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 ultr ahigh Vacuum (UHV) d.c. magnetron sputter deposition have shown independent ly by in situ low energy electron diffraction (LEED), scanning tunnelling m icroscopy (STM) and time-resolved in situ reflection high-energy electron d iffraction (RHEED) measurements that oxygen is present on the Mo surface du ring 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 oxy gen originates from the MgO substrate. The oxygen is causing the growing fi lm surface to continuously reconstruct with the (root 5 x root 5)R26 degree s 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' reconstr uction and show for the first time STM images of the surface structures whe re 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. T he STM measurements also revealed surfaces randomly interspersed with appar ent 2x2 'holes' not visible by techniques such as LEED due to their non-per iodic nature. (C) 1999 Published by Elsevier Science B.V. All rights reserv ed.