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Semiconductor surfaces provide efficient pathways for injecting native point defects into the underlying bulk. In the case of interstitial atoms in rutile, the TiO 2 (110) surface exemplifies this behavior, although extended defects in the bulk such as platelets and crystallographic shear planes act as net sources or sinks depending upon specific conditions. The present work constructs a quantitative microkinetic model to describe diffusion and based upon isotopic gas–solid exchange experiments. Key activation barriers for are 0.55 eV for surface injection, 0.50 eV for site-to-site hopping diffusion, and 3.3 eV for dissociation of titanium interstitials from extended defects.
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Simulated surface diffusion in nanoporous gold and its dependence on surface curvature
The morphological evolution of nanoporous gold is generally believed to be governed by surface diffusion. This work specifically explores the dependence of mass transport by surface diffusion on the curvature of a gold surface. The surface diffusivity is estimated by molecular dynamics simulations for a variety of surfaces of constant mean curvature, eliminating any chemical potential gradients and allowing the possible dependence of the surface diffusivity on mean curvature to be isolated. The apparent surface diffusivity is found to have an activation energy of ~0.74 eV with a weak dependence on curvature, but is consistent with the values reported in the literature. The apparent concentration of mobile surface atoms is found to be highly variable, having an Arrhenius dependence on temperature with an activation energy that also has a weak curvature dependence. These activation energies depend on curvature in such a way that the rate of mass transport by surface diffusion is nearly independent of curvature, but with a higher activation energy of ~1.01 eV. The curvature dependencies of the apparent surface diffusivity and concentration of mobile surface atoms is believed to be related to the expected lifetime of a mobile surface atom, and has the practical consequence that a simulation study that does not account for this finite lifetime could underestimate the activation energy for mass transport via surface diffusion by ~0.27 eV.
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- Award ID(s):
- 2003849
- PAR ID:
- 10517706
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Computational Materials Science
- Volume:
- 230
- ISSN:
- 0927-0256
- Page Range / eLocation ID:
- 112430
- Subject(s) / Keyword(s):
- nanoporous gold surface diffusion molecular dynamics
- Format(s):
- Medium: X Size: 10MB Other: pdf
- Size(s):
- 10MB
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.commatsci.2023.112430
