Gas-phase sorting of Carbon Nanotubes (GaPSoTube)

Carbon nanotubes are promising candidates for future nanotechnology realizations. A longstanding challenge is the separation of metallic and semiconducting nanotubes which are always together synthesized in an uncontrolled way. We here want to explore the possibilities of separation and manipulation of single-wall carbon nanotubes in the gas-phase. In the present project we aim at the generation of free beams of individual nanotubes. We favor pulsed laser desorption of individual nanotubes from an iced matrix to generate such a beam. This matrix consists of solvent which was used before to chemically isolate single nanotubes. This is a complete novel scheme and no nanotube beam was reported before. During preliminary studies in our laboratories we were able to generate a first nanotube beam by the laser desorption technique. In addition to single nanotubes mostly small networks of carbon nanotubes were identified. Optimization of beam generation parameters to increase the number of individual tubes is one of the aims of the present project. The generated nanotube beam will give the opportunity to sort nanotubes by their polarizability to mass ration (a/m). This ratio is strongly correlated to the structure of the nanotube and an enormous difference is present for semiconducting and metallic structures. We consider a three grating Moiré deflectometer to spatially separate semiconducting and metallic nanotubes. Related to the difference in a/m nanotubes will be deflected differently. The three grating setup enables a masking of the free beam to increase the sensitivity to smaller deflection differences. We experimentally realized such a sorting experiment for the fullerenes C60 and C70 in our Talbot-Lau deflectometer. Theoretical estimates show that metallic nanotubes can be enriched by 60% and semiconducting nanotubes by 40% in a single separation step. Furthermore the large a/m values of carbon nanotubes also give the opportunity to manipulate the orientation of nanotubes during the free flight. We plan to use this fact to deposit aligned nanotubes on substrates. This might have a high potential for nanotube applications. For instance oriented thin film carbon nanotube networks are interesting candidates for optoelectronic devices. The separated and aligned nanotubes will be deposited on surfaces like silicon single crystals for detection and characterization. The quality of nanotubes prepared by our gas-phase technique has to be characterized. Single nanotubes have to be checked regarding to their electronic properties. Techniques which enable the characterization of single nanotubes have to have a high spatial resolution. We therefore will use near-field optical spectroscopy. Such methods have shown to be able to perform photoluminescence and Raman spectroscopy with a resolution of 10 nm.