Tuesday, November 16

Nanotubes Make Antennas for Light

Technology Review: Nanotubes Make Antennas for Light
November 15, 2004

An antenna transmits and receives electromagnetic waves at wavelengths that are close to the length of the antenna, and it does so by converting electrical current to electromagnetic waves and vice versa. The electromagnetic spectrum spans radio waves, microwaves, heat waves, visible lightwaves, ultraviolet waves, x-rays, and gamma rays.

Carbon nanotubes, which are rolled-up sheets of carbon atoms that can be smaller than a nanometer in diameter, can act as antennas, but instead of transmitting and receiving radio waves, which are at the longest end of the electromagnetic spectrum, antennas of their size pick up the nanoscale wavelengths of visible light. A nanometer is one millionth of a millimeter. In contrast, radio wave wavelengths are measured in meters.

Researchers at Boston College, the U.S. Army Natick Soldier Center, Mega Wave Corporation and Florida International University have demonstrated the light antenna effect using arrays of multiwalled carbon nanotubes.

The method could be used to convert optical signals to electrical signals in communications equipment, to carry out optical computing, to detect different wavelengths of light including the infrared wavelengths used in telecommunications equipment, and to convert sunlight to electricity in solar energy applications, according to the researchers.

To make the light antennas, the researchers grew arrays of multiwalled carbon nanotubes that were 50 nanometers in diameter and varied in length from 200 to 1,000 nanometers. Visible lightwaves range from 400 to 700 nanometers long from crest to crest, which is about ten times smaller than a red blood cell.

The researchers measured the behavior of the carbon nanotube arrays by recording the lightwaves that the minuscule antennas reradiated.

Practical nanotube antennas could be developed in two to five years, according to the researchers. The work appeared in the September 27, 2004 issue of Applied Physics Letters."