Unconventional superconductivity and magnetism in Sr2RuO4 and related materials

We review the normal and superconducting state properties of the unconventional triplet superconductor Sr₂RuO₄ with an emphasis on the analysis of the magnetic susceptibility and the role played by strong electronic correlations. In particular, we show that the magnetic activity arises from the itinerant electrons in the Ru d‐orbitals and a strong magnetic anisotropy occurs (χ^+‐ < χ^zz) due to spin‐orbit coupling. The latter results mainly from different values of the g‐factor for the transverse and longitudinal components of the spin susceptibility (i.e. the matrix elements differ). Most importantly, this anisotropy and the presence of incommensurate antiferromagnetic and ferromagnetic fluctuations have strong consequences for the symmetry of the superconducting order parameter. In particular, reviewing spin fluctuation‐induced Cooper‐pairing scenario in application to Sr₂RuO₄ we show how p‐wave Cooper‐pairing with line nodes between neighboring RuO₂‐planes may occur. We also discuss the open issues in Sr₂RuO₄ like the influence of magnetic and non‐magnetic impurities on the superconducting and normal state of Sr₂RuO₄. It is clear that the physics of triplet superconductivity in Sr₂RuO₄ is still far from being understood completely and remains to be analyzed more in more detail. It is of interest to apply the theory also to superconductivity in heavy‐fermion systems exhibiting spin fluctuations.     

Optimized emitter contacting on multicrystalline silicon thin film solar cells

We present an optimized contacting scheme for multicrystalline silicon thin film solar cells on glass based on epitaxially crystallized emitters with a thin Al₂O₃ layer and a silver back reflector. In a first step a 6.5 µm thick amorphous silicon absorber layer is crystallized by a diode laser. In a second step a thin silicon emitter layer is epitaxially crystallized by an excimer laser. The emitter is covered by an Al₂O₃ layer with a thickness ranging from 1.0 nm to 2.5 nm, which passivates the surface and acts as a tunnel barrier. On top of the Al₂O₃ layer a 90–100 nm thick silver back reflector is deposited. The Al₂O₃ layer was found to have an optimal thickness of 1.5 nm resulting in solar cells with back reflector that achieve a maximum open‐circuit voltage of 567 mV, a short‐circuit current density of 27.9 mA/cm², and an efficiency of 10.9%. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Characterization of hydrothermally isolated xylan from beech wood by capillary electrophoresis with laser-induced fluorescence and mass spectrometry detection

Hemicelluloses such as xylans play an increasing role as renewable raw materials for technological applications. The complex and variable composition of hemicelluloses requires powerful analytical techniques in order to assess their composition. In the present study, the neutral fraction of hydrothermally isolated xylan from beech wood was characterized by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) upon derivatization with 8-aminopyrene-1,3,6-trisulfonic acid. Reproducible separation of the xylo-oligosaccharides was achieved using a polyvinyl alcohol coated capillary and a 25 mM sodium acetate buffer, pH 4.75, as background electrolyte at an applied voltage of ?30 kV. Intermediate precision expressed as relative standard deviation was below 2.0 % for migration times and below 10 % for relative peak areas except for the oligomers present at very low concentrations only. At the same time, derivatization conditions proved to be robust as well. Samples obtained by fractionation of the xylan were subsequently characterized by CE-LIF. In addition, capillary electrophoresis with mass spectrometry detection indicated the presence of small amounts of xylo-oligosaccharides containing additional sugar moieties such as 4-O-methylglucuronic acid. Moreover, minor components containing acetyl groups could be detected. The presence of these impurities was confirmed by nuclear magnetic resonance analysis of the fractions. In conclusion, although none of the techniques applied here gave a complete picture of the composition of the investigated xylan or its fractions, the combination provided insight into the complexity of the sample.     

