Helium nanodroplet assisted synthesis of bimetallic Ag@Au nanoparticles with tunable localized surface plasmon resonance

Abstract: Nanoparticles with tunable localized surface plasmon resonance have been prepared by synthesis in helium nanodroplets. Subsequent surface deposition allows for the formation of substrates which can be employed for surface-enhanced Raman spectroscopy (SERS). The assembly of Ag@Au core@shell clusters of about 5 nm diameter in helium droplets with different Ag:Au ratio allows to tune the surface plasmon resonance between the plain Ag resonance at 447 nm and the Au resonance at 555 nm. For the fabricated substrates only a single plasmon resonance is observed in the UV/vis absorption spectra. The prepared nanostructures have been functionalized with 4-methylbenzenethiol (4-MBT) molecules and SERS spectra have been recorded. The results demonstrate the potential of the helium droplet synthesis approach, opening up a new route to the formation of tailored plasmonic nanoparticles and functional nanostructures. Graphical abstract: [Figure not available: see fulltext.].