Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Tiny wires change behavior at nanoscale

30.08.2011
Rice University researchers surprised to see twin-induced brittle-like fractures in gold nanowires

Thin gold wires often used in high-end electronic applications are wonderfully flexible as well as conductive. But those qualities don't necessarily apply to the same wires at the nanoscale.

A new study from Rice University finds gold wires less than 20 nanometers wide can become "brittle-like" under stress. It appears in the journal Advanced Functional Materials.

The paper by Rice materials scientist Jun Lou and his lab shows in microscopic detail what happens to nanowires under the kinds of strain they would reasonably undergo in, for instance, flexible electronics.

Their technique provides a way for industry to see just how nanowires made of gold, silver, tellurium, palladium and platinum are likely to hold up in next-generation nanoelectronic devices.

Lou and his team had already established that metal wires have unique properties on the nanoscale. They knew such wires undergo extensive plastic deformation and then fracture on both the micro- and nanoscale. In that process, materials under stress exhibit "necking"; that is, they deform in a specific region and then stretch down to a point before they eventually break.

"Gold is extremely ductile," said Lou, an assistant professor of mechanical engineering and materials science. "That means you can stretch it, and it can withstand very large displacement.

"But in this work, we discovered that gold is not necessarily very ductile at the nanoscale. When we stress it in a slightly different way, we can form a defect called a twin."

The term "twinning" comes from the mirrorlike atomic structure of the defect, which is unique to crystals. "At the boundary, the atoms on the left and right sides exactly mirror each other," Lou said. Twins in nanowires show up as dark lines across the wire under an electron microscope.

"The material is not exactly brittle, like glass or ceramic, which fracture with no, or very little, ductility," he said. "In this case, we call it brittle-like, which means it has significantly reduced ductility. There's still some, but the fracture behavior is different from regular necking."

Their experiments on 22 gold wires of less than 20 nanometers involved the delicate operation of clamping them to a transmission electron microscope/atomic force microscope sample holder and then pulling them at constant loading speeds. Twins appeared under the shear component of the stress, which forced atoms to shift at the location of surface defects and led to a kind of nanoscale tectonic fault across the wire.

"Once you have those kinds of damage-initiation sites formed in the nanowire, you will have a lot less ductility. The metal will fracture prematurely," Lou said. "We didn't expect such twin-boundary formations would have such profound effects."

With current technology, it's nearly impossible to align the grip points on either side of the wire, so shear force on the nanowires was inevitable. "But this kind of loading mode will inevitably be encountered in the real world," he said. "We cannot imagine all the nanowires in an application will be stressed in a perfectly uniaxial way."

Lou said the results are important to manufacturers thinking of using gold as a nanomechanical element. "Realistically, you could have some off-axis angle of stress, and if these twins form, you would have less ductility than you would expect. Then the design criteria would have to change.

"That's basically the central message of this paper: Don't be fooled by the traditional definition of 'ductile,'" he said. "At the nanoscale, things can happen differently."

Lou's team included former Rice graduate student and the paper's first author, Yang Lu, now a postdoctoral researcher at MIT. Jun Song, an assistant professor at McGill University, and Jian Yu Huang, a scientist at Sandia National Laboratories, are co-authors of the paper.

Read the abstract at http://onlinelibrary.wiley.com/doi/10.1002/adfm.201101224/abstract

High-resolution photos are available at http://www.media.rice.edu/images/media/NEWSRELS/0826_Lou.jpg http://www.media.rice.edu/images/media/NEWSRELS/0826_Twinning_closeup.jpg http://www.media.rice.edu/images/media/NEWSRELS/0826_Twins_sequence.jpg

CAPTIONS:

(Lou)

Rice University Professor Jun Lou reported that gold nanowires don't behave the same way under stress as their macro-scale versions. (Credit: Rice University)

(Twinning closeup)

A single crystal nanowire shows evidence of twinning under tensile loading in this electron microscope image. A new study by the Rice University lab of Jun Lou determined that tiny gold wires change their behavior at the nanoscale. (Credit: Lou Lab/Rice University)

(Twins sequence)

This series of electron microscope images shows a gold nanowire with several twin boundaries, which show up as dark lines. The wire fractures at the site of a groove that appears at the bottom twin. (Credit: Lou Lab/Rice University)

Located on a 285-acre forested campus in Houston, Texas, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is known for its "unconventional wisdom." With 3,485 undergraduates and 2,275 graduate students, Rice's undergraduate student-to-faculty ratio is less than 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice has been ranked No. 1 for best quality of life multiple times by the Princeton Review and No. 4 for "best value" among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to

http://futureowls.rice.edu/images/futureowls/Rice_Brag_Sheet.pdf

David Ruth | EurekAlert!
Further information:
http://www.rice.edu

More articles from Materials Sciences:

nachricht Manchester scientists tie the tightest knot ever achieved
13.01.2017 | University of Manchester

nachricht CWRU directly measures how perovskite solar films efficiently convert light to power
12.01.2017 | Case Western Reserve University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>