Corral Sculpts Surface States

Richard Gaughan

While pursuing an understanding of the factors influencing the photonic local density of states that determines electromagnetic interactions near a surface, a research team has designed a structure that can manipulate these states.

Researchers have determined that, by controlling the placement of nanostructures on a planar surface, they can tailor the photonic local density of states within the corral. The phenomenon is similar to that observed in electron corrals of iron atoms on copper. Courtesy of Centre National de la Recherche Scientifique.

Gérard Colas des Francs and his colleagues at the Centre National de la Recherche Scientifique and the Université de Bourgogne in Dijon have calculated that a ring of dielectric cylinders would create an optical corral similar to those formed by iron atoms on copper that have demonstrated electron confinement. With 100-nm cylinders arranged in a 3.6-µm-diameter circle, the local density of states within the circle would be strongly modulated.

How does this influence the spectral properties of the region? The corral creates resonances at various wavelengths in its area. For example, the corral will be bright for 440 nm and dark for 465 nm.

Colas des Francs believes this is significant because it demonstrates that techniques such as lithography could offer the ability to tailor the photonic local density of states. In work being prepared for publication, researchers at the university have validated the theory by measuring the photonic local density with an adapted scanning near-field optical microscope.

Applications

Besides improving the understanding of surface states, manipulating the local density could enable practical applications, Colas des Francs said. Because fluorescence is dependent on the photonic local density of states at a molecule's position, he explained, controlling these states enables one to control fluorescence, "which has major applications in energy transfer, for example, between molecules adsorbed on a surface."