PNNL

Abstract

Self-diffusion is a fundamental physical process that, in solid materials, is intimately correlated with both microstructure and functional properties. Here, a universal approach is presented to precisely characterize self-diffusion in ionic solids by isotopically enriching anions and/or cations at specific locations within an epitaxial film stack, and characterize their redistribution at high spatial resolution with atom probe tomography. Nanoscale anion diffusivity is quantified in epitaxial ?-Fe2O3 thin films deposited by molecular beam epitaxy with a thin (10 nm) buried layer highly enriched in 18O. The isotopic sensitivity of the atom probe allows precise measurement of 18O distribution across the sharp interfaces between this layer and the surrounding Fe2O3 after annealing. Short-circuit anion diffusion through 1D and 2D structural defects in Fe2O3 are also directly visualized in 3D. This versatile approach to study precisely tailored thin film samples at high spatial and mass fidelity will facilitate a deeper understanding of atomic-scale diffusion phenomena.