Hierarchical Topographies Created by Controlled Evaporation of a Block Copolymer Solution
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ing, that are not superconductors on their own, but rather exhibit superconductivity at the interface between them. The layer identified as essential to the superconductivity by the zinc-substitution experiment represents the second copper-oxide layer away from the interface. The scientists found that the presence of zinc had no effect on the transition temperature at which superconductivity sets in, ~32 K (-241°C), except when placed in that particular layer. In the latter case, the scientists observed a dramatic drop in the transition temperature to 18 K (-255°C). The reduction in transition temperature provides a clear indication that that particular layer is the “hot” one responsible for the relatively high temperature at which superconductivity normally sets in for this material, according to the researchers. “We now have a clean experimental
Hierarchical Topographies Created by Controlled Evaporation of a Block Copolymer Solution Hierarchically ordered materials tend to have unique physical properties. For instance, the lotus leaf has both microand nanostructures which contribute to its superhydrophobicity. To produce materials with useful properties such as superhydrophobicity, simple methods for making hierarchical materials must be established. Block copolymers provide a way of creating nano-patterned surfaces because of their ability to self-assemble into their constituent blocks. Zhiqun Lin, Suck Won Hong, and Jun Wang at Iowa State University have shown that controlled evaporation of a diblock copolymer solution creates a serpentine-like microstructure, which can further be processed to have nanostructures. As described in the October 19 issue of Angewandte Chemie International Edition (DOI: 10.1002/anie.200903552; p. 8356), Lin and co-workers prepared a solution of polystyrene-block-poly(methylmetha -
How to Choose In-plane Ferroelectric Polarization States in Rhombohedral BiFeO3 An international team of researchers have devised a way to reliably manipulate the ferroelastic polarization states of rhombohedral multiferroic materials that allows coupling to the strain and magnetic properties of these materials. “The control of polarization switching to create different domain patterns with 894
proof that high-temperature superconductivity can exist, undiminished, in a single copper-oxide layer,” Božovi´c said. “This piece of information gives important input to our theoretical understanding of this phenomenon.” Božovi´c said that, in the material he studied, the electrons required for superconductivity actually come from the metallic material below the interface. They leak into the insulating material above the interface and achieve the critical level in that second copper-oxide layer. But in principle, he said, there are other ways to achieve the same concentration of electrons in that single layer, for example, by doping achieved by applying electric fields. That would result in high-temperature superconductivity in a single copperoxide layer measuring just 0.66 nm. From a practical viewpoint, this
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