(457e) Interplay Between Defect Propagation and Surface Hydrogen in Si Nanowire Kinking Superstructures

Semiconductor nanowires containing kinking superstructures – multiple, user-programmable changes to growth orientation – offer tantalizing opportunities to fabricate nanoelectronic bioprobes, generate metamaterials with chiraloptical response, and manipulate thermal conductivity. However, the synthesis of kinking superstructures with long-range structural coherence remains exceedingly challenging. 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 subtle interplay between defect propagation and surface chemistry during <211> → <111> and <211> → <211> kinking. 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. [Research supported by ORNL's Shared Research Equipment (ShaRE) User Program, which is sponsored by the Office of Basic Energy Sciences, the U.S. Department of Energy.]