Tilting catalyst-free InAs nanowires by 3D-twinning and unusual growth directions

Controlling the growth direction of nanowires is of strategic importance both for applications where nanowire arrays are contacted in parallel and for the formation of more complex nanowire networks. We report on the existence of tilted InAs nanowires on (111)B GaAs. The tilted direction is predominantly the result of a three-dimensional twinning phenomenon at the initial stages of growth, so far only observed in VLS growth. We also find some nanowires growing in '112' and other directions. We further demonstrate how the tilting of nanowires can be engineered by modifying the growth conditions, and outline the procedures to achieve fully vertical or tilted nanowire ensembles. Conditions leading to a high density of tilted nanowires also provide a way to grow nanoscale crosses. This work opens the path toward achieving control over nanowire structures and related hierarchical structures.