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

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 similar to 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 (root 5 x root 5)R26 degrees 33', p(2 x 2) and c(2 x 2) structures indicating O coverages ranging from similar to 0.8-1.0 ML. STM measurements confirm earlier X-ray diffraction (XRD) and STM measurements of the (root 5 x root 5)R26 degrees 33' reconstruction and show for the first time STM images of the surface structures where p(2 x 2) and c(2 x 2) reconstructions are present. Based on our STM data we suggest surface models for the p(2 x 2) and c(2 x 2) reconstructions. The STM measurements also revealed surfaces randomly interspersed with apparent 2x2 'holes' not visible by techniques such as LEED due to their non-periodic nature. (C) 1999 Published by Elsevier Science B.V. All rights reserved