Self-directed growth of molecular nanostructures on silicon

Advances in techniques for the nanoscale manipulation of matter are importa nt for the realization of molecule-based miniature devices(1-8) with new or advanced functions. A particularly promising approach involves the constru ction of hybrid organic-molecule/silicon devices(9-14). But challenges rema in-both in the formation of nanostructures that will constitute the active parts of future devices, and in the construction of commensurately small co nnecting wires. Atom-by-atom crafting of structures with scanning tunnellin g microscopes(15-17), although essential to fundamental advances, is too sl ow for any practical fabrication process; self-assembly approaches may perm it rapid fabrication(18), but lack the ability to control growth location a nd shape. Furthermore, molecular diffusion on silicon is greatly inhibited( 19), thereby presenting a problem for self-assembly techniques. Here we rep ort an approach for fabricating nanoscale organic structures on silicon sur faces, employing minimal intervention by the tip of a scanning tunnelling m icroscope and a spontaneous self-directed chemical growth process. We demon strate growth of straight molecular styrene lines-each composed of many org anic molecules-and the crystalline silicon substrate determines both the or ientation of the lines and the molecular spacing within these lines. This p rocess should, in principle, allow parallel fabrication of identical comple x functional structures.