Imaging ultrathin Al2O3 films with scanning tunneling microscopy

Reproducible scanning tunneling microscopic (STM) images were obtained from ultrathin Al2O3 films epitaxially grown on Re(0 0 0 1). Initially, the oxide films grow two-dimensionally in a layer-by-layer fashion with well-ordered surface morphologies. As the oxide film thickens to ca. 9 monolayer equivalents (MLE), the surface roughens and becomes more disordered yet still exhibits significant long-range, hexagonal periodicity as indicated by low energy electron diffraction (LEED). Because of limited conductivity, films thicker than ca. 9 MLE could not be imaged.