Measurement technique could enhance graphene production

Researchers at Pennsylvania’s Lehigh University have reported a breakthrough in efforts to non-invasively characterise the properties of graphene.

The group, led by Prof Slava V. Rotkin, used Raman spectroscopy, a powerful technique that collects light scattered off a material’s surface, and statistical analysis to take 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 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.

It is claimed that the work could enable scientists to rapidly monitor levels of strain as graphene is being fabricated, thereby helping to prevent the formation of defects.  “Scientists already knew that Raman spectroscopy could obtain implicitly useful information about strain in graphene,” said Rotkin. “We showed explicitly that you can map the strain and gather information about its effects.