Electron microscopy of GaAs/MnAs core/shell nanowires

GaAs/MnAs core/shell nanowire heterostructures were synthesized by catalyst-free molecular beam epitaxy. Transmission electron microscopy (TEM) reveals that the GaAs core predominantly grows with the zinc-blende crystal structure with a [111] growth direction. In a small population of wires, the crystal structure transitions from zinc blende to wurtzite with a [001] growth direction. Cross-sectional TEM shows that the MnAs grows epitaxially on the GaAs core in the NiAs prototype structure with an epitaxial relation of [20 (2) over bar1] MnAs parallel to[111]GaAs and (01 (1) over bar0) MnAs parallel to GaAs ((1) over bar 10). When the GaAs core is in the wurtzite structure, the epitaxial relation between the GaAs and MnAs changes to [0001] MnAs parallel to[0001]GaAs and ((1) over bar2 (1) over bar0) MnAs parallel to((1) over bar2 (1) over bar0)GaAs. (C) 2010 American Institute of Physics. [doi:10.1063/1.3481066]