Unusual layer-by-layer growth of epitaxial oxide islands during Cu oxidation

Meng Li,Stephen D House,Judith C Yang,Michael A Gresh-Sill,Wissam A Saidi,Matthew T Curnan

doi:10.1038/s41467-021-23043-w

Abstract

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics. However, current epitaxial oxide growth methods are based on macroscopic empirical knowledge, lacking fundamental guidance at the nanoscale. Using correlated in situ environmental transmission electron microscopy, statistically-validated quantitative analysis, and density functional theory calculations, we show epitaxial Cu2O nano-island growth on Cu is layer-by-layer along Cu2O(110) planes, regardless of substrate orientation, contradicting classical models that predict multi-layer growth parallel to substrate surfaces. Growth kinetics show cubic relationships with time, indicating individual oxide monolayers follow Frank-van der Merwe growth whereas oxide islands follow Stranski-Krastanov growth. Cu sources for island growth transition from step edges to bulk substrates during oxidation, contrasting with classical corrosion theories which assume subsurface sources predominate. Our results resolve alternative epitaxial island growth mechanisms, improving the understanding of oxidation dynamics critical for advanced manufacturing at the nanoscale.

Highlights

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics
Using density functional theory (DFT), we have investigated the energetics of several most probable diffusion paths, and corresponding thermodynamic states, that are proposed to underline studied experimental observations
Comparisons between statistical conclusions and environmental transmission electron microscopy (ETEM) observations made in “Correlating Statistical Results with Experimental Observations” (Supplementary Note 4) demonstrate that limitations in Cu sourced from adjacent island layers contribute to observed island shapes and relative layer growth rates

Summary

Introduction

Elucidating metal oxide growth mechanisms is essential for precisely designing and fabricating nanostructured oxides with broad applications in energy and electronics. One well-accepted kinetic process is the multilayer growth mechanism, which explains the formation of 3D islands as the simultaneous growth of multiple layers stacked parallel to the substrate surface, forming “wedding cake”-shaped islands[19–21]. By correlating the experimental observations and statistical validation of growth kinetics with density functional theory (DFT) modeling, we present an unusual epitaxial layer-by-layer growth mechanism for the oxide island along a preferred surface facet, unforeseen by previous crystal growth theories.

Results

Conclusion