Shining Light on Graphene-Metal Interactions

April 2, 2010 by Kendra Snyder
Measurement of the electronic bands of bilayer graphene on ruthenium, which have the characteristics of freestanding monolayer graphene. One of these characteristics is a typical cone-like shape of the bands near the Fermi energy. The inset shows a calculation of these "Dirac cones" for comparison. Shown in the background is a schematic rendering of the lattice structure of graphene.

( -- By controlling the layered growth of graphene - a relatively "new" form of carbon that's just a single atom thick - researchers at Brookhaven National Laboratory have uncovered intriguing details about the material's superior electrical and optical properties. Their findings could help position graphene as the next-generation material for future computers, digital displays, and electronic sensors.

"Graphene is a material that really has the potential to replace silicon in the electronics industry," said Peter Sutter, a materials scientist in Brookhaven's Center for Functional Nanomaterials. "It's thin, transparent, strong, and highly conductive - all extremely appealing characteristics for everything from computer chips to touch screens and ."

One of the biggest challenges facing researchers is figuring out how to produce graphene in large quantities. The simplest method is peeling off single sheets of graphene from , a material consisting of many graphene layers, with pieces of tape. But this method yields only small, jagged flakes that aren't useful for most applications.

At Brookhaven, Sutter's group grows graphene on a metal substrate, a technique that can produce single-layer sheets over very large areas, thousands of times larger than the pieces made with the "Scotch tape" method. First, a single crystal of ruthenium is heated up to temperatures higher than 1000 degrees Celsius while exposing it to a carbon-rich gas. At high temperatures, carbon atoms are able to squeeze into spaces within the metal crystal, similar to water being taken in by a sponge. As the crystal is slowly cooled, these carbon atoms are expelled to the surface of the metal, where they form individual layers of graphene. The number of layers formed can be controlled by the amount of carbon atoms initially absorbed into the ruthenium crystal.

"One of the unique aspects of this method is that we can control the thickness of the material, growing graphene layer by layer," Sutter said. "This has allowed us to see how the structure and electronic properties of the material change as single atomic carbon layers are added to the substrate one at a time."

Because the research group wanted to determine how the metal substrate affects the properties of graphene, it was important to monitor the layered material's characteristics as it was grown — a capability provided by a special microscope at NSLS beamline U5.

"First, we were able to watch how the material grew, and then, without moving it from the system, we were able to switch on the photon beam and determine its electronic structure," Stutter said. "It's extremely valuable to do everything in the same environment."

To obtain measurements for the material with different numbers of graphene sheets, the group used micro-angle-resolved photoelectron spectroscopy, a technique that allows researchers to study the electronic structure of very small regions of interest.

Their findings, published in the July 8, 2009 edition of , were surprising.

"We found that if a single graphene sheet is grown on a metal like ruthenium, the metal binds very strongly to the and disrupts the characteristic properties normally found in isolated graphene," Sutter said. "But those properties re-emerge in subsequent layers grown on the substrate."

In other words, the first graphene layer grown on satiates the metal substrate, allowing the rest of the layers to reclaim their normal properties.

"As a result of this growth process, a two-layer stack acts like an isolated monolayer of graphene and a three-layer stack acts like an isolated bilayer," Sutter said.

The findings of the group, which also includes Brookhaven researchers Mark Hybertsen, Jurek Sadowski, and Eli Sutter, lays groundwork for future graphene production for advanced technologies, and helps researchers understand how metals — for example in device contacts — change the properties of .

Explore further: Light-speed nanotech: Controlling the nature of graphene

More information: P. Sutter, M.S. Hybertsen, J.T. Sadowski, E. Sutter, "Electronic Structure of Few-Layer Epitaxial Graphene on Ru(0001)," Nano Lett., 9(7), 2654 (2009).

Related Stories

Light-speed nanotech: Controlling the nature of graphene

January 21, 2009

Researchers at Rensselaer Polytechnic Institute have discovered a new method for controlling the nature of graphene, bringing academia and industry potentially one step closer to realizing the mass production of graphene-based ...

Unzipping Carbon Nanotubes Can Make Graphene Ribbons

April 20, 2009

( -- By "unzipping" carbon nanotubes, researchers have shown how to make flat graphene ribbons. Graphene, which is a one-atom-thick sheet of carbon that looks like chicken wire, has unique electrical properties ...

Producing graphene layers using crystallization

March 2, 2010

( -- Ever since it's relatively recent discovery, graphene has generated a great deal of interest. Graphene is extracted from graphite in many cases, and consists of a sheet of carbon atoms bound together in a ...

A huge step toward mass production of graphene

March 10, 2010

Scientists have leaped over a major hurdle in efforts to begin commercial production of a form of carbon that could rival silicon in its potential for revolutionizing electronics devices ranging from supercomputers to cell ...

Recommended for you

Physicists develop new technique to fathom 'smart' materials

November 26, 2015

Physicists from the FOM Foundation and Leiden University have found a way to better understand the properties of manmade 'smart' materials. Their method reveals how stacked layers in such a material work together to bring ...

Mathematicians identify limits to heat flow at the nanoscale

November 24, 2015

How much heat can two bodies exchange without touching? For over a century, scientists have been able to answer this question for virtually any pair of objects in the macroscopic world, from the rate at which a campfire can ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Apr 04, 2010
Sub:Metal Dielectric interface-Glow
Information:Graphene is a material that really has the potential to replace silicon in the electronics industry,
Comments: This has more potential applications
Vidyardhi Nanduri

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.