Epitaxial stabilization and oxygen vacancy control of EuNiO3 thin films

Abstract

Rare-earth nickelates exhibit valuable behavior for neuromorphic computing at low temperature: Building blocks for biologically inspired microelectronic neurons like electrically driven insulator–metal transitions (IMTs), negative differential resistance, and self-oscillations have been shown up to 230 K for SmNiO3 and NdNiO3. EuNiO3 raises the IMT far above room temperature (460 K) but high-quality thin films are challenging to synthesize. Here, we explore the epitaxial stabilization of EuNiO3 using pulsed laser deposition. X-ray diffraction reciprocal space maps, x-ray absorption spectroscopy, and transmission electron microscopy show that higher growth temperature (800 °C) reduces oxygen vacancy concentrations in EuNiO3. Pseudomorphic EuNiO3 is demonstrated on both SrLaAlO4 and NdGaO3 substrates, and LaNiO3 buffer layers are incorporated to facilitate future vertical device fabrication. In contrast to bulk thermodynamic predictions, the greater oxidation and crystallinity at higher temperature we observe indicates that epitaxial substrates can stabilize EuNiO3 at O2 pressures less than 1 atm.