Scientists have developed a thin and flexible light-absorbing material called a near-perfect broadband absorber that absorbs more than 87 percent of near-infrared light with 98 percent absorption at 1,550 nanometers – the wavelength for fiber optic communication – thereby paving way for a number of energy and stealth applications.
Scientists at University of California San Diego have developed this material which they say is capable of absorbing light from every angle and can be customized, at least theoretically, to absorb certain wavelengths of light while letting others pass through. The new material is unlike any other materials that “perfectly” absorb light because the new material isn’t bulky and doesn’t break when bent.
Researchers explain that the new absorber relies on optical phenomena known as surface plasmon resonances, which are collective movements of free electrons that occur on the surface of metal nanoparticles upon interaction with certain wavelengths of light. Metal nanoparticles can carry a lot of free electrons, so they exhibit strong surface plasmon resonance — but mainly in visible light, not in the infrared. UC San Diego engineers reasoned that if they could change the number of free electron carriers, they could tune the material’s surface plasmon resonance to different wavelengths of light.
To leapfrog this hurdle, engineers designed and built an absorber from materials that could be modified, or doped, to carry a different amount of free electrons: semiconductors. Researchers used a semiconductor called zinc oxide, which has a moderate number of free electrons, and combined it with its metallic version, aluminum-doped zinc oxide, which houses a high number of free electrons — not as much as an actual metal, but enough to give it plasmonic properties in the infrared.
The materials were combined and structured in a precise fashion using advanced nanofabrication technologies in the Nano3 cleanroom facility at the Qualcomm Institute at UC San Diego. The materials were deposited one atomic layer at a time on a silicon substrate to create an array of standing nanotubes, each made of alternating concentric rings of zinc oxide and aluminum-doped zinc oxide. The tubes are 1,730 nanometers tall, 650 to 770 nanometers in diameter, and spaced less than a hundred nanometers apart. The nanotube array was then transferred from the silicon substrate to a thin, elastic polymer. The result is a material that is thin, flexible and transparent in the visible.