Carbon nanotubes have exceptional electron mobility, but their extremely small size makes it exceedingly difficult to integrate them into transistors. One barrier to commercialization of nanotube-based circuitry is the lack of quick and easy ways to accurately measure their performance. IBM's T. J. Watson Research Center has demonstrated a characterization technology for carbon-nanotube transistors that it claims is quick and accurate. By focusing a laser on the nanotube that is being tested, IBM measures the shift in Raman phonon frequency to determine whether the nanotube is metallic or semiconducting and to measure its electron- or charge-density. This type of probing method, absent until now, is essential to characterizing nanotube materials capable of commercialization.