unidos Fil: Canovas, H.. Utrecht University; Países Bajos Fil: Castellano, D.. Unione Astrofili Italiani; Italia Fil: Charnley, S. B.. National Aeronautics And Space Administration; Estados Unidos Fil: Chen, W. P.. National Taiwan Normal University; Corea del Sur Fil: Chiang, P.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Choi, Y. J.. Korea Astronomy and Space Science Institute; Corea del Sur Fil: Christian, D. J.. California State University; Estados Unidos Fil: Chuang, Y. L.. National Taiwan Normal University; Corea del Sur Fil: Cochran, A. L.. University of Texas; Estados Unidos Fil: Melita, Mario Daniel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina

Soft x-ray absorption experiments on the transition-metal ${L}_{2,3}$ edge of multiferroic ${\text{MnWO}}_{4}$ and antiferromagnetic ${\text{CoWO}}_{4}$ are presented. The observed linear polarization dependence, analyzed by full-multiplet calculations, is used to determine the ground-state wave function of the magnetic ${\text{Mn}}^{2+}$ and ${\text{Co}}^{2+}$ ions. The impact of the local structure and the spin-orbit coupling on the orbital moment is discussed in terms of the single-ion anisotropy. It is shown that the orbital moment in ${\text{CoWO}}_{4}$ is responsible for the collinear antiferromagnetism, while the small size of spin-orbit coupling effects make spiral magnetic order in ${\text{MnWO}}_{4}$ possible, enabling the material to be multiferroic.

We report on the local electronic structure of Fe impurities in MgO thin films. Using soft x-ray absorption spectroscopy, we verified that the Fe impurities are all in the $2+$ valence state. The fine details in the line shape of the $\text{Fe}\text{ }{L}_{2,3}$ edges provide direct evidence for the presence of a dynamical Jahn-Teller distortion. We are able to determine the magnitude of the effective ${D}_{4h}$ crystal field energies. We also observed a strong temperature dependence in the spectra which we can attribute to the thermal population of low-lying excited states that are present due to the spin-orbit coupling in the $\text{Fe}\text{ }3d$. Using this ${\text{Fe}}^{2+}$ impurity system as an example, we show that an accurate measurement of the orbital moment in ${\text{Fe}}_{3}{\text{O}}_{4}$ will provide a direct estimate for the effective local low-symmetry crystal fields on the ${\text{Fe}}^{2+}$ sites, important for the theoretical modeling of the formation of orbital ordering.

We addressed the so-far unresolved issue concerning the Co valence in the superconducting bilayer hydrated Na(x)CoO(2) · yH(2)O (x∼0.35, y∼1.3) using soft x-ray absorption spectroscopy at the Co-L(2,3) and O-K edges. We find that the valence state of the Co lies in a narrow range from +3.3 to +3.4 for all studied Na(x)CoO(2) · yH(2)O samples and their deuterated analogue with T(c)'s ranging from 3.8 to 4.7 K. These valence values are far from the often claimed +3.7, the number based on the Na content only. We propose to modify the phase diagram accordingly, where the basic electronic structure of the superconducting phase is very close to that of the Na(0.7)CoO(2) system, suggesting that the presence of in-plane spin fluctuations could play an important role for the superconductivity.

Linear-polarized soft-x-ray absorption (XAS) and inelastic neutron scattering (INS) experiments have been performed on $\text{Ce}M{\text{In}}_{5}$ with $M=\text{Rh}$, Ir, and Co to determine the crystal-field scheme and characteristic Kondo temperatures ${T}^{\ensuremath{\ast}}$ for the hybridization between $4f$ and conduction electrons. The ground-state wave functions are determined from the polarization-dependent soft-XAS data at the cerium ${M}_{4,5}$ edge and the crystal-field splittings from INS. The characteristic temperature ${T}^{\ensuremath{\ast}}$ has been determined from the line widths of the neutron scattering data. We find that the quasielastic linewidths of the superconducting compounds ${\text{CeCoIn}}_{5}$ and ${\text{CeIrIn}}_{5}$ are comparable with the low-energy crystal-field splitting.

We present a combined experimental and theoretical x-ray absorption spectroscopy study of the class of cobaltates ${\text{YBaCo}}_{4}{\text{O}}_{7}$ and ${\text{YBaCo}}_{3}M{\text{O}}_{7}$ $(M=\text{Al},\text{ }\text{Fe})$. The focus is on the local electronic and magnetic properties of the transition metal ions in these geometrically frustrated kagom\'e compounds. For the mixed valence cobaltate ${\text{YBaCo}}_{4}{\text{O}}_{7}$, both the ${\text{Co}}^{2+}$ and ${\text{Co}}^{3+}$ are found to be in the high-spin state. The stability of these high-spin states in tetrahedral coordination is compared with those in the more studied case of octahedral coordination. For the compound ${\text{YBaCo}}_{3}{\text{FeO}}_{7}$, we find exclusively ${\text{Co}}^{2+}$ and ${\text{Fe}}^{3+}$ as charge states.

