The semiconductors that constitute
the Princeton invention are grown
from crystals © Keith Drake
The new substance from the stuff of computer chips is in a relatively new class of materials called "metamaterials," which are made out of traditional substances, such as metals or semiconductors, arranged in very small alternating patterns that modify their collective properties. This approach enables metamaterials to manipulate light in ways that cannot be accomplished by normal materials.
Previous metamaterials were two-dimensional arrangements of metals, which limited their usefulness. The Princeton invention is the first three-dimensional metamaterial constructed entirely from semiconductors, the principal ingredient of microchips and optoelectronics.
Light waves and other forms of electromagnetic radiation bend whenever they pass from one medium to another. This phenomenon, called refraction, is readily observable when a straw placed into a glass of water appears to be bent or broken. Lenses in reading glasses or a camera work because of refraction.
All materials have an index of refraction, which measures the degree and direction that light is bent as it passes through them. While materials found in nature have positive refractive indices, the material recently invented by Princeton researchers has a negative index of refraction.
In the case of the straw in a glass, normal water would make the underwater portion of the straw appear to bend toward the surface. If water were able to refract light negatively, as the newly invented semiconductor does, the segment of straw under the water would appear as if it were bending away from the surface.
Far more than a neat optical illusion, negative refraction holds promise for the development of superior lenses.
The positive refractive indices of normal materials necessitate the use of curved lenses, which inherently distort some of the light that passes through them, in telescopes and microscopes. Flat lenses made from materials that exhibit negative refraction could compensate for this aberration and enable far more powerful microscopes that can "see" things as small as molecules of DNA.
COMPAMED.de; Quelle: Princeton University, Engineering School