Self-assembled growth of faceted epitaxial Fe(110) islands on Mo(110)/Al₂O₃(112¯0)

Self-assembled bcc Fe(110) nanocrystals were grown by pulsed laser deposition on a Mo(110) buffer layer at high temperature. In the growth temperature range of 600–800 K, the resulting epitaxial Fe islands display a well-defined faceted shape elongated parallel to the in-plane Fe [001] lattice direction (‖Mo[001]). The lateral and vertical aspect ratios of the islands equal L/w=1.9 and h/w=0.3, respectively, and remain nearly constant during the growth. The atomically flat facets were characterized by reflection high-energy electron diffraction and atomic force microscopy. They can be indexed as {010} and {110} bcc planes. The energy of an island was computed following the observed facet configuration, using tabulated data for surfaces and an interface energy E_int unknown a priori. The energy minimization calculation shows that the lateral and vertical aspect ratios correspond to the equilibrium shape of the crystal and also yields E_int=0.5±0.2J/m². Decreasing the temperature below 600 K induces important changes in the density and in the shape of the islands. Wire shapes are obtained with islands aligned along the atomic steps of Mo(110), which is ascribed to kinetic limitations in the diffusion processes. Preliminary magnetic measurements show that the mean island shape controls the magnetic anisotropy of the system.