Rigourous calculations of the imaging properties of metamaterials consisting of metal-coated semiconductor nanoparticles are presented. In particular, it is shown that under proper choice of geometric and materials parameters, arrays of such particles exhibit negative refractive index within the region of the excitonic resonance of the semiconductor. The occurrence of negative refractive index is predicted by the extended Maxwell-Garnett theory and confirmed by a layer-multiple scattering method for electromagnetic waves. By using the same method it is shown that within the negative refractive-index band, arrays of such nanoparticles amplify the transmitted near-field emitted while simultaneously narrow down its spatial profile leading to subwavelength resolution. The effect of material losses to the imaging properties of the arrays is also addressed.
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