Water-assisted structural manipulation of ferromagnetically filled carbon onions: The case of high pressure Fe3O4

Carbon nano-onions (CNOs) are quasi-spherical fullerene-like structures with self-arranged in graphitic carbon shells. Reversible controlled transformations of these nanostructures into carbon nanodiamonds (CNDs) have been recently demonstrated by using a laser wavelength of 532 nm. However, no studies have yet reported on structural transitions in metal/carbide filled CNOs (Me-C@CNOs). In this work we have investigated such structural transitions in the case of Fe-C@CNOs with controlled curvature. A novel re-crystallization effect which leads to progressive increase in the intensities of the D, G and 2D bands is found. This observation is supported by controlled temperature dependent X-ray diffraction measurements in vacuum. Further, the addition of the controlled amount of water to ferrocene in the synthesis allows the enhancement of the sp3 carbon-characteristics of CNOs, with a progressive oxidation of the encapsulated particles into a high pressure Fe3O4 phase.