environmental and retirée obligations as well as internai growth. Still, Darryl D. Fry, 54, Cytec chairman, president, and chief executive officer, is hopeful for success: "The spin-off will allow Cytec to fully capitalize on business opportunities around the world." Marc Reisch
E2 Pt wires Solvent with monomer and electrolyte
E1=+1.7V,
E2 = -0.5 V vs ref
E1 = -0.5 V, E2 = +1.7Vvsref
Chemical processmakes electrical 'nanowires' Scientists at the University of California, San Diego, led by assistant chemistry professor Michael J. Sailor, hâve developed an electrochemical polymerization technique that grows nanoscale connections between two or more pairs of platinum wires, without mechanical assistance. In some respects, the technique resembles the way neurons reach out and make connections with each other in the human brain. "This is the only System of its kind, outside a living System, that allows you to do this in three dimensions," says Sailor. Researchers who dream of making ultra-tiny electric circuits, artificial neural nets, and molecule-sized machines or robots are faced with a problem: How to wire them up? Progress in nanotechnology requires the ability to make electrical connections no thicker than a few atoms and to connect parts three-dimensionally to as many as hundreds of other nodes, a feat beyond current mechanical and photolithographic techniques. Sailor and coworkers at San Diego hâve brought the nanotechnologists' dream a step closer to reality [Science, 262, 2014 (1993)]. They electrically link a selected pair of platinum wires immersed in a monomer/electrolyte solution by growing dendritic (branched, or treelike) fibers of a conducting polymer between the wires. The technique exploits the ability of poly(3-methylthiophene) to be switched between conducting and nonconducting states. Because the polymer can grow only in the conducting state, switching between states also turns polymer fiber growth on and off. Sailor points out that dendritic growth of thèse polymers has been known for some time—in fact, ifs considered a nuisance in such applications as fabricating electrochromic films for "smart" window coatings. "The trick was to corne up with a way to get the fibers to connect up prop-
E1=+1.7V, E2 = -0.5 V vs ref
In above diagram, platinum wires ΕΊ and E2, immersed in monomer/electrolyte solution, become electrically connected as polymer fibers are stimulated to grow and link together (blue = conducting; red = nonconducting). Dendriticfibersfirstform at the positive électrode ΕΊ (+1.7 V), where the partially oxidized polymer chain is conductive. When potentials are switched (ΕΊ = -05 V, E2 = +1.7 V), growth stops at ΕΊ and begins at E2. The cycle is repeatedfor about 30 minutes until shunt is complète. In photo atright,conducting polymer grows in solution between two platinum wires about 3 mm apart, forming electrical connections. erly, instead of shorting out or Connecting to the wrong thing," he tells C&EN. His team does that by reversing the voltage applied to the platinum wires about every 30 seconds for half an hour, stimulating growth alternately at one and then the other wire until the fibers link up and the electrical shunt, or connection, is complète. The shunt "acts just like a wire, obeys Ohm's law, and allows current to flow in either direction," Sailor says. The shunts hâve passed up to 15 milliamperes of current over distances of up to 2 mm. To test the feasibility of making large arrays of multidimensional connections, the team insulated the first shunt and wired up a second. It evaluated two insulating techniques: electropolymerization and a dip-coating method. The next step is to try making 10 or 20 connections. But before anyone can wire up an android's brain, there are a few other détails to work out—among them, how to pro-
duce unidirectional current flow, as in a diode. Right now, the shunts pass current freely in both directions. A means to amplify signais also must be developed. "It's still in the realm of scientific curiosity," Sailor says. "But developing chemical tools to make connections is a key step in going to the next génération of electronics." Deborah Illman JANUARY 3,1994 C&EN 7
