Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters

Abstract: The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg2+) and monomethylmercury compounds (MeHg) in natural water samples at the pg L–1 level. The method is based on the simultaneous extraction of MeHg and Hg2+ dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na2S, removal of H2S by purging with N2, subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L–1 for MeHg and 0.06 ng L–1 for Hg2+ when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg2+. Recoveries were 90–110% for both species.

Photoluminescence from Liquid‐Exfoliated WS2 Monomers in Poly(Vinyl Alcohol) Polymer Composites

Abstract: While liquid phase exfoliation can be used to produce nanosheets stabilized in polymer solutions, very little is known about the resultant nanosheet size, thickness, or monolayer content. The present study uses semiquantitative spectroscopic metrics based on extinction, Raman, and photoluminescence (PL) spectroscopy to investigate these parameters for WS2 nanosheets exfoliated in aqueous poly(vinyl alcohol) (PVA) solutions. By measuring Raman and PL simultaneously, the monolayer content can be tracked via the PL/Raman intensity ratio while varying processing conditions. The PL is found to be maximized for a stabilizing polymer concentration of 2 g L−1. In addition, the monolayer content can be controlled via the centrifugation conditions, exceeding 5% by mass in some cases. These techniques have allowed tracking the ratio of PL/Raman in a droplet of polymer-stabilized WS2 nanosheets as the water evaporates during composite formation. No evidence of nanosheet aggregation is found under these conditions although the PL becomes dominated by trion emission as drying proceeds and the balance of doping from PVA/water changes. Finally, bulk PVA/WS2 composites are produced by freeze drying where >50% of the monolayers remain unaggregated, even at WS2 volume fractions as high as 10%.

Insulator to metal transition in WO3 induced by electrolyte gating

Abstract: Tungsten oxide and its associated bronzes (compounds of tungsten oxide and an alkali metal) are well known for their interesting optical and electrical characteristics. We have modified the transport properties of thin WO3 films by electrolyte gating using both ionic liquids and polymer electrolytes. We are able to tune the resistivity of the gated film by more than five orders of magnitude, and a clear insulator-to-metal transition is observed. To clarify the doping mechanism, we have performed a series of incisive operando experiments, ruling out both a purely electronic effect (charge accumulation near the interface) and oxygen-related mechanisms. We propose instead that hydrogen intercalation is responsible for doping WO3 into a highly conductive ground state and provide evidence that it can be described as a dense polaronic gas. The mechanism leading to large carrier density changes and even concomitant electronic phase transitions with electrolyte gating is under debate. An international team led by Ivan Božovic at USA’s Brookhaven National Laboratory and Yale University report a series of experiments based on WO3 films, which is found to exhibit an insultator-to-metal transition under gating, with both ionic liquids and polymer electrolytes. The experimental results allow to rule out some mechanisms—such as charge accumulation near the interface or oxygen vacancy formation—previously suggested in other material systems. Instead, the authors propose that the primary effect of electrolyte gating in WO3 is hydrogen intercalation. Hydrogenation leads to the formation of a dense polaronic gas that explains the conductive ground state. The doping mechanism behind electrolyte gating seems to be material dependent.

The attainable superconducting Tc in a model of phase coherence by percolating

Abstract: The onset of macroscopic phase coherence in superconducting cuprates is considered to be determined by random percolating between mesoscopic Jahn-Teller pairs, stripes or clusters. The model is found to predict the onset of superconductivity near 6% doping, maximum Tc near 15% doping and Tc T* at optimum doping, and accounts for the destruction of superconductivity by Zn doping near 7%. The model also predicts a relation between the pairing (pseudogap) energy and Tc in terms of experimentally measurable quantities.