| AVS 57th International Symposium & Exhibition | |
| Surface Science | Monday Sessions |
| Session SS2-MoA |
| Session: | Stress and Bonding Energetics in Nucleation and Growth |
| Presenter: | C. Yuen, Iowa State University & Ames Laboratory U.S. D.O.E. |
| Authors: | C. Yuen, Iowa State University & Ames Laboratory U.S. D.O.E. T. Duguet, Iowa State University & Ames Laboratory U.S. D.O.E. Y. Han, Institute of Physical Research and Technology J. Evans, Iowa State University P.A. Thiel, Iowa State University & Ames Laboratory U.S. D.O.E. |
| Correspondent: | Click to Email |
Both Au(110) and Ag(110) have a 0.29x0.41 nm2 rectangular surface unit cell matching almost perfectly that for NiAl(110). This provides the opportunity to grow epitaxial thin films free of lateral mismatch strain. One might expect in both cases layer-by-layer growth of two-dimensional fcc(110) islands given the low surface energy of Au and Ag. However, observed behavior is distinctly different for the two metals. Our STM experiments of Au deposition on NiAl(110) between 200-350 K reveal initial formation of islands with a height of 0.23-0.25 nm. Island densities and size distributions are determined. At 300 K, islands are irregular and regions with 3x1 periodicity are sometimes evident. For the coverage of about 60%, there is significant population by islands of second "layer" or level with heights of ~0.24 nm. Extensive DFT analysis were performed to determine low-energy structures of supported Au films for various coverages. Isolated Au atoms on NiAl(110) prefer sites between two Ni separated by 0.29 nm. However, rather than a simple (110) overlayer with Au at these sites, lower energy structures exist also populating 3-fold sites (e.g., NiAl2) and displaying combinations of square and hexagonal motifs of adatoms. We believe that observed islands have such structures and present a model for their formation. Behavior is contrasted with Ag/NiAl(110) where bilayer Ag(110) islands form due to quantum size effects (QSE) [1]. However, Ag/NiAl(110) is known to exhibit a bilayer-by-bilayer growth mode due to QSE [1], and the bulk Au(110) surface exhibits 2x1 and 3x1 reconstructions.
[1] Y. Han et al. PRL 100, 116105 (2008); PRB 81, 115462 (2010).