Use of Neutron Transmutation Doping for the Preparation of a New Candidate Reference Material for Zinc Determination in Metallic Copper

A new application of neutron transmutation doping is described. The method is useful to prepare graded zinc contents in highly pure copper materials. The research reactor BER II at the Hahn-Meitner-Institute, Berlin served as a neutron source. The zinc content produced in the samples was analyzed by determining the ⁶⁵Zn-activity via gamma-spectrometry. Simultaneously irradiated flux monitors were used to determine the neutron flux density. Since cylindrical sample geometries are favorable for a reference material application in optical emission (OE) spectroscopy, the spatial distribution of the induced activity in a cylinder with a diameter of 8 mm and a length of 35 mm was investigated.     

Calcium phosphate mineralization with linear poly(ethylene imine): a time-resolved study

We have earlier shown that linear poly(ethylene imine) (LPEI) is an efficient growth modifier for calcium phosphate mineralization from aqueous solution (Shkilnyy et al., Langmuir, 2008, 24 (5), 2102). The current study addresses the growth process and the reason why LPEI is such an effective additive. To that end, the solution pH and the calcium and phosphate concentrations were monitored vs. reaction time using potentiometric, complexometric, and photometric methods. The phase transformations in the precipitates and particle morphogenesis were analyzed by X-ray diffraction and transmission electron microscopy, respectively. All measurements reveal steep decreases of the pH, calcium, and phosphate concentrations along with a rapid precipitation of brushite nanoparticles early on in the reaction. Brushite transforms into hydroxyapatite (HAP) within the first 2 h, which is much faster than what is reported, for example, for calcium phosphate precipitated with poly(acrylic acid). We propose that poly(ethylene imine) acts as a proton acceptor (weak buffer), which accelerates the transformation from brushite to HAP by taking up the protons that are released from the calcium phosphate precipitate during the phase transformation.     

Characterization of Phase I Hepatic Metabolites of Anti-Premature Ejaculation Drug Dapoxetine by UHPLC-ESI-Q-TOF

Determination of the metabolism pathway of xenobiotics undergoing the hepatic pass is a crucial aspect in drug development since the presence of toxic biotransformation products may result in significant side effects during the therapy. In this study, the complete hepatic metabolism pathway of dapoxetine established according to the human liver microsome assay with the use of a high-resolution LC–MS system was described. Eleven biotransformation products of dapoxetine, including eight metabolites not reported in the literature so far, were detected and identified. N-dealkylation, hydroxylation, N-oxidation and dearylation were found to be the main metabolic reactions for the investigated xenobiotic. In silico analysis of toxicity revealed that the reaction of didesmethylation may contribute to the increased carcinogenic potential of dapoxetine metabolites. On the other hand, N-oxidation and aromatic hydroxylation biotransformation reactions possibly lead to the formation of mutagenic compounds.     

Chow points of $${\mathbb{C}}$$-orbits

We consider free algebraic actions of the additive group of complex numbers on a complex vector space X embedded in the complex projective space. We find an explicit formula for the map p that assigns to a generic point x ? X the Chow point of the closure of the orbit through x. The properties Hausdorff quotient topology and proper action are equivalently characterized by the closure of the image of p in the closed Chow variety.     

Effect of hydrofluoric acid treatment on the crystallisation behaviour of Zr–Ti–Cu–Al–Ni metallic glass

The surface of the metallic glass Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ has been modified by hydrofluoric acid (HF) etching treatment. The devitrification and crystallisation process has been mainly studied by isothermal differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The nucleation-growth process is the mechanism of crystallisation; nevertheless the JMA-model is not applicable in every situation. Alternative methods are used to interpret the data. Results show the devitrification process is strongly affected by surface nucleation, which depends on the surface topology. Zr₃Al₂ is the first phase formed on the concave areas whereas the quasicrystalline and Zr₂Ni-based phases appears in the flatter ones. Nevertheless, the presence of an oxide surface layer acts upon the surface nucleation and dwarfs the consequences of such topological differences. Moreover, the quasicrystalline formation appears also to be in competition with the parallel formation of ZrO₂ due to thermal re-oxidation during the DSC experiments.