STM-Induced Void Formation at the Al{sub 2}O{sub 3}/Ni{sub 3}Al(111) Interface [electronic resource].

Published:: Washington, D.C. : United States. Dept. of Energy, 2000.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description:: 18 pages : digital, PDF file
Additional Creators:: Sandia National Laboratories, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

Under UHV conditions at 300 K, the applied electric field and/or resulting current from an STM tip creates nanoscale voids at the interface between an epitaxial, 7.0 Å thick Al₂O₃ film and a Ni₃Al(111) substrate. This phenomenon is independent of tip polarity. Constant current (1 nA) images obtained at +0.1 V bias and +2.0 bias voltage (sample positive) reveal that voids are within the metal at the interface and, when small, are capped by the oxide film. Void size increases with time of exposure. The rate of void growth increases with applied bias/field and tunneling current, and increases significantly for field strengths >5 MV/cm, well below the dielectric breakdown threshold of 12 ± 1 MV/cm. Slower rates of void growth are, however, observed at lower applied field strengths. Continued growth of voids, to ∼30 Å deep and ∼500 Å wide, leads to the eventual failure of the oxide overlayer. Density Functional Theory calculations suggest a reduction-oxidation (REDOX) mechanism: interracial metal atoms are oxidized via transport into the oxide, while oxide surface Al cations are reduced to admetal species which rapidly diffuse away. This is found to be exothermic in model calculations, regardless of the details of the oxide film structure; thus, the barriers to void formation are kinetic rather than thermodynamic. We discuss our results in terms of mechanisms for the localized pitting corrosion of aluminum, as our results suggest nanovoid formation requires just electric field and current, which are ubiquitous in environmental conditions.

Report Numbers:

E 1.99:sand2000-2325j
sand2000-2325j

Subject(s):

Materials Science

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Note:

Published through SciTech Connect.
09/21/2000.
"sand2000-2325j"
Surface Science Letters FT
Jennison, D.R.; Kelber, J.A.; Niu, C.; Magtoto, N.P.; Anzaldura, M.

Funding Information:

AC04-94AL85000

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