Plasmons and inter-band transitions of hexagonal close packed gold nanoparticles

We report on surface plasmons in the visible range in hexagonal close-packed (HCP) gold nanoparticles, synthesized by metastable solidification of Au-Ge eutectic liquid catalyst droplets at the tips of germanium nanowires at the cessation of vapor-liquid-solid nanowire growth. Using 300kV electrons in a transmission electron microscope in scanning transmission mode with deep subnanometer spatial resolution, we characterize plasmons and interband transitions. Compared to conventional face-centered cubic (FCC) gold nanoparticles, plasmons and interband transitions are observed at different energies in HCP gold nanoparticles. We confirm lattice parameters unique to HCP gold by convergent beam electron diffraction and x-ray diffraction. Energy dispersive spectroscopy measured in a scanning transmission electron microscope verifies minimal impurity concentration in the HCP gold nanoparticles. These experimental results confirm that HCP gold is structurally distinct from FCC plasmonic materials, and also exhibits different electronic and optical properties. Published under license by AIP Publishing.