The unique and remarkably diverse electronic and optical properties of single-wall carbon
nanotubes (SWCNTs), which depend critically on their exact chiral structure, have proven to be both a blessing and a curse, as synthesis methods generally produce inhomogeneous mixtures, while applications demand more uniform properties. To realize the numerous potential applications, there is a high need for post-synthesis separation and purification, as well as specialized characterization methods to distinguish SWCNTs based on their structure-dependent electronic and optical properties. Exactly in these particular aspects I have made important breakthroughs, combining original preparation methods with advanced high-resolution spectroscopic characterization.
Most important contributions:
I found that when opened and dispersed in aqueous solution, SWCNTs immedeately get filled with water. Therefore aqeuous dispersions of SWCNTs always contain a mixture of empty (closed) and water-filled (opened) SWCNTs (cover Advanced Materials). I also found that even the thinnest SWCNTs can be filled with water, providing the first experimental proof of single-file water-filling inside SWCNTs (Phys. Rev. Lett., editorial in physics). I furthermore macroscopically separated the empty and water-filled SWCNTs using density gradient ultracentrifugation and showed that the empty SWCNTs provide an enhanced diameter sorting (cover Angewandte Chemie).
Recently, I have obtained single-chirality SWCNT dispersions by the newly developed aqueous two-phase separation method and showed the versatility of this new method as well as revealed the role of surfactants in this sorting mechanism. Furthermore the method can be easily adapted for the isolation of individual SWCNTs from bundles and other impurities in a bulk sample.
Finally, I aligned dipolar molecules inside SWCNTs to yield a large second-order nonlinear optics (published in Nature Nanotechnology and highlighted in a News and Views article - Nonlinear optics: dipoles align inside a nanotube).