Synthetic Pathways to Mesostructured Superconductors: Quantum Materials from Block Copolymer Self-Assembly
The ability to precisely control the properties of materials using atomic structure developed over the last 50 years directly led to the high-performance semiconductor based devices that have revolutionized modern life. Complex ordered mesoscale structures such as those prepared by block copolymer self-assembly may prove to be a powerful tool for tuning the electronic properties of materials, but few have explored this area, largely due to a lack of connections between the disparate fields of atomic quantum materials and soft matter self-assembly. In particular, the impact of three- dimensional mesoscale order on superconductors has not been explored at all, despite the possibility for emergent properties including increased critical fields, angle- dependent magnetic behavior, and symmetry-forbidden nonlinear magnetic and electronic properties. In this thesis, three routes to mesostructured superconductors using block copolymer self-assembly are developed to bridge this gap and form a stable platform for future mesostructure-superconductivity correlation studies. In the first route, poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock terpolymers are used to structure-direct niobium (V) oxides, which are subsequently converted to niobium nitrides via an optimized annealing procedure in ammonia gas. The resulting materials are superconductors with Tc of 7.8K. We demonstrate that the length scale and morphology of these materials can be tuned by varying the block copolymer dimensions and show first evidence of magnetic flux pinning on the mesoscale pores of the material. In the second route, intermediate oxynitrides are converted into carbonitrides, using a variety of times, temperatures, and gas compositions to more fully explore the compositional flexibility of the niobium-(oxygen)-nitrogen-carbon pseudo-ternary system. The best resulting carbonitrides have increased Tc of up to 16.0 K, nearing values expected for the bulk material, as well as improved mesostructure retention despite treatment at temperatures of up to 1000 ̊C. To demonstrate the versatility of this approach, materials with four distinct morphologies (alternating gyroid network, perforated lamellae, double gyroid matrix, and inverse hexagonal cylinders) are prepared using a single parent ISO terpolymer. In the final route, mesoporous Si(ON) ceramic single mesocrystals are infiltrated with molten indium at pressures up to 40,000 psi. The resulting materials exhibit an inversion of the magnetic response from a type-I behavior characteristic of bulk In to a type-II behavior, coupled with an order-of-magnitude increase in the upper critical field. These results serve as a first demonstration of the plethora of fascinating emergent properties expected for superconducting mesostructures, and provide a robust, versatile, stable foundation for extensive mesostructure-superconductivity correlation studies.
in situ x-ray; mesostructure; superconductor; Physics; Materials Science; block copolymer; Chemistry
Wiesner, Ulrich B.
Gruner, Sol Michael; Disalvo, Francis J.
Materials Science and Engineering
Ph. D., Materials Science and Engineering
Doctor of Philosophy
dissertation or thesis