Magazine article Science News

Hydrogen Can Peel Atoms off Layer by Layer

Magazine article Science News

Hydrogen Can Peel Atoms off Layer by Layer

Article excerpt

By harnessing hydrogen's tendency to be selective about the chemical bonds it breaks, chemists can now peer at the underlying structure of semiconductors and control the growth and quality of thin films more precisely.

Recent advances in scanning tunneling microscopy made it possible to resolve atomic details of a material's surface, but little of what lies below. Now, chemist John J. Boland of the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y., has used hydrogen to remove or shove aside atoms on the surface of semiconductors so that he can train his microscope on atoms one or more layers down. By peeling layers away, "we get an in-depth view, almost a cross-section," Boland says.

Other scientists have had to probe underlying structure by trying to look between atoms on the surface, he adds.

Within any material, atoms tend to arrange themselves into a stable, low-energy configuration. Because they lack an upper layer with which to bond, however, those on the surface must arrange themselves differently. The germanium atoms on a semiconductor surface, for example, form three strained bonds with like atoms below, leaving one unlinked "bond" protruding upward.

In Boland's studies, incoming hydrogen atoms first link up with any free bonds sticking out of the semiconductor. Then hydrogen goes after the most strained bonds, which exist between the surface atoms and those directly below. Sometimes four hydrogen atoms surround -- and free -- a germanium atom, releasing it as a volatile compound. In other cases, hydrogen forces the surface atoms to clump, exposing patches of an underlying layer. …

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