From the Very First Stages of Mn Deposition on Ge(001) to Phase Segregation

Abstract

In this work, we have combined scanning tunneling microscopy with high-resolution transmission electron microscopy (HR-TEM) to investigate the initial stages of Mn deposition on Ge(001) surfaces. The growth temperature was chosen to be (353 ± 5) K, which is typical for the synthesis of Ge1–xMnx thin films. At the early stage of the Mn deposition, two distinct kinds of islands are observed even for Mn coverage much smaller than a monolayer with an average size of 1–2 nm and 4–5 nm, respectively. Small islands were found to nucleate in the hollow between the Ge dimer rows, and they were formed by consuming Ge from two adjacent rows. This indicates that Mn–Ge alloying has been taken place even at the early stage of the Mn deposition. When the Mn coverage increases, coarsening between small islands with newly deposited ad-atoms occurs, giving rise to the formation of monosized islands. Interestingly, these nanostructures have an average size of 4–5 nm and separated by a spacing of 7–8 nm that are similar to the spatial ordering of nanocolumns resulting from spinodal decomposition in (Ge,Mn) thin films. HR-TEM analyses indicate that those nanoislands are epitaxial, defect-free, and perfectly coherent with the Ge substrate. A subsequent anneal will result in the formation of Mn5Ge3 islands.