Infrared Nanoimaging of Hydrogenated Perovskite Nickelate Synaptic Devices

TL;DR

This study uses operando infrared nanoimaging to visualize how hydrogen dopants distribute and influence conductivity in perovskite nickelate devices, revealing nanoscale mechanisms crucial for neuromorphic computing.

Contribution

It introduces a novel nanoscale imaging approach to understand dopant behavior and its impact on device properties in correlated oxides.

Findings

Dopant distribution forms stripe phases affecting macroscale conductivity.

Multiple vibrational states of hydrogen are mapped and linked to dopant concentration.

Lattice expansion acts as a barrier to further dopant diffusion.

Abstract

Solid-state devices made from correlated oxides such as perovskite nickelates are promising for neuromorphic computing by mimicking biological synaptic function. However, comprehending dopant action at the nanoscale poses a formidable challenge to understanding the elementary mechanisms involved. Here, we perform operando infrared nanoimaging of hydrogen-doped correlated perovskite, neodymium nickel oxide (H-NdNiO3) devices and reveal how an applied field perturbs dopant distribution at the nanoscale. This perturbation leads to stripe phases of varying conductivity perpendicular to the applied field, which define the macroscale electrical characteristics of the devices. Hyperspectral nano-FTIR imaging in conjunction with density functional theory calculations unveil a real-space map of multiple vibrational states of H-NNO associated with OH stretching modes and their dependence on the dopant concentration. Moreover, the localization of excess charges induces an out-of-plane lattice expansion in NNO which was confirmed by in-situ - x-ray diffraction and creates a strain that acts as a barrier against further diffusion. Our results and the techniques presented here hold great potential to the rapidly growing field of memristors and neuromorphic devices wherein nanoscale ion motion is fundamentally responsible for function.