Solid-State Amorphization in Al/Pd Multilayer during Near-Room-Temperature Molecular-Beam Deposition

We studied the growth behavior and structures of two [Al (t nm)/Pd (0.6 nm)] multilayers (t = 0.4, 0.8) and a single-layered Al film, which were grown on 50-nm-thick (100) Pd buffer layers using molecular-beam deposition. In situ reflection high-energy electron diffraction and ex situ X-ray diffraction analyses revealed the following features. The multilayer of t = 0.4 starting from an Al layer grew epitaxially for the first Al/Pd bilayer but showed an amorphous-like surface structure during growth of the second to fiftieth bilayers. The multilayer had an amorphous structure without compositional modulation despite the growth near room temperature. The multilayer of t = 0.8 showed an amorphous-like surface structure from the first Al layer to about the fiftieth bilayer. This multilayer having 100 bilayers finally consisted of an amorphous matrix with compositional modulation and fine crystallites of B2-type AlPd compound. The Al film changed its surface structure depending on its thickness t: (100) epitaxy for t ≤0.5, nearly amorphous for 0.5 < t < 2.5, and a <111>-oriented fibrous structure for t ≥2.5. The relationships between interdiffusion and solid-state amorphization are discussed.