In Situ Transmission Electron Microscopy of Disorder-Order Transition in Epitaxially Stabilized FeGe2

Isothermal crystallization of amorphous Ge deposited on a cubic Fe3Si/GaAs(001) substrate is performed by in situ annealing within a transmission electron microscope. It was found that the formation of epitaxially aligned tetragonal FeGe2 is associated with a disorder-order phase transition mainly consisting of a rearrangement of the Fe/vacancy sublattice from a random distribution to alternating filled and empty layers. Additionally, atomically resolved high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that the vertical lattice spacing of the Ge sublattice reduces across vacancy layers, indicating that strain minimization plays a role in the phase transition process. Crystallization and ordering are both found to proceed layer-by-layer and with square-root-shaped kinetics with a smaller transition rate for the latter.

Automated summary

Isothermal crystallization of amorphous Ge on a cubic Fe3Si/GaAs(001) substrate results in the formation of epitaxially aligned tetragonal FeGe2 through a disorder-order phase transition involving rearrangement of the Fe/vacancy sublattice and reduction of the vertical lattice spacing across vacancy layers in the Ge sublattice for strain minimization. Crystallization and ordering proceed layer-by-layer with square-root-shaped kinetics, with a slower transition rate for ordering.