We report the structure and chemistry of the self-assembled oxide nanopillars that form in superconducting Co-doped BaFe2As2 thin film grown by pulsed laser deposition. The oxide nanopillars consist of a BaFeO2 phase, form epitaxially on the SrTiO3 template, and grow coherently with the BaFe2As2 film. The nanopillars are square with a uniform size of 4–5 nm, which is close to twice the superconducting coherence length. Despite a volume content of ∼5%, the nanopillars do not degrade the structural quality of the BaFe2As2 matrix. Indeed the nanopillars provide exceptionally strong vortex pinning and high critical current density due to the very close correlation of pillar and vortex core diameters.
We measured the THz reflectance properties of a high quality epitaxial thin film of the Fe-based superconductor BaFe1.84Co0.16As2 with Tc=22.5 K. The film was grown by pulsed laser deposition on a DyScO3 substrate with an epitaxial SrTiO3 intermediate layer. The measured RS/RN spectrum, i.e. the reflectivity ratio between the superconducting and normal state reflectance, suggests the presence of a superconducting gap ∆A close to 15 cm −1 . A detailed data analysis shows that a two-band, two-gap model is necessary to obtain a good description of the measured RS/RN spectrum. The low-energy ∆A gap results to be well determined (∆A=15.5±0.5 cm −1 ), while the value of the high-energy gap ∆B is more uncertain (∆B=55±7 cm −1 ). Our results provide evidence of two electronic contributions to the system conductivity with the presence of two optical gaps corresponding to 2∆/kTc values close to 2 and 7.
We developed a novel light enhancing film for an organic light emitting diode (OLED) based on polymer dispersed liquid crystal (PDLC). In the film, the liquid crystal droplets are unidirectionally aligned along the film normal direction and exhibit selective scattering. The film scatters light emitted only in directions with large incident angles but not light emitted in directions with small incident angles. When the light is scattered, it changes propagation direction and exits the OLED. The PDLC film reduces the total internal reflection and thus can significantly increase the light efficiency of the OLED.
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