Preparation of isolated semiconducting single-wall carbon nanotubes by oxygen-assisted floating catalyst chemical vapor deposition

Semiconducting single-wall carbon nanotubes (s-SWCNTs) are promising for use in flexible electronics as a channel material. However, it remains a big challenge to directly grow high purity, high-quality s-SWCNTs in large scale. Here we report the synthesis of isolated s-SWCNTs by an oxygen-assisted floating catalyst chemical vapor deposition method. By controlling the density of nucleated SWCNTs, isolated or small-bundled, rather than large-bundled SWCNTs were generated in a floating state, so that the oxygen introduced could more efficiently selectively etch the metallic-SWCNTs formed. In addition, it was found that the oxygen also functions in limiting the size of Fe catalyst nanoparticles in a narrow range of 5–8 nm. As a result, isolated s-SWCNTs with a narrow diameter distribution were synthesized. The content of s-SWCNTs reached ∼96%, and the percentage of isolated tubes was estimated to be ∼83%. Thin-film transistors (TFTs) constructed using the s-SWCNT film showed high on/off ratios ranging from 2.1 × 104 to 1.2 × 106, verifying the effective enrichment of s-SWCNTs.