Increasing the Density of Single-Walled Carbon Nanotube Arrays by Multiple Catalysts Reactivation

High-density single-walled carbon nanotube (SWNT) array is a basic premise for its application in nanoelectronic devices in the future. Generally, it is considered that the improvement in catalyst efficiency is a possible route to increase the density. Here, we designed a multiple-catalysts reactivation method to increase the catalyst efficiency. By multiple H-2 treatment, we could successfully improve the density of the SWNT arrays by an average of 65%. Moreover, a new model to describe the multiple-catalysts reactivation process was established to deeply understand the mechanism of catalyst poisoning, and two possible types of catalyst poisoning: physical poisoning (PP) and structural poisoning (SP) were proposed. Only poisoned catalysts with PP type could be reactivated to produce new carbon nanotubes. By comparing different metal catalysts, we found that the ratio of PP to SP catalysts was highly related to the growth model, including vapor-solid (VS) and vapor-liquid-solid (VLS) model. Specifically, catalysts with VS mechanism (like W or Cu) showed higher PP ratio than those with VLS mechanism (like Co). The relationship between poisoning type and growth model mode may also contribute to the further catalyst design for high-density SWNT arrays.