Team aims to create graphene nanoribbon 'wires' capable of carrying information thousands of times faster

February 14, 2014 by Wallace Ravven, University of California - Berkeley

A single graphene nanoribbon on a gold surface measures just one atom thick. The image was taken by a scanning tunneling microscope.
"Ballistic transport " – it sounds like a blast into the future. And it is.

By fabricating strips of carbon only one-atom thick and less than 15 atoms wide, researchers aim to create molecular-scale "wires" capable of carrying information thousands of times faster than is possible today.

Crammed into integrated circuits, these microscopic strips known as graphene could increase by more than 10,000 times the number of transistors per area in computer chips. The exceptionally fast current transport along would not only increase chip performance, but could refine the sensitivity of sensors to monitor circuit performance or subtle environmental changes.

First conceived only ten years ago, nanoribbon technology is, of course, a very hot field. To successfully exploit graphene's great promise, though, the absolute dimensions of the nanoribbons and their internal symmetry must be precise and predictable. Variations in structure generate performance uncertainty and inefficiency. Today's fabrication techniques aren't yet up to the job.

Felix Fischer, a chemist at Berkeley, is using his support from the Bakar Fellows Program to develop a totally new and extraordinarily precise way to create nanoribbons.

Fischer is also a recipient of a David and Lucille Packard Foundation Fellowship, awarded this year to 16 of the nation's most innovative young scientists and engineers.

The conductivity and other electrical properties of nanoribbons are essentially defined by their dimensions. This, in turn, derives from their absolute atomic structure. Adding just one or two to a 15-atom-wide ribbon, for example, degrades its ability to work at .

Current fabrication methods rely on relatively crude physical means to create the microscopic strips – if something at the scale of less than a billionth of an inch can truly be called crude.

"The conventional approach uses a focused beam to carve nanoribbons from sheets of graphene," Fischer says. "You chisel out the structure you want from a larger chunk of carbon. It can be done relatively quickly, but you don't have precise control over the position of each carbon atom in the ribbon.

"We want nanoribbons in which we know exactly where each atom is."

Instead of physically sculpting strips of graphene, Fischer chemically concocts them. By creating nanoribbons from their molecular subunits, he can control the position and number of each atom in the ribbon and achieve predictable control over their performance, he says.

His lab synthesizes molecular building blocks made from rings of carbon and hydrogen atoms, similar to the chemical structure of benzene. They then heat the molecules to link the building blocks into linear daisy-chains. In a second heating step the excess hydrogen atoms are stripped from the carbon skeleton yielding a uniform backbone of carbon-carbon bonds.

The assembly's atomic arrangement and its supporting substrate look like snakeskin or a tire track – though at a phenomenally small scale. If 10,000 nanoribbons were placed side by side they would form a structure about as wide as a human hair.

Electrons can travel along the uniform graphene ribbon essentially with no atoms to block their way. Their straight trajectory enables them to transport current thousands of times faster over short distances than they would through a traditional metallic conductor like copper wire.

That, in turn, means that transistors can be switched on and off much faster – one of the keys to increasing a circuit's speed.

Fischer has found that nanoribbons can operate as room temperature semiconductors when they are between 10 to 20 atoms wide.

"The wider the ribbon, the narrower the band gap (a determinant of electrical conductance)," he says. "If you go to much wider ones, the properties we need fizzle out."

The graphene strips could enable much faster transport, storage, and retrieval of data than can today's semiconductors. Their structure also dissipates heat well, which would allow computers and other large circuits to work longer and more efficiently.

Leaning back in his chair, arms folded behind his head and a cheery smile on his face, Fischer likens his interest in nanoribbons to the excitement of a child dreaming of being an astronaut. "It's being somewhere where no one has been before. In chemistry, you can make new things every day. You're only limited by your imagination and creativity."

