Bimetallic flowers, beads, and buds: synthesis, characterization, and Raman imaging of unique mesostructures.

We demonstrate the creation of a new class of nano/mesostructures, such as Au/Ag flowers, Au/Pt buds, and Au/Pt beads, through the directed overgrowth of Ag or Pt on Au/oligoaniline nanowires (Au/OA NWs). Different stages of the formation of these mesostructures have been studied using various spectroscopic and microscopic techniques. The surface plasmon resonance (SPR) of the Au/OA NWs can be tuned by the incorporation of bimetallicity into the nanowire. Raman based spectral imaging of the bimetallic Au/Ag mesoflower and Au/Pt mesobud revealed the molecular details and the nature of interaction of oligoaniline with the different metal domains. Raman study also suggested a substrate effect due to the different domains of the mesostructures, and spectral images distinguished these two regions. The single particle spectral images suggest that the material is surface-enhanced Raman active.