Large tuning of the optical properties of nanoscale NdNiO3 via electron doping

TL;DR

This study demonstrates how electron doping via lithium-ion intercalation can significantly alter the optical properties of NdNiO3 films, enabling tunable optical functionalities with potential applications in adaptive optics.

Contribution

It introduces a method to reversibly switch NdNiO3 between metallic and insulating phases with distinct optical properties through electron doping.

Findings

Doped films exhibit a refractive index of ~2 in the insulator phase.

The insulator phase has a band gap of approximately 3-4 eV.

Doping induces a gradient of dopant concentration, creating insulator-metal bilayers.

Abstract

We synthesized crystalline films of neodymium nickel oxide (NdNiO3), a perovskite quantum material, switched the films from a metal phase (intrinsic) into an insulator phase (electron-doped) by field-driven lithium-ion intercalation, and characterized their structural and optical properties. Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) showed that the intercalation process resulted in a gradient of the dopant concentration along the thickness direction of the films, turning the films into insulator-metal bilayers. We used variable-angle spectroscopic ellipsometry to measure the complex refractive indices of the metallic and insulating phases of NdNiO3. The insulator phase has a refractive index of n ~ 2 and low absorption in the visible and near infrared, and analysis of the complex refractive indices indicated that the band gap of the insulating phase is roughly 3-4 eV. Electrical control of the optical band gap, with corresponding large changes to the optical refractive indices, creates new opportunities for tunable optics.