IBM creates world's smallest light-emitting molecule. (Top Technology Showcase).

IBM researchers announced in early May that they have created the world's smallest solid-state light emitter. The light-emitting carbon nanotubes represent the first electrically controlled single-molecule light emitter ever constructed.

Carbon nanotubes are tube-shaped molecules that are 50,000 times thinner than the average human hair. IBM's researchers detected light with a wavelength of 1.5 micrometers, which the company says is particularly valuable because it is the wavelength widely used in optical communications. Nanotubes with different diameters could generate light with different wavelengths used in other applications, IBM says.

IBM's light emitter is a single nanotube, 1.4 nanometers in diameter, configured into a three-terminal transistor. As in a conventional semiconductor transistor, applying a low voltage to the transistor's gate switches the current passing between opposite ends of the nanotube (the device's source and drain).

IBM scientists engineered the device to be "ambipolar' so they could simultaneously inject negative charges (electrons) from a source electrode and positive charges (holes) from a drain electrode into a single carbon nanotube. When the electrons and holes meet in the nanotube, they neutralize each other and generate light.

Because it is a transistor, Big Blue's light emitter can be switched on and off depending on the voltage applied to the gate of the device. Electrical control of the light emission of individual nanotubes allows detailed investigations of the optical physics of these one-dimensional materials, the researchers say. "Nanotube light emitters have the potential to be built in arrays or integrated with carbon nanotube or silicon electronic components," says Dr. Phaedon Avouris, manager of nanoscale science at IBM Research. "[This opens] new possibilities in electronics and optoelectronics," he adds.

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