Selective Synthesis of Large-Diameter, High-Quality and Metallic Single-Walled Carbon Nanotubes Via Thiophene-Assisted Method

We developed a method that produces enriched metallic nanotubes (m-SWNTs) with large diameter, high quality and high yield. In our research, it was observed that m-SWNTs are dominant species when their diameters are larger than 3 nm under most growth conditions we have tested, which implies that catalyst nanoparticles with larger sizes might have a preference to nucleate m-SWNTs. Based on this observation, a thiophene-assisted CVD method was developed to selectively synthesize metallic carbon nanotubes with large diameters (> 3 nm). It is believed that the up-shift in diameter distribution is sourced from the higher capability of thiophene for carbon supply which can activate larger catalyst particles. Back-gate FETs were fabricated based on individual SWNTs to characterize the as-prepared SWNTs and it was determined that the ratio of m-SWNTs is ~95%. Clearly, the SWNTs synthesized with thiophene in the precursor have a higher percentage of metallic nanotubes. This result is consistent with the rules for selective growth reported in our previous study and provides a facile method for the synthesis of m-SWNTs which can be applied to fabricate transparent conductive films. This is a strong evidence that the growth conditions play an important role in determining the types of nanotubes grown in a CVD process.