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[摘要]：Nanoparticles of foreign element catalytic agents (FECAs) are widely employed for nanotube synthesis. Today these FECA nanoparticles include metals, semiconductors, oxides, clusters, polymers, and ceramics. Despite their very diverse characteristics, they all mediate nanotube growth. It is not known how they do it; their catalytic role has not been really understood. Attempts have been made to address this in some detail. For this, a wide variety of metals (transition metals, noble metals, alkali metals, etc.), oxides (SiO2, GeO2, MgO, CaO, etc.), semiconductors (Si, Ge, etc.), and even clusters, polymers, and ceramics (e.g., SiC), have been considered. The surface energy, chemical reactivity, and thermodynamic imbalance of FECAs; solubility of the nanotube source species in FECAs; supersaturation of the nanotube source species in FECAs; and the porosity of shells at the FECA peripheral surface have been studied. The fluctuations of FECAs resulting from thermodynamic imbalance and the dissociation of the precursors of the nanotube growth species on the FECA surface have also been examined. Together they appear to reveal a common platform that governs the chemical potential and catalytic activity of all possible FECAs. They explain why supersaturation needed, for example, for single-walled carbon nanotube growth, is possible even for very small FECAs. They elucidate why bimetallic and polymetallic FECAs have higher chemical reactivity for nanotube synthesis than monometallic FECAs and reveal the basic reasons why nanotubes of very small diameter may not be produced at all. Based on the science thus uncovered, some general rules for nanotube synthesis have been proposed. Attempts to quantify the validity of various findings and rules are substantiated by available experiments. The solutions thus obtained may have a significant impact on nanotube science and technology. |
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