Facetted growth of Fe₃Si shells around GaAs nanowires on Si(111)

GaAs nanowires and GaAs/Fe₃Si core/shell nanowire structures were grown by molecular-beam epitaxy on oxidized Si(111) substrates and characterized by transmission electron microscopy. The surfaces of the original GaAs NWs are completely covered by magnetic Fe₃Si, exhibiting nanofacets and an enhanced surface roughness compared to the bare GaAs NWs. Shell growth at a substrate temperature of T_S=200 °C leads to regular nanofacetted Fe₃Si shells. These facets, which lead to thickness inhomogeneities in the shells, consist mainly of well-pronounced Fe₃Si(111) planes. The crystallographic orientation of core and shell coincides, i.e. they are pseudomorphic. The nanofacetted Fe₃Si shells found in the present work are probably the result of the Vollmer-Weber island growth mode of Fe₃Si on the {110} side facets of the GaAs NWs.