Scientists form-fit diamond-like cloak.

Scientists form-fit diamond-like cloak

In the material world, diamond gleams in its own celebrity. Its combination of optical transparency, superlative hardness, electrical insulating abilities and unmatched talent for conducting heat would make it ideal for, say, making a faster generation of electronic chips that withstand high temperatures or creating coatings that protect the sensitive and fragile infrared detectors common in today's military targeting systems.

Since naturally occurring diamond -- an ultra-regular three-dimensional grid of carbon atoms -- is ill-suited for such uses, scientists have tried for years to devise laboratory methods for building--carbon atom by carbon atom -- diamond and diamond-like films.

At a Materials Research Society meeting in San Diego this week, electrical engineer John A. Woollam reported his group's success in devising a way to coat a variety of optical materials with a thin film of hard, semi-transparent diamond-like carbon that both blocks moisture and reduces reflection of light from the underlying material. The efficiency of solar cells and radiation detectors degrades when portions of incoming light reflect away.

Made from ionized and fragmented methane molecules (each composed of carbon and hydrogen atoms), the resulting hydrogen-containing films resemble diamond but do not form into the regular, crystalline lattice of genuine carbon-only diamond, says Woollam, of the University of Nebraska in Lincoln. He worked with colleagues at the university and at the NASA Lewis Research Center in Cleveland.

Since different materials bend and reflect light to differing degrees, no single anti-reflective diamond-like carbon coat can fit them all. But by controlling such factors as the film thickness and the temperature at which the diamond-like carbon deposits, the researchers can tailor the coat for most cases, Woollam says. The coatings eliminate reflection from semiconductor substrates such as silicon and greatly reduce reflection from other materials such as diamond and specialized glasses containing heavy metals. Diamond-like carbon does a poorer job of preventing reflection from common glasses, Woollam notes.

The researchers also found that diamond-like carbon can serve as a primer coat for the tougher feat of getting a film of genuine diamond to adhere to normally incompatible materials such as metals. The small grains of the resulting diamond films scatter light, so the films cannot serve in optical devices. But Woollam remains optimistic that further work will disarm such problems.