Double-whammy analysis to probe nanotubes

US chemists and physicists have probed the electronic and physical structure of single-walled carbon nanotubes (SWNTs) in unprecedented detail using both Raman scattering spectroscopy and electron diffraction.

Matthew Sfeir and colleagues from Columbia University, New York, claim their findings have provided the first experimental verification of predictions made by the most widely used mathematical model of SWNTs - the single-particle tight-binding model.

SWNTs are simple structures: a sheet of graphite rolled into a tube. But numerous SWNT varieties can be made, each with different atomic and electronic properties, depending on the precise direction in which the graphite sheet is rolled. SWNT structures are classified as armchair, zigzag or chiral, and differing electronic properties can cause SWNTs to be metallic or semi-conducting.

Previously, Sfeir had tried, but failed, to work out the precise structure of individual SWNTs using a specially-developed Rayleigh scattering spectroscopy technique alone. 

’We needed a technique compatible with our sample geometry and which could provide independent structural verification,’ explained Sfeir. ’Fortunately, our colleagues in the electron microscopy group at Brookhaven National Laboratory were interested in the problem as well and were able to provide a solution - electron diffraction.’

By combining the two techniques, Sfeir and his colleagues have conducted detailed structural analyses of SWNTs. This has allowed them to confirm predictions of SWNT electronic structure made by the single-particle tight-binding model. 

’For example, we have directly verified the systematic changes of a semi-conducting nanotube’s transition energy with its chiral index, an important prediction known as "family behaviour",’ Sfeir told Chemistry World.

Jon Evans