Growth and morphology of thin epitaxial Pd films on Au(001) film grown on Fe-buffered MgO(001) substrate

Abstract

We have investigated the growth of thin Pd films on a Au(001) surface, which was a Au(001) film grown on a Fe-buffered MgO(001) substrate, at 290 K up to 4 monolayer (ML) thickness and the effect of post-annealing (PA) at 470 K. The surface morphology and structure are determined using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). The LEED patterns of the as-grown and PA films indicate that the Pd(001) films grow epitaxially on the Au(001) surface with noticeable in-pain lattice expansion of 4.5% relative to the bulk Pd, indicating a tensely strained tetragonal deformation. The Pd film does not grow in the layer-by-layer growth mode at 290 K. Instead, numerous Pd islands grow anisotropically along the 〈110〉 direction. The surface morphology of the films improves significantly after the PA at 470 K due to the coalescence of the elongated Pd islands. Consequently, the room temperature growth of the Pd layers followed by PA at 470 K enables us to fabricate the high-quality epitaxial Pd(001) film, which has large and atomically flat terraces without Au segregation. Additional Pd growth up to 8 ML thickness onto such 4 ML PA films kept at 470 K is also studied by STM. This specific three-step method facilitates the quasi-layer-by-layer growth and opens a chance for practical use in the future.