Functionalizing Silicon

BY DEVELOPING A WAY to apply a common chemical reaction to silicon surfaces, researchers in Delaware have broadened techniques available for modifying semiconductors with organic molecules. The work details a procedure for carrying out surface-dehydrative condensation reactions using standard equipment and mild conditions (J. Am. Chem. Soc., DOI: 10.1021/ja802645t).

An overarching strategy for advancing the emerging field of molecular electronics calls for marrying organic chemistry—a discipline with a huge number of well-studied chemical transformations—with semiconductors, the platform on which microelectronics is built.

Working toward that goal in recent years, scientists have devised surface-chemistry analogs of classic organic processes, including Diels-Alder, Grignard-type, and cycloaddition reactions. The Delaware team has now extended that list.

Timothy R. Leftwich, Mark R. Madachik, and Andrew V. Teplyakov have shown that silicon wafers with hydrogen-terminated surfaces are readily functionalized via dehydrative cyclocondensation reactions.

Demonstrating that process, the group showed that nitrobenzene reacts to form a surface-bound nitrosobenzene adduct. The process combines two surface hydrogens with an oxygen from the nitro group to eliminate a molecule of water. Using surface spectroscopy methods, the team verified that nitrosobenzene is attached to the surface via one O–Si bond and one N–Si bond and that the C–N bond and phenyl ring remain intact.

Teplyakov points out that in contrast to other organic surface reactions, the new process can be carried out with standard laboratory equipment and does not require radical initiators, photochemical steps, or chemical solutions of modifier compounds, which are possible sources of contamination.

"This work describes an interesting and potentially useful addition to the toolbox of reactions for functionalizing silicon surfaces," says Kate Queeney, a surface chemist at Smith College, in Northampton, Mass. Although the reaction has the drawback of forming adducts that adsorb to the surface in more than one way, it provides a way to introduce functional groups that are not cleanly accessible by other routes, she adds.