Depth-resolved amorphization and nonuniformity in square-planar nickelate films

Superconducting nickelate films are typically fabricated via post-processing of a parent perovskite or Ruddlesden-Popper film, most commonly a high-temperature anneal in the presence of a strong reducing agent such as CaH2, which removes oxygen from the apical sites and facilitates a topotactic transformation to the superconducting phase. Achieving uniform and highly crystalline reduced films has posed a longstanding fabrication challenge. Using neutron reflectometry and SIMS, the authors reveal the interplay between reduction conditions, vertical uniformity, defect distribution, and amorphization of the film. They find evidence for decreased amorphization near the film/substrate interface and competition between crystal quality and vertical uniformity.