Structural study of graphite-encapsulated iron nanoparticles via chemical vapor deposition combined with spray method

摘要

Interest in carbon arcs and arc products has renewed after the discovery of the carbon arc process for the production of fullcrenes by Huffman-Kratschmer 1. The availability of macroscopic quantities of fullerene-contain-ing powder immediately led to the discovery of other products of this process, such as endohedral fullcrenes, carbon nanotubes, and carbon coated nanoparticles 2-5. Although nanocrystalline ferromagnetic metals are readily available, they have a disadvantage of being prone to rapid environmental degradation due to a very high surface area to volume ratio and high reactivity. This tends to limit the potential of industrial application and scientific evaluation of the properties of nanoparticles. In this regard, a recent breakthrough is the encapsulation of magnetic nanoparticles with graphite layers, which only protects the nanoparticles and their intrinsic magnetic properties. The core structures of these graphite-encapsulated iron nanoparticles are classified into a metallic phase and a carbide phase. The role of the graphite layer is to magnetically isolate the particles from each other. Therefore, a graphite layer avoids the problems caused by interactions among the particles when they are closely compacted as magnetic bits, and provides the oxidation resistance of bare metal nanoparticles. Because of these combined attributes, the graphite-encapsulated metal nanoparticles are interesting candidates for many bio-engineering applications including drug delivery, biosensors, magnetic hyperther-mia, and magnetic contrast agents for magnetic resonance imaging. As a result, graphite-encapsulated magnetic nanoparticles have resulted in a great number of researches conducted across the world in the past a few years.