Thin film growth of Fe-based superconductors: from fundamental properties to functional devices. A comparative review.

Fe-based superconductors bridge a gap between MgB2 and the cuprate high temperature superconductors as they exhibit multiband character and transition temperatures up to around 55 K. Investigating Fe-based superconductors thus promises answers to fundamental questions concerning the Cooper pairing mechanism, competition between magnetic and superconducting phases, and a wide variety of electronic correlation effects. The question addressed in this review is, however, is this new class of superconductors also a promising candidate for technical applications? Superconducting film-based technologies range from high-current and high-field applications for energy production and storage to sensor development for communication and security issues and have to meet relevant needs of today's society and that of the future. In this review we will highlight and discuss selected key issues for Fe-based superconducting thin film applications. We initially focus our discussion on the understanding of physical properties and actual problems in film fabrication based on a comparison of different observations made in the last few years. Subsequently we address the potential for technological applications according to the current situation.

Microbiological community analysis of vermicompost tea and its influence on the growth of vegetables and cereals.

Vermicompost, the digestion product of organic material by earthworms, has been widely reported to have a more positive effect on plant growth and plant health than conventional compost. A study was conducted to investigate the effects of different vermicompost elutriates (aerated compost teas) on soils and plant growth. The teas were analyzed by chemical, microbiological, and molecular methods accompanied by plant growth tests at laboratory and field scale. The number of microorganisms in the teas increased during the extraction process and was affected by substrate addition. The vermicompost tea found to increase plant growth best under laboratory tests was applied to cereals (wheat and barley) and vegetables (Raphanus sativus, Rucola selvatica, and Pisum sativum) in a field study. The results revealed no effects of tea application on plant yield; however, sensoric tests indicated an improvement in crop quality. The soils from laboratory and field studies were investigated to detect possible microbial or chemical changes. The results indicated that minor changes to the soil microbial community occurred following tea application by foliar spray in both the laboratory-scale and field-scale experiments.

Nb 1-y Fe 2+y thin film growth and characterization.

We report on the growth of c-axis oriented thin films of NbFe(2) prepared by pulsed laser deposition. Variation of the deposition conditions results in variation of the composition of the Nb(1-y)Fe(2+y) films in the range from Nb rich to Fe rich films. Films near the stoichiometric composition (y ≈ 0) are the most interesting. However, microstructural investigations of these films reveal two kinds of grain, which exhibit different shape, epitaxial relation and chemical composition. The different chemical compositions of opposing doping character result in two magnetic phases confirmed by means of magnetization and Hall measurements. This investigation demonstrates the possibility of NbFe(2) thin film growth and discusses the microstructural inhomogeneities occurring.

Critical current scaling and anisotropy in oxypnictide superconductors.

Having succeeded in the fabrication of epitaxial superconducting LaFeAsO(1-x)F(x) thin films we performed an extensive study of electrical transport properties. In the face of multiband superconductivity we can demonstrate that an anisotropic Ginzburg-Landau scaling of the angular dependent critical current densities can be adopted, although being originally developed for single band superconductors. In contrast with single band superconductors the mass anisotropy of LaFeAsO(1-x)F(x) is temperature dependent. A very steep increase of the upper critical field and the irreversibility field can be observed at temperatures below 6 K, indicating that the band with the smaller gap is in the dirty limit. This temperature dependence can be theoretically described by two dominating bands responsible for superconductivity. A pinning force scaling provides insight into the prevalent pinning mechanism and can be specified in terms of the Kramer model.

High upper critical fields and evidence of weak-link behavior in superconducting LaFeAsO1-xFx thin films.

Superconducting LaFeAsO1-xFx thin films were grown on single crystalline LaAlO3 substrates with critical temperatures (onset) up to 28 K. Resistive measurements in high magnetic fields up to 40 T reveal a paramagnetically limited upper critical field mu{0}H{c2}(0) around 77 T and a remarkable steep slope of -6.2 T K-1 near T{c}. From transport measurements we observed weak-link behavior in low magnetic fields and evidence for a broad reversible regime.

In vitro analysis of xenoestrogens by enzyme linked receptor assays (ELRA).

Receptor binding assays are a modern approach to the effects-related analysis of xenoendocrines. Human estrogen receptors are used to develop an analytical tool for the detection of estrogenic substances in environmental samples. A sensitive Enzyme Linked Receptor Assay (ELRA) was developed in a microwell plate format. The receptor assay is based on similar principles as competitive immunoassays (ELISA). However, receptor binding always implies a biological effect, either agonistic or antagonistic. The choice of suitable tracers or hapten conjugates is an important step in assay development. For this purpose and for the determination of receptor-affinities of relevant xenoestrogens, a surface plasmon resonance (SPR) biosensor (BIAcore) was used for binding studies with immobilized receptors. Results with commercially available hapten-conjugates (estradiol-BSA) show a direct correlation between the amount of immobilized estradiol receptor and the amount of bound hapten-conjugate. Based on these BIAcore experiments an ELRA was developed. The calibration curves show a detection limit of 0.1 microgram/l for 17 beta-estradiol. Cross-reactivities of different steroids and xenoestrogens are reported.