"We desperately need to find a practical way to make a 1-3 nm nanogap between not two, but three or four, electrodes," said Robert Metzger of the University of Alabama, "so that we can put a single potential transistor molecule [with three terminations] within that gap, covalently attached to these three or four electrodes, and measure its electrical characteristics."

To form the ditches, Metzger and his student Tao Xu, who invented the technique, used single- and multiwalled carbon nanotubes as a contact mask. First they deposited carbon nanotubes onto silicon wafers covered with SiO2. Then they evaporated a layer of titanium 5-30 nm thick onto the sample so that it barely buried the nanotubes. Finally, ultrasound treatment removed the nanotubes, to create nanoditches as narrow as 10 nm and up to a few microns long.

"We can control the width of the gap by the width of the sonicated nanotube, and at least put many two-termination molecules, such as bithiols, all in parallel in the gap," said Metzger.

What's more, removing T-shaped nanotubes or two nanotubes that crossed resulted in pseudo-three-terminal or four-terminal electrodes in the titanium film.

And the future? "We can hope to synthesize candidate transistor molecules - the molecular equivalent of n-p-n junction transistors - and test whether power gain can be derived from that," said Metzger. "Our approach is not an FET [field-effect transistor] structure but a single-molecule device, which by its intrinsic properties should exhibit power gain within the right electronic circuit."