Adatom-Driven Oxygen Intermixing during the Deposition of Oxide Thin Films by Molecular Beam Epitaxy

Journal Article · Fri Jun 10 04:00:00 EDT 2022 · Nano Letters

DOI:https://doi.org/10.1021/acs.nanolett.2c01678· OSTI ID:1886258

Kaspar, Tiffany C. ^[1]; Hatton, Peter ^[2]; Yano, Kayla H. ^[1]; Taylor, Sandra D. ^[1]; Spurgeon, Steven R. ^[3]; Uberuaga, Blas P. ^[2]; Schreiber, Daniel K. ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Washington, Seattle, WA (United States)

Thin film deposition from the vapor phase is a complex process involving adatom adsorption, movement, and incorporation into the growing film. While simulations have been able to capture key aspects of these processes to reproduce film morphology, these models typically ignore any subsurface diffusion that occurs. The results of these diffusion and intermixing processes are often observed experimentally, but cannot be explained by invoking bulk lattice diffusion at the deposition temperature. In this work, we present quantitative experimental data that reveals anion and cation intermixing over long length scales during the deposition of epitaxial Fe₂O₃ and Cr₂O₃ films and heterostructures by oxygen-plasma-assisted molecular beam epitaxy. We track this diffusion by incorporating well-defined tracer layers containing ¹⁸O and/or ⁵⁷Fe, and measure their redistribution on the nanometer scale with atom probe tomography. Molecular dynamics simulations suggest potential intermixing events, which are then examined via nudged elastic band calculations. These reveal that adatoms on the film surface act to “pull up” subsurface O and Fe. Subsequent ring-like rotation mechanisms involving both adatom and subsurface anions then facilitate their mixing. A simple model incorporating these events qualitatively agrees with the experimental intermixing results. In addition to film deposition, these intermixing mechanisms may to be operant during other surface-mediated processes such as heterogeneous catalysis and corrosion.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Energy Frontier Research Center (EFRC) (United States). Fundamental Understand of Transport Under Reactor Extremes (FUTURE); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: AC05-76RL01830; 89233218CNA000001
• OSTI ID: 1886258
• Report Number(s): PNNL-SA-172523
• Journal Information: Nano Letters, Journal Name: Nano Letters Journal Issue: 12 Vol. 22; ISSN 1530-6984
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
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diffusion
interface abruptness
molecular beam epitaxy
surface exchange