Anisotropic Local Structure of SrFe2-xNixAs2 (x = 0.00, 0.16, and 0.23) Superconductor Probed by Polarized X-ray Absorption Fine Structure Measurements.

We have investigated the effect of the Ni substitution on the local structure and the valence electronic states of the SrFe2-xNixAs2 (x = 0.00, 0.16, and 0.23) superconductor with a multi-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy. The As K-edge and Fe K-edge EXAFS measurements in the two polarizations (E‖ab and E‖c) show a clear change in the local structure with Ni concentration. The near-neighbor bondlengths and the related mean-square relative displacements (MSRDs) decrease as the Ni content increases. The polarized XANES spectra at the As, Fe and Ni K edges reveal a systematic change in the anisotropy of the valence electronic structure. The results suggest that the quasi 2D electronic structure of this system tends to become more isotropic as the Ni content increases. The local structure and the valence electronic states are discussed in the frame of the evolving electronic transport of the SrFe2-xNixAs2 system.

Temperature dependent local inhomogeneity and magnetic moments of (Li1-xFex)OHFeSe superconductors.

We have combined the extended X-ray absorption fine structure (EXAFS) and X-ray emission spectroscopy (XES) to investigate the local structure and the local iron magnetic moments of (Li1-xFex)OHFeSe (x∼0.2) superconductors. The local structure, studied by Fe K-edge EXAFS measurements, is found to be inhomogeneous that is characterized by different Fe-Se bond lengths. The inhomogeneous phase exhibits a peculiar temperature dependence with lattice anomalies in the local structural parameters at the critical temperature Tc (36 K) and at the spin density wave (SDW) transition temperature TN (130 K). Fe Kß XES shows iron to be in a low spin state with the local Fe magnetic moment evolving anomalously as a function of temperature. Apart from a quantitative measurement of the local structure of (Li1-xFex)OHFeSe, providing direct evidence of nanoscale inhomogeneity, the results provide further evidence of the vital role that the coupled electronic, lattice and magnetic degrees of freedom play in the iron-based superconductors.

The CLEAR X-ray emission spectrometer available at the CLAESS beamline of ALBA synchrotron.

The CLEAR X-ray emission spectrometer installed at the CLAESS beamline of the ALBA synchrotron is described. It is an energy-dispersive spectrometer based on Rowland circle geometry with 1 m-diameter circle. The energy dispersion is achieved by the combination of a diced analyzer crystal and a unidimensional detector. A single unconventional dynamically bent analyzer crystal (Si 111) permits a wide energy range to be covered, just by exploiting its different reflections (333, 444, 555, 777, 888): 6-22 keV, with a spectrometer efficiency that decreases above 11 keV because of the Si detector thickness (Mythen, 350 µm), while the relative scattering intensities for the Si 333, 444, 555, 777 and 888 reflections correspond to 36, 40, 21, 13 and 15, respectively. The provided energy resolution is typically below 1-2 eV and depends on the beam size, working Bragg angle and reflection exploited. In most cases the energy dispersion ranges from 10 to 20 eV and can be enlarged by working in the out-of-Rowland geometry up to 40 eV. The spectrometer works in full backscattering geometry with the beam passing through the two halves of the analyzer. The vacuum beam path and the particular geometry allow a typical average noise of only 0.5 counts per second per pixel. The spectrometer is mainly used for measuring emission lines and high-resolution absorption spectra, with a typical scanning time for highly concentrated systems of around half an hour, including several repeats. The intrinsic energy dispersion allows systematic collection of resonant X-ray emission maps by measuring high-resolution absorption spectra. Moreover, it allows spectra to be measured on a single-shot basis. Resonant inelastic X-ray scattering experiments to probe electronic excitations are feasible, although the spectrometer is not optimized for this purpose due to the limited energy resolution and scattering geometry provided. In that case, to minimize the quasi-elastic line, the spectrometer is able to rotate along the beam path. Advantages and disadvantages with respect to other existing spectrometers are highlighted.

The Local Structure and Metal-Insulator Transition in a Ba3Nb5-xTixO15 System.

