Fabrication of α-FeSi2 nanowhiskers and nanoblades via electron beam physical vapor deposition

Highlights: • α-FeSi₂ whiskers are grown at 900 °C on TiC/Si(100) by evaporation of Fe. • Whiskers are freestanding and defect-free; surface facets are {100} planes. • Fe adatoms and Si bulk atoms interdiffuse at the interface yielding α-FeSi₂. • Not thermodynamic equilibrium defines the geometrical shape, but kinetic process. -- Abstract: Iron disilicide nanowhiskers and nanoblades are synthesized by depositing Fe onto Si(100) substrates at about 900 °C via electron beam physical vapor deposition. The nanostructures are determined as single crystalline α-FeSi₂ with tetragonal lattice. The nanostructures are stable with prolong exposure under ambient condition, and no transformation towards β-FeSi₂ is detected after 2 h annealing at 500 °C and 800 °C under high vacuum condition (10⁻⁶ mbar). The growth directions of the whiskers are found as either [001] or [100]. However, in the blades we observe grow only in [100] crystallographic direction. Changing cross-sectional shape of the α-FeSi₂ whiskers from octagon at the root to rectangle at the upper part is observed and believed to be a result of the thermodynamic and kinetic anisotropy. SiO₂ layer formed on the surface of the structures because of its lower surface energy compared to all iron oxides. By this a passivation, which prevents further oxidization, of the nanowhiskers is achieved. The α-FeSi₂ whiskers form by root growth.