Graphene – Carbon’s Fascinating Allotrope


Article by Mark Sparrow
This is the second in a series of blog posts on Raman spectroscopy 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–forms of carbon that differ from each other at the molecular level and exhibit different chemical and physical properties–than any other element. One of the three naturally occurring carbon allotropes is graphite, a form of carbon that consists of hundreds of thousands of layers. Graphene is a single layer of graphite that was first successfully isolated as an allotrope in 2004 by researchers at the University of Manchester. Graphene is only a single atom thick, and the thinnest and strongest material known to exist. As a result, new applications and uses for graphene are being developed at a rapid pace 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 presents some challenges, however, such as finding the best substrate on which to grow the layers and also determining the best way to remove the layers without modifying their structure. How graphene performs is determined by the number of layers, chemical and physical properties. The thickness of graphene can have an effect on the electronic and physical properties, making it extremely important to correctly identify  the number of layers for technology R&D or product development. Raman spectroscopy has been used from the outset for characterizing graphene due to its ability to accurately and easily probe the structure of graphene, and even map single and multiple layers of graphene.

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.

 

sparrow graphite table 2

 

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.