  Precious metal alloys enables new possibilities to tailor materials for
specific optical functions. Here we present a systematic study of the effects
of a nanoscale alloying on the permittivity of Au-Ag-Cu metals at 38 different
atomic mixing ratios. The permittivity was measured and analyzed numerically by
applying the Drude model. X-ray diffraction (XRD) revealed the face centered
cubic lattice of the alloys. Both, optical spectra and XRD results point
towards an equivalent composition-dependent electron scattering behavior.
Correlation between the fundamental structural parameters of alloys and the
resulting optical properties is elucidated. Plasmonic properties of the
Au-Ag-Cu alloy nanoparticles were investigated by numerical simulations.
Guidelines for designing plasmonic response of nano- structures and their
patterns are presented from the material science perspective.
