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Register a new userSubwavelength imaging of light by arrays of metal-coated semiconductor nanoparticles: a theoretical study
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Vassilios Yannopapas
Publication date
2008
fields
Physics
and research's language is
English
Authors
Vassilios Yannopapas
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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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It has been demonstrated in previous experimental and computational work that doping CeO2 with transition metals is an effective way of tuning its properties. However, each previous study on CeO2 doping has been limited to a single or a few dopants. In this paper, we systematically study the formation energies, structural stability and electronic properties of CeO2 doped with the entire range of the ten 3d transition metals using density functional theory (DFT) calculations at the hybrid level. The formation energies of oxygen vacancies, and their effects on electronic properties, were also considered. It is found that most of the 3d transition metal dopants can lower the band gap of CeO2, with V and Co doping significantly reducing the band gap to less than 2.0 eV. Furthermore, all of the dopants can lower the formation energy of oxygen vacancies, and those with higher atomic numbers, particularly Cu and Zn, are most effective for this purpose. The electronic structures of doped CeO2 compensated by oxygen vacancies show that the presence of oxygen vacancies can further lower the band gap for most of the dopants, with V-, Cr-, Fe-, Co-, Ni-, and Cu-doped CeO2 all having band gaps of less than 2.0 eV. These results suggest that doping CeO2 with 3d transition metals could enhance the photocatalytic performance under visible light and increase the oxygen vacancy concentration, and they could provide a meaningful guide for the design of CeO2-based materials with improved photocatalytic and catalytic performance as well as enhanced ionic conductivity.
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