We have performed a series of ab initio calculations to determine the atomic structure, ideal work of adhesion (Wad), and bonding character of the Al(111)/α-A12O3(0001) interface. Six candidate interface geometries were considered, including Al and O terminations of the oxide. Minimization of the Hellman-Feynman forces resulted in substantial changes to the atomic structure of the metal near the interface, wherein some atoms adopted positions consistent with a continuation of the oxide's Al-sublattice crystal structure across the interface. Consequently, the lowest-energy structures (i.e., having the largest Wad) are those that facilitate this "oxide extension" mechanism. By applying several methods of analysis we have thoroughly characterized the electronic structure and have determined that Al-O bonds constitute the primary interfacial bonding interaction. These bonds are very similar to the cation-anion bonds found in the oxide bulk and are mainly ionic, yet maintain a small amount of covalent character. In addition, there is evidence of metal-cation bonding at the optimal Al-terminated interface. Taking into account recent theoretical and experimental evidence suggesting an Al termination of the clean oxide surface, our calculations predict Wad = 1.36 J/m2 [local density approximation (LDA)] and 1.06 J/m2 [generalized gradient approximation (GGA)] for the optimal Al-terminated structure, which are in good agreement with the experimental value of 1.13 J/m2 as scaled to 0 K. These values are approximately an order of magnitude smaller than what is found for the optimal O-terminated interface: 10.70 J/m2 (LDA) and 9.73 J/m2 (GGA). Although cleavage preferentially occurs at the interface for the Al termination, strong bonding at the O-terminated interface favors cleavage within the metal.
|Original language||English (US)|
|Number of pages||7687369|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - Feb 15 2002|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics