Materials structured on the nanometer scale can lead to improved and sometimes surprising properties. This can be found both in Nature and more recently in the laboratory. Natural composite materials, such as shells where organic and inorganic components alternate leading to exceptional mechanical properties, are good examples and sources of inspiration. To achieve similar material organization in a systematic manner in the laboratory is one of the challenges in the decades to come. Structure, and preferably composition, need to be controlled at all scales, playing on different types of interactions. It requires bringing together the knowledge from various fields such as chemistry, biology, physics and material science.
The potential of nanostructured materials will be illustrated in some detail by our own work on the extraordinary optical properties acquired by metal films if they are simply structured with periodic voids (ref. 1-6). Metallic films perforated with sub-wavelength holes (~150 nm) can transmit the light with an efficiency thousand times larger than what theory predicts for single holes. The efficency can even be larger than the fractional area of the holes, which means that even the light falling beside the holes emerges on the other side of the sample. This extraordinary transmission is due to the coupling of the incident light with the surface plasmons of the film. The transmission spectrum contains peaks attributed to surface-plasmon modes that depend on both the symmetry and the 2D lattice parameter of the surface corrugation. We have shown that this phenomenon can also be used to tune and enhance the transmission of single subwavelength apertures. These results have broad fundamental and practical implications and show that, with modern fabrication techniques, surface plasmons can be engineered and controlled to yield unique optical properties.
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