The local structure of the filled tetragonal tungsten bronze (TTB) niobate Ba3Nb5-xTixO15 (x = 0, 0.1, 0.7, 1.0), showing a metal-insulator transition with Ti substitution, has been studied by Nb K-edge extended X-ray absorption fine structure (EXAFS) measurements as a function of temperature. The Ti substitution has been found to have a substantial effect on the local structure, that remains largely temperature independent in the studied temperature range of 80-400 K. The Nb-O bonds distribution shows an increased octahedral distortion induced by Ti substitution, while Nb-Ba distances are marginally affected. The Nb-O bonds are stiffer in the Ti substituted samples, which is revealed by the temperature dependent mean square relative displacements (MSRDs). Furthermore, there is an overall increase in the configurational disorder while the system with Nb 4d electrons turns insulating. The results underline a clear relationship between the local structure and the electronic transport properties suggesting that the metal-insulator transition and possible thermoelectric properties of TTB structured niobates can be tuned by disorder.

Mn substitution effect on the local structure of La(Fe1-x Mn x )AsO studied by temperature dependent x-ray absorption measurements.

The local structure of La(Fe1-x Mn x )AsO has been investigated using temperature dependent Fe K-edge extended x-ray absorption fine structure (EXAFS) measurements. The EXAFS data reveal distinct behavior of Fe-As and Fe-Fe atomic displacements with a clear boundary between x ⩽ 0.02 and x > 0.02. The Fe-As bondlength shows a gradual thermal expansion while the Fe-Fe bond manifests a temperature dependent anomaly at ∼180 K for x > 0.02. It is interesting to find characteristically different nature of Fe-As and Fe-Fe bondlengths shown by the temperature dependent mean square relative displacements. Indeed, the Fe-As bond, stiffer than that of the Fe-Fe, gets softer for x ⩽ 0.02 and hardly shows any change for x > 0.02. On the other hand, Fe-Fe bond tends to be stiffer for x ⩽ 0.02 followed by a substantial softening for x > 0.02. Such a distinction has been seen also in the As K-edge x-ray absorption near edge structure, probing local geometry around As atom together with the valence electronic structure. The results suggest that local atomic displacements by Mn substitution inducing increased iron local magnetic moment that should be the main reason for its dramatic effect in iron-based superconductors.

Magnetosomes could be protective shields against metal stress in magnetotactic bacteria.

Magnetotactic bacteria are aquatic microorganisms with the ability to biomineralise membrane-enclosed magnetic nanoparticles, called magnetosomes. These magnetosomes are arranged into a chain that behaves as a magnetic compass, allowing the bacteria to align in and navigate along the Earth's magnetic field lines. According to the magneto-aerotactic hypothesis, the purpose of producing magnetosomes is to provide the bacteria with a more efficient movement within the stratified water column, in search of the optimal positions that satisfy their nutritional requirements. However, magnetosomes could have other physiological roles, as proposed in this work. Here we analyse the role of magnetosomes in the tolerance of Magnetospirillum gryphiswaldense MSR-1 to transition metals (Co, Mn, Ni, Zn, Cu). By exposing bacterial populations with and without magnetosomes to increasing concentrations of metals in the growth medium, we observe that the tolerance is significantly higher when bacteria have magnetosomes. The resistance mechanisms triggered in magnetosome-bearing bacteria under metal stress have been investigated by means of x-ray absorption near edge spectroscopy (XANES). XANES experiments were performed both on magnetosomes isolated from the bacteria and on the whole bacteria, aimed to assess whether bacteria use magnetosomes as metal storages, or whether they incorporate the excess metal in other cell compartments. Our findings reveal that the tolerance mechanisms are metal-specific: Mn, Zn and Cu are incorporated in both the magnetosomes and other cell compartments; Co is only incorporated in the magnetosomes, and Ni is incorporated in other cell compartments. In the case of Co, Zn and Mn, the metal is integrated in the magnetosome magnetite mineral core.

Temperature dependent local atomic displacements in NaSn2As2 system.

