Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Physicists map the strain, pixel by pixel, in wonder material graphene

30.09.2015

This week, an international group of scientists is reporting a breakthrough in the effort to characterize the properties of graphene noninvasively while acquiring information about its response to structural strain.

Using Raman spectroscopy and statistical analysis, the group succeeded in taking nanoscale measurements of the strain present at each pixel on the material's surface. The researchers also obtained a high-resolution view of the chemical properties of the graphene surface.


This image shows a sample morphology probed by Raman spectroscopy.

Credit

C. Neumann, S. Reichardt, P. Venezuela, M. Drögeler, L. Banszerus, M. Schmitz, K. Watanabe, T. Taniguchi, F. Mauri, B. Beschoten, S. V. Rotkin & C. Stampfer

The results, says Slava V. Rotkin, professor of physics and also of materials science and engineering at Lehigh University, could potentially enable scientists to monitor levels of strain quickly and accurately as graphene is being fabricated. This in turn could help prevent the formation of defects that are caused by strain.

"Scientists already knew that Raman spectroscopy could obtain implicitly useful information about strain in graphene," says Rotkin. "We showed explicitly that you can map the strain and gather information about its effects.

"Moreover, using statistical analysis, we showed that it is possible to learn more about the distribution of strain inside each pixel, how quickly the levels of strain are changing and the effect of this change on the electronic and elastic properties of the graphene."

The group reported its results in Nature Communications in an article titled "Raman spectroscopy as probe of nanometer-scale strain variations in graphene."

In addition to Rotkin, the article was authored by researchers from RWTH/Aachen University and the Jülich Research Centre in Germany; the Université Paris in France; Universidade Federal Fluminense in Brazil; and the National Institute for Materials Science in Japan.

Graphene is the thinnest material known to science, and one of the strongest as well. A 1-atom-thick sheet of carbon, graphene was the first 2-dimensional material ever discovered. By weight, it is 150 to 200 times stronger than steel. It is also flexible, dense, virtually transparent and a superb conductor of heat and electricity.

In 2010, Andre Geim and Konstantin Novoselov won the Nobel Prize in Physics for their innovative experiments with graphene. Using ordinary adhesive tape, the two British physicists succeeded in peeling layers of graphene from graphite--no easy task considering that 1 millimeter of graphite consists of 3 million layers of graphene.

In the decade or so since Geim and Novoselov began publishing the results of their research into graphene, the material has found its way into several applications, ranging from tennis rackets to smartphone touch screens. The 2013 market for graphene in the U.S., according to a 2014 article in Nature, was estimated at $12 million.

Several obstacles are holding up further commercialization of graphene. One of these is the presence of defects that impose strain on graphene's lattice structure and adversely affects its electronic and optical properties. Related to this is the difficulty in producing high-quality graphene at low cost and in large quantities.

"Graphene is stable and flexible and can expand without breaking," says Rotkin, who spent the fall of 2013 working at the RWTH/University of Aachen. "But it has wrinkles, or bubbles, on its surface, which give the surface a hilly feel and interfere with potential applications."

A layer of graphene is typically made on a substrate of silicon dioxide by a process called chemical vapor deposition. The material can be strained by contamination that occurs during the process or because the graphene and the substrate have different thermal expansion coefficients and thus cool and shrink at different rates.

To determine the properties of graphene, the group used Raman spectroscopy, a powerful technique that collects light scattered off a material's surface. The group also applied a magnetic field to gain additional information about the graphene. The magnetic field controls the behavior of the electrons in graphene, making it possible to see more clearly the effects of the Raman spectroscopy, Rotkin says.

"The Raman signal represents the 'fingerprint' of the graphene's properties," said Rotkin. "We're trying to understand the influence of the magnetic field on the Raman signal. We varied the magnetic field and noticed that each Raman line in the graphene changed in response to these variations."

The typical spatial resolution of the "Raman map" of graphene is about 500 nanometers (nm), or the width of the laser spot, the group reported in Nature Communications. This resolution makes it possible to measure variations in strain on a micrometer scale and determine the average amount of strain imposed on the graphene.

By performing a statistical analysis of the Raman signal, however, the group reported that it was able to measure the strain at each pixel and to map the strain, and the variations in strain, one pixel at a time.

Thus, the group reported, it was able to "distinguish between strain variations on a micrometer scale, which can be extracted from spatially resolved Raman maps, and nanometer-scale strain variations, which are on sub-spot-size length scales and cannot be directly observed by Raman imaging, but are considered as important sources of scattering for electronic transport."

The group produced its graphene samples using chemical vapor deposition (CVD) at the RWTH/University of Aachen.

Media Contact

Lori Friedman
lof214@lehigh.edu
610-758-3224

 @lehighunews

http://www.lehigh.edu 

Lori Friedman | EurekAlert!

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Global study of world's beaches shows threat to protected areas

19.07.2018 | Earth Sciences

New creepy, crawly search and rescue robot developed at Ben-Gurion U

19.07.2018 | Power and Electrical Engineering

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>