Spin-coated mesoporous thin-film quantum materials from block copolymer self-assembly*

Superconducting niobium carbonitride thin films are prepared from the self-assembly of block copolymers (BCPs) and niobia sol nanoparticles. The fabrication pathway starts with spin-coating the hybrid solution of an amphiphilic triblock terpolymer poly(isoprene-b-styrene-b-ethylene oxide) (ISO) with its hydrophilic PEO block swollen by the niobia sol. The mesostructured hybrid film undergoes heat treatment in air to become a mesoporous niobium oxide. Following treat treatments in ammonia and carburizing gas (mixture of methane, hydrogen, and nitrogen) at up to 1000 °C, superconducting niobium carbonitride thin films are obtained, showing a superconducting transition temperature (T_c) at 13 K. Grazing-incidence X-ray scattering at both small and wide angles confirms controllable mesoporosity, nanocrystallinity of the superconducting film. The granular nature of the materials results in a sharp rise in resistivity before superconducting transition, which is associated with a thermally activated conduction mechanism. The upper critical field performance of such BCP-templated mesoporous superconductors exceeds that of bulk materials. For nanofabrication of microelectronic devices, this solution-processable materials system is amenable to patterning through common photolithographic technique. Patterned thin strips are also superconducting, albeit with a lower T_c. The network mesostructure from BCP self-assembly together with patternable dimensions through lithography may lead to discovery of new physics emergent form structural topology, while the large surface area could enjoy potential use in sensing and detection applications. This unique pathway from BCP self-assembly to mesostructured superconductors serves as an emergent technology for novel quantum materials fabrication.