Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Even graphene has weak spots: Rice, Tsinghua theorists find junctions in polycrystalline graphene sap strength of super material

New work by theorists at Rice and Tsinghua universities shows defects in polycrystalline forms of graphene will sap its strength. The illustration from a simulation at left shows a junction of grain boundaries where three domains of graphene meet with a strained bond in the center. At right, the calculated stress buildup at the tip of a finite-length grain boundary.Credit: Vasilii Artyukhov/Rice University
New work by theorists at Rice and Tsinghua universities shows defects in polycrystalline forms of graphene will sap its strength. The illustration from a simulation at left shows a junction of grain boundaries where three domains of graphene meet with a strained bond in the center. At right, the calculated stress buildup at the tip of a finite-length grain boundary.

Credit: Vasilii Artyukhov/Rice University

Abstract:
Graphene, the single-atom-thick form of carbon, has become famous for its extraordinary strength. But less-than-perfect sheets of the material show unexpected weakness, according to researchers at Rice University in Houston and Tsinghua University in Beijing.

Even graphene has weak spots: Rice, Tsinghua theorists find junctions in polycrystalline graphene sap strength of super material

Houston, TX | Posted on March 28th, 2013

The kryptonite to this Superman of materials is in the form of a seven-atom ring that inevitably occurs at the junctions of grain boundaries in graphene, where the regular array of hexagonal units is interrupted. At these points, under tension, polycrystalline graphene has about half the strength of pristine samples of the material.

Calculations by the Rice team of theoretical physicist Boris Yakobson and his colleagues in China were reported this month in the American Chemical Society journal Nano Letters. They could be important to materials scientists using graphene in applications where its intrinsic strength is a key feature, like composite materials and stretchable or flexible electronics.

Graphene sheets grown in a lab, often via chemical vapor deposition, are almost never perfect arrays of hexagons, Yakobson said. Domains of graphene that start to grow on a substrate are not necessarily lined up with each other, and when these islands merge, they look like quilts, with patterns going in every direction.

The lines in polycrystalline sheets are called grain boundaries, and the atoms at these boundaries are occasionally forced to change the way they bond by the unbreakable rules of topology. Most common of the "defects" in graphene formation studied by Yakobson's group are adjacent five- and seven-atom rings that are a little weaker than the hexagons around them.

The team calculated that the particular seven-atom rings found at junctions of three islands are the weakest points, where cracks are most likely to form. These are the end points of grain boundaries between the islands and are ongoing trouble spots, the researchers found.

"In the past, people studying what happens at the grain boundary looked at it as an infinite line," Yakobson said. "It's simpler that way, computationally and conceptually, because they could just look at a single segment and have it represent the whole."

But in the real world, he said, "these lines form a network. Graphene is usually a quilt made from many pieces. I thought we should test the junctions."

They determined through molecular dynamics simulation and "good old mathematical analysis" that in a graphene quilt, the grain boundaries act like levers that amplify the tension (through a dislocation pileup) and concentrate it at the defect either where the three domains meet or where a grain boundary between two domains ends. "The details are complicated but, basically, the longer the lever, the greater the amplification on the weakest point," Yakobson said. "The force is concentrated there, and that's where it starts breaking."

"Force on these junctions starts the cracks, and they propagate like cracks in a windshield," said Vasilii Artyukhov, a postdoctoral researcher at Rice and co-author of the paper. "In metals, cracks stop eventually because they become blunt as they propagate. But in brittle materials, that doesn't happen. And graphene is a brittle material, so a crack might go a really long way."

Yakobson said that conceptually, the calculations show what metallurgists recognize as the Hall-Petch Effect, a measure of the strength of crystalline materials with similar grain boundaries. "It's one of the pillars of large-scale material mechanics," he said. "For graphene, we call this a pseudo Hall-Petch, because the effect is very similar even though the mechanism is very different.

"Any defect, of course, does something to the material," Yakobson said. "But this finding is important because you cannot avoid the effect in polycrystalline graphene. It's also ironic, because polycrystals are often considered when larger domains are needed. We show that as it gets larger, it gets weaker.

"If you need a patch of graphene for mechanical performance, you'd better go for perfect monocrystals or graphene with rather small domains that reduce the stress concentration."

Co-authors of the paper are graduate student Zhigong Song and his adviser, Zhiping Xu, an associate professor of engineering mechanics at Tsinghua. Xu is a former researcher in Yakobson's group at Rice. Yakobson is Rice's Karl F. Hasselmann Professor of Mechanical Engineering and Materials Science and professor of chemistry.

The Air Force Office of Scientific Research and the National Science Foundation supported the work at Rice. The National Natural Science Foundation of China, the Tsinghua University Initiative Scientific Research Program and Tsinghua National Laboratory for Information Science and Technology of China supported the work at Tsinghua.

Follow Rice News and Media Relations via Twitter @RiceUNews.

####

For more information, please click here

Contacts:
David Ruth
713-348-6327


Mike Williams
713-348-6728

Copyright © Rice University

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Read the abstract at:

Yakobson Group:

Zhiping Xu Group:

Related News Press

Graphene

FLAG-ERA and TNT2014 join efforts: Graphene Networking at its higher level in Barcelona: Encourage the participation in a joint transnational call July 30th, 2014

News and information

University of Manchester selects Anasys AFM-IR for coatings and corrosion research July 30th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Analytical solutions from Malvern Instruments support University of Wisconsin-Milwaukee researchers in understanding environmental effects of nanomaterials July 30th, 2014

FEI Unveils New Solutions for Faster Time-to-Analysis in Metals Research July 30th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers July 30th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Tough foam from tiny sheets: Rice University lab uses atom-thick materials to make ultralight foam July 29th, 2014

A new way to make microstructured surfaces: Method can produce strong, lightweight materials with specific surface properties July 29th, 2014

Discoveries

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers July 30th, 2014

From Narrow to Broad July 30th, 2014

Optimum inertial design for self-propulsion: A new study investigates the effects of small but finite inertia on the propulsion of micro and nano-scale swimming machines July 29th, 2014

A new way to make microstructured surfaces: Method can produce strong, lightweight materials with specific surface properties July 29th, 2014

Materials/Metamaterials

From Narrow to Broad July 30th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Tough foam from tiny sheets: Rice University lab uses atom-thick materials to make ultralight foam July 29th, 2014

A new way to make microstructured surfaces: Method can produce strong, lightweight materials with specific surface properties July 29th, 2014

Announcements

University of Manchester selects Anasys AFM-IR for coatings and corrosion research July 30th, 2014

Nature inspires a greener way to make colorful plastics July 30th, 2014

Analytical solutions from Malvern Instruments support University of Wisconsin-Milwaukee researchers in understanding environmental effects of nanomaterials July 30th, 2014

FEI Unveils New Solutions for Faster Time-to-Analysis in Metals Research July 30th, 2014

Research partnerships

Breakthrough laser experiment reveals liquid-like motion of atoms in an ultra-cold cluster: University of Leicester research team unlocks insights into creation of new nano-materials July 25th, 2014

A*STAR and industry form S$200M semiconductor R&D July 25th, 2014

A Crystal Wedding in the Nanocosmos July 23rd, 2014

Penn Study: Understanding Graphene’s Electrical Properties on an Atomic Level July 22nd, 2014

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE