Epitaxial growth of Al9Ir2 intermetallic compound on Al(100): Mechanism and interface structure

The adsorption of Ir adatoms on Al(100) has been investigated under various exposures and temperature conditions. The experimental and theoretical results reveal a diffusion of Ir adatoms within the Al(100) surface selvedge already at 300 K. Above 593 K, two domains of a (√ 5× √ 5)R26.6 • phase are identified by low energy electron diffraction (LEED) and scanning tunneling microscopy measurements. This phase corresponds to the initial growth of an Al 9 Ir 2 compound at the Al(100) surface. The Al 9 Ir 2 intermetallic domains are terminated by bulklike pure Al layers. The structural stability of Al 9 Ir 2 (001) grown on Al(100) has been analyzed by density functional theory based calculations. Dynamical LEED analysis is consistent with an Ir adsorption leading to the growth of an Al 9 Ir 2 intermetallic compound. We propose that the epitaxial relationship Al 9 Ir 2 (001)Al(100) and Al 9 Ir 2 [100]Al[031]/[013] originates from a matching of Al atomic arrangements present both on Al(100) and on pure Al(001) layers present in the Al 9 Ir 2 compound. Finally, the interface between Al 9 Ir 2 precipitates and the Al matrix has been characterized by transmission electron microscopy measurements. The cross-sectional observations are consistent with the formation of Al 9 Ir 2 (001) compounds. These measurements indicate an important Ir diffusion within Al(100) near the surface region. The coherent interface between Al 9 Ir 2 and the Al matrix is sharp.