Growth of epitaxial FeGe_γ nanocrystals with incommensurate Nowotny chimney-ladder phase on Si substrate

We developed the growth technique of epitaxial nanocrystals of FeGe_γ (γ > 1.52), a recently-found new crystal with incommensurate Nowotny chimney-ladder phase, on Si(001) substrates. This bulk material is promising for thermoelectric application, and now their films and nanostructures are expected to be fabricated. However, it was difficult to grow single phase epitaxial FeGe_γ directly on Si substrates by conventional growth method. On the other hand, we successfully formed almost single phase epitaxial FeGe_γ nanocrystals on Si substrates covered with ultrathin SiO₂ films with nanowindows. Reflection high energy electron diffraction indicated that the nanocrystals had the Nowotny chimney-ladder structure, the lattice constants of which were approximately consistent with those of FeGe_γ bulk. This indicated strain relaxation in nanocrystals due to the hemispherical shape. This will open a road to realize high performance thermoelectric nanomaterials on Si substrates.