Subscribe free to our newsletters via your
. 24/7 Space News .




CARBON WORLDS
Understanding Graphene's Electrical Properties on an Atomic Level
by Staff Writers
University Park PA (SPX) Jul 24, 2014


An illustration of a graphene nanoribbon shaped by the beam of a transmission electron microscope. (Credit: Robert Johnson)

Graphene, a material that consists of a lattice of carbon atoms, one atom thick, is widely touted as being the most electrically conductive material ever studied. However, not all graphene is the same. With so few atoms comprising the entirety of the material, the arrangement of each one has an impact on its overall function.

Now, for the first time, researchers from the University of Pennsylvania have used a cutting-edge microscope to study the relationship between the atomic geometry of a ribbon of graphene and its electrical properties.

A deeper understanding of this relationship will be necessary for the design of graphene-based integrated circuits, computer chips and other electronic devices.

The study was led by professors A.T. Charlie Johnson and Marija Drndic, both of the Department of Physics and Astronomy in Penn's School of Arts and Sciences, along with Zhengqing John Qi, a member of Johnson's lab, and Julio Rodriguez-Manzo from Drndic's lab. Sung Ju Hong, then a member of Johnson's lab, also contributed to the study.

The Penn team collaborated with researchers at Brookhaven National Laboratory, the Universite Catholique de Louvain in Belgium and Seoul National University in South Korea. Their study was published in the journal Nano Letters.

The team's experiments were enabled by Brookhaven's aberration-corrected transmission electron microscope, or AC-TEM. By focusing the microscope's electron beam, the researchers were able to controllably cut sheets of graphene into ribbons with widths as small as 10 nanometers, while keeping them connected to an electricity source outside the microscope.

They then could use the AC-TEM's nanoscopic resolution to distinguish between individual carbon atoms within those ribbons. This level of precision was necessary to determine how the carbon atoms on the edges of the nanoribbons were oriented.

"We're relating the structure of the graphene - its atomic arrangement - to its electrical transport properties," said Drndic. "In particular, we were looking at the edges, which we were able to identify the geometry of."

"Graphene looks like chicken wire, and you can cut up this hexagonal lattice of carbon atoms in different ways, producing different shapes on the edge," she said. "But if you cut it one way, it might behave more like a metal, and, if you cut it another way, it could be more like a semiconductor."

For any piece of graphene, either the pointy or flat sides of its carbon hexagons might be at the piece's edge. Where the pointy sides face outward, the edge has a "zig-zag" pattern. Flat sides produce "armchair" pattern when they are on an edge. Any given edge might also display a mix of the two, depending on how the piece of graphene was initially cut and how that edge degrades under stress.

Because the graphene nanoribbons were connected to an electricity source while they were inside the AC-TEM, the researchers were able to simultaneously trace the outline of the ribbons and measure their conductivity. This allowed the two figures to be correlated.

"If you want to use graphene nanoribbons in computer chips, for example, you absolutely need to have this information," Johnson said. "People have looked at these ribbons under the microscope, and people have measured their electrical properties without looking at them but never both at the same time."

After studying the nanoribbons with relatively low levels of electron flow, the researchers turned up the intensity, much like turning up a light bulb using a dimmer switch The combination of the electron bombardment from the microscope and the large amount of electrons flowing through the nanoribbons caused their structures to gradually degrade.

As carbon bonds within the nanoribbons broke, they became thinner and the shape of their edges changed, providing additional data points.

"By doing everything within the microscope," Rodriguez-Manzo said, "we can just follow this transformation to the end, measuring currents for the nanoribbons even when the get smaller than 1 nanometer across. That's five atoms wide."

This kind of stress testing is critical to the future design of graphene electronics.

"We have to see how much current we can transport before these nanoribbons fall apart. Our data shows that this figure is high compared to copper," Rodriguez-Manzo said.

The harsh conditions also caused some of the ribbons to fold up on themselves, producing nanoscopic graphene loops. Serendipitously, the team found that these loops had desirable properties.

"When the edges wrap around and form the loops we see," Johnson said, "it helps hold the structure together, and it makes the current density a thousand higher than what is currently state of the art. That structure would be useful in making interconnects [which are the conducting paths that connect transistors together in integrated circuits]."

Future research in this field will involve directly comparing the electrical properties of graphene nanoribbons with different widths and edge shapes.

"Once we can cut these nanoribbons atom by atom," Drndic said, "there will be a lot more we can achieve."

.


Related Links
University of Pennsylvania
Carbon Worlds - where graphite, diamond, amorphous, fullerenes meet






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





CARBON WORLDS
Construction starts on carbon capture plant in Kentucky
Washington (UPI) Jul 22, 2013
The U.S. Department of Energy said construction started on a $19.5 million carbon capture research project at a coal power station in Kentucky. Kentucky Gov. Steve Beshear and state Energy Secretary Len Peters joined Department of Energy officials and other dignitaries for a ribbon-cutting ceremony for the construction of the pilot project at Kentucky Utilities' E.W. Brown Generating St ... read more


CARBON WORLDS
China's biggest moon challenge: returning to earth

Lunar Pits Could Shelter Astronauts, Reveal Details of How 'Man in the Moon' Formed

Manned mission to Moon scheduled by Roscosmos for 2020-2031

Landsat Looks to the Moon

CARBON WORLDS
India could return to Mars as early as 2017

Curiosity's images show Earth-like soils on Mars

NASA Seeks Proposals for Commercial Mars Data Relay Satellites

Emirates paves way for Middle East space program with mission to Mars

CARBON WORLDS
Voyager Spacecraft Might Not Have Reached Interstellar Space

New Fort Knox: A means to a solar-system-wide economy

Sierra Nevada Completes Major Dream Chaser NASA CCiCap Milestone

NASA Partners Punctuate Summer with Spacecraft Development Advances

CARBON WORLDS
Lunar rock collisions behind Yutu damage

China to launch HD observation satellite this year

China's Fast Track To Circumlunar Mission

Chinese moon rover designer shooting for Mars

CARBON WORLDS
Next ISS Cargo Spacecraft Rolls Out to Pad

Russian cargo craft docks with ISS, science satellite fails

Russian Cargo Craft Launches for 6-Hour Trek to ISS

ATV-5: loaded and locked

CARBON WORLDS
SpaceX Soft Lands Falcon 9 Rocket First Stage

China to launch satellite for Venezuela

SpaceX Falcon 9 v1.1 Flights Deemed Successful

ISS 'space truck' launch postponed: Arianespace

CARBON WORLDS
'Challenges' in quest to find water on Earth-like worlds: study

Transiting Exoplanet with Longest Known Year

Brown Dwarfs May Wreak Havoc on Orbits of Nearby Planets

NASA Mission To Reap Bonanza of Earth-sized Planets

CARBON WORLDS
New material puts a twist in light

Efficient structures help build a sustainable future

Future Electronics May Depend on Lasers, Not Quartz

USAF orders ground approach radar for Saudi Arabia




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.