Formation of bimetallic core-shell nanowires along vortices in superfluid He nanodroplets

We report on the formation of one-dimensional Au/Ag core-shell nanostructures in superfluid helium nanodroplets (He-N) and their subsequent surface deposition under soft landing conditions. In vortex charged He-N, dopant atoms and clusters prefer to agglomerate along vortex cores, which serve as personal cryo-templates for each nanowire. A sequential pickup scheme enables the fabrication of Au/Ag structures with either Au as core and Ag as shell or vice versa. The core-shell structure is in both cases shown by energy-dispersive x-ray spectroscopy (EDX) in a scanning transmission electron microscope (STEM). The inherent spatial resolution and element sensitivity of this method allows a direct observation of the two different phases. High resolution STEM studies elucidate morphological details of the Au/Ag nanostructures and, together with the EDX analysis, indicate that the nanowires are formed in a multicenter aggregation process.