Synthesis of NiCl2nanotubes and fullerene-like structures by laser ablation: theoretical considerations and comparison with MoS2nanotubes

Abstract

Laser ablation has been extensively used for the synthesis of nanoparticles of various sorts, and in particular single wall carbon nanotubes and C₆₀ molecules. NiCl₂ nanotubes were recently also produced using this technique. While fullerene-like NiCl₂ structures can be obtained through regular ablation, vapor phase enriched with CCl₄ gas (reactive ablation) is necessary for the synthesis of the nanotubes. The experimental results indicate that the synthesis of such nanotubes is much more difficult than the synthesis of say MoS₂ or WS₂ nanotubes. Moreover, the NiCl₂ nanotubes are of larger diameter and consist on the average of more layers than their MoS₂ predecessors. First principle calculations show that single layer NiCl₂ nanotubes of diameter smaller than 54 nm are unstable and lose their outer chlorine atoms. In contrast, MoS₂ nanotubes with diameter of 2 nm and larger are found to be stable using the same kind of calculations. To gain better understanding of the differences between the materials, a review of the mechanical properties of layered metal dihalide and metal dichalcogenide compounds is undertaken. First principle calculations show that the Young's and bending moduli of NiCl₂ are almost twice larger than those of MoS₂. The large ionicity of NiCl₂ entails much larger shear and stacking fault energies for this compound as compared to MoS₂, which explains its smaller propensity to bend and fold. These observations are supported by analysis of the corresponding Raman modes.Furthermore, metal dihalide compounds are very hygroscopic making their handling, and especially their analysis more difficult. This analysis explains the greater difficulties to grow NiCl₂ nanotubes or fullerene-like nanoparticles, as compared to their MoS₂ analogues.