Abstract
A key challenge in the fabrication of ferromagnetically filled carbon nano-onions (CNOs) is the control of their thickness, dimensions and electric properties. Up to now literature works have mainly focused on the encapsulation of different types of ferromagnetic materials including α-Fe, Fe3C, Co, FeCo, FePd3 and others within CNOs. However, no report has yet shown a suitable method for controlling both the number of shells, diameter and electric properties of the produced CNOs. Here, we demonstrate an advanced chemical vapour deposition approach in which the use of small quantities of sulfur during the pyrolysis of ferrocene allows for the control of (i) the diameter of the CNOs, (ii) the number of shells and (iii) the electric properties. We demonstrate the morphological, structural, electric and magnetic properties of these new types of CNOs by using SEM, XRD, TEM, HRTEM, EIS and VSM techniques.
Highlights
Carbon nano-onions (CNOs) are generally described as fullerenelike carbon structures consisting of concentrically arranged nested graphitic layers surrounding a C60 core
We find that the presence of small quantities of sulfur species in the pyrolysis of ferrocene can allow a high control of the diameter and thickness of CNOs
In order to better visualize the cross-sectional morphology of individual CNOs comprised in the buckypaper, the use of transmission electron microscopy (TEM) and high resolution TEM (HRTEM) was considered
Summary
Carbon nano-onions (CNOs) are generally described as fullerenelike carbon structures consisting of concentrically arranged nested graphitic layers surrounding a C60 core. Thanks to the important chemical and physical properties, these structures have recently 2 become an important focus of research which show promise for applications in aerospace as additive [9], energy storage as capacitors [10] and miniaturized fuel cells [8] These structures have been reported to exhibit giant capacitance and high conductivity (10 S cm−2) [10]. Our results suggest that the presence of sulfur allows the trapping of these phases within CNOs and inhibits the formation of Fe3C crystals due to intrinsic local changes in the carbon diffusion/extrusion flux dynamics The properties of these structures are characterized in detail by using numerous techniques: scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), temperature-dependent X-ray diffraction (T-XRD), temperaturedependent vibrating sample magnetometry (T-VSM). The impedance properties of these structures have been characterized with electrochemical impedance spectroscopy (EIS) and compared with those of Fe3C-filled CNOs
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