Graphene – Carbon’s Fascinating Allotrope

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  • 1:04PM Oct 22, 2015
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Article by Mark Sparrow
This article discussing graphene in Raman spectroscopy is the second in a series of  posts by Scientist Mark Sparrow, an expert in Raman Spectroscopy analysis, electron and optical microscopy, EDS, FTIR spectroscopy, thermal methods and mercury porosimetry. 

Carbon has the most allotropes, which are forms of carbon that differ from each other at the molecular level and exhibit different chemical and physical properties, than any other element. Graphite is one of the three naturally occurring carbon allotropes, a form of carbon that consists of hundreds of thousands of layers. Graphene is a single layer of graphite, and was first successfully isolated as an allotrope in 2004 by researchers at the University of Manchester. Only a single atom thick, it is the thinnest and strongest material known to exist. New applications and uses for graphene are rapidly being developed, and there has been a surge in graphene-related patents in recent years. However, difficulty in producing high-quality graphene has limited the commercial possibilities of devices using this material.

Why Identifying Graphene Quality Is Important

Graphene is not naturally occurring, so it must be grown. One of the most common and reliable methods is to grow graphene in layers from crystals of silicon carbide. This does present some challenges, however, such as finding the best substrate on which to grow the layers, as well as determining the best way to remove the layers without modifying their structure. The number of layers, chemical and physical properties determine how graphene performs. The graphene’s thickness can also have an effect on the electronic and physical properties, making the correct identification of the numbers of layers extremely important for technology R&D or product development. Raman spectroscopy has been used to characterize graphene from the outset, due to its ability to accurately and easily probe the structure of graphene, and even map single and multiple layers of the allotrope.

The Role of the Raman

Raman spectroscopy has long been used to characterize carbon in its many forms due to its ability to distinguish between its many allotropes. There are two primary features to most carbon spectra:

  • D-band or the “disorder” band, and
  • G-band or the “graphitic” band.

Raman spectroscopy uses band technology for material analysis, such as graphene testing.

When characterizing graphene, the G-band and the 2nd order band are important because they are sensitive to the number of graphene layers present. The G-band and the 2nd order band also show reproducible frequency shifts between 1, 2, 3 and 4-layer graphene, enabling the analyst to measure and image the number of layers in graphene with a high degree of accuracy.

Raman spectroscopy is a key technique in meeting the challenge to accurately analyze and identify graphene layers and their physical properties to help speed development of new applications.

To learn more about raman spectroscopy, please contact one of our experts.