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
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)
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)
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
David Ruth | EurekAlert!
Argon is not the 'dope' for metallic hydrogen
24.03.2017 | Carnegie Institution for Science
Researchers make flexible glass for tiny medical devices
24.03.2017 | Brigham Young University
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy