Single Crystal Metals Encapsulated in Carbon Nanoparticles

Abstract

Single-domain microcrystals of LaC 2 encapsulated within nanoscale polyhedral carbon particles have been synthesized in a carbon arc. Typical particle sizes are on the order of 20 to 40 nanometers. The stoichiometry and phase of the La-containing crystals have been assigned from characteristic lattice spacings observed by high-resolution transmission electron microscopy and energy dispersive spectroscopy (EDS). EDS spectra show that La and C are the only elements present. Characteristic interatomic distances of 3.39 and 2.78 angstroms identify the compound inside the nanoparticle cavities as α-LaC 2 , the phase of LaC 2 that is stable at room temperature. Bulk α-LaC 2 is metallic and hydrolytic. Observation of crystals of pure encapsulated α-LaC 2 that were exposed to air for several days before analysis indicates that the LaC 2 is protected from degradation by the carbon polyhedral shells of the nanoparticles. A high percentage of the carbon nanoparticles have encapsulated LaC 2 single crystals. These carbon-coated metal crystals form a new class of materials that can be protected in their pure or carbide forms and may have interesting and useful properties.