Reproducibility and off-stoichiometry issues in nickelate thin films grown by pulsed laser deposition

TL;DR

This paper investigates the reproducibility issues in growing NdNiO$_3$ thin films via pulsed laser deposition, linking off-stoichiometry to transport property variability and proposing solutions for consistent film quality.

Contribution

It identifies off-stoichiometry as a key factor affecting reproducibility in NdNiO$_3$ thin films and demonstrates that using single-phase targets improves consistency.

Findings

Transport properties vary significantly in nominally identical films.

Off-stoichiometry affects Ni valence and bandwidth.

Single-phase targets improve reproducibility.

Abstract

Rare-earth nickelates are strongly correlated oxides displaying a metal-to-insulator transition at a temperature tunable by the rare-earth ionic radius. In PrNiO$_3$ and NdNiO$_3$, the transition is very sharp and shows an hysteretic behavior akin to a first-order transition. Both the temperature at which the transition occurs and the associated resistivity change are extremely sensitive to doping and therefore to off-stoichiometry issues that may arise during thin film growth. Here we report that strong deviations in the transport properties of NdNiO$_3$ films can arise in films grown consecutively under nominally identical conditions by pulsed laser deposition; some samples show a well-developed transition with a resistivity change of up to five orders of magnitude while others are metallic down to low temperatures. Through a detailed analysis of \textit{in-situ} X-ray photoelectron spectroscopy data, we relate this behavior to large levels of cationic off-stoichoimetry that also translate in changes in the Ni valence and bandwidth. Finally, we demonstrate that this lack of reproducibility can be remarkably alleviated by using single-phase NdNiO$_3$ targets.