Mysterious Black Silicon Could Have Bright Future in Many Fields
When researchers at Harvard University first looked at the strange silicon chip they had produced in their lab, they couldn't believe their eyes. The chip, which had been bombarded by powerful laser bursts lasting less than a trillionth of a second, had turned as black as tar.
The chip appeared black because it absorbed virtually all the light that fell on its surface; but when the researchers looked at it with an electron microscope, the mystery only deepened.
The researchers thought they might have fried the surface, leaving it covered with soot, but the microscope revealed something quite different.
"We saw these incredible spikes," physics professor Eric Mazur said. Billions of needlelike silicon spikes, about two-thousandths of an inch high with tips one-hundredth the diameter of a human hair, blanketed the surface like a forest of tiny needles.
The researchers had accidentally discovered black silicon, and if it lives up to its promise, it could revolutionize everything from solar cells to optical communications.
Light striking the surface of black silicon bounces back and forth between the spikes, and virtually none of it escapes. That absorbing power makes it an astonishingly effective candidate for a wide range of applications.
The researchers made their discovery more than a year ago, but "we tried to keep it low-key for a while just because we wanted to be 100% sure that this was something truly interesting," Mazur said.
But last March, they presented their findings to a meeting of the American Physical Society in Atlanta.
Since then, Mazur has been bombarded with requests from various industries for samples, including manufacturers of photovoltaic solar cells. The National Aeronautics and Space Administration is also involved because of possible use of the material for ultra-sensitive atmospheric monitoring.
All of the attention is both "thrilling" and "bewildering" to Mazur for two reasons: "There's no question that we can create a material that has absorption characteristics that are unlike anything that has ever been seen before," Mazur said. "But it is totally mystifying and baffling as to why it happens."
In short, there is no explanation for why the laser pulses etched such a dramatic pattern on the surface of the silicon.
Furthermore, researchers will need months of testing in various labs to see if the absorbed light produces enough of an electric current to make it commercially valuable.
