Microstructure characterization of ion-beam synthesized β-FeSi 2 phase by transmission electron microscopy

Abstract

β-FeSi 2 is a new material showing semiconductor properties, which has been characterized to consist of the abundant and not toxic constituents, iron and silicon. The ion implantation method is one of the most useful techniques to make a good quality β-FeSi 2 phase on a Si wafer, although it is polycrystalline. Using field-emission transmission electron microscopy, the formation process of the β-FeSi 2 particles and layer-grown β-FeSi 2 phase was investigated. With annealing at 800°C after 56Fe + ion implantation at energy of 100 keV, an amorphous-like damaged layer changed to the single phase of β-FeSi 2 and Si single crystal phase. It was characterized that the precipitation always occurred from the Si wafer surface, resulting in the possibility of the formation of a layered β-FeSi 2 structure on the Si wafer. By controlling the Fe concentration at the damaged layer with multiple ion implantation, a layer grown β-FeSi 2 poly-crystals was obtained. The morphology of a grain of the layered poly-crystals is dendrite, of 5–10 μm in diameter. High resolution electron microscope observations further revealed that the each dendrite grain of β-FeSi 2 consists of more fine domains of 50–100 nm in size, resulting in the release of a large lattice misfit strain for the Si single crystal.