Stacking-faults and moiré superlattice nucleation within the graphitic layers of partially-collapsed carbon nano-onions filled with γ-Fe: the role of indium isopropoxide as a growth-promoter

The recent observations of superconductive ordering in low-dimensional systems comprising twisted and rhombohedral ABC-stacked multilayer graphene have attracted significant attention. One-dimensional moiré superlattices and flat-bands have been interestingly reported to occur also in collapsed chiral carbon nanotubes. In this work we report the unusual stabilization of hexagonal moiré-like superlattices in partially-collapsed carbon nano-onions (CNOs). Such a structural transition was identified by employing indium-isopropoxide as a growth-promoter, during the pyrolysis of fixed quantities of ferrocene, dichlorobenzene and sulfur. Raman point and mapping spectroscopy analyses highlight a significant enhancement in the D-band intensity with the increase of the indium-isopropoxide concentration, up to a maximum for a precursor quantity of 10 mg. A uniform growth product consisting of stacking-faults-rich partially collapsed CNOs is demonstrated. Larger amounts of indium-isopropoxide were instead found to yield a transition from CNO to carbon nanotubes (CNTs) and consequential depletion of the D-band intensity-parameter.