Metamaterials Made by Etching Process Could Create Unique Lenses

DNA, viruses, proteins, and other objects smaller than the wavelength of visible light could soon be viewed with a special lens created from metal gyroid metamaterials. Researchers from Cornell University (Ithaca, NY) have found a way to use self-assembling block copolymers to make 3D structures with special light bending capabilities.

Previously, metamaterials have only been created in single layers using atomic sputtering or electron-beam lithography methods, but by using an etching process with block copolymers, part of the structure can be chemically removed, leaving a complex shape with nanometer-sized features. In the Cornell team's concept, two polymer molecules are joined at the ends, creating a twisty shape with a repeating pattern called a gyroid. One of the polymers is chemically etched away, leaving behind a mold that is filled with silver or gold metal. The second polymer is then burned away, resulting in a porous metal structure that could bend light in unique ways. Metal gyroids allow light to pass through with a negative index of refraction, so the materials bend light in the opposite way of a typical transparent material like glass or plastic.

The Cornell team took several different metal gyroids that could be created with this process, and made computer simulations of how light would pass through them. The amount of refraction could be adjusted by changing the size of the features that repeat in the metamaterial. In theory, a small object could even be made invisible by configuring the negative refraction materials to bend light around the object.

Though all the materials that are tested with the simulation haven't been actually made yet, the researchers are working on creating them. So far, only silver structures have achieved good results, though the calculations made assumptions that the gyroids would be made from other metals including gold and aluminum. The Cornell team's idea was presented in the journal Angewandte Chemie's online edition.