Silicon Nanowire Kinking Superstructures - surface hydrogen and twin boundary propagation

초록

Semiconductor nanowires containing kinking superstructures composed of multiple changes to growth orientation with user-programmability offer various opportunities to fabricate nanoelectronic bioprobes, generate metamaterials with chiroptical responses, reduce thermal conductivity, and explore nanomechanical behaviour. Despite these tantalizing possibilities, it remains difficult to fabricate such structures, particularly those with long-range structural coherence. Here, we combine high-resolution electron microscopy with operando infrared spectroscopy to show why this is the case for Si nanowires and, in doing so, reveal the interplay between defect propagation and surface chemistry during ⟨211⟩ → ⟨111⟩ and ⟨211⟩ → ⟨211⟩ kinking1. Our experiments show that adsorbed hydrogen atoms are responsible for selecting ⟨211⟩-oriented growth and indicate that a twin boundary imparts structural coherence. The twin boundary, only continuous at ⟨211⟩ → ⟨211⟩ kinks, reduces the symmetry of the trijunction and limits the number of degenerate directions available to the nanowire. These findings constitute a general approach for rationally engineering kinking superstructures and also provide important insight into the role of surface chemical bonding during vapor–liquid–solid synthesis.