Rice University theorists show environments can alter 2-D materials' basic properties
What if peanut brittle, under certain conditions, behaved like taffy? Something like that happens to a two-dimensional dichalcogenide analyzed by scientists at Rice University.
Calculations by Rice University scientists show that a two-dimensional layer of molybdenum disulfide can become superplastic by changing its environmental conditions. In an atmosphere with sulfur and under the right temperature and pressure, the energy barrier is lowered, allowing dislocations along the grain boundaries to shift and changing the material's properties. S2 refers to a disulfur molecule; VS2 is a two-sulfur-atom vacancy.
Credit: Xiaolong Zou/Rice University
Rice researchers calculated that atomically thin layers of molybdenum disulfide can take on the qualities of plastic through exposure to a sulfur-infused gas at the right temperature and pressure.
That means one can deform it without breaking it -- a property many materials scientists who study two-dimensional materials should find interesting, according to Rice theoretical physicist Boris Yakobson and postdoctoral researcher Xiaolong Zou; they led the study that appeared in the American Chemical Society journal Nano Letters.
Molybdenum disulfide, the object of study in many labs for its semiconducting properties, interested the Rice lab because of the characteristics of its grain boundaries. Two-dimensional materials like graphene are actually flat, atom-thick sheets. But 2-D molybdenum disulfide is a sandwich, with layers of sulfur above and below the molybdenum atoms.
When two sheets join at different angles during growth in a furnace, atoms at the boundaries have to compensate by improvising "defective" arrangements, called dislocations, where they come together.
The researchers determined it may be possible to promote the movement of those dislocations through environmental control of the gas medium. This would change the material's properties to give it superplasticity, which allows it to be deformed beyond its usual breaking point.
Plastic materials can be rearranged and will hold their new shape. For example, a plumber can bend a metal pipe; that bendable quality is plasticity. Yakobson noted such materials can become brittle again with further changes in the environment.
"Generally, the coupling of chemistry and mechanics is quite rare and scientifically difficult to understand," said Yakobson, whose group at Rice analyzes materials by calculating the energies that bind their atoms. "Corrosion is the best example of how chemistry affects mechanical behavior, and the science of corrosion is still in development."
For molybdenum disulfide, they found two mechanisms by which boundaries could overcome activation energy barriers and lead to superplasticity. In the first, called direct rebonding, only one molybdenum atom in a dislocation would shift in response to external forces. In the second, bond rotation, several atoms would shift in opposite directions.
They calculated that the barrier for direct rebonding, while less dramatic, is much lower than for bond rotation. "Through the rebonding path, the mobility of this defect changes by several orders of magnitude," Yakobson said. "We know from the mechanics of materials that brittle or ductile qualities are defined by the mobility of these dislocations. What we show is that we can affect the tangible property, the stretchability, of the material."
Yakobson suggested it may be possible to tune the plasticity of dichalcogenides in general and that it may also be possible to eliminate the defects from a 2-D dichalcogenide sheet by treating the dislocations "to allow them to rapidly diffuse away and vanish or to form interesting aggregated states." That would likely open the way to the easier manufacture of dichalcogenides that need particular electrical or mechanical properties for applications, he said.
"We think of these two-dimensional materials as an open canvas, theoretically speaking," he said. "You can very quickly read and write changes to them. Bulk materials don't have this openness, but here, every atom is in immediate proximity to the environment."
Rice graduate student Mingjie Liu and Zhiming Shi, an exchange graduate student in Yakobson's group from Jilin University, Changchun, China, are co-authors of the paper. Yakobson is Rice's Karl F. Hasselmann Professor of Materials Science and NanoEngineering, a professor of chemistry and a member of Rice's Richard E. Smalley Institute for Nanoscale Science and Technology.
A Multidisciplinary University Research Initiative grant through the United States Army Research Office and the Robert Welch Foundation supported the research. The researchers utilized the National Science Foundation-supported DAVinCI supercomputer administered by Rice's Ken Kennedy Institute for Information Technology.
Read the abstract at http://pubs.
This news release can be found online at http://news.
Follow Rice News and Media Relations via Twitter @RiceUNews
Yakobson Research Group: http://biygroup.
Department of Materials Science and NanoEngineering: http://msne.
David Ruth | EurekAlert!
Move over, Superman! NIST method sees through concrete to detect early-stage corrosion
27.04.2017 | National Institute of Standards and Technology (NIST)
Control of molecular motion by metal-plated 3-D printed plastic pieces
27.04.2017 | Ecole Polytechnique Fédérale de Lausanne
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences