Strontium Titanate Capping Layers as Kinetic Regulators of Redox Phase Transitions in Oxide Heterostructures

Abstract

Oxide capping layers are widely used to protect and stabilize thin-film heterostructures, yet their role in governing phase-transition kinetics remains largely unexplored. Here, we uncover the kinetic function of few-nanometer-thick SrTiO${}_3$ (STO) capping layers in controlling oxidation and reduction processes, using real-time in situ optical spectroscopic ellipsometry. We show that oxygen diffusion through the nanoscale capping layer constitutes the rate-limiting step, giving rise to diffusion-controlled phase transitions in the underlying materials. As a result, both capping-layer thickness and oxygen partial pressure provide effective handles to tune phase transition temperatures. Quantitative analysis yields an activation energy of $E_A$ = 0.64 $\pm$0.06 eV for oxygen diffusion through STO, highlighting its suitability for precise control of redox reactions in diverse material systems. These results establish oxide capping layers as active kinetic regulators of redox-driven phase transitions and offer a general framework for engineering redox dynamics in complex oxide heterostructures.

arXiv comment10 pages, 4 figures