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.
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.
Lori Friedman | EurekAlert!
Nagoya physicists resolve long-standing mystery of structure-less transition
21.08.2017 | Nagoya University
Scientists from the MSU studied new liquid-crystalline photochrom
21.08.2017 | Lomonosov Moscow State University
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
21.08.2017 | Materials Sciences
21.08.2017 | Health and Medicine
21.08.2017 | Materials Sciences