The new device works in a manner more similar to the vacuum tubes from the 1930s than the transistors found in modern radios. In the new radio, a single carbon fiber a few hundred nanometers (billionths of a meter) long, and only a few molecules thick, stands glued to a negatively charged base of tungsten that acts as a cathode. Roughly one millionth of a meter directly across from the base lies a positively charged piece of copper that acts as an anode.
Power in the form of streaming electrons travels from an attached battery through the cathode, into the nanotube, and across a vacuum to the anode via a field-emission tunneling process.
"The field emission process could be likened to a runner jumping across a ditch; you only make it across if you have enough speed, i.e. energy, to begin with," says Zettl. "So electrons jump the physical gap from cathode to anode when you supply enough energy to the device from the battery."
The stream of electrons along the nanotube changes when a radio wave encoded with information--simply a wave of photons that travels in a controlled manner--washes across the tube and causes it to resonate. This mechanical action is what amplifies and demodulates, or decodes, the radio signal.
Returning to Zettl's runner analogy, the vibrating nanotube is akin to a ditch with a constantly changing width. Just as the runner's chances of making the leap depend on how far the gap is, the chances of electrons making the leap depend on the distance of the nanotube tip from the anode.
"This coupling of the mechanical waving motion of the nanotube to the success rate of electrons jumping the gap is key to the functioning of the radio," says Zettl. "What emerges from the anode is then the information signal, which can be transferred to additional amplifiers and a speaker to re
|Contact: Josh Chamot|
National Science Foundation