Structure of ultrathin MgO films on Mo(001)

• Published in: Thin solid films 2003-11, Vol.445 (1), p.90-95
• Main Authors: Gallagher, M.C., Fyfield, M.S., Bumm, L.A., Cowin, J.P., Joyce, S.A.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; CRYSTAL GROWTH; CRYSTAL STRUCTURE; Electron, ion, and scanning probe microscopy; ENVIRONMENTAL MOLECULAR SCIENCES LABORATORY, SCANNING TUNNELING MICROSCOPY; Exact sciences and technology; Interface structure and roughness; MAGNESIUM OXIDES; MATERIALS SCIENCE; Methods of deposition of films and coatings; film growth and epitaxy; MOLYBDENUM; MORPHOLOGY; Physics; ROUGHNESS; Scanning probe microscopy: scanning tunneling, atomic force, scanning optical, magnetic force, etc; Scanning tunneling microscopy; Solid surfaces and solid-solid interfaces; Structure of solids and liquids; crystallography; SUBSTRATES; SURFACE DEFECTS; SURFACE STRUCTURE; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); THIN FILMS; TOPOGRAPHY; Vacuum deposition
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2003.09.016

We have studied the structure of ultrathin MgO films grown on a single crystal Mo(001) surface. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to investigate the effect of substrate temperature and oxygen partial pressure on the growth and morphology of these films. LEED indicates the growth of (100) films with MgO 〈110〉 directions oriented along 〈100〉 directions of the substrate. Despite the insulating nature of bulk MgO, films up to 25-Å thick are sufficiently conducting to perform STM measurements. STM reveals Mg deposition in an oxygen ambient at substrate temperatures from 300 to 900 K produces uniform films. Films as thick as eight atomic layers typically have only three layers exposed. These films consist of small domains between 20 and 60 Å in diameter. The domain shapes are random and the perimeters show no preferred orientation. In contrast, films grown at temperatures in excess of 1000 K exhibit larger three-dimensional MgO islands (Volmer–Weber growth). Steps on these high temperature films orient preferentially along thermodynamically favored MgO 〈100〉 directions. STM images of films deposited at high temperature exhibit a checkerboard pattern. The dimensions and symmetry of this pattern are consistent with the coincidence arising from the mismatch of the MgO(100) and Mo(001) lattice. Annealing room temperature deposited films results in island coalescence and produces uniform films with domains in excess of 100 Å. The perimeters of these domains are oriented along MgO 〈100〉 directions.