Characterization of quasicrystalline Al-Cu-Fe nanoclusters as catalysts for the synthesis of carbon nanotubes

Quasicrystalline (QC) Al-Cu-Fe nanoclusters as catalysts for the synthesis of carbon nanotubes (CNTs) were characterized in this study. It was shown in previous work that armchair-type CNTs are preferentially synthesized by using Al-Cu-Fe ultrathin films as catalysts in catalytic-chemical vapour deposition. We postulated a plausible mechanism that facets of QC nanoclusters with fivefold symmetry play an important role in the nucleation of a CNT cap with specific six-pentagon-configuration, which gives rise to the selective synthesis of armchair-type CNTs. To verify this hypothesis, the morphology and structure of Al-Cu-Fe nanoclusters were investigated by using transmission electron microscopy and electron diffraction (ED) as well as X-ray diffraction. As a result, it was found that the morphology of their nanoclusters is generally faceted-polyhedra, and the average diameter is similar to 4 nm, ranging from 1 to 10 nm, which indicates to correlate with the diameter of CNTs synthesized by using these nanoclusters as catalysts. Their ED patterns could be attributed to an icosahedral (i) Al-Cu-Fe phase. It was also found that multi-walled CNTs are synthesized successfully by using i-Al-Cu-Fe, i-Al-Pd-Re, and decagonal-Al-Ni-Co bulk-alloy systems as catalysts, respectively.