Metamaterials Bend Light To New Levels

Two breakthrough developments in the fabrication of metamaterials are reported in a pair of research papers by Xiang Zhang and coworkers at the University of California, Berkeley. Metamaterials are composites designed to have a negative index of refraction, which imparts the extraordinary capability to bend light away from or around an object made from or coated with the material. These composites could lead to lenses that permit optical imaging at the molecular level, nanocircuits for more powerful computers, and, to the thrill of science-fiction lovers, cloaking devices that render objects invisible to the human eye. In one study, Zhang and coworkers alternated thin layers of silver and magnesium fluoride on a substrate, then cut nanoscale “fishnet” patterns into the layers (Nature, DOI: 10.1038/nature07247). The composite, which has a negative refractive index in near-infrared light, is the first three-dimensional metamaterial in the optical region; in the past, metamaterials have been limited to thin layers or longer wavelength microwaves. In a second study, the team built a metamaterial from silver nanowires electrochemically deposited in porous aluminum oxide (Science 2008, 321, 930). This composite exhibits negative refraction down to 660 nm, the first example of a bulk metamaterial in the visible region.