Meanwhile, engineers at Hewlett-Packard Laboratories have devised a miniature wireless chip that could eventually replace RFID tags in many applications. Called the Memory Spot, the chip can hold up to four megabits of flash memory and transfer that data to a reader at 10 megabits per second. Whereas an RFID tag carries only about 500 bits -- just enough to store a serial number -- a Memory Spot could contain a short video clip, several images or dozens of pages of text. Measuring a few millimeters across, the chips could be embedded into passports, postcards, pharmaceutical labels and hospital wristbands. The devices, however, are not expected to be commercially available until two to five years from now.--Mark Alpert

Chicken-Wire Electronics

Carbon structures provide new devices and remarkable physics

Since the 1985 discovery of buckyballs (such as buckminsterfullerene-a nanoscopic sphere of 60 carbon atoms connected in a pattern similar to a traditional soccer ball), researchers have focused intense attention on various chicken-wirelike carbon structures. They have sought both to uncover the basic chemistry and physics of these novel compounds and to develop micro- and nanoelectronic devices that might someday outperform conventional silicon technology. The latest addition to the menagerie is structurally the simplest: graphene, a flat single layer of carbon atoms bonded together in the standard hexagonal pattern of graphite.

In November 2005, two independent research groups, one led by Andre K. Geim of the University of Manchester and one by Philip Kim of Columbia University, experimentally confirmed some extraordinary electronic properties of graphene that were first predicted as long ago as 1947. In an ordinary metal or semiconductor, electrons in many ways behave like particles obeying Newton's laws of motion, just with a so-called effective mass that is different from the electron's real mass because of the interactions with the material's lattice of atoms.

In graphene, however, the electrons' effective mass is zero and they behave like elementary particles obeying a version of Einsteinian relativity, albeit in a realm where the ultimate speed limit is about 800 kilometers per second instead of the usual 300,000 kilometers per second. The electrons travel at that limiting speed no matter what energy they have, just as a photon (a particle of light) always travels at the speed of light in a vacuum. The results open up a remarkable new domain of relativistic physics that can be explored in tabletop experiments.

The development of graphene devices, which might eventually outperform silicon, took a major step forward when Walter de Heer of the Georgia Institute of Technology, along with collaborators there and at the National Center for Scientific Research in France, used standard lithography and etching techniques of the microelectronics industry to make graphene circuitry. The group constructed proof-of-principle transistors and looplike structures called quantum interference devices and studied the properties of graphene ribbons. The ease with which graphene can be shaped to order could give it the edge over carbon nanotubes, which are like strips of graphene rolled into long, thin cylinders and which share many of its electronic properties but are much harder to build into the complex, precise patterns required for many devices.

Nanotube researchers are also constantly breaking new ground. Prabhakar R. Bandaru of the University of California, San Diego, and his coworkers there and at Clemson University demonstrated a radically new kind of nanotube-based transistor. In previous designs, a broad metal electrode acts as the "gate" that controls the current passing through a nanotube lying on top of it. Bandaru and coworkers instead made use of Y-shaped nanotubes; any one of the three branches can be used as the gate electrode whose voltage controls the current flowing through the other two branches. The absence of the metal gate allows the transistor to be much smaller than its unbranched cousins, providing a possible pathway to miniaturization beyond that possible with conventional silicon microelectronics.