Doped and deadly

BY ITSELF, silicon is not an effective conductor.It does not leave its electronsfree for smooth flow of information. Tomake it less rigid, impurities are introducedinto a pure silicon chip. Theimpurities free an electron or two andmake the element a better conductor.This is called doping--a process essentialto creating the heart of every electronicdevice.

Concentrations as small as oneatom of boron, arsenic or phosphorus(impurities) per 100 million atoms ofsilicon have been effective so far. Butwith the world increasingly devisingchips smaller than a strand of humanhair, the definition of doping had tochange, too. This was the challengeJames Tour and his team of researchersfrom the Rice University accepted.The study published in the July issueof the Journal of the American ChemicalSociety suggests attaching a single layerof molecules on to the surface of the siliconchip, rather than mixingthem in, serves the same purposeas doping but works betterat the nanolevel. For this,

the team bathed the nanosiliconchip in the dopant solution,just like one creates aphotographic film. "We callit silicon with afterburners,"said Tour who teacheschemistry at Rice University.

The nanochipshave very little volume and youhave to deal with them accordingly," heexplained. Dopants mixed with siliconin the usual way destroy its homoge -neity and hamper conductivity.

Years of research into replacing siliconwith a better semiconductor hasyielded little. "So we decided to complementsilicon, rather than supplant it,"said Tour. "This research gives the Intelsand the Samsungs of the world anothertool to try, and I guarantee you they'llbe trying it," he added.