Aug 11, 2009
Pyrene series reveals electronic-grade CNTs in solution
Metallic and semiconducting single-walled nanotubes (SWNTs) have been successfully separated by a scalable method involving pyrene derivatives. The chemical technique provides a convenient way of preparing pure metallic/semiconducting SWNTs for electronic device applications.
Semiconducting single-walled carbon nanotubes have superior carrier mobility and field-effect transistor behaviour. In addition, they are solution-processable, printable and suitable for large-area or macro-electronics such as solar panels and flexible electronics.
SWNTs can significantly outperform alternative semiconductors, such as conducting polymers, organic molecules and amorphous silicon, for printable or macro-electronics. However, all known SWNT synthesis methods produce mixtures of semiconducting and metallic nanotubes. The metallic nanotubes are problematic because they create unwanted conduction paths in the semiconducting active elements of transistors. As a result, there is a great need to separate metallic carbon nanotubes from semiconducting ones.
Solving the problem
Researchers in Singapore have recently designed and synthesized a series of compounds that can separate metallic nanotubes from semiconducting ones. The series is based on pyrene, a large aromatic molecule with four benzene rings, which is structurally similar to the nanotubes. Each of the group's three pyrene-based compounds has side chains with different lengths. These side chains modify the interaction with nanotubes to produce a degree of diameter and metallic versus semiconducting selectivity.
Resonant Raman scattering spectra of nanotube samples treated with the pyrene-based compounds indicate that two of them are selective to large diameter (D>1 nm) metallic-SWNTs. The third compound is selective to small diameter (D<1.03 nm) metallic-SWNTs.
The selection process is performed in solution, which is readily scalable to industrial-scale processing for widespread low-cost applications. The dependence of the selectivity on the chemical structures of the compounds suggests the feasibility of tuning the selectivity by tailoring the chemical structures.
The researchers presented their work in Nanotechnology.
About the author
Xiaoyong Pan is a full-time PhD student in Prof. Mary B Chan-Park's group in the School of Chemical and Biomedical Engineering at Nanyang Technological University, Singapore. He is currently focusing on the development of new compounds for SWNT separation/enrichment according to electronic properties/diameters as well as the application of electronic-property-enriched SWNTs in electronic devices. Associate professor Mary B Chan-Park is with the School of Chemical and Biomedical Engineering at Nanyang Technological University (NTU) where she is also the associate chair of research and a pioneer of the school. She obtained her BEng (chemistry) from the National University of Singapore in 1986 and PhD (polymers) from MIT in 1993 and has since been working on the applications of polymers. She was a senior manager at Sipix Imaging before joining NTU in 2001. Her current interests include carbon nanotubes and micro- and nano-patterning. She has published about 100 SCI papers and more than 15 patents/patent applications. She is also the lead PI of the recently inaugurated multi-PI five-year project "Towards Manufacturability of Carbon Nanotube-based Electronics".