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

Abstract

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 SiO 2 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.

Nowotny Chimney Ladder Phases with Group 5 Metals: Crystal and Electronic Structure and Relations to the CrSi2 Structure Type

“…NCL phases are widely known and crystallize in more than 10 structure types [9][10][11][12][13][14][15][16]. Despite the variety of the crystal structures, they all have common dominant features.…”

“…For many such compounds, the corresponding approximant structures have been proposed. Thus, single crystals of Fe 2 Ge 3 possess a precise composition and commensurate structure, while a polycrystalline sample is characterized by a complex incommensurate crystal structure [10][11][12]. In addition, helices can be formed by more than one element.…”