If electronic circuits are ever to get really small, as in nanotechnology small, engineers will need a host of even more miniscule components such as resistors, capacitors, and diodes. Researchers at Lawrence Berkeley National Laboratory in California have taken a step in that direction, developing what could be an on-off switch for nanoelectronics.

The switch uses a gold tip on a scanning tunneling microscope poised just above a gold surface. By repeatedly dipping the tip into the surface, engineers at the lab found a way to insert a molecule between the tip and surface. Using techniques they developed, they could ensure the molecule was bipyridine, a benzenelike ring containing nitrogen.

Tests showed that this junction has two conductive states, which led researchers to correctly theorize that the states correlated to different configurations of the molecule between the tip and surface. When the molecule is vertical, conductance is low, but when the molecule is angled, conductance is higher.

Using STM technology, the team found that mechanically pushing the tip toward the surface makes the molecule consistently become angular or crooked. And pulling the tip away from the surface straightens the molecule. The researchers say this device could serve as a mechanical switch with well-defined on and off states.

They hope to expand their studies to include more complicated molecular junctions useful for organic photovoltaics and converting solar energy to electricity.