Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

2-D material a brittle surprise

14.11.2016

Rice University researchers finds molybdenum diselenide not as strong as they thought

Scientists at Rice University have discovered that an atom-thick material being eyed for flexible electronics and next-generation optical devices is more brittle than they expected.


A nanomechanical device designed by Rice University scientists is used to measure the strength of two-dimensional nanomaterials like molybdenum diselenide, the subject of a recent Rice study that found it far more brittle than graphene.

Credit: Lou Group/Rice University

The Rice team led by materials scientist Jun Lou tested the tensile strength of two-dimensional, semiconducting molybdenum diselenide and discovered that flaws as small as one missing atom can initiate catastrophic cracking under strain.

The team's report appears this month in Advanced Materials.

The finding may cause industry to look more carefully at the properties of 2-D materials before incorporating them in new technologies, he said.

"It turns out not all 2-D crystals are equal," said Lou, a Rice professor of materials science and nanoengineering. "Graphene is a lot more robust compared with some of the others we're dealing with right now, like this molybdenum diselenide. We think it has something to do with defects inherent to these materials."

The defects could be as small as a single atom that leaves a vacancy in the crystalline structure, he said. "It's very hard to detect them," he said. "Even if a cluster of vacancies makes a bigger hole, it's difficult to find using any technique. It might be possible to see them with a transmission electron microscope, but that would be so labor-intensive that it wouldn't be useful."

Molybdenum diselenide is a dichalcogenide, a two-dimensional semiconducting material that appears as a graphene-like hexagonal array from above but is actually a sandwich of metallic atoms between two layers of chalcogen atoms, in this case, selenium. Molybdenum diselenide is being considered for use as transistors and in next-generation solar cells, photodetectors and catalysts as well as electronic and optical devices.

Lou and colleagues measured the material's elastic modulus, the amount of stretching a material can handle and still return to its initial state, at 177.2 (plus or minus 9.3) gigapascals. Graphene is more than five times as elastic. They attributed the large variation to pre-existing flaws of between 3.6 and 77.5 nanometers.

Its fracture strength, the amount of stretching a material can handle before breaking, was measured at 4.8 (plus or minus 2.9) gigapascals. Graphene is nearly 25 times stronger.

Part of the project led by Rice postdoctoral researcher Yingchao Yang required moving molybdenum diselenide from a growth chamber in a chemical vapor deposition furnace to a microscope without introducing more defects. Yang solved the problem using a dry transfer process in place of a standard acid washing that would have ruined the samples.

To test samples, Yang placed rectangles of molybdenum diselenide onto a sensitive electron microscope platform invented by the Lou group. Natural van der Waals forces held the samples in place on springy cantilever arms that measured the applied stress.

Lou said the group attempted to measure the material's fracture toughness, an indicator of how likely cracks are to propagate, as they had in an earlier study on graphene. But they found that pre-cutting cracks into molybdenum diselenide resulted in it shattering before stress could be applied, he said.

"The important message of this work is the brittle nature of these materials," Lou said. "A lot of people are thinking about using 2-D crystals because they're inherently thin. They're thinking about flexible electronics because they are semiconductors and their theoretical elastic strength should be very high. According to our calculations, they can be stretched up to 10 percent.

"But in reality, because of the inherent defects, you rarely can achieve that much strength. The samples we have tested so far broke at 2 to 3 percent (of the theoretical maximum) at most," Lou said. "That should still be fine for most flexible applications, but unless they find a way to quench the defects, it will be very hard to achieve the theoretical limits."

###

Co-authors of the paper are Rice graduate students Emily Hacopian, Weibing Chen, Jing Zhang and Bo Li, alumna Yongji Gong and Pulickel Ajayan, chair of Rice's Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry; Xing Li of Rice and Peking University, China; Minru Wen of Tsinghua University, China, and the Georgia Institute of Technology; Wu Zhou of Oak Ridge National Laboratory, Oak Ridge, Tenn.; Qing Chen of Peking University; and Ting Zhu of the Georgia Institute of Technology.

The research was supported by the Air Force Office of Scientific Research, the Welch Foundation, the Department of Energy Office of Basic Energy Sciences, the National Science Foundation and the National Science Foundation of China.

Read the abstract at http://onlinelibrary.wiley.com/doi/10.1002/adma.201604201/abstract

This news release can be found online at http://news.rice.edu/2016/11/14/2-d-material-a-brittle-surprise/

Follow Rice News and Media Relations via Twitter @RiceUNews

Related materials:

Lou Group: http://n3lab.rice.edu

Department of Materials Science and NanoEngineering: http://msne.rice.edu

George R. Brown School of Engineering: http://engr.rice.edu

Video: https://youtu.be/uvhyi5TwZXA

Located on a 300-acre forested campus in Houston, 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 home to the Baker Institute for Public Policy. With 3,910 undergraduates and 2,809 graduate students, Rice's undergraduate student-to-faculty ratio is 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for happiest students and for lots of race/class interaction by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance. To read "What they're saying about Rice," go to http://tinyurl.com/RiceUniversityoverview.

Media Contact

David Ruth
david@rice.edu
713-348-6327

 @RiceUNews

http://news.rice.edu 

David Ruth | EurekAlert!

More articles from Materials Sciences:

nachricht Atomic structure of ultrasound material not what anyone expected
21.02.2018 | North Carolina State University

nachricht Hidden talents: Converting heat into electricity with pencil and paper
20.02.2018 | Helmholtz-Zentrum Berlin für Materialien und Energie

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

Im Focus: Hybrid optics bring color imaging using ultrathin metalenses into focus

For photographers and scientists, lenses are lifesavers. They reflect and refract light, making possible the imaging systems that drive discovery through the microscope and preserve history through cameras.

But today's glass-based lenses are bulky and resist miniaturization. Next-generation technologies, such as ultrathin cameras or tiny microscopes, require...

Im Focus: Stem cell divisions in the adult brain seen for the first time

Scientists from the University of Zurich have succeeded for the first time in tracking individual stem cells and their neuronal progeny over months within the intact adult brain. This study sheds light on how new neurons are produced throughout life.

The generation of new nerve cells was once thought to taper off at the end of embryonic development. However, recent research has shown that the adult brain...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Stiffness matters

22.02.2018 | Life Sciences

Magnetic field traces gas and dust swirling around supermassive black hole

22.02.2018 | Physics and Astronomy

First evidence of surprising ocean warming around Galápagos corals

22.02.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>