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

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. Keywords: Electron beam evaporation, α-FeSi2, Whisker, Transmission electron microscopy, Atom probe tomography, Physical vapor deposition