Electrical current distribution across a metal-insulator-metal structure during bistable switching

Combining scanning electron microscopy (SEM) and electron-beam-induced current (EBIC) imaging with transport measurements, it is shown that the current flowing across a two-terminal oxide-based capacitor-like structure is preferentially confined in areas localized at defects. As the thin-film device switches between two different resistance states, the distribution and intensity of the current paths, appearing as bright spots, change. This implies that switching and memory effects are mainly determined by the conducting properties along such paths. A model based on the storage and release of charge carriers within the insulator seems adequate to explain the observed memory effect.Comment: 8 pages, 7 figures, submitted to J. Appl. Phy

0-pi Josephson tunnel junctions with ferromagnetic barrier

We fabricated high quality Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Using a ferromagnetic layer with a step-like thickness, we obtain a 0-pi junction, with equal lengths and critical currents of 0 and pi parts. The ground state of our 330 microns (1.3 lambda_J) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0-pi step and carrying ~6.7% of the magnetic flux quantum Phi_0. The dependence of the critical current on the applied magnetic field shows a clear minimum in the vicinity of zero field.Comment: submitted to PR

The consequences of compromising the EU's free movement of persons principle on Swiss research: how to survive constrained access to regional funding

Between 2014 and 2016, Switzerland's access to some of the EU funding was limited after a referendum against mass immigration was accepted and the country refused to sign the free movement accord to the EU's newest member, Croatia. It is well documented that Switzerland has suffered from a drop in participation, funding and a decrease in consortium lead positions. However, there is no account of the consequences on institutional level. We therefore aimed at describing the immediate- and longer-term impact of the partial association status to the Swiss Tropical and Public Health Institute (Swiss TPH) and to identify key strategies for minimizing institutional damage during a limited access period to a key regional funding source. A quantitative analysis of the institute's grants database, from 2007 to 2019, did not show any clear trends related to the partial association status of Switzerland for funding and projects awarded. The qualitative outcomes changed along the timeline assessed; whereas in 2014 a range of negative effects were stated by Swiss TPH researchers, a survey conducted in 2019 with Swiss TPH applicants and project partners to Horizon 2020, revealed that most project leaders felt that the partial association did neither affect their external partners' willingness to collaborate nor Swiss TPH's role in the proposal or consortium. On the other hand, the institutional strategic goal of taking on consortia leads was delayed by several years as a direct consequence of the partial association. Also, the exclusion from European research networks and the lack of consultation of expertise by the European partner institutions was widely seen as damaging. A policy of favouring long-term partnerships over ad-hoc collaborations, along with constant and trustful communication, as immediate mitigation measure, helped averting some of the reputational and access damage. Moreover, the Swiss TPH business model based on a three-way strategy of research, education and services has proven highly viable allowing to build a large pool of potential funding sources internationally, resulting in relative resilience in terms of income lost

Inhomogeneity of donor doping in SrTiO3 substrates studied by fluorescence-lifetime imaging microscopy

Fluorescence-lifetime imaging microscopy (FLIM) was applied to investigate the donor distribution in SrTiO3 single crystals. On the surfaces of Nb- and La-doped SrTiO3, structures with different fluorescence intensities and lifetimes were found that could be related to different concentrations of Ti3+. Furthermore, the inhomogeneous distribution of donors caused a non-uniform conductivity of the surface, which complicates the production of potential electronic devices by the deposition of oxide thin films on top of doped single crystals. Hence, we propose FLIM as a convenient technique (length scale: 1 $\mu$m) for characterizing the quality of doped oxide surfaces, which could help to identify appropriate substrate materials

Light Scattering of High Polymer Solutions

In principle it is possible to determine the molecular weight distribution of a high polymer, containing no excessively large molecules, from interpretation of its light scattering in solutions at various concentrations. Actually there appear to be severe limitations to this method. Not only is it evident that, considering experimental error, the resolving power is low for the detection in any part of the molecular weight distribution curve of a group of components of similar molecular weights (as contrasted to a single component), it may also happen, in consequence of the restriction of the data to a certain concentration range, that components at the ends of the distribution curve will not be detected and, moreover, that the conclusions regarding the remainder of the distribution will be distorted