NaSn2As2 is mechanically exfoliable layered van der Waals (vdW) Zintl phase that is getting interesting due to its low thermal conductivity and recently observed superconductivity. Here, we have investigated the temperature dependent local structure of NaSn2As2 by a combined analysis of As K-edge and Sn K-edge extended x-ray absorption fine structure measurements. The system is intrinsically disordered with the interatomic distances largely consistent to those estimated by average structure measurements. The stretching force constants of different bond distances have been determined using temperature dependent mean square relative displacements. The Sn-As distance is the strongest bond in this system, having covalent nature, unlike the weaker interlayer distances which are characterized by vdW type bonding. Among them, As-Na distance is slightly weaker than Sn-Sn(i) below ∼200 K and tends to get stronger above this temperature. The anomalous behavior of As-Na bond suggests that the mechanical exfoliation in this system is likely to be temperature dependent. The anomaly in the interlayer atomic correlations may be due to a charge density wave-like instability around this temperature, indicated by earlier experiments. The local structure and disorder are discussed in relation to the physical properties of NaSn2As2.

A high-energy-resolution resonant inelastic X-ray scattering spectrometer at ID20 of the European Synchrotron Radiation Facility.

An end-station for resonant inelastic X-ray scattering and (resonant) X-ray emission spectroscopy at beamline ID20 of ESRF - The European Synchrotron is presented. The spectrometer hosts five crystal analysers in Rowland geometry for large solid angle collection and is mounted on a rotatable arm for scattering in both the horizontal and vertical planes. The spectrometer is optimized for high-energy-resolution applications, including partial fluorescence yield or high-energy-resolution fluorescence detected X-ray absorption spectroscopy and the study of elementary electronic excitations in solids. In addition, it can be used for non-resonant inelastic X-ray scattering measurements of valence electron excitations.

A large-solid-angle X-ray Raman scattering spectrometer at ID20 of the European Synchrotron Radiation Facility.

An end-station for X-ray Raman scattering spectroscopy at beamline ID20 of the European Synchrotron Radiation Facility is described. This end-station is dedicated to the study of shallow core electronic excitations using non-resonant inelastic X-ray scattering. The spectrometer has 72 spherically bent analyzer crystals arranged in six modular groups of 12 analyzer crystals each for a combined maximum flexibility and large solid angle of detection. Each of the six analyzer modules houses one pixelated area detector allowing for X-ray Raman scattering based imaging and efficient separation of the desired signal from the sample and spurious scattering from the often used complicated sample environments. This new end-station provides an unprecedented instrument for X-ray Raman scattering, which is a spectroscopic tool of great interest for the study of low-energy X-ray absorption spectra in materials under in situ conditions, such as in operando batteries and fuel cells, in situ catalytic reactions, and extreme pressure and temperature conditions.

High resolution x-ray absorption and emission spectroscopy of Li x CoO2 single crystals as a function delithiation.

The effect of delithiation in Li x CoO2 is studied by high resolution Co K-edge x-ray absorption and x-ray emission spectroscopy. Polarization dependence of the x-ray absorption spectra on single crystal samples is exploited to reveal information on the anisotropic electronic structure. We find that the electronic structure of Li x CoO2 is significantly affected by delithiation in which the Co ions oxidation state tending to change from 3+ to 4+. The Co intersite (intrasite) 4p-3d hybridization suffers a decrease (increase) by delithiation. The unoccupied 3d t 2g orbitals with a 1g symmetry, containing substantial O 2p character, hybridize isotropically with Co 4p orbitals and likely to have itinerant character unlike anisotropically hybridized 3d e g orbitals. Such a peculiar electronic structure could have significant effect on the mobility of Li in Li x CoO2 cathode and hence the battery characteristics.

Temperature dependent local atomic displacements in ammonia intercalated iron selenide superconductor.

Recently, ammonia-thermal reaction has been used for molecular intercalation in layered FeSe, resulting a new Lix(NH3)yFe2Se2 superconductor with Tc ~ 45 K. Here, we have used temperature dependent extended x-ray absorption fine structure (EXAFS) to investigate local atomic displacements in single crystals of this new superconductor. Using polarized EXAFS at Fe K-edge we have obtained direct information on the local Fe-Se and Fe-Fe bondlengths and corresponding mean square relative displacements (MSRD). We find that the Se-height in the intercalated system is lower than the one in the binary FeSe, suggesting compressed FeSe4 tetrahedron in the title system. Incidentally, there is hardly any effect of the intercalation on the bondlengths characteristics, revealed by the Einstein temperatures, that are similar to those found in the binary FeSe. Therefore, the molecular intercalation induces an effective compression and decouples the FeSe slabs. Furthermore, the results reveal an anomalous change in the atomic correlations across Tc, appearing as a clear decrease in the MSRD, indicating hardening of the local lattice mode. Similar response of the local lattice has been found in other families of superconductors, e.g., A15-type and cuprates superconductors. This observation suggests that local atomic correlations should have some direct correlation with the superconductivity.

