Real-world graphene devices may have a bumpy ride

Jan 19, 2011

( -- Electronics researchers love graphene. A two-dimensional sheet of carbon one atom thick, graphene is like a superhighway for electrons, which rocket through the material with 100 times the mobility they have in silicon. But creating graphene-based devices will be challenging, say researchers at the National Institute of Standards and Technology, because new measurements show that layering graphene on a substrate transforms its bustling speedway into steep hills and valleys that make it harder for electrons to get around.

In a new article in , NIST scientists also say that graphene may be an ideal medium for probing interactions between electric conductors and insulators using a (STM).

According to NIST Fellow Joseph Stroscio, graphene's ideal properties are only available when it is isolated from the environment.

"To get the most benefit from graphene, we have to understand fully how graphene's properties change when put in real-world conditions, such as part of a device where it is in contact with other kinds of materials," Stroscio says.

Typical semiconductor chips are a complicated "sandwich" of alternating conducting, semiconducting and insulating layers and structures. To perform their experiment, the NIST group made their own sandwich with a single atomic sheet of graphene and another conductor separated by an insulating layer. When the bottom conductor is charged, it induces an equal and opposite charge in the graphene.

Examined under an STM, which is sensitive to the charged state of the graphene, the high should make the graphene look like a featureless plane. But, says NIST researcher Nikolai Zhitenev, "What we found is that variations in the electrical potential of the insulating substrate are interrupting the orbits of the electrons in the graphene, creating wells where the electrons pool and reducing their mobility."

This effect is especially pronounced when the group exposes the substrate-mounted graphene to high magnetic fields. Then the , already made sluggish by the substrate interactions, lack the energy to scale the mountains of resistance and settle into isolated pockets of "quantum dots," nanometer-scale regions that confine electrical charges in all directions.

It's not all bad news. Direct access to the graphene with a scanned probe also makes it possible to investigate the physics of other substrate interactions on a nanoscopic scale, something which is less possible in conventional semiconductor devices where the important transport layers are buried below the surface.

"Usually, we cannot study insulators at atomic scale," says Stroscio. "The STM works with a closed loop system that keeps a constant tunneling current by adjusting the tip-sample distance. On an insulator there is no current available, so the system will keep pushing the tip closer to the substrate until it eventually crashes into the surface. The lets us get close enough to these substrate materials to study their electrical properties, but not so close that we damage the and instrument."

Explore further: Synthesis of a new lean rare earth permanent magnetic compound superior to Nd2Fe14B

More information: S. Jung, G. Rutter, N. Klimov, D. Newell, I. Calizo, A. Hight-Walker, N. Zhitenev and J. Stroscio. Evolution of microscopic localization in graphene in a magnetic field from scattering resonances to quantum dots. Nature Physics. Published online Jan. 9, 2010, DOI:10.1038/nphys1866

Related Stories

Seeing Moire in Graphene

Apr 27, 2010

( -- Researchers at the National Institute of Standards and Technology and the Georgia Institute of Technology have demonstrated that atomic scale moiré patterns, an interference pattern ...

Light-speed nanotech: Controlling the nature of graphene

Jan 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 ...

Research gives insight into using graphene in electronics

Sep 22, 2010

( -- New findings from the laboratory of University of Illinois researcher Joe Lyding are providing valuable insight into graphene, a single two-dimensional layer of graphite with numerous electronic and mechanical ...

Graphene Yields Secrets to Its Extraordinary Properties

May 14, 2009

( -- Applying innovative measurement techniques, researchers from the Georgia Institute of Technology and the National Institute of Standards and Technology have directly measured the unusual energy ...

Highlight: Nanopatterning of Graphene

Mar 11, 2010

Center for Nanoscale Materials (CNM) at Argonne National Laboratory users from Politecnico di Milano in Italy, working collaboratively with researchers in the Electronic & Magnetic Materials & Devices Group, ...

Producing graphene layers using crystallization

Mar 02, 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 ...

Recommended for you

Cooling with molecules

18 hours ago

An international team of scientists have become the first ever researchers to successfully reach temperatures below minus 272.15 degrees Celsius – only just above absolute zero – using magnetic molecules. ...

A 'Star Wars' laser bullet

19 hours ago

Action-packed science-fiction movies often feature colourful laser bolts. But what would a real laser missile look like during flight, if we could only make it out? How would it illuminate its surroundings? ...

User comments : 0