Epitaxial growth of UHV magnetron sputtered Mo thin films on MgO(001) substrates, oxygen segregation and surface reconstructions

Abstract

Studies of epitaxial growth of Mo thin films on MgO(001) substrates by ultrahigh vacuum (UHV) d.c. magnetron sputter deposition have shown independently by in situ low energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and time-resolved in situ reflection high-energy electron diffraction (RHEED) measurements that oxygen is present on the Mo surface during the initial stages of growth. Oxygen induced reconstructions are only found for films thinner than ∼50 nm, and it is shown that the oxygen originates from the MgO substrate. The oxygen is causing the growing film surface to continuously reconstruct with the ( 5 × 5 )R26°33′ , p(2×2) and c(2×2) structures indicating O coverages ranging from ∼0.8–1.0 ML. STM measurements confirm earlier X-ray diffraction (XRD) and STM measurements of the ( 5 × 5 )R26°33′ reconstruction and show for the first time STM images of the surface structures where p(2×2) and c(2×2) reconstructions are present. Based on our STM data we suggest surface models for the p(2×2) and c(2×2) reconstructions. The STM measurements also revealed surfaces randomly interspersed with apparent 2×2 ‘holes’ not visible by techniques such as LEED due to their non-periodic nature.