Formation of tetrahedral islands in epitaxial NiO layers deposited on MgO(1 1 1)

We studied NiO layers epitaxially grown on a stabilized MgO(1 1 1) substrate at various temperatures between 700°C and 900°C. The epitaxial growth and surface structures were investigated using reflection high energy electron diffraction, atomic force microscopy, X-ray diffraction and high resolution transmission electron microscopy. The experiments indicate that nickel oxide tetrahedra with {1 0 0} facets have grown on the surface. We present the evolution of the surface morphology as a function of deposition temperature and thickness. The role of the surface energy minimization in the occurrence of tetrahedral islands is demonstrated.