UC Berkeley

A novel metal-semiconductor bi-lobed nanoparticle is introduced as a hybrid plasmonic nanostructure. This nanostructure, comprised of a lobe of Ag and a lobe of Ge, forms in a matrix due to phase segregation of the constituents and is thermodynamically stable at room temperature. The interface structure is imaged with high–resolution electron microscopy and found to be an incoherent interface with the {111} planes of the Ag and Ge components parallel to each other explaining the low Ag–Ge interfacial energy. The hemispherical shape of the silver fraction and the shared Ag–Ge interface produce a unique surface plasmon resonance in the visible to near infra–red range. This localized surface plasmon resonance is measured as an ensemble average using optical spectrophotometry and the resonance near 1.5 eV is assigned to the plasmon mode located at the Ag–Ge interface in agreement with numerical simulations. It is proposed that the metal surface plasmon couples to the semiconductor at the shared interface and that the magnitude of this coupling can be probed with a surface–enhanced Raman experiment. Single particle electron energy–loss spectra and energy–filtered transmission electron images elucidate the electronic transitions in the semiconductor and metal as well as localized surface plasmon modes and bulk plasmon modes for both semiconductor and metal. Pulsed laser melting of the bi-lobed structure, followed by quenching to a mixed non–equilibrium Ag–Ge phase, results in significant reduction of the measured localized surface plasmon, which demonstrates the application of an optical switch.