Crystal structure transfer in core/shell nanowires.

Structure engineering is an emerging tool to control opto-electronic properties of semiconductors. Recently, control of crystal structure and the formation of a twinning superlattice have been shown for III-V nanowires. This level of control has not been obtained for Si nanowires, the most relevant material for the semiconductor industry. Here, we present an approach, in which a designed twinning superlattice with the zinc blende crystal structure or the wurtzite crystal structure is transferred from a gallium phosphide core wire to an epitaxially grown silicon shell. These materials have a difference in lattice constants of only 0.4%, which allows for structure transfer without introducing extra defects. The twinning superlattices, periodicity, and shell thickness can be tuned with great precision. Arrays of free-standing Si nanotubes are obtained by a selective wet-chemical etch of the core wire.