  The optical response of metal nanoparticles is governed by plasmonic
resonances, which are dictated by the particle morphology. A thorough
understanding of the link between morphology and optical response requires
quantitatively measuring optical and structural properties of the same
particle. Here we present such a study, correlating electron tomography and
optical micro-spectroscopy. The optical measurements determine the scattering
and absorption cross-section spectra in absolute units, and electron tomography
determines the 3D morphology. Numerical simulations of the spectra for the
individual particle geometry, and the specific optical setup used, allow for a
quantitative comparison including the cross-section magnitude. Silver
nanoparticles produced by photochemically driven colloidal synthesis, including
decahedra, tetrahedra and bi-tetrahedra are investigated. A mismatch of
measured and simulated spectra is found when assuming pure silver particles,
which is resolved by the presence of a few atomic layers of tarnish on the
surface, not evident in electron tomography. The presented method tightens the
link between particle morphology and optical response, supporting the
predictive design of plasmonic nanomaterials.
