Sowing Clean-Release Salt Catalyst for the Synthesis of Contamination-Free Single-walled Carbon Nanotube Arrays

Horizontal arrays of single-walled carbon nanotubes (SWCNTs) have shown immense potential for application in emerging devices due to their excellent electrical and thermal properties. The direct growth of SWCNT arrays using high-activity metal catalysts is one of the promising methods to approach the mass production of dense SWCNT arrays. However, an inevitable obstacle lies in the post-purification of metal residual. Herein, a sowing strategy to prepare size-tunable potassium chloride (KCl) catalysts for the efficient growth of the SWCNT array with a density of 10 tubes per micron is reported. Through a controllable etching process, numerous surface defects (e.g., vacancies and kinks) are uniformly generated on the substrate as seed pit-like sites for the accommodation and anchoring of catalysts. The well-distributed KCl catalysts with a homogeneous size of ≈1.4 nm enable the growth of ≈1.3 nm SWCNTs through a vapor-liquid-solid mechanism. Importantly, 94 at.% KCl catalysts can be dramatically removed through a simple water-washing process, thus leaving contamination-free SWCNT arrays behind. Interestingly, 85% of nanotubes show metallic properties, which is demonstrated by the combination of electrical characterization and the multi-laser Raman spectroscopy. This sowing strategy contributes to the direct growth of uncontaminated high-density SWCNT arrays.