Eventually, semiconductor manufacturers wont be able to cram any more transistors onto silicon chips. So Jia Chen is working on an alternative: electronic circuits and devices that use cylindrical, nanometer-wide carbon molecules called carbon nanotubes. Among their other advantages, some types of nanotubes can conduct electricity 100 times better than silicon. So far, most transistors made out of carbon nanotubes have been p-type, meaning they use positive charge carriers; negative – n-type – nanotube transistors have been much more difficult to produce. Chen, however, has found a simpler way to make them, which could be an important step toward integrating carbon nanotubes into conventional electronics. Chen discovered that attaching certain kinds of molecules to nanotubes would add electrons to them or draw electrons out, yielding either p- or n-type devices. Another problem with nanotube transistors is their need for metal electrodes, which are necessarily much larger than the nanotubes. The size difference tends to cause current leakage, reducing electrical efficiency. Chen found she could add certain impurities to a small segment of a nanotube to allow the nanotube to serve as an electrode, but one with little leakage. Her nanotube transistors carried 100 times as much electrical current as previous ones. The properties of nanotubes vary depending on their diameters. Choosing a particular diameter causes a tube to emit light at a particular wavelength. Chen was able to control the positive and negative charges in a nanotube to make it emit light 100 times brighter than the light from earlier devices. This could give nanotubes the ability to serve as optical interconnects – transmitting data among circuits more efficiently than copper does. Eventually, every device on a chip could be made from nanotubes. “Imagine a circuit with the same material acting as sensors, transistors, light emitters, and also interconnects,” says Chen.