Friday, March 23, 2007

Superlenses and Smaller Computer Chips

Researchers report using metamaterials to make devices that could transform computing, data storage, and optical microscopy.

By Kevin Bullis

Hyperlens: A new lens overcomes the limits of optical microscopes that make it impossible to see the real-time movement of viruses. Light (orange arrows) passes through designs with nanoscale features etched into a sheet of chromium (light blue). It then encounters a series of alternating silver and aluminum-oxide layers. These layers magnify the image carried by light waves until it is big enough to be observed with a conventional optical microscope. Credit: Xiang Zhang, University of California at Berkeley

How small one can fabricate transistors, the detail that can be seen in an optical microscope, and the amount of data that can be squeezed onto a DVD--all these things are limited by the way light moves through materials. But several separate advances reported this week in Science describe new materials for manipulating light in exotic ways, potentially leading to vastly improved electronic circuitry, microscopy, and data storage.

The three Science papers are part of a fledging field of research called metamaterials, in which novel optical properties are introduced by combining multiple materials in structures smaller than certain types of electromagnetic waves, whether these be microwaves or waves of visible light. The researchers were able to manipulate visible wavelengths by assembling metals (such as gold or silver) with other materials in precise nanoscale layers.

Last year researchers reported metamaterials that could make an object invisible to microwaves by smoothly routing the waves around the object. (See "Cloaking Breakthrough.") The new devices reported this week manipulate visible light in the green to ultraviolet range. While the devices only work to cloak very small, probably microscopic objects, manipulating visible light could be useful in optical microscopes, photolithography, and optical storage such as DVDs.

In one study, researchers at the University of California, Berkeley, used a metamaterials-based lens paired with a conventional optical lens to reveal patterns too small to be discerned with an ordinary optical microscope. In one experiment, the lens was able to distinguish two 35-nanometer lines etched 150 nanometers apart. Without the metamaterials, the microscope showed only one thick line.

Such a lens could be used to watch cellular processes that have been impossible to see. Conversely, it could be used to project an image with extremely fine features onto a photoresist as a first step in photolithography, a process used to make computer chips. Such detailed resolution would also make it possible to represent more data on the surface of a DVD.

The other two papers describe related advances. Caltech researchers built a microscopic prism using metamaterials that bends green light the opposite way it would bend with an ordinary prism. This could make it possible to create lenses in shapes not possible now, such as space-saving flat lenses.

In the third paper, researchers from the University of Maryland built a lens that can magnify rays of blue-green light emanating from dots just 70 nanometers across. The rays become big enough to be seen by an ordinary optical microscope, giving the device an effective resolution of 70 nanometers. Even better resolution might be observed if smaller dots were used, says Igor Smolyaninov, a Maryland research scientist and author of the paper. He estimates that the method could resolve features as small as 10 nanometers.