ATOMIC SCALE LOCOMOTIVES. Miniaturization has produced several examples of nm-sized rotors, ratchets, and gears, but not yet nano-steam engines. But to move raw materials around the freight yards of future nano-factories one needs nano-locomotives.

Scientists at Tel Aviv University in Israel (Markus Porto, 011-972-3-640-7229), have proposed how this can be done. In their scheme the freight yard consists of a lithographically prepared corrugated surface, something like the shape of an egg carton (on the microscopic level, anyway; to the naked eye the surface looks flat). The engine, in its simplest form, consists of three tiny clusters of metal atoms connected by two "springs." Each spring is actually a photochromophore molecule, one whose length can be expanded or shrunk with light. So to get the engine to move, laser light is shot in from above, the molecule expands, and one metal particle moves into depression on the surface.

By careful timing and correlating of the light pulses, the engine can be made to move along like an inchworm (see movie at Physics News Graphics). Cargo consisting of, say, inactive chains of molecules or other atomic material would be coupled to the locomotive and transported to where it is needed. (Porto et al., Physical Review Letters 26 June /pnu/2000/; Select Article.)