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J. Nanophoton. 5, 052502 (Aug 10, 2011) dx.doi.org/10.1117/1.3609266
Ecole Centrale Marseille, Technopôle de château Gombert, 38 rue Joliot Curie, 13451 Marseille cedex 13, France
Aix-Marseille University, Institut Matériaux Microélectronique Nanosciences de Provence IM2NP CNRS UMR 6242, Campus de Saint-Jérôme, Avenue Escadrille Normandie Niemen Service 231, F-13397 Marseille Cedex 20, France
Thalès Optronique S.A., 2 Avenue Gay-Lussac, 78995 Elancourt Cedex, France
Depending on the size of the smallest feature, the interaction of light with structured materials can be very different. This fundamental problem is treated by different theories. If first order theories are sufficient to describe the scattering from low roughness surfaces, second order or even higher order theories must be used for high roughness surfaces. Random surface structures can then be designed to distribute the light in different propagation directions. For complex structures such as black silicon, which reflects very little light, the theory needs further development. When the material is periodically structured, we speak about photonic crystals or metamaterials. Different theoretical approaches have been developed and experimental techniques are rapidly progressing. However, some work still remains to understand the full potential of this field. When the material is structured in dimension much smaller than the wavelength, the notion of complex refractive index must be revisited. Plasmon resonance can be excited by a progressing wave on metallic nanoparticles inducing a shaping of the absorption band and of the dispersion of the extinction coefficient. This addresses the problem of the permittivity of such metallic nanoparticles. The coupling between several metallic nanoparticles induces a field enhancement in the surrounding media, which can increase phenomena like scattering, absorption, luminescence, or Raman scattering. For semiconductor nanoparticles, electron confinement also induces a modulated absorption spectra. The refractive index is then modified. The bandgap of the material is changed because of the discretization of the electron energy, which can be controlled by the nanometers size particles. Such quantum dots behave like atoms and become luminescent. The lifetime of the electron in the excited states are much larger than in continuous energy bands. Electrons in coupled quantum dots behave as they do in molecules. Many applications should be forthcoming in the near future in this field of research.
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Akhlesh Lakhtakia, Ph.D., D.Sc.
The Charles G. Binder (Endowed) Professor of Engineering Science and Mechanics
Pennsylvania State University, University Park, PA 16802-6812, USA
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