RHEED study of the growth of Pd-Al/MgO bimetallic system

A Pd-Al bimetallic system was prepared on a MgO (0 0 1) single-crystalline substrate surface by vacuum deposition. The early stages of the growth in dependence of Pd and/or Al deposition sequence were studied. The reflection high-energy electron diffraction method was used for structural investigation during the deposition. The results can be interpreted in terms of formation of stable Pd-Al alloy covered by an aluminum overlayer. Under all deposition conditions the diffraction patterns indicated that the Pd-Al system is composed of three-dimensional epitaxial particles having the following orientation relationship with respect to the substrate surface: Pd-Al (0 0 1) || MgO (0 0 1), Pd-Al [1 1 0] || MgO [1 1 0]. When Pd was deposited at first the evolution of lattice parameter and diffraction spot intesity during the growth showed the formation of a Pd pseudomorphic layer which was spread by a strong Pd-Al bimetallic interaction during subsequent Al deposition. Applying the opposite sequence of deposited materials or simultaneous deposition of both metals three-dimensional growth of clusters was observed from the beginning of the deposition process.