Optical properties of synthetic-opal films with a copper-filled pore sublattice

The opal-copper composite structures in which the surface of the $a$-SiO$_2$ spheres forming pores of an opal matrix is coated by a copper film have been prepared by the autocatalytic method. The reflection spectra of these structures in the optical and near-IR ranges have been investigated as a function of the pore filling by copper and the angle of light incidence. At low fillings, the spectrum exhibits a Bragg reflection line shifted toward the long-wavelength range with respect to the original opal. At high fillings, the spectrum exhibits several features whose position does not depend on the angle of light incidence. These features have been assigned to excitation of hybridized Mie plasma modes of a periodic ensemble of nanoshells. Calculation of the reflection spectra performed by the finite-difference method in the time domain provides a qualitatively good fit to the spectral features observed at high fillings.