Controlled fabrication of monolayer carbon foam continuously filled with ferromagnetic FePd₃ crystals: The key role of filled bilayer/monolayer carbon onions-like capsules as synthesis-precursors

A major challenge in the growth of ferromagnetically-filled‑carbon-foam (FFCFM) materials is the achievement of a carbon-monolayer configuration. Up to now, the fabrication of this type of materials has been indeed strongly limited by the difficulties in controlling the characteristics (i.e. the number of carbon layers) of their carbon onions (CNOs) precursors. In this work we addressed this problem and we investigated the formation-mechanism of such monolayer FFCFM using novel bilayer CNOs-like capsules filled with Fe₃Pd and FePd₃ crystals as precursor-materials. These novel bilayer CNOs-capsules were obtained by pyrolysis of great excess of ferrocene and dichlorocyclooctadiene palladium mixtures. The modification of the surface characteristics of these capsules and the conversion-mechanism into monolayer FFCFM were investigated through two main methods, namely i) high temperature post-synthesis annealing and ii) post-synthesis high temperature Raman-laser-irradiation. The presence of a monolayer configuration in the FFCFM was firstly probed by the use of multiple techniques such as SEM, TEM, XRD, XPS and Raman spectroscopy and confirmed further by HRTEM/STEM. This novel method of production opens new avenues toward the control of the surface-characteristics of FFCFM-materials for applications involving mass-transport-phenomena, low-dimensional-materials-synthesis and others. In addition the bilayer/monolayer CNOs used as FFCFM precursor may find additional applications in shape-memory-devices.