Temperature dependent EXAFS study on transition metal dichalcogenides MoX2 (X = S, Se, Te).

The local structure of molybdenum dichalcogenide MoX2 (X = S, Se, Te) single crystal has been studied by means of multi-edge (Mo, Se, and Te K-edges) extended x-ray absorption fine-structure spectroscopy as function of temperature. The temperature dependences of the interatomic distances Mo-X, Mo-Mo and X-X (X = S, Se, and Te) and of the corresponding Debye-Waller factors have been extracted over the 70-500 K temperature range. Exploiting the correlated Einstein model, we found that the Einstein frequencies of Mo-X and X-X bonds obtained by present data are in close agreement with the frequencies of the optical (Raman and infrared) stretching modes for both MoS2 and MoSe2, whereas a significant deviation has been found for MoTe2. A similar anomaly has been found for the force constants related to the Mo-X bonds in the MoTe2 case. Our findings, accordingly with the results reported in a recent theoretical paper, support the idea that the optical vibrational modes have a dominant role in MoS2 and MoSe2, whereas the effects of acoustic vibrational modes cannot be neglected in the case of MoTe2.

A study of temperature dependent local atomic displacements in a Ba(Fe(1-x)Co(x))2As2 superconductor.

We have studied the local structure of a Ba(Fe(1-x)Co(x))2As2 superconductor using temperature dependent extended X-ray absorption fine structure (EXAFS) measurements. Polarized EXAFS at the Fe K-edge on an optimally doped (x = 0.06) single crystal has permitted us to determine atomic displacements across the superconducting transition temperature (T(c)). The Fe-As bondlength hardly shows any change with temperature; however, the Fe-Fe sublattice reveals a sharp anomaly across T(c), indicated by a significant drop in mean square relative displacements, similar to the one known for cuprates and A15-type superconductors. We have also found a large atomic disorder around the substituted Co, revealed by polarized Co K-edge EXAFS measurements. The Co-Fe/Co bonds are more flexible than the Fe-Fe bonds with the As-height in Co-containing tetrahedra being larger than the one in FeAs4. The results suggest that the local Fe-Fe bondlength fluctuations and the atomic disorder in this sub-lattice should have some important role in the superconductivity of Ba(Fe(1-x)Co(x))2As2 pnictides.

Epitope mapping by solution NMR spectroscopy.

Antibodies play an ever more prominent role in basic research as well as in the biotechnology and pharmaceutical sectors. Characterizing their epitopes, that is, the region that they recognize on their target molecule, is useful for purposes ranging from molecular biology research to vaccine design and intellectual property protection. Solution NMR spectroscopy is ideally suited to the atomic level characterization of intermolecular interfaces and, as a consequence, to epitope discovery. Here, we illustrate how NMR epitope mapping can be used to rapidly and accurately determine protein antigen epitopes. The basic concept is that differences in the NMR signal of an antigen free or bound by an antibody will identify epitope residues. NMR epitope mapping provides more detailed information than mutagenesis or peptide mapping and can be much more rapid than X-ray crystallography. Advantages and drawbacks of this technique are discussed together with practical considerations.

Laparoscopic management of left paraduodenal hernia. Case report and review of literature.

We report a rare case of left paraduodenal hernia in patient with symptoms of abdominal subobstruction treated successful with laparoscopic management in urgent situation that have reduced the length of stay and postoperative pain. Internal hernia is only 1% of the causes of abdominal obstruction and the left paraduodenal hernia about 50% of them; it is a congenital defect that derive from malrotation and abnormal mesenteric adhesion. The modern imaging techniques help for the correct diagnosis despite difficult identification of the pathology for the various clinical presentation. The treatment of choice is the surgical intervention; the laparoscopic approach is rarely described in literature but it can reduce the morbidity, postoperative pain and the length of hospital stay.

Temperature dependent nanoscale atomic correlations in Ir1-xPtxTe2 (x = 0.0, 0.03 and 0.04) system.

