Holey Metal Films Go Transparent

Thin metal films dotted with microscopic holes can unexpectedly be made transparent by coating the metal with light-absorbing dye molecules, according to a study (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201006019). This discovery may spawn new research directions in optical materials and photonic devices that are under investigation for energy-conversion applications. James A. Hutchison, Thomas W. Ebbesen, and coworkers at the University of Strasbourg, in France, used an ion-beam method to drill an array of 100-nm-diameter holes in a 200-nm-thick silver film. They measured the film’s optical transmission before and after modifying it with a 30-nm-thick layer of a thiacarbocyanine compound. In the absence of the dye, the main transmission band peaks at 518 nm and almost no light is transmitted at nearby wavelengths. But when the dye is present, the system transmits roughly 700-nm light intensely, the team reports. This phenomenon, which the researchers propose is based on electron waves known as surface plasmons, counterintuitively opens transmission windows at wavelengths at which the molecules absorb strongly—exactly where one would expect to see no transmission.