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.