X-ray absorption near-edge structure (XANES) spectroscopy has been used to investigate the unoccupied electronic states and local geometry of Ir1-xPtxTe2(x = 0.0, 0.03 and 0.04) as a function of temperature. The Ir L3-edge absorption white line, as well as high energy XANES features due to the photoelectron multiple scatterings with near neighbours, reveal clear changes in the unoccupied 5d-electronic states and the local geometry with Pt substitution. We find an anomalous spectral weight transfer across the known first-order structural phase transition from the trigonal to monoclinic phase in IrTe2, which characterizes the reduced atomic structure symmetry below the transition temperature. No such changes with temperature are seen in the Pt substituted superconducting samples. In addition, a gradual increase of the spectral weight transfer is observed in IrTe2 with a further decrease in temperature below the transition, indicating that the low temperature phase is likely to have a symmetry lower than the monoclinic one. The results suggest that the interplay between inter-layer and intra-layer atomic correlations should have a significant role in the properties of an Ir1-xPtxTe2 system.

Is HE4 serum level a valid screening test in women candidates for kidney transplant? A case report and a review of literature.

While studying a candidate for kidney transplant it is essential to exclude active malignant diseases. Serum biomarkers help to exclude specific cancers. Tumor markers are proteins secreted by neoplastic cells that can mark their activities. HE4 is a new tumor marker used in ovarian cancer. It is an epithelium protein that appears overexpressed in ovarian cancer, but it is also present in other normal human tissues. Often in patients with kidney failure serum biomarkers are increased compared to healthy people. We report a case of a Caucasian woman suffering from kidney failure examined by our team to be included on the kidney transplantation list. Patient had a known pelvic mass. Determination of serum biomarkers, CA125 and HE4, was performed to exclude pelvic tumor, and we found high levels of HE4 with normal levels of CA125. A new transvaginal ultrasound was performed on the patient and it showed a pelvic mass near the left ovary. This mass resulted bigger than in the previous ultrasound, performed about a month before. We decided to perform a pelvic CT for improved diagnostic accuracy. The reports of this exam showed that the mass was a hematoma correlated with a previous knee prosthetic surgery. Even tough many serum biomarkers are higher in patients with renal failure, there is no study to demonstrate that HE4 blood levels are modified in these patients. This case report shows how HE4 can be elevated in people in hemodialysis in a benign situation, also in a pelvic mass not from the genital tract. There is no similar case described in literature.

Temperature dependence of crystal field excitations in CuO.

We report a study on the temperature dependence of charge-neutral crystal field (dd) excitations in cupric oxide, using nonresonant inelastic x-ray scattering spectroscopy. Thanks to a very high-energy resolution (ΔE = 60 meV), we observe thermal effects on the dd excitation spectrum fine structure between temperatures of 10-320 K. The spectra broaden considerably with increasing temperature, consistently with an enhancement of the coupling between crystal field excitations and the temperature-dependent continuum of states above the band gap. We discuss this and other mechanisms that may explain this temperature dependence.

Study of the electronic and magnetic properties as a function of isoelectronic substitution in SmFe(1-x)RuxAsO0.85F0.15.

We have studied the electronic and magnetic properties of SmFe(1-x)RuxAsO0.85F0.15 (x = 0, 0.05, 0.25, 0.33, 0.5) by high-resolution x-ray absorption and x-ray emission spectroscopy. The local Fe magnetic moment (µ) tends to decrease for a small Ru substitution, but it shows a clear increase with further substitution. It appears that impurity scattering prevails in reducing the µ with small Ru substitution due to an extended Ru d-band. A nanoscale phase separation, that decouples the FeAs layers from the spacer layers, drives the increase of µ at higher Ru substitution. The results provide important information on nanoscale phase separation due to isoelectronic substitution in the active layers of iron-based 1111-superconductors and its effect on the local magnetic properties.

Abdominal emergency in elderly: a case of small bowel obstruction and ischemia caused by bulky IA ovarian cancer.

Bowel obstruction resulting from colorectal and ovarian cancer is a serious and distressing complication of these malignancies. This may be caused by diffuse peritoneal carcinomatosis, bulky masses filling the pelvis and abdomen or postoperative adhesions, and should be carefully worked out by pre-operative imaging. We report the case of a small bowel obstruction and intestinal ischemia caused by a bulky (20x40 cm in diameter) cystic ovarian neoplasm that was found to be a stage IA G2 cystadenocarcinoma, successfully managed by uterus-sparing surgery.