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 (HeN) and their subsequent surface deposition under soft landing conditions. In vortex charged HeN, 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.