Synthesis of semiconducting or metallic single-walled carbon nanotubes by gas-phase selective etching

Single-walled carbon nanotubes(SWCNTs) can be either semiconducting or metallic, depending on their chirality. As-synthesized SWCNT samples are usually mixtures of semiconducting and metallic species, and separation of the two is important for their use in electronic devices. In recent years, notable progress in the synthesis of semiconducting or metallic SWCNTs has been made. Among the methods reported, selective removal of one type of SWCNTs by gas-phase etching shows the advantages of simplicity, scalability, and high efficiency. This paper introduces the principles of the gas-phase etching method. In particular, recent progress in synthesizing SWCNTs of uniform electronic type by this strategy is reviewed. Finally, the main challenges and development trends in gas-phase etching of SWCNTs are considered.