Sorting single walled carbon nanotube by length and chirality

• Main Author: Si, Rongmei
• Other Authors: Chen Yuan
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/55432
• Institution: Nanyang Technological University

Monodisperse single walled carbon nanotubes (SWCNTs) with defined properties are needed for their potential applications in electronics and medicine. However, there are currently no synthesis methods which can control the structure of SWCNTs precisely. The objectives of this thesis are to develop novel post-synthetic sorting technologies to obtain SWCNTs with uniform structures (diameter, chirality, length), and develop new characterization methods, and test the performances of length-sorted SWCNTs in electronic devices. First, the density gradient ultracentrifugation method was applied to prepare length-sorted SWCNT suspensions containing individualized surfactant wrapped SWCNTs. A convenient analysis method was developed to characterize the length distribution rapidly and accurately through absorption spectroscopy in conjunction with advanced chemometric techniques. The results show that extended inverted signal correction and Gaussian process regression provide good predictions of the length distribution of SWCNTs with satisfactory agreement with the atomic force microscope measurements. Next, the performances of thin-film transistors (TFTs) fabricated using sodium deoxycholate-dispersed SWCNTs with different lengths were investigated. The results show that the performance of SWCNT–TFTs is tube length dependent. Shorter tubes need higher tube density to form semiconducting paths, leading to lower on/off ratio and higher contact resistance. Surfactant-wrapped SWCNTs will bundle into ropes of different sizes when tube density is high. Therefore, it is critical to control tube length as well as surfactant residue content to build high performance SWCNT-TFTs. Last, a fluorene-based polymer named poly [(9,9-dihexylfluorenyl-2,7-diyl)-co-(9,10-anthracene)] (PFH-A) was found to selectively extract SWCNTs synthesized from the CoSO4/SiO2 catalyst, resulting in the enrichment of 78.3% (9,8) and 12.2% (9,7) nanotubes among all semiconducting species. Furthermore, molecular dynamics simulations suggest that the extraction selectivity of PFH-A relates to the bending and alignment of its alkyl chains and the twisting of its two aromatic backbone units (biphenyl and anthracene) relative to SWCNTs. The strong - interaction between polymers and SWCNTs would increase extraction yield, but it is not beneficial for chiral selectivity.