Molecules positioned on silicon

Researchers from Northwestern University have demonstrated a fabrication process that allows them to pattern molecular structures consisting of more than one type of molecule on silicon surfaces with atomic precision.

The process, dubbed multi-step feedback control lithography, allows for single molecule control in all three spatial directions at room temperature, according to the researchers.

The method could be used to construct prototype molecular electronic devices for future technologies in areas like consumer electronics and biomedical diagnostics.

Scientists have previously demonstrated that coating a silicon surface with a single layer of hydrogen atoms, removing one of the atoms with a scanning tunneling microscope, and exposing the surface to styrene molecules causes one of the molecules to attach at the site of the missing hydrogen atom. When it attaches, the molecule removes an adjacent hydrogen atom, which sparks a chain reaction that yields a single-molecule-wide line of styrene on the silicon.

The Northwestern researchers have found a way to use another molecule to confine the styrene reactions and cause styrene reactions to reverse direction to produce double-wide lines. The technique should be compatible with a wide range organic molecules, according to the researchers.

The researchers are working on ways to speed up the process. The current setup is capable of constructing devices, but is too slow and expensive to be commercially viable. One way to overcome this problem is to use a large array of scanning tunneling microscope tips working in parallel, according to the researchers.

The molecular fabrication process could be used practically in 10 to 20 years, according to the researchers. The work appeared in the September 27, 2004 issue of Applied Physics Letters.