Bending of GaAs–InP Core–Shell Nanowires by Asymmetric Shell Deposition: Implications for Sensors

Freestanding semiconductor nanowires have opened up possibilities for semiconductor devices, enabling geometries, material combinations, and strain states, which were not previously possible. Along these lines, spontaneous bending in asymmetric core–shell nanowire heterostructures has recently been proposed as a means to realize previously unimagined device geometries, strain-gradient engineering, and bottom-up device fabrication. The synthesis of these nanostructures makes use of the nanowire geometry and the directionality of the shell deposition process. Here, we explore the underlying mechanisms of this bending process by following the evolution of nanowires during asymmetric shell deposition. We show how bending can lead to dramatic local shell thickness, curvature, and strain variations along the length of the nanowire, and we elucidate the dependence of shell growth and bending on parameters such as the core and shell dimensions and materials and angle of incidence of the deposition source. In addition, deposition shadowing by neighboring nanowires is explored and employed to connect nanowire pairs, which could be used to fabricate nanowire sensors. GaAs–InP and GaAs–(Al,In)As core–shell nanowire growth experiments are compared to model results. These findings will guide future experiments and help pave the way to bent nanowire devices.