Surface plasmon resonances in the absorption spectra of nanocrystalline cupric oxide

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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.