Quantifying Oxygen Diffusion Rates at The Nanoscale in Epitaxial SrTiO₃ Films

Oxygen ion migration is an increasingly viable route to control electronic and magnetic phase transitions in nanoscale oxide thin films and harness those phase transitions for next-generation, energy-efficient electronics [1]. Nanoscale oxygen migration is central to the operation of promising emerging information technologies like resistive random-access memory and magnetoionic memory [2,3]. Heterostructure design elements like strain, interface symmetry, and layer stacking can all control the ion diffusion rates and energy barriers that underpin the operation of these devices. However, due to the difficulty of measuring small concentrations of oxygen ions (~1 at%) moving nanoscale distances, we do not have a framework for how these heterostructure design elements can be tuned to improve and optimize device functionality. This project aims to address this by developing a methodology to quantitatively determine oxygen diffusion rates and migration energy barriers in nanoscale thin films using reflectometry techniques.<br/><br/>Nanoscale “oxide diffusion couples” are fabricated from epitaxially grown SrTiO₃ (STO) and a sputtered metal cap, then annealed in vacuum to drive oxygen from the epitaxial oxide layer into the metal. X-ray reflectometry (XRR) scans are taken before and after vacuum annealing and used to establish an oxygen concentration depth profile from changes to the interface roughness between the STO and metal layers. These concentration profiles are then fit to known diffusion couple solutions to Fick’s Second Law and used to calculate an oxygen diffusion coefficient for each annealing study [4]. This poster will further explain our proposed methodology and preliminary results.<br/><br/><b>References</b><br/>[1] F. Gunkel, et al., <i>Appl. Phys. Lett.</i> 116 (2020) 120505<br/>[2] F. Zahoor, et al., <i>Nanoscale Res. Lett.</i> 15 (2020) 90<br/>[3] M. Nichterwitz, et al.,<i> APL Mater.</i> 9 (2021) 030903<br/>[4] S. Brennan, et al. <i>Metall. Mater. Trans. A</i>, 43 (2012) 4043