We have succeeded in preparing high-quality Gd-doped single-crystalline EuO films. Using Eu-distillation-assisted molecular beam epitaxy and a systematic variation in the Gd and oxygen deposition rates, we have been able to observe sustained layer-by-layer epitaxial growth on yttria-stabilized cubic zirconia (001). The presence of Gd helps to stabilize the layer-by-layer growth mode. We used soft x-ray absorption spectroscopy at the Eu and Gd M4,5 edges to confirm the absence of Eu3+ contaminants and to determine the actual Gd concentration. The distillation process ensures the absence of oxygen vacancies in the films. From magnetization measurements we found the Curie temperature to increase smoothly as a function of doping from 70 K up to a maximum of 125 K. A threshold behavior was not observed for concentrations as low as 0.2%., 8 pages, 9 figures

We present a combined study of the electronic structure of the superconducting skutterudite derivative SrPt4Ge12 by means of x-ray photoelectron spectroscopy and full-potential band structure calculations including an analysis of the chemical bonding. We establish that the states at the Fermi level originate predominantly from the Ge 4p electrons and that the Pt 5d shell is effectively full. We find excellent agreement between the measured and the calculated valence-band spectra, thereby validating that band structure calculations in combination with photoelectron spectroscopy can provide a solid basis for the modeling of superconductivity in the compound series MPt4Ge12 M=Sr,Ba,La,Pr.

We have tested the concept of image charge screening as a new approach to restore magnetic ordering temperatures and superexchange interactions in correlated oxide ultrathin films. Using a three-monolayer NiO(100) film grown on Ag(100) and an identically thin film on MgO(100) as model systems, we observed that the N\'eel temperature of the NiO film on the highly polarizable metal substrate is 390 K while that of the film on the poorly polarizable insulator substrate is below 40 K. This demonstrates that screening by highly polarizable media may point to a practical way toward designing strongly correlated oxide nanostructures with greatly improved magnetic properties.

Using $\mathrm{Co}\mathrm{\text{\ensuremath{-}}}{L}_{2,3}$ and $\mathrm{O}\mathrm{\text{\ensuremath{-}}}K$ x-ray absorption spectroscopy, we reveal that the charge ordering in ${\mathrm{La}}_{1.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_{4}$ involves high spin ($S=3/2$) ${\mathrm{Co}}^{2+}$ and low spin ($S=0$) ${\mathrm{Co}}^{3+}$ ions. This provides evidence for the spin-blockade phenomenon as a source for the extremely insulating nature of the ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{4}$ series. The associated ${e}_{g}^{2}$ and ${e}_{g}^{0}$ orbital occupation accounts for the large contrast in the Co-O bond lengths and, in turn, the high charge ordering temperature. Yet, the low magnetic ordering temperature is naturally explained by the presence of the nonmagnetic ($S=0$) ${\mathrm{Co}}^{3+}$ ions. From the identification of the bands we infer that ${\mathrm{La}}_{1.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_{4}$ is a narrow band material.

We have succeeded in growing epitaxial and highly stoichiometric films of EuO on yttria-stabilized cubic zirconia (YSZ) (001). The use of the Eu-distillation process during the molecular beam epitaxy assisted growth enables the consistent achievement of stoichiometry. We have also succeeded in growing the films in a layer-by-layer fashion by fine tuning the Eu vs. oxygen deposition rates. The initial stages of growth involve the limited supply of oxygen from the YSZ substrate, but the EuO stoichiometry can still be well maintained. The films grown were sufficiently smooth so that the capping with a thin layer of aluminum was leak tight and enabled ex situ experiments free from trivalent Eu species. The findings were used to obtain recipes for better epitaxial growth of EuO on MgO (001)., 10 pages, 15 figures

X-ray-absorption near-edge structure (XANES) measurements have been performed for a variety of boron-doped and undoped diamond films at the C K edge using the sample drain current mode. The C K-edge XANES spectra of B-doped diamonds resemble that of the undoped diamond regardless of the B concentration, which suggests that the overall bonding configuration of the C atom is unaltered. B impurities are found to enhance both the sp3- and sp2-bond derived resonance features in the XANES spectra.

This work investigates the charge transfer and A1 (Ga) p-Ni d hybridization effects in the intermetallic Ni3Al (Ni3Ga) alloy using the Ni L3~- and K-edge and Al (Ga) K x-ray absorption near edge structure (XANES) measurements. We find that the intensity of white-line features at the Ni L3~-edge in the Ni3Al (Ni3Ga) alloy decreased in comparison with that of pure Ni, which can be attributed to the enhancement of Ni 3d states filling and the depletion of the density of Ni 3d unoccupied states in the Ni3A1 (Ni3Ga) alloy. Two clear features are also observed in the Ni3Al (Ni3Ga) XANES spectrum at the Al (Ga) K-edge, which can be assigned to the Al (Ga) unoccupied 3p (4p) states and their hybridized states with the Ni 3d/4sp states above the Fermi level in Ni3Al (Ni3Ga). The threshold at Al K-edge XANES for Ni3Al clearly shifts towards higher photon energies relative to that of pure Al, indicating that Al loses charges upon forming Ni3AI. On the other hand, the Ni K-edge shifts towards lower photon energies in Ni3Al (Ni3Ga) relative to that of pure Ni, which is consistent with the results of the Al K-edge XANES spectrum and is indicative of a charge transfer from Al to Ni sites. Our data support that no significant net charge flow occurs on and off sites in Ni3AI 0Nli3Ga ).