Polarization states of polydomain epitaxial Pb(Zr1-xTix)O3 thin films and their dielectric properties

Ferroelectric and dielectric properties of polydomain (twinned) single-crystal Pb(Zr1-xTix)O3 thin films are described with the aid of a nonlinear thermodynamic theory, which has been developed recently for epitaxial ferroelectric films with dense laminar domain structures. For Pb(Zr1-xTix)O3 (PZT) films with compositions x = 0.9, 0.8, 0.7, 0.6, 0.5, and 0.4, the "misfit strain-temperature" phase diagrams are calculated and compared with each other. It is found that the equilibrium diagrams of PZT films with x > 0.7 are similar to the diagram of PbTiO3 films. They consist of only four different stability ranges, which correspond to the paraelectric phase, single-domain tetragonal ferroelectric phase, and two pseudo-tetragonal domain patterns. In contrast, at x = 0.4, 0.5, and 0.6, the equilibrium diagram displays a rich variety of stable polarization states, involving at least one monoclinic polydomain state. Using the developed phase diagrams, the mean out-of-plane polarization of a poled PZT film is calculated as a function of the misfit strain and composition. Theoretical results are compared with the measured remanent polarizations of PZT films grown on SrTiO3. Dependence of the out-of-plane dielectric response of PZT films on the misfit strain in the heterostructure is also reported.Comment: 23 pages, 4 figure

Pollinator Selection, Quantitative Genetics, and Predicted Evolutionary Responses of Floral Traits in Penstemon Centranthifolius (Scrophulariaceae)

Much of the remarkable diversity of angiosperm flowers is thought to have evolved in response to selection by animal pollinators. Selection during pollination can readily be documented, but the extent to which it leads to evolutionary change depends on the genetic basis of floral traits. Here we combine estimates of genetic variance and covariance for several traits of flowers and inflorescences in a wild plant species, with estimates of natural selection by hummingbird pollinators. Analysis of phenotypic selection through two components of pollination success indicates direct selection of plants toward larger size and toward bearing shorter flowers that produce more nectar. Predictions of selection response that account for genetic correlations among traits generally exceed the simple predictions based on apparent selection and heritabilities of single traits. This underscores the importance of genetic correlations and demonstrates that univariate, strictly phenotypic, analyses of natural selection can be misleading. A sample of fruits from one of the two years of our study also indicates that total selection at the end of the reproductive cycle is weaker than selection during pollination. Thus a second caution is in order, against relying too strongly on differential pollination success as an estimate of overall selection

Invasive oysters as new hosts for native shell-boring polychaetes: Using historical shell collections and recent field data to investigate parasite spillback in native mussels in the Dutch Wadden Sea

Biological invasions can have manifold effects on native biota, including impacts on species interactions in invaded ecosystems. Among those are effects on parasite-host interactions, for example in cases where invaders serve as a new host for native parasites, leading to an amplification of the parasite population which may ultimately result in increased infection levels in the original native hosts (parasite spillback). In this study, we investigated the potential spillback of the native shell-boring polychaete Polydora ciliata from invasive Pacific oysters (Crassostrea (Magallana) gigas) to native mussels (Mytilus edulis) in the Dutch Wadden Sea. A field survey in the intertidal revealed that the majority of P. ciliata can nowadays be found in the shells of live but also dead Pacific oysters and much less in shells of other potential host species: mussels and periwinkles (Littorina littorea). Using a unique historical shell collection based on long-term sampling programmes in the intertidal and subtidal of the western Dutch Wadden Sea, we compared P. ciliata infections in mussels before and after the invasion of the Pacific oyster by means of x-ray scans. Both for the intertidal and subtidal, we did not detect differences in prevalence of P. ciliata in mussels between pre- and post-invasion periods. This suggests that the invasion of the Pacific oyster may not have caused a strong spillback to mussels regarding P. ciliata and thus the invasion probably had little indirect infection-mediated effects on the condition and fitness of native mussels. Instead, the acquisition of native P. ciliata by the invasive oysters suggests that they may themselves be affected by the new infections and this may warrant further research