He mentions the often-cited Moore's Law that predicts the performance to computer chips to double every two years. "Many manufacturers have worried that we might be hitting a ceiling. You have to think of how you can produce electronic devices that can work faster without generating more heat. These nanoribbons might be a key to keeping up with Moore's Law."

Certainly imagining that possibility is the first step.

Explore further: Ballistic transport in graphene suggests new type of electronic device

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not rated yet Feb 15, 2014
capable of carrying information thousands of times faster than is possible today.

Speed of light through fiber: around 0.69 c. Thousands of time faster would be . . .

Wow - Einstein must be rolling in his grave.

I know they intend information carrying capacity when they say speed. It nonetheless grates.
5 / 5 (1) Feb 15, 2014
Speed of light through fiber: around 0.69 c. Thousands of time faster would be . . .

Wow - Einstein must be rolling in his grave.

We're talking electrons as information carrying entities here - not photons. And they are indeed talking about the speed of these electrons.
not rated yet Feb 15, 2014
The graphene got its interest just because it already spreads the charge fast like the thin 2D sheet. The slicing of this sheet into thin 1D ribbons the mobility of electrons will increase even more, because of conceptual similarity with charge stripes within superconductors. For to make the artificial superconductor from it, we just need to attract more electrons to these nanoribons for to increase the charge density even more. The classical doping with electron acceptors could work. The doping of graphene with iodine wapor works even for graphite trace drawn with pencil on paper. Also, the huge iodine atoms help in separation of graphite layers. The nitration of graphene makes it superconductive even in form of 2D compact sheet bellow 5 K. The main problem is, these thin nanoribbons are increasingly prone to oxidation too: the air attacks the graphene sheet from sides.
not rated yet Feb 15, 2014
Whereas the finely ground graphite is stable at room temperature, the iodized graphite is pyrophoric . It has amazing catalytic properties too. Also, the graphite layers can be separated with their hydration in water - the resulting material exhibits traces of superconductivity too. IMO it's already time for replication of this finding, or not? Why the scientists are always getting so shocked with every breakthrough finding?
not rated yet Feb 15, 2014
IMO the well known crunching and squeaking of fresh snow at low temperatures is a manifestation of ballistic transport of water molecules in thin layers of liquid water at the surface of ice, too. Along thin needles of snowflakes this layer forms a nanoribbons, which enforces the ice regelation effect which makes the ice slippery with quantum mechanics. It's an example of supersolidity or temporal superfluidity at room temperature. Maybe the similar effect could be utilized for lubrication with polar asymetric molecules in nanomechanics.
not rated yet Feb 17, 2014
Speed of light through fiber: around 0.69 c. Thousands of time faster would be . . .

Wow - Einstein must be rolling in his grave.

We're talking electrons as information carrying entities here - not photons. And they are indeed talking about the speed of these electrons.

quote from wiki "speed of electricity"
"In everyday electronics, the signals or energy travel quickly, as electromagnetic waves, while the electrons themselves move slowly."
this statement is enough to make me question this entire article.

speed of a photon is irrelevant to nano/microcomputing. the speed of the electron won't exceed the current speed of electromagnetic waves.
really, this is a development in heat and size. with the projected increase in heat dissipation we're looking at a game changer, we've been historically limited by heat. with the size decrease we'll see much shorter gates, packed more tightly- Shorter total path = faster rate
we're also looking at an incredible (cont)
not rated yet Feb 17, 2014
increase in the power efficiency over the long haul. These systems are inherently more power efficient because the electrons can be easily recycled as they will be much more heavily controlled. current technology blatantly ignores individual electrons, while I'm aware of systems that recycle the excess power, I've read it's comparatively low efficiency.
we're currently working on 12nm gates, This will allow 3nm gates. Very difficult to see it getting much smaller than that using electricity.
with gold as the track and the lower heat, we'd be much more capable of stacking, most transistors are essentially 2d, 3dimensionalizing it has been a holy grail of computing since turing.
Feb 17, 2014
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