Number 74 (Story #2), April 2, 1992 by Phillip F. Schewe and Ben Stein PAIRS OF SILICON ATOMS are arranged like teeter-totters on certain silicon surfaces, recent STM measurements indicate. Like diamonds, silicon crystals can be cleaved in many different ways, but these bonded pairs, known as "dimers," are formed on only one type of silicon surface, the so-called Si(100) surface, which is widely used in electronics devices because of its favorable electronic properties. Room-temperature STM images had previously suggested that the dimers lie flat on the Si(100) surface. But low-temperature (120K) STM images taken by Robert Wolkow of AT&T show that the dimers are tilted with respect to the surface, implying that the room-temperature STM images are actually time-averaged views of thermally-excited dimers bobbing up and down between extreme positions. X-ray spectroscopy measurements by Gunther Wertheim and co-workers at AT&T show that the upper atom in the dimer has 0.3 electronic charge units more than its partner. The properties of surface atoms on Si(100) are believed to be important factors in processes which involve surface reactions, such as semiconductor etching, oxide film formation, and chemical vapor deposition. (Chemical & Engineering News, 30 March 1992.)