A researcher at Stanford University has provided strong experimental evidence that ribbons of carbon atoms can be used for future generations of ultrafast processors.

Hongjie Dai, a professor of chemistry at Stanford, and his colleagues have demonstrated a new chemical process that produces extremely thin ribbons of a carbon-based material called graphene. He has demonstrated that these ribbons, once incorporated into transistors, show excellent electronic properties. Such properties have been predicted theoretically, Dai says, but not demonstrated in practice. These properties make graphene ribbons attractive for use in logic transistors in processors.

The discovery could lead to even greater interest in the experimental material, which has already attracted the attention of researchers at IBM, HP, and Intel. Graphene, which consists of carbon atoms arranged in a one-atom-thick sheet, is a component of graphite. Its structure is related to carbon nanotubes, another carbon-based material that's being studied for use in future generations of electronics. Both graphene and carbon nanotubes can transport electrons extremely quickly, which could allow very fast switching speeds in electronics. Graphene-based transistors, for example, could run at speeds a hundred to a thousand times faster than today's silicon transistors.

But graphene sheets have one significant disadvantage compared with the silicon used in today's chips. Although graphene can be switched between different states of electrical conductivity--the basic characteristic of semiconductor transistors--the difference between these states, called the on/off ratio, isn't very high. That means that unlike silicon, which can be switched off, graphene continues to conduct a lot of electrons even in its "off" state. A chip made of billions of such transistors would waste an enormous amount of energy and therefore be impractical.

Researchers had theorized, however, that it might be possible to dramatically improve these on/off ratios by carving graphene sheets into very narrow ribbons just a few nanometers wide. There had been early evidence supporting these theories from researchers at IBM and Columbia University, but the ratios produced were still much lower than those in silicon.

Robot-assisted brain surgery a reality

Despite advances in technology and technique, there will always be one limiting factor in the operating room: the surgeon. Hours of exacting work can tire anybody, especially someone navigating the delicate intricacies of the human brain.

The solution is as old as science fiction, but the technology has only recently caught up to the concept. The Robot-Assisted Microsurgery (RAMS) prototype is a robotic surgical tool first developed for space use and later refined as a precision instrument for microsurgery. Peter D. LeRoux, MD, a neurosurgeon at the University of Pennsylvania Medical Center, reports on the feasibility of RAMS in brain surgery in the March issue of Neurosurgery.

"The RAMS system works like an extension of the surgeon's hands," said LeRoux. In essence, the system consists of a set of robotic arms: a master arm, which functions like a joystick; and an operating arm, which actually performs the surgery. The surgeon manipulates the master arm just as they would hold a surgical instrument, and the operating arms mimic the surgeon's movements on the patient. "Robotic surgery is not about replacing surgeons, but enhancing their abilities in the operating room," explained LeRoux.

Wireless power

In the late 19th century, the realization that electricity could be coaxed to light up a bulb prompted a mad dash to determine the best way to distribute it. At the head of the pack was inventor Nikola Tesla, who had a grand scheme to beam electricity around the world. Having difficulty imagining a vast infrastructure of wires extending into every city, building, and room, Tesla figured that wireless was the way to go. He drew up plans for a tower, about 57 meters tall, that he claimed would transmit power to points kilometers away, and even started to build one on Long Island. Though his team did some tests, funding ran out before the tower was completed. The promise of airborne power faded rapidly as the industrial world proved willing to wire up.

Then, a few years ago, Marin Soljačić, an assistant professor of physics at MIT, was dragged out of bed by the insistent beeping of a cell phone. "This one didn't want to stop until you plugged it in for charging," says Soljačić. In his exhausted state, he wished the phone would just begin charging itself as soon as it was brought into the house.

So Soljačić started searching for ways to transmit power wirelessly. Instead of pursuing a long-distance scheme like Tesla's, he decided to look for midrange power transmission methods that could charge--or even power--portable devices such as cell phones, PDAs, and laptops. He considered using radio waves, which effectively send information through the air, but found that most of their energy would be lost in space. More-targeted methods like lasers require a clear line of sight--and could have harmful effects on anything in their way. So Soljačić sought a method that was both efficient--able to directly power receivers without dissipating energy to the surroundings--and safe.

He eventually landed on the phenomenon of resonant coupling, in which two objects tuned to the same frequency exchange energy strongly but interact only weakly with other objects. A classic example is a set of wine glasses, each filled to a different level so that it vibrates at a different sound frequency. If a singer hits a pitch that matches the frequency of one glass, the glass might absorb so much acoustic energy that it will shatter; the other glasses remain unaffected.

Soljačić found magnetic resonance a promising means of electricity transfer because magnetic fields travel freely through air yet have little effect on the environment or, at the appropriate frequencies, on living beings. Working with MIT physics professors John Joannopoulos and Peter Fisher and three students, he devised a simple setup that wirelessly powered a 60-watt light bulb.

The researchers built two resonant copper coils and hung them from the ceiling, about two meters apart. When they plugged one coil into the wall, alternating current flowed through it, creating a magnetic field. The second coil, tuned to the same frequency and hooked to a light bulb, resonated with the magnetic field, generating an electric current that lit up the bulb--even with a thin wall between the coils.