February 07, 2016

First self-assembled 3D superconductor structure created

Prof. Ulrich Wiesner, material science and engineering, created the first ever self-assembled, three-dimensional superconductor with a research group of graduate students and professors of different disciplines.

This is the first time a superconductor has self-assembled into a porous, three-dimensional gyroidal structure. After years of collaboration with co-author Prof. Sol Gruner, physics, Wiesner developed the idea for the gyroidal structure, employing niobium nitride as the superconducting material brought the idea to fruition.

“The superconductors have this so-called gyroid nanostructure which provides a network of nanopores of around 15 nanometers that percolates the entire superconducting structure,” Wiesner said. “The width of the superconducting struts separating the pores itself is only of order 10 to 20 nanometers.”

Diverging from the typical bulk material used to create superconductors, Wiesner’s team utilized a self-assembling, synthetic block copolymer assembled in Wiesner’s labs.

Wiesner’s achievement also expands possibilities for the future research and creation of superconductors, he said.

“The gyroid structure is only one of many, many spontaneous structures that polymers and other self-assembly systems form,” Wiesner said. “We can now start to test how these structures will change the properties of superconductors.”

GA structure and sample/structure evolution from initial compounds to final NbN superconductors. (A) GA before and after processing, with the unit cell indicated by the black cube. (B) (Top) Chemical structures of compounds and (bottom) schematic of synthesis and processing steps with photographs of the final materials. Block terpolymers (ISO) are combined with the Nb2O5 sol-gel precursors in a common solvent. Hybrid block copolymer/Nb2O5 GA structures are generated by solvent evaporation–induced self-assembly. After calcination in air, the mesoporous Nb2O5 GAs are transformed to NbN GAs in a two-step nitriding process. Scale bars in all photographs represent 1 cm. NH3, ammonia.

Science Advances - Block copolymer self-assembly–directed synthesis of mesoporous gyroidal superconductors



Abstract

Superconductors with periodically ordered mesoporous structures are expected to have properties very different from those of their bulk counterparts. Systematic studies of such phenomena to date are sparse, however, because of a lack of versatile synthetic approaches to such materials. We demonstrate the formation of three-dimensionally continuous gyroidal mesoporous niobium nitride (NbN) superconductors from chiral ABC triblock terpolymer self-assembly–directed sol-gel–derived niobium oxide with subsequent thermal processing in air and ammonia gas. Superconducting materials exhibit a critical temperature (Tc) of about 7 to 8 K, a flux exclusion of about 5% compared to a dense NbN solid, and an estimated critical current density (Jc) of 440 A cm−2 at 100 Oe and 2.5 K. We expect block copolymer self-assembly–directed mesoporous superconductors to provide interesting subjects for mesostructure-superconductivity correlation studies.

SOURCE - Block copolymer self-assembly–directed synthesis of mesoporous gyroidal superconductors, Spencer W. Robbins, Peter A. Beaucage, Hiroaki Sai1, Kwan Wee Tan1, Jörg G. Werner, James P. Sethna, Francis J. DiSalvo, Sol M. Gruner, Robert B. Van Dover and Ulrich Wiesner, Science Advances 29 Jan 2016: Vol. 2, no. 1, e1501119 DOI: 10.1126/sciadv.1501119

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