Surface plasmon resonances in the absorption spectra of nanocrystalline cupric oxide

Optical absorption spectra of nanocrystalline cupric oxide CuO samples, obtained using the converging spherical shock wave procedure, reveal significant spectral weight red-shift as compared with spectra of single crystalline CuO samples. In addition, some of these samples manifest the remarkable temperature-dependent "peak-dip-hump" feature near 1.3-1.6 eV. The minimal model suggested to explain both effects implies the nanoceramic CuO to be a system of two species of identical metallic-like droplets with volume fractions p1 >> p2 and damping parameters gamma1 >> gamma2, respectively, dispersed in an effective insulating matrix. In other words, both effects are assigned to the surface plasmon (Mie) resonances due to a small volume fraction of metallic-like nanoscale droplets with Drude optical response embedded in the bare insulating medium. Simple effective medium theory is shown to provide the reasonable description of the experimental spectra.