Carbon nanomaterials, such as nanotubes (CNT) and graphene, offer excellent electronic and physical properties. Graphene (first reported in Science in 2004) consists of single molecular layers of highly crystalline graphite, and can be considered the basic structural element of other carbon allotropes such as graphite, carbon nanotubes and fullerenes. Carbon nanotubes can be considered as rolled tube of a single graphene layer.

Raman micro-spectroscopy can answer many questions about the fundamental properties of these carbon nanomaterials. For carbon nanontubes such information includes their diameter and chirality, an assessment of structural order/disorder and also whether their electronic behaviour is metallic or semiconductor in nature. For graphene, Raman can quickly provide information about the number of layers in the material, the presence of stress/strain, and an assessment of structural order/disorder.

• Localization of single carbon nanotubes
• Diameter and chirality of carbon nanotubes
• Purity and quality assessment of new materials
• Electronic behaviour of nanotubes (semiconducting/metallic)
• Number of layers in graphene materials
• Stress/strain characterization in graphene structures

Combined Raman-AFM analysis of single walled carbon nanotube – the precise location and sizing of the nanotube is possible using the AFM (top left image), whereas Raman spectroscopy allows the quality and chemical characteristics of the nanontube to be assessed (top right and bottom images). The Raman spectrum and chemical image clearly distinguishes betweent the highly ordered carbon nanotube (in red), and the disordered carbon material (in green).

Raman mapping of graphene, showing the optical image (bottom left) and total G band intensity Raman image (top left). Graphene’s inherently strong Raman signal allows such images to be generated in the matter of seconds or minutes. The spectra shown on the right hand side illustrate the strong dependence of the 2D band shape on the number of layers present. Even graphene materials comprising just one, two or three layers can be easily distinguished with Raman.

Single walled carbon nanotubes (SWCNTs) are strongly resonance Raman active. Exciting at several wavelengths allows several resonance conditions to be used in order to observe the existence of various species of carbon nanotubes in the sample. The image above clearly demonstrates that this procedure is a good way to enhance selectively the Raman spectrum of different single walled carbon nanotubes, as illustrated by the widely differing Raman spectra when a mixture of nanotubes are excited at 514nm, 633nm, 785nm and 1064nm.